Age-Dependent Activation of Pannexin1 Function Contributes to the Development of Epileptogenesis in Autosomal Dominant Sleep-related Hypermotor Epilepsy Model Rats.

To explore the processes of epileptogenesis/ictogenesis, this study determined the age-dependent development of the functional abnormalities in astroglial transmission associated with pannexin1-hemichannel using a genetic rat model of autosomal dominant sleep-related hypermotor epilepsy (ADSHE) named 'S286L-TG'. Pannexin1 expression in the plasma membrane of primary cultured cortical astrocytes and the orbitofrontal cortex (OFC), which is an ADSHE focus region, were determined using capillary immunoblotting. Astroglial D-serine releases induced by artificial high-frequency oscillation (HFO)-evoked stimulation, the removal of extracellular Ca2+, and the P2X7 receptor agonist (BzATP) were determined using ultra-high performance liquid chromatography (UHPLC). The expressions of pannexin1 in the plasma membrane fraction of the OFC in S286L-TG at four weeks old were almost equivalent when compared to the wild type. The pannexin1 expression in the OFC of the wild type non-statistically decreased age-dependently, whereas that in S286L-TG significantly increased age-dependently, resulting in relatively increasing pannexin1 expression from the 7- (at the onset of interictal discharge) and 10-week-old (after the ADSHE seizure onset) S286L-TG compared to the wild type. However, no functional abnormalities of astroglial pannexin1 expression or D-serine release through the pannexin1-hemichannels from the cultured astrocytes of S286L-TG could be detected. Acutely HFO-evoked stimulation, such as physiological ripple burst (200 Hz) and epileptogenic fast ripple burst (500 Hz), frequency-dependently increased both pannexin1 expression in the astroglial plasma membrane and astroglial D-serine release. Neither the selective inhibitors of pannexin1-hemichannel (10PANX) nor connexin43-hemichannel (Gap19) affected astroglial D-serine release during the resting stage, whereas HFO-evoked D-serine release was suppressed by both inhibitors. The inhibitory effect of 10PANX on the ripple burst-evoked D-serine release was more predominant than that of Gap19, whereas fast ripple burst-evoked D-serine release was predominantly suppressed by Gap19 rather than 10PANX. Astroglial D-serine release induced by acute exposure to BzATP was suppressed by 10PANX but not by Gap19. These results suggest that physiological ripple burst during the sleep spindle plays important roles in the organization of some components of cognition in healthy individuals, but conversely, it contributes to the initial development of epileptogenesis/ictogenesis in individuals who have ADSHE vulnerability via activation of the astroglial excitatory transmission associated with pannexin1-hemichannels.

Therapeutic Potential and Limitation of Serotonin Type 7 Receptor Modulation.

Although a number of mood-stabilising atypical antipsychotics and antidepressants modulate serotonin type 7 receptor (5-HT7), the detailed contributions of 5-HT7 function to clinical efficacy and pathophysiology have not been fully understood. The mood-stabilising antipsychotic agent, lurasidone, and the serotonin partial agonist reuptake inhibitor, vortioxetine, exhibit higher binding affinity to 5-HT7 than other conventional antipsychotics and antidepressants. To date, the initially expected rapid onset of antidepressant effects-in comparison with conventional antidepressants or mood-stabilising antipsychotics-due to 5-HT7 inhibition has not been observed with lurasidone and vortioxetine; however, several clinical studies suggest that 5-HT7 inhibition likely contributes to quality of life of patients with schizophrenia and mood disorders via the improvement of cognition. Furthermore, recent preclinical studies reported that 5-HT7 inhibition might mitigate antipsychotic-induced weight gain and metabolic complication by blocking other monoamine receptors. Further preclinical studies for the development of 5-HT7 modulation against neurodevelopmental disorders and neurodegenerative diseases have been ongoing. To date, various findings from various preclinical studies indicate the possibility that 5-HT7 modifications can provide two independent strategies. The first is that 5-HT7 inhibition ameliorates the dysfunction of inter-neuronal transmission in mature networks. The other is that activation of 5-HT7 can improve transmission dysfunction due to microstructure abnormality in the neurotransmission network-which could be unaffected by conventional therapeutic agents-via modulating intracellular signalling during the neurodevelopmental stage or via loss of neural networks with aging. This review attempts to describe the current and novel clinical applications of 5-HT7 modulation based on preclinical findings.

Brivaracetam and Levetiracetam Suppress Astroglial L-Glutamate Release through Hemichannel via Inhibition of Synaptic Vesicle Protein.

To explore the pathophysiological mechanisms of antiseizure and adverse behavioural/psychiatric effects of brivaracetam and levetiracetam, in the present study, we determined the effects of brivaracetam and levetiracetam on astroglial L-glutamate release induced by artificial high-frequency oscillation (HFO) bursts using ultra-high-performance liquid chromatography. Additionally, the effects of brivaracetam and levetiracetam on protein expressions of connexin43 (Cx43) and synaptic vesicle protein 2A (SV2A) in the plasma membrane of primary cultured rat astrocytes were determined using a capillary immunoblotting system. Acutely artificial fast-ripple HFO (500 Hz) burst stimulation use-dependently increased L-glutamate release through Cx43-containing hemichannels without affecting the expression of Cx43 or SV2A in the plasma membrane, whereas acute physiological ripple HFO (200 Hz) stimulation did not affect astroglial L-glutamate release or expression of Cx43 or SV2A. Contrarily, subchronic ripple HFO and acute pathological fast-ripple HFO (500 Hz) stimulations use-dependently increased L-glutamate release through Cx43-containing hemichannels and Cx43 expression in the plasma membrane. Subchronic fast-ripple HFO-evoked stimulation produced ectopic expression of SV2A in the plasma membrane, but subchronic ripple HFO stimulation did not generate ectopic SV2A. Subchronic administration of brivaracetam and levetiracetam concentration-dependently suppressed fast-ripple HFO-induced astroglial L-glutamate release and expression of Cx43 and SV2A in the plasma membrane. In contrast, subchronic ripple HFO-evoked stimulation induced astroglial L-glutamate release, and Cx43 expression in the plasma membrane was inhibited by subchronic levetiracetam administration, but was not affected by brivaracetam. These results suggest that brivaracetam and levetiracetam inhibit epileptogenic fast-ripple HFO-induced activated astroglial transmission associated with hemichannels. In contrast, the inhibitory effect of therapeutic-relevant concentrations of levetiracetam on physiological ripple HFO-induced astroglial responses probably contributes to the adverse behavioural/psychiatric effects of levetiracetam.

Dose-Dependent Biphasic Action of Quetiapine on AMPK Signalling via 5-HT7 Receptor: Exploring Pathophysiology of Clinical and Adverse Effects of Quetiapine.

Recent pharmacological studies indicated that the modulation of tripartite-synaptic transmission plays important roles in the pathophysiology of schizophrenia, mood disorders and adverse reactions. Therefore, to explore the mechanisms underlying the clinical and adverse reactions to atypical antipsychotics, the present study determined the effects of the sub-chronic administration of quetiapine (QTP: 3~30 µM) on the protein expression of 5-HT7 receptor (5-HT7R), connexin43 (Cx43), cAMP level and intracellular signalling, Akt, Erk and adenosine monophosphate-activated protein kinase (AMPK) in cultured astrocytes and the rat hypothalamus, using ultra-high-pressure liquid chromatography with mass spectrometry and capillary immunoblotting systems. QTP biphasically increased physiological ripple-burst evoked astroglial D-serine release in a concentration-dependent manner, peaking at 10 µM. QTP enhanced the astroglial signalling of Erk concentration-dependently, whereas both Akt and AMPK signalling's were biphasically enhanced by QTP, peaking at 10 µM and 3 µM, respectively. QTP downregulated astroglial 5-HT7R in the plasma membrane concentration-dependently. Protein expression of Cx43 in astroglial cytosol and intracellular cAMP levels were decreased and increased by QTP also biphasically, peaking at 3 µM. The dose-dependent effects of QTP on the protein expression of 5-HT7R and Cx43, AMPK signalling and intracellular cAMP levels in the hypothalamus were similar to those in astrocytes. These results suggest several complicated pharmacological features of QTP. A therapeutically relevant concentration/dose of QTP activates Akt, Erk and AMPK signalling, whereas a higher concentration/dose of QTP suppresses AMPK signalling via its low-affinity 5-HT7R inverse agonistic action. Therefore, 5-HT7R inverse agonistic action probably plays important roles in the prevention of a part of adverse reactions of QTP, such as weight gain and metabolic complications.

Brexpiprazole Reduces 5-HT7 Receptor Function on Astroglial Transmission Systems.

Several atypical antipsychotics exert mood-stabilising effects via the modulation of various monoamine receptors and intracellular signallings. Recent pharmacodynamic studies suggested that tripartite synaptic transmission can contribute to the pathophysiology of schizophrenia and mood disorders, their associated cognitive impairment, and several adverse reactions to atypical antipsychotics. Therefore, to explore the mechanisms underlying the antidepressive mood-stabilising and antipsychotic effects of brexpiprazole (Brex), we determined the effects of subchronic administration of therapeutically relevant concentrations/doses of Brex on the protein expression of 5-HT receptors, connexin43, cAMP levels, and intracellular signalling in cultured astrocytes and rat hypothalamus using ultra-high-pressure liquid chromatography with mass spectrometry and capillary immunoblotting systems. Subchronic administration of a therapeutically relevant concentration of Brex (300 nM) downregulated both 5-HT1A (5-HT1AR) and 5-HT7 (5-HT7R) receptors, in addition to phosphorylated Erk (pErk), without affecting phosphorylated Akt in the astroglial plasma membrane. Subchronic administration of 300 nM Brex decreased and increased phosphorylated AMPK and connexin43, respectively, in the astroglial cytosol fraction. A therapeutically relevant concentration of Brex acutely decreased the astroglial cAMP level, whereas, under the inhibition of 5-HT1AR, Brex did not affect astroglial cAMP levels. However, the 5-HT7R-agonist-induced increased astroglial cAMP level was inhibited by Brex. In contrast to the in vitro study, systemic subchronic administration of effective doses of Brex (3 and 10 mg/kg/day for 14 days) increased the cAMP level but did not affect phosphorylated AMPK in the rat hypothalamus. These results suggest several complicated pharmacological features of Brex. Partial 5-HT1AR agonistic action predominates in the low range of therapeutically relevant concentrations of Brex, whereas in the high range, 5-HT7R inverse agonist-like action is overlapped on the 5-HT1A agonistic action. These unique suppressive effects of Brex on 5-HT7R play important roles in the clinical features of Brex regarding its antidepressive mood-stabilising actions.

Effects of Atypical Antipsychotics, Clozapine, Quetiapine and Brexpiprazole on Astroglial Transmission Associated with Connexin43.

Recently, accumulating preclinical findings suggest the possibility that functional abnormalities of tripartite synaptic transmission play important roles in the pathophysiology of schizophrenia and affective disorder. Therefore, to explore the novel mechanisms of mood-stabilizing effects associated with tripartite synaptic transmission, the present study determined the effects of mood-stabilizing antipsychotics, clozapine (CLZ), quetiapine (QTP) and brexpiprazole (BPZ), on the astroglial l-glutamate release and expression of connexin43 (Cx43) in the astroglial plasma membrane using cortical primary cultured astrocytes. Neither acute (for 120 min) nor subchronic (for 7 days) administrations of CLZ, QTP and BPZ affected basal astroglial l-glutamate release, whereas both acute and subchronic administration of CLZ, QTP and BPZ concentration-dependently enhanced astroglial l-glutamate release through activated hemichannels. Subchronic administration of therapeutic-relevant concentration of valproate (VPA), a histone deacetylase inhibiting mood-stabilizing antiepileptic drug, enhanced the stimulatory effects of therapeutic-relevant concentration of CLZ, QTP and BPZ on astroglial l-glutamate release through activated hemichannel. Subchronic administration of therapeutic-relevant concentration of CLZ, QTP and BPZ did not affect Cx43 protein expression in the plasma membrane during resting stage. After subchronic administration of VPA, acute and subchronic administration of therapeutic-relevant concentrations of CLZ increased Cx43 protein expression in the plasma membrane. Both acute administrations of therapeutic-relevant concentrations of QTP and BPZ did not affect, but subchronic administrations enhanced Cx43 protein expression in the astroglial plasma membrane. Furthermore, protein kinase B (Akt) inhibitor suppressed the stimulatory effects of CLZ and QTP, but did not affect Cx43 protein expression in the astroglial plasma membrane. These results suggest that three mood-stabilizing atypical antipsychotics, CLZ, QTP and BPZ enhance tripartite synaptic glutamatergic transmission due to enhancement of astroglial Cx43 containing hemichannel activities; however, the Cx43 activating mechanisms of these three mood-stabilizing antipsychotics were not identical. The enhanced astroglial glutamatergic transmission induced by CLZ, QTP and BPZ is, at least partially, involved in the actions of these three mood-stabilizing antipsychotics.

Distinct Effects of Escitalopram and Vortioxetine on Astroglial L-Glutamate Release Associated with Connexin43.

It has been established that enhancement of serotonergic transmission contributes to improvement of major depression; however, several post-mortem studies and experimental depression rodent models suggest that functional abnormalities of astrocytes play important roles in the pathomechanisms/pathophysiology of mood disorders. Direct effects of serotonin (5-HT) transporter inhibiting antidepressants on astroglial transmission systems has never been assessed in this context. Therefore, to explore the effects of antidepressants on transmission associated with astrocytes, the present study determined the effects of the selective 5-HT transporter inhibitor, escitalopram, and the 5-HT partial agonist reuptake inhibitor, vortioxetine, on astroglial L-glutamate release through activated hemichannels, and the expression of connexin43 (Cx43), type 1A (5-HT1AR) and type 7 (5-HT7R) 5-HT receptor subtypes, and extracellular signal-regulated kinase (ERK) in astrocytes using primary cultured rat cortical astrocytes in a 5-HT-free environment. Both escitalopram and 5-HT1AR antagonist (WAY100635) did not affect basal astroglial L-glutamate release or L-glutamate release through activated hemichannels. Subchronic (for seven days) administrations of vortioxetine and the 5-HT7R inverse agonist (SB269970) suppressed both basal L-glutamate release and L-glutamate release through activated hemichannels, whereas 5-HT1AR agonist (BP554) inhibited L-glutamate release through activated hemichannels, but did not affect basal L-glutamate release. In particular, WAY100635 did not affect the inhibitory effects of vortioxetine on L-glutamate release. Subchronic administration of vortioxetine, BP554 and SB269970 downregulated 5-HT1AR, 5-HT7R and phosphorylated ERK in the plasma membrane fraction, but escitalopram and WAY100635 did not affect them. Subchronic administration of SB269970 decreased Cx43 expression in the plasma membrane but did not affect the cytosol; however, subchronic administration of BP554 increased Cx43 expression in the cytosol but did not affect the plasma membrane. Subchronic vortioxetine administration increased Cx43 expression in the cytosol and decreased it in the plasma membrane. WAY100635 prevented an increased Cx43 expression in the cytosol induced by vortioxetine without affecting the reduced Cx43 expression in the plasma membrane. These results suggest that 5-HT1AR downregulation probably increases Cx43 synthesis, but 5-HT7R downregulation suppresses Cx43 trafficking to the plasma membrane. These results also suggest that the subchronic administration of therapeutic-relevant concentrations of vortioxetine inhibits both astroglial L-glutamate and Cx43 expression in the plasma membrane via 5-HT7R downregulation but enhances Cx43 synthesis in the cytosol via 5-HT1AR downregulation. This combination of the downregulation of 5-HT1AR, 5-HT7R and Cx43 in the astroglial plasma membrane induced by subchronic vortioxetine administration suggest that astrocytes is possibly involved in the pathophysiology of depression.

Chronic Administrations of Guanfacine on Mesocortical Catecholaminergic and Thalamocortical Glutamatergic Transmissions.

It has been established that the selective α2A adrenoceptor agonist guanfacine reduces hyperactivity and improves cognitive impairment in patients with attention-deficit/hyperactivity disorder (ADHD). The major mechanisms of guanfacine are considered to involve the activation of the postsynaptic α2A adrenoceptor of glutamatergic pyramidal neurons in the frontal cortex, but the effects of chronic guanfacine administration on catecholaminergic and glutamatergic transmissions associated with the orbitofrontal cortex (OFC) are yet to be clarified. The actions of guanfacine on catecholaminergic transmission, the effects of acutely local and systemically chronic (for 7 days) administrations of guanfacine on catecholamine release in pathways from the locus coeruleus (LC) to OFC, the ventral tegmental area (VTA) and reticular thalamic-nucleus (RTN), from VTA to OFC, from RTN to the mediodorsal thalamic-nucleus (MDTN), and from MDTN to OFC were determined using multi-probe microdialysis with ultra-high performance liquid chromatography. Additionally, the effects of chronic guanfacine administration on the expression of the α2A adrenoceptor in the plasma membrane fraction of OFC, VTA and LC were examined using a capillary immunoblotting system. The acute local administration of therapeutically relevant concentrations of guanfacine into the LC decreased norepinephrine release in the OFC, VTA and RTN without affecting dopamine release in the OFC. Systemically, chronic administration of therapeutically relevant doses of guanfacine for 14 days increased the basal release of norepinephrine in the OFC, VTA, RTN, and dopamine release in the OFC via the downregulation of the α2A adrenoceptor in the LC, OFC and VTA. Furthermore, systemically, chronic guanfacine administration did not affect intrathalamic GABAergic transmission, but it phasically enhanced thalamocortical glutamatergic transmission. The present study demonstrated the dual actions of guanfacine on catecholaminergic transmission-acute attenuation of noradrenergic transmission and chronic enhancement of noradrenergic transmission and thalamocortical glutamatergic transmission. These dual actions of guanfacine probably contribute to the clinical effects of guanfacine against ADHD.

Effects of Subchronic Administrations of Vortioxetine, Lurasidone, and Escitalopram on Thalamocortical Glutamatergic Transmission Associated with Serotonin 5-HT7 Receptor.

The functional suppression of serotonin (5-HT) type 7 receptor (5-HT7R) is forming a basis for scientific discussion in psychopharmacology due to its rapid-acting antidepressant-like action. A novel mood-stabilizing atypical antipsychotic agent, lurasidone, exhibits a unique receptor-binding profile, including a high affinity for 5-HT7R antagonism. A member of a novel class of antidepressants, vortioxetine, which is a serotonin partial agonist reuptake inhibitor (SPARI), also exhibits a higher affinity for serotonin transporter, serotonin receptors type 1A (5-HT1AR) and type 3 (5-HT3R), and 5-HT7R. However, the effects of chronic administration of lurasidone, vortioxetine, and the selective serotonin reuptake inhibitor (SSRI), escitalopram, on 5-HT7R function remained to be clarified. Thus, to explore the mechanisms underlying the clinical effects of vortioxetine, escitalopram, and lurasidone, the present study determined the effects of these agents on thalamocortical glutamatergic transmission, which contributes to emotional/mood perception, using multiprobe microdialysis and 5-HT7R expression using capillary immunoblotting. Acute local administration of a 5-HT7R agonist and antagonist into the mediodorsal thalamic nucleus (MDTN) enhanced and reduced thalamocortical glutamatergic transmission, induced by N-methyl-D-aspartate (NMDA)/glutamate receptor inhibition in the reticular thalamic nucleus (RTN). Acute local administration of a relevant therapeutic concentration of vortioxetine and lurasidone into the MDTN suppressed the thalamocortical glutamatergic transmission via 5-HT7R inhibition, whereas that of escitalopram activated 5-HT7R. Subchronic administration of effective doses of vortioxetine and lurasidone (for 7 days) reduced the thalamocortical glutamatergic transmission, but escitalopram did not affect it, whereas subchronic administration of these three agents attenuated the stimulatory effects of the 5-HT7R agonist on thalamocortical glutamatergic transmission. Subchronic administration of effective doses of vortioxetine, lurasidone, and escitalopram downregulated the 5-HT7R expression of the plasma membrane in the MDTN; the 5-HT7R downregulation induced by vortioxetine and lurasidone was observed at 3 days, but that induced by escitalopram required a longer duration of 7 days. These results indicate that chronic administration of vortioxetine, escitalopram, and lurasidone generate downregulation of 5-HT7R in the thalamus; however, the direct inhibition of 5-HT7R associated with vortioxetine and lurasidone generates more rapid downregulation than the indirect elevation of the extracellular serotonin level via serotonin transporter inhibition by escitalopram.

Age-Dependent and Sleep/Seizure-Induced Pathomechanisms of Autosomal Dominant Sleep-Related Hypermotor Epilepsy.

The loss-of-function S284L-mutant α4 subunit of the nicotinic acetylcholine receptor (nAChR) is considered to contribute to the pathomechanism of autosomal dominant sleep-related hypermotor epilepsy (ADSHE); however, the age-dependent and sleep-related pathomechanisms of ADSHE remain to be clarified. To explore the age-dependent and sleep-induced pathomechanism of ADSHE, the present study determined the glutamatergic transmission abnormalities associated with α4ß2-nAChR and the astroglial hemichannel in the hyperdirect and corticostriatal pathways of ADSHE model transgenic rats (S286L-TG) bearing the rat S286L-mutant Chrna4 gene corresponding to the human S284L-mutant CHRNA4 gene of ADSHE, using multiprobe microdialysis and capillary immunoblotting analyses. This study could not detect glutamatergic transmission in the corticostriatal pathway from the orbitofrontal cortex (OFC) to the striatum. Before ADSHE onset (four weeks of age), functional abnormalities of glutamatergic transmission compared to the wild-type in the cortical hyperdirect pathway, from OFC to the subthalamic nucleus (STN) in S286L-TG, could not be detected. Conversely, after ADSHE onset (eight weeks of age), glutamatergic transmission in the hyperdirect pathway of S286L-TG was enhanced compared to the wild-type. Notably, enhanced glutamatergic transmission of S286L-TG was revealed by hemichannel activation in the OFC. Expression of connexin43 (Cx43) in the OFC of S286L-TG was upregulated after ADSHE onset but was almost equal to the wild-type prior to ADSHE onset. Differences in the expression of phosphorylated protein kinase B (pAkt) before ADSHE onset between the wild-type and S286L-TG were not observed; however, after ADSHE onset, pAkt was upregulated in S286L-TG. Conversely, the expression of phosphorylated extracellular signal-regulated kinase (pErk) was already upregulated before ADSHE onset compared to the wild-type. Both before and after ADSHE onset, subchronic nicotine administration decreased and did not affect the both expression of Cx43 and pErk of respective wild-type and S286L-TG, whereas the pAkt expression of both the wild-type and S286L-TG was increased by nicotine. Cx43 expression in the plasma membrane of the primary cultured astrocytes of the wild-type was increased by elevation of the extracellular K+ level (higher than 10 mM), and the increase in Cx43 expression in the plasma membrane required pErk functions. These observations indicate that a combination of functional abnormalities, GABAergic disinhibition, and upregulated pErk induced by the loss-of-function S286L-mutant α4ß2-nAChR contribute to the age-dependent and sleep-induced pathomechanism of ADSHE via the upregulation/hyperactivation of the Cx43 hemichannels.

Astroglial Connexin43 as a Potential Target for a Mood Stabiliser.

Mood disorders remain a major public health concern worldwide. Monoaminergic hypotheses of pathophysiology of bipolar and major depressive disorders have led to the development of monoamine transporter-inhibiting antidepressants for the treatment of major depression and have contributed to the expanded indications of atypical antipsychotics for the treatment of bipolar disorders. In spite of psychopharmacological progress, current pharmacotherapy according to the monoaminergic hypothesis alone is insufficient to improve or prevent mood disorders. Recent approval of esketamine for treatment of treatment-resistant depression has attracted attention in psychopharmacology as a glutamatergic hypothesis of the pathophysiology of mood disorders. On the other hand, in the last decade, accumulated findings regarding the pathomechanisms of mood disorders emphasised that functional abnormalities of tripartite synaptic transmission play important roles in the pathophysiology of mood disorders. At first glance, the enhancement of astroglial connexin seems to contribute to antidepressant and mood-stabilising effects, but in reality, antidepressive and mood-stabilising actions are mediated by more complicated interactions associated with the astroglial gap junction and hemichannel. Indeed, several depressive mood-inducing stress stimulations suppress connexin43 expression and astroglial gap junction function, but enhance astroglial hemichannel activity. On the other hand, monoamine transporter-inhibiting antidepressants suppress astroglial hemichannel activity and enhance astroglial gap junction function, whereas several non-antidepressant mood stabilisers activate astroglial hemichannel activity. Based on preclinical findings, in this review, we summarise the effects of antidepressants, mood-stabilising antipsychotics, and anticonvulsants on astroglial connexin, and then, to establish a novel strategy for treatment of mood disorders, we reveal the current progress in psychopharmacology, changing the question from "what has been revealed?" to "what should be clarified?".

Candidate Strategies for Development of a Rapid-Acting Antidepressant Class That Does Not Result in Neuropsychiatric Adverse Effects: Prevention of Ketamine-Induced Neuropsychiatric Adverse Reactions.

Non-competitive N-methyl-D-aspartate/glutamate receptor (NMDAR) antagonism has been considered to play important roles in the pathophysiology of schizophrenia. In spite of severe neuropsychiatric adverse effects, esketamine (racemic enantiomer of ketamine) has been approved for the treatment of conventional monoaminergic antidepressant-resistant depression. Furthermore, ketamine improves anhedonia, suicidal ideation and bipolar depression, for which conventional monoaminergic antidepressants are not fully effective. Therefore, ketamine has been accepted, with rigorous restrictions, in psychiatry as a new class of antidepressant. Notably, the dosage of ketamine for antidepressive action is comparable to the dose that can generate schizophrenia-like psychotic symptoms. Furthermore, the psychotropic effects of ketamine precede the antidepressant effects. The maintenance of the antidepressive efficacy of ketamine often requires repeated administration; however, repeated ketamine intake leads to abuse and is consistently associated with long-lasting memory-associated deficits. According to the dissociative anaesthetic feature of ketamine, it exerts broad acute influences on cognition/perception. To evaluate the therapeutic validation of ketamine across clinical contexts, including its advantages and disadvantages, psychiatry should systematically assess the safety and efficacy of either short- and long-term ketamine treatments, in terms of both acute and chronic outcomes. Here, we describe the clinical evidence of NMDAR antagonists, and then the temporal mechanisms of schizophrenia-like and antidepressant-like effects of the NMDAR antagonist, ketamine. The underlying pharmacological rodent studies will also be discussed.

A Working Hypothesis Regarding Identical Pathomechanisms between Clinical Efficacy and Adverse Reaction of Clozapine via the Activation of Connexin43.

Clozapine (CLZ) is an approved antipsychotic agent for the medication of treatment-resistant schizophrenia but is also well known as one of the most toxic antipsychotics. Recently, the World Health Organization's (WHO) global database (VigiBase) reported the relative lethality of severe adverse reactions of CLZ. Agranulocytosis is the most famous adverse CLZ reaction but is of lesser lethality compared with the other adverse drug reactions of CLZ. Unexpectedly, VigiBase indicated that the prevalence and relative lethality of pneumonia, cardiotoxicity, and seizures associated with CLZ were more serious than that of agranulocytosis. Therefore, haematological monitoring in CLZ patients monitoring system provided success in the prevention of lethal adverse events from CLZ-induced agranulocytosis. Hereafter, psychiatrists must amend the CLZ patients monitoring system to protect patients with treatment-resistant schizophrenia from severe adverse CLZ reactions, such as pneumonia, cardiotoxicity, and seizures, according to the clinical evidence and pathophysiology. In this review, we discuss the mechanisms of clinical efficacy and the adverse reactions of CLZ based on the accumulating pharmacodynamic findings of CLZ, including tripartite synaptic transmission, and we propose suggestions for amending the monitoring and medication of adverse CLZ reactions associated with pneumonia, cardiotoxicity, and seizures.

Vortioxetine Subchronically Activates Serotonergic Transmission via Desensitization of Serotonin 5-HT1A Receptor with 5-HT3 Receptor Inhibition in Rats.

Vortioxetine is a novel, multimodal antidepressant with unique targets, including the inhibition of the serotonin transporter (SET), of serotonin 5-HT3 (5-HT3R), and of 5-HT7 (5-HT7R) receptors and partial agonism to serotonin 5-HT1A (5-HT1AR) receptors in humans. Vortioxetine has a lower affinity to 5-HT1AR and 5-HT7R in rats compared with humans, but several behavior studies have demonstrated its powerful antidepressant-like actions. In spite of these efforts, detailed effects of the subchronic administration of vortioxetine on serotonergic transmission remain to be clarified. This study examined the mechanisms underlying the clinical effects of vortioxetine by measuring the releases of 5-HT and GABA in the medial prefrontal cortex (mPFC) of freely moving rats compared with the selective SET inhibitor, escitalopram. Inhibition of 5-HT3R in the mPFC enhanced regional 5-HT release via GABAergic disinhibition. Activation of somatodendritic 5-HT1AR in the dorsal raphe nucleus (DRN) and presynaptic 5-HT1AR in the mPFC inhibited 5-HT release in the mPFC. Escitalopram subchronically activated mesocortical serotonergic transmission via desensitization of 5-HT1AR in the mPFC and DRN and of 5-HT3R in the mPFC; however, vortioxetine also subchronically activated mesocortical serotonergic transmission via desensitization of 5-HT1AR in the mPFC and DRN but not of 5-HT3R in the mPFC. These demonstrations, the desensitization of 5-HT1AR with the inhibition of 5-HT3R (without 5-HT3R desensitization), at least partially, contribute to the multimodal antidepressant action of vortioxetine in rats.

Carbamazepine Attenuates Astroglial L-Glutamate Release Induced by Pro-Inflammatory Cytokines via Chronically Activation of Adenosine A2A Receptor.

Carbamazepine (CBZ) binds adenosine receptors, but detailed effects of CBZ on astroglial transmission associated with adenosine receptor still need to be clarified. To clarify adenosinergic action of CBZ on astroglial transmission, primary cultured astrocytes were acutely or chronically treated with CBZ, proinflammatory cytokines (interferon γ (IFNγ) and tumor necrosis factor α (TNFα)), and adenosine A2A receptor (A2AR) agonist (CGS21680). IFNγ and TNFα increased basal, adenophostin-A (AdA)-evoked, and 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA)-evoked astroglial L-glutamate releases. In physiological condition, CGS21680 increased basal astroglial L-glutamate release but glutamate transporter inhibition prevented this CGS21680 action. CBZ did not affect basal release, whereas glutamate transporter inhibition generated CBZ-induced glutamate release. Furthermore, AdA-evoked and AMPA-evoked releases were inhibited by CBZ but were unaffected by CGS21680. Contrary to physiological condition, chronic administrations of IFNγ and TNFα enhanced basal, AdA-, and AMPA-evoked releases, whereas IFNγ and TNFα decreased and increased CGS21680-evoked releases via modulation A2AR expression. Both chronic administration of CGS21680 and CBZ suppressed astroglial L-glutamate release responses induced by chronic cytokine exposer. Especifically, chronic administration of CBZ and CGS21680 prevented the reduction and elevation of A2AR expression by respective IFNγ and TNFα. These findings suggest that A2AR agonistic effects of CBZ contribute to chronic prevention of pathomechanisms developments of several neuropsychiatric disorders associated with proinflammatory cytokines.

Cystine/Glutamate Antiporter and Aripiprazole Compensate NMDA Antagonist-Induced Dysfunction of Thalamocortical L-Glutamatergic Transmission.

To explore pathophysiology of schizophrenia, this study analyzed the regulation mechanisms that are associated with cystine/glutamate antiporter (Sxc), group-II (II-mGluR), and group-III (III-mGluR) metabotropic glutamate-receptors in thalamo-cortical glutamatergic transmission of MK801-induced model using dual-probe microdialysis. L-glutamate release in medial pre-frontal cortex (mPFC) was increased by systemic- and local mediodorsal thalamic nucleus (MDTN) administrations of MK801, but was unaffected by local administration into mPFC. Perfusion into mPFC of activators of Sxc, II-mGluR, and III-mGluR, and into the MDTN of activators of Sxc, II-mGluR, and GABAA receptor inhibited MK801-evoked L-glutamate release in mPFC. Perfusion of aripiprazole (APZ) into MDTN and mPFC also inhibited systemic MK801-evoked L-glutamate release in mPFC. Inhibition of II-mGluR in mPFC and MDTN blocked inhibitory effects of Sxc-activator and APZ on MK801-evoked L-glutamate release; however, their inhibitory effects were blocked by the inhibition of III-mGluR in mPFC but not in MDTN. These results indicate that reduced activation of the glutamate/NMDA receptor (NMDAR) in MDTN enhanced L-glutamate release in mPFC possibly through GABAergic disinhibition in MDTN. Furthermore, MDTN-mPFC glutamatergic transmission receives inhibitory regulation of Sxc/II-mGluR/III-mGluR functional complex in mPFC and Sxc/II-mGluR complex in MDTN. Established antipsychotic, APZ inhibits MK801-evoked L-glutamate release through the activation of Sxc/mGluRs functional complexes in both MDTN and mPFC.

Impacts of exposure to and subsequent discontinuation of clozapine on tripartite synaptic transmission.

BACKGROUND AND PURPOSE: Clozapine is an effective antipsychotic for treatment-resistant schizophrenia, but its discontinuation leads to discontinuation syndrome/catatonia complicated by benzodiazepine-resistance and rhabdomyolysis. EXPERIMENTAL APPROACH: This study determined time-dependent effects of exposure and subsequent discontinuation of clozapine on expression of connexin43, 5-HT receptors, intracellular L-ß-aminoisobutyrate (L-BAIBA) and 2nd-messengers and signalling of AMPK, PP2A and Akt in cultured astrocytes and rat frontal cortex. KEY RESULTS: Intracellular L-BAIBA levels increased during clozapine exposure but immediately recovered after discontinuation. Both exposure to clozapine and L-BAIBA increased connexin43 and signalling of AMPK/Akt time-dependently, but reduced PP2A signalling, 5-HT receptor expression and IP3 level. These changes recovered within 2 weeks after discontinuation, while 5-HT receptors and IP3 transiently increased during the recovery process. L-BAIBA activated AMPK signalling, leading to attenuated PP2A signalling. Astroglial D-serine release was increased by clozapine exposure but continued to increase within 1 week after discontinuation via activation of IP3 receptor function. CONCLUSION AND IMPLICATIONS: Clozapine discontinuation restored PP2A signalling due to decreased L-BAIBA, increased 5-HT receptor expression via probably enhanced 5-HT receptor recycling, but increased astroglial D-serine release persisted by transiently activated IP3 receptors via transiently increased IP3 level. Decreased L-BAIBA caused by clozapine discontinuation is, at least partially, involved in the transiently increased 5-HT receptor and astroglial D-serine release.

Age-Dependent Activation of Purinergic Transmission Contributes to the Development of Epileptogenesis in ADSHE Model Rats.

To explore the developmental processes of epileptogenesis/ictogenesis, this study determined age-dependent functional abnormalities associated with purinergic transmission in a genetic rat model (S286L-TG) of autosomal-dominant sleep-related hypermotor epilepsy (ADSHE). The age-dependent fluctuations in the release of ATP and L-glutamate in the orbitofrontal cortex (OFC) were determined using microdialysis and ultra-high-performance liquid chromatography with mass spectrometry (UHPLC-MS). ATP release from cultured astrocytes was also determined using UHPLC-MS. The expressions of P2X7 receptor (P2X7R), connexin 43, phosphorylated-Akt and phosphorylated-Erk were determined using capillary immunoblotting. No functional abnormalities associated with purinergic transmission could be detected in the OFC of 4-week-old S286L-TG and cultured S286L-TG astrocytes. However, P2X7R expression, as well as basal and P2X7R agonist-induced ATP releases, was enhanced in S286L-TG OFC in the critical ADSHE seizure onset period (7-week-old). Long-term exposure to a modest level of P2X7R agonist, which could not increase astroglial ATP release, for 14 d increased the expressions of P2X7R and connexin 43 and the signaling of Akt and Erk in astrocytes, and it enhanced the sensitivity of P2X7R to its agonists. Akt but not Erk increased P2X7R expression, whereas both Akt and Erk increased connexin 43 expression. Functional abnormalities, enhanced ATP release and P2X7R expression were already seen before the onset of ADSHE seizure in S286L-TG. Additionally, long-term exposure to the P2X7R agonist mimicked the functional abnormalities associated with purinergic transmission in astrocytes, similar to those in S286L-TG OFC. Therefore, these results suggest that long-term modestly enhanced purinergic transmission and/or activated P2X7R are, at least partially, involved in the development of the epileptogenesis of ADSHE, rather than that of ictogenesis.

A Novel Gliotransmitter, L-ß-Aminoisobutyric Acid, Contributes to Pathophysiology of Clinical Efficacies and Adverse Reactions of Clozapine.

Clozapine is listed as one of the most effective antipsychotics and has been approved for treating treatment-resistant schizophrenia (TRS); however, several type A and B adverse reactions, including weight gain, metabolic complications, cardiotoxicity, convulsions, and discontinuation syndromes, exist. The critical mechanisms of clinical efficacy for schizophrenia, TRS, and adverse reactions of clozapine have not been elucidated. Recently, the GABA isomer L-ß-aminoisobutyric acid (L-BAIBA), a protective myokine in the peripheral organs, was identified as a candidate novel transmission modulator in the central nervous system (CNS). L-BAIBA activates adenosine monophosphate-activated protein kinase (AMPK) signalling in both the peripheral organs and CNS. Activated AMPK signalling in peripheral organs is an established major target for treating insulin-resistant diabetes, whereas activated AMPK signalling in the hypothalamus contributes to the pathophysiology of weight gain and metabolic disturbances. Clozapine increases L-BAIBA synthesis in the hypothalamus. In addition, the various functions of L-BAIBA in the CNS have recently been elucidated, including as an activator of GABA-B and group-III metabotropic glutamate (III-mGlu) receptors. Considering the expressions of GABA-B and III-mGlu receptors (localised in the presynaptic regions), the activation of GABA-B and III-mGlu receptors can explain the distinct therapeutic advantages of clozapine in schizophrenia or TRS associated with N-methyl-D-aspartate (NMDA) receptor disturbance compared with other atypical antipsychotics via the inhibition of the persistent tonic hyperactivation of thalamocortical glutamatergic transmission in the prefrontal cortex. L-BAIBA has also been identified as a gliotransmitter, and a detailed exploration of the function of L-BAIBA in tripartite synaptic transmission can further elucidate the pathophysiology of effectiveness for treating TRS and/or specific adverse reactions of clozapine.

Opposing effects of clozapine and brexpiprazole on ß-aminoisobutyric acid: Pathophysiology of antipsychotics-induced weight gain.

Clozapine is one of the most effective antipsychotics and has the highest risk of weight gain and metabolic complications; however, the detailed pathophysiology of its clinical action and adverse reactions remains to be clarified. Therefore, the present study determined the chronic effects of clozapine (high risk of weight gain) and brexpiprazole (relatively low risk of weight gain) on intracellular and extracellular levels of ß-aminoisobutyric acid (BAIBA) enantiomers, which are endogenous activators of AMP-activated protein kinase (AMPK). L-BAIBA is the dominant BAIBA enantiomer in the rat hypothalamus and cultured astrocytes, whereas L-BAIBA accounts for only approximately 5% of the total plasma BAIBA enantiomers. L-BAIBA displayed GABAB receptor agonistic action in the extracellular space and was released through activated astroglial hemichannels, whereas in the intracellular space, L-BAIBA activated AMPK signalling. Chronic administration of the effective doses of clozapine increased intracellular and extracellular levels of L-BAIBA in the hypothalamus and cultured astrocytes, whereas that of brexpiprazole decreased them. These results suggest that enhancing hypothalamic AMPK signalling by increasing intracellular L-BAIBA levels is, at least partially, involved in the pathophysiology of clozapine-induced weight gain and metabolic complications.