Pharmacological evaluation of lateral habenula and rostromedial tegmental nucleus in the expression of ethanol-induced place preference.

Although ethanol administration produces a range of physiological effects, the rewarding aspect associated with its consumption is a major contributory factor to its abuse liability. Recently, lateral habenula (LHb) has been shown to be engaged by both rewarding and aversive stimuli. Its major glutamatergic output, the fasciculus retroflexus, projects to the rostromedial tegmental nucleus (RMTg) and controls the activity of the ventral tegmental area (VTA) dopaminergic system to promote reward circuitry. While several attempts have been made to understand the relationship between LHb and addiction, there is still a lack of knowledge in relation to ethanol addiction. In the present study, by pharmacologically exacerbating or inhibiting the LHb or RMTg neuronal activity during a post-conditioning test, we investigated the role of LHb-RMTg fasciculus retroflexus in ethanol-induced reward behavior using the conditioned place preference (CPP) test. We found that activation of LHb glutamatergic system by intra-LHb administration of l-trans-2,4-pyrrolidine dicarboxylate (PDC) (glutamate transporter inhibitor) significantly decreased CPP score; on the contrary, lamotrigine (inhibits glutamate release) significantly increased CPP score and showed a rewarding effect in CPP. Instead, intra-RMTg administration of muscimol (GABAA receptor agonist) significantly increased CPP score, whereas bicuculline (GABAA antagonist) treatment decreased CPP score. In immunohistochemistry, we found that PDC administration significantly decreased, whereas lamotrigine treatment significantly increased tyrosine hydroxylase immunoreactivity (TH-ir) in VTA and nucleus accumbens (NAc). Furthermore, while intra-RMTg administration of muscimol increased, the bicuculline treatment significantly decreased the TH-ir in VTA and NAc. Together, our behavioral and immunohistochemical results signify the role of LHb and RMTg in the expression of ethanol-conditioned reward behavior.

Cerebrolysin reduces excitotoxicity by modulation of cell-death proteins in delayed hours of ischemic reperfusion injury.

Recent preclinical and clinical reports suggest that cerebrolysin shows neuroprotective properties similar to endogenous neurotrophic factors in neurodegenerative disorders including ischemic stroke. However, little is known about its underlying antiexcitotoxic action. Adult male Wistar rats were intraperitoneally treated with cerebrolysin (0.15 or 0.30 mg/kg) or vehicle at 3, 6 and 12 h after ischemic reperfusion and were assessed 24 h after reperfusion in ischemic rats. We added cerebrolysin (2.5 or 5 mg/ml) or vehicle in primary cortical culture cells at 3, 6 and 12 h of post-glutamate exposure and performed cell viability assays at 24 h. Our in-vivo and in-vitro findings showed that cerebrolysin substantially reduced neuronal cell death in delayed hours of post ischemic- and glutamate-insult conditions respectively. Further, we have assessed the influence of NR-2 A/-2B receptor antagonism on neuroprotective action of cerebrolysin at 6 h in in-vivo as well as in-vitro conditions. Neuroprotective effect of cerebrolysin at 6 h of reperfusion was enhanced by pretreatment of NR2B antagonist RO25-6981.We found that cerebrolysin restrained upregulation of extrasynaptic NR2B responsible for triggering apoptotic pathways. Cerebrolysin reduced expression of important cell death proteins such as, JNK, PTEN, Calpain and Caspase-3 components. Importantly, we also found that cerebrolysin reduced SREBP1 expression, which gets activated only after 6 h of ischemia. These results demonstrate that cerebrolysin reduces excitotoxicity and protect neuronal cells in delayed hours of ischemic reperfusion injuries by decreasing cell death proteins.

Facilitation of GluN2C-containing NMDA receptors in the external globus pallidus increases firing of fast spiking neurons and improves motor function in a hemiparkinsonian mouse model.

Globus pallidus externa (GPe) is a nucleus in the basal ganglia circuitry involved in the control of movement. Recent studies have demonstrated a critical role of GPe cell types in Parkinsonism. Specifically increasing the function of parvalbumin (PV) neurons in the GPe has been found to facilitate motor function in a mouse model of Parkinson's disease (PD). The knowledge of contribution of NMDA receptors to GPe function is limited. Here, we demonstrate that fast spiking neurons in the GPe express NMDA receptor currents sensitive to GluN2C/GluN2D-selective inhibitors and glycine site agonist with higher efficacy at GluN2C-containing receptors. Furthermore, using a novel reporter model, we demonstrate the expression of GluN2C subunits in PV neurons in the GPe which project to subthalamic nuclei. GluN2D subunit was also found to localize to PV neurons in GPe. Ablation of GluN2C subunit does not affect spontaneous firing of fast spiking neurons. In contrast, facilitating the function of GluN2C-containing receptors using glycine-site NMDA receptor agonists, D-cycloserine (DCS) or AICP, increased the spontaneous firing frequency of PV neurons in a GluN2C-dependent manner. Finally, we demonstrate that local infusion of DCS or AICP into the GPe improved motor function in a mouse model of PD. Together, these results demonstrate that GluN2C-containing receptors and potentially GluN2D-containing receptors in the GPe may serve as a therapeutic target for alleviating motor dysfunction in PD and related disorders.

Protocatechuic Acid Prevents Early Hour Ischemic Reperfusion Brain Damage by Restoring Imbalance of Neuronal Cell Death and Survival Proteins.

OBJECTIVE: To investigate the neuroprotective effect of protocatechuic acid (PCA) on cell death/survival protein imbalance in a rat model of middle cerebral artery occlusion and reperfusion. METHODS: Focal ischemia was induced by middle cerebral artery occlusion in adult male Wistar rats and confirmed by measuring infarction of brain by 2,3,5-Triphenyltetrazolium chloride (TTC) staining. Rats were treated with vehicle or PCA at 10, 30 or 50 mg/kg dose intraperitoneally and subjected to neurological deficits or beam walk assessment at 24 h of reperfusion. Effective dose of PCA (50 mg/kg) was administered at 1, 2 and 3 h time point of post-ictus ischemia. Cellular damage and nuclear condensation was observed by haematoxylin and eosin (H and E) staining and Hoechst 33342 staining respectively. Additionally, immunohistochemical expression of caspase 3 and cAMP-response element binding protein (CREB) and their mRNA's were observed. RESULTS: PCA at 30 and 50 mg/kg significantly improved behavioural performance and reduced infarction. Maximum neuroprotective effect of PCA (50 mg/kg) was found at 1 h (early hours) post-ictus ischemia along with reduction in cellular damage and nuclear condensation. PCA increased CREB protein and it's mRNA, while suppressed caspase-3 protein and mRNA at 1 h of reperfusion injury. CONCLUSION: PCA exhibit the potential to prevent early hour (1h) reperfusion injury restoring balance of survival and death protein may offer a cost effective adjuvant therapy in stroke.

Antipsychotic-like profile of CIQ isomers in animal models of schizophrenia.

Earlier, we have shown the efficacy of racemic (±) CIQ, a positive allosteric modulator of GluN2C/2D receptor against MK-801 induced impairment of prepulse inhibition as well as working memory. The present study investigated the antipsychotic-like profile of different CIQ (±, +, -) isomers against schizophrenia-like symptoms in series of behavioural animal models like apomorphine climbing, social isolation behaviour and NMDA receptor antagonist MK-801 induced cognitive deficits. Further, we also tested CIQ (±, +, -) isomers in neurodevelopmental model against MK-801induced deficits using open field test, Y-maze test and novel object recognition test. CIQ (±, +, -) isomers decreased climbing behaviour, increased social interaction and improved the MK-801 induced deficits in working memory in Y-maze. Further, CIQ (±, +) but not CIQ (-) improved the recognition memory in novel object recognition test as well as reduced hyperlocomotion and stereotyped behaviour. We conclude that CIQ (±, +) but not CIQ (-) exhibit the significant antipsychotic-like profile.

Dapsone prolong delayed excitotoxic neuronal cell death by interacting with proapoptotic/survival signaling proteins.

BACKGROUND: Dapsone prevents ischemic injury, inhibits apoptosis and shows functional improvement post-ischemia. However, its effect on proapoptotic or survival proteins in delayed ischemia remains unclear. METHODS: Male adult Wistar rats were subjected to middle cerebral artery occlusion (MCAO) for 90 min followed by 24 h of ischemic reperfusion (I/R). Dapsone [9.375 or 12.5 mg/kg, intraperitoneally (IP)] was administered at 3, 6 and 12 h of I/R followed by behavioural assessment, brain infarction, histological alteration and cell viability study. Further, dapsone (25 and 50 µM) was added at 3, 6 and 12 h after L-glutamate (100 µM) in primary cortical culture (DIV 14) and cell viability, cytotoxicity, apoptosis was observed. Proteins expression were observed using immunocytochemistry. All experiments were performed after 24 h of I/R (In-Vivo) and 24 h of recovery post glutamate insult (In-Vitro). RESULTS: Reduced brain infarction, improved neurobehavioural functions in addition to reduction in abnormal morphological structures of ischemic brain and improvement in cell viability was observed with treatment of dapsone (12.5 mg/kg) administered upto 6 h. Similarly, dapsone (25, 50 µM) increased cell survival post glutamate insult in cortical culture (In-vitro). Further, dapsone treatment at delayed hours (6 h) reduced apoptotic nuclei and proapoptotic proteins JNK, PTEN, Calpain, Caspase 3 expression along with activation of prosurvival protein BDNF expression post-glutamate insult. CONCLUSION: Our results suggest that dapsone has the potential to limit the neuronal damage post-glutamate insult in delayed hours (6 h) through repressing proapoptotic proteins JNK, PTEN, Calpain, Caspase-3 of cerebral ischemia along with activation of pro-survival protein BDNF.

Effect of D-cycloserine in conjunction with fear extinction training on extracellular signal-regulated kinase activation in the medial prefrontal cortex and amygdala in rat.

D-cycloserine (DCS) is currently under clinical trials for a number of neuropsychiatric conditions and has been found to augment fear extinction in rodents and exposure therapy in humans. However, the molecular mechanism of DCS action in these multiple modalities remains unclear. Here, we describe the effect of DCS administration, alone or in conjunction with extinction training, on neuronal activity (c-fos) and neuronal plasticity [phospho-extracellular signal-regulated kinase (pERK)] markers using immunohistochemistry. We found that intraperitoneal administration of DCS in untrained young rats (24-28 days old) increased c-fos- and pERK-stained neurons in both the prelimbic and infralimbic division of the medial prefrontal cortex (mPFC) and reduced pERK levels in the lateral nucleus of the central amygdala. Moreover, DCS administration significantly increased GluA1, GluN1, GluN2A, and GluN2B expression in the mPFC. In a separate set of animals, we found that DCS facilitated fear extinction and increased pERK levels in the infralimbic prefrontal cortex, prelimbic prefrontal cortex intercalated cells and lateral nucleus of the central amygdala, compared with saline control. In the synaptoneurosomal preparation, we found that extinction training increased iGluR protein expression in the mPFC, compared with context animals. No significant difference in protein expression was observed between extinction-saline and extinction-DCS groups in the mPFC. In contrast, in the amygdala DCS, the conjunction with extinction training led to an increase in iGluR subunit expression, compared with the extinction-saline group. Our data suggest that the efficacy of DCS in neuropsychiatric disorders may be partly due to its ability to affect neuronal activity and signaling in the mPFC and amygdala subnuclei.

Agmatine attenuates acquisition but not the expression of ethanol conditioned place preference in mice: a role for imidazoline receptors.

The present study investigated the effect of agmatine on acquisition and expression of ethanol conditioned place preference (CPP) and its modulation by imidazoline agents. Swiss albino mice were treated intraperitoneally with saline or agmatine (20-40 mg/kg) before injection of ethanol (1.25 mg/kg) during conditioning days or on a test day (20-120 mg/kg), to observe the effect on acquisition or expression of CPP, respectively. Agmatine inhibited the acquisition but not the expression of ethanol CPP. Furthermore, both the I1 receptor antagonist, efaroxan (9 mg/kg) and the I2 receptor antagonist, BU224 (5 mg/kg) attenuated the agmatine-induced inhibition of the ethanol CPP acquisition. In contrast, the I2 receptor agonist, 2-BFI (5 mg/kg) and I1 receptor agonist, moxonidine (0.4 mg/kg) alone, or a combination of their subeffective doses, significantly attenuated the effect of agmatine (20 mg/kg) on acquisition of ethanol CPP. Agmatine or imidazoline agents alone produced neither place preference nor aversion, and at the doses used in the present study did not affect locomotor activity. Thus, agmatine attenuates the acquisition of ethanol CPP at least in part by imidazoline (I1 or I2) receptors. In future studies, agmatine or agents acting at the imidazoline receptors could be explored for their therapeutic potential in ethanol dependence.

Prevention of glutamate excitotoxicity in lateral habenula alleviates ethanol withdrawal-induced somatic and behavioral effects in ethanol dependent mice.

Ethanol withdrawal commonly leads to anxiety-related disorder, a central factor toward negative reinforcement leading to relapse. The lateral habenula (LHb), an epithalamic nucleus, has emerged to be critical for both reward and aversion processing. Recent studies have also implicated the hyperactivity of LHb, adding to the emergence of negative emotional states during withdrawal from addictive drugs. Herein, we have studied the effects of glutamate transporter inhibitor (PDC), GluN2B-containing NMDAR antagonist (Ro25-6981), and intracellular calcium chelator (BAPTA-AM) injection in LHb on ethanol withdrawal symptoms. We found that ethanol 4 g/kg 20 % w/v intragastric (i.g.) for 10 days followed by 24 h of withdrawal showed a significant increase in somatic signs characterized by vocalization, shaking, and scratching. It also increased locomotor activity and anxiety-like behavior, collectively showing expression of ethanol withdrawal symptoms. The intra-LHb administration of PDC (0.5 ng) worsened the effect of ethanol withdrawal, whereas Ro25-6981 (2 and 4 ng) and BAPTA-AM (6.5 and 13 ng) significantly reversed ethanol withdrawal-induced behavior evident by a decrease in somatic signs, locomotor activity, and anxiety-like behavior. Further, pretreatment of Ro25-6981 and BAPTA-AM reduced the neuronal loss, whereas PDC increased it compared to the vehicle-treated group, as evidenced by NeuN staining. Altogether, our results suggest that increased glutamate, GluN2B activation, and likely calcium increase indicative of glutamate excitotoxicity-induced neuronal loss in LHb possibly endorse the emergence of ethanol withdrawal symptoms, while their inhibition might help in alleviating the ethanol withdrawal symptoms.

Differential effect of NMDA receptor GluN2C and GluN2D subunit ablation on behavior and channel blocker-induced schizophrenia phenotypes.

The GluN2C- and GluN2D-containing NMDA receptors are distinct from GluN2A- and GluN2B-containing receptors in many aspects including lower sensitivity to Mg2+ block and lack of desensitization. Recent studies have highlighted the unique contribution of GluN2C and GluN2D subunits in various aspects of neuronal and circuit function and behavior, however a direct comparison of the effect of ablation of these subunits in mice on pure background strain has not been conducted. Using knockout-first strains for the GRIN2C and GRIN2D produced on pure C57BL/6N strain, we compared the effect of partial or complete ablation of GluN2C and GluN2D subunit on various behaviors relevant to mental disorders. A large number of behaviors described previously in GluN2C and GluN2D knockout mice were reproduced in these mice, however, some specific differences were also observed possibly representing strain effects. We also examined the response to NMDA receptor channel blockers in these mouse strains and surprisingly found that unlike previous reports GluN2D knockout mice were not resistant to phencyclidine-induced hyperlocomotion. Interestingly, the GluN2C knockout mice showed reduced sensitivity to phencyclidine-induced hyperlocomotion. We also found that NMDA receptor channel blocker produced a deficit in prepulse inhibition which was prevented by a GluN2C/2D potentiator in wildtype and GluN2C heterozygous mice but not in GluN2C knockout mice. Together these results demonstrate a unique role of GluN2C subunit in schizophrenia-like behaviors.

Neurosteroid allopregnanolone mediates anxiolytic effect of etifoxine in rats.

Etifoxine (6-chloro-2-ethylamino-4-methyl-4-phenyl-4H-3,1-benzoxazine hydrochloride), a nonbenzodiazepine anxiolytic drug, potentiates GABA(A) receptor function perhaps through stimulation of neurosteroid biosynthesis. However, the exact mechanism of etifoxine action is not fully understood. In this study, we have assessed the possible role of GABAergic neurosteroid like allopregnanolone (ALLO) in the anxiolytic-like effect of etifoxine in rats using elevated plus maze test. Selective GABA(A) receptor agonist, muscimol, ALLO or neurosteroidogenic agents like progesterone, metyrapone or mitochondrial diazepam binding inhibitor receptor (MDR) agonist, FGIN 1-27 significantly heightened the etifoxine-induced anxiolysis. On the other hand, GABA(A) receptor antagonist, bicuculline or neurosteroid biosynthesis inhibitors like finasteride, indomethacin, trilostane or PBR antagonist, PK11195 significantly blocked the effect of etifoxine. Bilateral adrenalectomy did not influence anti-anxiety effect of etifoxine thereby ruling out contribution of adrenal steroids. Thus, our results provide behavioral evidence for the role of neurosteroids like ALLO in the anti-anxiety effect of etifoxine.

Chronic progesterone treatment augments while dehydroepiandrosterone sulphate prevents tolerance to ethanol anxiolysis and withdrawal anxiety in rats.

We have recently shown that the neurosteroid allopregnanolone modulates anxiolytic effect of ethanol. In the present report, we attempted to examine whether neurosteroids progesterone and dehydroepiandrosterone sulphate (DHEAS), which modulate gamma-aminobutyric acid (GABA(A)) receptor function, affects development of tolerance to ethanol anxiolysis and withdrawal anxiety. Rats on ethanol (6% v/v in nutritionally balanced liquid diet) for prolong period (10 days) were injected twice daily either with vehicle, progesterone (a precursor of allopregnanolone, positive GABA(A) receptor modulator), finasteride (5alpha-reductase inhibitor) or DHEAS (negative GABA(A) receptor modulator). During this period, rats were acutely challenged periodically with ethanol (2 g/kg, i.p., 8% w/v) and subjected to the elevated plus maze test. For withdrawal studies, similar treatment protocols (except ethanol challenge) were employed and on day 11, rats were subjected to the elevated plus maze test at different time intervals post-ethanol withdrawal. While progesterone significantly advanced the development of tolerance to ethanol anxiolysis and enhanced withdrawal anxiety, DHEAS and finasteride prevented such behavioral alterations. These data highlight the important role played by GABAergic neurosteroids progesterone and DHEAS in the development of tolerance to ethanol anxiolysis and withdrawal anxiety in rats. Moreover, it points to the potential usefulness of specific neurosteroids as targets in the treatment of alcoholism.

Interactions of nitric oxide with α2 -adrenoceptors within the locus coeruleus underlie the facilitation of inhibitory avoidance memory by agmatine.

BACKGROUND AND PURPOSE: Agmatine, a putative neurotransmitter, plays a vital role in learning and memory. Although it is considered an endogenous ligand of imidazoline receptors, agmatine exhibits high affinity for α-adrenoceptors, NOS and NMDA receptors. These substrates within the locus coeruleus (LC) are critically involved in learning and memory processes. EXPERIMENTAL APPROACH: The hippocampus and LC of male Wistar rat were stereotaxically cannulated for injection. Effects of agmatine, given i.p. or intra-LC, on acquisition, consolidation and retrieval of inhibitory avoidance (IA) memory were measured. The NO donor S-nitrosoglutathione, non-specific (L-NAME) and specific NOS inhibitors (L-NIL, 7-NI, L-NIO), the α2 -adrenoceptor antagonist (yohimbine) or the corresponding agonist (clonidine) were injected intra-LC before agmatine. Intra-hippocampal injections of the NMDA antagonist, MK-801 (dizocilpine), were used to modify the memory enhancing effects of agmatine, SNG and yohimbine. Expression of tyrosine hydroxylase (TH) and eNOS in the LC was assessed immunohistochemically. KEY RESULTS: Agmatine (intra-LC or i.p.) facilitated memory retrieval in the IA test. S-nitrosoglutathione potentiated, while L-NAME and L-NIO decreased, these effects of agmatine. L-NIL and 7-NI did not alter the effects of agmatine. Yohimbine potentiated, whereas clonidine attenuated, effects of agmatine within the LC. The effects of agmatine, S-nitrosoglutathione and yohimbine were blocked by intra-hippocampal MK-801. Agmatine increased the population of TH- and eNOS-immunoreactive elements in the LC. CONCLUSIONS AND IMPLICATIONS: The facilitation of memory retrieval in the IA test by agmatine is probably mediated by interactions between eNOS, NO and noradrenergic pathways in the LC.

The NMDA receptor GluN2C subunit controls cortical excitatory-inhibitory balance, neuronal oscillations and cognitive function.

Despite strong evidence for NMDA receptor (NMDAR) hypofunction as an underlying factor for cognitive disorders, the precise roles of various NMDAR subtypes remains unknown. The GluN2C-containing NMDARs exhibit unique biophysical properties and expression pattern, and lower expression of GluN2C subunit has been reported in postmortem brains from schizophrenia patients. We found that loss of GluN2C subunit leads to a shift in cortical excitatory-inhibitory balance towards greater inhibition. Specifically, pyramidal neurons in the medial prefrontal cortex (mPFC) of GluN2C knockout mice have reduced mEPSC frequency and dendritic spine density and a contrasting higher frequency of mIPSCs. In addition a greater number of perisomatic GAD67 puncta was observed suggesting a potential increase in parvalbumin interneuron inputs. At a network level the GluN2C knockout mice were found to have a more robust increase in power of oscillations in response to NMDAR blocker MK-801. Furthermore, GluN2C heterozygous and knockout mice exhibited abnormalities in cognition and sensorimotor gating. Our results demonstrate that loss of GluN2C subunit leads to cortical excitatory-inhibitory imbalance and abnormal neuronal oscillations associated with neurodevelopmental disorders.

Evaluation of GABAergic neuroactive steroid 3alpha-hydroxy-5alpha-pregnane-20-one as a neurobiological substrate for the anti-anxiety effect of ethanol in rats.

RATIONALE: Acute systemic ethanol administration is known to elevate plasma and cerebral levels of neuroactive steroid 3alpha-hydroxy-5alpha-pregnane-20-one (3alpha, 5alpha-THP; allopregnanolone) to a concentration sufficient to potentiate GABA(A) receptors. We have earlier demonstrated that 3alpha, 5alpha-THP mediates the antidepressant-like effect of ethanol in Porsolt forced swim test. OBJECTIVE: The aim of the present study is to explain the relationship between endogenous GABAergic neurosteroids and anxiolytic effect of ethanol in Sprague-Dawley rats. METHOD: The mediation of 3alpha, 5alpha-THP in the anti-anxiety effect of ethanol was assessed by pharmacological interactions of ethanol with various endogenous neurosteroidal modulators and using simulated physiological conditions of altered neurosteroid content in elevated plus maze (EPM) test. RESULTS: Pretreatment of 3alpha, 5alpha-THP (0.5-2.5 mug/rat, i.c.v.) or neurosteroidogenic agents such as 3alpha, 5alpha-THP precursor progesterone (5 or 10 mg/kg, i.p.), 11-beta hydroxylase inhibitor metyrapone (50 or 100 mg/kg, i.p.) or the GABA(A) receptor agonist muscimol (25 ng/rat, i.c.v.) significantly potentiated the anti-anxiety effect of ethanol (1 g/kg, i.p.). On the other hand, the GABAergic antagonistic neurosteroid dehydroepiandrosterone sulphate (DHEAS) (1 mg/kg, i.p.), the GABA(A) receptor blocker bicuculline (1 mg/kg, i.p.), the 5alpha-reductase inhibitor finasteride (50 x 2 mg/kg, s.c.) or the mitochondrial diazepam binding inhibitory receptor antagonist PK11195 (1 mg/kg, i.p.) reduced ethanol-induced preference of time spent and number of entries into open arms. Anti-anxiety effect of ethanol was abolished in adrenalectomized (ADX) rats as compared to sham-operated control. This ADX-induced blockade was restored by prior systemic injection of progesterone, signifying the contribution of peripheral steroidogenesis in ethanol anxiolysis. Socially isolated animals known to exhibit decreased brain 3alpha, 5alpha-THP and GABA(A) receptor functions displayed reduced sensitivity to the effects of ethanol and 3alpha, 5alpha-THP in EPM test. CONCLUSIONS: Our results demonstrated the contributory role of neuroactive steroid 3alpha, 5alpha-THP in the anti-anxiety effect of ethanol. It is speculated that ethanol-induced modulation of endogenous GABAergic neurosteroids, especially 3alpha, 5alpha-THP, might be crucial pertinent to the etiology of 'trait' anxiety (tension reduction) and ethanol abuse.

Role of neuroactive steroid allopregnanolone in antipsychotic-like action of olanzapine in rodents.

Olanzapine increases brain allopregnanolone (ALLO) levels sufficiently to modulate neuronal activity by allosterically regulating GABAA receptors. Recently, we reported the antipsychotic-like profile of ALLO in rodents. The present study examined the hypothesis that olanzapine-induced elevation of endogenous neurosteroid ALLO is vital for its neuroleptic-like action. The conditioned avoidance response (CAR) and apomorphine-induced climbing behavioral paradigms were used in rodents. Administration of ALLO (1 microg, intracerebroventricular (i.c.v.)) or neurosteroidogenic agents such as the mitochondrial diazepam binding inhibitor receptor agonist, FGIN 1-27 (0.5 microg, i.c.v.) or the ALLO precursor, progesterone (10 mg/kg, i.p.) significantly potentiated olanzapine-induced blockade of CAR and apomorphine-induced climbing. In contrast, these agents failed to alter the antipsychotic-like effect of risperidone and haloperidol. On the other hand, inhibition of the endogenous biosynthesis of neurosteroids by the 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane (30 mg/kg, i.p.), the 3alpha-hydroxysteroid oxidoreductase inhibitor, indomethacin (5 mg/kg, i.p.), or the GABAA receptor antagonist bicuculline (1 mg/kg, i.p.) and dehydroepiandrosterone sulfate (DHEAS) (1 mg/kg, i.p.) blocked the effect of olanzapine, but not of risperidone and haloperidol. Socially isolated animals, known to exhibit decreased brain ALLO and GABAA receptor functions, displayed a shortening in the muscimol-induced loss of righting reflex and an increased susceptibility to apomorphine-induced climbing. Administration of olanzapine, but not of haloperidol and risperidone, normalized the duration of muscimol-elicited loss of righting reflex. Although all three antipsychotics proved capable of antagonizing the apomorphine-induced climbing, a dose almost five times higher of olanzapine was required in socially isolated animals. The data obtained suggest that enhancement of the GABAergic tone plays a key role in the antipsychotic-like effect exerted by olanzapine in rodents, likely as a consequence of augmented levels of neuroactive steroids, in particular ALLO, in the brain. The present findings provide the first specific behavioral evidence in support of the hypothesis that neuroactive steroid ALLO- mediated GABAergic modulation is essential for the antipsychotic-like action of olanzapine.

Neurosteroid allopregnanolone attenuates development of nicotine withdrawal behavior in mice.

Avoidance of the nicotine withdrawal syndrome as well as the positive subjective effects of nicotine is the major predisposing factor to motivate nicotine abuse. However, its underlying neurobehavioral mechanisms remain perplexing. In the present study, we investigated the influence of the neurosteroid allopregnanolone (ALLO; 0.5-2mg/kg) on the development of nicotine withdrawal in mice. Chronic nicotine injections (2mg/kg, four times daily, 10 days) followed by its withdrawal, elicited severe somatic signs, anxiety and marked reduction in locomotion. However, these withdrawal signs were not evident in animals pretreated with ALLO or progesterone (Day 8-10) daily before 1st injection of nicotine. This effect of neurosteroid on the nicotine withdrawal signs was reversed by indomethacin and finasteride the inhibitors of neurosteroid biosynthesis. On the contrary, single or repeated dose administration of ALLO or progesterone during nicotine withdrawal (Day 11) did not affect the expression of nicotine withdrawal signs. Thus, compounds that modulate endogenous neurosteroid ALLO are likely to have therapeutic potential for treating various aspects of nicotine dependence and withdrawal.

Agmatine, an endogenous imidazoline receptor ligand modulates ethanol anxiolysis and withdrawal anxiety in rats.

Present study investigated the role of agmatine in ethanol-induced anxiolysis and withdrawal anxiety using elevated plus maze (EPM) test in rats. The anxiolytic-like effect of ethanol was potentiated by pretreatment with imidazoline I(1)/I(2) receptor agonist agmatine (10-20 mg/kg, i.p.), imidazoline I(1) receptor agonists, moxonidine (0.25 mg/kg, i.p.) and clonidine (0.015 mg/kg, i.p.), imidazoline I(2) receptor agonist, 2-BFI (5 mg/kg, i.p.) as well as by the drugs known to increase endogenous agmatine levels in brain viz., L-arginine, an agmatine biosynthetic precursor (100 microg/rat, i.c.v.), ornithine decarboxylase inhibitor, DFMO (125 microg/rat, i.c.v.), diamine oxidase inhibitor, aminoguanidine (65 microg/rat, i.c.v.) and agmatinase inhibitor, arcaine (50 microg/rat, i.c.v.). Conversely, prior administration of I(1) receptor antagonist, efaroxan (1 mg/kg, i.p.), I(2) receptor antagonist, idazoxan (0.25mg/kg, i.p.) and arginine decarboxylase inhibitor, D-arginine (100 microg/rat, i.c.v.) blocked the anxiolytic-like effect of ethanol. Moreover, ethanol withdrawal anxiety was markedly attenuated by agmatine (10-20 mg/kg, i.p.), moxonidine (0.25 mg/kg, i.p.), clonidine (0.015 mg/kg, i.p.), 2-BFI (5 mg/kg, i.p.), L-arginine (100 microg/rat, i.c.v.), DFMO (125 microg/rat, i.c.v.), aminoguanidine (65 microg/rat, i.c.v.) and arcaine (50 microg/rat, i.c.v.). The anti-anxiety effect of agmatine in ethanol-withdrawn rats was completely blocked by efaroxan (1 mg/kg, i.p.) and idazoxan (0.25 mg/kg, i.p.). These results suggest that agmatine and imidazoline receptor system may be implicated in ethanol-induced anxiolysis and withdrawal anxiety and strongly support further investigation of agmatine in ethanol dependence mechanism. The data also project agmatine as a potential therapeutic target in overcoming alcohol withdrawal symptoms such as anxiety.

Antidepressant like effect of selective serotonin reuptake inhibitors involve modulation of imidazoline receptors by agmatine.

Recent findings demonstrated the dysregulation of imidazoline receptor binding sites in major depression and their normalization by chronic treatment with antidepressants including selective serotonin reuptake inhibitors (SSRIs). Present study investigated the role of agmatine and imidazoline receptors in antidepressant like effect of SSRIs and imipramine in mouse forced swimming test (FST) paradigm. The antidepressant like effect of fluoxetine or paroxetine was potentiated by imidazoline I(1)/I(2) receptor agonist agmatine (5-10 mg/kg, ip), imidazoline I(1) receptor agonists, moxonidine (0.25-0.5 mg/kg, ip) and clonidine (0.015-0.03 mg/kg, ip), imidazoline I(2) receptor agonist, 2-(2-benzofuranyl)-2-imidazoline (5-10 mg/kg, ip) as well as by the drugs known to increase endogenous agmatine levels in brain viz., L-arginine, an agmatine biosynthetic precursor (40 microg/mouse, icv), ornithine decarboxylase inhibitor, difluoromethyl ornithine (12.5 microg/mouse, icv), diamine oxidase inhibitor, aminoguanidine (6.5 microg/mouse, icv) and agmatinase inhibitor, arcaine (50 microg/mouse, icv). Conversely, prior administration of I(1) receptor antagonist, efaroxan (1 mg/kg, ip), I(2) receptor antagonist, idazoxan (0.25 mg/kg, ip) and arginine decarboxylase inhibitor, d-arginine (100 mg/kg, ip) blocked the antidepressant like effect of paroxetine (10 mg/kg, ip) and fluoxetine (20 mg/kg, ip). On the other hand, antidepressant like effect of imipramine was neither augmented nor attenuated by any of the above drugs. Mice pretreated with SSRIs but not imipramine and exposed to FST showed higher concentration of agmatine in brain as compared to saline control. This effect of SSRIs on agmatine levels was completely blocked by arginine decarboxylase inhibitor d-arginine but not by imidazoline receptor antagonists, efaroxan or idazoxan. These results demonstrate that modulation of imidazoline receptors by agmatine are implicated in the antidepressant like effect of SSRIs and may be projected as a potential therapeutic target for the treatment of depressive disorders.