Neurobiological basis of emergence from anesthesia.

The suppression of consciousness by anesthetics and the emergence of the brain from anesthesia are complex and elusive processes. Anesthetics may exert their inhibitory effects by binding to specific protein targets or through membrane-mediated targets, disrupting neural activity and the integrity and function of neural circuits responsible for signal transmission and conscious perception/subjective experience. Emergence from anesthesia was generally thought to depend on the elimination of the anesthetic from the body. Recently, studies have suggested that emergence from anesthesia is a dynamic and active process that can be partially controlled and is independent of the specific molecular targets of anesthetics. This article summarizes the fundamentals of anesthetics' actions in the brain and the mechanisms of emergence from anesthesia that have been recently revealed in animal studies.

Zuranolone, a neuroactive drug, used in the treatment of postpartum depression by modulation of GABAA receptors.

BACKGROUND: Postpartum depression [PPD] is a prevalent and debilitating mood disorder that affects mothers in the weeks to months after childbirth. Zuranolone (Zurzuvae) is a novel pharmaceutical agent that was approved by the US FDA on 4 August 2023 for the management of PPD. This review article provides a comprehensive overview of zuranolone, focusing on its dosing, chemistry, mechanism of action, clinical trials, adverse drug reaction, and overall conclusion regarding its utility in the management of PPD. It also discusses the recommended dosing strategies to achieve optimal efficacy while minimizing adverse effects as the dosage regimen of zuranolone is critical for its therapeutic application. Moreover, it gives insights into neurobiological pathways involved in PPD. METHODOLOGY: Data from randomized controlled trials and observational studies was collected to provide a comprehensive understanding of zuranolone in the management and treatment of PPD. CONCLUSION: Zuranolone represents a promising therapeutic option for women suffering from postpartum depression. However, ongoing research and post-marketing surveillance are essential to further elucidate its long-term safety and efficacy. The integration of zuranolone into clinical practice may significantly improve the quality of life for mothers facing the challenges of postpartum depression.

Ginger (Zingiber Officinale Roscoe) ameliorates ethanol-induced cognitive impairment by modulating NMDA and GABA-A receptors in rat hippocampus.

Brain damage caused by ethanol abuse may lead to permanent damage, including severe dementia. The aim of this study was to investigate the effects of ginger powder on ethanol-induced cognitive disorders by examining oxidative damage and inflammation status, and the gene expression of N-methyl-D-aspartate (NMDA) and γ-Aminobutyric acid (GABA)-A receptors in the hippocampus of male rats. 24 adult male Sprague-Dawley rats were allocated randomly to four groups as follows control, ethanol (4g/kg/day, by gavage), ginger (1g/kg/day, by gavage), and ginger-ethanol. At the end of the study, memory and learning were evaluated by the shuttle box test. Moreover, to explore mechanisms involved in ethanol-induced cognitive impairment and the protective effect of ginger, the expression of Nuclear factor kappa B (NF-κB), nuclear factor erythroid 2-related factor 2 (Nrf2), NMDA receptor, and GABA-A receptor was measured along with inflammatory and oxidative biomarkers in the hippocampus tissue. The results showed that ethanol could induce cognitive impairment in the ethanol group, while pretreatment with ginger could reverse it. The gene expression of the NF-κB/ Tumor necrosis factor (TNF)-α/Interleukin (IL)-1ß pathway and NMDA and GABA-A receptors significantly increased in the ethanol group compared to the control group. While pretreatment with ginger could significantly improve ethanol-induced cognitive impairment through these pathways in the ginger-ethanol group compared to the ethanol group (P < 0.05). It can be concluded that ginger powder could ameliorate ethanol-induced cognitive impairment by modulating the expression of NMDA and GABA-A receptors and inhibiting oxidative damage and the NF-κB/TNF-α/IL-1ß pathway in the rat hippocampus.

α5GABAA receptor: A potential therapeutic target for perioperative neurocognitive disorders, a review of preclinical studies.

Perioperative neurocognitive disorders (PND) are a common complication in elderly patients following surgery, which not only prolongs the recovery period but also affects their future quality of life and imposes a significant burden on their family and society. Multiple factors, including aging, vulnerability, anesthetic drugs, cerebral oxygen desaturation, and severe pain, have been associated with PND. Unfortunately, no effective drug is currently available to prevent PND. α5 γ-aminobutyric acid subtype A (α5GABAA) receptors have been implicated in cognitive function modulation. Positive or negative allosteric modulators of α5GABAA receptors have been found to improve cognitive impairment under different conditions. Therefore, targeting α5GABAA receptors may represent a promising treatment strategy for PND. This review focuses on preclinical studies of α5GABAA receptors and the risk factors associated with PND, primarily including aging, anesthetics, and neuroinflammation. Specifically, positive allosteric modulators of α5GABAA receptors have improved cognitive function in aged experimental animals. In contrast, negative allosteric modulators of α5GABAA receptors have been found to facilitate cognitive recovery in aged or adult experimental animals undergoing anesthesia and surgery but not in aged experimental animals under anesthesia alone. The reasons for the discordant findings have yet to be elucidated. In preclinical studies, different strategies of drug administration, as well as various behavioral tests, may influence the stability of the results. These issues need to be carefully considered in future studies.

Pathogenic variants of human GABRA1 gene associated with epilepsy: A computational approach.

Critical for brain development, neurodevelopmental and network disorders, the GABRA1 gene encodes for the α1 subunit, an abundantly and developmentally expressed subunit of heteropentameric gamma-aminobutyric acid A receptors (GABAARs) mediating primary inhibition in the brain. Mutations of the GABAAR subunit genes including GABRA1 gene are associated with epilepsy, a group of syndromes, characterized by unprovoked seizures and diagnosed by integrative approach, that involves genetic testing. Despite the diagnostic use of genetic testing, a large fraction of the GABAAR subunit gene variants including the variants of GABRA1 gene is not known in terms of their molecular consequence, a challenge for precision and personalized medicine. Addressing this, one hundred thirty-seven GABRA1 gene variants of unknown clinical significance have been extracted from the ClinVar database and computationally analyzed for pathogenicity. Eight variants (L49H, P59L, W97R, D99G, G152S, V270G, T294R, P305L) are predicted as pathogenic and mapped to the α1 subunit's extracellular domain (ECD), transmembrane domains (TMDs) and extracellular linker. This is followed by the integration with relevant data for cellular pathology and severity of the epilepsy syndromes retrieved from the literature. Our results suggest that the pathogenic variants in the ECD of GABRA1 (L49H, P59L, W97R, D99G, G152S) will probably manifest decreased surface expression and reduced current with mild epilepsy phenotypes while V270G, T294R in the TMDs and P305L in the linker between the second and the third TMDs will likely cause reduced cell current with severe epilepsy phenotypes. The results presented in this study provides insights for clinical genetics and wet lab experimentation.

Abusive use of Zolpidem as a Result of COVID-19 and Perspectives of Continuity of the Problem in the Post-Pandemic Period.

Zolpidem is a non-benzodiazepine hypnotic drug that works as a positive modulator of Gamma-Amino Butyric Acid-A (GABA-A) receptors, with high selectivity for α1 subunits. Given this selective binding, the drug has a strong hypnotic activity. Social isolation during the SARS-CoV-2 pandemic has contributed to increased rates of anxiety, depression, and insomnia. As a result, studies have pointed to a possible increase in the indiscriminate use of drugs with sedative effects, such as Zolpidem, during the pandemic. The aim of this work was to present prospective evidence that warns of the possibility of the abusive use of Zolpidem even after the pandemic. High rates of addiction to this drug have been reported around the world after the emergence of the coronavirus. Data from the National Survey on Drug Use and Health and from Medicaid support the continuing growth in prescription and indiscriminate use of Zolpidem during the pandemic and afterward. Therefore, there is enough evidence to support the indiscriminate use of this drug since the beginning of the pandemic. Rates of indiscriminate use of sedatives may continue to increase in the post-pandemic period, especially if strict control measures are not taken by health authorities.

Epilepsy plus blindness in microdeletion of GABRA1 and GABRG2 in mouse and human.

OBJECTIVE: GABAA receptor subunit gene (GABR) mutations are significant causes of epilepsy, including syndromic epilepsy. This report for the first time, describes intractable epilepsy and blindness due to optic atrophy in our patient, who has a microdeletion of the GABRA1 and GABRG2 genes. We then characterized the molecular phenotypes and determined patho-mechanisms underlying the genotype-phenotype correlations in a mouse model who is haploinsufficient for both genes (Gabra1+/-/Gabrg2+/- mouse). METHODS: Electroencephalography was conducted in both human and mice with the same gene loss. GABAA receptor expression was evaluated by biochemical and imaging approaches. Optic nerve atrophy was evaluated with fundus photography in human while electronic microscopy, visual evoked potential and electroretinography recordings were conducted in mice. RESULTS: The patient has bilateral optical nerve atrophy. Mice displayed spontaneous seizures, reduced electroretinography oscillatory potential and reduced GABAA receptor α1, ß2 and γ2 subunit expression in various brain regions. Electronic microscopy showed that mice also had optic nerve degeneration, as indicated by increased G-ratio, the ratio of the inner axonal diameter to the total outer diameter, suggesting impaired myelination of axons. More importantly, we identified that phenobarbital was the most effective anticonvulsant in mice and the patient's seizures were also controlled with phenobarbital after failing multiple anti-seizure drugs. CONCLUSIONS: This study is the first report of haploinsufficiency of two GABR epilepsy genes and visual impairment due to altered axonal myelination and resultant optic nerve atrophy. The study suggests the far-reaching impact of GABR mutations and the translational significance of animal models with the same etiology.

Structure and dynamics of differential ligand binding in the human ρ-type GABAA receptor.

The neurotransmitter γ-aminobutyric acid (GABA) drives critical inhibitory processes in and beyond the nervous system, partly via ionotropic type-A receptors (GABAARs). Pharmacological properties of ρ-type GABAARs are particularly distinctive, yet the structural basis for their specialization remains unclear. Here, we present cryo-EM structures of a lipid-embedded human ρ1 GABAAR, including a partial intracellular domain, under apo, inhibited, and desensitized conditions. An apparent resting state, determined first in the absence of modulators, was recapitulated with the specific inhibitor (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid and blocker picrotoxin and provided a rationale for bicuculline insensitivity. Comparative structures, mutant recordings, and molecular simulations with and without GABA further explained the sensitized but slower activation of ρ1 relative to canonical subtypes. Combining GABA with picrotoxin also captured an apparent uncoupled intermediate state. This work reveals structural mechanisms of gating and modulation with applications to ρ-specific pharmaceutical design and to our biophysical understanding of ligand-gated ion channels.

Structure-function Studies of GABA (A) Receptors and Related computer-aided Studies.

The γ-aminobutyric acid type A receptor (GABA (A) receptor) is a membrane protein activated by the neurotransmitter GABA. Structurally, this major inhibitory neurotransmitter receptor in the human central nervous system is a pentamer that can be built from a selection of 19 subunits consisting of α(1,2,3,4,5 or 6), ß (1,2 or 3), γ (1,2 or 3), ρ (1,2 or 3), and δ, π, θ, and ε. This creates several possible pentameric arrangements, which also influence the pharmacological and physiological properties of the receptor. The complexity and heterogeneity of the receptors are further increased by the addition of short and long splice variants in several subunits and the existence of multiple allosteric binding sites and expansive ligands that can bind to the receptors. Therefore, a comprehensive understanding of the structure and function of the receptors is required to gain novel insights into the consequences of receptor dysfunction and subsequent drug development studies. Notably, advancements in computational-aided studies have facilitated the elucidation of residual interactions and exploring energy binding, which may otherwise be challenging to investigate. In this review, we aim to summarize the current understanding of the structure and function of GABA (A) receptors obtained from advancements in computational-aided applications.

CGP7930 - An allosteric modulator of GABABRs, GABAARs and inwardly-rectifying potassium channels.

Type-A and -B GABA receptors (GABAARs/GABABRs) control brain function and behaviour by fine tuning neurotransmission. Over-time these receptors have become important therapeutic targets for treating neurodevelopmental and neuropsychiatric disorders. Several positive allosteric modulators (PAMs) of GABARs have reached the clinic and selective targeting of receptor subtypes is crucial. For GABABRs, CGP7930 is a widely used PAM for in vivo studies, but its full pharmacological profile has not yet been established. Here, we reveal that CGP7930 has multiple effects not only on GABABRs but also GABAARs, which for the latter involves potentiation of GABA currents, direct receptor activation, and also inhibition. Furthermore, at higher concentrations, CGP7930 also blocks G protein-coupled inwardly-rectifying K+ (GIRK) channels diminishing GABABR signalling in HEK 293 cells. In male and female rat hippocampal neuron cultures, CGP7930 allosteric effects on GABAARs caused prolonged rise and decay times and reduced the frequency of inhibitory postsynaptic currents and potentiated GABAAR-mediated tonic inhibition. Additional comparison between predominant synaptic- and extrasynaptic-isoforms of GABAAR indicated no evident subtype selectivity for CGP7930. In conclusion, our study of CGP7930 modulation of GABAARs, GABABRs and GIRK channels, indicates this compound is unsuitable for use as a specific GABABR PAM.

Inhibitory Effects of Honokiol on Substantia Gelatinosa Neurons of the Trigeminal Subnucleus Caudalis in Juvenile Mice.

Inhibitory neurotransmitters such as gamma-aminobutyric acid (GABA) and glycine are known to be abundant in the substantia gelatinosa (SG) of the trigeminal subnucleus caudalis (Vc). Thus, it has been recognized as an initial synaptic site for regulating orofacial nociceptive stimuli. Honokiol, a principal active ingredient derived from the bark of Magnolia officinalis, has been exploited in traditional remedies with multiple biological effects, including anti-nociception on humans. However, the anti-nociceptive mechanism of honokiol on SG neurons of the Vc remains fully elusive. In this study, effects of honokiol on SG neurons of the Vc in mice were investigated using the whole-cell patch-clamp method. In a concentration-dependent manner, honokiol significantly enhanced frequencies of spontaneous postsynaptic currents (sPSCs) that were independent of action potential generation. Notably, honokiol-induced increase in the frequency of sPSCs was attributed to the release of inhibitory neurotransmitters through both glycinergic and GABAergic pre-synaptic terminals. Furthermore, higher concentration of honokiol induced inward currents that were noticeably attenuated in the presence of picrotoxin (a GABAA receptor antagonist) or strychnine (a glycine receptor antagonist). Honokiol also exhibited potentiation effect on glycine- and GABAA receptor-mediated responses. In inflammatory pain model, the increase in frequency of spontaneous firing on SG neurons induced by formalin was significantly inhibited by the application of honokiol. Altogether, these findings indicate that honokiol might directly affect SG neurons of the Vc to facilitate glycinergic and GABAergic neurotransmissions and modulate nociceptive synaptic transmission against pain. Consequently, the inhibitory effect of honokiol in the central nociceptive system contributes to orofacial pain management.

Pre- and postsynaptic modulation of hippocampal inhibitory synaptic transmission by pregnenolone sulphate.

Neurosteroids are important endogenous modulators of GABAA receptor-mediated neurotransmission within the CNS and play a vital role in maintaining normal healthy brain function. Research has mainly focussed on neurosteroids such as allopregnanolone and tetrahydro-deoxycorticosterone (THDOC) which are allosteric potentiators of GABAA receptors, whilst the sulphated steroids, including pregnenolone sulphate (PS), which inhibit GABAA receptor function, have been relatively neglected. Importantly, a full description of PS effects on inhibitory synaptic transmission, at concentrations that are expected to inhibit postsynaptic GABAA receptors, is lacking. Here, we address this deficit by recording inhibitory postsynaptic currents (IPSCs) from rat hippocampal neurons both in culture and in acute brain slices and explore the impact of PS at micromolar concentrations. We reveal that PS inhibits postsynaptic GABAA receptors, evident from reductions in IPSC amplitude and decay time. Concurrently, PS also causes an increase in synaptic GABA release which we discover is due to the activation of presynaptic TRPM3 receptors located close to presynaptic GABA release sites. Pharmacological blockade of TRPM3 receptors uncovers a PS-evoked reduction in IPSC frequency. This second presynaptic effect is caused by PS activation of inwardly-rectifying Kir2.3 channels on interneurons, which act to depress synaptic GABA release. Overall, we provide a comprehensive characterisation of pre- and postsynaptic modulation by PS of inhibitory synaptic transmission onto hippocampal neurons which elucidates the diverse mechanisms by which this understudied neurosteroid can modulate brain function.

Neurosteroid enantiomers as potentially novel neurotherapeutics.

Endogenous neurosteroids and synthetic neuroactive steroids (NAS) are important targets for therapeutic development in neuropsychiatric disorders. These steroids modulate major signaling systems in the brain and intracellular processes including inflammation, cellular stress and autophagy. In this review, we describe studies performed using unnatural enantiomers of key neurosteroids, which are physiochemically identical to their natural counterparts except for rotation of polarized light. These studies led to insights in how NAS interact with receptors, ion channels and intracellular sites of action. Certain effects of NAS show high enantioselectivity, consistent with actions in chiral environments and likely direct interactions with signaling proteins. Other effects show no enantioselectivity and even reverse enantioselectivity. The spectrum of effects of NAS enantiomers raises the possibility that these agents, once considered only as tools for preclinical studies, have therapeutic potential that complements and in some cases may exceed their natural counterparts. Here we review studies of NAS enantiomers from the perspective of their potential development as novel neurotherapeutics.

Mutation of valine 53 at the interface between extracellular and transmembrane domains of the ß2 principal subunit affects the GABAA receptor gating.

GABAA receptors (gamma-aminobutyric acid type A receptors) are pentameric ligand-gated ion channels mediating inhibition in adult mammalian brains. Their static structure has been intensely studied in the past years but the underlying molecular activatory mechanisms remain obscure. The interface between extracellular and transmembrane domains has been recognized as a key player in the receptor gating. However, the role of the valine 53 in the ß1-ß2 loop of the principal subunit (ß2) remains controversial showing differences compared to homologous residues in some cys-loop counterparts such as nAChR. To address the role of the ß2V53 residue in the α1ß2γ2L receptor gating, we performed high resolution macroscopic and single-channel recordings. To explore underlying molecular mechanisms a variety of substituting amino acids were investigated: Glutamate and Lysine (different electric charge), Alanine (aliphatic, larger than Valine) and Histidine (same residue as in homologous α1H55). We report that mutation of the ß2V53 residue results in alterations of nearly all gating transitions including opening/closing, preactivation and desensitization. A dramatic gating impairment was observed for glutamate substitution (ß2V53E) but ß2V53K mutation had a weak effect. The impact of histidine substitution was also small while ß2V53A markedly affected the receptor but to a smaller extent than ß2V53E. Considering available structures in desensitized and bicuculline blocked shut states we propose that strongly detrimental effect of ß2V53E mutation on receptor activation results from electrostatic interaction between the glutamate and ß2K274 on the loop M2-M3 which stabilizes the receptor in the shut state. We conclude that ß2V53 is strongly involved in mechanisms underlying the receptor gating.

The Mechanism of Enantioselective Neurosteroid Actions on GABAA Receptors.

The neurosteroid allopregnanolone (ALLO) and pregnanolone (PREG), are equally effective positive allosteric modulators (PAMs) of GABAA receptors. Interestingly, the PAM effects of ALLO are strongly enantioselective, whereas those of PREG are not. This study was aimed at determining the basis for this difference in enantioselectivity. The oocyte electrophysiology studies showed that ent-ALLO potentiates GABA-elicited currents in α1ß3 GABAA receptors with lower potency and efficacy than ALLO, PREG or ent-PREG. The small PAM effect of ent-ALLO was prevented by the α1(Q242L) mutation in the intersubunit neurosteroid binding site between the ß3 and α1 subunits. Consistent with this result, neurosteroid analogue photolabeling with mass spectrometric readout, showed that ent-ALLO binds weakly to the ß3-α1 intersubunit binding site in comparison to ALLO, PREG and ent-PREG. Rigid body docking predicted that ent-ALLO binds in the intersubunit site with a preferred orientation 180° different than ALLO, PREG or ent-PREG, potentially explaining its weak binding and effect. Photolabeling studies did not identify differences between ALLO and ent-ALLO binding to the α1 or ß3 intrasubunit binding sites that also mediate neurosteroid modulation of GABAA receptors. The results demonstrate that differential binding of ent-ALLO and ent-PREG to the ß3-α1 intersubunit site accounts for the difference in enantioselectivity between ALLO and PREG.

Biomarkers and treatments for mood disorders encompassing the neurosteroid and endocannabinoid systems.

Mood disorders, including major depressive disorder, postpartum depression, post-traumatic stress disorder and suicidality are highly prevalent, associated with a significant economic burden, and remain poorly diagnosed and poorly treated psychiatric conditions. In part, this may result from the lack of biomarkers that can guide precision medicine with individualized treatments for millions of individuals who suffer these debilitating conditions worldwide. While several biomarker candidates have been proposed for mood disorders, none has been implemented in clinical practice and the treatment still relies in the prescription of selective serotonin reuptake inhibitors that shows mixed efficacy and significant side effects. Both neurosteroid biosynthesis and the endocannabinoid system have recently provided evidence for pharmacological targets to improve mood symptoms and the neuroactive steroid allopregnanolone has recently been approved by the USA Food and Drug Administration for the treatment of post-partum depression. Clinical studies also show efficacy for the management of major depression and more studies are being conducted to study efficacy in post-traumatic stress disorder. Likewise, the endocannabinoid-like modulator, N-palmioyl ethanolamide (PEA) has shown efficacy in the treatment of major depression and bipolar disorder. While these new agents are coming forward in the field of neuropsychopharmacology as a new generation of fast-acting antidepressants, the hypothesis of whether their deficits underlying mood disorders could constitute valid predictive biomarkers to facilitate diagnosis and treatment of these conditions is under consideration.

Correlation of age at seizure onset with GABAA receptor subunit and chloride Co-transporter configuration in Focal cortical dysplasia (FCD).

Focal cortical dysplasia (FCD) represents a group of malformations of cortical development, which are speculated to be related to early developmental defects in the cerebral cortex. According to dysmature cerebral development hypothesis of FCD altered GABAA receptor function is known to contribute to abnormal neuronal network. Here, we studied the possible association between age at seizure onset in FCD with the subunit configuration of GABAA receptors in resected brain specimens obtained from patients with FCD. We observed a significantly higher ratio of α4/α1 subunit-containing GABAA receptors in patients with early onset (EO) FCD as compared to those with late onset (LO) FCD as is seen during the course of development where α4-containing GABAA receptors expression is high as compared to α1-containing GABAA receptors expression. Likewise, the influx to efflux chloride co-transporter expression of NKCC1/KCC2 was also increased in patients with EO FCD as seen during brain development. In addition, we observed that the ratio of GABA/Glutamate neurotransmitters was lower in patients with EO FCD as compared to that in patients with LO FCD. Our findings suggest altered configuration of GABAA receptors in FCD which could be contributing to aberrant depolarizing GABAergic activity. In particular, we observed a correlation of age at seizure onset in FCD with subunit configuration of GABAA receptors, levels of NKCC1/KCC2 and the ratio of GABA/Glutamate neurotransmitters such that the patients with EO FCD exhibited a more critically modulated GABAergic network.

Pharmacological activation of mediodorsal thalamic GABA-A receptors modulates morphine/cetirizine-induced changes in the prefrontal cortical GFAP expression in a rat model of neuropathic pain.

The present study investigated the involvement of mediodorsal thalamic (MD) GABA-A receptors in cetirizine/morphine-induced anti-allodynia using a rat model of neuropathic pain. To assess the importance of the prefrontal cortex (PFC) for chronic pain processing, its expression level changes of glial fibrillary acidic protein (GFAP) were measured following drug treatments. Each animal was subjected to chronic constriction of the sciatic nerve surgery simultaneously with the MD cannulation under stereotaxic surgery. The results showed that the administration of morphine (3-5 mg/kg) or cetirizine (1-3 mg/kg) produced significant analgesia in neuropathic rats. Systemic administration of cetirizine (2.5 and 3 mg/kg) potentiated the analgesic response to a low and intolerance dose of morphine (3 mg/kg). Intra-MD microinjection of muscimol, a selective GABA-A receptor agonist (0.005-0.01 µg/rat), increased the cetirizine/morphine-induced anti-allodynia, while muscimol by itself did not affect neuropathic pain. The neuropathic pain was associated with the increased PFC expression level of GFAP, suggesting the impact of chronic pain on PFC glial management. Interestingly, the anti-allodynia was associated with a decrease in the PFC expression level of GFAP under the drugs' co-administration. Thus, cetirizine has a significant potentiating effect on morphine response in neuropathic pain via interacting with the MD GABA-A receptors. It seems that neuropathic pain affects the prefrontal cortex GFAP signaling pathway. In clinical studies, these findings can be considered to create a combination therapy with low doses of GABA-A receptor agonist plus cetirizine and morphine to manage neuropathic pain.

Aconitum Alkaloid Songorine Exerts Potent Gamma-Aminobutyric Acid-A Receptor Agonist Action In Vivo and Effectively Decreases Anxiety without Adverse Sedative or Psychomotor Effects in the Rat.

Songorine (SON) is a diterpenoid alkaloid from Aconitum plants. Preparations of Aconitum roots have been employed in traditional oriental herbal medicine, however, their mechanisms of action are still unclear. Since GABA-receptors are possible brain targets of SON, we investigated which subtypes of GABA-receptors contribute to the effects of SON, and how SON affects anxiety-like trait behavior and psychomotor cognitive performance of rats. First, we investigated the effects of microiontophoretically applied SON alone and combined with GABA-receptor agents picrotoxin and saclofen on neuronal firing activity in various brain areas. Next, putative anxiolytic effects of SON (1.0-3.0 mg/kg) were tested against the GABA-receptor positive allosteric modulator reference compound diazepam (1.0-5.0 mg/kg) in the elevated zero maze (EOM). Furthermore, basic cognitive effects were assessed in a rodent version of the psychomotor vigilance task (PVT). Local application of SON predominantly inhibited the firing activity of neurons. This inhibitory effect of SON was successfully blocked by GABA(A)-receptor antagonist picrotoxin but not by GABA(B)-receptor antagonist saclofen. Similar to GABA(A)-receptor positive allosteric modulator diazepam, SON increased the time spent by animals in the open quadrants of the EOM without any signs of adverse psychomotor and cognitive effects observed in the PVT. We showed that, under in vivo conditions, SON acts as a potent GABA(A)-receptor agonist and effectively decreases anxiety without observable side effects. The present findings facilitate the deeper understanding of the mechanism of action and the widespread pharmacological use of diterpene alkaloids in various CNS indications.