GABAA Receptor Complex Research Articles

Differential behavioral effects of low efficacy positive GABAA modulators in combination with benzodiazepines and a neuroactive steroid in rhesus monkeys

In the clinic, low efficacy positive GABAA modulators might be preferred to high efficacy positive modulators insofar as low efficacy modulators might have comparatively less abuse and dependence liability. Drug discrimination was used to examine the behavioral effects of L-838,417 and bretazenil, two low efficacy positive GABAA modulators that act at benzodiazepine sites, alone and in combination with benzodiazepines and a neuroactive steroid (alfaxolone). In rhesus monkeys (n = 5) discriminating midazolam, alfaxolone substituted for midazolam. In four monkeys, L-838,417 and bretazenil did not substitute for, but rather dose-dependently antagonized, midazolam; L-838-417 and bretazenil, as well as flumazenil, enhanced the midazolam-like effects of alfaxolone. L-838,417 and bretazenil substituted for midazolam in a fifth monkey. In a separate group of rhesus monkeys (n = 3) that received 5.6 mg kg(-1) per day of diazepam and that discriminated flumazenil, L-838,417 and bretazenil substituted for flumazenil. These results demonstrate that L-838,417, bretazenil, and flumazenil can have agonist or antagonist actions in the same animal depending upon whether they are studied in combination with a higher efficacy positive GABAA modulator acting at the same (benzodiazepine) or a different (neuroactive steroid) site. Thus, combinations of low efficacy positive modulators acting at different sites on the GABAA receptor complex could yield drug mixtures with significant therapeutic effects and with reduced abuse and dependence liability, as compared to higher efficacy positive modulators such as currently available benzodiazepines.

Role of Endogenous Benzodiazepine Ligands and Their GABA-A-Associated Receptors in Hepatic Encephalopathy

Benzodiazepine receptor ligands are suggested to play a role in the pathogenesis of hepatic encephalopathy (HE). Accumulation of these ligands in brain was suggested to explain in part the notion of"increased GABAergic tone," the rational for which arose initially from reports of a beneficial effect of the selective benzodiazepine antagonist flumazenil in HE patients. It was suggested on the basis of the effect of flumazenil in human HE that liver failure may result in alterations of the density and/or affinity of the benzodiazepine-associated GABA-A receptor site. Subsequent controlled-clinical trials showed that fumazenil had a transient beneficial effect in only a subpopulation of HE patients. In contrast to the antagonists, partial inverse agonists of the benzodiazepine receptor have unequivocal beneficial effects on behavioral and electro-physiological performance in all experimental models of HE studied so far. Benzodiazepine-associated GABA-A receptors have consistently been demonstrated to be unaltered in both human and experimental HE. Contrary to initial reports, the so-called "endogenous benzodiazepines" do not appear to be significantly related to the pathogenesis of HE. On the other hand, nonbenzodiazepine GABA-A receptor complex modulators, such as neuro-steroids, recently identified in brain in human and experimental HE, may provide a new mechanistic basis for this disorder and lead to novel treatments for human HE.

Synthesis and Evaluation of Homologous Analogs of Anticonvulsant 5-Substituted 3,3-Diethyl-4,5-Dighdro-2(3H)-Furanones

Anticonvulsant 4,5 dihydro-3,3-dialkyl-2(3H)-furanones act at sites on the GABAA receptor complex. Novel 5-substituted esters and homologous ester and amido derivatives of 4,5 dihydro-3,3-diethyl-2(3H)-furanone were synthesized and evaluated for anticonvulsant activity in rodents and for affinity to a site on the GABAA receptor complex ([3H]TBOB). The data suggest that the esters and the homologs prepared are devoid of anticonvulsant activity. The compounds reported herein are not promising anticonvulsants but are useful in directing future studies involving novel anticonvulsant lactones.

Neuroactive Flavonoids Interacting with GABAA Receptor Complex

Classical benzodiazepines (BZs) are the most widely prescribed drugs acting on the central nervous system (CNS). They exert their therapeutic effects via binding to the BZ-site of GABAA receptors, and allosterically modulating the chloride flux through the ion channel complex. Given the multiple actions of classical BZs, the serious limitations to their usefulness have directed much research into development of novel ligands for the BZ-site with retained therapeutic effectiveness and minimal side effects. From the studies of CNS-active chemical constituents of medicinal herbs, some members of the family of flavonoids were demonstrated to have moderate binding affinities for the BZ-site. In vivo studies revealed that these compounds were mostly partial agonists of GABAA receptors, and only a few flavonoids were shown to possess antagonistic activities. At effective anxiolytic doses, the actions of partial agonistic flavonoids were often not accompanied by sedative and myorelaxant side effects. Based on structure-activity relationship (SAR) studies, incorporation of electronegative groups to the C6 and C3' on the flavone backbone was found to yield significant increases in the binding affinities for the BZ-site. It was also shown that 2'-hydroxyl was a critical moiety on flavonoids with regard to BZ-site binding. These have guided the identification of several synthetic flavonoids with high BZ-site binding affinity and in vivo activity, and further quantitative SAR studies resulted in the development of several pharmacophore models. This review attempts to summarize these findings, which has led to the establishment of flavonoids as potential therapeutics for GABAA receptor-mediated disorders.

Development and localisation of GABAA receptor α1, α2, β2 and γ2 subunit mRNA in the chick optic tectum

An in situ hybridisation technique was used to analyse the spatial and temporal pattern of expression of the mRNA encoding the four gamma-aminobutyric acid A (GABA(A)) receptor subunits (alpha1, alpha2, beta2, and gamma2) in the developing chick optic tectum. As a rule, layer i, layer h, and transient cell compartment 3 (TCC3) show the highest levels of expression, especially of alpha1, alpha2 and beta2, which undergo striking changes as a function of time. Apart from these common features, the global pattern is highly complex and dynamic. Such complexity derives from the fact that each subunit exhibits a characteristically distinct pattern of expression and the temporal evolution of each differs in the different layers of the tectum. The influence of several developmental cell behaviours such as proliferation, neuronal migration, programmed cell death, and differentiation must be taken into account to understand pattern complexity and dynamics. Our results suggest that differences in the rate of subunit expression, particularly of alpha1, alpha2, and beta2, could have significant consequences on GABA(A) receptor complex subunit composition along development and on the functional properties of the GABA neurotransmitter system.

Differential effects of ammonia on the benzodiazepine modulatory site on the GABA-A receptor complex of human brain

Ammonia is a key factor in the pathogenesis of encephalopathies associated with liver failure. A direct effect of ammonia on GABAergic neurotransmission was proposed as a mechanism that may explain its neurotoxic effect on the basis of electrophysiological and biochemical studies performed in animal models of liver failure. In the present study, we investigated using a radiometric assay the effect of ammonia on the binding of GABA-A receptor ligands to membranes from normal human brains. Ammonium tartrate significantly decreased the maximal binding of [ 3H]flunitrazepam to well-washed frontal cortical membranes (366 ± 63 fmol/mg protein in absence of ammonia versus 294.1 ± 51 fmol/mg protein in presence of 2 mM ammonia; p < 0.05). The efficacy of the effects of ammonia was within the millimolar range (IC 50 = 4.8 mM). This effect was not seen in cerebellum or hippocampus. Ammonia exposure decreased the maximal binding of [ 3H]flumazenil (284.9 ± 24.2 fmol/mg protein in absence of ammonia versus 146.4 ± 15.6 fmol/mg protein in presence of 2 mM ammonia; p < 0.01). This effect was seen with a greater potency ( I max = 32.4%) and a lower IC 50 (0.1 mM). Inhibition of [ 3H]flumazenil binding was significant in all brain regions. The apparent ammonia-induced decrease of [ 3H]flunitrazepam and [ 3H]flumazenil binding was due to a decrease in the binding affinities of these ligands for the benzodiazepine site. In contrast, ammonium tartrate exposure did not cause significant changes to the binding of [ 3H]muscimol in any brain region. These findings demonstrate that ammonia interacts negatively with components of the benzodiazepine-associated site at the GABA-A receptor complex in human brain in contrast to previous reports in the rat, and thus, does not support the notion that ammonia directly activates the GABA-A receptor complex resulting in increased GABAergic neurotransmission in human hepatic encephalopathy. These findings also suggest that positron emission tomography studies in cirrhotic patients using [ 11C]flumazenil may be underestimating GABA-A receptor sites depending upon the degree of hyperammonemia of the patient.

Zopiclone dependence after insomnia related to torticollis

Zopiclone is a cyclopyrrolone derivative belonging to the group of selective benzodiazepine receptor agonists, which was introduced in Germany in 1991 for the treatment of insomnia. Zopiclone is chemically unrelated to benzodiazepines, but has a similar effect of potentiating the function of γ-aminobutyric acid (GABA) at the GABAA receptor complex (Karle and Nielsen, 1998). It is an effective hypnotic in sleep disorders of various aetiologies, and is considered to have an advantageous side-effect profile (Hesse et al., 2003; Karle and Nielsen, 1998; Noble et al., 1998). It has a weaker muscle-relaxant potential compared to benzodiazepines (Karle and Nielsen, 1998).

P.1.010 Effects of selective nNOS inhibitor TRIM on behaviour of mice after chronic ethanol inhalation and withdrawal

Neuroactive steroids such as allopregnanolone do not only act as transcriptional factors in the regulation of gene expression after intracellular back-oxidation into the 5-α pregnane steroids but may also alter neuronal excitability through interactions with specific neurotransmitter receptors. In particular, certain 3α-reduced metabolites of progesterone such as 3α,5α-tetrahydroprogesterone (allopregnanolone) and 3α,5β-tetrahydroprogesterone (pregnanolone) are potent positive allosteric modulators of the GABAA receptor complex. During the last years, the downregulation of neurosteroid biosynthesis has been intensively discussed to be a possible contributor to the development of anxiety and depressive disorder. Reduced levels of allopregnanolone in the peripheral blood or cerebrospinal fluid were found to be associated with major depression, anxiety disorders, premenstrual dysphoric disorder, negative symptoms in schizophrenia, or impulsive aggression. The importance of allopregnanolone for the regulation of emotion and its therapeutical use in depression and anxiety may not only involve GABAergic mechanisms, but probably also includes enhancement of neurogenesis, myelination, neuroprotection, and regulatory effects on HPA axis function. Certain pharmacokinetic obstacles limit the therapeutic use of natural neurosteroids (low bioavailability, oxidation to the ketone). Until now synthetic neuroactive steroids could not be established in the treatment of anxiety disorders or depression. However, the translocator protein (18 kDa) (TSPO) which is important for neurosteroidogenesis has been identified as a potential novel target. TSPO ligands such as XBD 173 increase neurosteroidogenesis and have anxiolytic effects with a favorable side effect profile.

Increased Brain Concentrations of Endogenous (Non-benzodiazepine) GABA-A Receptor Ligands in Human Hepatic Encephalopathy

It has been suggested that alterations of GABAergic neurotransmission are implicated in the pathophysiology of hepatic encephalopathy (HE). Increased concentrations of endogenous benzodiazepines with positive allosteric modulatory properties at the GABA-A receptor complex were proposed as a pathophysiological mechanism to explain increased GABAergic tone in HE. However, results of controlled trials with benzodiazepine receptor antagonists have yielded equivocal results and increases in benzodiazepine levels in body fluids of cirrhotic patients were suggested to be largely accounted for by previous pharmaceutical benzodiazepine intake. In the present study the issue of benzodiazepine receptor ligands in brains of cirrhotic patients, and their contribution to alterations of GABA-A receptor complex in HE are addressed. "Benzodiazepine-like" ligands were present in trace amounts in autopsied brain tissue from control subjects (0.2 +/- 0.2 ng/g tissue), and from cirrhotic patients not previously exposed to benzodiazepine medication (0.8 +/- 0.4 ng/g tissue). In contrast, these ligands accumulate in brain extracts from cirrhotic patients previously exposed to benzodiazepines by up to 200-fold (161.5 +/- 93.2 DE ng/g tissue). Brain extracts from cirrhotic patients increased the binding of the GABA-A receptor agonist [3H]muscimol. This increase was minimal with brain extracts from controls (6.8 +/- 2.8%), but was significant with brain extracts from cirrhotic patients without (29.4 +/- 2.7%), or with (55.1 +/- 7.6%) previous exposure to benzodiazepines. Addition of flumazenil, a selective benzodiazepine receptor antagonist did not significantly modify the increase of [3H]muscimol binding by brain extracts from patients without prior exposure to benzodiazepines and only partially inhibited the increase of [3H]muscimol binding in presence of brain extracts from cirrhotic patients previously exposed to benzodiazepines. These findings suggest the presence of nonbenzodiazepine substances (possibly neurosteroids) with positive allosteric modulatory properties at the GABA-A receptor complex in brain in hepatic encephalopathy.

From Electrophysiology to Chromatin: A Bottom‐Up Approach to Angelman Syndrome

Angelman syndrome is one of the most studied human diseases related to a gene that is expressed on the maternal chromosome only in at least some brain cells. It is caused by inactivation of the UBE3A gene in the brain due to various abnormalities of the 15q11-q13 chromosome inherited from the mother. It is characterized by severe developmental delay, seizures, virtual absence of speech, motor impairment, and a particular behavioral phenotype. Studies of cortical, electromyographic and cerebellar electrophysiology in patients with Angelman syndrome and a mouse model revealed unique rhythmic neurophysiological activities in the cerebral cortex, cerebellar cortex, and muscles. The oscillatory patterns may be linked to molecular pathophysiology of the syndrome involving dysregulation of synaptic neurotransmission through UBE3A-related modulation of functional GABAA receptor complexes.

GABA-A Receptor Complex and Memory Processes

Considerable evidence has been provided these last years for the involvement of the GABAA receptor complex in memory processes. Compounds that enhance the action of GABA, such as benzodiazepines, impair memory processing. On the contrary, compounds that reduce the action of GABA, such as ß-CCM, pentylenetetrazol or picrotoxin, have the opposite action, that is : enhance memory processing. All these actions seem to focus mainly on the acquisition (learning) processes. Depending on the dose, the same compounds also have effects on anxiety and on seizuring. Benzodiaze-pines are well - known anxiolytic and anticonvulsant agents whereas compounds that reduce the action of GABA have been found to produce anxiogenic and convulsant actions. The GABAA receptor complex might thus be the location of a possible link between a pathological state (epilepsy) and two normal functions (anxiety and learning). This link is likely to involve common genetic pathways. In the normal subject, these data also emphasize the idea that normal memory processing involves a moderate level of anxiety. Keywords: benzodiazepine, carboxylate, gaba, learning, anxiety, epilepsy

Coexistence and Concentrations of Ethanol and Diazepam in Postmortem Blood Specimens: Risk for Enhanced Toxicity?

Both ethanol and diazepam are classified as depressants of the central nervous system and exert their effects via the GABAA receptor complex. We report the coexistence and concentrations of ethanol, diazepam, and its primary metabolite nordiazepam in a case series of 234 forensic autopsies collected over a ten-year period. Diazepam, nordiazepam, and ethanol were determined in femoral venous blood by highly selective gas chromatographic methods. The mean (median) femoral blood concentrations were ethanol 0.24 g/100 mL (0.25 g/100 mL), diazepam (D) 0.23 microg/g (0.10 microg/g), nordiazepam (ND) 0.24 micro/g (0.20 microg/g), sum (D + ND) 0.43 microg/g (0.30 microg/g), and the ratio D/ND was 1.19 (1.0). When cause of death was attributed to alcohol and/or drug intoxication (N = 50), the mean and median blood-ethanol concentration was higher, being 0.36 g/100 mL and 0.38 g/100 mL, respectively, whereas the mean (median) and range of blood-diazepam concentrations were about the same, 0.23 microg/g (0.10 microg/g) and 0.05 to 1.2 microg/g. The femoral-blood concentrations of diazepam and nordiazepam were highly correlated (r = 0.73), but there was no correlation between the concentrations of ethanol and diazepam (r = -0.15). In another 114 fatalities (all causes of death) with diazepam and/or nordiazepam as the only drugs present, the mean (median) and range of blood-diazepam concentrations were 0.22 microg/g (0.10 microg/g) and 0.03 to 3.5 microg/g. The pathologists report showed that none of these deaths were classed as drug intoxications. The impression gleaned from this study of ethanol-diazepam deaths is that high blood-ethanol concentration is the major causative factor. We found no evidence that concurrent use of diazepam enhanced the acute toxicity of ethanol, although interpretation is complicated by the high blood-ethanol concentration (median 0.38 g/100 mL), making it difficult to discern an added effect of diazepam.

Normal coupling of brain benzodiazepine and neurosteroid modulatory sites on the GABA-A receptor complex in human hepatic encephalopathy

To assess the possible implication of the allosteric coupling of different modulatory sites at the GABA-A receptor complex in hepatic encephalopathy (HE), we investigated in autopsied frontal cortex of six cirrhotic patients and six appropriately-matched controls, the modulatory effects of the benzodiazepine site agonist flunitrazepam on the binding of [ 3 H] muscimol and the effect of the neurosteroid site agonist allopregnanolone (5α-pregnan-3α-ol-20-one) on the binding of [ 3 H] muscimol and [ 3 H] flunitrazepam. There were no significant differences in either the magnitude E max: 11.5±1.1% (controls) versus 10.2±2.2% (HE patients) or the efficacy EC 50: 20.2±5.5 nM (controls) versus 17.7±6.2 nM (HE patients) of flunitrazepam modulation of [ 3 H] muscimol binding. Allopregnanolone also showed modulation of both sites to a comparable extent in brain tissue from cirrhotic patients and controls E max: [ 3 H] muscimol, 15.1±2.8% (controls) versus 13.8±1.9% (HE patients); [ 3 H] flunitrazepam, 17.9±2.3% (controls) versus 19.1±2.3% (HE patients), EC 50: [ 3 H] muscimol, 386.5±25.8 nM (controls) versus 373.8±13.1 nM (HE patients); [ 3 H] flunitrazepam, 49.8±22.9 nM (controls) versus 55.5±14.0 nM (HE patients). These findings demonstrate unequivocally that the GABA-A sites and their benzodiazepine and neurosteroid modulatory sites manifest normal allosteric coupling in brain in human HE. Therefore, if increased “GABAergic tone” is implicated in the pathophysiology of HE, this must be the consequence of increased brain concentrations of endogenous benzodiazepine and/or neurosteroid ligands for components of the GABA-A receptor complex rather than alterations of the receptor proteins themselves.

Interaction of Calcineurin and Type-A GABA Receptor γ2Subunits Produces Long-Term Depression at CA1 Inhibitory Synapses

Long-term depression (LTD) is an activity-dependent weakening of synaptic efficacy at individual inhibitory synapses, a possible cellular model of learning and memory. Here, we show that the induction of LTD of inhibitory transmission recruits activated calcineurin (CaN) to dephosphorylate type-A GABA receptor (GABA(A)Rs) via the direct binding of CaN catalytic domain to the second intracellular domain of the GABA(A)R-gamma(2) subunits. Prevention of the CaN-GABA(A) receptor complex formation by expression of an autoinhibitory domain of CaN in the hippocampus of transgenic mice blocks the induction of LTD. Conversely, genetic expression of the CaN catalytic domain in the hippocampus depresses inhibitory synaptic responses, occluding LTD. Thus, an activity-dependent physical and functional interaction between CaN and GABA(A) receptors is both necessary and sufficient for inducing LTD at CA1 individual inhibitory synapses.

Deletion of the alpha1 or beta2 subunit of GABAA receptors reduces actions of alcohol and other drugs.

Enhancement of the activation of GABAA receptors is a common feature of many sedative and hypnotic drugs, and it is probable that the GABAA receptor complex is a molecular target for these drugs in the mammalian central nervous system. We set out to elucidate the role of the two predominant (alpha1 and beta2) subunits of GABAA receptor in sedative drug action by studying mice lacking these two subunits. Both alpha1 (-/-) and beta2 (-/-) null mutant mice showed markedly decreased sleep time induced by nonselective benzodiazepine, flurazepam, and GABAA agonist, 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol. The sleep time induced by the beta-selective drug etomidate was decreased only in beta2 (-/-) knockout mice. In contrast, alpha1 (-/-) mice were more resistant to the alpha1-selective drug zolpidem than beta2 (-/-) or wild-type animals. Knockout mice of both strains were similar to wild-type mice in their responses to pentobarbital. The duration of loss of the righting reflex produced by ethanol was decreased in male mice for both null alleles compared with wild-type mice, but there were no differences in ethanol-induced sleep time in mutant females. Deletion of either the alpha1 or beta2 subunits reduced the muscimol-stimulated 36Cl36 influx in cortical microsacs suggesting that these mutant mice have reduced number of functional brain GABAA receptors. Our results show that removal of either alpha1 or beta2 subunits of GABAA receptors produce strong and selective decreases in hypnotic effects of different drugs. Overall, these data confirm the crucial role of the GABAA receptor in mechanisms mediating sedative/hypnotic effects.

Discriminative stimulus effects of positive GABAA modulators and other anxiolytics, sedatives, and anticonvulsants in untreated and diazepam-treated monkeys.

Positive GABAA modulators and other sedatives, anxiolytics, and anticonvulsants were used to evaluate mechanisms underlying the discriminative stimulus effects of midazolam in untreated monkeys and of flumazenil in monkeys treated with diazepam (5.6 mg/kg/day). Positive GABAA modulators at benzodiazepine (e.g., flunitrazepam and abecarnil) and neuroactive steroid sites (e.g., androsterone) substituted for midazolam in all monkeys; the neuroactive steroids dihydroandrosterone and epipregnanolone substituted for midazolam in two of three monkeys. All positive GABAA modulators attenuated flumazenil in diazepam-treated monkeys; doses of flunitrazepam and abecarnil larger than doses substituting for midazolam were required to attenuate flumazenil, whereas doses of neuroactive steroids smaller than doses substituting for midazolam attenuated flumazenil. Drugs with mechanisms that do not predominantly involve allosteric modulation of GABA (e.g., buspirone, ketamine, valproic acid, and diphenhydramine) did not substitute for midazolam or flumazenil. However, valproic acid enhanced the midazolam discriminative stimulus and attenuated the flumazenil discriminative stimulus; diphenhydramine attenuated the midazolam discriminative stimulus. These results suggest that drugs not sharing a mechanism of action with benzodiazepines can modulate the behavioral effects of benzodiazepines. In addition, this study demonstrates that endogenous ligands, presumably by acting at neuroactive steroid sites on the GABAA receptor complex, share discriminative stimulus effects with benzodiazepines. This study also suggests that positive GABAA-modulating neuroactive steroids are especially potent in attenuating behavioral effects that are related to diazepam withdrawal.

Consensus on Drug Treatment, Definition and Diagnosis for Insomnia

Thirty-four experts and a literature supervisor got together in order to reach a 'consensus' regarding the definition, diagnosis and pharmacological treatment of insomnia. Insomnia is a subjective perception of dissatisfaction with the amount and/or quality of sleep. It includes difficulty in initiating or maintaining sleep or early awakening with inability to fall asleep again. It is associated with complaints of non-restorative sleep and dysfunction of diurnal alertness, energy, cognitive function, behaviour or emotional state, with a decrease in quality of life. The diagnosis is based on clinical and sleep history, physical examination and additional tests, although polysomnography is not routinely indicated. Therapy should include treatment of the underlying causes, cognitive and behavioural measures and drug treatment. Hypnotic therapy can be prescribed from the onset of insomnia and non-benzodiazepine selective agonists of the GABA-A receptor complex are the drugs of first choice. It is recommended that hypnotic treatment be maintained in cases where withdrawal impairs the patient's quality of life and when all other therapeutic measures have failed. Experience suggests that intermittent treatment is better than continuous therapy. The available data do not confirm safety of hypnotics in pregnancy, lactation and childhood insomnia. Benzodiazepines are not indicated in decompensated chronic pulmonary disease but no significant adverse effects on respiratory function have been reported with zolpidem and zopiclone in stable mild to moderate chronic obstructive pulmonary disease and in treated obstructive sleep apnoea syndrome. Data for zaleplon are inconclusive. If the patient recovers subjective control over the sleep process, gradual discontinuation of hypnotic treatment can be considered.

GABA-A receptor complex and memory processes.

Considerable evidence has been provided these last years for the involvement of the GABAA receptor complex in memory processes. Compounds that enhance the action of GABA, such as benzodiazepines, impair memory processing. On the contrary, compounds that reduce the action of GABA, such as -CCM, pentylenetetrazol or picrotoxin, have the opposite action, that is : enhance memory processing. All these actions seem to focus mainly on the acquisition (learning) processes. Depending on the dose, the same compounds also have effects on anxiety and on seizuring. Benzodiaze-pines are well-known anxiolytic and anticonvulsant agents whereas compounds that reduce the action of GABA have been found to produce anxiogenic and convulsant actions. The GABAA receptor complex might thus be the location of a possible link between a pathological state (epilepsy) and two normal functions (anxiety and learning). This link is likely to involve common genetic pathways. In the normal subject, these data also emphasize the idea that normal memory processing involves a moderate level of anxiety.

Sleep is differently modulated by basal forebrain GABA(A) and GABA(B) receptors.

There is evidence that GABA plays a major role in sleep regulation. GABA(A) receptor agonists and different compounds interacting with the GABA(A) receptor complex, such as barbiturates and benzodiazepines, can interfere with the sleep/wake cycle. On the other hand, there is very little information about the possible role of GABA(B) receptors in sleep modulation. The nucleus basalis of Meynert (NBM), a cholinergic area in the basal forebrain, plays a pivotal role in the modulation of sleep and wakefulness, and both GABA(A) and GABA(B) receptors have been described within the NBM. This study used unilateral infusions in the NBM to determine the effects of 3-hydroxy-5-aminomethylisoxazole hydrobromide (muscimol hydrobromide, a GABA(A) receptor subtype agonist) and beta-(aminomethyl)-4-chlorobenzenepropanoic acid (baclofen, a GABA(B) receptor subtype agonist) on sleep parameters in freely moving rats by means of polygraphic recordings. Muscimol (0.5 nmol) and baclofen (0.7 nmol) induced an increase in slow-wave sleep and an inhibition of wakefulness. Muscimol, but not baclofen, also caused a decrease in desynchronized sleep parameters. The results reported here indicate that 1) the NBM activation of both GABA(A) and GABA(B) receptors influences the sleep/wake cycle, and 2) GABA(A) but not GABA(B) receptors are important for desynchronized sleep modulation, suggesting that the two GABAergic receptors play different roles in sleep modulation.

Pharmacodynamic profile of Zaleplon, a new non-benzodiazepine hypnotic agent.

The challenge in developing hypnotic agents for the treatment of insomnia is to balance the sedative effect needed at bedtime with the residual sedation on awakening. Zaleplon is a novel pyrazolopyrimidine hypnotic agent that acts as a selective agonist to the brain omega(1) receptor situated on the alpha(1) subunit of the GABA(A) receptor complex. Zaleplon was proven to be an effective hypnotic drug as it consistently and significantly reduced latency to persistent sleep in insomniac patients for doses of 10 mg and above in polysomnography studies. The pharmacodynamic profile of zaleplon on psychomotor performance, actual driving and cognitive function, including memory, was assessed in several randomized, double-blind, placebo-controlled studies in healthy young subjects as well as insomniac patients by using various positive controls (zolpidem, zopiclone, triazolam and flurazepam). The recommended hypnotic dose of zaleplon in young adults (10 mg) produced minimal or no impairment of psychomotor and memory performance even when administered during the night as little as 1 h before waking. No impairment of actual driving was observed when zaleplon 10 mg was administered either at bedtime or in the middle of the night as little as 4 h before waking. Zaleplon 20 mg, twice the recommended dose, generally produced significant impairment of performance and cognitive functions when these functions were measured at the time of peak plasma concentration, i.e. 1 h after dose administration, and no impairment of driving abilities was observed 4 h after a middle-of-the-night administration. In contrast, consistent detrimental residual effects on various aspects of psychomotor and cognitive functions were observed with the therapeutic doses of the various commonly prescribed hypnotic agents used as comparators, e.g. zolpidem 10 mg up to 5 h after dose administration, zopiclone 7.5 mg up to 10 h after, flurazepam 30 mg up to 14 h after and triazolam 0.25 mg up to 6 h after. Also, zolpidem 10 mg and zopiclone 7.5 mg were also shown to significantly impair driving ability the next morning when this was measured 4 h and up to 10 h after dose administration, respectively. The present review shows that zaleplon 10 mg has little or no residual effect when administered in the middle of the night, as late as 1 h before waking, and is devoid of impairment of driving abilities as assessed by actual driving 4 h after dose administration. The lack of clinically significant or minimally statistically significant residual effects of zaleplon even at its peak concentration may be explained by its unique pharmacokinetic (rapid elimination half-life) and pharmacodynamic (low affinity, and specific binding profile to various subunits of the GABA(A)receptor) profiles. These properties allow zaleplon to be used for treatment of symptoms only when they occur, either at bedtime or later in the night, without incurring significant risk of developing next-day impairment of psychomotor and cognitive functioning. Copyright 2001 John Wiley & Sons, Ltd.