GABAA receptor modulation of memory: the role of endogenous benzodiazepines

Chronic exposure to butyl-paraben causes photosensitivity disruption and memory impairment in adult zebrafish

Limited studies on neurotoxicity following chronic exposure to butyl‑paraben (BuP) have been conducted. In this study, neurobehavior in zebrafish adults was assessed using the novel tank test, photomotor response test, and T-maze test after exposure to BuP for 28 days at concentrations of 0, 0.01, 0.1, and 1.0 mg/L. To comprehensively understand the underlying molecular perturbations in the brain, alterations in transcripts, neurotransmitters, and neurosteroids were measured. We found that BuP penetrated the blood-brain barrier and impaired neurobehavior in photosensitivity at 1.0 mg/L and in memory at 0.1 and 1.0 mg/L. RNA-seq analysis showed that phototransduction, tight junctions, and neuroactive ligand receptor activity were significantly affected, which explains the observed abnormal neurobehaviors. Neurosteroid analysis revealed that BuP increased cortisol levels in a concentration-dependent manner and specifically reduced allopregnanolone levels at all tested concentrations, suggesting that cortisol and allopregnanolone are significant neurosteroid markers associated with photosensitivity and memory deficits. Collectively, we demonstrated that BuP can cross the blood-brain and modulate the levels of transcripts, associated with phototransduction and circadian rhythm, and neurosteroidal cortisol and allopregnanolone, resulting in abnormal neurobehavioral responses to light stimulation and learning and memory.

Pentylenetetrazole-induced seizures cause impairment of memory acquisition and consolidation in zebrafish (Danio rerio)

Epilepsy is characterized by the occurrence seizures, and the high prevalence of epilepsy-associated comorbidities affects the quality of patients' life. We investigated the effects of pentylenetetrazole (PTZ) exposure in zebrafish cognitive performance on inhibitory avoidance test. The animals were exposed to the 7.5mM PTZ for 10minutes, in the acquisition (before training) and in the consolidation memory phases (after training). In the acquisition phase, the animals were submitted to PTZ-induced seizures and trained in periods of 1, 24, or 48hours after exposure, and 24hours after training were tested. In the consolidation phase, animals were trained and exposed to PTZ 10minutes after training and were tested 24hours later. Control groups in periods of 1, 24, or 48hours before or 10minutes after training showed a significantly increased latency to enter the dark compartment. The latencies between training and test sessions did not differ in PTZ groups of animals exposed and trained 1 and 24hours or exposed to PTZ 10minutes after training. At 48hours, animals exposed to PTZ showed an increased latency to enter the dark compartment. Animals exposed to PTZ and trained 1h after increased the traveled distance, when compared to the control group. Traveled distance did not differ in animals that were exposed to PTZ and trained 24 and 48hours, or 10minutes after training. Our findings indicate that PTZ causes a cognitive deficit in the pre-and post-training phase, allowing us to explore the influence of seizures at different memory phases.

Effects of Ketamine and Midazolam on Simultaneous EEG/fMRI Data During Working Memory Processes

Reliable measures of cognitive brain activity from functional neuroimaging techniques may provide early indications of efficacy in clinical trials. Functional magnetic resonance imaging and electroencephalography provide complementary spatiotemporal information and simultaneous recording of these two modalities can remove inter-session drug response and environment variability. We sought to assess the effects of ketamine and midazolam on simultaneous electrophysiological and hemodynamic recordings during working memory (WM) processes. Thirty participants were included in a placebo-controlled, three-way crossover design with ketamine and midazolam. Compared to placebo, ketamine administration attenuated theta power increases and alpha power decreases and midazolam attenuated low beta band decreases to increasing WM load. Additionally, ketamine caused larger blood-oxygen-dependent (BOLD) signal increases in the supplementary motor area and angular gyrus, and weaker deactivations of the default mode network (DMN), whereas no difference was found between midazolam and placebo. Ketamine administration caused positive temporal correlations between frontal-midline theta (fm-theta) power and the BOLD signal to disappear and attenuated negative correlations. However, the relationship between fm-theta and the BOLD signal from DMN areas was maintained in some participants during ketamine administration, as increasing theta strength was associated with stronger BOLD signal reductions in these areas. The presence of, and ability to manipulate, both positive and negative associations between the BOLD signal and fm-theta suggest the presence of multiple fm-theta components involved in WM processes, with ketamine administration disrupting one or more of these theta-linked WM strategies.

The effect of zolpidem on targeted memory reactivation during sleep

According to the active system consolidation theory, memory consolidation during sleep relies on the reactivation of newly encoded memory representations. This reactivation is orchestrated by the interplay of sleep slow oscillations, spindles, and theta, which are in turn modulated by certain neurotransmitters like GABA to enable long-lasting plastic changes in the memory store. Here we asked whether the GABAergic system and associated changes in sleep oscillations are functionally related to memory reactivation during sleep. We administered the GABAA agonist zolpidem (10 mg) in a double-blind placebo-controlled study. To specifically focus on the effects on memory reactivation during sleep, we experimentally induced such reactivations by targeted memory reactivation (TMR) with learning-associated reminder cues presented during post-learning slow-wave sleep (SWS). Zolpidem significantly enhanced memory performance with TMR during sleep compared with placebo. Zolpidem also increased the coupling of fast spindles and theta to slow oscillations, although overall the power of slow spindles and theta was reduced compared with placebo. In an uncorrected exploratory analysis, memory performance was associated with slow spindle responses to TMR in the zolpidem condition, whereas it was associated with fast spindle responses in placebo. These findings provide tentative first evidence that GABAergic activity may be functionally implicated in memory reactivation processes during sleep, possibly via its effects on slow oscillations, spindles and theta as well as their interplay.

GABAergic dysfunction, neural network hyperactivity and memory impairments in human aging and Alzheimer's disease

In this review, we focus on the potential role of the γ-aminobutyric acidergic (GABAergic) system in age-related episodic memory impairments in humans, with a particular focus on Alzheimer's disease (AD). Well-established animal models have shown that GABA plays a central role in regulating and synchronizing neuronal signaling in the hippocampus, a brain area critical for episodic memory that undergoes early and significant morphologic and functional changes in the course of AD. Neuroimaging research in humans has documented hyperactivity in the hippocampus and losses of resting state functional connectivity in the Default Mode Network, a network that itself prominently includes the hippocampus-presaging episodic memory decline in individuals at-risk for AD. Apolipoprotein ε4, the highest genetic risk factor for AD, is associated with GABAergic dysfunction in animal models, and episodic memory impairments in humans. In combination, these findings suggest that GABA may be the linchpin in a complex system of factors that eventually leads to the principal clinical hallmark of AD: episodic memory loss. Here, we will review the current state of literature supporting this hypothesis. First, we will focus on the molecular and cellular basis of the GABAergic system and its role in memory and cognition. Next, we report the evidence of GABA dysregulations in AD and normal aging, both in animal models and human studies. Finally, we outline a model of GABAergic dysfunction based on the results of functional neuroimaging studies in humans, which have shown hippocampal hyperactivity to episodic memory tasks concurrent with and even preceding AD diagnosis, along with factors that may modulate this association.

Ginkgo biloba treatments reverse the impairment of conditioned suppression acquisition induced by GluN2B-NMDA and 5-HT1A receptor blockade: Modulatory effects of the circuitry of the dorsal hippocampal formation

To improve our understanding of the effects of standardized extract of Ginkgo biloba (EGb) as a cognitive enhancer, we investigated the conditioned lick suppression-induced expression (mRNA and protein) of the GluN2B-containing N-methyl-D-aspartic acid receptor (GluN2B-NMDAR), serotonin (5-HT) 1A receptor (5-HT_1AR), gamma-aminobutyric acid type A receptor (GABA_AR) and glial fibrillary acidic protein (GFAP) in the dorsal hippocampal formation (dHF) of untreated and EGb-treated (0.25, 0.5 and 1.0 g.kg^-1) groups of rats. To substantiate our data, we analysed the molecular changes in dHF following treatment with vehicle, with agonists or antagonists of GABA_AR, GluN2B-NMDAR and 5-HT_1AR or with one of these antagonists prior to EGb and fear memory acquisition. Additionally, we performed a pharmacological analysis of the drug-receptor-receptor interactions and their supplemental role in fear memory by blocking individual receptors and analysed the possible changes in expression level with each of the other receptors in the study as well as astrocytes. Our data show for the first time that EGb treatment not only upregulated GluN2B, GABA_AR-α5, and GFAP compared with the control but also differentially upregulated GABA_AR-α1 in the dHF and 5HT_1AR in the CA3. We found that the activation of GABA_ARs (diazepam) and the inactivation of GluN2B-NMDARs (Ro25-6981) or 5-HT_1AR ((S)-WAY100135) resulted in memory impairment. Further, higher doses of EGb treatment reversed the effect of blocking GluN2B (P < 0.001) and 5-HT_1AR (P < 0.001). Here, treatment with Ro25-6981 + EGb or (S)-WAY100135 + EGb prevented the impairment of the acquisition of lick suppression in association with the upregulation or prevention of the downregulation of Grin2b expression as well as the expression of GluN2B-NMDA and/or α1 and α5 subunit-containing GABA_AR in the CA1 (P < 0.0001). Our data are in line with previous findings concerning the necessity of GluN2B for fear memory formation and add to the current knowledge of the role of the GABA_AR-α1 and -α5 subunits and of GluN2B as a target of cognitive enhancers. Furthermore, our data show that these receptors play a complementary role in controlling the neural circuitry in the dHF that seems to be essential to conditioned lick suppression and the modulatory effects of EGb.

Flumazenil but not bicuculline counteract the impairing effects of anesthetic ketamine on recognition memory in rats. Evidence for a functional interaction between the GABAA-benzodiazepine receptor and ketamine?

Experimental evidence indicates that anesthetic doses of the non-competitive NMDA receptor antagonist ketamine impair memory abilities in rodents. The mechanism by which anesthetic ketamine produces its adverse behavioural effects is not yet clarified. In this context, it has been proposed that the effects of anesthetic ketamine on memory might be attributed to its agonistic properties on the GABA type A receptor. The present study was designed to address this issue. Thus, we investigated the ability of the benzodiazepine receptor antagonist flumazenil (1, 3, 6 mg/kg, i.p.) and the GABA_A receptor antagonist bicuculline (0.5, 1.5, 3 mg/kg, i.p.) to counteract recognition memory deficits produced by anesthetic ketamine (100 mg/kg, i.p.) in rats. For this purpose, the novel object recognition task, a behavioural paradigm assessing recognition memory abilities in rodents was used. Compounds were coadministered 24 h before testing or retention. Pre (24 h before testing) or post-training (24 h before retention) administration of flumazenil (6 mg/kg, i.p.) counteracted anesthetic ketamine-induced performance deficits in the novel object recognition memory task. Conversely, bicuculline failed to attenuate the recognition memory deficits caused by anesthetic ketamine. Our findings propose a functional interaction between anesthetic ketamine and the GABA_A receptor allosteric modulator flumazenil on recognition memory.

Effects of standard ethanolic extract from Erythrina velutina in acute cerebral ischemia in mice

The objective of this study was to verify a possible neuroprotective effect of the ethanolic extract of Erythrina velutina (EEEV). Male Swiss mice were submitted to transient cerebral ischemia by occlusion of both carotid arteries for 30 min and treated for 5 days with EEEV (200 or 400 mg/kg) or Memantine (MEM) 10 mg/kg, with initiation of treatment 2 or 24 h after Ischemia. On the 6th day after the induction of ischemia, the animals were submitted to evaluation of locomotor activity and memory and then sacrificed. The brains were dissected for the removal of the prefrontal cortex (PFC), hippocampus (HC) and striatum (ST) for determination of amino acid concentrations. In the step down and Y-maze tests, ischemia caused damage to the animals and treatment with EEEV or MEM reversed this effect. The animals submitted to ischemia also showed memory deficit in the object recognition test, an effect that was reverted by EEEV400 and MEM10. Amino acid dosage showed an increase in excitatory amino acid concentrations in the PFC of the ischemic animals and this effect was reversed by the treatment with EEEV400/24H. Regarding the inhibitory amino acids, ischemia caused an increase of taurine in the PFC while treatment with MEM10/24H or EEEV400/24H reversed this effect. In HC, an increase in excitatory amino acids was also observed in ischemiated animals having treatment with EEEV200/2H or EEEV400/24H reversed this effect. Similar effect was also observed in the same area in relation to the inhibitory amino acids with treatment with MEM10/24H or EEEV400/24H. In the ST, ischemia was also able to cause an increase in excitatory amino acids that was reversed more efficiently by the treatments with MEM10/24H and EEEV200. Also in this area, an increase of taurine and GABA was observed and only the treatment with EEEV200/2H showed a reversion of this effect. In view of these findings, EEEV presents a neuroprotective effect possibly due to its action on amino acid concentrations, and is therefore a potential therapeutic tool in reducing the damage caused by ischemia.

Inhibition of GABA A receptor improved spatial memory impairment in the local model of demyelination in rat hippocampus

Cognitive impairment and memory deficit are common features in multiple Sclerosis patients. The mechanism of memory impairment in MS is unknown, but neuroimaging studies suggest that hippocampal demyelination is involved. Here, we investigate the role of GABA A receptor on spatial memory in the local model of hippocampal demyelination. Demyelination was induced in male Wistar rats by bilaterally injection of lysophosphatidylcholine (LPC) 1% into the CA1 region of the hippocampus. The treatment groups were received daily intraventricular injection of bicuculline (0.025, 0.05μg/2μl/animal) or muscimol (0.1, 0.2μg/2μl/animal) 5days after LPC injection. Morris Water Maze was used to evaluate learning and memory in rats. We used Luxol fast blue staining and qPCR to assess demyelination extention and MBP expression level respectively. Immunohistochemistry (IHC) for CD45 and H&E staining were performed to assess inflammatory cells infiltration. Behavioral study revealed that LPC injection in the hippocampus impaired learning and memory function. Animals treated with both doses of bicuculline improved spatial learning and memory function; however, muscimol treatment had no effect. Histological and MBP expression studies confirmed that demylination in LPC group was maximal. Bicuculline treatment significantly reduced demyelination extension and increased the level of MBP expression. H&E and IHC results showed that bicuculline reduced inflammatory cell infiltration in the lesion site. Bicuculline improved learning and memory and decreased demyelination extention in the LPC-induced hippocampal demyelination model. We conclude that disruption of GABAergic homeostasis in hippocampal demyelination context may be involved in memory impairment with the implications for both pathophysiology and therapy.

Towards a Better Understanding of GABAergic Remodeling in Alzheimer's Disease

γ-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the vertebrate brain. In the past, there has been a major research drive focused on the dysfunction of the glutamatergic and cholinergic neurotransmitter systems in Alzheimer’s disease (AD). However, there is now growing evidence in support of a GABAergic contribution to the pathogenesis of this neurodegenerative disease. Previous studies paint a complex, convoluted and often inconsistent picture of AD-associated GABAergic remodeling. Given the importance of the GABAergic system in neuronal function and homeostasis, in the maintenance of the excitatory/inhibitory balance, and in the processes of learning and memory, such changes in GABAergic function could be an important factor in both early and later stages of AD pathogenesis. Given the limited scope of currently available therapies in modifying the course of the disease, a better understanding of GABAergic remodeling in AD could open up innovative and novel therapeutic opportunities.

Alteration of transcriptional networks in the entorhinal cortex after maternal immune activation and adolescent cannabinoid exposure

Maternal immune activation (MIA) and adolescent cannabinoid exposure (ACE) have both been identified as major environmental risk factors for schizophrenia. We examined the effects of these two risk factors alone, and in combination, on gene expression during late adolescence. Pregnant rats were exposed to the viral infection mimic polyriboinosinic-polyribocytidylic acid (poly I:C) on gestational day (GD) 15. Adolescent offspring received daily injections of the cannabinoid HU210 for 14days starting on postnatal day (PND) 35. Gene expression was examined in the left entorhinal cortex (EC) using mRNA microarrays. We found prenatal treatment with poly I:C alone, or HU210 alone, produced relatively minor changes in gene expression. However, following combined treatments, offspring displayed significant changes in transcription. This dramatic and persistent alteration of transcriptional networks enriched with genes involved in neurotransmission, cellular signalling and schizophrenia, was associated with a corresponding perturbation in the expression of small non-coding microRNA (miRNA). These results suggest that a combination of environmental exposures during development leads to significant genomic remodeling that disrupts maturation of the EC and its associated circuitry with important implications as the potential antecedents of memory and learning deficits in schizophrenia and other neuropsychiatric disorders.

A multi-ingredient dietary supplement abolishes large-scale brain cell loss, improves sensory function, and prevents neuronal atrophy in aging mice

Transgenic growth hormone mice (TGM) are a recognized model of accelerated aging with characteristics including chronic oxidative stress, reduced longevity, mitochondrial dysfunction, insulin resistance, muscle wasting, and elevated inflammatory processes. Growth hormone/IGF-1 activate the Target of Rapamycin known to promote aging. TGM particularly express severe cognitive decline. We previously reported that a multi-ingredient dietary supplement (MDS) designed to offset five mechanisms associated with aging extended longevity, ameliorated cognitive deterioration and significantly reduced age-related physical deterioration in both normal mice and TGM. Here we report that TGM lose more than 50% of cells in midbrain regions, including the cerebellum and olfactory bulb. This is comparable to severe Alzheimer's disease and likely explains their striking age-related cognitive impairment. We also demonstrate that the MDS completely abrogates this severe brain cell loss, reverses cognitive decline and augments sensory and motor function in aged mice. Additionally, histological examination of retinal structure revealed markers consistent with higher numbers of photoreceptor cells in aging and supplemented mice. We know of no other treatment with such efficacy, highlighting the potential for prevention or amelioration of human neuropathologies that are similarly associated with oxidative stress, inflammation and cellular dysfunction. Environ. Mol. Mutagen. 57:382-404, 2016. © 2016 Wiley Periodicals, Inc.

The Long and Winding Road to Gamma-Amino-Butyric Acid as Neurotransmitter

This review centers on the discoveries made during more than six decades of neuroscience research on the role of gamma-amino-butyric acid (GABA) as neurotransmitter. In doing so, special emphasis is directed to the significant involvement of Canadian scientists in these advances. Starting with the early studies that established GABA as an inhibitory neurotransmitter at central synapses, we summarize the results pointing at the GABA receptor as a drug target as well as more recent evidence showing that GABAA receptor signaling plays a surprisingly active role in neuronal network synchronization, both during development and in the adult brain. Finally, we briefly address the involvement of GABA in neurological conditions that encompass epileptic disorders and mental retardation.

Effects of a Flavonoid-Rich Fraction on the Acquisition and Extinction of Fear Memory: Pharmacological and Molecular Approaches

The effects of flavonoids have been correlated with their ability to modulate the glutamatergic, serotoninergic, and GABAergic neurotransmission; the major targets of these substances are N-methyl-D-aspartic acid receptor (NMDARs), serotonin type1A receptor (5-HT_1ARs), and the gamma-aminobutyric acid type A receptors (GABA_ARs). Several studies showed that these receptors are involved in the acquisition and extinction of fear memory. This study assessed the effects of treatment prior to conditioning with a flavonoid-rich fraction from the stem bark of Erythrina falcata (FfB) on the acquisition and extinction of the conditioned suppression following pharmacological manipulations and on gene expression in the dorsal hippocampus (DH). Adult male Wistar rats were treated before conditioned fear with FfB, vehicle, an agonist or antagonist of the 5-HT_1AR, GABA_ARs or the GluN2B-NMDAR or one of these antagonists before FfB treatment. The effects of these treatments on fear memory retrieval, extinction training and extinction retrieval were evaluated at 48, 72, and 98 h after conditioning, respectively. We found that activation of GABA_ARs and inactivation of GluN2B-NMDARs play important roles in the acquisition of lick response suppression. FfB reversed the effect of blocking GluN2B-NMDARs on the conditioned fear and induced the spontaneous recovery. Blocking the 5-HT_1AR and the GluN2B-NMDAR before FfB treatment seemed to be associated with weakening of the spontaneous recovery. Expression of analysis of DH samples via qPCR showed that FfB treatment resulted in the overexpression of Htr1a, Grin2a, Gabra5, and Erk2 after the retention test and of Htr1a and Erk2 after the extinction retention test. Moreover, blocking the 5-HT1ARs and the GluN2B-NMDARs before FfB treatment resulted in reduced Htr1a and Grin2b expression after the retention test, but played a distinct role in Grin2a and Erk2 expression, according session evaluated. We show for the first time that the serotoninergic and glutamatergic receptors are important targets for the effect of FfB on the conditioned fear and spontaneous recovery, in which the ERK signaling pathway appears to be modulated. Further, these results provide important information regarding the role of the DH in conditioned suppression. Taken together, our data suggest that FfB represents a potential therapy for preventing or treating memory impairments.

Efficacy and security of ivermectin given orally to rats naturally infected with Syphacia spp., Giardia spp. and Hymenolepis nana

The results of this study show that the oral administration of ivermectin (48 mg/L) repeatedly for 72 h used in accordance with the present protocol is a safe and highly effective treatment for Giardia spp. and Hymenolepis nana in laboratory rat colonies. The drug can be easily and safely administered using drinking water. This simple regimen should control pinworm infection (Syphacia muris), a problem that can be endemic in laboratory colonies. Experiments using healthy animals are likely to generate more consistent results, thereby requiring a reduced number of animals per group.

Genes and signaling pathways involved in memory enhancement in mutant mice

Mutant mice have been used successfully as a tool for investigating the mechanisms of memory at multiple levels, from genes to behavior. In most cases, manipulating a gene expressed in the brain impairs cognitive functions such as memory and their underlying cellular mechanisms, including synaptic plasticity. However, a remarkable number of mutations have been shown to enhance memory in mice. Understanding how to improve a system provides valuable insights into how the system works under normal conditions, because this involves understanding what the crucial components are. Therefore, more can be learned about the basic mechanisms of memory by studying mutant mice with enhanced memory. This review will summarize the genes and signaling pathways that are altered in the mutants with enhanced memory, as well as their roles in synaptic plasticity. Finally, I will discuss how knowledge of memory-enhancing mechanisms could be used to develop treatments for cognitive disorders associated with impaired plasticity.

The behavioral pharmacology of zolpidem: evidence for the functional significance of α1-containing GABA(A) receptors

RATIONALE

Zolpidem is a positive allosteric modulator of γ-aminobutyric acid (GABA) with preferential binding affinity and efficacy for α1-subunit containing GABA(A) receptors (α1-GABA(A)Rs). Over the last three decades, a variety of animal models and experimental procedures have been used in an attempt to relate the behavioral profile of zolpidem and classic benzodiazepines (BZs) to their interaction with α1-GABA(A)Rs.

OBJECTIVES

This paper reviews the results of rodent and non-human primate studies that have evaluated the effects of zolpidem on motor behaviors, anxiety, memory, food and fluid intake, and electroencephalogram (EEG) sleep patterns. Also included are studies that examined zolpidem's discriminative, reinforcing, and anticonvulsant effects as well as behavioral signs of tolerance and withdrawal.

RESULTS

The literature reviewed indicates that α1-GABA(A)Rs play a principle role in mediating the hypothermic, ataxic-like, locomotor- and memory-impairing effects of zolpidem and BZs. Evidence also suggests that α1-GABA(A)Rs play partial roles in the hypnotic, EEG sleep, anticonvulsant effects, and anxiolytic-like of zolpidem and diazepam. These studies also indicate that α1-GABA(A)Rs play a more prominent role in mediating the discriminative stimulus, reinforcing, hyperphagic, and withdrawal effects of zolpidem and BZs in primates than in rodents.

CONCLUSIONS

The psychopharmacological data from both rodents and non-human primates suggest that zolpidem has a unique pharmacological profile when compared with classic BZs. The literature reviewed here provides an important framework for studying the role of different GABA(A)R subtypes in the behavioral effects of BZ-type drugs and helps guide the development of new pharmaceutical agents for disorders currently treated with BZ-type drugs.

Basolateral amygdala GABA-A receptors mediate stress-induced memory retrieval impairment in rats

The present study was designed to investigate the involvement of GABA-A receptors of the basolateral amygdala (BLA) in the impairing effect of acute stress on memory retrieval. The BLAs of adult male Wistar rats were bilaterally cannulated and memory retrieval was measured in a step-through type passive avoidance apparatus. Acute stress was evoked by placing the animals on an elevated platform for 10, 20 and 30 min. The results indicated that exposure to 20 and 30 min stress, but not 10 min, before memory retrieval testing (pre-test exposure to stress) decreased the step-through latency, indicating stress-induced memory retrieval impairment. Intra-BLA microinjection of a GABA-A receptor agonist, muscimol (0.005-0.02 μg/rat), 5 min before exposure to an ineffective stress (10 min exposure to stress) induced memory retrieval impairment. It is important to note that pre-test intra-BLA microinjection of the same doses of muscimol had no effect on memory retrieval in the rats unexposed to 10 min stress. The blockade of GABA-A receptors of the BLA by injecting an antagonist, bicuculline (0.4-0.5 μg/rat), 5 min before 20 min exposure to stress, prevented stress-induced memory retrieval. Pre-test intra-BLA microinjection of the same doses of bicuculline (0.4-0.5 μg/rat) in rats unexposed to 20 min stress had no effect on memory retrieval. In addition, pre-treatment with bicuculline (0.1-0.4 μg/rat, intra-BLA) reversed muscimol (0.02 μg/rat, intra-BLA)-induced potentiation on the effect of stress in passive avoidance learning. It can be concluded that pre-test exposure to stress can induce memory retrieval impairment and the BLA GABA-A receptors may be involved in stress-induced memory retrieval impairment.

The relationships between pesticide metabolites and neurobehavioral test performance in the third National Health and Nutrition Examination Survey

Regression analysis was used to estimate and test for relationships between urinary pesticide metabolites and neurobehavioral test performance in adults, 20 to 59 years old, participating in the third National Health and Nutrition Examination Survey. The 12 pesticide metabolites included 2 naphthols, 8 phenols, a phenoxyacetic acid, and a pyridinol. The 3 neurobehavioral tests included in the survey were simple reaction time, symbol-digit substitution, and serial digit learning. As the 2,4-dichlorophenol, 2,5-dichlorophenol, and the pentachlorophenol concentrations increased, performance on the serial digit learning test improved. As the 2,5-dichlorophenol concentration increased, performance on the symbol-digit substitution test improved. At low concentrations, the parent compounds of these metabolites may act at acetylcholine and γ-aminobutyric acid synapses in the central nervous system to improve neurobehavioral test performance.

Possible interaction of cholinergic and GABAergic systems between MS and CA1 upon memory acquisition in rats

The present study explored the possibility that cholinergic and GABAergic systems of medial septum (MS) might influence acquisition of memory by regulation of acetylcholine (Ach) and γ-aminobutyric acid (GABA) receptors function in hippocampus and vice versa. The step-through passive avoidance (PA) task was used. The results showed that pre-training intra-MS/CA1 administration of nonselective muscarinic Ach antagonist, scopolamine (0.5, 1 and 2 μg/rat) and GABA(A) receptor agonist, muscimol (0.01 and 0.02 μg/rat) impaired, while acetylcholinesterase inhibitor, physostigmine (0.5 and 1 μg/rat) and GABA(A) receptor antagonist, bicuculline (0.25 μg/rat) improved memory acquisition. Moreover, intra-CA1/MS administration of a subthreshold dose of muscimol or bicuculline increased and reversed the impairment induced by scopolamine in MS/CA1 respectively (cross injection). Also, the result revealed that, intra-CA1/MS administration subthreshold dose of muscimol reduced improvement of memory induced by physostigmine in the MS/CA1, respectively (cross injection). On the other hand, subthreshold dose of bicuculline in CA1/MS did not alter memory improvement induced by physostigmine in the other site (MS/CA1). In conclusion, both cholinergic and GABAergic systems not only seem to play a role in the modulation of memory in the MS and CA1 but also to have a complex interaction.

Suppression of PKR promotes network excitability and enhanced cognition by interferon-γ-mediated disinhibition

The double-stranded RNA-activated protein kinase (PKR) was originally identified as a sensor of virus infection, but its function in the brain remains unknown. Here, we report that the lack of PKR enhances learning and memory in several behavioral tasks while increasing network excitability. In addition, loss of PKR increases the late phase of long-lasting synaptic potentiation (L-LTP) in hippocampal slices. These effects are caused by an interferon-γ (IFN-γ)-mediated selective reduction in GABAergic synaptic action. Together, our results reveal that PKR finely tunes the network activity that must be maintained while storing a given episode during learning. Because PKR activity is altered in several neurological disorders, this kinase presents a promising new target for the treatment of cognitive dysfunction. As a first step in this direction, we show that a selective PKR inhibitor replicates the Pkr(-/-) phenotype in WT mice, enhancing long-term memory storage and L-LTP.

A Simple Densitometric Method for the Quantification of Inhibitory Neurotransmitter Gamma-Aminobutyric Acid (GABA) in Rat Brain Tissue

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian central nervous system which is involved in various physiological and pathological processes. The present study demonstrates a simple high-performance thin-layer chromatography (HPTLC) method which was developed for the estimation of GABA in rat brain tissue. The method was validated in terms of precision, recovery, reproducibility, and variability. Instrumental precision was found to be 0.5891% CV and reproducibility of the method was found to be 0.4141% CV. Interday and intraday precision of the method was found to be 0.9453% and 1.3236% CV, respectively. Accuracy of the method was checked by the recovery study, and the average recovery of GABA was found to be 97.98% at 40 ng and 96.15% at 80 ng levels. The present HPTLC method for GABA estimation was found to be simple, precise, reproducible, sensitive, and accurate. No doubt, this proposed method will be a useful tool for the estimation of GABA in rat brain tissue.

Midazolam reduces the selective activation of the rhinal cortex by contextual fear stimuli

Independent brain circuits appear to underlie different forms of conditioned fear, depending on the type of conditioning used, such as a context or explicit cue paired with footshocks. Several clinical reports have associated damage to the medial temporal lobe (MTL) with retrograde amnesia. Although a number of studies have elucidated the neural circuits underlying conditioned fear, the involvement of MTL components in the aversive conditioning paradigm is still unclear. To address this issue, we assessed freezing responses and Fos protein expression in subregions of the rhinal cortex and ventral hippocampus of rats following exposure to a context, light or tone previously paired with footshock (Experiment 1). A comparable degree of freezing was observed in the three types of conditioned fear, but with distinct patterns of Fos distribution. The groups exposed to cued fear conditioning did not show changes in Fos expression, whereas the group subjected to contextual fear conditioning showed selective activation of the ectorhinal (Ect), perirhinal (Per), and entorhinal (Ent) cortices, with no changes in the ventral hippocampus. We then examined the effects of the benzodiazepine midazolam injected bilaterally into these three rhinal subregions in the expression of contextual fear conditioning (Experiment 2). Midazolam administration into the Ect, Per, and Ent reduced freezing responses. These findings suggest that contextual and explicit stimuli endowed with aversive properties through conditioning recruit distinct brain areas, and the rhinal cortex appears to be critical for storing context-, but not explicit cue-footshock, associations.

Scopolamine- and diazepam-induced amnesia are blocked by systemic and intraseptal administration of substance P and choline chloride

Systemic (IP) and/or intraseptal (IS) administration of scopolamine (SCP) and diazepam (DZP) induce amnesia, whereas IP injection of the neuropeptide substance P (SP) and choline chloride (ChCl) produce memory facilitation. The septohippocampal cholinergic system has been pointed out as a possible site of SCP and DZP-induced amnesia as well as for the mnemonic effects induced by SP and ChCl. We performed a series of experiments in order to investigate the interactions between cholinergic and GABA/benzodiazepine (GABA/BZD) systems with the SPergic system on inhibitory avoidance retention. Male Wistar rats were trained and tested in a step-down inhibitory avoidance task (1.0 mA footshock). Animals received, pre-training, IP (1.0 mg/kg) or IS (1.0 nM/0.5 microl) injection of DZP, SCP (SCP; 1.0 mg/kg - IP or 0.5 microM/0.5 microl--IS) or vehicle (VEH). Immediately after training they received an IP or IS injections of SP 1-11 (50 microg/kg--IP or 1.0 nM/0.5 microl--IS), SP 1-7 (167 microg/kg--IP or 1.0 nM/0.5 microl--IS), ChCl (20 mg/kg--IP or 0.3 microM/0.5 microl--IS) or VEH. Rats pretreated with SCP and DZP showed amnesia. Post-trial treatments with SP 1-11, SP 1-7 or ChCl blocked the amnesic effects of SCP and DZP. These findings suggest an interaction between SPergic and cholinergic mechanisms with GABAergic systems in the modulation of inhibitory avoidance retention and that the effects of these treatments are mediated, at least in part, by interactions in the septohippocampal pathway.

Pentylenetetrazol produces a state-dependent conditioned place aversion to alcohol withdrawal in mice

The purpose of this study was to determine if aversive effects of alcohol withdrawal could be detected in mice using the place conditioning procedure and whether the GABA(A) receptor antagonist, pentylenetetrazol (PTZ), would increase the aversive effects of alcohol withdrawal and increase the probability of detecting conditioned place aversion. Subjects were alcohol-naïve mice from a specific line selectively bred for low alcohol preference (LAP1; n=91) and were assigned to three groups: alcohol withdrawal, PTZ alone, and PTZ+alcohol withdrawal. On four trials, mice received either a 4.0 g/kg intraperitoneal (i.p.) injection of alcohol (alcohol withdrawal, PTZ+alcohol withdrawal groups) or saline (PTZ group) 8 h prior to being placed on a distinctive floor texture for a 30-min conditioning session. Five minutes before these sessions, mice in the PTZ and PTZ+alcohol withdrawal groups received PTZ (5.0 mg/kg; i.p.) and the alcohol withdrawal group received saline. On intervening days mice received two saline injections at the same time points prior to being placed on a different floor texture. Post-conditioning floor preference was assessed in two 60-min tests; the first test was drug-free and the second test was state-dependent. Neither alcohol withdrawal nor PTZ produced significant place conditioning. The PTZ+alcohol withdrawal group showed a significant place aversion during the state-dependent test. These data suggest that the combined stimulus properties of PTZ and alcohol withdrawal facilitated the expression of conditioned place aversion to alcohol withdrawal.

Amnestic effect of cocaine after the termination of its stimulant action

The effects of cocaine on memory are controversial. Furthermore, the psychostimulant action of cocaine can be a critical issue in the interpretation of its effects on learning/memory models. The effects of a single administration of cocaine on memory were investigated during the presence of its motor stimulating effect or just after its termination. The plus-maze discriminative avoidance task (PM-DAT) was used because it provides simultaneous information about memory, anxiety and motor activity. In Experiment I, mice received saline, 7.5, 10, 15 or 30 mg/kg cocaine 5 min before the training session. In Experiment II, mice were trained 30 min after the injection of saline, 7.5, 10, 15 or 30 mg/kg cocaine. In Experiment III, mice received 30 mg/kg cocaine 30 min pre-training and pre-test. In Experiment IV, mice received 30 mg/kg cocaine immediately post-training. Tests were always conducted 24 h following the training session. Given 5 min before training, cocaine promoted a motor stimulant effect at the highest dose during the training session but did not impair memory. When cocaine was injected 30 min pre-training, the drug did not modify motor activity, but produced marked amnestic effects at all doses tested. This amnesia induced by cocaine given 30 min pre-training was not related to a state-dependent learning because it was not abolished by pre-test administration of the drug. Post-training cocaine administration did not induce memory deficits either. Our results suggest that the post-stimulant phase is the critical moment for cocaine-induced memory deficit in a discriminative task in mice.

Disruptive effect of midazolam on fear memory reconsolidation: decisive influence of reactivation time span and memory age

Benzodiazepine (BDZ) administered shortly after retrieval disrupts the reconsolidation of fear memory. In this research, we explored the way in which different factors that limit the emergence of such process may affect BDZ's disruptive effect on fear memory reconsolidation. Animals were conditioned in a contextual fear paradigm; the consolidated memory was reactivated by exposure to the associated context for different periods of time that were followed by midazolam (MDZ) administration. We also studied MDZ amnesic effect after reactivating fear memories of several ages. We finally analyzed the effectiveness of different MDZ doses in preventing the reconsolidation of different age fear memories. The memory trace was disrupted following MDZ when the reactivation session lasted 3-5 min but it was not after a briefer 1-min reactivation period. Over a 10-min reactivation session, all animals gradually reduced their fear response, which indicates the emergence of the extinction process. When tested, MDZ rats exhibited a robust fear, suggesting that MDZ impaired the consolidation of extinction. In a 3-min reactivation session, MDZ (1-1.5 mg/kg) prevented the reconsolidation of recently acquired memories. A 21-day-old fear memory was only vulnerable to MDZ at a 1.5 mg/kg dose with a reactivation session of 5 and not 3 min, whereas a 36-day-old memory was only disrupted with a higher MDZ dose (3 mg/kg) regardless of the reactivation trial's duration. This study demonstrated MDZ's interference on fear-memory reconsolidation within a relatively short reactivation period in recently acquired memories. Over longer reexposure, MDZ disrupts the consolidation of extinction. A longer duration of the reexposure session, as well as higher MDZ doses, is required to prevent the reconsolidation process of remote fear memories.

Drug enhancement of memory consolidation: historical perspective and neurobiological implications

INTRODUCTION

Studies of drug enhancement of cognition began with Lashley's (Psychobiology 1:141-170, 1917) report that strychnine administered before daily training trials enhanced rats' maze learning. Many subsequent studies confirmed that finding and found that stimulant drugs also enhance the learning of a wide range of tasks.

DISCUSSION

A central problem in interpreting such findings is that of distinguishing the drug effects on brain processes underlying memory formation from many other possible effects of the drugs on the behavior used to assess learning. The subsequent finding that comparable learning enhancement can be obtained by posttraining drug administration provided compelling evidence that drugs can enhance memory by acting on memory consolidation processes. Such evidence stimulated the investigation of endogenous regulation of memory consolidation by arousal-released adrenal stress hormones.

CONCLUSION

Considerable evidence now indicates that such hormones regulate memory consolidation via activation of the basolateral amygdala and subsequent influences on many efferent brain regions involved in processing recent experiences. The implications of these findings for the development of cognitive enhancing drugs are discussed.

Acute cold exposure and rewarming enhanced spatial memory and activated the MAPK cascades in the rat brain

Cold is a common stressor that is likely to occur in everyday occupational or leisure time activities. Although there is substantial literature on the effects of stress on memory from behavioral and pharmacologic perspectives, the effects of cold stress on learning and memory were little addressed. The aims of the present work were to investigate the effects of acute cold exposure on Y-maze learning and the activation of cerebral MAPK cascades of rats. We found that the 2-hour cold exposure (-15 degrees C) and a subsequent 30-min rewarming significantly increased the performance of the rats in the Y-maze test. Serum corticosterone (CORT) level was increased after the cold exposure. After a transient reduction following the cold exposure, the P-ERK levels in the hippocampus and PFC drastically increased 30 min later. The levels of P-JNK increased gradually after the cold exposure in all the three brain regions we investigated, but the level of P-p38 only increased in the PFC. The levels of GABAA receptor alpha1 subunit remained unchanged after the cold exposure. Furthermore, the performance of rats treated with cold plus muscimol or bicuculline in the Y-maze test was similar to that of the rats treated with those GABAergic agents alone. These results demonstrated that acute cold exposure and the subsequent rewarming could result in enhanced performance of spatial learning and memory, and the activation of MAPKs in the brain. However, GABAA receptor may not be involved in the acute cold exposure-induced enhancement of memory.

Mice with targeted genetic reduction of GABA(A) receptor alpha1 subunits display performance differences in Morris water maze tasks

Recent research has begun to demonstrate that specific subunits of GABA(A) receptors may be involved in the normal expression of specific behaviors. The present research used mice with GABA(A) receptors whose alpha1 subunits contained mutations of serine 270 to histidine and leucine 277 to alanine in the TM2 region. The purpose was an attempt to examine the possible role that this particular subunit may have in learning the spatial and nonspatial version of the Morris water maze task. Mutant animals, compared to controls, displayed elevated levels of pool circling in both the spatial task and the nonspatial task. These results suggested that normal performance of the spatial and nonspatial water maze tasks may be dependent upon a natural alpha1 subunit array.

Extinction learning: neurological features, therapeutic applications and the effect of aging

Extinction learning consists of the usually gradual inhibition of the retrieval of a previously learned response or behavior. It is widely used for the treatment of syndromes of learned fear, such as phobias and post-traumatic stress disorder. It relies on well-identified molecular processes in the hippocampus, basolateral amygdala, ventromedial prefrontal cortex (vmPFC) and entorhinal cortex. In humans, thickness of the orbital cortex, vmPFC and the anterior cingulate cortex correlates with the capacity to extinguish. The three regions are functionally inter-related (see below). The development of learned fear syndromes in humans is viewed by many as being due to a deficit of extinction, and so of the capacity to deal with fear. Blockade of NMDA receptors, inhibition of protein synthesis in the vmPFC or blockade of protein synthesis or of various molecular signaling cascades in the hippocampus, amygdala or entorhinal cortex impairs extinction. d-cycloserine, a partial agonist at NMDA receptors, enhances extinction in animals and humans and may help extinction to exert its therapeutic effect. Cannabinoids also enhance extinction, acting through CB1 receptors, but their therapeutic use is not warranted.

Evidence for a role of GABAA receptor in the acute restraint stress-induced enhancement of spatial memory

Stress exerts complex effects on learning and memory; however, the understanding of the molecular mechanisms involved in stress effects on brain and behavior is rather limited. In this study, we investigated the regulation of the activation of MAPK (mitogen-activated protein kinase) cascades in the rat brain by GABAA receptor in a learning and memory task under acute restraint stress conditions. We found that the acute restraint stress improved the performance of the rats in the Morris water maze. Furthermore, the acute restraint stress significantly increased the phosphorylation of ERK and JNK in the hippocampus and prefrontal cortex (PFC), but not in the striatum. The increase paralleled the time course of the decrease of the level of GABAA receptor alpha1 subunit. The increase of P-ERK levels was inhibited by the agonist of GABAA receptor, muscimol, and further increased by the antagonist of the receptor, bicuculline. However, neither muscimol nor bicuculline affected the levels of P-JNK and P-p38. Finally, injection of muscimol partly reversed the acute restraint stress-induced enhancement of performance in the Morris water maze, and injection of bicuculline improved it. These results demonstrated that the changes in ERK phosphorylation in hippocampus and PFC were regulated by GABAA receptor in a learning and memory paradigm under acute restraint stress conditions.

Differential effects of low and high doses of topiramate on consolidation and retrieval of novel object recognition memory in rats

Topiramate is a new antiepileptic drug proposed to facilitate synaptic inhibition and block excitatory receptors. However, little is known about the effects of topiramate on memory. In the first experiment, intraperitoneal injection of topiramate at doses of 10.0 and 100.0 mg/kg, immediately after training, induced a deficit in short-term memory (STM) of a novel object recognition (NOR) task tested 1.5 hours after training in rats. In a long-term memory (LTM) test given to the same rats 24 hours after training, topiramate 0.1mg/kg enhanced, whereas 10.0 and 100.0 mg/kg impaired, NOR retention. In the second experiment, administration of topiramate 0.01 and 0.10 mg/kg 1 hour prior to the LTM retention test improved NOR retention, whereas 10.0 and 100.0 mg/kg produced retrieval deficits. The results indicate that low doses of topiramate improve, whereas high doses impair, consolidation and retrieval of recognition memory in rats.

The role of the medial prefrontal cortex-amygdala circuit in stress effects on the extinction of fear

Stress exposure, depending on its intensity and duration, affects cognition and learning in an adaptive or maladaptive manner. Studies addressing the effects of stress on cognitive processes have mainly focused on conditioned fear, since it is suggested that fear-motivated learning lies at the root of affective and anxiety disorders. Inhibition of fear-motivated response can be accomplished by experimental extinction of the fearful response to the fear-inducing stimulus. Converging evidence indicates that extinction of fear memory requires plasticity in both the medial prefrontal cortex and the amygdala. These brain areas are also deeply involved in mediating the effects of exposure to stress on memory. Moreover, extensive evidence indicates that gamma-aminobutyric acid (GABA) transmission plays a primary role in the modulation of behavioral sequelae resulting from a stressful experience, and may also partially mediate inhibitory learning during extinction. In this review, we present evidence that exposure to a stressful experience may impair fear extinction and the possible involvement of the GABA system. Impairment of fear extinction learning is particularly important as it may predispose some individuals to the development of posttraumatic stress disorder. We further discuss a possible dysfunction in the medial prefrontal cortex-amygdala circuit following a stressful experience that may explain the impaired extinction caused by exposure to a stressor.

Neurobiology of memory and anxiety: from genes to behavior

Interaction of anxiety and memory represents an essential feature of CNS functioning. This paper reviews experimental data coming from neurogenetics, neurochemistry, and behavioral pharmacology (as well as parallel clinical findings) reflecting different mechanisms of memory-anxiety interplay, including brain neurochemistry, circuitry, pharmacology, neuroplasticity, genes, and gene-environment interactions. It emphasizes the complexity and nonlinearity of such interplay, illustrated by a survey of anxiety and learning/memory phenotypes in various genetically modified mouse models that exhibit either synergistic or reciprocal effects of the mutation on anxiety levels and memory performance. The paper also assesses the putative role of different neurotransmitter systems and neuropeptides in the regulation of memory processes and anxiety, and discusses the role of neural plasticity in these mechanisms.

GABA(A) receptors of hippocampal CA1 regions are involved in the acquisition and expression of morphine-induced place preference

In the present study, the effects of bilateral intra-hippocampal CA1 (intra-CA1) injections of GABA(A) receptor agonist and/or antagonist on the acquisition and expression of morphine-induced place preference in male Wistar rats have been investigated. The conditioning treatments with subcutaneous (s.c.) injections of different doses of morphine (0.5-7.5 mg/kg) induced a conditioned place preference (CPP) for the drug-associated place in a dose-dependent manner. Intra-CA1 administration of the GABA(A) receptor agonist, muscimol (0.25, 0.5 and 1 microg/rat) significantly inhibited the morphine (5 mg/kg, s.c.)-induced CPP. Intra-CA1 injections of different doses of the GABA(A) receptor antagonist, bicuculline (0.25, 0.5 and 1 microg/rat), in combination with an ineffective dose of morphine (0.5 mg/kg, s.c.) elicited a significant CPP. However, muscimol or bicuculline by themselves did not elicit any effect on place conditioning. Furthermore, the muscimol-induced inhibition of morphine response was reversed by bicuculline (1 microg/rat, intra-CA1) administration. On the other hand, the bilateral intra-CA1 injections of muscimol (0.25, 0.5 and 1 microg/rat) or bicuculline (0.5, 1 and 2 microg/rat) significantly decreased the expression of morphine-induced CPP. Intra-CA1 administration of different doses of muscimol or bicuculline had no effect on locomotor activity in the testing phase. Our data indicated that the GABA(A) receptors of the hippocampal CA1 regions may play an important role in the acquisition and expression of morphine-induced place preference.

The role of the GABA(A) agonist muscimol on memory performance: reward contingencies determine the nature of the deficit

A matching-to-position (MTP) paradigm was altered to influence the type of associations a rat would use to solve the task. Our main behavioral manipulation was the application of the differential outcomes procedure (DOP). The DOP involves correlating each to-be-remembered event with a distinct reward condition. This procedure results in the development of unique reward expectancies that enhance and guide choice behavior. Such distinct reward expectancies are not formed when either a common or random assignment of reward is used (a non-differential outcomes procedure [NOP]). Intracerebroventricular infusions of the amnestic agent muscimol (GABA(A) agonist) or aCSF were delivered to male rats trained on a delayed MTP task that implemented either the DOP or the NOP. Muscimol impaired performance in a dose dependent fashion in both groups--but the nature of the deficit differed as a function of reinforcement contingencies. Rats trained with the DOP displayed a non-mnemonic delay-independent impairment: performance at all delay intervals was disrupted. In contrast, NOP-trained rats displayed a delay-dependent impairment demonstrating that muscimol can also have memory-disrupting effects. The difference in pattern of impairment appears to be a function of the associations formed during training and the type of cognitive strategies involved in maintaining behavior on a conditional delayed discrimination task when reinforcement contingencies are varied. Thus, these results demonstrate that increasing GABA(A) receptor activation impairs a range of associative and memory functions.

Bidirectional effects of benzodiazepine binding site ligands on active avoidance acquisition and retention: differential antagonism by flumazenil and beta-CCt

RATIONALE

The pharmacological approach, using subtype selective ligands, complements genetic studies on the specific contribution of individual receptor subtypes to the various effects of benzodiazepines.

OBJECTIVE

The aim of this study was to examine the relative significance of alpha1-containing GABA(A) receptors in the effects of modulators at the benzodiazepine site on anxiety and memory processes.

METHODS

We tested the effects of the nonselective antagonist flumazenil, the preferential alpha1-subunit selective antagonist beta-carboline-3-carboxylate-t-butyl ester (beta-CCt), the nonselective agonist midazolam, the preferential alpha1-subunit selective agonist zolpidem, and the nonselective inverse agonist methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) in a two-way active avoidance task in rats. The influence of flumazenil (10.0 mg/kg) and beta-CCt (30.0 mg/kg) on the effects of the two agonists were also examined. In the schedule 2 x 30 trials, drugs were administered i.p. 20 min before the training session. Avoidance responses in the training session are an anxiety-mediated behavior, whereas performance in the retention session relates to the effects on memory.

RESULTS

Flumazenil and beta-CCt did not affect behavior. Midazolam (2.0 mg/kg) facilitated acquisition performance, while DMCM (1.0 and 2.0 mg/kg) induced the opposite effect. Flumazenil antagonized both effects. Beta-CCt potentiated the effect of midazolam, and partly antagonized the effect of DMCM. Midazolam (0.5 and 1.0 mg/kg) and zolpidem (1.0-3.0 mg/kg) impaired, while DMCM (0.1 mg/kg) facilitated the subjects' performance in the retention test. The amnesic effects were attenuated but not fully reversed, while the effect of DMCM was counteracted by both antagonists.

CONCLUSION

The results indicate the alpha1-subunit interferes with the anxiolytic effect of a benzodiazepine site agonist and may contribute to the DMCM-induced anxiogenic effect. It is also substantially involved in the bidirectional memory processing in the active avoidance paradigm.