Involvement of the dorsal hippocampus in mediation of the antianxiety action of tandospirone, a 5-hydroxytryptamine1A agonistic anxiolytic

Evaluation of behavioural selection processes in conflict scenarios using a newly developed mouse behavioural paradigm

Selecting an appropriate behaviour is critical for survival in conflict scenarios, wherein animals face both appetitive and aversive stimuli. Behavioural selection consists of multiple processes: (1) animals remain quiet in a safe place to avoid aversive stimuli (suspension), (2) once they decide to take risks to approach appetitive stimuli, they assess the risks (risk assessment), and (3) they act to reach the reward. However, most studies have not addressed these distinct behavioural processes separately. Here, we developed a new experimental paradigm called the three-compartment conflict task to quantitatively evaluate conflict processes. Our apparatus consisted of start, flat, and grid compartments. Mice needed to explore the grid compartment, where they might receive foot shocks while trying to obtain sucrose. Applying foot shocks increased sucrose acquisition latency in subsequent trials, reflecting elevated conflict levels throughout trials. The time spent in the start compartment and the number of retreats were determined to measure the conflict levels in suspension and risk assessment, respectively. Foot shocks increased these parameters, whereas diazepam decreased them. Our new paradigm is valuable for quantitatively evaluating distinct behavioural processes and contributes to developing effective treatments for psychiatric disorders associated with maladaptive behaviours in conflict scenarios.

Pathway-specific GABAergic inhibition contributes to the gain of resilience against anorexia-like behavior of adolescent female mice

Anorexia nervosa is one of the most debilitating mental illnesses that emerges during adolescence, especially among females. Anorexia nervosa is characterized by severe voluntary food restriction and compulsive exercising, which combine to cause extreme body weight loss. We use activity-based anorexia (ABA), an animal model, to investigate the neurobiological bases of vulnerability to anorexia nervosa. This is a Mini-Review, focused on new ideas that have emerged based on recent findings from the Aoki Lab. Our findings point to the cellular and molecular underpinnings of three ABA phenomena: (1) age-dependence of ABA vulnerability; (2) individual differences in the persistence of ABA vulnerability during adolescence; (3) GABAergic synaptic plasticity in the hippocampus and the prefrontal cortex that contributes to the suppression of the maladaptive anorexia-like behaviors. We also include new data on the contribution to ABA vulnerability by cell type-specific knockdown of a GABA receptor subunit, α4, in dorsal hippocampus. Although the GABA system recurs as a key player in the gain of ABA resilience, the data predict why targeting the GABA system, singularly, may have only limited efficacy in treating anorexia nervosa. This is because boosting the GABAergic system may suppress the maladaptive behavior of over-exercising but could also suppress food consumption. We hypothesize that a sub-anesthetic dose of ketamine may be the magic bullet, since a single injection of this drug to mid-adolescent female mice undergoing ABA induction enhances food consumption and reduces wheel running, thereby reducing body weight loss through plasticity at excitatory synaptic inputs to both excitatory and inhibitory neurons. The same treatment is not as efficacious during late adolescence but multiple dosing of ketamine can suppress ABA vulnerability partially. This caveat underscores the importance of conducting behavioral, synaptic and molecular analyses across multiple time points spanning the developmental stage of adolescence and into adulthood. Since this is a Mini-Review, we recommend additional literature for readers seeking more comprehensive reviews on these subjects.

Suppression of food restriction-evoked hyperactivity in activity-based anorexia animal model through glutamate transporters GLT-1 at excitatory synapses in the hippocampus

Severe voluntary food restriction is the defining symptom of anorexia nervosa (AN), but anxiety and excessive exercise are maladaptive symptoms that contribute significantly to the severity of AN and which individuals with AN have difficulty suppressing. We hypothesized that the excitability of hippocampal pyramidal neurons, known to contribute to anxiety, leads to the maladaptive behavior of excessive exercise. Conversely, since glutamate transporter GLT-1 dampens the excitability of hippocampal pyramidal neurons through the uptake of ambient glutamate and suppression of the GluN2B-subunit containing NMDA receptors (GluN2B-NMDARs), GLT-1 may contribute toward dampening excessive exercise. This hypothesis was tested using the mouse model of AN, called activity-based anorexia (ABA), whereby food restriction evokes the maladaptive behavior of excessive wheel running (food restriction-evoked running, FRER). We tested whether individual differences in ABA vulnerability of mice, quantified based on FRER, correlated with individual differences in the levels of GLT-1 at excitatory synapses of the hippocampus. Electron microscopic immunocytochemistry (EM-ICC) was used to quantify GLT-1 levels at the excitatory synapses of the hippocampus. The FRER seen in individual mice varied more than 10-fold, and Pearson correlation analyses revealed a strong negative correlation (p = .02) between FRER and GLT-1 levels at the axon terminals of excitatory synapses and at the surrounding astrocytic plasma membranes. Moreover, synaptic levels of GluN2B-NMDARs correlated strongly with GLT-1 levels at perisynaptic astrocytic plasma membranes. There is at present no accepted pharmacotherapy for AN, and little is known about the etiology of this deadly illness. Current findings suggest that drugs increasing GLT-1 expression may reduce AN severity through the reduction of GluN2B-NMDAR activity.

Voluntary Wheel Running Exercise Evoked by Food-Restriction Stress Exacerbates Weight Loss of Adolescent Female Rats But Also Promotes Resilience by Enhancing GABAergic Inhibition of Pyramidal Neurons in the Dorsal Hippocampus

Adolescence is marked by increased vulnerability to mental disorders and maladaptive behaviors, including anorexia nervosa. Food-restriction (FR) stress evokes foraging, which translates to increased wheel running exercise (EX) for caged rodents, a maladaptive behavior, since it does not improve food access and exacerbates weight loss. While almost all adolescent rodents increase EX following FR, some then become resilient by suppressing EX by the second-fourth FR day, which minimizes weight loss. We asked whether GABAergic plasticity in the hippocampus may underlie this gain in resilience. In vitro slice physiology revealed doubling of pyramidal neurons' GABA response in the dorsal hippocampus of food-restricted animals with wheel access (FR + EX for 4 days), but without increase of mIPSC amplitudes. mIPSC frequency increased by 46%, but electron microscopy revealed no increase in axosomatic GABAergic synapse number onto pyramidal cells and only a modest increase (26%) of GABAergic synapse lengths. These changes suggest increase of vesicular release probability and extrasynaptic GABAA receptors and unsilencing of GABAergic synapses. GABAergic synapse lengths correlated with individual's suppression of wheel running and weight loss. These analyses indicate that EX can have dual roles-exacerbate weight loss but also promote resilience to some by dampening hippocampal excitability.

Single injection of ketamine during mid-adolescence promotes long-lasting resilience to activity-based anorexia of female mice by increasing food intake and attenuating hyperactivity as well as anxiety-like behavior

OBJECTIVE

This study tested the effects of ketamine on vulnerability of female adolescent mice to activity-based anorexia (ABA).

METHOD

Twenty-four female C57Bl/6 J mice underwent ABA induction, which involved exposing wheel-acclimated adolescent mice to two bouts of food restriction (FR)-the first ABA (P41-44, mid-adolescence) and the second ABA (P55-59, late adolescence), with recovery in between. Ketamine (3 or 30 mg/kg) or vehicle was given once, on the second day of FR of the first ABA (P42). Food consumption, body weight and wheel running activity were measured daily. Anxiety-like behaviors were accessed by elevated plus maze on P49 and P62, after weight restoration during the recovery phase.

RESULTS

Ketamine (30 mg/kg) increased food intake during the first ABA (+38%, p = .015) and facilitated weight gain during recovery (+42%, p = .003). During the second ABA, the effect was manifested as increased food intake (+38%, p = .001) and weight gain (+47%, p = .001) while attenuating FR-induced wheel running activity (-24%, p = .09) and weight loss (-17%, p = .056). Ketamine also reduced anxiety-like behaviors.

DISCUSSION

Thus, single injection of ketamine during mid-adolescence effectively attenuates vulnerability of female mice to repeated ABA exposures.

α4-GABAA receptors of hippocampal pyramidal neurons are associated with resilience against activity-based anorexia for adolescent female mice but not for males

Activity-based anorexia (ABA) is an animal model of anorexia nervosa, a mental illness with highest mortality and with onset that is most frequently during adolescence. We questioned whether vulnerability of adolescent mice to ABA differs between sexes and whether individual differences in resilience are causally linked to α4βδ-GABAAR expression. C57BL6/J WT and α4-KO adolescent male and female mice underwent ABA induction by combining wheel access with food restriction. ABA vulnerability was measured as the extent of food restriction-evoked hyperactivity on a running wheel and body weight losses. α4βδ-GABAAR levels at plasma membranes of pyramidal cells in dorsal hippocampus were assessed by electron microscopic immunocytochemistry. Temporal patterns and extent of weight loss during ABA induction were similar between sexes. Both sexes also exhibited individual differences in ABA vulnerability. Correlation analyses revealed that, for both sexes, body weight changes precede and thus are likely to drive suppression of wheel running. However, the suppression was during the food-anticipatory hours for males, while for females, suppression was delayed by a day and during food-access hours. Correspondingly, only females adaptively increased food intake. ABA induced up-regulation of α4βδ-GABAARs at plasma membranes of dorsal hippocampal pyramidal cells of females, and especially those females exhibiting resilience. Conversely, α4-KO females exhibited greater food restriction-evoked hyperactivity than WT females. In contrast, ABA males did not up-regulate α4βδ-GABAARs, did not exhibit genotype differences in vulnerability, and exhibited no correlation between plasmalemmal α4βδ-GABAARs and ABA resilience. Thus, food restriction-evoked hyperactivity is driven by anxiety but can be suppressed through upregulation of hippocampal α4βδ-GABAARs for females but not for males. This knowledge of sex-related differences in the underlying mechanisms of resilience to ABA indicates that drugs targeting α4βδ-GABAARs may be helpful for treating stress-induced anxiety and anorexia nervosa of females but not males.

5-HT1A receptor-dependent modulation of emotional and neurogenic deficits elicited by prolonged consumption of alcohol

Repeated episodes of binge-like alcohol consumption produce anxiety, depression and various deleterious effects including alterations in neurogenesis. While the involvement of the serotonin receptor 1 A (5-HT1A) in the regulation of anxiety-like behavior and neurogenesis is well documented, its contribution to alcohol withdrawal-induced anxiety and alcohol-induced deficits in neurogenesis is less documented. Using the Drinking-In-the-Dark (DID) paradigm to model chronic long-term (12 weeks) binge-like voluntary alcohol consumption in mice, we show that the selective partial activation of 5-HT1A receptors by tandospirone (3 mg/kg) prevents alcohol withdrawal-induced anxiety in a battery of behavioral tests (marble burying, elevated-plus-maze, open-field), which is accompanied by a robust decrease in binge-like ethanol intake (1 and 3 mg/kg). Furthermore, using triple immunolabelling of proliferation and neuronal differentiation markers, we show that long-term DID elicits profound deficits in neurogenesis and neuronal fate specification in the dorsal hippocampus that are entirely reversed by a 2-week chronic treatment with the 5-HT1A partial agonist tandospirone (3 mg/kg/day). Together, our results confirm previous observations that 5-HT1A receptors play a pivotal role in alcohol drinking behavior and the associated emotional and neurogenic impairments, and suggest that 5-HT1A partial agonists represent a promising treatment strategy for alcohol abuse.

Serotonin in the ventral hippocampus modulates anxiety-like behavior during amphetamine withdrawal

Withdrawal from amphetamine is associated with increased anxiety and sensitivity to stressors which are thought to contribute to relapse. Rats undergoing amphetamine withdrawal fail to exhibit stress-induced increases in serotonin (5-HT) release in the ventral hippocampus and show heightened anxiety-like behaviors. Therefore, we tested the hypothesis that reducing 5-HT levels in the ventral hippocampus is a causal mechanism in increasing anxiety-like behaviors during amphetamine withdrawal. First, we tested whether reducing 5-HT levels in the ventral hippocampus directly increases anxiety behavior. Male rats were bilaterally infused with 5,7-dihydroxytryptamine (5,7-DHT) into the ventral hippocampus, which produced a 83% decrease in ventral hippocampus 5-HT content, and were tested on the elevated plus maze (EPM) for anxiety-like behavior. Reducing ventral hippocampus 5-HT levels decreased the time spent in the open arms of the maze, suggesting that diminished ventral hippocampus 5-HT levels increases anxiety-like behavior. Next, we tested whether increasing 5-HT levels in the ventral hippocampus reverses anxiety behavior exhibited by rats undergoing amphetamine withdrawal. Rats were treated daily with either amphetamine (2.5-mg/kg, i.p.) or saline for 2weeks, and at 2weeks withdrawal, were infused with the selective serotonin reuptake inhibitor paroxetine (0.5μM) bilaterally into the ventral hippocampus and tested for anxiety-like behavior on the EPM. Rats pre-treated with amphetamine exhibited increased anxiety-like behavior on the EPM. This effect was reversed by ventral hippocampus infusion of paroxetine. Our results suggest that 5-HT levels in the ventral hippocampus are critical for regulating anxiety behavior. Increasing 5-HT levels during withdrawal may be an effective strategy for reducing anxiety-induced drug relapse.

α4βδ-GABAARs in the hippocampal CA1 as a biomarker for resilience to activity-based anorexia

Anorexia nervosa (AN) is a psychiatric illness characterized by restricted eating and an intense fear of gaining weight. Most individuals with AN are females, diagnosed first during adolescence, 40-80% of whom exhibit excessive exercise, and an equally high number with a history of anxiety disorder. We sought to determine the cellular basis for individual differences in AN vulnerability by using an animal model, activity-based anorexia (ABA), that is induced by combining food restriction (FR) with access to a running wheel that allows voluntary exercise. Previously, we showed that by the fourth day of FR, the ABA group of adolescent female rats exhibit >500% greater levels of non-synaptic α4βδ-GABAARs at the plasma membrane of hippocampal CA1 pyramidal cell spines, relative to the levels found in age-matched controls that are not FR and without wheel access. Here, we show that the ABA group exhibits individual differences in body weight loss, with some losing nearly 30%, while others lose only 15%. The individual differences in weight loss are ascribable to individual differences in wheel activity that both precedes and concurs with days of FR. Moreover, the increase in activity during FR correlates strongly and negatively with α4βδ-GABAAR levels (R=-0.9, p<0.01). This negative correlation is evident within 2days of FR, before body weight loss approaches life-threatening levels for any individual. These findings suggest that increased shunting inhibition by α4βδ-GABAARs in spines of CA1 pyramidal neurons may participate in the protection against the ABA-inducing environmental factors of severe weight loss by suppressing excitability of the CA1 pyramidal neurons which, in turn, is related indirectly to suppression of excessive exercise. The data also indicate that, although exercise has many health benefits, it can be maladaptive to individuals with low levels of α4βδ-GABAARs in the CA1, particularly when combined with FR.

Anxiolytic effects of Julibroside C1 isolated from Albizzia julibrissin in mice

Julibroside C1 is a saponin-containing compound isolated from Albizzia julibrissin Durazz. In this study, we investigated the putative anxiolytic effects of Julibroside C1 using the elevated plus maze (EPM) in mice. Julibroside C1 at doses of 0.5 and 1 mg/kg significantly increased the time spent in the open arms and the number of entries into the open arms of the EPM compared to the control group. Moreover, the anxiolytic-like effects of Julibroside C1 (0.5 mg/kg) were blocked by WAY-100635 (5-HT1A receptor antagonist), bicuculline (GABA(A) receptor antagonist), and flumazenil (antagonist of the GABA(A) receptor benzodiazepine site). However, Julibroside C1 did not change locomotor activity or induce myorelaxant effects. We used quantitative receptor autoradiography to investigate the effects of Julibroside C1 on alterations in mouse brain receptors. After acute treatment with Julibroside C1 (0.5 mg/kg), [(3)H]-8-OH-DPAT binding was significantly decreased in the CA1 region of the hippocampus and [(3)H]-flunitrazepam binding was decreased remarkably in the cingulate cortex region. However, [(3)H]-muscimol binding did not show a significant change in any brain region. Taken together, our findings suggest that Julibroside C1 shows anxiolytic-like effects, which might be mediated by the 5-HT1A and GABA(A)-benzodiazepine receptor systems.

Adolescent female C57BL/6 mice with vulnerability to activity-based anorexia exhibit weak inhibitory input onto hippocampal CA1 pyramidal cells

Anorexia nervosa (AN) is an eating disorder characterized by self-imposed severe starvation and often linked with excessive exercise. Activity-based anorexia (ABA) is an animal model that reproduces some of the behavioral phenotypes of AN, including the paradoxical increase in voluntary exercise following food restriction (FR). Although certain rodents have been used successfully in this animal model, C57BL/6 mice are reported to be less susceptible to ABA. We re-examined the possibility that female C57BL/6 mice might exhibit ABA vulnerability during adolescence, the developmental stage/sex among the human population with particularly high AN vulnerability. After introducing the running wheel to the cage for 3 days, ABA was induced by restricting food access to 1h per day (ABA1, N=13) or 2 h per day (ABA2, N=10). All 23 exhibited increased voluntary wheel running (p<0.005) and perturbed circadian rhythm within 2 days. Only one out of five survived ABA1 for 3 days, while 10 out of 10 survived ABA2 for 3 days and could subsequently restore their body weight and circadian rhythm. Exposure of recovered animals to a second ABA2 induction revealed a large range of vulnerability, even within littermates. To look for the cellular substrate of differences in vulnerability, we began by examining synaptic patterns in the hippocampus, a brain region that regulates anxiety as well as plasticity throughout life. Quantitative EM analysis revealed that CA1 pyramidal cells of animals vulnerable to the second ABA2 exhibit less GABAergic innervation on cell bodies and dendrites, relative to the animals resilient to the second ABA (p<0.001) or controls (p<0.05). These findings reveal that C57BL/6J adolescent females can be used to capture brain changes underlying ABA vulnerability, and that GABAergic innervation of hippocampal pyramidal neurons is one important cellular substrate to consider for understanding the progression of and resilience to AN.

Mu-opioid receptor knockout mice are more sensitive to chlordiazepoxide-induced anxiolytic behavior

We have previously demonstrated benzodiazepine binding in the cortex and hippocampus of mu-opioid receptor knockout (KO) mice. It is known that benzodiazepine receptors are involved in regulating anxiety-like behaviors. Thus, the present study was designed to examine whether there are changes in anxiety-like behavior in mice lacking mu-opioid receptors. To produce anxiolytic activity (less anxiety), the prototype benzodiazepine receptor agonist chlordiazepoxide (CDP, 5 mg/kg) was intraperitoneally administered in wild type (WT) and mu-opioid receptor KO mice. We found that compared to WT mice, mu-opioid receptor KO mice showed enhanced anxiolytic activity to CDP, including increased number of entries into open arm, increased percentage of the time spent in open arms, and decreased percentage of the time spent in enclosed arms in the elevated plus-maze test. We also assessed protein expression of the gamma-aminobutyric acid (GABA) synthetic enzyme (glutamic acid decarboxylase; GAD). Western blotting data indicated that neither the lack of mu-opioid receptors nor CDP treatment altered cortical or hippocampal GAD₆₅ or GAD₆₇ protein expression. These data indicate that compared with WT, mu-opioid receptor KO mice experienced less anxiety and exhibited enhanced anxiolytic activity to CDP treatment, and these effects were not dependent on GAD₆₅ or GAD₆₇ protein expression. Our previous and present data suggest that the anxiolytic activity displayed in mu-opioid receptor KO mice is associated with upregulation of the benzodiazepine receptor system.

Anxiolytic activity of tenoten and diazepam depends on conditions in Vogel conflict test

We compared two modifications of Vogel conflict test and assessed anxyolitic activity of two drugs: diazepam (benzodiazepine anxiolitic) and tenoten (ultra-low doses of antibodies to S-100 protein) in both modifications of the test. It was found that the intensity of anxiolitic effect of the drugs depends on the conditions of Vogel test.

Adolescent female rats exhibiting activity-based anorexia express elevated levels of GABA(A) receptor α4 and δ subunits at the plasma membrane of hippocampal CA1 spines

Activity-based anorexia (ABA) is an animal model for anorexia nervosa that has revealed genetic links to anxiety traits and neurochemical characteristics within the hypothalamus. However, few studies have used this animal model to investigate the biological basis for vulnerability of pubertal and adolescent females to ABA, even though the great majority of the anorexia nervosa cases are females exhibiting the first symptoms during puberty. GABAergic inhibition of the hippocampus strongly regulates anxiety as well as plasticity throughout life. We recently showed that the hippocampal CA1 of female mice undergo a dramatic change at puberty onset--from expressing virtually none of the nonsynaptic α4βδ GABA(A) receptors (GABARs) prepubertally to expressing these GABARs at ~7% of the CA1 dendritic spine membranes at puberty onset. Furthermore, we showed that this change underlies the enhanced modulation of anxiety, neuronal excitability, and NMDA receptor-dependent synaptic plasticity in the hippocampus by the stress neurosteroid, THP (3α-OH-5α[β]-pregnan-20-one or [allo]pregnanolone). Here, we used quantitative electron microscopy to determine whether ABA induction in female rats during adolescence also elevates the expression of α4 and δ subunits of α4βδ GABARs, as was observed at puberty onset for mice. Our analysis revealed that rats also exhibit a rise of α4 and δ subunits of α4βδ GABARs at puberty onset, in that these subunits are detectable at ~6% of the dendritic spine membranes of CA1 pyramidal cells at puberty onset (postnatal day 32-36; P32-36) but this drops to about 2% by P40-P44. The levels of α4 and δ subunits at the CA1 spines remained low following exposure of females to either of the two environmental factors needed to generate ABA--food restriction and access to a running wheel for 4 days--from P40 to P44. This pattern contrasted greatly from those of ABA animals, for which the two environmental factors were combined. Within the hippocampus of ABA animals, 12% of the spine profiles were labeled for α4, reflecting a sixfold increase, relative to hippocampi of age-matched (P44) control females (p < 0.005). Concurrently, 7% of the spine profiles were labeled for δ, reflecting a 130% increase from the control values of 3% (p = 0.01). No measurable change was detected for spine size. The observed magnitude of increase in the α4 and δ subunits at spines is sufficient to increase both tonic inhibition of hippocampus and anxiety during stress, thereby likely to exacerbate hyperactivity and weight loss.

Cellular correlates of anxiety in CA1 hippocampal pyramidal cells of 5-HT1A receptor knockout mice

RATIONALE

5-HT(1A) receptor knockout (1AKO) mice have a robust anxiety phenotype. Tissue-specific "rescue" strategies and electrophysiology have implicated a critical role for postsynaptic 5-HT(1A) receptors, particularly in the CA1 region of the hippocampus.

OBJECTIVES

In this study, we evaluated differences in membrane properties and synaptic activity in CA1 hippocampal pyramidal cells between 1AKOs and wild-type (WT) controls to better understand the cellular correlates of anxiety in this mouse model.

METHODS

Whole-cell patch-clamp recordings were conducted in CA1 pyramidal cells in hippocampal brain slices from 1AKOs and WTs that had previously been screened for anxiety with the elevated-plus maze. Spontaneous miniature inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs) and stimulus-evoked eIPSCs and eEPSCs were recorded in addition to the effect of the benzodiazepine agonist diazepam or the inverse agonist FG 7142 on γ-aminobutyric acid (GABA)ergic eIPSCs.

RESULTS

Evoked EPSC amplitude was greater in 1AKOs than WTs. When subjects were pooled across genotypes, anxiety measures correlated with eEPSC amplitude, indicating enhanced postsynaptic glutamate synaptic activity under conditions of synaptic activation in anxious subjects. While GABA synaptic activity and sensitivity to diazepam were not affected by genotype or correlated with anxiety, sensitivity to the anxiogenic FG 7142 was smaller in anxious subjects.

CONCLUSIONS

These data indicate enhanced postsynaptic glutamate receptor sensitivity and decreased GABAergic inhibition by a benzodiazepine inverse agonist in CA1 hippocampal neurons of anxious mice are produced by deletion of the 5-HT(1A) receptor. These data provide new information about interactions between 5-HT, GABA, and glutamate systems during the expression of chronic anxiety.

Therapeutic role of 5-HT1A receptors in the treatment of schizophrenia and Parkinson's disease

5-HT(1A) receptors have long been implicated in the pathogenesis and treatment of anxiety and depressive disorders. Recently, several lines of studies have revealed new insights into the therapeutic role of 5-HT(1A) receptors in treating schizophrenia and Parkinson's disease. Specifically, 5-HT(1A) receptors seem to be a promising target for alleviating antipsychotic-induced extrapyramidal side effects (EPS) and cognitive/affective disorders in schizophrenia. In the treatment of patients with Parkinson's disease, 5-HT(1A) agonists are expected to improve not only affective symptoms (e.g., anxiety and depression), but also the core parkinsonian symptoms as well as antiparkinsonian agents-induced side effects (e.g., L-DOPA-induced dyskinesia). Here, the therapeutic mechanisms mediated by 5-HT(1A) receptors in schizophrenia and Parkinson's disease are reviewed. This evidence should encourage discovery of new 5-HT(1A) ligands, which can resolve the unmet clinical needs in the current therapy.

Involvement of the GABA/benzodiazepine receptor in the axiolytic-like effect of nociceptin/orphanin FQ

We investigated the mechanism underlying the anxiolytic actions of the neuropeptide nociceptin/orphanin FQ (N/OFQ) with an elevated plus-maze test. In mice, intracerebroventricular (i.c.v.) infusions of N/OFQ (0.1 and 0.32 nmol) led to an increase in time spent in the open arms (anxiolytic-like effects). A non-peptidyl N/OFQ receptor (NOP) antagonist, J-113397(1-{(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl}-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one), (1.0 and 3.2 mg/kg, s.c.) blocked the increase induced by N/OFQ. On the other hand, a benzodiazepine receptor antagonist, flumazenil, (10 mg/kg, i.p.) and a GABAA receptor antagonist, (+)-bicuculline, (5.6 mg/kg, i.p.) also inhibited the increase induced by N/OFQ. In rats, microinfusions of N/OFQ (10 and 32 pmol) into the amygdala led to an increase in time spent in the open arms. However, intracranial infusions of N/OFQ (10-100 pmol) into the dorsal hippocampus did not affect the time spent in the open arms. These findings suggest that the anxiolytic-like effects of N/OFQ may be related to the GABA/benzodiazepine system in the amygdala.

Synergistic effects of tandospirone and selective serotonin reuptake inhibitors on the contextual conditioned fear stress response in rats

The purpose of this study was to investigate the effects of co-administration of tandospirone (a 5-HT(1A) receptor agonist) and individual selective serotonin reuptake inhibitors (SSRIs) on the contextual conditioned fear stress, using an anxiety model in rats. One day after fear conditioning, tandospirone (0.3-3 mg/kg, s.c.), paroxetine (5-20 mg/kg, i.p.), fluvoxamine (30-60 mg/kg, i.p.) and citalopram (3-30 mg/kg, i.p.) significantly inhibited the conditioned freezing in a dose-dependent manner, whereas, 14 days after fear conditioning, the anxiolytic effects of these drugs were weakened. Fourteen days after fear conditioning, co-administration of tandospirone (0.3 mg/kg, s.c.) with each SSRI [paroxetine (5 mg/kg, i.p.), fluvoxamine (30 mg/kg, i.p.) and citalopram (10 mg/kg, i.p.)], given at subeffective doses, markedly inhibited the conditioned freezing without affecting the locomotor activities and CYP3A4-related pharmacokinetic drug-drug interaction. These results elucidate the pharmacodynamic synergistic effects of tandospirone and SSRIs. Therefore, this augmentation therapy (SSRI+5-HT(1A) receptor agonist) may prove useful for some anxiety disorders.

Anxiolytic-like effect of cannabidiol in the rat Vogel conflict test

Cannabidiol (CBD) is a major constituent of the Cannabis sativa plant. It inhibits the anxiogenic activity of high doses of Delta9-tetrahydrocannabinol and induces anxiolytic-like effects. However, the mechanisms underlying the actions of CBD are unknown. Therefore, the aim of the present study was to test the effects of CBD in the Vogel test, a widely used animal model of anxiety. In addition, it was verified if these effects would depend on benzodiazepine-receptor activation. After 24 h of water deprivation, male Wistar rats were subjected to an initial 3-min non-punished (pre-test) drinking session. This was followed by an additional 24-h period of water deprivation followed by a 3-min punished-licking session (test). Diazepam (3 mg/kg) or CBD (2.5, 5 or 10 mg/kg) were intraperitoneally injected 30 min before the test session. CBD (10 mg/kg) and diazepam had similar anticonflict effects, increasing the number of punished licks. The effect of diazepam, but not of CBD, was prevented by the benzodiazepine-receptor antagonist flumazenil (10 mg/kg). To exclude that the anticonflict effects were reflecting non-specific drug effects, we checked the effects of CBD on water consumption and nociceptive response. The drug did not interfere on the former variable in a non-punished test session. Moreover, contrary to morphine (5 mg/kg), CBD was ineffective in the tail-flick test. In conclusion, CBD induced an anticonflict effect not mediated by benzodiazepine receptors or by non-specific drug interference on nociceptive threshold or water consumption. These results reinforce the hypothesis that this cannabinoid has anxiolytic properties.

5-HT1A receptor agonist affects fear conditioning through stimulations of the postsynaptic 5-HT1A receptors in the hippocampus and amygdala

Evidence from preclinical and clinical studies has shown that 5-HT(1A) receptor agonists have anxiolytic actions. The anxiolytic actions of 5-HT(1A) receptor agonists have been tested by our previous studies using fear conditioning. However, little is known about the brain regions of anxiolytic actions of 5-HT(1A) receptor agonists in this paradigm. In the present study, we investigated the effects of bilateral microinjections of flesinoxan, a selective 5-HT(1A) receptor agonist, into the hippocampus, amygdala and medial prefrontal cortex on the expression of contextual conditioned freezing and the defecation induced by conditioned fear stress in rats. These results reveal that both intrahippocampal and intraamygdala injections of flesinoxan decreased the expression of conditioned freezing, while injections into the medial prefrontal cortex did not. In addition, intraamygdala injection of flesinoxan attenuated the increased defecation induced by conditioned fear, but injections into the hippocampus and medial prefrontal cortex failed. These results suggest that flesinoxan exerts its anxiolytic actions in the fear conditioning through stimulations of the postsynaptic 5-HT(1A) receptors in the hippocampus and amygdala.

Hippocampal serotonergic system is involved in anxiety-like behavior induced by corticotropin-releasing factor

To clarify the interaction between anxiety-like behavior produced by corticotropin-releasing factor (CRF) and the 5-HT system, we investigated the effects of intracerebroventricular (i.c.v.) administration of CRF on an elevated plus-maze performance as indices of anxiety, measuring extracellular levels of 5-HT in the ventral hippocampus using an in vivo brain dialysis method in rats. The time spent in the open arms of the maze and the number of open arm entries were decreased in a dose-dependent manner by the administration of CRF (0.3-1.0 microg/rat). These effects of CRF were prevented by pretreatment with a 5-HT(1A) receptor agonist, 8-OH-DPAT (0.5 mg/kg, s.c.). In biochemical studies, CRF increased 5-HT release about 150-250% above baseline in the ventral hippocampus and this elevation was significantly inhibited by a CRF receptor antagonist, alpha-Helical CRF(9-41) (50 mug/rat), and 5-HT(1A) receptor agonist, 8-OH-DPAT (0.5 mg/kg, s.c.). These results suggested that the anxiety-like effect produced by CRF may have involved increased 5-HT transmission in the ventral hippocampus. Taken with the evidence for hypersecretion of CRF in patients with depression and anxiety-related disorders, our findings lead to the intriguing hypothesis that interaction between CRF and 5-HT, especially in the ventral hippocampus, plays a role in the etiology of affective and anxiety disorders.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Involvement of 5-hydroxytryptamine4 receptor in the exacerbation of neuronal loss by psychological stress in the hippocampus of SHRSP with a transient ischemia

A transient forebrain ischemia produced a delayed neuronal death of the hippocampus pyramidal cells in stroke-prone spontaneously hypertensive rats (SHRSP). Long term exposure of rats to stress has been reported to induce deleterious effects on the brain including morphological neuronal degeneration in the hippocampus. The present study was designed to examine the effects of psychological and physical stress on the ischemia-related neuronal death and the effects of 5-hydroxytryptamine(4) (5-HT(4)) receptor antagonist. SHRSP were exposed to the psychological or physical stress for 60 min in the communication box once or repeatedly for 3 days and occluded. SB204070, a 5-HT(4) receptor antagonist was injected before the occlusion. Seven days after the occlusion, the number of the neurons damaged morphologically was examined. A transient bilateral carotid occlusion produced a neuronal death of the CA1 subfield of the hippocampus in a time-dependent manner between 3 and 10 min. A 4 min occlusion induced very little morphological damage and a 5 min one produced a significant neuronal death. Exposure of rats to the psychological stress during 60 min for 3 days before the ischemic insults damaged the pyramidal cells by 4 min ischemia much more than without stress. Physical stress daily for 3 times also increased the damaged neurons. Pretreatment of SB204070 0.1 mg/kg after the stress exposure for 3 days significantly decreased the neuronal damage exacerbated by the stress exposure; however, it did not alter the damage induced by 4 or 10 min occlusion without stress. These results suggest that the repeated exposure of animals to the stress dramatically exacerbates the neuronal death by a transient ischemia and the 5-HT(4) receptor may be involved in the stress-induced exacerbating mechanism of the neuronal damage.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

The anxiolytic effects of the 5-hydroxytryptamine-1A agonist tandospirone before otolaryngologic surgery

We studied 160 ASA I or II patients undergoing elective otolaryngologic surgery in order to compare the anxiolytic effects of a novel 5-hydroxytryptamine-1A agonist, tandospirone, with diazepam. To monitor preoperative anxiety, the following variables were used: systolic and diastolic arterial pressure, heart rate, and the state anxiety score yielded by the Spielberger State-Trait Anxiety Inventory. We performed pretreatment evaluation on the day before surgery and posttreatment examination immediately after entry into the operating room. In a double-blinded, randomized design, four groups of 40 patients each received one of the following oral medications 90 min before entry into the operating room: 1) tandospirone 10 mg (T10 group); 2) tandospirone 30 mg (T30 group); 3) diazepam 10 mg (D group); or 4) placebo (P group). After premedication, the State-Trait Anxiety Inventory state anxiety decreased in the T10 (P < 0.02), T30 (P < 0.02), and D groups (P < 0.001), but it increased in the P group (P < 0.001). Tandospirone, 10 and 30 mg, safely reduced preoperative anxiety to a similar extent as oral diazepam 10 mg in patients undergoing elective otolaryngologic surgery.

IMPLICATIONS

Oral tandospirone reduces preoperative anxiety to a similar extent as oral diazepam in patients undergoing elective otolaryngologic surgery. This finding implies that tandospirone can be used as an oral premedicant drug for relieving anxiety before surgery.

Inhibitory effects of tandospirone, a 5-HT1A agonist, on medial vestibular nucleus neurons responding to lateral roll tilt stimulation in rats

An electrophysiological study was performed using chloral hydrate-anesthetized rats to determine whether tandospirone, a 5-HT1A agonist, affects neuronal activities of the medial vestibular nucleus (MVN), since serotonergic innervation and 5-HT1A receptors are present in this nucleus. Tandospirone applied microiontophoretically at a current of 20-60 nA caused an inhibition of tilt-induced firing of alpha-type neurons, which showed increased and decreased firing with lateral tilt ipsilateral and contralateral to the recording site, respectively, along with that of beta-type neurons which exhibited the reverse responses to ipsilateral and contralateral tilt stimulation. The inhibition was antagonized during simultaneous, iontophoretic application of WAY-100635 (20-60 nA), a 5-HT1A receptor antagonist, although WAY-100635 alone rarely affected spontaneous or tilt-induced firing in either type of neurons. These results suggest that tandospirone acts on a 5-HT1A receptor to inhibit transmission of otolith information to alpha- and beta-type MVN neurons.

Effects of 8-OHDPAT administration into the dorsal raphe nucleus and dorsal hippocampus on fear behavior and regional brain monoamines distribution in rats

The effects of R(+)-8-hydroxy-dipropylaminotetralin (8-OHDPAT) administration into the dorsal raphe nucleus (DRN) or bilaterally into the dorsal hippocampus (HIP) on fear behavior in a modified version of the light-dark transitions test and regional brain monoamines (NA, DA, 5-HT) and their metabolites (MHPG, DOPAC, 5-HIAA) in the hypothalamus, midbrain central gray matter, amygdala, hippocampus and pons were examined. The experiments were performed on 36 male, 3-month old Wistar rats. Administration of 8-OHDPAT (200 ng) into the DRN reduced time out from the illuminated part of the chamber and time of motionless behavior in the illuminated part, increased the number of returns from the dark to illuminated part and number of head dipping from the dark to illuminated part without effect on time of motionless behavior in the dark part and on time of locomotor activity in the illuminated as well as in dark part of the chamber. HPLC analysis showed reduction of 5-HT content in the midbrain and amygdala, reduction of 5-HIAA content in pons, increased 5-HIAA/5-HT ratio in the hippocampus and increased DOPAC/DA ratio in the hypothalamus, midbrain, hippocampus and pons without affecting the MHPG/NA ratio and NA content. The administration of 8-OHDPAT (100 ng per site) into the HIP reduced time out from the illuminated part of chamber, time of locomotor activity in the illuminated part and head dipping from the dark to illuminated part without effect on the number of returns from the dark to illuminated part, time of locomotor activity in the dark part and time of motionless in the illuminated as well as in the dark part of chamber. HPLC analysis showed reduction of NA content in the hypothalamus, amygdala and pons, increased the MHPG content in all the investigated structures, increased MHPG/NA ratio in all the investigated structures except the hypothalamus. Dopamine content decreased in the hypothalamus and amygdala, and DOPAC/DA ratio increased in the amygdala and hippocampus. Concentrations of 5-HT, 5-HIAA and 5-HIAA/5-HT ratio were unchanged. The results obtained indicate that 8-OHDPAT acting on the pre-synaptic 5-HT1A receptors decreases fear behavior and acting on 5-HT1A post-synaptic receptors increases fear behavior in the light-dark transitions test. The neurochemical base of anxiolytic and anxiogenic effects evoked by 8-OHDPAT is being discussed.

Extracellular serotonin is enhanced in the striatum, but not in the dorsal hippocampus or prefrontal cortex, in rats subjected to an operant conflict procedure

In rats trained in an operant fixed-interval-30-s schedule of food reward (FI-30s), acute exposure to contingent footshock resulted in a response suppression that was released by diazepam (DZP; 4 mg/kg ip) but not by buspirone (0.25 or 0.50 mg/kg ip). Compared with baseline, hippocampal and cortical extracellular levels of serotonin (5-HText) did not change, regardless of operant period (punished or nonpunished) and drug. In contrast, in the striatum, an increase of 5-HText levels (535%) occurred during the punished period, counteracted by DZP. This effect was observed only in rats that were low responders during both nonpunished and punished periods, that is, those that exerted an efficacious control over responding. Uncontrollable shocks or exposure to an unfamiliar open field did not modify striatal 5-HText. Together, these results suggest that an acute activation of 5-HT neurons afferent to the striatum allows the rats to efficiently block responses that are negatively reinforced.

Hippocampal and septal injections of nicotine and 8-OH-DPAT distinguish among different animal tests of anxiety

1. Different animal tests model different anxiety disorders. Thus, the social interaction test is a model of generalised anxiety disorder, plus-maze Trial 1 models elements of panic disorder and Trial 2 in the elevated plus-maze is a model of specific phobia. 2. Studies of the neuroanatomical and neurochemical pathways controlling behaviour in these different tests provides information on the neurobiological mechanisms modulating anxiety disorders. 3. In the social interaction test, nicotine and 8-OH-DPAT had anxiogenic effects when injected into the dorsal hippocampus or the lateral septum. 4. These ligands were without effect on Trial 1 in the plus-maze when injected into the dorsal hippocampus, but had anxiogenic effects when injected into the lateral septum. 5. On Trial 2 in the elevated plus-maze, nicotine had an anxiolytic effect, but 8-OH-DPAT had an anixiogenic effect when injected into the dorsal hippocampus.

The role of the dorsal hippocampal serotonergic and cholinergic systems in the modulation of anxiety

A review of the literature suggests that the dorsal hippocampal serotonergic system, and, in particular, the postsynaptic 5-HT(1A) receptor, mediates an anxiogenic response, whereas endogenous dorsal hippocampal cholinergic tone mediates an anxiolytic response. Accordingly, it has been shown that direct dorsal hippocampal administration of the 5-HT(1A) receptor agonist, 8-OH-DPAT, the nicotinic receptor antagonist, mecamylamine, and the M(1) muscarinic receptor antagonist, pirenzepine, all have anxiogenic effects in rats tested in the social interaction test. It is therefore surprising that nicotine also has an anxiogenic effect in this test following dorsal hippocampal administration. However, the anxiogenic effects of mecamylamine and nicotine in the dorsal hippocampus are blocked by coadministration of the 5-HT(1A) receptor antagonist, WAY 100635, suggesting that both of these compounds act by enhancing hippocampal serotonergic transmission, thereby stimulating postsynaptic 5-HT(1A) receptors. This conclusion is supported by the observation that both nicotine and mecamylamine stimulate basal [3H]-5-HT release from dorsal hippocampal slices. A possible mechanism by which nicotinic receptor ligands modulate hippocampal 5-HT release is discussed, and it is proposed that the dorsal hippocampal serotonergic and cholinergic systems are tightly coupled and function antagonistically in the modulation of anxiety, as measured in the social interaction test. These systems are relatively unimportant in controlling behaviour on trial 1 in the plus-maze. On trial 2 in the elevated plus-maze, a model of specific phobia, the endogenous cholinergic system, nicotine, and the M(1) receptor agonist, McN-A-343, all mediate an anxiolytic effect, whereas stimulation of 5-HT(1A) receptors mediates an anxiogenic effect. It is proposed that the hippocampus may predominantly control the avoidance components of phobic anxiety, with other regions, such as the dorsomedial hypothalamus, controlling the escape components.

Roles of 5-HT(1A) receptors in the dorsal raphe and dorsal hippocampus in anxiety assessed by the behavioral effects of 8-OH-DPAT and S 15535 in a modified Geller-Seifter conflict model

8-OH-DPAT [8-hydroxy-2-(di-N-propylamino)tetralin], a 5-HT(1A) receptor agonist, and S 15535 (4-benzodioxan-5-yl)1-(indan-2-yl)piperazine, a partial agonist at 5-HT(1A) receptors, were administered into the dorsal raphe nucleus and dorsal hippocampus and their behavioral effects were assessed in a modified Geller-Seifter conflict model. Injected into the dorsal raphe nucleus 8-OH-DPAT, 1 microg but not 0.04 or 0.2 microg 0.5 microl(-1), and S 15535, 2.5 microg but not 0.1 or 0.5 microg 0.5 microl(-1), significantly increased punished responding with no effect on rates of unpunished or time-out responding. WAY 100635, a selective 5-HT(1A) receptor antagonist, injected subcutaneously at 0. 3 mg kg(-1) 30 min before 1 microg 8-OH-DPAT or 2.5 microg S 15535 in the dorsal raphe, completely antagonized their effects on punished responding. At doses ranging from 1 to 10 microg microl(-1) injected into the CA1 region of the dorsal hippocampus neither 8-OH-DPAT nor S 15535 modified punished responding or the rates of time-out. At the highest doses, 8-OH-DPAT significantly reduced unpunished responding whereas S 15535 had the opposite effect. The results suggest that stimulation of 5-HT(1A) receptors in the dorsal raphe nucleus has anxiolytic-like effects whereas stimulation of postsynaptic receptors in the dorsal hippocampus has no anxiolytic or anxiogenic effects, at least judging from changes in rates of punished responding. These results are compatible with the hypothesis that 5-HT(1A) receptor agonists and partial agonists attenuate anxiety by reducing serotonergic transmission in brain areas innervated by the dorsal raphe nucleus.

Anxiolytic effects of the neuroactive steroid pregnanolone (3 alpha-OH-5 beta-pregnan-20-one) after microinjection in the dorsal hippocampus and lateral septum

The anxiolytic effects of the neuroactive steroid, 3 alpha-OH-5 beta-pregnan-20-one (pregnanolone), were determined after injection into the dorsal hippocampus or lateral septum in adult male rats. An increase in the proportion of time spent on the open arms of the elevated plus-maze was found after 2.5 and 5 micrograms of pregnanolone in the hippocampus, but not in the lateral septum. Intrahippocampal injection of 2.5 micrograms of the 3 beta-epimer of pregnanolone did not affect behavior in the plus-maze; a higher dose of 5 micrograms produced an anxiogenic effect. In the shock-probe burying test latency to burying behavior was increased by intrahippocampal or intraseptal injection of 2.5 and 5 micrograms of pregnanolone; the duration of burying behavior was decreased by 0.5, 2.5 and 5 micrograms of pregnanolone injection in the dorsal hippocampus or lateral septum. The number of contacts with the shock probe was not affected by any dose of pregnanolone in either intracranial site of injection. The anxiolytic effects of intrahippocampal or intraseptal injection of pregnanolone were blocked by intracranial pretreatment with 20 ng of picrotoxin, but not by microinjection of 5 micrograms of flumazenil or 200 ng of PK 11195. Thus, inhibition of the hippocampus, mediated by the pregnanolone's action at the GABAA receptor, produces a general anxiolytic effect. However, similar inhibition in the lateral septum attenuates active avoidance of anxiogenic stimuli (i.e., decreased burying behavior), but not passive avoidance of aversive stimuli (i.e., exploration of open arms of the plus-maze and number of shocks in the probe burying test).

Limited anxiolytic-like effects of non-benzodiazepine hypnotics in rodents

The present experiments compared the anxiolytic-like effects of the benzodiazepine (BZD) hypnotic triazolam with those of four non-BZD hypnotics including one non-selective (zopiclone) and three omega1-BZD selective (zolpidem, zaleplon and SX-3228) receptor ligands, in classical animal models including conflict tests (punished lever pressing and punished drinking tests in rats) and exploratory models (elevated plus-maze test in rats and light/dark choice test in mice), and a recently developed mouse defence test battery (MDTB) which has been validated for the screening of anxiolytic drugs. Results from both conflict procedures showed that zopiclone (0.3-10 mg/kg) produced anxiolytic-like effects comparable to those of triazolam (0.1-3 mg/kg), whereas the selective omega1-BZD receptor hypnotics zolpidem (0.3-3 mg/kg), zaleplon (0.1-3 mg/kg) and SX-3228 (0.1-1 mg/kg) displayed weaker and/or non-specific anxiolytic-like effects. Similarly, in the light/dark test in mice, zolpidem (0.1-1 mg/kg), zaleplon (0.3-10 mg/kg) and SX-3228 (0.03-0.3 mg/kg) showed a reduced potential to produce anxiolytic-like effects as compared to the non-selective omega-BZD receptor hypnotics triazolam (0.03-1 mg/kg) and zopiclone (1-30 mg/kg). In the elevated plus-maze test, zopiclone (1-10 mg/kg), zolpidem (0.1-1 mg/kg), zaleplon (0.3-3 mg/kg) and SX-3228 (0.1-1 mg/kg) displayed anxiolytic-like activity at doses close to those producing behavioural impairment, whereas triazolam (0.03-1 mg/kg) exhibited anxiolytic-like effects over a wide dose range in the absence of decreases in general activity. In the MDTB, zaleplon (0.3-10 mg/kg) decreased all defensive responses, a profile which was similar to that of triazolam (0.03-1 mg/kg), while zopiclone (1-30 mg/kg), zolpidem (0.3-10 mg/kg) and SX-3228 (0.03-1 mg/kg) had fewer effects on defensive behaviours with several effects occurring only at motor-impairing doses. Taken together, these results demonstrate that, although selective omega1-BZD receptor hypnotics display anxiolytic-like activity, the effects are generally weaker than those observed with non-selective omega-BZD receptor selective hypnotics such as triazolam or zopiclone. In particular, the anxiety-reducing potential of the omega1-BZD receptor selective compounds is limited to certain anxiety measures and may be confounded and/or masked by behavioural suppression.

Effects of centrally administered anxiolytic compounds in animal models of anxiety

The effect of intra-cerebrally infused compounds in animal models of anxiety were reviewed. A large body of evidence suggested that benzodiazepine agonists in different brain regions--including areas of the raphe, hypothalamus, periaqueductal gray, septum, hippocampus, and amygdala--produce reasonably consistent anxiolytic effects in a variety of animal models. However, evidence regarding the effects on anxiety of 5-HT1A agonists, 5-HT2 compounds, and 5-HT3 antagonists was somewhat less extensive, both anatomically and behaviourally, and more complex. For example, establishing receptor specificity for 5-HT ligand effects was often complicated by the lack of 'silent' and/or selective antagonists. Neuropeptides had significant effects on anxiety, but these were shown in a smaller number of animal models and in a limited number of brain regions. Regardless of the compounds tested, however, there seemed to be a surprising number of double dissociations (brain site by behavioural test). In fact in some instances, different fear reactions appeared to be controlled by distinct receptor subpopulations within particular parts of the limbic system. These results suggest that the neural control of anxiety might be analogous in organization to sensorimotor systems, i.e., anxiety is controlled by complex systems of multiple, distributed, parallel pathways.

Withdrawal from 3alpha-OH-5alpha-pregnan-20-One using a pseudopregnancy model alters the kinetics of hippocampal GABAA-gated current and increases the GABAA receptor alpha4 subunit in association with increased anxiety

In the present study, we have characterized properties of steroid withdrawal using a pseudopregnant rat model. This paradigm results in increased production of endogenous progesterone from ovarian sources and as such is a useful physiological model. "Withdrawal" from progesterone induced by ovariectomy on day 12 of pseudopregnancy resulted in increased anxiety, as determined by a decrease in open arm entries on the elevated plus maze compared to control rats and pseudopregnant animals not undergoing withdrawal. Similar findings were obtained 24 hr after administration of a 5alpha-reductase blocker to a pseudopregnant animal, suggesting that it is the GABAA-modulatory 3alpha-OH-5alpha-pregnan-20-one (3alpha, 5alpha-THP) that produces anxiogenic withdrawal symptoms. Twenty-four hours after steroid withdrawal, the time constant for decay of GABAA-gated current was also reduced sixfold, assessed using whole- cell patch-clamp procedures on pyramidal neurons acutely dissociated from CA1 hippocampus. Thus, 3alpha,5alpha-THP withdrawal results in a marked decrease in total GABAA current, a possible mechanism for its anxiogenic, proconvulsant sequelae. In addition, 3alpha,5alpha-THP withdrawal resulted in insensitivity to the normally potentiating effect of the benzodiazepine lorazepam (LZM) on GABAA-gated Cl- current. This withdrawal profile is similar to that reported for other GABAA-modulatory drugs such as the benzodiazepines (BDZs), barbiturates, and ethanol. These changes were also associated with significant two and threefold increases in both the mRNA and protein for the alpha4 subunit of the GABAA receptor, respectively, in hippocampus. The pseudopregnancy paradigm may be a useful model for periods of endogenous 3alpha,5alpha-THP withdrawal such as premenstrual syndrome and postpartum or postmenopausal dysphoria, when increased emotional lability and BDZ insensitivity have been reported.

Effects of chronic diazepam treatment on pre- and postsynaptic 5-HT1A receptors in the rat brain

Biochemical and electrophysiological approaches were used to assess possible changes in 5-HT1A receptors in the rat brain after long-term treatment with an anxiolytic benzodiazepine. Rats were treated with diazepam (2 mg/kg i.p. daily) during 14 days and then untreated for 1 day (protocol A) or 5 days (protocol C) until they were killed for in vitro investigations on 5-HT1A receptors. In addition, other rats (protocol B) received the same 14-day treatment with diazepam, followed by 1 mg/kg of the drug on days 15 and 16, and 0.5 mg/kg on days 17 and 18, and were killed 24 h after the last injection. In vitro binding and quantitative autoradiographic experiments with [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) showed that the characteristics of 5-HT1A receptor binding sites in the hippocampus and the dorsal raphe nucleus were not significantly altered by the administration of diazepam under the treatment protocols A, B and C. Furthermore, in vitro electrophysiological recordings of serotoninergic neurons in the dorsal raphe nucleus of brain stem slices revealed no modification in the sensitivity of somatodendritic 5-HT1A autoreceptors in rats treated with diazepam according to the protocols A and B. However, under the conditions of protocol C, the potency of 8-OH-DPAT to depress the firing rate of serotoninergic neurons was significantly enhanced, as expected of a hypersensitivity of somatodendritic 5-HT1A autoreceptors. These data support the hypothesis that some functional changes in these receptors could occur during benzodiazepine withdrawal. However, they do not support the idea of a reduced anxiolytic efficacy of 5-HT1A receptor agonists as a result of prior treatment with a benzodiazepine.

New benzocycloalkylpiperazines, potent and selective 5-HT1A receptor ligands

A series of 1-(benzocycloalkyl)-4-(benzamidolkyl)piperazine derivatives was prepared in order to obtain compounds with a high affinity and selectivity for 5-HT1A receptors. The modifications of aromatic substituents, the length of the alkyl chain, and the size of the ring were explored. Most of N-(1,2,3,4-tetrahydronaphthyl)-N'-(benzamidoethyl)piperazines (32-37) were bound to 5-HT1A receptors in a nanomolar range and presented a high degree of selectivity. After resolution, levorotatory enantiomers showed affinity and selectivity higher than those of dextrorotory ones for 5-HT1A sites. The agonist type activity of selected derivatives was also confirmed in vitro on the inhibition of the activation of adenylate cyclase induced by forskolin and, in vivo, on the induction of the lower lip retraction in rats.

Conflict situation increases serotonin release in rat dorsal hippocampus: in vivo study with microdialysis and Vogel test

The release of serotonin (5-hydroxytryptamine, 5-HT) in the dorsal hippocampus was measured using an in vivo microdialysis method in rats subjected to the Vogel type conflict test. The conflict situation significantly increased 5-HT release in the dorsal hippocampus. Midazolam (0.75 and 1.5 mg/kg i.p.) suppressed the dosage-dependently this increased 5-HT release, an inhibition closely associated with the attenuation of conflict behavior. These findings suggest that the activation of serotonergic neuronal activity in the dorsal hippocampus is linked to mediation of anxiety-related behavior.

Anticonflict effects of a competitive NMDA receptor antagonist and a partial agonist at strychnine-insensitive glycine receptors

Using the conflict drinking Vogel test in rats as a model, in the present study we examined the anxiolytic-like activity of DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 37849), a competitive N-methyl-D-aspartate (NMDA) receptor antagonist and 1-aminocyclopropanecarboxylic acid (ACPC), a partial agonist at strychnine-insensitive glycine receptors associated with the NMDA receptor complex, after their intraperitoneal (i.p.) and intrahippocampal (IHP) administration. CGP 37849, administered in doses of 1.25-5 mg/kg i.p., produced an anticonflict effect in a dose-dependent manner, but was inactive when injected in doses of 0.01-0.1 micrograms IHP. At the same time, when administered in higher doses (10 mg/kg i.p. or 0.3 micrograms IHP), that drug induced motor impairment. On the other hand, ACPC exhibited an anxiolytic-like activity after both i.p. (100-200 mg/kg) and IHP (3-30 micrograms) administration. These results, as well as the literature data on the lack of motor-impairing effects of ACPC, indicate that the latter drug seems to be more advantageous than CGP 37849 as a potential therapeutic agent in the treatment of anxiety disorders. Furthermore, they also show that the hippocampus may be one of the neuroanatomical sites of the anxiolytic-like effect of ACPC, but not of CGP 37849.

The role of hippocampal 5-hydroxytryptamine 1A (5-HT1A) receptors in the anticonflict activity of beta-adrenoceptor antagonists

The nonselective beta-adrenoceptor antagonists pindolol and cyanopindolol, which bind to 5-HT1A and 5-HT1A receptors showed an anticonflict effect by increasing the number of punished licks in the Vogel conflict test in rats, when administered directly into the CA, region of the dorsal hippocampus (i.hp.). The maximum effect was observed after intrusion of 1 microgram of pindolol and 3 microgram of cyanopindolol. However, the selective beta 1-and beta2-adrenoceptor antagonists betaxolol and ICI 118,551, respectively, which have a negligible affinity for 5-HT receptors, did not affect the punished responding, when administered i.hp. in doses up to 10 micrograms. The anticonflict effect of pindolol (1 microgram) was significantly reduced by (S)-WAY 100135, a selective 5-HT1A-receptor antagonist, administered i.hp (0.1 microgram) or s.c. (10 mg/kg). Furthermore, (S)-WAY 100135 injected i.hp (0.3 micrograms) significantly antagonized the anticonflict effect of pindolol injected i.p. (8 mg/kg). (S)-WAY 100135 given alone i.hp. (0.03-3 micrograms) or s.c. (5-10 mg/kg) did not affect the punished responding in rats. These results indicate that the anticonflict effect of the beta-blockers which were tested, or at least pindolol, depends on their agonist action on postsynaptic 5-HT1A receptors located in the hippocampus.

5-HT1A receptor agonists: recent developments and controversial issues

During the last decade, serotonin (5-HT)1A receptors have been a major target for neurobiological research and drug development. 5-HT1A receptors have been cloned and a variety of selective agonists, such as the aminotetraline 8-OH-DPAT and the pyrimidinylpiperazine ipsapirone, have become available. Demonstrations of apparent intrinsic activity of these ligands at 5-HT1A receptors, however, depend highly on the particular assay system. This may be due to the possible existence of receptor subtypes and to assay (or brain region)-dependent differences in receptor reserve and the nature of receptor-effector coupling. Nevertheless, the apparent intrinsic activity of 8-OH-DPAT seems to be higher (although possibly not yet maximal) than that of the pyrimidinylpiperazines. In the brain, 5-HT1A receptors are located presynaptically as somatodendritic receptors on 5-HT neurons and postsynaptically in particular limbic and cortical regions. Although it is generally accepted that presynaptic 5-HT1A receptors control 5-HT neuronal activity, recent evidence suggests an additional role of postsynaptic 5-HT1A receptors in cortex as part of a negative feedback loop. Anxiolytic and antidepressive properties of selective 5-HT1A receptor agonists have now been confirmed by clinical studies. Although it is well established that the latter properties depend on the agonistic activity of these compounds, the optimal level of intrinsic activity is still a matter of debate and may be dependent on the clinical indication. Such compounds may also have antiaggressive effects, and possibly anticraving effects (manifested by their alcohol intake-reducing effects in dependent animals), but the specificity of these so-called anti-impulsivity effects is still controversial and not yet tested clinically. Anticataleptic, antiemetic and neuroprotective properties have been demonstrated in different species. Behavioral studies on the mechanisms underlying the anxiolytic and antidepressive effects have examined the relative contribution of pre- and postsynaptic 5-HT1A receptors by means of local cerebral application and lesion techniques. Most evidence points towards a critical involvement of presynaptic receptors in the anxiolytic effects of 5-HT1A receptor agonists (although a possible contribution of postsynaptic receptors cannot be excluded). With regard to the antidepressive properties, a case can be made for the reverse; i.e., a strong involvement of postsynaptic receptors and a questionable contribution of presynaptic receptors. However, as the therapeutic effects of those 5-HT1A receptor (partial) agonists which have been tested clinically require repeated administration, attention has been directed increasingly towards chronic studies.(ABSTRACT TRUNCATED AT 400 WORDS)