Animal models for the study of anti-anxiety agents: a review

Anxiogenic activity of intraventricularly administered bradykinin in rats

The anxiogenic action of bradykinin was investigated in rats and compared with that of yohimbine, a known anxiogenic agent. Bradykinin (0.5, 1 and 2 μg/rat) was administered intracerebroventricularly (i.c.v.), whereas yohimbine (2 mg/kg) was administered i.p. The experimental methods used were the open- field, elevated plus-maze, social interaction and novelty suppressed feeding latency tests, and estimation of brain tribulin activity in terms of endogenous monoamine oxidase (MAO) A and MAO B inhibition. The behavioural and biochemical effects induced by bradykinin were qualitatively similar to those of yohimbine. Thus, both the drugs reduced ambulation and rears, and increased immobility and defecation, in the open-field test. They decreased the number of entries and time spent on the open arms of the elevated plus-maze, reduced social interaction in paired rats and increased the feeding latency in an unfamiliar environment in 48 h food-deprived rats. These effects are known to be associated with anxiety in animals. Bradykinin and yohimbine increased rat brain tribulin activity, the effect on the MAO A inhibitor component being more marked than that on the MAO B inhibitor component. The MAO A inhibitor component has been postulated to be the major anxiogenic moiety of tribulin. Lorazepam, a well known benzodiazepine anxiolytic agent, attenuated the anxiogenic effects of bradykinin and yohimbine, which may not be a functional effect. The investigation indicates that, like cholecystokinin (CCK), bradykinin may function as an endogenous anxiogenic peptide.

The effect of corticosterone in rats submitted to the elevated plus-maze and to to pentylenetetrazol-induced convulsions

1. In order to examine the effects of corticosterone in the anxiety response, the effect of acute, subchronic and chronic corticosterone (CORT) administration were studied using two animal models to study anxiolytic effects of drugs: the elevated plus-maze and the blockade of pentylenetetrazol (PTZ)-induced clonic convulsion. 2. The results obtained with the plus-maze showed an increase in the percentage of open arm entries and time spent in the open arms after acute treatment with the CORT. These results may be interpreted as an anxiolytic effect of corticosterone. Three days of vehicle treatment followed by an acute CORT administration, produced results that should also indicate anxiolytic effect of the corticosteroid. No effect was seen after 14 days of vehicle treatment followed by an acute CORT injection. Subchronic or chronic CORT treatment did not produce results different from controls. CORT treatment did not affect the PTZ-induced clonic convulsion. 3. In conclusion these results suggest that the acute anxiolytic effect observed in the elevated plus-maze did not occur after repeated CORT administration or mild stressors. Moreover they also suggest that the anxiolytic effect did not involve GABA mechanisms.

The elevated T-maze: a new animal model of anxiety and memory

In an attempt to analyze different types of anxiety, and at the same time assess memory, a new experimental model was developed. The apparatus, named the elevated T-maze, consisted of three arms of equal dimensions (50 x 10 cm) elevated 50 cm from the ground. One arm, enclosed by 40-cm high walls, was perpendicular to two open arms. The first experimental session was conducted 25 min after IP injection of either drug or saline. To assess inhibitory (passive) avoidance, the rat was placed at the end of the enclosed arm and the time taken to withdraw from this arm was recorded three times in succession. Soon afterwards, the rat was placed at the end of one of the open arms and the time taken to withdraw from this arm was measured, thus estimating one-way escape. To assess memory, inhibitory avoidance and escape were measured again 3 days later, without drug. Dose-response curves were determined for the benzodiazepine anxiolytic and amnestic agent diazepam (DZP, 0.5-4 mg/kg), as well as for ipsapirone (IPS, 0.25-2 mg/kg), an azapirone anxiolytic that is devoid of clinically significant amnestic effects. The doses of 1, 2, and 4 mg/kg DZP and of 1 and 2 mg/kg IPS impaired inhibitory avoidance, an effect that may be viewed as anxiolytic. Inhibitory avoidance remained impaired 3 days later in the rats treated with 1-4 mg/kg DZP, indicating anterograde amnesia. This effect was not due to state-dependent learning, because rats injected both at pretraining and pretesting with 2 mg/kg DZP still showed complete amnesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-releasing hormone (CRH) antisense oligodeoxynucleotide treatment attenuates social defeat-induced anxiety in rats

1. The neuropeptide corticotropin-releasing hormone (CRH) is the main mediator of the neuroendocrine and behavioral response to stress. End-capped phosphorothioate antisense and sense oligodeoxynucleotides (ODN) corresponding to the start coding region of rat CRH mRNA were infused intracerebroventricularly (30 micrograms/3 microliters per injection) three times at 12 hr intervals. Six hours after the last injection rats were subjected to social defeat stress and subsequently tested on the elevated plus maze. 2. Socially defeated CRH antisense-treated rats displayed markedly reduced anxiety-related behavior, as they spent significantly more time in the open arms of the plus maze compared to sense ODN- and vehicle-treated animals. 3. In controls, social defeat evoked a stress-induced elevation of CRH mRNA and CRH in the hypothalamus and a significant increase in plasma corticotropin (ACTH) levels. These parameters were attenuated in antisense-injected rats. 4. Our results suggest that CRH antisense treatment is effectively suppressing the neuroendocrine and behavioral effects of social defeat.

Comparison of different behavioral test situations used in psychopharmacology for measurement of anxiety

In order to estimate the consistency of variables measured in different test situations classically used in psychopharmacology, a set of hybrid mice was confronted with five testing situations: responses to a novel object introduced in a familiar environment, responses to novel places, behavior in a light/dark choice situation, on the holeboard, and in an elevated plus maze. A principal component analysis was performed using two variables per device as active variables and 26 others as supplementary variables. The first factor was clearly due to opposition between high and low levels of neophobia. Only variables from the first two tests were strongly correlated to this factor. Variables from the holeboard and from the plus maze were highly correlated one another and with the second factor, which grouped locomotion and exploration criteria. The light/dark choice test was intermediate and seemed to be moderately related to both locomotion and neophobia. These results point out the difficulty in comparing different test devices from a psychological point of view.

New animal models of anxiety

In an attempt to develop new animal models of anxiety with face and predictive validity for the spectrum of human anxiety disorders, two new animal paradigms have been described, stress-induced hyperthermia (SIH) in mice and ultrasonic pup vocalizations (UV) in rats. In SIH mice develop enhanced body temperature in anticipation of an aversive event. This SIH can be antagonized by benzodiazepines, alcohol and 5-HT1A receptor agonists, but not by specific 5-HT reuptake inhibitors (SSRIs) or 5-HT3 receptor antagonists. When rat pups are separated from their mother and littermates they produce ultrasonic sounds, indicative of a separation distress. Benzodiazepines, 5-HT1A receptor agonists and SSRIs decrease this calling, whereas 5-HT3 receptor antagonists have no effect. Antidepressants in general do not decrease pup calling because in contrast to the SSRIs, noradrenergic uptake blockers enhance calling. These two animal models of anxiety can be added to the range of anxiety models and will be of help in predicting new putative anxiolytic drugs.

Shock-induced ultrasonic vocalization in young adult rats: a model for testing putative anti-anxiety drugs

A putative animal model of anxiety based on shock-induced ultrasonic vocalization was pharmacologically validated in young adult rats. Suppression of shock-induced ultrasonic vocalization was obtained with diazepam, chlordiazepoxide, meprobamate and pentobarbital; the serotonin (5-HT)1A receptor agonists 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin], buspirone, ipsapirone, gepirone and tandospirone; the nonselective 5-HT receptor agonists TFMPP [1-(3-trifluoromethylphenyl)piperazin], mCPP [1-(3-chlorophenyl)piperazin] and DOI (1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane); the NMDA antagonists PCP (phencyclidine) and MK-801; the alpha 2-adrenoceptor antagonists idazoxane, yohimbine and 1-PP (1-pyrimidinylpiperazine); and the atypical neuroleptic clozapine. The alpha 2-adrenoceptor agonist clonidine, the 5-HT2/5-HT1C antagonist ritanserin, the 5-HT3 antagonists ondansetron and ICS-205,930, and the 5-HT reuptake inhibitor fluoxetine did not, or only partially, reduce ultrasonic vocalization. Tricyclic and tetracyclic, as well as some atypical antidepressants and a monoamineoxidase (MAO) inhibitor, showed no ultrasonic vocalization reducing effects, or reduced ultrasonic vocalization only at high doses. An opiate, an antimuscarinic, (pro)convulsants and typical neuroleptics did not reduce ultrasonic vocalization. The present findings suggest that the ultrasonic vocalization model specifically measures anxiolytic effects. Because ultrasonic vocalization responding develops within five days, remains stable for at least three months and gives highly reproducible results, the test appears suitable for rapid and repeated testing of new anxiolytics in the same animals.

Atypical anxiolytic profile of buspirone and a related drug, SM-3997, in a modified forced swim test employing straw suspension

Previous reports have shown that immobility time increases in the presence of suspended straws in association with an inhibition of straw-climbing behavior after acute administration of a prototypical anxiolytic benzodiazepine (BZD) such as diazepam. In this modified forced swim (MFS) test employing straw suspension, the effects of two new non-BZD compounds were tested and compared with those of diazepam (0.5, 1, and 5 mg/kg, IP) used in a previous MFS test. After a 5-min test of forced swimming, four straws were suspended just above the surface of the water and subsequently the straw-climbing trials were counted for 5 min as an index of escape behaviors induced by negative emotionality (stress and/or anxiety). Rats were injected IP with either saline, buspirone HCl (0.5, 1, and 5 mg/kg), or a related compound, SM-3997 (5, 10, and 20 mg/kg), 30 min before testing. At lower doses, both buspirone (0.5, 1 mg/kg) and SM-3997 (5, 10 mg/kg) reduced the duration of immobility, as opposed to that of diazepam. Conversely, buspirone at the highest dose of 5 mg/kg significantly prolonged the duration of immobility, and SM-3997 at 20 mg/kg also prolonged its duration, indicating a biphasic effects. All doses of buspirone and SM-3997 inhibited straw-climbing counts, in the same manner as diazepam. These results suggest that buspirone may possess relatively weak and/or atypical anxiolytic effects at lower doses, whereas at 5 mg/kg this compound may have an anxiolytic effect. In addition, SM-3997 may be a less potent anxiolytic drug than buspirone in the MFS test following a single-injection protocol.

Modification of the anxiolytic effects of 5-HT1A agonists by shock intensity

Contradictory evidence exists concerning the anxiolytic effects of 5-HT1A agonists in the conflict test. In the present work, a modification of the Vogel conflict model was used to assess different doses of diazepam (0.1-5.6 mg/kg), ipsapirone (1.0-17.8 mg/kg), buspirone (1.7-17.8 mg/kg), and indorenate (0.56-17.8 mg/kg) in rats receiving two different electric shock intensities (0.16 and 0.32 mA). The results show that the three 5-HT1A agonists had a smaller anticonflict effect than diazepam. The anticonflict effect with each compound was of a greater magnitude at 0.16 mA intensity than at 0.32 mA. This study shows that, using different electric shock intensities, compounds produce a differential effect: the anticonflict effects were more pronounced with the lower electric shock intensity than with the higher intensity. The present results suggest that the use of different shock intensities can play distinct roles over the drug's effect in the conflict test.

Conditioned defeat in the Syrian golden hamster (Mesocricetus auratus)

When singly housed under laboratory conditions, male Syrian golden hamsters routinely attack novel conspecific intruders introduced into their home cages. As we report here, after being repeatedly defeated by a larger, more aggressive intruder, such normal territorial aggression on the part of the resident hamsters is replaced by defensive behavior and flight. We have found that such conditioned defeat (CD) can be reliably induced by a series of 5-min trials with an aggressive intruder whether these trials are spread over 4 days or are all given on the same day. A useful behavioral criterion for the appearance of CD during acquisition is the first occurrence of anticipatory flight (AF), i.e., the first time the resident flees from the next aggressive intruder before being attacked. CD shows generalization: Animals trained to the AF criterion (AF Group) subsequently show defensive behavior toward, and even flee from, intruders which show absolutely no sign of aggressiveness. Animals in the AF Group persisted in such defense behavior for two test sessions; animals given three additional defeat trials beyond the appearance of AF (AF + 3 Group) showed a greater magnitude and persistence of defense and flight. A comparison of CD-trained animals which met a non-aggressive intruder (NAI) every day for 5 days to similarly trained animals which met the intruder only on the fifth day after acquisition suggests that CD diminishes passively as a function of time and not as the consequence of repeated encounters with a nonaggressive stimulus animal. We also found that near ideal NAIs could be prepared by treating nonaggressive hamsters with high doses of diazepam: animals so treated locomote more or less continuously around the cage virtually ignoring the subject. An unexpected observation was that subjects in the AF Group tended to closely follow these diazepam-treated, rapidly locomoting NAIs around the cage. Following may be an example of the "risk assessment" activities directed toward a potential threat. The development of a rapid and reliable technique for inducing CD in hamsters sets the stage for further physiological and pharmacological work on this interesting phenomenon.

Changes in experimental anxiety during pregnancy and lactation

The animals' reactivity and the levels of experimental anxiety during pregnancy and lactation in female rats were studied using the burying behavior test. The three main parameters analyzed in this test were: the cumulative burying behavior, the burying behavior latency, and the number of shocks necessary for displaying the behavior. The burying behavior was studied at the 7th, 14th, and 21st days of pregnancy and lactation. An additional group tested 12 h after parturition was also included. Simultaneously, in all animals, the ambulatory behavior was evaluated. All results were compared with those obtained in a control group of ovariectomized females. At the end of pregnancy a clear increase in burying behavior latency accompanied by a decrease in cumulative burying behavior was observed. Similarly, a clear reduction in burying behavior immediately after parturition was found. The number of shocks necessary for displaying the burying behavior were not modified along pregnancy and lactation with the exception of a clear decrease for the 7th lactation day. Changes in locomotor activity were observed at pregnancy, but not along lactation. These changes do not account for the reduction in burying behavior observed at the 14th gestation day. Data related to the reduction in burying behavior observed during gestation are discussed on the possible participation of progestins, while those found during lactation are discussed on the bases of the variations in serotonin and beta-endorphins that normally occur during this period.

Beta-adrenergic antagonists attenuate withdrawal anxiety in cocaine- and morphine-dependent rats

Rats were treated chronically with either cocaine (20 mg/kg/day, 14 days), morphine (incrementing doses of 10 mg/kg/day to 80 mg/kg, 11 days) or saline. During morphine or cocaine abstinence (48 h), dependent rats showed increased anxiety-like behavior in a conditioned defensive burying paradigm as evidenced by significantly shorter latencies to begin burying as well as a 4-fold increase in burying duration relative to saline-treated animals. This withdrawal-induced increase in burying behavior was blocked by pretreatment with either the beta-adrenergic antagonist propranolol (5 mg/kg) or the lipophobic selective beta 1-antagonist, atenolol (5 mg/kg). These results are consistent with the possibility that activation of peripheral beta 1 receptors may substantially contribute to withdrawal-induced anxiety and that beta-adrenergic antagonists could be useful in treating in cocaine and morphine dependent addicts.

Vulnerability to stress ulcerogenesis in rats differing in anxiety: a dopaminergic correlate

Dopamine and its agonists, acting through D1/DA1 receptors, have been shown to be effective protective factors against stress ulcerogenesis. Since anxiety has been related to stress ulcer development, we chose to examine dopaminergic activity in rats screened for the extremes of behaviorally manifest anxiety. High anxious rats develop more stress ulcers and more ethanol ulcers, relative to low anxious animals. High anxious rats require greater amounts of dopaminergic agonists for 50% protection against stress ulcer formation. In conditions of exposure to a stressor, high anxious rats lose amygdalar dopamine at a faster rate than do low anxious rats. These results suggest that anxiety is a significant factor in stress ulcer development and that central dopaminergic function is critically involved in mediating this pathogenetic factor.

Nitrous oxide induces an anxiolytic-like effect in the conditioned defensive burying paradigm, which can be reversed with a benzodiazepine receptor blocker

To investigate the anxiolytic effects of nitrous oxide (N2O), male hooded rats were tested in the conditioned defensive burying (CDB) test, a paradigm that exploits a propensity of rats to bury objects associated with aversive stimulation. A single, brief electrical shock was delivered to rats upon contact with an electrified prod, before exposure to one of four mixtures of N2O and oxygen (O2) (10-40% N2O) or room air (RA). Compared to RA-exposed animals, rats exposed to N2O exhibited a concentration-related reduction in duration and height of prod-directed "defensive" burying with floor bedding material; these measures reached statistical significance at 30% N2O. Pretreatment with 20 mg/kg of the benzodiazepine receptor blocker flumazenil, which alone had no effect, effectively antagonized a 30% N2O-induced decrease in burying. Horizontal locomotion and rearing were not significantly affected at concentrations of N2O that attenuated prod-directed burying. Treatment with the benzodiazepine anxiolytic standard, chlordiazepoxide (2.5-10.0 mg/kg) also resulted in dose-related attenuation of burying behavior. These findings show that N2O can induce effects similar to those of known anxiolytics in this paradigm and suggest a benzodiazepine mechanism in its mediation.

Effects of angiotensin II on behavioral responses of defensive burying paradigm in rats

The effects of angiotensin II (ATII) administered intracerebroventricularly in male Wistar rats in doses of 0.1, 0.5, and 1.0 micrograms, as well as of ATII (1.0 micrograms) + saralasin (SAR, an analog ATII) (5.0 micrograms), on behavioral responses of the defensive burying paradigm were studied. ATII-treated animals displayed significantly less defensive burying behavior (less time spent in defensive burying and less frequent burying than in vehicle-treated rats) in a dose-dependent manner. SAR at a dose of 5 micrograms did not affect burying behavior significantly; it also did not modify the inhibition effects of ATII on behavioral responses of the defensive burying test. These results provide evidence that ATII can exert anxiolytic actions on central transmitter systems mediating conditioned fear-related behaviors (i.e., defensive burying). The present study suggests that the defensive burying animal model is a rather sensitive test fulfilling the pharmacological criteria of dose-dependent sensitivity for studying the central effects of neuropeptides (e.g., ATII).

Maudsley reactive (MR/Har) and nonreactive (MNRA/Har) rats: performance in an operant conflict paradigm

The present studies were designed to characterize the behavior of Maudsley reactive (MR/Har) and nonreactive (MNRA/Har) rats in a modification of the Geller-Seifter operant conflict paradigm. Food-restricted (85% of free-feeding weights) female MR/Har and MNRA/Har rats were trained to lever press for food reinforcement in a multiple-schedule operant conflict paradigm. In the absence of a tone, a fixed ratio-30 (FR-30) schedule for reinforcement only was in effect (i.e., every 30th lever press resulted in the delivery of a 45-mg food pellet). During the presence of a tone, a fixed ratio-1 (FR-1) schedule of both reinforcement (food) and punishment (0.20 mA footshock applied for 500 ms) was in effect (i.e., each lever press resulted in both food and shock delivery). The tone periods were 27 s in duration and were presented on a variable interval (VI)-120-s schedule (approximately 20 tones/40-min session). Behavioral testing was conducted 5 days/week for 35 weeks. Initially, punished responding between the MR/Har and MNRA/Har rat strains did not differ dramatically. However, over the course of many weeks of conflict testing, rats of the MNRA/Har strain came to accept significantly more shocks than did subjects of the MR/Har strain. A direct examination of footshock sensitivity in these rats revealed that this difference in conflict behavior over time was not due to strain differences in shock sensitivity. The mechanism for this time-dependent difference in conflict behavior between the MR/Har and MNRA/Har rats remains undetermined.

Neuroendocrine and behavioral responses during conditioned active and passive behavior in the defensive burying/probe avoidance paradigm: effects of ipsapirone

Plasma epinephrine (E), norepinephrine (NE), and corticosterone (CORT) concentrations were determined in the rat before, during, and after a 15-min exposure to a nonelectrified probe on day after receiving electric shock (1.5 mA) through a probe mounted on the wall of the home cage. Rats displayed burying (active coping) if sawdust was provided on the floor and immobility (passive coping) if bedding was absent both during training and testing. The conditioned burying was accompanied by high plasma NE but low E and CORT concentrations, whereas immobility was associated with high CORT and low NE levels. A forced switch from the active to passive coping (training with and testing without sawdust) led to the highest rise in E concentration. The 5-HT1A agonist ipsapirone, with anxiolytic properties, dose-dependently (0.5 and 2.5 mg/kg, IV) reduced defensive burying behavior and increased the amount of time spent on feeding behavior in the presence of bedding material. Both plasma E and CORT levels were further elevated by the higher dose of ipsapirone. In the absence of bedding material, ipsapirone failed to affect immobility behavior, but it dose-dependently elevated the stress-induced increase in E, NE, and CORT concentrations. Accordingly, the behavioral anxiolytic action of the 5-HT1A agonist ipsapirone was restricted to active coping, whereas neuroendocrine activation by the drug was present in all conditions. It is suggested that the effects of ipsapirone on behavioral coping and neuroendocrine regulation are produced by different populations of 5-HT1A receptors in the brain.

Role of anxiety in subordinate male mice sexual behavior

Dominant and subordinate male mice behave differently when exposed to a female, with subordinates showing impairment of their sexual performance in the presence of the male antagonist. In the present study, we investigate whether these rank-related behavioral differences can be modified by an anxiolytic treatment. In a first experiment, diazepam (0.25 mg/kg) improves the performance of subordinate mice toward the female, as shown by the increase of proxemic behavior, anogenital sniffing, and social grooming of the female. Social grooming of the female is the only behavior modified by a higher dose of the anxiolytic drug (0.5 mg/kg). A second experiment, in which dominant and isolated mice are subjected to the same experimental procedure, demonstrates that social behavior of these two classes of males is not affected by the pharmacological treatment. The results are discussed in terms of the advantages of using subordinate males in such a sexual context as a model for the study of anxiolytic drugs.

MDL 73,147EF, a 5-HT3 antagonist, facilitates latent inhibition in the rat

Latent inhibition (LI) is a behavioral model of selective attention that has been used to study the attentional deficits seen in schizophrenia. In the present study, we examined the effect of 5-hydroxytryptamine3 (5-HT3) receptor blockade on LI using the conditioned emotional response (CER) procedure. Prior exposure to 20, 30, or 40 stimulus presentations significantly, and almost completely, inhibited the CER to that stimulus. This LI effect was much weaker when only 10 preexposures were given. 1H-indole-3-carboxylic acid, trans-octahydro-3-oxo-2,6-methano-2H-quinolizin-8-yl ester methanesulfonate (MDL 73,147EF), a selective 5-HT3 receptor antagonist, significantly facilitated the LI effect observed after 10 preexposures at 0.1 mg/kg but not at 0.01 mg/kg. The magnitude of this effect was comparable to that observed with the classical neuroleptic haloperidol (0.1 mg/kg). Neither MDL 73,147EF nor haloperidol affected the CER in animals not preexposed to the stimulus. These results strongly corroborate suggestions that 5-HT3 receptor antagonists will be of use in the treatment of schizophrenia.

Excitotoxic lesions of the septum produce anxiolytic effects in the elevated plus-maze and the shock-probe burying tests

Our previous research has shown that electrolytic lesions of the posterior septum result in dramatic, antianxiety effects in two different animal models of anxiolytic drug action, i.e., a selective increase in open-arm activity in the elevated plus-maze test, and a selective abolition of defensive burying in the shock-probe burying test. Although these results suggest that posterior regions of the septum play an important role in the expression of anxiety in these tests, it is unclear whether destruction of septal nuclei themselves mediated these effects, since electrolytic lesions also destroy fibers of passage. Accordingly, in the present experiments, the anxiolytic effects of electrolytic lesions of the septum were compared to those of excitotoxic lesions, which preferentially destroy cell bodies, leaving fibers of passage intact. In the first experiment, both electrolytic and kainic acid lesions of the posterior septum produced complete anxiolytic effects in the elevated plus-maze (an increase in the percentage of open-arm entries and percentage of time in open arms), and partial anxiolytic effects in the shock-probe test (an increase in contact-induced probe shocks), compared to sham-lesioned controls. These antianxiety effects could not be attributed to an increase in general activity, or a decrease in reactivity to shock. In the second experiment, excitotoxic lesions of the posterior septum were produced by a more selective agent, quisqualic acid. Quisqualic acid, like electrolytic lesions, produced clear, anxiolytic effects in both the plus-maze and the shock-probe tests, compared to sham-lesioned control. Taken together, these results strongly suggest that cells originating in posterior regions of the septum mediate anxiety-related responses.

The performance of WKY rats on three tests of emotional behavior

The behavior of Wistar, Fischer-344, and WKY male rats was observed on three tests of emotional behavior. These included the defensive-withdrawal test, the elevated plus maze, and the conditioned defensive-burying test. Rats were subsequently exposed to the water-restraint ulcerogenic procedure. Fischer-344 rats were more active in the defensive-withdrawal tests, but other behavioral measures in this test did not discriminate between the three strains. Scores reflecting anxiety in the elevated plus maze were lowest for Fischer-344 rats and highest for WKY rats, but the anxiety scores of WKY rats did not differ significantly from Wistar rats. The behavior of WKY rats was significantly different from the other two strains in the conditioned defensive burying test. While the degree of anxiety is measured by burying behavior, elicited by the novelty of prod shock, immobility was the prevalent response of WKY rats. WKY rats also revealed significantly higher ulcer severity scores when exposed to water-restraint stress after each behavioral test procedure. We propose that WKY rats are hyperresponsive to stress and that novelty stress elicits depression-like behavior, which is the prevalent behavioral stress response in WKY rats.

Evidence for a postsynaptic action of the serotonergic anxiolytics: Ipsapirone, indorenate and buspirone

In the present experiment we analyzed whether the antianxiety action of the serotonergic 1A agonists buspirone (5 mg/kg), ipsapirone (5 mg/kg), indorenate (5 mg/kg), and 8-OH-DPAT (0.5 mg/kg) were mediated through the stimulation of pre- or postsynaptic serotonergic receptors. The experimental anxiety values were determined with the burying behavior test, where a reduction in the cumulative time of burying behavior was interpreted as a reduction in anxiety. To that purpose we analyzed the putative anxiolytic action of these drugs in animals with lesion of the serotonergic fibers after the intracerebroventricular (ICV) injection of 5,7-dihydroxytyptamine (5,7-DHT, 10 or 150 micrograms/10 microliters). The neurochemical analysis shows that these treatments produce a statistically significant reduction in 5-HT and 5-HIAA levels in various brain areas. The results of the behavioral experiments reveal that buspirone, ipsapirone, and indorenate produced exactly the same reduction in burying behavior in lesioned animals as compared with control rats. The reduction in burying behavior produced by 8-OH-DPAT was effectively prevented by the lesion with 5,7-DHT. These data suggest that the anxiolytic effect of buspirone, ipsapirone, and indorenate is mediated via the stimulation of postsynaptic receptors, while the somatodendritic receptors are involved in the antianxiety effect of 8-OH-DPAT.

The MSH/ACTH analog ORG 2766 in anxiety disorders

The anxiolytic effects of the MSH/ACTH analog ORG 2766 were assessed in three different groups of patients with an anxiety disorder: panic disorder, generalized anxiety and social phobia. Patients were treated with capsules containing 20 mg ORG 2766 or placebo and received 4 capsules daily for six weeks. A slight reduction on the Hamilton Anxiety Scale was found after ORG 2766 treatment in the panic disorder patients, while the peptide did not affect the number of panic attacks in these patients. In the other two patient groups no anxiolytic effect of ORG 2766 was observed.

Species differences in the mechanism through which the serotonergic agonists indorenate and ipsapirone produce their anxiolytic action

The effect of three anxiolytic drugs, indorenate, ipsapirone and diazepam, on the burying behaviour of rats and mice was studied. All three drugs induced a reduction in burying behaviour interpreted as a reduction in anxiety. However, a species difference in the diazepam sensitivity was found: rats showed a clear effect after 1.0 mg/kg while already at 0.25 mg/kg an action was observed in mice. The serotonergic anxiolytics produced similar responses at similar doses (2.5-5.0 mg/kg) in both species. The serotonergic antagonists, pindolol (3.1 mg/kg), alprenolol (5.0 mg/kg) and methiotepin (0.31 mg/kg), induced a slight reduction in the time spent burying but effectively counteracted the anxiolytic action of the serotonergic agonists in mice but not in rats. By contrast, in rats, the beta blocker, practolol (0.5 mg/kg), was the only drug effective in preventing the anxiolytic actions of ipsapirone. The combined treatment of indorenate and methiotepin resulted in an impairment of motor coordination and ambulatory behaviour in both species studied, thereby suggesting that the lack of effect of such combination was mediated by altering the motor behaviour. Finally, the reduction in ambulatory behaviour in mice produced by ipsapirone was effectively prevented by the antagonists methiotepin, pindolol and alprenolol indicating the involvement of a serotonergic receptor in this effect. From these results it is concluded that a different mechanism underlies the anxiolytic actions of indorenate and ipsapirone in mice and rats.

Clozapine: strong antiaggressive effects with minimal motor impairment

Clinical studies have shown clozapine to be effective in the treatment of schizophrenia and associated with an extremely low incidence of extrapiramidal side effects. Diverse studies indicate that clozapine is an atypical neuroleptic with a preferential activity on the mesolimbic structures and a lower affinity for striatal D2 receptors than the classical antipsychotics. The purpose of this study was to assess the behavioral properties of clozapine, especially its effects on aggressive and motor behaviors. Individually housed male mice of the OF1 strain were exposed to anosmic "standard opponents" 30 minutes after the last drug administration. One category of animals received a single IP dose of the compound (0.2, 0.5, 1 or 1.5 mg/kg). Another category received daily doses (0.5, 1 or 1.5 mg/kg) for 21 days. Encounters were videotaped and behavior evaluated using an ethologically based analysis. Clozapine, in the acute treatment condition, produced a significant decrease in "attack" and "threat" behaviors without "immobility" being significantly increased. These results suggest a rather specific antiaggressive action of the compound with little motor impairment. In the chronic administration, no significant change in aggressive behavior was observed which may be attributed to the development of some degree of tolerance.

The effects of acute administration of gepirone in rats trained on conflict schedules having different degrees of predictability

The anticonflict activity of gepirone, a putative anxiolytic and antidepressant, was examined on three schedules which conditioned the suppression of licking. The novel schedules differed in the degree to which they predicted (signalled) the presentation of a conflict-inducing electric shock. Three doses of gepirone (1.25, 2.5, and 5 mg/kg SC) were evaluated on a predictable, a moderately predictable, and an unpredictable schedule of shock presentation. Gepirone induced a nondose-dependent increase from baseline in punished licking on the predictable schedule on the last two days of a five-day test period. The lowest dose (1.25 mg/kg) of gepirone induced a significant increase in punished licking on the moderately predictable schedule on the last two days of testing. The highest dose (5 mg/kg) induced initial decreases in overall responding on this schedule. However, responding returned to baseline over the course of the four days of testing. When administered to rats trained on an unpredictable schedule of shock presentation, all doses of gepirone induced an initial decrease from baseline. The lowest dose group returned to baseline control response levels over the next four days, whereas the suppressive effects of the higher doses persisted. The initial decrease in responding observed on all schedules may be due to the effects of gepirone on motor functioning. However, the 2.5-mg/kg dose induced a proconflict or anxiogenic effect on the last test day (decreased punished responding alone) on the unpredictable schedule, while inducing an anticonflict effect on the predictable one. The unpredictable schedule is sensitive to detecting decreases as well as increases in punished responding and as such may be a unique conflict model for evaluating novel anxiolytics.(ABSTRACT TRUNCATED AT 250 WORDS)

Anxiolytic activity of the progesterone metabolite 5 alpha-pregnan-3 alpha-o1-20-one

3 alpha-hydroxylated pregnane steroids have been shown to possess anesthetic, hypnotic, anticonvulsant and anxiolytic properties. In this study, metabolites of progesterone and deoxycorticosterone, 5 alpha-pregnan-3 alpha-o1-20-one (3 alpha-OH-DHP) and 5 alpha-pregnan-3 alpha,21-diol-20-one (5 alpha-THDOC), respectively, were tested for anxiolytic effects in N.I.H. Swiss-Webster mice using the light/dark transition, open-field and lick-suppression tests. Similar to the benzodiazepine (BZ) diazepam, 3 alpha-OH-DHP (5-40 mg/kg) and 5 alpha-THDOC (5-40 mg/kg) significantly increased the number of light/dark transitions. 3 alpha-OH-DHP's effects were stereospecific as its diasteriomer, 3 beta-OH-DHP was devoid of activity. The benzodiazepine antagonist CGS-8216 (10 mg/kg) blocked diazepam's (1.0 mg/kg) anxiolytic effects, but did not have any effect against 3 alpha-OH-DHP (20 mg/kg). The data indicate that the pregnane steroids produce their anxiolytic effects through a separate mechanism than the BZs. 3 alpha-OH-DHP (20 mg/kg), 5 alpha-THDOC (20 mg/kg) and diazepam (1.0 mg/kg) increased activity in a open-field test. 3 beta-OH-DHP had no effect in the open-field test. Furthermore, 3 alpha-OH-DHP produced a 235% increase in punished responding in a lick-suppression test. These results demonstrate that the endogenous pregnane steroids possess anxiolytic effects that may be clinically relevant.

ICS 205-930 and feeding responses to amino acid imbalance: a peripheral effect?

Serotonin3 (5-HT3) receptor antagonists (ICS 205-930 and MDL 72222) have been shown to block or ameliorate the anorectic response of the rat to amino acid imbalanced (IMB) diets. Two experiments were conducted to determine whether the effects of these antagonists are mediated through central or peripheral 5-HT3 receptors. In Experiment One, ICS 205-930 (ICS) was injected centrally, into either the lateral ventricle (doses: 0.3 pmol to 10 nmol), or the cisterna magna (62 nmol). The intake of rats fed an isoleucine IMB diet was not affected by these injections. In Experiment Two, rats received an IP injection of either saline, ICS, or a quaternized derivative of ICS (Q-ICS) that should not cross the blood-brain barrier. Both ICS- and Q-ICS-injected rats ate significantly more (p less than 0.05) IMB diet than saline-injected rats. Intake of IMB diet was not different (p greater than 0.4) between ICS and Q-ICS groups. From these results, it appears that ICS restores intake of IMB through a peripheral component.

Effects of 5-HT uptake inhibitors, agonists and antagonists on the burying of harmless objects by mice; a putative test for anxiolytic agents

1. The effects of 5-hydroxytryptamine (5-HT) uptake inhibitors, agonists and antagonists have been evaluated on mouse marble-burying behaviour, a putative test for anxiolytic agents. The high levels of locomotor activity occurring on first exposure to a circular runway (runway were used as a separate test of non-specific drug effects. 2. Fluvoxamine, zimeldine, indalpine and citalopram dose-dependently inhibited burying without affecting runway activity. 5-Hydroxytryptophan (5-HTP, with carbidopa), 5-methoxy-N,N-dimethyltryptamine, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OHDPAT), buspirione, gepirone and ipsapirone reduced burying only at doses reducing runway activity. RU 24969 increased runway activity at all effective doses. 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI), 1,-(3-trifluoromethylphenyl) piperazine (TFMPP) and 1-(3-chlorophenyl)-piperazine (mCPP) potently and differentially reduced burying at doses below those affecting runway activity. 3. 5-HT antagonists only reduced burying at high doses which also reduced runway activity. Burying inhibition by DOI was antagonized by ritanserin, ICI 169,369 and cyproheptadine but not by pindolol or a low (0.25 mg kg-1) dose of metergoline. Burying inhibition by mCPP was not altered by any of these agents except that it was potentiated by pindolol 5 mg kg-1. 4. Zimeldine burying inhibition was potentiated by ritanserine, ICI 169,369, ICS 205-930, cyproheptadine and pindolol. Runway activity was not affected by these drug combinations. 5. Zimeldine was administered in drinking water at a dose of 10 mg kg-1 daily for 21 days. Burying inhibition had disappeared by day 14 and did not recur 24 or 48h after withdrawal at which times responses to DOI were at control levels.6. Selective inhibition of marble burying was not found to be a property of 5-HT-related putative and actual anxiolytics such as buspirone, gepirone, ipsapirone, ritanserin and ondansetron. Nevertheless it was a general property of both 5-HT uptake inhibitors and 5-HT releasing agents; this generality suggests that elevated synaptic 5-HT could be responsible for the effects of these latter agents. The action of DOI may be attributable to effects at the 5-HT2 receptor but those of the 5-HT agonist and releasing agent mCPP, and the uptake inhibitor zimeldine, could not be attributed to effects at any one 5-HT receptor subtype. This, together with the potentiating effect of several 5-HT antagonists on the response to zimeldine, raises the possibility of multiple interactions between 5-HT receptor subtypes.

Effects of specific dopaminergic agonists and antagonists in the open-field test

It has been found that dopaminergic transmission could be involved in some aspects of anxiety. The present study aims to explore this hypothesis further, using specific DA1 (SKF 38393) and DA2 (bromocriptine) agonists or DA1 (SCH 23390), and DA2 (zetidoline) antagonists in the open-field test. The results confirm previous studies indicating that DA1 and DA2 agonists predominantly increase locomotor activity, while DA1 and DA2 antagonists predominantly decrease it. However, at low doses, the four drugs increase the peripheral ambulation score significantly and, with the exception of zetidoline, also increase the central ambulation score. The observations made with zetidoline confirm the hypothesis that a specific presynaptic DA2 antagonism could be determinant for the disinhibitory effects of low doses of neuroleptics. A collateral action on 5HT transmission is also suggested to explain an hypothetic anxiolytic action of DA agonists and SCH 23390 at lower doses.

Central and peripheral benzodiazepine receptors: involvement in an organism's response to physical and psychological stress

The present review discusses the current knowledge of the molecular pharmacology and neuroanatomical and subcellular localization of both the central benzodiazepine/GABA-chloride ionophore receptor complex and the peripheral benzodiazepine receptor. It then reviews all of the literature to date on how these two receptor sites are modulated by environmental stress. The possible role of these sites in learning and memory is also discussed. Finally, a theoretical model is presented which examines the differential, and perhaps complementary, alterations of these two sites in an organism's response to stress.

Amino acid imbalance, a nutritional model: serotonin3 mediation of aversive responses

The feeding responses to essential dietary amino acid (AA) disproportion have been useful in nutritional studies. These responses involve first: recognition of the imbalance and second: rejection of the diet, likely via development of a learned aversion. In the rat, we have studied the role of the limiting AA and protein synthesis in the recognition phase by replacement of the limiting AA into a brain area essential for the initial depressed feeding response. We have also reported a reciprocal relationship between serotonin (5HT) activity and intake of imbalanced diets. High doses of the 5HT3 receptor antagonist, ICS 205-930 (ICS; 9 mg/kg IP), restored food intake to 85% or more of control intake. In the present experiments, similar treatment with ICS blocked the classical conditioned taste aversion to a saccharin solution paired with lithium chloride. These results suggest that the increased intake of AA imbalanced diets after ICS may be due to 5HT-mediated blockade of a learned aversion.

Differential role of serotonin and noradrenaline on anxiety reduction after ejaculation in the rat

As previously reported, a reduction in anxiety after ejaculation was observed. In a previous report it was demonstrated that the GABA-benzodiazepine system is involved in the mediation of this reduction in anxiety. The anxiety levels were measured using a defensive burying model. This work was performed to elucidate the serotonin and noradrenaline participation in the mediation of this phenomenon. Two experiments were made. In the first experiment the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT, 10 micrograms/10 microliters) was intracerebroventricularly injected. Five days after its administration the behavioral tests were performed. In the second experiment, the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4, 50 mg/kg X 2) was IP administered. The neurochemical data reveal a drastic reduction in various brain areas respective monoamine levels after these treatments. The lesion produced by 5,7-DHT was able to reverse the reduction in anxiety in copulating males, but produced no changes in noncopulating animals. This finding supports the idea that the serotonergic system is involved in the reduction of anxiety observed after ejaculation. The results of the DSP4 experiment suggest that there is not a direct participation of the noradrenergic system in the anxiety reduction observed after ejaculation.

Benzodiazepines, putative anxiolytics and animal models of anxiety

Anxiety is a complex state that includes a broad range of classified symptoms. Anxiolytic treatment has been dominated by the use of benzodiazepine drugs (BZs), which is often prolonged. However, the multiplicity of anxiety states and the lack of BZ specificity preclude the potent targeting of the drugs to different states, and point to the problem of drug dependence. Furthermore, animal models of anxiety give different results when challenged with apparently similar drugs. The search for alternative drugs with a higher specificity has led to 5-HT receptor subtypes. In this review, Simon Green describes how recent research might have dual benefits: in improving drug therapy of anxiety in humans, and in analysing and categorizing more clearly the concept of anxiety itself.

Failure of naloxone to block the reduction in burying behaviour after ejaculation in male rats

In the present study we analyzed whether the opiate nociceptive system participates in the reduction in burying behaviour observed after ejaculation. To that purpose the opiate antagonist naloxone (0.5, 1.0 and 2.0 mg/kg) was administered before ejaculation. The results showing that this antagonist does not interfere with the drastic reduction in burying behaviour suggest that an opiate nociceptive mechanism is not involved in this effect. Present data further support the idea that the reduction in burying behaviour is reflecting a specific reduction in anxiety.

Anxiogenic activity of isatin, a putative biological factor, in rodents

Isatin (2,3-dioxoindole) has been proposed as a new biological factor, responsible for at least part of the activity of tribulin, an endogenous monoamine oxidase and benzodiazepine receptor binding inhibitory factor, which may serve as an endocoid marker of stress and anxiety. The putative anxiogenic activity of isatin was investigated in rats and mice. The doses chosen for the study, namely 15 mg/kg i.p. in mice and 20 mg/kg i.p. in rats, were based on preliminary behavioural studies. Yohimbine, a well established anxiogenic agent, was used for comparison and used at doses of 2 and 2.5 mg/kg i.p. in mice and rats, respectively. The experimental paradigms chosen have been shown to stand the tests of validity and reliability. Isatin induced significant anxiogenic activity in the open-field and elevated plus-maze tests in mice, and the social interaction test in rats, which were comparable to those induced by yohimbine. In addition, both isatin and yohimbine attenuated the effects of the anxiolytic agent diazepam in the open-field test. The investigations indicate that isatin has significant anxiogenic effect and support the contention that it and/or its biotransformation products may be responsible for at least part of the activity of tribulin demonstrated previously in animal models and in clinical situations of stress and anxiety.

Evaluation of marble-burying behavior as a model of anxiety

On individual placement in a cage with 20 evenly spaced glass marbles, female MF1 mice buried 7.8 +/- 0.2 marbles. Olfactory stimuli from experimenters hands and sex of mice had no influence on number buried, but most marbles were buried when they were evenly spaced. There was no habituation to these novel objects on serial testing or prehousing with marbles and, in a two-compartment box, mice did not avoid marbles, spending half their time on the marble side. In the pharmacological experiments, locomotor activity was measured separately to indicate the possibility of nonspecific effects. The anxiogenic agents yohimbine and ethyl-beta-carboline-3-carboxylate (beta-CCE) did not enhance burying, yohimbine decreased burying at doses also reducing locomotor activity. Diazepam effects depended on dose: 0.1 mg/kg increased burying, 0.25 mg/kg had no effect and 1.0-5.0 mg/kg reduced it. Diazepam increased locomotor activity from 0.1-2.5 mg/kg and had no effect at 5.0 mg/kg. Zimeldine, 10.0 mg/kg, reduced burying but not locomotor activity. Inhibition of marble burying may be a correlational model for detection of anxiolytics rather than an isomorphic model of anxiety.

Animal models of anxiety and the development of novel anxiolytic drugs

1. The behavioural effects of classical anxiolytics such as barbiturates and benzodiazepines have been well characterised. However, recent research has been aimed at the development of novel anxiolytics without problems of sedation, muscle relaxation, amnesia and dependence. 2. A number of novel omega (benzodiazepine) receptor ligands with anxiolytic properties have been described including alpidem, bretazenil, suriclone and abecarnil. Although these compounds share some behavioural effects with older anxiolytic drugs, such as increasing punished drinking, they also show many differences. Their novel profiles may be related to low intrinsic activity or to selectivity for omega receptor subtypes. 3. The possibility that novel anxiolytics may be found among compounds active at serotonin receptors remains a strong hypothesis. Compounds, which, like buspirone, are active at 5HT1A receptors may be anxiolytic as may be antagonists at 5HT2 and 5HT3 receptors. All these compounds have behavioural effects which differ from those of benzodiazepines. 4. In order more effectively to screen for and develop novel anxiolytics it will be necessary to refine behavioural models in the light of feedback from the clinic.

Sulpiride has an antiaggressive effect in mice without markedly depressing motor activity

The atypical neuroleptic, sulpiride is a selective D2 antagonist, having a preferential action on mesolimbic regions. The effects of acute and chronic treatment with sulpiride on aggressive behaviour in male mice were studied using an ethologically based analysis. It was hypothesized that sulpiride would diminish "threat" and "attack" but would not produce marked "immobility", because of the mesolimbic effect referred to above. Isolated albino male mice (experimental animals) were confronted by "standard opponents". Acutely-treated experimental animals received an intraperitoneal injection of sulpiride (20, 50 or 100 mg/kg) 30 min before testing. Chronically-treated animals received sulpiride (10, 20 or 50 mg/kg) once a day for 7 or 14 consecutive days. Acute treatment with sulpiride had an obvious antiaggressive effect, with significantly decreased time devoted to "attack" and "threat" behaviour. Although time spent in "immobility" was modestly increased, the time devoted to other motor behaviour was also increased. Chronic treatment for 1 or 2 weeks did not change any behavioural category, except "immobility". The antiaggressive action of acutely administered sulpiride is interpreted as a relatively specific dopaminergic antagonist effect and not as merely a non-specific correlate of its disruptive action on motor behaviour. The possible anxiolytic action of sulpiride is also discussed.

A comparison of benzodiazepine, serotonin, and dopamine agents in the taste-reactivity paradigm

Previous studies have shown that rats' positive, palatability-dependent consummatory reactions to infused tastes are selectively facilitated by a benzodiazepine agonist (chlordiazepoxide), and that this effect can be blocked by the coadministration of benzodiazepine antagonists (e.g., Ro 15-1788). The purpose of the present study was to determine whether agents acting at other receptor sites (dopaminergic, serotonergic), which have been shown to modulate food consumption, might also modify rats' palatability-dependent reactivity to infused tastes. In this experiment, the benzodiazepine agonist, diazepam, facilitated positive palatability reactions, while dopaminergic agents (haloperidol, apomorphine, amphetamine) had no significant effects on either positive or aversive reactions. The putative 5-HT1A agonists, buspirone and gepirone, had a general inhibitory action on both positive and aversive palatability reactions. These results are surprising in view of the effects of serotonergic and dopaminergic agents on food and fluid intake. Our results suggest that the benzodiazepine receptor system may play a special role in the neural control of appetite through its enhancement of the positive palatability of tastes. Dopamine systems, by contrast, appear to control food intake by modulating processes that are independent of food affect evaluation.

Anxiolytic potential of a microgram dose of chlordiazepoxide in the open-field test

Diazepam, when administered in very low doses (100 micrograms/kg), can induce a specific inhibition of coarse and ambulation activities in the rat, suggesting a novel mechanism of action occurring in the microgram dose range. This study fails to reproduce the same effects with chlordiazepoxide. On the contrary, greater stimulant and anxiolytic effects were measured with the lowest dose tested (0.1 mg/kg). These results demonstrate that the familiar effects of benzodiazepines should not be extrapolated uncritically to lower dose ranges without empirical testing.

Alpha 1- and beta-adrenoceptor stimulation potentiate the anticonflict effect of a benzodiazepine

Interactions between different noradrenaline (NA)-active drugs and the benzodiazepine alprazolam (APZ) were examined in a modified Vogel's drinking conflict test in the rat. In a dose (0.5 mg/kg) which did not alter the behavior by itself, the alpha 2-adrenoceptor antagonist yohimbine consistently was found to enhance the anticonflict effect of APZ (0.5 mg/kg). The yohimbine induced potentiation of the APZ effect was counteracted both by the selective alpha 1-adrenoceptor antagonist prazosin (0.25 mg/kg) and the beta-adrenoceptor antagonist propranolol (2.0 mg/kg), but not by the selective beta 1-adrenoceptor antagonist metoprolol (2.0 mg/kg). Similar potentiating phenomena were obtained after co-administration of APZ (0.5 mg/kg) with the selective alpha 1-adrenoceptor agonist ST 587 (0.5-1.0 mg/kg) as well as with the suggested beta 2-adrenoceptor agonist clenbuterol (1.0 mg/kg). The results indicate that the potentiative effects of alpha 2-adrenoceptor antagonists on BDZ induced anticonflict action may be due to increased stimulation of alpha 1- and beta-adrenoceptors, via enhanced NA release. The findings are discussed in relation to the signal-to-noise hypothesis of NA function, and in relation to the suggested NA involvement in anxiety-related behavior.