A comparison of the effects of buspirone and diazepam on plasma corticosterone levels in rat

Anxiolytic-like effects of leptin on fixed interval responding

Leptin has been shown to affect energy homeostasis, learning and memory, and some models of anxiolytic action. However, leptin has produced inconsistent results in previous non-operant behavioural tests of anxiety. Here, we test the anxiolytic potential of leptin in an operant paradigm that has produced positive results across all classes of anxiolytic so far tested. Rats were tested in the Fixed Interval 60 Seconds (FI60) task following administration of 0/0.5/1.0mg/kg (i.p.) leptin or an active anxiolytic control of 5mg/kg (i.p.) chlordiazepoxide (CDP). By the end of the 14days of testing in the FI60 task, 0.5mg/kg leptin released suppressed responding in a manner similar to CDP, and 1.0mg/kg leptin produced a relative depression in responding, a similar outcome pattern to previously tested 5HT-agonist anxiolytics. This suggests that leptin behaves similarly to established serotonergic anxiolytics such as buspirone and fluoxetine; with the delay in development of effect during testing, and the inverted-U dose-response curve explaining the inconsistent behaviour of leptin in behavioural tests of anxiety, as this type of pattern is common to serotonergic anxiolytics.

The involvement of noradrenergic mechanisms in the suppressive effects of diazepam on the hypothalamic-pituitary-adrenal axis activity in female rats

Aim

To elucidate the involvement of noradrenergic system in the mechanism by which diazepam suppresses basal hypothalamic-pituitary-adrenal (HPA) axis activity.

Methods

Plasma corticosterone and adrenocorticotropic hormone (ACTH) levels were determined in female rats treated with diazepam alone, as well as with diazepam in combination with clonidine (α₂-adrenoreceptor agonist), yohimbine (α₂-adrenoreceptor antagonist), alpha-methyl-p-tyrosine (α-MPT, an inhibitor of catecholamine synthesis), or reserpine (a catecholamine depleting drug) and yohimbine.

Results

Diazepam administered in a dose of 2.0 mg/kg suppressed basal HPA axis activity, ie, decreased plasma corticosterone and ACTH levels. Pretreatment with clonidine or yohimbine failed to affect basal plasma corticosterone and ACTH concentrations, but abolished diazepam-induced inhibition of the HPA axis activity. Pretreatment with α-MPT, or with a combination of reserpine and yohimbine, increased plasma corticosterone and ACTH levels and prevented diazepam-induced inhibition of the HPA axis activity.

Conclusion

The results suggest that α₂-adrenoreceptors activity, as well as intact presynaptic noradrenergic function, are required for the suppressive effect of diazepam on the HPA axis activity.

Increased plasma corticosterone levels after periaqueductal gray stimulation-induced escape reaction or panic attacks in rats

The hypothalamo-pituitary-adrenal (HPA) axis is involved in stress, depression and anxiety. Controversy exists on HPA axis activation during panic attacks (PAs). We examined whether the HPA axis is involved in the escape or panic-like response in an animal model of PAs induced by electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) in rats. Additionally, rats were also treated with chronic administration of buspirone (BUSP) and escitalopram (ESCIT), respectively; and they were stimulated in the open-field arena for panic-like reaction. Levels of stress hormone corticosterone were measured following 30 min after escape or panic condition. Our results demonstrated that the levels of plasma corticosterone were significantly increased after the induction of escape or panic-like response in comparison with the sham animals. The levels of corticosterone were significantly decreased in the dlPAG stimulated groups after rats were treated chronically with the ESCIT but not the BUSP as compared to the saline treated animals. Importantly, the increase of corticosterone level after escape or panic-like response was paralleled by an increase of neuronal activation of c-Fos in both the parvocellular and magnocellular paraventricular nucleus of the hypothalamus. Moreover, the c-Fos data also showed a decrease in the number of positive cells particularly for the ESCIT as well as the BUSP in comparison with the saline stimulated animals. In conclusion, the present study clearly demonstrated that PA or escape response activates the HPA axis and it remains difficult to anticipate the mechanism underlying HPA axis during PAs and its relationship with 5-HT drugs.

Cannabinoids and their interactions with diazepam on modulation of serum corticosterone concentration in male mice

Experimental results indicate a mutual interaction between cannabinoidergic and GABAergic systems; however, the interaction between these systems on corticosterone release has not been fully investigated. In this study, we treated male mice with either cannabinoid compounds alone or in combination with diazepam. Blood samples were collected at 60 min post-injection. The serum corticosterone (CORT) level was measured using ELISA technique. Acute treatment of mice by cannabinoid receptor agonist WIN55212-2 (2.5 mg/kg; i.p.) resulted in a significant reduction of CORT, while treatment with either endocannabinoid reuptake inhibitor AM404 or endocannabinoid degradation enzyme inhibitor URB597 increased CORT compared to control group. Co-administration of AM404 or URB597 with cannabinoid CB1 receptor antagonist AM251 blocked the effect of these compounds on CORT. Treatment of mice with different doses of diazepam alone did not alter CORT compared to control group. However, co-administration of diazepam and either AM404 or WIN55212-2 significantly reduced CORT compared to the respective group treated with cannabinoid compound alone. Co-administration of ineffective dose of URB597 and ineffective dose of diazepam increased CORT level compared to groups treated with each compound alone. In conclusion, our findings suggest that the endogenous cannabinoid system is active as a modulator of CORT in mice and diazepam can alter the effect of cannabinoid system in the modulation of neuroendocrine functions.

Hypothalamic-pituitary-adrenal axis activity, dehydroepiandrosterone sulphate and their relationships with aggression in early and late alcohol withdrawal

The study aims at investigating the relationship between hypothalamic-pituitary-adrenal (HPA) axis alterations and aggression level in alcoholic patients during early and late alcohol withdrawal. Serum levels of basal cortisol and dehydroepiandrosterone sulphate (DHEAS) were measured three times, and cortisol and DHEAS response to dexamethasone twice during the early and late withdrawal periods in alcohol dependent males (n=30) and once in healthy control males (n=20). Abnormal cortisol non-suppression response to dexamethasone in dexamethasone suppression test (DST) was observed in some proportion of the patients in early withdrawal, which normalized in late withdrawal. The study revealed reduced basal DHEAS levels and reduced DHEAS response to dexamethasone in late withdrawal. When the patients were assessed in two separate groups as high- and low-aggressives, in the high-aggression group abnormality in DST was observed during both early and late withdrawal periods, in the low-aggression group it was observed only in early withdrawal. While basal DHEAS levels were low in the high-aggression group only in early withdrawal, it was reduced in the low-aggression group during late withdrawal period. Some alterations of the HPA axis during alcohol withdrawal might be associated not only with alcohol use per se but also with aggressivity tendency of alcoholic patients.

Are benzodiazepines really anxiolytic? Evidence from a 3D maze spatial navigation task

The effects of diazepam and chlordiazepoxide were assessed in a 3D maze which is a modification of an 8-arm radial maze. Each arm of the maze is attached to a bridge radiating from a central platform. Animals exposed for the first time to the maze do not venture beyond the line that separate a bridge from an arm. The prime criteria set for an anxiolytic effect is whether mice would increase the frequency of entries onto arms and increase arm/bridge entries ratio. C57 mice readily cross the line on first exposure and make more than 8 arm visits onto arms on second exposure, while other strains (CD-1 and Balb/c) hold back and rarely cross the line on first exposure and require more sessions to make more than 8 arm entries. An anxiolytic drug is expected to encourage intermediate (CD-1) and high (Balb/c) anxiety mice to adventure onto the arms of the maze and make more visits to the arms to comparable levels seen with low anxiety c57 mice. In the present report, administration of different doses of diazepam (0.625, 1.25, 2.5 and 5 mg kg(-1) i.p.) and chlordiazepoxide (5, 10 and 15 mg kg(-1) i.p.) did not reduce anxiety in animals, with the lowest dose of diazepam increasing motor activity in Balb/c and increasing anxiety in c57 mice while the highest doses of both diazepam (2.5 and 5 mg kg(-1) i.p.) and chlordiazepoxide (15 mg kg(-1) i.p.) induced mild sedation. Our results raise some concerns about the methodological foundations in the current assessment of anxiety and anxiolytic compounds both in animal and human studies.

Anxiolytic-like effects of nociceptin/orphanin FQ in the elevated plus maze and in the conditioned defensive burying test in rats

Different reports suggest that nociceptin/orphanin FQ (N/OFQ) may have either anxiolytic- or anxiogenic-like effect in rodents. Since N/OFQ elicits hypolocomotion, which undergoes rapid tolerance, and hypolocomotion may be associated to emotional consequences, the present study was designed to investigate the effect of N/OFQ on anxiety after development of tolerance to its hypolocomotor effect. The effect of single or double intracerebroventricular (i.c.v.) injection of N/OFQ was evaluated on anxiety-related behaviors in rats, in the elevated plus maze (EPM) and conditioned defensive burying (CDB) tests. After single administration, N/OFQ displayed an anxiogenic-like pattern of response on the elevated plus maze but hypolocomotion was also observed. Conversely, in the CDB test, N/OFQ induced a clear-cut anxiolytic pattern. To produce tolerance to N/OFQ-induced hypolocomotion the peptide was administered by two i.c.v. injections separated by 120 min; in these conditions it decreased the expression of anxiety-related behaviors in both tests without affecting locomotor activity. The nociceptin/orphanin FQ peptide (NOP) receptor antagonist UFP-101 significantly reduced the effects of N/OFQ to control values in either tests. Corticosterone levels were significantly increased after a single N/OFQ administration (not in a dose-dependent manner) but this increase did not reach significance after double administration (1 nmol/rat). Our results support the idea that N/OFQ may act as an anxiolytic-like agent in the rat; the apparent anxiogenic-like effect observed following its single administration in the EPM may be consequent to its effect on locomotion.

Validation of a motor activity system by a robotically controlled vehicle and using standard reference compounds

INTRODUCTION

A series of experiments were undertaken to evaluate the accuracy, precision, specificity, and sensitivity of an automated, infrared photo beam-based open field motor activity system, the MotorMonitor v. 4.01, Hamilton-Kinder, LLC, for use in a good laboratory practices (GLP) Safety Pharmacology laboratory.

METHODS

This evaluation consisted of two phases: (1) system validation, employing known inputs using the EM-100 Controller Photo Beam Validation System, a robotically controlled vehicle representing a rodent and (2) biologic validation, employing groups of rats treated with the standard pharmacologic agents diazepam or D-amphetamine. The MotorMonitor's parameters that described the open-field activity of a subject were: basic movements, total distance, fine movements, x/y horizontal ambulations, rearing, and total rest time. These measurements were evaluated over a number of zones within each enclosure.

RESULTS

System validation with the EM-100 Controller Photo Beam Validation System showed that all the parameters accurately and precisely measured what they were intended to measure, with the exception of fine movements and x/y ambulations. Biologic validation using the central nervous system depressant diazepam at 1, 2, or 5 mg/kg, i.p. produced the expected dose-dependent reduction in rat motor activity. In contrast, the central nervous system stimulant D-amphetamine produced the expected increases in rat motor activity at 0.1 and 1 mg/kg, i.p, demonstrating the specificity and sensitivity of the system.

DISCUSSION

Taken together, these studies of the accuracy, precision, specificity, and sensitivity show the importance of both system and biologic validation in the evaluation of an automated open field motor activity system for use in a GLP compliant laboratory.

Effects of benzodiazepines receptor agonists on the hypothalamic–pituitary–adrenocortical axis

Previous studies have demonstrated that classical benzodiazepines decrease hypothalamic-pituitary-adrenocortical cortex (HPA) axis activity. Paradoxically, high doses of benzodiazepines also stimulate basal circulating corticosterone levels in some conditions. Because benzodiazepine agonists display little selectivity to any of the alpha subtypes of the gamma-amino butyric acid (GABA)(A) receptor to which they bind, we propose that the unequivocal results are due to an alpha subtype-dependent modulation of the hypothalamic-pituitary-adrenocortical cortex axis output. To test this, basal hormonal output and induction of Fos in the hypothalamic paraventricular nucleus were measured after administration of various benzodiazepine ligands in mice. Zolpidem, a selective alpha1 subtype agonist, produced a very strong increase in plasma adrenocorticotropic hormone and corticosterone whereas the inverse agonist FG7142 induced a small rise in plasma corticosterone. More surprisingly, the non-selective full agonists diazepam and zopiclone induced a lower increase in circulating corticosterone than after zolpidem. In contrast, the alpha(2,3,5)-selective benzodiazepine agonist and alpha1 antagonist L-838,417 had no effect on corticosterone levels. Strong induction of Fos in the paraventricular nucleus was found in response to zolpidem, diazepam, and zopiclone, but not after L-838,417. Finally, pre-administration of L-838,417 prior to zolpidem strongly inhibited the effect of zolpidem on corticosterone. Likewise, the non-selective agonists diazepam and zopiclone at a dose that alone had no effect on corticosterone also inhibited the effect of zolpidem. Taken together, these results suggest that benzodiazepine ligands modulate the hypothalamic-pituitary-adrenocortical cortex axis through partly opposite mechanisms; and that the net effect is dependent on the composition of the GABA(A) receptor subunits to which they bind.

Nociceptin/orphanin FQ increases anxiety-related behavior and circulating levels of corticosterone during neophobic tests of anxiety

Intracranial administration of nociceptin/orphanin FQ (N/OFQ) increases circulating concentrations of adrenocorticotrophic hormone and corticosterone in unstressed rats, and elevates the responsiveness of these hormones during mild stress. Furthermore, N/OFQ and its cognate receptor are both abundant in a variety of limbic nuclei, and stress exposure decreases neuronal N/OFQ content in forebrain neurons. In light of these and other findings, we examined the potential involvement of N/OFQ in regulation of anxiety-related behaviors in rats. In the open field, elevated plus maze, and dark-light neophobic tests, intracerebroventricular N/OFQ (1.0 pmole-1.0 nmole) increased the expression of anxiety-related behaviors. Specifically, N/OFQ increased the latency to enter, decreased the number of entries into, and decreased the time spent in the exposed or brightly lit environments of all three tests. N/OFQ also enhanced thigmotactic responses in the open field test. The effects of diazepam and of the benzodiazepine inverse agonist FG 7142 were also assessed in independent groups of rats. In all three tests, the behavioral effects of N/OFQ resembled the anxiogenic actions of FG 7142, and contrasted with the anxiolytic actions of diazepam. N/OFQ administration also increased circulating concentrations of corticosterone during anxiety testing, in comparison with the concentrations in vehicle-treated controls. We conclude that N/OFQ administration is anxiogenic, and elevates responsiveness of the hypothalamic pituitary-adrenal axis during neophobic tests of anxiety. This supports the possibility that N/OFQ neurotransmission participates in processing of emotionally-salient and stressful stimuli, and suggests that normal functioning of the N/OFQ system may be important in physiological and psychological well-being.

Stress-induced hyperthermia and anxiety: pharmacological validation

When mammals, including man, are confronted with a stressful event, their core body temperature rises, stress-induced hyperthermia. In mice, the stress-induced hyperthermia procedure has been developed to measure antistress or anxiolytic-like effects of psychoactive drugs. Group-housed and singly housed versions of the stress-induced hyperthermia generate comparable results. Because the number of animals needed to perform an experiment is much lower in the singly housed versus the group-housed procedure, the former is the test of choice for pharmacological testing. A typical stress-induced hyperthermia test starts with an injection 60 min before the first rectal temperature measurement (T(1)), followed by a second temperature measurement (T(2)) 10-15 min later. The difference DeltaT (=T(2)-T(1)) is the stress-induced hyperthermia. The procedure also measures the intrinsic activity of drugs on the basal body temperature and DeltaT is relatively independent from the intrinsic temperature effects of drugs. Anxiolytic drugs (benzodiazepines, 5-HT(1A) receptor agonists, alcohol) reduce DeltaT suggestive of anxiolytic-like effects. Because the parameter measured for anxiety in the stress-induced hyperthermia procedure is not dependent on locomotor activity, like in almost all other anxiety tests, the stress-induced hyperthermia procedure is an attractive addition to tests in the anxiety field. Because the stress-induced hyperthermia is also present with a comparable pharmacological profile in females, this procedure has a wide species and gender validity. The procedure was applied in various genetically modified mice [5-HT(1A) and 5-HT(1B) receptor knockout (KO) mice and corticotropin-releasing hormone overexpressing (CRH-OE) mice] to study phenotypic influences of the various mutations on aspects of anxiety. The stress-induced hyperthermia test in singly housed male and female mice appears a useful and extremely simple test to measure effects of drugs on certain aspects of anxiety or to help to determine phenotypic differences in mutant mice.

Effect of the serotonin agonist buspirone on behaviour and hypothalamic-pituitary-adrenal axis in confident and fearful mink

Behavioural and hypothalamic-pituitary-adrenal (HPA) axis responses were investigated in farm mink (Mustela vison) selected for either confident or fearful behaviour for nine generations. Two groups of 2-year-old confident (n=12) and fearful (n=12) female mink were given the serotonin (5-HT) 1A receptor agonist buspirone (1.25 mg/kg/day), whereas two other groups of 2-year-old confident (n=12) and fearful (n=12) female mink were given saline, continuously for 5 weeks via osmotic minipumps. Behavioural reactions towards a novel object and towards humans were tested after 19-25 days, and HPA axis reactivity [adrenocorticotropic hormone (ACTH), cortisol] was measured after 28-31 days of treatment. Confident mink were more exploratory than fearful mink towards humans and a novel object. Confident mink spent more time in contact with the object than did fearful mink during saline-but not during buspirone-treatment. buspirone increased approach-withdrawal conflict behaviour towards a object in fearful mink only. The chronic dose of buspirone did not reduce fear towards humans and did not affect latencies to reaction, number of contacts, number and duration of manipulations, and stereotypic behaviour in a Novel Object test. Different HPA axis responses have emerged between confident and fearful mink, together with a different degree of fear-related behaviour. Fearful mink have a higher cortisol combined with a lower ACTH secretion than confident mink in response to capture and blood sampling. The central serotonergic system may be involved, and even though the precise underlying mechanisms are presently unknown, treatment with a 5-HT(1A) receptor agonist reduces the difference between confident and fearful mink in HPA axis reactivity.

Actions of serotonergic agents on hypothalamic-pituitary-adrenal axis activity in the rat

1. The effects of ipsapirone, nefazodone, tiaspirone, BMS-20661, buspirone and gepirone on the hypothalamic-pituitary-adrenal (HPA) axis were studied. These drugs were selected because they have serontonin 1A (5-HT1A) receptor-binding capability and have the potential for therapeutic activity in the treatment of major affective or anxiety disorders or both. 2. Plasma corticosterone level was used as the end point for determining the effect of each drug on the HPA axis. Each drug increased the plasma corticosterone levels in a dose-dependent manner. The ED50 values were 0.8 mg/kg for BMS-20661, 3.5 mg/kg for gepirone, 3.9 mg/kg for buspirone, 5.3 mg/ kg for tiaspirone, 10.5 mg/kg for ipsapirone and 73.5 mg/kg for nefazodone. Ipsapirone and buspirone were more efficacious than the other four drugs. 3. The effect of a 10-mg/kg (35 mg/kg for nefazodone) test dose of each drug reached a peak between 30 min and 1 hr, and plasma corticosterone levels generally returned to control levels after 2 hr. 4. When the drugs were given 30 min before decapitation, in conjunction with a rotatory stress, BMS-20661 significantly inhibited the stress-induced rise, whereas ipsapirone and gepirone caused a significant increase in plasma corticosterone levels. However, when the drugs were given 2 hr before decapitation, nefazodone caused a significant decrease, whereas ipsapirone, BMS-20661 and gepirone produced significant increases in HPA axis activity. An 0800 hr dose of 0.1 mg/kg of dexamethasone suppressed the 1500 hr HPA activity by 73.1%. The 0.1-mg/kg dose of dexamethasone significantly reduced the drug-activated HPA axis activity of all of the drugs from their saline-control levels. The rank order, from least to greatest inhibitory effect, produced by this dexamethasone treatment on the drug-control levels was gepirone (-42.6%), tiaspirone (-48.9%), buspirone (-56.1%), nefazodone (-68.5%), insapirone (-70.0%), and BMS-20661 (-74.3%).

Neuroendocrine effects of diazepam and flesinoxan in the stress-induced hyperthermia test in mice

In the stress-induced hyperthermia (SIH) paradigm in mice, both a benzodiazepine receptor agonist, diazepam, and a 5-HT1A receptor agonist, flesinoxan, reduced the stress-induced increase in rectal temperature. The SIH procedure itself enhanced plasma ACTH and corticosterone levels but not plasma glucose levels. Diazepam (3, 6, and 12 mg/kg p.o.) did neither affect basal plasma ACTH, corticosterone, or glucose levels, nor did it suppress the stress-induced rises in these parameters. Flesinoxan (1, 3, and 10 mg/kg p.o.) enhanced plasma ACTH and corticosterone concentrations under nonstress conditions but did not affect the stress-induced increases in ACTH and corticosterone secretion. No clear effects of flesinoxan on plasma glucose levels were found. Our results indicate that in mice the anxiolytic effects of diazepam and flesinoxan in the SIH paradigm are not paralleled by a blockade of stress-induced increases in plasma ACTH, corticosterone, and glucose levels.

Effects of repeated doses of azapirones on rat brain 5-HT1A receptors and plasma corticosterone levels

Chronic buspirone or ipsapirone (3 mg/kg, twice daily) administration to rats for 10 days decreased the sensitivity of inhibition of single-unit activity of serotonergic dorsal raphe neurons to a challenge by each drug. The ED50 for buspirone was increased from 0.1 mg/kg to 1.8 mg/kg, and the ED50 for ipsapirone was increased from 0.7 mg/kg to 1.2 mg/kg. The binding properties (Kd and Bmax) of [3H]8-OH-DPAT to membranes of cerebral cortex and hippocampus were unaffected by chronic administration of either buspirone or ipsapirone. Chronic buspirone or ipsapirone administration increased the tolerance of the hypothalamic-pituitary-adrenal axis (HPAA) following a challenge by each drug. The ED50 for elevation of plasma corticosterone levels was increased from 4.0 mg/kg to 7.6 mg/kg for buspirone and 6.2 mg/kg to 8.0 mg/kg for ipsapirone. Chronic buspirone administration decreased the basal activity of the HPAA by 63%. Chronic buspirone administration did not alter the plasma corticosterone response of the HPAA to a 1-min episode of rotational stress. (Mg2+)-ATPase, (Na+ + K+)-ATPase, (Ca2+ + Mg2+)-ATPase and calmodulin-stimulated (Ca2+ + Mg2+)-ATPase activities of erythrocyte plasma membrane were unaffected by either chronic or acute buspirone treatment, or by the addition of the drug to the in vitro assay systems.

The anxiolytic effects of flesinoxan, a 5-HT1A receptor agonist, are not related to its neuroendocrine effects

The effects of flesinoxan, a selective 5-HT1A receptor agonist, were studied under basal non-stress conditions and in the shock-probe burying paradigm. Flesinoxan (1 and 3 mg/kg s.c.) significantly reduced burying and freezing behaviour, indicating clear anxiolytic properties. Under non-stress conditions, injection of 3 mg/kg flesinoxan significantly enhanced plasma corticosterone and glucose levels, whereas prolactin secretion was significantly enhanced after both 1 mg/kg and 3 mg/kg flesinoxan. Flesinoxan (1 and 3 mg/kg) did not suppress shock-probe stress-induced rises in plasma corticosterone and glucose levels. The enhanced plasma prolactin levels induced by flesinoxan were not further affected by shock-probe exposure. Our data show that the anxiolytic effects of flesinoxan in the shock-probe burying paradigm are not related to increases in plasma corticosterone and glucose levels.

Minimal changes with long-term administration of anxiolytics on septal driving of hippocampal rhythmical slow activity

In free-moving male rats, the function relating frequency to the threshold current required to drive hippocampal rhythmical slow activity (RSA; "theta") with septal stimulation has a minimum at 7.7 Hz. Classical anxiolytics all increase thresholds in the region of 7.7 Hz, and so does the novel anxiolytic buspirone. However, unlike classical anxiolytics, 2 or 3 weeks are normally required for the onset of the clinical effects of buspirone. This study tested the effects of long-term administration of chlordiazepoxide and buspirone on septal driving of RSA. Separate groups of naive rats received three IP injections per day of chlordiazepoxide (0.4 mg/kg), buspirone (0.1 mg/kg) or saline for 50 days. Both chlordiazepoxide and buspirone increased thresholds at 7.7 Hz, as expected. These acute effects were not significantly changed with chronic administration. Buspirone and chlordiazepoxide produced similar, statistically significant, but small cumulative reductions in thresholds at 6.9 Hz. The present experiments suggest that if the effects of anxiolytic drugs on septally driven RSA provide any basis for their clinical action, then classical anxiolytics may have two actions: an immediate effect on euphoria and tension and a delayed effect on anxiety proper--with buspirone sharing only the latter effect.

The corticosterone-enhancing effects of the 5-HT1A receptor antagonist, (S)-UH301, are not mediated by the 5-HT1A receptor

We tried to antagonize the endocrine and behavioural changes induced by the selective 5-HT1A receptor agonist, flesinoxan, with the putative 5-HT1A receptor antagonist, (S)-UH301 ((S)-5-fluoro-8-hydroxy-2-(di-n-propylamino)tetralin). The interaction of (S)-UH301 (3 and 10 mg/kg s.c.) with flesinoxan (3 mg/kg s.c.) showed no antagonistic effects of (S)-UH301 on flesinoxan-induced corticosterone secretion. In fact, like flesinoxan (1 and 3 mg/kg s.c.), (S)-UH301 (3 and 10 mg/kg s.c.) itself dose dependently increased plasma corticosterone levels. Unlike flesinoxan, (S)-UH301 did not induce hyperglycemia, lower lip retraction and flat body posture. Moreover, flesinoxan-induced hyperglycemia and behavioural changes were effectively antagonized by (S)-UH301, showing potent 5-HT1A receptor antagonistic effects of (S)-UH301. Therefore we conclude that (S)-UH301 is a potent 5-HT1A receptor antagonist and that the (S)-UH301-induced corticosterone secretion is mediated by a non-5-HT1A receptor mechanism.

Role of dopaminergic mechanisms in the regulation of stress responses in experimental animals

The effects of some dopaminergic agents were evaluated on stress responses in normal and immunized experimental animals. Restraint stress (RS) consistently induced gastric mucosal lesions and elevated plasma corticosterone in rats. Pretreatment with alpha-methyltyrosine (alpha-MT), haloperidol, or sulpiride aggravated both responses, whereas bromocriptine attenuated them. In rats immunized with sheep red blood cells (SRBCs), RS prevented the booster-induced rise in anti-SRBC antibody titre. This response was further suppressed by alpha-MT, haloperidol, or sulpiride pretreatment, whereas bromocriptine potentiated the humoral immune response. In mice immunized with SRBCs, antigen challenge-induced increase in footpad thickness was inhibited by RS. Similar inhibitions in this response were also seen after alpha-MT or haloperidol treatment. The results are discussed in light of complex dopaminergic mechanisms in the regulation of visceral, endocrinological, and immune responses during stress.

Ultrasound vocalization is not related to corticosterone response in isolated rat pups

Isolated from their mother, rat pups respond with changes in ultrasound vocalization (USV), a paradigm that can be used as a test for a large range of anxiolytics. Because the relation between corticosterone (CORT) and putative stress responses like USV is not clear, we examined the effects of the benzodiazepine drugs chlordiazepoxide and diazepam vs. the nonbenzodiazepine drugs buspirone and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on USV and plasma CORT concentrations. All drugs caused a dose-related decrease in USV, but only buspirone and 8-OH-DPAT induced a dose-related increase in CORT. We suggest that the seemingly paradoxical effects of buspirone and 8-OH-DPAT, that is, the decrease in USV and the concomitant increase in plasma CORT, are due to the fact that these two drugs act as full agonists at both pre- and postsynaptic 5-HT1A receptors. Our results indicate that, when measured as an increase in the activity of the pituitary adrenocortical axis, the stress response can be interpreted in markedly different ways, depending on whether the increased activity is elicited by an environmental stressor or by pharmacological manipulation.

Inhibitory effect of diazepam on the activity of the hypothalamic-pituitary-adrenal axis in female rats

The acute intraperitoneal administration of anxiolytic diazepam (2 mg/kg) inhibits the activity of the hypothalamic-pituitary-adrenal (HPA) axis, i.e., it decreases the concentration of adrenocorticotropic hormone (ACTH) and corticosterone in female rats. This fall of ACTH and corticosterone levels was reversed by an antagonist of central benzodiazepine receptors-flumazenil. The antagonist of peripheral benzodiazepine receptors-PK 11195, failed to affect diazepam-induced decrement of plasma ACTH and corticosterone levels. The suppressed HPA function obtained after diazepam administration was also antagonized by bicuculline, an antagonist of GABA recognition sites, and by picrotoxin, a drug that blocks the GABA-A receptor associated chloride channel. These results suggest that central benzodiazepine receptors, the part of GABA-A macromolecular complex, are involved in diazepam-induced inhibition of the activity of the HPA axis.

Changes in free amino acids in peripheral blood (PB) lymphocytes and polymorphonuclear (PMN) leukocytes after treatment with diazepam

The effect of single and chronic (15 days) i.p. injections (1.0 and 8.0 mg/kg) of diazepam (DZ) on free amino acid profile in peripheral blood (PB) lymphocytes and polymorphonuclear (PMN) leukocytes of male Wistar Albino rats were investigated. Depletion of some free amino acids was observed in the lymphocytes (mixed T- and B-lymphocytes) and PMN leukocytes (91-95%) neutrophils especially after chronic DZ-treatment. A dose-dependent depletion in the lymphocyte amino acids, Tau, Gly, Ala, Met and Ile, was found after both acute and chronic DZ-treatment. A similar depletion of Tau, Asp, Glu and Met appeared in the PMN leukocytes after single doses as well as chronic DZ-treatment. These results suggest that administration of 1.0-8.0 mg/kg of DZ in single dose or after chronic administration may interfere with the transport of certain important amino acids and/or protein turnover in PB lymphocytes and PMN leukocytes. On the other hand, the basic amino acids Lys, His and Arg were significantly increased in PMN leukocytes after chronic administration of 1.0 mg/kg DZ. It was suggested that the increased levels of the basic amino acids in the neutrophils may interact with the intracellular changes in pH that normally accompany the respiratory burst.

Physiopharmacological interactions between stress hormones and central serotonergic systems

The present review tries to delineate some mechanisms through which the sympathetic nervous system (SNS) and the hypothalamo-pituitary-adrenal (HPA) interact with central serotonergic systems. The recent progress in 5-hydroxytryptamine (5-HT) receptor pharmacology has helped to define the means by which central serotonergic activity may alter the respective activities of the SNS (sympathetic nerves and adrenomedulla) and of the HPA axis. These pharmacological findings have also helped to characterize the differential effects of central 5-HT upon different branches of the SNS and the numerous sites at which 5-HT exerts stimulatory influences upon the HPA axis. Although relevant to stress-related neuroendocrinology, the extent to which these interactions are involved in the antidepressant/anxiolytic properties of some serotonergic agents still remains to be clarified. Beside these findings, there is also abundant evidence for a tight control of central serotonergic systems by stress hormones. Activation of the SNS increases, by numerous means, central availability of tryptophan, whereas glucocorticoids exert differential actions upon the intra- and the extraneuronal regulation of 5-HT function. Actually, a significant number of these mechanisms is involved in the maintenance of homeostasis during stressful events, thereby conferring to these mechanisms a key role in adaptation processes.

Fluorimetric detection of serum corticosterone using high-performance liquid chromatography

A simple, sensitive, specific and reproducible method for the determination of corticosterone concentrations in rat serum using high-performance liquid chromatography (HPLC) with fluorimetric detection is described. Corticosterone is detectable down to 0.1 ng injected onto the HPLC column. Cortisol is used as an internal standard. Ethyl acetate was used for both initial serum corticosteroid extraction and the subsequent fluorophore extraction after sulfuric acid hydrolysis; thus sulfuric acid does not enter the HPLC system. The resultant fluorophores for both corticosterone and cortisol are stable for at least two weeks at ambient temperature not requiring storage at -20 degrees C. The procedure is highly suitable for use with HPLC systems utilising automatic sample injectors. The method is specific for corticosterone; dexamethasone, cortisone and gonadal steroids are not detectable and do not interfere in this assay.

The 5,7-DHT-induced anticonflict effect is dependent on intact adrenocortical function

We have recently reported that the anxiolytic-like effect observed in rats severely depleted of brain serotonin (5-HT) by means of 5,7-DHT is indirect and probably involves the GABA(A)/benzodiazepine chloride ionophore receptor complex (GABAA/BDZ-RC). One tentative explanation for this effect considered the involvement of corticosteroids. In the present series of experiments we have therefore investigated the effect of adrenalectomy (ADX) on the 5,7-DHT-induced anxiolytic-like effect displayed by rats in Vogel's conflict test. ADX totally abolished the anticonflict effect of the 5,7-DHT lesion. Replacement treatment with corticosterone, but not with dexamethasone, reinstated the anticonflict effect. These results indicate that an intact adrenocortical function, possibly via brain steroid type I receptors, is required for the expression of the 5,7-DHT-induced anxiolytic-like effect. It is postulated that ADX lowers the concentration of endogenous positive modulators at the GABAA/BDZ-RC to a level no longer sufficient to produce anxiolytic-like effects in 5,7-DHT-lesioned animals. The finding that 5,7-DHT-lesioned animals were more sensitive than sham-lesioned controls to the anticonflict effect of the barbiturate-like corticosteroid THDOC provides further support for the contention that an increased endogenous activity at the GABAA/BDZ-RCes is involved in the anxiolytic-like effect observed in rats with a severe depletion of brain 5-HT.

Buspirone inhibits corticotropin-releasing factor and stress-induced cecal motor response in rats by acting through 5-HT1A receptors

The effect of buspirone on corticotropin-releasing factor (CRF) and stress-stimulated cecal motility and its antagonism by 5-HT1A (spiroxatrine) and sigma (BMY 14802) antagonists were evaluated by electromyography in rats equipped with chronically implanted electrodes on the cecum and a small catheter into the right lateral ventricle of the brain. Exposure to mental stress, consisting of a fear-conditioned response, increased during 30 min the frequency of cecal spike bursts significantly (P less than 0.01). The frequency of cecal spike bursts was also increased following intracerebroventricular injection of CRF (500 ng/kg). Buspirone (1 mg/kg s.c.) abolished the stimulatory effects of mental stress and CRF on cecal motility. Whereas spiroxatrine (0.5 mg/kg s.c.) blocked the effect of buspirone on the colonic hypermotility induced by i.c.v. injection of CRF, BMY 14802 at a similar dose (0.5 mg/kg s.c.) was unable to block the action of buspirone. It is concluded that s.c. administration of buspirone suppresses the stress-induced cecal motor response through 5-HT1A receptors, probably by inhibiting the central or peripheral pathways involved in CRF mediation of these effects.

Molecular basis of buspirone's anxiolytic action

Buspirone has been available in the United States for over four years for the treatment of anxiety. It was anticipated this drug would offer certain advantages over the established benzodiazepines. In contrast to diazepam, early studies found no evidence for the interaction of buspirone with GABAergic mechanisms. Behavioural, electrophysiological and receptor binding experiments gradually led to the idea that buspirone owes much of its anxiolytic activity to its ability to attenuate central 5-hydroxytryptamine neurotransmission. Specifically, it appears to act as an agonist at presynaptic 5-HT1A receptors, particularly in the raphe nuclei. Although buspirone also shows an affinity for dopamine D2 receptors, where it seems to behave as an antagonist, there is much doubt that this effect is related to its anxiolytic action. Even though buspirone and the benzodiazepines do not obviously share a common mode of action, the possibility is discussed that there is an underlying common mechanism of responsible for their antianxiety effects.

Role of histaminergic mechanisms in the regulation of some stress responses in rats

The involvement of histaminergic mechanisms in the regulation of some stress responses was studied in rats. The brain neuronal histamine (HA) depletor, alpha-fluoromethyl histidine (alpha-FMH), at doses (50 or 100 mg/kg) which markedly lower brain HA, significantly attenuated the gastric ulcer formation and the elevation in plasma corticosterone in response to cold restraint stress (CRS). alpha-FMH also appreciably reduced gastric mucosal HA content. The H1-antagonist, pheniramine (25 mg/kg), attenuated both the gastric mucosal and endocrine response to CRS, while the effects of the H2-antagonist, cimetidine (200 mg/kg), were on the plasma corticosterone levels. These results are discussed in light of complex HA-ergic mechanisms in the maintenance of physiological homeostasis during stress.

Neurochemically dissimilar anxiolytic drugs have common effects on hippocampal rhythmic slow activity

Previous experiments have shown that anxiolytic drugs reduce the frequency of hippocampal rhythmic slow activity, induced by high frequency stimulation of the reticular formation and flatten the function relating threshold septal stimulation to the frequency of driven rhythmic slow activity. All of the drugs involved are known to augment GABAergic transmission. The present experiments investigated the effects of the novel anxiolytic compound buspirone which, unlike conventional anxiolytics, does not interact with GABA, yet is a clinically effective anxiolytic. Buspirone (0.156-40 mg/kg, i.p.) was found to reduce the frequency of reticular-elicited rhythmic slow activity, in a similar manner to chlordiazepoxide (0.019-20 mg/kg, i.p.). Buspirone did not change the linearity of the voltage-frequency function. Buspirone (10 mg/kg, i.p.) also altered the threshold for septal driving of rhythmic slow activity, in a similar manner to classical anxiolytics. The combination of chlordiazepoxide (5 mg/kg, i.p.) with corticosterone (0.2 mg, s.c.) removed the minor differences between buspirone and chlordiazepoxide in both the septal and reticular tests. These results show that buspirone altered the control of rhythmic slow activity in the hippocampus, in a manner which appeared functionally equivalent to other anxiolytics but which depends on mechanisms which are likely to be neurally and pharmacologically distinct from those of other anxiolytic drugs.

Differences in the duration of sedative and anxiolytic effects of desmethyldiazepam in two outbred Wistar strains

Different sensitivities to benzodiazepines have been described for various strains of both rats and mice suggesting that variations in biological features of the animals are responsible for these differences. Since all reports concern inbred strains, we studied two outbred Wistar strains which are used routinely in several research disciplines. The pharmacodynamics of desmethyldiazepam (DMD), the main active metabolite of diazepam in man, were compared for male rats of the Riv:TOX strain (from the National Institute of Public Health and Environmental Protection) and the Crl:(WI)BR strain. The duration of sedative action of DMD after oral administration, as derived from suppression of the nocturnal locomotor activity, was longer in the Riv:TOX strain than in the Crl:(WI)BR strain. Accordingly, suppression of novelty-induced corticosterone release as an index of anxiolytic action was observed 11 hours after DMD administration in Riv:TOX rats but not in Crl:(WI)BR rats. At that time, serum DMD concentration was shown to be higher in the Riv:TOX strain than in the Crl:(WI)BR strain. The data are discussed in relation with possible metabolic differences between the two strains.

Effects of buspirone and chlordiazepoxide on plasma catecholamine and corticosterone levels in stressed and nonstressed rats

The effects of intragastric administration of the prototypical benzodiazepine (BDZ) anxiolytic drug chlordiazepoxide (CDP) and the non-BDZ anxiolytic agent buspirone (BUSP) on basal and stress-elevated plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) contents were investigated. Acute dosing of CDP (1-27 mg/kg) produced dose-related increases in basal CS secretion but was without effect on basal NA levels. The high dose of CDP caused a slight short-term A increase. Dose-dependent increases in plasma A, NA and CS contents were observed after acute treatment with BUSP (2 and 20 mg/kg). A medium dose of CDP (9 mg/kg) attenuated the stress-induced CS and A elevations. High doses of CDP that elevated basal CS release prevented a further increase of CS by stress and inhibited the NA and A response to stress. BUSP (2 and 20 mg/kg) was not effective in decreasing the stress-elicited rise of CS, NA or A. Conversely, the 20 mg/kg dose of BUSP enhanced the stress-induced A response. Repeated administration of CDP (9 mg/kg/day for six days) produced tolerance to the elevation of basal CS triggered by acute CDP treatment, but increased the efficacy of the drug's CS and A attenuating action in stressed rats. Repeated administration of BUSP (2 mg/kg/day for six days) also produced tolerance to the acute BUSP-induced effect on basal CS release, but did not affect the stress-induced CS, NA and A responses. It is concluded that the clinically effective anxiolytic BUSP does not have the BDZ-like property to inhibit stress-induced elevations in CS, NA and A. Furthermore, the present data support other evidence that activation of 5-HT1A receptor mechanisms increases plasma catecholamine and corticosterone concentrations.

Sigma receptor ligands alter concentrations of corticosterone in plasma in the rat

Both BMY-14802 (alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine-butanol hydrochloride) and gevotroline (WY-47384; 8-fluoro-2,3,4,5-tetrahydro-2-[3-(3-pyridinyl)-propyl]-1H-pyrido[4,3-b] indole hydrochloride) are known to antagonize the psychotomimetic action of N-allyl-normetazocine (NAN; SKF-10047) and exhibit a high affinity for the sigma receptor. Unexpectedly, the putative antagonists BMY-14802 and gevotroline acted like the agonist NAN and increased activity in the hypothalamic-pituitary-adrenal axis to elevate levels of corticosterone in plasma. During the acrophase (peak) of the effects of the circadian rhythm on the hypothalamic-pituitary-adrenal axis, the ED50 was 6.5 mmol/kg for BMY-14802 and 9.6 mmol/kg for gevotroline. The ED50s for BMY-14802 and gevotroline during the low activity phase were 15.8 and 21.2 mmol/kg, respectively. The efficacies during both phases of the circadian rhythm were similar for each drug. Additive effects on the levels of corticosterone in plasma were observed when the animals were pretreated with doses above the respective ED50 values and then subjected to a rotational stress, but a small dose of BMY-14802 (0.5 mg/kg) had the opposite effect and completely inhibited the stress-related increases in corticosterone in plasma. Neither drug, at large doses, altered the increase in levels of corticosterone in plasma generated by the circadian rhythm, but at smaller doses BMY-14802 did lower circadian-related levels of corticosterone. Pretreatment with dexamethasone blocked the gevotroline-related increase in corticosterone in plasma, but not the BMY-14802-related increase. These data suggest that central sigma receptor mechanisms are involved in the regulation of the hypothalamic-pituitary-adrenal axis and that therapeutic agents that affect these receptors may alter the activity in this axis.

Interactions of anxiolytic and antidepressant drugs with hormones of the hypothalamic-pituitary-adrenal axis

Changes in hormones of the hypothalamic-pituitary-adrenal (HPA) axis in patients suffering from anxiety and depressive disorders are reviewed, and the changes that occur when animals are exposed to test situations used preclinically to model anxiety or depression. The effects of exogenous administration of HPA hormones both clinically and in animal tests is discussed and the effects of clinically used anxiolytics and antidepressants on hormones of the HPA axis. The final section discusses stress-induced changes in the CNS.

Effects of buspirone on plasma catecholamines, heart rate, and blood pressure in stressed and nonstressed rats

The influence of buspirone upon plasma catecholamine levels, heart rate, and mean arterial blood pressure was studied in stressed and nonstressed rats. Measures were obtained directly via indwelling aortic catheters. Drug or vehicle were given acutely (10 mg/kg, IP) or twice a day for 10 days (10 mg and 20 mg/kg, SC). In nonstressed rats, a single dose of buspirone increased markedly plasma norepinephrine and epinephrine levels and decreased significantly heart rate with no effect on blood pressure. During stress, stress-induced increases in catecholamine levels were further elevated by the drug, whereas stress-induced increases of heart rate and mean arterial blood pressure were reduced. In chronically-pretreated rats, the effects of buspirone were similar to those observed after an acute injection. These effects of buspirone on plasma catecholamines are very different from those seen with other anxiolytics, whereas effects on heart rate and blood pressure are more similar.

The effects of gepirone and 1-(2-pyrimidinyl)-piperazine on levels of corticosterone in rat plasma

It was found that gepirone and 1-(2-pyrimidinyl)-piperazine (1-PP) increased levels of corticosterone in plasma in the intact rat. Gepirone was more potent and more efficacious than its metabolite, 1-PP. The ED50 was 6.4 mumol/kg for gepirone and 65.4 mumol/kg for 1-PP. Forty-five min after intraperitoneal administration, gepirone and 1-PP produced maximum increases in corticosterone of 283% and 211%, respectively, above control values. The amplitude and duration of the effects of the drugs were dependent on the ongoing activity in the hypothalamic-pituitary-adrenal axis. Consequently, the greatest absolute increases in corticosterone were produced during the afternoon when the activity in the hypothalamic-pituitary-adrenal axis was greatest. A single 10 mg/kg dose of gepirone significantly elevated levels of corticosterone in plasma (313% after 1 hr) above control values for 2 hr during afternoon trials and for 1 hr (244%) during morning trials. In addition, it was found that the effects of the administration of gepirone and of stress on the levels of corticosterone in plasma were additive. In the light of other work on the hypothalamic-pituitary-adrenal axis, these results suggest that the increased levels of corticosterone, elicited by gepirone, were mediated through a serotonergic action rather than through noradrenergic activity.

Acute effects of alprazolam and adinazolam on the concentrations of corticotropin-releasing factor in the rat brain

Corticotropin-releasing factor (CRF) is the major physiological regulator of the hypothalamic-pituitary-adrenal (HPA) axis. However, considerable evidence indicates that CRF may be responsible for integrating not only the endocrine, but the autonomic and behavioral responses of an organism to stress as well. In addition, clinical studies indicate that CRF of both hypothalamic and extrahypothalamic origin may be hypersecreted in major depression as well as other psychiatric disorders. These findings, taken together, led to the hypothesis that the efficacy of antidepressant and/or anxiolytic drugs may be related to their actions on CRF-containing neural pathways in the central nervous system (CNS). Therefore, alterations of CRF concentrations in 18 rat brain regions were studied after acute administration of a tricyclic antidepressant (imipramine) or one of two triazolobenzodiazepines (alprazolam or adinazolam) that possess anxiolytic properties typical of benzodiazepines, as well as purported antidepressant activity unique to these compounds. Treatment with alprazolam or adinazolam increased hypothalamic CRF concentrations, which was associated with lower plasma ACTH concentrations. In contrast, the concentration of CRF was markedly reduced in the locus coeruleus, amygdala, and several cortical regions by either triazalobenzodiazepine. Acute treatment with imipramine was without effect on CRF concentrations in any brain region studied. Of particular interest is the finding that the two triazolobenzodiazepines exert effects on CRF concentrations in the locus coeruleus and hypothalamus that are opposite to CRF changes seen after stress.