Tolerance in the anxiolytic profile following repeated administration of diazepam but not buspirone is associated with a decrease in the responsiveness of postsynaptic 5-HT-1A receptors

To understand the role of serotonin (5-hydroxytryptamine; 5-HT)-1A receptors in the treatment of anxiety and the development of tolerance to benzodiazepines the present study was designed to monitor the responsiveness of postsynaptic 5-HT-1A receptors following repeated administration of diazepam and buspirone. Results show that tolerance in the anxiolytic profile is produced following repeated administration (2 weeks) of diazepam (2 mg/kg) but not buspirone (0.5 mg/kg). The behavioral effects of 8-OH-DPAT at a dose of 0.25 mg/kg were monitored 3 days after repeated administration of saline or buspirone or diazepam. The results show that 8-OH-DPAT elicited forepaw treading was smaller in repeated diazepam but not repeated buspirone injected rats, while hyperlocomotive effects of 8-OH-DPAT were smaller in both repeated buspirone and repeated diazepam injected rats. The results suggest that postsynaptic 5-HT-1A receptor-dependent responses were attenuated following long-term administration of diazepam but not buspirone. Role of 5-HT-1A receptors in the development of tolerance to the anxiolytic effects of diazepam but not buspirone is discussed.     

Effect of buspirone and diazepam on cGMP level in the rat cerebellum

Diazepam at a dose of 5 and 10 mg/kg significantly decreases (by 50 and 60%, respectively) cGMP content 30 min following intraperitoneal injection to rats. Buspirone, at a dose of 2.5-25 mg/kg produced a nonsignificant (up to 18%) and at a dose of 50 mg/kg a statistically significant (p less than 0.05) 30% decrease in cerebellum cGMP content. Taking into account the identical anxiolytic effects of diazepam and buspirone, it is suggested that pharmacological effects of buspirone are not linked to the activation of GABA-ergic system.     

Analysis of the influence of anxiolytics on the pain reactions of rats compared to the effect of morphine

Anxiolytic agents, buspirone and diazepam, increase the paw lick latency of rats in hot plate test, the effect being dose-dependent and exceeding that of morphine. The action of buspirone was not accompanied by ataxic and sedative effects which were observed in rats on diazepam. Buspirone (up to 25 mg/kg) and diazepam (up to 5 mg/kg) neither change the tail flick latency nor potentiate the action of morphine in this test. The effect of buspirone on the paw lick reaction in rats may be related to the inhibition of emotional-motivation component of pain reaction.     

Relations between anxiolytic effects of diazepam and changes in the EEG spectral power

The influence of diazepam (1; 5; 10 mg/kg, i. p.), chlorpromazine (1 mg/kg) and amphetamine (1; 5 mg/kg) on the Fourier's spectral EEG power of sensomotor cortex and dorsal hippocampus and conflict behavior freely moving albino and cotton (Sigmondon hispidus) rats was studied. Effects of diazepam (5 mg/kg) in cotton rats were similar, but influence on the theta-activity was more expressed. Correlation between slowing of theta-activity and extent of anxiolytic effect in conflict situation was showed. On the basis of the results obtained the authors discuss possible mutual relations between the influence of diazepam on EEG and anxiolytic effect of benzodiazepines.     

Effects of systemically administered monoamine reuptake blocking agents on patterns of buspirone-induced analgesia in rats

We have recently shown the serotonin 5-HT1A receptor agonist buspirone to produce analgesia in several pain tests in rats. As a 5-HT1A agonist, buspirone may change serotonergic (5-HT) tone to alter the balance of central monoaminergic (MA) systems that function in analgesia. MA-reuptake blocking drugs have been shown to produce analgesia, both when given alone and in combination with a variety of other agents, presumably via their action upon MA neurochemistry. The present study was undertaken to examine the effect of systemic administration of the 5-HT-reuptake blocker amitriptyline (AMI: 10 mg/kg), NE-reuptake blocker desipramine (DMI: 10 mg/kg) or DA-reuptake blocker GBR-12909 (7.5 mg/kg) on patterns of analgesia produced by buspirone (1-5 mg/kg) in thermal and mechanical pain tests in rats. Neither reuptake blocking agents or buspirone, when administered alone or in combination, produced overt changes in motor activity at the doses tested. AMI alone was not analgesic in either thermal or mechanical pain tests. In both assays, AMI reduced the analgesic action of buspirone, with greater effects seen in the thermal test. When administered alone, DMI produced significant analgesia against thermal and mechanical pain. DMI significantly attenuated the analgesic action of all doses of buspirone in both pain tests. Alone, GBR-12909 did not affect nociception in thermal or mechanical tests. GBR-12909 decreased buspirone-induced analgesia at all doses in the thermal test, while having no effect on buspirone-induced analgesia against mechanical pain. These results demonstrate that facilitation of 5-HT, NE and DA function with reuptake blocking drugs did not enhance the analgesic action of buspirone. These data indicate against the adjuvant use of reuptake blocking compounds and buspirone as analgesics. Furthermore, such findings may suggest other possible non-MA substrates of buspirone-induced analgesia.     

Effects of cholecystokinin tetrapeptide (CCK(4)) and of anxiolytic drugs on GABA outflow from the cerebral cortex of freely moving rats

The effect of cholecystokinin tetrapeptide (CCK(4)) and of different anxiolytic drugs on GABA outflow from the cerebral cortex was investigated in freely moving rats, by using the epidural cup technique. CCK(4) (3-30 microg/kg, i.p.) increased GABA outflow and induced objective signs of anxiety. These neurochemical and behavioral responses were prevented by the CCK(B) antagonist GV150013 at 0.1 microg/kg (i.p.). At higher doses (up to 30 microg/kg) this compound per se reduced GABA release and caused sedation, suggesting the presence of a CCKergic positive tonic modulation on GABA interneurons. Similarly the GABA(A) receptors modulator, diazepam (2mg/kg, i.p.) and the 5-HT(1A) agonist buspirone (3mg/kg, i.p.) reduced GABA outflow and caused the expected behavioral effects (reduced muscle tone, mild 5-HT syndrome) which were prevented by the respective, selective antagonists, flumazenil (1mg/kg, i.p.) and NAN-190 (3mg/kg, i.p.). These findings support the idea that GV150013, diazepam and buspirone inhibit GABAergic cortical activity, through the respective receptors. This neurochemical effect may represent the end-effect of various anxiolytic compounds affecting the cortical circuitry.     

Ro 15-1788 antagonizes the discriminative stimulus effects of diazepam in rats but not similar effects of pentobarbital

The benzodiazepine antagonist properties of Ro 15-1788 were evaluated in rats trained to discriminate between saline and either 1.0 mg/kg of diazepam or 10 mg/kg of pentobarbital in a two-choice discrete-trial shock avoidance procedure. When administered alone, 1.0 mg/kg of diazepam and 10 mg/kg of pentobarbital produced comparable amounts of drug-appropriate responding (> 84%), whether rats were trained to discriminate between diazepam or pentobarbital and saline. Ro 15-1788 (3–32 mg/kg, p.o.), administered 10 min before diazepam or pentobarbital, produced a dose-related blockade of the discriminative effects of diazepam in both groups of rats, but was completely ineffective in blocking the discriminative effects of pentobarbital. The dose-effect curve for the discriminative effects of diazepam was shifted to the right in a parallel fashion 3- and 13-fold by 10 and 32 mg/kg of Ro 15-1788, respectively, indicating that Ro 15-1788 acts as a surmountable, competitive antagonist of diazepam. When administered alone, Ro 15-1788 (32–100 mg/kg, p.o.) produced primarily saline-appropriate responding, although 100 mg/kg of Ro 15-1788 produced drug-appropriate responding in one out of eight rats. When administered orally 30 min after diazepam, Ro 15-1788 (32 mg/kg) completely reversed within 10 min the discriminative effects of diazepam. The blockade of diazepam's discriminative effects by 32 mg/kg of Ro 15-1788 appeared to last at least as long (approximately 2 hr) as the effects of diazepam alone.     

Antinociceptive effect of sumatriptan in mice.

Antinociceptive effect of the antimigraine drug sumatriptan (5-HT1A agonist) was studied against acetic acid-induced writhing in mice. Sumatriptan produced the effect in a dose-dependent manner (1, 5, 10 and 20 mg/kg, s.c.). Naloxone (1 mg/kg i.p.) an opiate antagonist failed to reverse sumatriptan-induced antinociception. Cholinomimetic physostigmine (0.05 mg/kg, i.p.) potentiated and the muscarinic antagonist atropine (5 mg/kg, i.p.) blocked the antinociceptive effect of sumatriptan, respectively. The antinociceptive effect of sumatriptan was compared with an another 5-HT agonist (5-HT1A) buspirone which also produced antinociception. Like sumatriptan-analgesia, the buspirone response was also potentiated by physostigmine in atropine sensitive way. Further, buspirone potentiated the analgesic effect of sumatriptan. These observations suggest that 5-HT1A agonists produce antinociception possibly by modulating central cholinergic activity.     

Naloxone antagonism of diazepam-induced feeding in the Syrian hamster

Three experiments investigated the effects of the intragastric administration of the benzodiazepine diazepam on feeding in non-deprived Syrian hamsters ($\text{mesocricetus auratus}$). In the first experiment diazepam (0, 0.5, 1.0, 2.0, and 4.0 mg/kg) produced dose dependant increases in feeding. 4.0 mg/kg of diazepam produced significantly more feeding than the other doses tested and the lowest dose tested (0.5 mg/kg) produced a significant increase in feeding. In the second experiment naloxone (10 mg/kg) partially antagonized the effect of 4 mg/kg of diazepam on feeding. In the third experiment the ability of naloxone (0.1, 1.0, 5.0, 10.0 or 20 mg/kg) to reduce feeding produced by either 4 mg/kg or 2 mg/kg of diazepam was tested. Naloxone partially antagonized the effects of 4 mg/kg of diazepam on feeding in a dose dependant manner. While 2 mg/kg of diazepam produced significantly less feeding than 4 mg/kg, naloxone did not antagonize the effect of 2 mg/kg on feeding. The results suggest that two mechanisms are involved in diazepam-induced feeding in hamsters. The high dose of diazepam may produce increased feeding by activating the endorphin system while the low dose of diazepam produces increased feeding via a naloxone insensitive mechanism.     

Effects of GABA(A) compounds on mCPP drug discrimination in rats

Male Long-Evans rats were trained to discriminate mCPP (1.4 mg/kg, i.p.) from saline, using a two-lever, food-reinforced operant task. The GABA(A) antagonist, bicuculline (0.16-0.64 mg/kg), partially substituted for mCPP, whereas the benzodiazepine antagonist, flumazenil (1-10 mg/kg), and the benzodiazepine inverse agonist, Ro 15-4513 (0.25-2.5 mg/kg), failed to substitute for mCPP. Bicuculline produced no change in response rate, whereas Ro 15-4513 dose-dependently decreased responding. Flumazenil produced a small increase in response rates. Flumazenil (10 mg/kg), Ro 15-4513 (1.25 mg/kg), and the benzodiazepine agonists alprazolam (0.64 mg/kg) and diazepam (5 mg/kg) full agonist all failed to block the mCPP discriminative stimulus. When given in combination with mCPP, Ro15-4513 and alprazolam both produced lower response rates than did mCPP alone, whereas flumazenil and diazepam did not significantly alter response rates. These findings provide evidence that GABA(A) antagonists modulate the discriminative stimulus effects of mCPP, but that these effects are not mediated by activity at the benzodiazepine site.     

Convulsant component of a depressant benzodiazepine

The convulsant influence of high doses of diazepam, in the presence of the benzodiazepine receptor antagonist Ro 15-1788, was studied in rats. Animals were implanted with permanent cortical screw electrodes for EEG recording. EEG spiking and accompanying clonic activity was observed in rats receiving greater than or equal to 200 mg/kg diazepam, followed 10 minutes later by Ro 15-1788 (20 mg/kg). Pentylenetetrazole and picrotoxin seizure thresholds, measured during constant rate iv infusion, were significantly lowered by pretreatment with diazepam (250 mg/kg) and Ro 15-1788 (20 mg/kg) administered 30 and 20 minutes, respectively, before seizure threshold measurement. It is proposed that this convulsive activity of diazepam is mediated through the picrotoxinin receptor.     

Effects of chronic buspirone treatment on female mice exposed to the long-lasting psychoemotional influence

The effects of chronic treatment (30 days) with the 5-HT1A receptor partial agonist buspirone (0.05, 1 and 10 mg/kg i.p.) on the behaviour of C57BL/6J female mice exposed to long-lasting psychoemotional influence were studied. The influence involved forced living of each female with an aggressive male separated with a perforated transparent partition in the same cage and daily female's presence during 10-min intermale confrontations behind a partition caused by introducing of another male to the aggressive male. Chronic buspirone injection (in all used doses) did not affect the behaviour of females estimated in the "partitions" and "open field" tests at the end of the drug treatment. The anxiolytic effect of buspirone only at the dose of 1 mg/kg on the female's plus-maze behaviour was revealed. In the Porsolt, test buspirone in the dose of 1 mg/kg caused a slight increase in the duration of immobility indicating a slight pro-depressive effect. Thus, chronic buspirone treatment of females exposed to the long-lasting psychoemotional impact has a different effect on their behaviour depending on the dose and test conditions.     

beta-Carboline-3-carboxylate-t-butyl ester: a selective BZ1 benzodiazepine receptor antagonist

The effectiveness of beta-carboline-3-carboxylate-t-butyl ester (beta CCtB) in antagonizing the anticonvulsant, ataxic and antipunishment effects of diazepam were evaluated. In mice, beta CCtB at doses of 3 and 10 mg/kg produced a dose-related antagonism of the anticonvulsant effects of diazepam against pentylenetetrazole (80 mg/kg). A dose of 30 mg/kg of beta CCtB did not produce a further shift in the diazepam dose-effect curve, apparently because beta CCtB failed to block the muscle-relaxant effects of diazepam. Further, beta CCtB (30 mg/kg) failed to antagonize the ataxic effects of diazepam in an inverted screen test. Rats responded under a multiple schedule where in one component every twentieth response (FR20) resulted in water presentation (unpunished component) and in another component every twentieth response (FR20) resulted in both shock and water presentation (punished component). Diazepam p.o. (0.1 to 10 mg/kg) first increased and then decreased rates in the punished component but only decreased rates in the unpunished component. beta CCtB had no effect on response rates when administered alone, but antagonized the rate-increasing effects of diazepam in the punished component. beta CCtB did not alter the rate-decreasing effects of diazepam in either component. Thus, beta CCtB selectively antagonized the effects of diazepam on punished behavior as well as the anticonvulsant effects of diazepam, but beta CCtB failed to antagonize the rate-decreasing and ataxic effects of diazepam. These results are consistent with the interpretation that beta CCtB is a selective BZ1 benzodiazepine receptor antagonist.     

Different effects of intracerebral and systemic administration of buspirone in the forced swimming test: involvement of a metabolite

Buspirone, a drug with high affinity for serotonin1A receptors, was studied for its ability to reduce rats' immobility in the forced swimming test when injected systemically or into the nucleus raphe dorsalis (DR). Between 0.1 and 10 mg/kg buspirone had no effect on rats' immobility when injected systemically as a single dose or as a 3-injection course during 24 hours. Direct injection of 1 and 5 mu/0.5 microliter buspirone in the DR significantly reduced the duration of immobility without changing rats' activity in an open field. The anti-immobility effect of 1 microgram/0.5 microliter buspirone in the DR was completely prevented by injecting 2.5 micrograms (-)-propranolol in the same area. Oral administration of 0.3-1.0 mg/kg 1-(2-pyrimidinyl)piperazine (1-PP), one of the main metabolites of buspirone, and 0.3-3.0 mg/kg s.c. idazoxan, two substances with alpha 2 adrenergic blocking properties, completely antagonized the effect of 0.25 mg/kg s.c. 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), an agent with selective affinity for serotonin1A receptors. The anti-immobility effect of an infusion of 1 microgram/0.5 microliter buspirone or 8-OH-DPAT in the DR was also antagonized by 1 mg/kg p.o. 1-PP. The results suggest that buspirone possesses potential antidepressant properties but its effects may be masked in certain tests by its metabolite, 1PP, through its alpha 2 adrenergic blocking activity.     

Effect of buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine on hippocampal serotoninergic system, studied in freely moving rats.

The effects of the anxiolytic drug buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine (1PP) were studied on the serotoninergic system in the hippocampus of freely moving rats. Pulse voltammetry was used in association with chronically implanted carbon fiber microelectrodes to record 5HIAA, the serotonin metabolite in the extracellular space, almost continuously. Buspirone, 2.5 mg/kg i.p. was ineffective, but the dose of 10 mg/kg lowered 5HIAA between about 45 and 150 min; the same decrease was obtained with 40 mg/kg. This effect can be explained by an agonistic action on 5HT1 A receptors. The metabolite 1PP, which displays alpha 2 adrenoceptor blocking properties, either had no effect or raised extracellular 5HIAA, depending on the dose (1.5 or 6 mg/kg). The rapid metabolization of buspirone to 1PP can thus explain the short time course of the drug effect. Pretreatment with 1PP could only partially prevent buspirone's effect on the serotoninergic system.     

Effect of anxiolytics on blood sugar level in rabbits

Anxiety disorders are more prevalent not only in normal individuals but also in diabetes mellitus. Diazepam, a benzodiazepine, and buspirone, an azaspirodecanedione, are the most often prescribed anxiolytics. Present study was aimed to investigate the effect of diazepam and buspirone on the blood sugar levels in rabbits. Buspirone (0.5 mg/kg/day p.o.) and diazepam (0.6 mg/kg/day p.o.) did not affect the glucose levels in rabbits even after one month of treatment. Present findings suggest that these two anxiolytics have minimal effect on blood sugar control.     

Anxiolytic effect of berberine on exploratory activity of the mouse in two experimental anxiety models: interaction with drugs acting at 5-HT receptors

The aim of this study was to assess the anxiolytic effect of berberine (abbrev. BER) using two experimental anxiety models in the mouse. In the black and white test of anxiety, berberine (100, 500 mg/kg) produced an increase in the first time entry, time spent in the white section, and total changes between two compartments. On the other hand, in the elevated plus-maze test, berberine (100, 500 mg/kg) produced an increase in the time spent and arm entries in the open arms, and a decrease in the time spent and arm entries in the closed arms. Berberine (500 mg/kg) decreased locomotor activity in mice. Furthermore, BER at 100, 500 mg/kg decreased concentrations of NE, DA and 5-HT, and increased the concentrations of VMA, HVA and 5-HIAA in the brain stem. BER also attenuated the anxiogenic effect of WAY-100635, 8-OH DPAT and DOI and enhanced the anxiolytic effect of BUS, p-MPPI and RIT in the elevated plus-maze. These results suggested that berberine at 100 mg/kg had a significant anxiolytic-like effect, which was similar to that observed with 1 mg/kg diazepam and 2 mg/kg buspirone. The anxiolytic mechanism of BER might be related to the increase in turnover rates of monoamines in the brain stem and decreased serotonergic system activity. Moreover, BER decreased serotonergic system activity via activation of somatodendritic 5-HT1A autoreceptors and inhibition of postsynaptic 5-HT1A and 5-HT2 receptors.     

Effects of acute and chronic administration of the serotonin1A agonist buspirone on serotonin synthesis in the rat brain

The effects of acute and chronic administration of buspirone, a serotonin 5-HT1A agonist, on the 5-HT synthesis rates in various rat brain structures were investigated using alpha-[14C]methyl-L-tryptophan (alpha-[14C]MTrp) and an autoradiographic method. In the acute treatment study, buspirone (10 mg/kg) was injected subcutaneously 30 min before alpha-[14C]MTrp administration (30 microCi over 2 min) into a femoral vein. In the chronic treatment study, buspirone was given in a sustained fashion (10 mg/kg/day) for 14 days using an osmotic minipump implanted subcutaneously. Rats were killed 60 and 150 min after alpha-[14C]MTrp administration (two-time point method). A single dose of buspirone induced a significant decrease of 5-HT synthesis throughout the brain with the exception of the pineal body. However, the chronic treatment with buspirone did not induce significant differences in 5-HT synthesis in the brain. There was no significant difference in plasma free tryptophan concentration between any of the groups. The unaltered 5-HT synthesis rates in the chronic treatment study likely reflect a normalization of this parameter due to a desensitization of 5-HT1A autoreceptors on the cell body of 5-HT neurons, which has been previously shown to occur following long-term treatment with 5-HT1A agonists.     

Yohimbine induced anxiety and increased noradrenergic function in humans: effects of diazepam and clonidine

Yohimbine (30 mg) produced significant increases in subjective anxiety, autonomic symptoms, blood pressure, and plasma 3-methoxy-4-hydroxy-phenylethyleneglycol (MHPG) in ten healthy subjects. The effects of pretreatment with diazepam (10 mg) or clonidine (5 micrograms/kg) on these yohimbine induced changes was examined. Both diazepam and clonidine significantly antagonized yohimbine-induced anxiety, but only clonidine significantly attenuated the yohimbine induced increases in plasma MHPG, blood pressure, and autonomic symptoms. When given alone, clonidine significantly decreased plasma MHPG and blood pressure, whereas diazepam did not. These findings indicate that: (1) noradrenergic hyperactivity may be a factor in the production of some anxiety states; (2) the anti-anxiety effects of clonidine appear to result from its actions on receptors which decrease noradrenergic activity; (3) diazepam reverses yohimbine-induced anxiety without effects on several physiological or biochemical indicators of noradrenergic activity in humans.     

Regionally specific effects of diazepam on brain serotonin metabolism in rats: Sustained effects following repeated administration

The effects of single (1mg/kg) and repeated (1mg/kg 2¹ daily for 4 days) diazepam administration are investigated on brain regional 5-hydroxytryptamine (5-HT; serotonin) and 5-hydroxy indoleacetic acid (5-HIAA) concentration in rats. Daily treatment decreased food intakes but body weights did not decrease. Administration of diazepam (1mg/kg) to 4 day sahne injected rats on the 5th day decreased 5-HT levels in the hippocampus and increased it in the hypothalamus. 5-HIAA levels were increased in the striatum and decreased in the hypothalamus. 4 day diazepam injected rats injected with sahne on the 5th day also exhibited silmilar changes of 5-HT and 5-HIAA. Cortical levels of 5-HIAA were also smaller in these rats. Administration of diazepam to 4 day diazepam injected rats again decreased 5-HT in the hippocampus and 5-HIAA in the hypothalamus. 5-HT and 5-HIAA were both decreased in the striatum. Regionally specific effects of diazepam on brain serotonin metabolism are discussed in relation to their possible functions.