Effects of gepirone, an aryl-piperazine anxiolytic drug, on aggressive behavior and brain monoaminergic neurotransmission

Serotonin and Consciousness-A Reappraisal

The serotonergic system of the brain is a major modulator of behaviour. Here we describe a re-appraisal of its function for consciousness based on anatomical, functional and pharmacological data. For a better understanding, the current model of consciousness is expanded. Two parallel streams of conscious flow are distinguished. A flow of conscious content and an affective consciousness flow. While conscious content flow has its functional equivalent in the activity of higher cortico-cortical and cortico-thalamic networks, affective conscious flow originates in segregated deeper brain structures for single emotions. It is hypothesized that single emotional networks converge on serotonergic and other modulatory transmitter neurons in the brainstem where a bound percept of an affective conscious flow is formed. This is then dispersed to cortical and thalamic networks, where it is time locked with conscious content flow at the level of these networks. Serotonin acts in concert with other modulatory systems of the brain stem with some possible specialization on single emotions. Together, these systems signal a bound percept of affective conscious flow. Dysfunctions in the serotonergic system may not only give rise to behavioural and somatic symptoms, but also essentially affect the coupling of conscious affective flow with conscious content flow, leading to the affect-stained subjective side of mental disorders like anxiety, depression, or schizophrenia. The present model is an attempt to integrate the growing insights into serotonergic system function. However, it is acknowledged, that several key claims are still at a heuristic level that need further empirical support.

Morphology and distribution of neurons expressing serotonin 5-HT1A receptors in the rat hypothalamus and the surrounding diencephalic and telencephalic areas

Disorders of serotonergic neurotransmission are involved in disturbances of numerous hypothalamic functions including circadian rhythm, mood, neuroendocrine functions, sleep and feeding. Among the serotonin receptors currently recognized, 5-HT(1A) receptors have received considerable attention due to their importance in the etiology of mood disorders. While previous studies have shown the presence of 5-HT(1A) receptors in several regions of the rat brain, there is no detailed map of the cellular distribution of 5-HT(1A) receptors in the rat diencephalon. In order to characterize the distribution and morphology of the neurons containing 5-HT(1A) receptors in the diencephalon and the adjacent telencephalic areas, single label immunohistochemistry was utilized. Large, multipolar, 5-HT(1A)-immunoreactive (IR) neurons were mainly detected in the magnocellular preoptic nucleus and in the nucleus of diagonal band of Broca, while the supraoptic nucleus contained mainly fusiform neurons. Medium-sized 5-HT(1A)-IR neurons with triangular or round-shaped somata were widely distributed in the diencephalon, populating the zona incerta, lateral hypothalamic area, anterior hypothalamic nucleus, substantia innominata, dorsomedial and premamillary nuclei, paraventricular nucleus and bed nucleus of stria terminalis. The present study provides schematic mapping of 5-HT(1A)-IR neurons in the rat diencephalon. In addition, the morphology of the detected 5-HT(1A)-IR neural elements is also described. Since rat is a widely used laboratory animal in pharmacological models of altered serotoninergic neurotransmission, detailed mapping of 5-HT(1A)-IR structures is pivotal for the neurochemical characterization of the neurons containing 5-HT(1A) receptors.

Risperidone exerts potent anti-aggressive effects in a developmentally immature animal model of escalated aggression

BACKGROUND

Risperidone has been shown to be clinically effective for the treatment of aggressive behavior in children, yet no information is available regarding whether risperidone exhibits aggression-specific suppression in preclinical studies that use validated developmentally immature animal models of escalated aggression. Previously, we have shown that exposure to low doses of the psychostimulant cocaine-hydrochloride (.5 mg/kg intraperitoneally) during the majority of pubertal development (postnatal days [P]27-57) generates animals that exhibit a high level of offensive aggression. This study examined whether risperidone exerts selective aggression-suppressing effects by using this pharmacologic animal model of highly escalated offensive aggression.

METHODS

Experimental hamsters were tested for offensive aggression after the acute administration of risperidone (.05-1.0 mg/kg, intraperitoneally).

RESULTS

Risperidone dose-dependently reduced the highly aggressive phenotype, with a significant reduction observed at .1-.2 mg/kg for most aggressive responses measured. Experimental animals treated with higher doses of risperidone (.3-1.0 mg/kg) showed significant reductions in aggression and social interest toward intruders, indicating more general behavioral inhibition.

CONCLUSIONS

These studies provide evidence that risperidone exerts specific aggression-suppressing effects in a developmentally immature animal model of escalated aggression.

Conflict behavior and the effects of 8-OHDPAT treatment in rats selectively bred for differential 5-HT(1A)-induced hypothermia

The high DPAT sensitivity (HDS) and low DPAT sensitivity (LDS) rat lines are the result of selective breeding for differences in the hypothermic response to acute treatment with the 5-HT(1A) receptor agonist 8-hydroxydipropylaminotetralin (8-OHDPAT). The HDS rats exhibit a much greater hypothermic response than do the LDS rats. The present study examined conflict anxiety-like behavior and the effects of acute challenges with 8-OHDPAT and phenobarbital (PhB) on conflict behavior in HDS and LDS rats. Water-restricted (24-h deprivation) HDS and LDS rats were trained to drink from a tube that was occasionally electrified. The 5-s bouts of drinking tube electrification occurred on a fixed interval (FI) 30-s schedule and were signaled by the presence of a tone. Under this schedule, responding is suppressed approximately 10-fold during the tone-on periods compared to the no-tone periods. After two weeks of training in this repeated measures drink suppression conflict paradigm, the effects of acute challenges with 8-OHDPAT (30-500 microg/kg, SC, +10 min) or PhB (20 mg/kg, IP, +10 min) were determined. In control (i.e. , non-drug) conflict test sessions, rats of the HDS line accepted significantly fewer shocks than did rats of the LDS line. Acute treatment with 8-OHDPAT resulted in a modest increase in punished responding (maximum increase: +30-40 shocks/session) in both lines at doses of 60 and 125 microg/kg. Higher doses produced significant general behavioral disruption and substantial reductions in water intake (unpunished responding) in both HDS and LDS rats. Neither the increase in shocks received nor the decrease in water intake produced by these 8-OHDPAT challenges differed between HDS and LDS rats. In both lines, acute PhB treatment resulted in a more dramatic increase in punished responding than did 8-OHDPAT (+55-65 shocks/session) and an increase in water intake. The effects of PhB also did not differ between HDS and LDS rats. These data suggest that the HDS and LDS rats exhibit differences in baseline anxiety-like behavior in the conflict task, but do not differ in their response to acute challenges with PhB or 8-OHDPAT.

Effects of prenatal exposure to styrene on neurochemical levels in rat brain

Styrene was evaluated to determine its neurochemical effects in the offspring of rats exposed during the gestation period. Maternal Wistar rats were exposed to 0, 50 or 300 ppm styrene during gestation days 6 to 20 and the neurochemical effects on their offspring were compared with their pair-feeding and ad lib. feeding controls. The cerebrum weights at birth on day 0 were significantly lower than those for an ad lib. feeding control group. Neurotransmitter analyses showed decreases of neuroamines, especially 5-hydroxytryptamine and homovanillic acid in the cerebrum of newborn offspring of dams receiving a 300 ppm styrene exposure compared with the ad lib. fed control group and homovanillic acid was also decreased compared to the pair-feeding control. On postnatal day 21, the styrene-exposure pups showed a significant decrease of 5-hydroxyindoleacetic acid in the frontal neocortex compared with the ad lib. control group. In the hippocampus a significant decrease of 5-hydroxyindoleacetic acid was observed compared with both control groups. Moreover, the ratio of 5-HIAA/5-HT in the hippocampus was significantly decreased among the styrene-exposure groups. The 50 ppm styrene exposed group induced increase of concentrations of 5-hydroxytryptamine in the striatum. These results suggest that prenatal styrene exposure affects the developing fetal brain in terms of a few signs of neurochemical alteration.

The novel buspirone analogue, 8-[4-[2-(1,2,3,4-tetrahydroisoquinolinyl)[butyl]-8-azaspiro [4.5 ]decane-7,9-dione, with anxiolytic-like and antidepressant-like effects in rats

In the conflict drinking test, used as a model to examine anxiolytic-like activity, the novel buspirone analogue 8-[4-[2-(1,2,3,4-tetrahydroisoquinolinyl)]butyl)-8-azaspiro[ 4.5]decane-7,9-dione (MM199) (0.62-2.5 mg/kg) and buspirone (0.62-5 mg/kg), significantly increased the punished drinking in water-deprived rats, without affecting water consumption or perception of the stimulus. The anticonflict activity of MM199 (1.25 mg/kg) was blocked by (S)-WAY 100135 (20 mg/kg), a 5-hydroxytrypatmine1A (5-HT1A) receptor antagonist. In the forced swimming test, used as a model to examine the antidepressant-like activity, MM199 (5-20 mg/kg) reduced the immobility time, while buspirone (5-20 mg/kg) had no such effect. The reduced immobility induced by MM199 (20 mg/kg) was antagonized by (S)-WAY100135 (10 mg/kg). The above findings suggest that MM199 possesses potent anxiolytic- and antidepressant-like properties which are mediated by activation of 5-HT1A receptors.

Combined effects of Gepirone and (+)WAY 100135 on territorial aggression in mice

The purpose of this investigation was to elucidate the involvement of the serotonergic 5-HT1A system in the control of aggression. The paradigm was the response of a resident mouse to an intruder into its territory. Three experiments were performed to assess the action of various doses of Gepirone (a partial agonist) and (+)WAY 100135 (a putative antagonist), separately and in combination, on aggression and on rectal body temperature. The most consistent action of Gepirone was an increase in the latency to attack. After initiation of fighting, rates of attack, chase, and tail rattling were reduced in a dose-dependent manner by i.p. administration of 2.5, 5, and 10 mg/kg of Gepirone. There was no evidence of sedation or motor impairment, but autogrooming was decreased. When doses of 2.5, 5, and 10 mg/kg of (+)WAY 100135 (WAY) were given, no effects whatsoever on aggressive or other behaviors were observed. In a third experiment, a two-factor design was followed in which injection of WAY (0, 2.5, and 5 mg/kg) was followed 15 min later by injection of Gepirone (0, 2.5, 5, and 10 mg/kg). WAY decreased attack latency, increased attack rate, and attenuated the marked dose-dependent aggression reducing properties of Gepirone. The test procedure resulted in "stress hyperthermia," which was reduced by Gepirone and increased by WAY. In both behavioral and temperature measures, the larger dose of WAY proved to be less effective than the smaller one. The results support the involvement of the 5-HT1A system in the modulation of some forms of aggression.

Effect of 5-[3-[((2S)-1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3-benzodioxole HCl (MKC-242), a novel 5-HT1A-receptor agonist, on aggressive behavior and marble burying behavior in mice

Behavioral effects of 5-[3-[((2S)-1,4-benzodioxan-2-ylmethyl)amino]propoxy]-1,3-be nzodioxole HCl (MKC-242), a novel 5-HT1A-receptor agonist, were evaluated using animal models of anxiety and obsessive compulsive disorder and compared against reference compounds. MKC-242 suppressed foot shock-induced fighting behavior without loss of motor coordination in mice as the reference compounds did. The ED50 values of MKC-242, buspirone, tandospirone and diazepam were 1.7, 42, 80 and 2.0 mg/kg, p.o., respectively. The duration of the suppression of fighting by MKC-242 was longer than those of buspirone and tandospirone and comparable to that of diazepam. Similar results were also obtained with the water-lick conflict test in rats. The plasma concentration of MKC-242 in rats was much higher than the reported value of buspirone during 0.25-6 hr after oral administration. In addition, MKC-242 reduced marble burying behavior without reduction of motor activity. Fluoxetine, tandospirone and diazepam also reduced the behavior at non-sedative doses. These findings indicate that MKC-242 possesses a longer-lasting anxiolytic effect than azapirones. This might be due to the high concentration of the compound in plasma. In addition, it is also suggested that MKC-242 possesses an antiobsessional effect.

Serotonin 5-HT1A and 5-HT2/1C receptors in the midbrain periaqueductal gray differentially modulate defensive rage behavior elicited from the medial hypothalamus of the cat

Recent studies have established that the expression of defensive rage behavior in the cat is mediated over a descending pathway from the medial hypothalamus to the dorsolateral quadrant of the midbrain periaqueductal gray matter (PAG). The present study was designed to determine the roles played by 5-HT1A and 5-HT2/1C receptors in this region of PAG in modulating defensive rage behavior elicited from the cat's medial hypothalamus. Monopolar stimulating electrodes were implanted into the medial hypothalamus from which defensive rage behavior could be elicited by electrical stimulation. During the course of the study, the 'hissing' component of the defensive rage response was used as a measure of defensive rage behavior. Cannula-electrodes were implanted into sites within the PAG from which defensive rage could also be elicited by electrical stimulation in order that 5-HT compounds could be microinjected into behaviorally identifiable regions of the PAG at a later time. Microinjections of the selective 5-HT1A agonist, (+)-8-hydroxy-dipropylaminotetralin hydrobromide (8-OHDPAT) (50 pmol, 2.0 and 3.0 nmol), into the PAG suppressed the hissing response in a dose-dependent manner. Administration of the selective 5-HT1A antagonist, 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl] ethyl]-N-2-pyridinyl-benzamide hydrochloride (p-MPPI) (1.5 and 3.0 nmol), blocked the suppressive effects of 8-OHDPAT upon hissing. In contrast, microinjections of the 5-HT2/1C receptor agonist (+)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride ((+)-DOI hydrochloride) (0.01, 1.0 and 1.5 nmol) facilitated the occurrence of hissing elicited from the medial hypothalamus in a dose-dependent manner. Immunohistochemical analysis revealed the presence of 5-HT axons and preterminals throughout the PAG, and in particular, in its dorsolateral aspect which receives major inputs from the medial hypothalamus in association with defensive rage behavior. The overall findings of the study provide evidence that activation of 5-HT1A and 5-HT2/1C receptors within the midbrain PAG differentially modulate the expression of defensive rage behavior elicited from the medial hypothalamus of the cat.

Vasopressin/serotonin interactions in the anterior hypothalamus control aggressive behavior in golden hamsters

Studies in several species of rodents show that arginine vasopressin (AVP) acting through a V1A receptor facilitates offensive aggression, i.e., the initiation of attacks and bites, whereas serotonin (5-HT) acting through a 5-HT1B receptor inhibits aggressive responding. One area of the CNS that seems critical for the organization of aggressive behavior is the basolateral hypothalamus, particularly the anterior hypothalamic region. The present studies examine the neuroanatomical and neurochemical interaction between AVP and 5-HT at the level of the anterior hypothalamus (AH) in the control of offensive aggression in Syrian golden hamsters. First, specific V1A and 5-HT1B binding sites in the AH are shown by in vitro receptor autoradiography. The binding for each neurotransmitter colocalizes with a dense field of immunoreactive AVP and 5-HT fibers and putative terminals. Putative 5-HT synapses on AVP neurons in the area of the AH are identified by double-staining immunocytochemistry and laser scanning confocal microscopy. These morphological data predispose a functional interaction between AVP and 5-HT at the level of the AH. When tested for offensive aggression in a resident/intruder paradigm, resident hamsters treated with fluoxetine, a selective 5-HT reuptake inhibitor, have significantly longer latencies to bite and bite fewer times than vehicle-treated controls. Conversely, AVP microinjections into the AH significantly shorten the latency to bite and increase biting attacks. The action of microinjected AVP to increase offensive aggression is blocked by the pretreatment of hamsters with fluoxetine. These data suggest that 5-HT inhibits fighting, in part, by antagonizing the aggression-promoting action of the AVP system.

Serotonergic control of androgen-induced dominance

The present study investigates the role of serotonergic systems in anabolic steroid-induced aggression. An animal model of aggressive dominance was used to assess the chronic effects of testosterone propionate. When rats that had become dominant following administration of testosterone propionate received serotonergic agonists with selectivity for the 5-HT1A receptor (8-OH-DPAT, buspirone, gepirone), the 5-H1B receptor (eltoprazine, TFMPP), or the 5-HT2A/2C receptor (DOM), a dose-dependent decrease in dominance was demonstrated. Pretreatment with three serotonergic antagonists (pizotyline, pirenpirone, and pindolol) blocked agonist-induced reductions in dominance in varying degrees. Nonserotonergic agonists with CNS depressant effects were also tested in dominant animals. The benzodiazepine, chlordiazepoxide, did not reduce dominance except at doses that interfered with motor behavior. The opioid agonist, morphine, dose dependently decreased dominance, but this effect was reversible with administration of the serotonergic antagonist, pirenpirone, suggesting the antidominant effect of morphine had a serotonergic component. Biochemical experiments demonstrated that following chronic testosterone propionate, there was a decrease in levels of 5-HT and 5-HIAA in the hippocampus but not in the striatum or the frontal cortex. Chronic testosterone propionate also caused an increase in the affinity of [3H]8-OH-DPAT for the 5-HT1A receptor but no corresponding change in the density of 5-HT1A binding sites in the hippocampus. There was also no change in the properties of the 5-HT2 receptor in the frontal cortex following chronic testosterone propionate. These data suggest that serotonergic systems may play an important role in the control of anabolic steroid-induced aggressive dominance.

5-HT1A receptor-mediated inhibition in the hippocampus of the alert rat--effects of repeated gepirone treatment

The effects of acute and repeated treatment with the 5-HT1A receptor ligand gepirone on hippocampal excitatory synaptic transmission were investigated. Recordings of the electrically evoked field population excitatory postsynaptic potentials (e.p.s.p.s) were made in the stratum radiatum of the CA1 region of the dorsal hippocampus of alert male Wistar rats. Acute injection of gepirone reduced the e.p.s.p. amplitude in a transient dose-dependent (0.5-10 mg/kg, i.p.) manner. This effect was blocked by the 5-HT1A receptor antagonist MDL 73005EF (8-[2-(2,3-dihydro-1,4-benzodioxin-2-yl methylaminoethys]-8- azaspiro[4,5]decane-7,9-dione methyl sulphonate, 2 mg/kg, i.p.). Gepirone (1 mg/kg per day, i.p.) administered for 7 days produced a gradual reduction in the daily pre-injection baseline e.p.s.p. amplitude coupled with a concomitant reduction of the acute response to the drug. The chronic baseline reduction was transiently reversed by the 5-HT1A receptor antagonist spiroxatrine and complete recovery to pretreatment levels was observed 48 h after the last gepirone dose. The data indicate that with repeated administration, a prolongation and enhancement of the 5-HT1A receptor-mediated reduction in the e.p.s.p. by gepirone occurs. This delayed effect may contribute to the slow onset of therapeutic action of gepirone.

Comparison of the action of the 5-HT2 antagonists amperozide and trazodone on preference for alcohol in rats

Previous studies in the rat demonstrated that the 5-hydroxytryptamine2 (5-HT2) antagonist amperozide attenuates the volitional intake of both alcohol and cocaine solutions in a free-choice situation. However, another 5-HT2 antagonist, ritanserin, has not been found to reduce alcohol drinking consistently in the rat. In this study, trazodone was compared to amperozide for its effect on the volitional consumption of alcohol because, like amperozide, trazodone is a potent 5-HT2 receptor antagonist but a weak inhibitor of 5-HT reuptake. Male Sprague-Dawley rats were induced to drink alcohol by 10 mg/kg cyanamide injected for 3 days b.i.d. One week later the rats were offered a choice of water and increasing concentrations of alcohol solutions ranging from 3% to 30% v/v in a three-bottle two-choice paradigm. After the concentration of alcohol that produced maximal daily intake was determined for each rat, trazodone or amperozide was injected b.i.d. SC in doses of 1.0 mg/kg or 2.5 mg/kg for three days. Whereas the higher dose of amperozide produced a significant, 55.6% decrease from pretreatment baseline of alcohol intake, trazodone did not alter alcohol preference at either the 1.0- or 2.5-mg/kg dose. These results are discussed in terms of whether the antagonism of 5-HT2 receptors by amperozide is critical to its attenuating effect on preference for alcohol solutions.

Gepirone and 1-(2-pyrimidinyl)-piperazine-induced reduction of aversively evoked ultrasonic vocalisation in the rat

Ultrasonic (22 kHz) vocalisation in response to a mildly aversive foot shock was measured in the dark compartment of a light-dark box both immediately and 24 h after the shock. Gepirone (1 and 5 mg/kg, IP) produced a reduction in the duration of vocalisation at both times. Although a metabolic inhibitor, proadifen (40 mg/kg) did not reduce this effect of gepirone, the gepirone hepatic metabolite, 1-(2-pyrimidinyl)-piperazine (1-PP, 1 mg/kg), was also active in the test. Performance of a 24 h step-through passive avoidance task was impaired by gepirone only at a dose, 5 mg/kg, which also reduced spontaneous locomotor and rearing activity in the apparatus. It would appear that mild foot shock-evoked ultrasonic vocalisation may provide a more sensitive indicator of the effect of gepirone and related drugs on the affective response of rats to aversive stimulation.

Prenatal exposure to cocaine: effects on aggression in Sprague-Dawley rats

Social/aggressive behavior in adult rat offspring (beginning at postnatal Day 180) prenatally exposed to saline, cocaine, or amfonelic acid (AFA) was examined. Pregnant rats received injections of 15 mg/kg of cocaine, or 0.9% saline twice daily, s.c., or on 2 consecutive days at 4-day intervals, or 1.5 mg/kg amfonelic acid daily throughout gestational Days 1-20. Frequency, duration, and latency of 11 social/aggressive behaviors were recorded for two 15-min sessions during which a smaller male intruder replaced an ovariectomized female in the resident's home cage. Subjects received a s.c. saline injection before Session 1 and 2.0 mg/kg of gepirone, a 5HT1a partial agonist, prior to Session 2. Prenatal cocaine treatment resulted in alterations of aggressive behavior. Aggressive behavior was reduced by gepirone in all groups but to a lesser extent in the AFA group.

Neuropharmacology of 5-hydroxytryptamine1B/D receptor ligands

In spite of a lack of compounds acting selectively at the 5-hydroxytryptamine (5-HT)1B and 5-HT1D receptor subtypes, by cross-relating the available data, this review attempts to tentatively assign behavioural and other in vivo correlates of these receptor subtypes. In addition, a summary of data from microdialysis studies is included to develop an integrated view. Finally, a suggestion is made as to the possible pathophysiological consequences of 5-HT1D receptor dysfunction in man.

Changes in dopamine, serotonin and their metabolites in discrete brain areas of rat offspring after in utero exposure to cocaine or related drugs

The concentrations of dopamine (DA), serotonin (5HT) and their metabolites were quantified in 5 brain areas of rats exposed to saline, cocaine (15 mg/kg b.i.d.), amitriptyline (10 mg/kg), or amfonelic acid (AFA, 1.5 mg/kg) throughout gestation. Male pups from 3 similarly treated dams were fostered to 2 surrogate dams. The process of breeding and rearing was repeated 4 times with new dams to build the groups to 4-12, since only one pup per litter was used for any one measurement. AFA was used to mimic the dopamine (DA) uptake blockade and stimulant properties of cocaine and amitriptyline was used to mimic the other pharmacological effects of cocaine. At postnatal days (PND) 30, 60, and 180, one pup per litter was removed for HPLC analysis of monoamines. A second pup received 0.3 mg/kg haloperidol, catalepsy assessed after 1 hr, and the brain used for analysis. The cataleptic response to haloperidol was unaffected by any prenatal treatment. The striatum from PND 30 cocaine rats had decreased levels of DA without a decrease in DA metabolites. At PND 60 in cocaine exposed rats, DA and DOPAC concentrations were increased, and 5HT levels were decreased in the striatum. The amitriptyline-exposed group exhibited decreased 5HT and 5-HIAA levels in the striatum. The hypothalamus of the cocaine group had lower levels of 5-HIAA, and other brain areas had a trend for lower levels of 5HT and 5-HIAA. At PND 180, DOPAC was increased in the striatum and prefrontal cortex of the cocaine group. Haloperidol-induced altered monoamine metabolism was unaffected by any prenatal treatment at any age. These data suggest that age-related changes in the DA and 5HT neurotransmission systems occur in rats exposed prenatally to cocaine. However, the ability of the dopaminergic system to respond to a challenge by a DA receptor blocker is unaltered by these in utero treatments.

Role of resocialization and of 5-HT1A receptor activation on the anxiogenic effects induced by isolation in the elevated plus-maze test

Rats were isolated for periods varying from 1 h to 2 weeks and the exploratory activity of these animals on the elevated plus-maze was studied. Rats isolated from periods of 2 h on displayed a significant reduction in the number of entries and time spent in the open arms of the plus-maze compared to socially housed controls. This effect was not correlated with the decrease in the total number of entries also produced by isolation. Acute treatment with midazolam or resocialization for a 24-h period clearly reversed these responses produced by prior 2-h isolation in the elevated plus-maze. It is suggested that exposure to a 2-h isolation period could be a useful nonpharmacological means of generating anxiety in laboratory rodents. Chronic treatment, but not acute treatment, with gepirone, a 5-HT1A agonist, inhibited the anxiogenic effects caused by a 2-week period of isolation. The reduction in aversiveness promoted by resocialization may be due to a recovery in the 5-HT activity depressed by isolation in a much faster way than observed with chronic gepirone administration.

Effects of pindobind 5-hydroxytryptamine1A (5-HT1A), a novel and potent 5-HT1A antagonist, on social and agonistic behaviour in male albino mice

In view of inconsistent results reported for 5-hydroxytryptamine1A (5-HT1A) receptor involvement in murine social conflict, this study examined the effects of N1-(bromoacetyl)-N8-[3-(4-indolyloxy)-2- hydroxypropyl]-(Z)-1,8-diamino-p-menthane (pindobind) 5-HT1A, a novel 5-HT1A antagonist, on agonistic and social behaviour in mice. Employing a resident-intruder paradigm, administration of pindobind 5-HT1A (0.5-10 mg/kg) to resident animals produced a reduction in offensive sideways and chasing behaviour. Defensive postures were unchanged except for evasion, which was reduced. Within social behaviour, nonspecific social behaviour and following behaviour were reduced while stretch/attend behaviour was enhanced. Nonsocial behavioural changes included an increase in resident cage exploration and rearing. Intruder data indicated no significant change in offensive behaviours, an attenuation of defensive sideways posturing and evasion, decreases in attend behaviour, and increases in cage exploration, rearing, and digging. Results are discussed in relation to the effects of 5-HT1A receptor (ant)agonism on murine offensive behaviour.

The role of serotonergic mechanisms in inhibition of isolation-induced aggression in male mice

The role of serotonergic (5-HT) receptor subtypes in mediation of aggressive behaviour in isolated male mice has been studied. Increase of attack latency was used as a simple measure of antiaggressive behaviour. 5-HT1A agonists (BAY R 1531, 8-OHDPAT, flesinoxan, gepirone, 5MeO DMT, buspirone, ipsapirone, BMY 14802) completely inhibit the aggressive behaviour irrespective of their intrinsic activities. Also the putative antagonists spiroxatrine and NAN 190 as well as the non-selective 5-HT1 agonists RU 24969, TFMPP, mCPP and eltoprazine have an antiaggressive effect. The mixed 5-HT1A and beta-adrenoceptor antagonists (-)-alprenolol and pindolol are ineffective and do not inhibit the effect of 8-OHDPAT. Neither does the non-selective 5-HT antagonist metergoline. The antiaggressive effect correlates with 5-HT1A receptor affinity in vitro and with generalization to the 8-OHDPAT-induced discriminative stimulus. The selective 5-HT uptake inhibitor citalopram does not inhibit aggressive behaviour. The 5-HT2 agonist DOI has an antiaggressive effect only at high doses, whereas the 5-HT2 antagonist ritanserin and the 5-HT3 antagonist ondansetron are ineffective. Prazosin (alpha 1-adrenoceptor antagonist), clonidine (alpha 2-adrenoceptor agonist), clenbuterol (beta-adrenoceptor agonist), ketanserin (5-HT2 receptor and alpha 1-adrenoceptor antagonist), clozapine and (-)-octoclothepin (dopamine (DA), 5-HT2 receptor and alpha 1-adrenoceptor antagonist) all show an antiaggressive effect. SCH 23390 (DA D1 receptor antagonist) and emonapride (DA D2 receptor antagonist) are ineffective. In conclusion, 5-HT1A receptors are involved in mediation of isolation-induced aggressive behaviour in mice. The involvement of other 5-HT receptor subtypes needs further clarification. The adrenergic system may also be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of gepirone on increases in tryptophan hydroxylase in response to sound stress

Pretreatment (15 min) of male rats with gepirone given parenterally (10 mg/kg i.p.) or intracranially into the dorsal raphe nucleus (14 or 21 micrograms) blocks the rapidly reversible increase in brain tryptophan hydroxylase activity and 5-hydroxyindolamine acetic acid tissue levels seen in vitro after 1-h acute sound stress. Chronic gepirone treatment over 28 days (40 mg/day s.c.) prevents the stable enzyme activity increase induced by repeated sessions of sound stress, and the rapidly reversible increase always observed following sound stress. The gepirone metabolite, 1-(2-pyrimidinyl)-1-piperazine, is inactive in each of these experiments. Transient blood pressure elevations occur with each sound presentation, but no persistent hypertension is observed with repeated sound-stress exposures. Gepirone may block the sound stress-induced biochemical increases by its inhibition of serotonergic neuronal firing in the dorsal raphe nucleus that is mediated by its agonist action at the somatodendritic (5-HT1A) autoreceptors.

Buspirone impairs performance of a three-choice working memory water escape task in rats

Two studies were conducted to assess the effects of buspirone and alprazolam on a three-choice working memory water escape task. Both studies involved giving rats three daily trials, each trial consisting of an information run during which guillotine doors forced the rats to swim into the correct escape alley and a test run during which the rats could enter any of the three alleys but escape only on entering the same alley to which they had been forced on the information run. In the first experiment, rats were trained to a 70% correct choice criterion with 5-min interrun intervals and then tested for performance with 5, 20, 20 with distraction, and 60-min interrun intervals. In the second experiment, rats in each of the drug groups were tested after receiving one of three different doses of their respective drug. Results suggest that 1.0, 3.0, and 10.0 mg/kg buspirone but not 0.5, 1.0, and 2.0 mg/kg alprazolam impaired performance of rats on a three-choice working memory water escape task.

On central muscle relaxants, strychnine-insensitive glycine receptors and two old drugs: zoxazolamine and HA-966

Zoxazolamine is in the centrally-acting muscle relaxant class of drugs, which reportedly act by decreasing CNS interneuronal activity. These drugs, but not anxiolytics, decrease dopaminergic turnover and induce a pacemaker-like discharge pattern in dopaminergic neurons. A mechanism for these effects was not found in previous reports. We observed that (+)-HA-966, an inhibitor of the glycine modulatory site on the NMDA receptor, has a similar effect on dopaminergic impulse flow, which suggested that this may be the possible site of action of classical muscle relaxants. However, a competitive antagonist of NMDA receptors, NPC-12626, had little effect on impulse flow. Binding of 20 nM [3H]-glycine to cortical synaptosomal membranes was inhibited by (+)-HA-966, IC50 = 3.16 microM, but only poorly by zoxazolamine, IC50 V 474 microM, and chlorzoxazone, a related drug, caused no displacement. The drugs were then tested for protection from amphetamine neurotoxicity. Neither 50 mg/kg zoxazolamine nor 30 mg/kg (+)-HA-966 prevented (+)-amphetamine (0.1 mmol/kg plus 10 mg/kg iprindole) depletion of striatal dopamine (DA), but 3.0 mg/kg of MK-801, a non-competitive NMDA receptor antagonist, did protect DA content. Since baclofen induces a regular firing rate in DA neurons, zoxazolamine and (+)-HA-966 were tested for displacement of 10 nM [3H]-1-baclofen from cortical synaptosomal GABAb receptors, but were ineffective. Thus, the effects of these muscle relaxants on DA neurons are mediated by a mechanism other than strychnine-insensitive glycine or GABAb receptors.

Effects of blockade of 5-HT2 receptors and activation of 5-HT1A receptors on the exploratory activity of rats in the elevated plus-maze

Acute administration of gepirone, a 5-HT1A agonist, caused a dose dependent (1-10 mg/kg, IP) reduction in the locomotor activity (open and closed arms) of rats tested in the elevated plus-maze. However, rats housed in individual cages and submitted to chronic treatment with gepirone (10 mg/kg PO) showed a marked increase in the percentages of number and time spent in the open arms as compared to controls. These results are compatible with the idea that the antiaversive effect due to long-term treatment with 5-HT1A agonists is the result of a progressive desensitization of the somatodendritic 5-HT autoreceptor with the consequent recovery of firing rate of 5-HT neurons along with an activation of normosensitive postsynaptic 5-HT neurons. Ketanserin caused a biphasic effects on the exploratory behavior of rats in the plus-maze. The lower dose (0.5 mg/kg) decreased the aversion to the open arms and the higher dose (1.0 mg/kg) caused an unspecific decrease in the overall activity of the animals. Ketanserin is supposed to have antagonistic action on 5-HT2 and on alpha-adrenergic receptors. As prazosin (0.5-1.0 mg/kg), an alpha-adrenergic receptor blocker, did not present any significant effect in the present work it is suggested that the effects of the lower dose of ketanserin was due to its high antagonistic action on 5-HT2 receptors.

Rodent models of aggressive behavior and serotonergic drugs

Various models of rodent agonistic behaviour are described, which differentiate between offensive and defensive/flight models. Particular attention is given to one male and one female paradigm for offensive aggression, viz. resident-intruder or territorial (RI) and maternal aggression (MA). After an overview of the serotonin (5-HT) system in the CNS, a description is given of the ligands available. Subsequently the effects of various drugs affecting serotonergic transmission in the RI- and MA-paradigms are described. The 5-HT1A agonists buspirone, ipsapirone and 8-OH-DPAT decreased aggression in RI and MA, but simultaneously led to a marked decrease in social interest and activity, indicative of a non-specific anti-aggressive profile. Non-selective 5-HT1 agonists, such as RU 24969, eltoprazine (DU 28853), and TFMPP reduced aggression quite specific and did not decrease social interest or exploration, but sometimes even increased these behaviours. In RI and MA the behavioural effects of these drugs were roughly similar. In contrast, MA was more sensitive to the treatment with the 5-HT reuptake blocker fluvoxamine, which blocked RI aggression only non-specifically at the highest dose. DOI, a 5-HT2 and 5-HT1C agonist, decreased aggressive behaviour and increased inactivity, without affecting social interest and exploration in RI as well as MA. This was, however, accompanied by 'wet dog shaking', characteristic of 5-HT2-receptor stimulation. The non-specific 5-HT agonist (and 5-HT3 antagonist) quipazine also induced 'wet dog shaking' at doses which suppressed aggression, social interest and exploration but increased inactive behaviours (sitting and lying). The discussion attempts to delineate a role for 5-HT receptor subtype involvement in the modulation of aggression, with the restrictions we clearly face with regard to the lack of specific serotonergic agonists and antagonists for certain receptor subtypes. By and large, male and female rats react similarly to treatment with serotonergic drugs stressing the consistent role of 5-HT in different forms of aggression.

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)

Serotonergic measures in suicide brain: 5-HT1A binding sites in frontal cortex of suicide victims

The density of 5-HT1A binding using 3H-8-hydroxy-2-(di-n-propyl-amino) tetralin (8-OH-DPAT) as binding ligand, was studied in human frontal cortex of suicide victims and normal controls who died due to medical disease or accidentally. There was no difference in the maximum number of binding site (Bmax) or Kd (an inverse measure of affinity) of 5-HT1A receptor binding sites between normal controls and the entire group of suicide victims. However, nonviolent suicides had significantly higher Bmax (22-25%) compared to both controls and violent suicides. A negative correlation between age and Bmax of 5-HT1A binding sites was found in male controls but not in female controls or suicide victims. This relationship was less apparent among the male controls over age 60.

Effects of serotonergic agents on isolation-induced aggression

A series of serotonergic agents were assessed for their ability to antagonize isolation-induced aggression and their activity to disrupt performance in the rotorod motor coordination test. All compounds with 5-HT1A activity [buspirone, gepirone, ipsapirone, tandospirone (SM-3997), 8-OH-DPAT, Wy-48,723, BMY-7378, Wy-47,846] reduced aggression at doses below those which produced debilitation in the rotorod motor coordination test. In addition, the 5-HT3 antagonist zacopride failed to attenuate aggression or produce debilitation at any of the doses tested; however, the 5-HT2 antagonist ritanserin inhibited aggressive behavior at a high dose which was not debilitating. Benzodiazepines (chlordiazepoxide, diazepam and lorazepam), and antidepressant (desipramine) and an antipsychotic (haloperidol) reduced aggressive behavior only at debilitating doses. Activity at the 5-HT1A receptor, and possibly nonsedative anxiolytic activity, appears to be related to antagonism of isolation-induced aggression.

Involvement of 5-HT1A receptors in the antidepressant-like activity of gepirone in the forced swimming test in rats

The antidepressant-like activity of gepirone, a drug with a high and selective affinity for 5-hydroxytryptamine1A (5-HT1A) receptors, was studied in the forced swimming test in rats. The drug, administered intraperitoneally in single doses of 2.5-20 mg/kg, potently and dose-dependently shortened the immobility time. The anti-immobility effect of gepirone (10 mg/kg) was dose-dependently antagonized by the 5-HT1A receptor and alpha 1-adrenoceptor antagonist, NAN-190 (0.25 and 0.5 mg/kg), the beta-adrenoceptor blocker with the affinity for 5-HT1A and 5-HT1B receptors, pindolol (2 and 4 mg/kg), the 5-HT1A, 5-HT2 and dopamine receptor blocker spiperone (0.01 and 0.03 mg/kg) and by the dopamine receptor antagonist, haloperidol (0.125 and 0.25 mg/kg). On the other hand, the non-selective 5-HT receptor antagonist, metergoline (2 and 4 mg/kg), the selective 5-HT2 receptor antagonist, ketanserin (1 and 2 mg/kg), the selective alpha 1-adrenoceptor blocker, prazosin (0.25 and 0.5 mg/kg) and the beta-blockers with no affinity for 5-HT receptors, betaxolol (4 and 8 mg/kg) and ICI 118,551 (4 and 8 mg/kg), did not affect the anti-immobility effect of gepirone. The effect of gepirone was not modified, either, in animals with a lesion of the 5-HT system, produced by p-chloroamphetamine (PCA, 2 x 10 mg/kg) or p-chlorophenylalanine (PCPA, 3 x 300 mg/kg). The results obtained suggest that the anti-immobility effect of gepirone is mediated by activation of 5-HT1A receptors, most probably located postsynaptically and that dopamine may be involved in this action.

Effects of subchronic amphetamine or amfonelic acid on rat brain dopaminergic and serotonergic function

Repeated doses of direct or indirect CNS stimulants are known to cause behavioral hypersensitivity. The biochemical basis for hypersensitization remains unclear. Since the dopaminergic system uses a large storage pool that is only slowly mobilized to releasable sites, a change in this relationship may underlie the biochemical changes leading to increased responsiveness to stimulants. To test this hypothesis, rats were first tested with low doses of 2.5 mg/kg amphetamine or 1.0 mg/kg amfonelic acid (AFA) for their locomotor response, then 5.0 mg/kg amphetamine or 2.5 mg/kg AFA were injected daily for 7 days and the rats retested with the lower doses of amphetamine or AFA, respectively. Both drugs produced hypersensitivity, but the cataleptic response to acute dopamine (DA) receptor blockade by haloperidol was unaltered. The ability of haloperidol to increase DA metabolism was unaltered and the ability of acute AFA to synergize with haloperidol was similar in the striatum of stimulant and saline treated rats, but reduced in the medial prefrontal cortex of both AFA and d-amphetamine treated rats. Additional rats had DA2 receptor sensitivity measured in the striatum and frontal cortex, but no significant differences were found. Only amphetamine caused a significant decrease in frontal cortex serotonin type 2 receptors. Since there was no alteration in the ability of AFA to increase neurogenic release of DA in the striatum and a decrease occurred in prefrontal cortex, an increase in the storage to functional pool exchange in the nigrostriatal and mesocortical DA containing neurons seems unlikely. In contrast, both the amphetamine and AFA treatment groups had their brain 5HT and 5HIAA levels reduced by about 50%. This suggests that changes in other transmitter systems may have a permissive effect allowing exaggerated responses to excessive DA release.

Influence of taste and food texture on the feeding responses induced by 8-OH-DPAT and gepirone

Previously it has been shown that 5-hydroxy-tryptamine (5-HT)1A agonists such as 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and gepirone increase food intake in free-feeding rats. These experiments were conducted to examine the possible influence of taste and textural factors on the feeding responses induced by these two drugs. Separate groups of non-water-deprived rats were given access to one of a variety of different solutions of saccharin (0.02, 0.04, 0.20 and 2.0% w/v) or water for 2 h each day. Rats were then treated with different doses of 8-OH-DPAT (10, 60 or 100 micrograms/kg) or gepirone (1 or 2.5 mg/kg) in a repeated measures design. Under saline injection an inverted-U shaped concentration-response curve was obtained, with the highest level of intake occurring in rats drinking from the 0.20% saccharin solution. The highest doses of 8-OH-DPAT and gepirone suppressed drinking of saccharin, particularly over the first 30 min of the test period, leading to a flattening of the concentration response curve. At 2 h post-injection 60 micrograms/kg 8-OH-DPAT enhanced the consumption of the 0.04% saccharin solution only. In a second experiment, 8-OH-DPAT or gepirone was administered to rats eating either standard pelleted chow or the same food presented in powdered form. Both drugs stimulated feeding. However, interactions with food type were found. At 60 and 100 micrograms/kg 8-OH-DPAT increased eating of both food types equally, but with 500 micrograms/kg rats are significantly more of the pelleted food.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in serotonin 5-HT1A receptors in prefrontal and temporal cortices of brains from patients with chronic schizophrenia

Binding studies with [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT), a specific serotonin1A (5-HT1A) receptor agonist, were done on the autopsied brains from control subjects and from patients with chronic schizophrenia. All the patients and controls were of the Japanese race. In the controls, representative Scatchard plots for the specific [3H]8-OH-DPAT bindings in the prefrontal cortex and hippocampus revealed a single component of high affinity binding site (Kd value = 5.7 and 5.9 nM, Bmax value = 80.1 and 101.0 fmol/mg protein, respectively). The [3H]8-OH-DPAT bindings to the prefrontal cortex and hippocampus were potently inhibited by serotonin (IC50 = 6.3 x 10(-9) M) and 5-HT1A agonists (IC50 = 5.0 x 10(-9) - 2.3 x 10(-7) M), while other neurotransmitters, 5-HT2 and 5-HT3 related compounds did not inhibit the binding (IC50 greater than 10(-5) M). The bindings were decreased in the presence of 0.1mM GTP and 0.1mM GppNHp but not in the presence of 0.1mM GMP. In the prefrontal and temporal cortices of schizophrenics, there was a significant increase in the specific [3H]8-OH-DPAT binding, by 40% and 60%, respectively, with no change in the hippocampus, amygdala, cingulum, motor cortex, parietal or occipital cortex, as compared to findings in the controls. Scatchard analysis showed that this increased binding reflects changes in the number of sites but not in the affinity. The effect of 0.1mM GppNHp on the binding to prefrontal cortex was observed in both controls and schizophrenic patients. The bindings were significantly greater in the schizophrenic patients than in controls, in the presence of 0.1mM GppNHp. Our findings suggest that there are GTP-sensitive 5-HT1A sites in the human brain and that selective increases in GTP-sensitive 5-HT1A sites in the prefrontal and temporal cortices of schizophrenics relate to the pathophysiology of schizophrenia.

Unique modulation of central 5-HT2 receptor binding sites and 5-HT2 receptor-mediated behavior by continuous gepirone treatment

The effect of continuous treatment with the selective 5-HT1A agonist gepirone upon 5-HT2-mediated behavior and cortical 5-HT2 receptor binding sites was examined in naive rats or rats receiving noradrenergic (DSP4) or serotonergic (5,7-DHT) lesions. Continuous administration of gepirone in non-lesioned rats for 3, 7, or 14 days enhanced the head shake response to the 5-HT agonist quipazine. This enhancement of 5-HT2-mediated behavior occurred despite concomitant down-regulation of cortical 5-HT2 binding sites. However, 28 days of gepirone administration significantly reduced behavioral responsiveness to quipazine. The gepirone-induced facilitation of 5-HT2-mediated behavior observed after 7 days of continuous treatment was blocked in both DSP4 and 5,7-DHT-lesioned rats. However, both noradrenergic and serotonergic denervation failed to modify the down-regulation of 5-HT2 receptor binding sites produced by continuous gepirone administration. These results suggest that the curious dissociation of behavioral and biochemical indices of 5-HT2 receptor function produced by continuous gepirone treatment may be the result of a dual yet separate action of the drug on central presynaptic noradrenergic and serotonergic mechanisms and postsynaptic 5-HT receptors. Furthermore, the postsynaptic action of gepirone which reduces the maximal number of cortical 5-HT2 receptor binding sites may be the result of gepirone's agonist action at postsynaptic 5-HT1A receptors.

The anti-aggressive drug eltoprazine preferentially binds to 5-HT1A and 5-HT1B receptor subtypes in rat brain: sensitivity to guanine nucleotides

Eltoprazine (DU 28853) inhibits offensive aggressive behaviour in several animal species. We characterized the binding of radiolabelled eltoprazine in rat brain by autoradiography. [3H]Eltoprazine displayed saturable and high-affinity binding to several brain areas, including the basal ganglia, hippocampal formation and cerebral cortex (Kd values ranging from 4.2 to 9.5 nM). The maximal binding capacities (Bmax) for [3H]eltoprazine were similar to those for [3H]5-HT and were highest in the substantia nigra and subiculum. Competition with eltoprazine for [3H]ligand binding to the various 5-HT1 receptor subtypes revealed preferential binding to 5-HT1A (IC50 values ranging from 42 to 50 nM) and 5-HT1B (IC50 values ranging from 25 to 38 nM) recognition sites. The drug had moderate affinity for 5-HT1C sites (IC50 = 282 nM). Addition of GTP or its stable analogue Gpp(NH)p to the radioligand assay caused a marked reduction (50-90%) in both [3H]eltoprazine and [3H]5-HT binding. These effects were substantially less in the choroid plexus. The binding of the antagonist (-)[125I]Iodocyanopindolol ([125I]ICYP) to 5-HT1B recognition sites, as quantified in the subiculum and substantia nigra, was either unaltered or slightly enhanced by the addition of 10(-3) M GTP. Furthermore, GTP did not affect the competition for [125I]ICYP binding by the 5-HT1-antagonist methiothepin, whereas it did significantly reduce the displacement by eltoprazine, resulting in an almost twofold increase in IC50 values. The data indicate that the anti-aggressive drug eltoprazine preferentially binds to 5-HT1A and 5-HT1B receptor sites and that this interaction is modulated by guanine nucleotides.

Cortisol and growth hormone responses to the 5-HT1A agonist gepirone in depressed patients

The 5-HT1A agonist properties of gepirone were used to test for effects on serum cortisol levels in humans, 90 min after a 10 mg oral dose. Fourteen patients with major depression were tested in a single-blind, within-subjects, placebo design. Serum cortisol levels were significantly higher 90 min after gepirone compared to placebo (p less than 0.05). Baseline Hamilton depression ratings were correlated with the serum cortisol levels after acute administration of gepirone (r = 0.54, p less than 0.05), but not placebo. Cortisol levels after a 10 mg gepirone challenge were significantly (p less than 0.02) attenuated after 3-6 weeks chronic administration of gepirone. These preliminary findings suggest that relatively low doses of gepirone may stimulate human cortisol secretion in depressed patients, and cortisol levels after gepirone challenge may correlate with depression severity. Furthermore, a desensitization to gepirone's effects on cortisol may occur after chronic gepirone administration.

The involvement of 5-hydroxytryptaminergic and dopaminergic mechanisms in the eating induced by buspirone, gepirone and ipsapirone

1. The roles of 5-hydroxytryptamine (5-HT) and dopamine systems in mediating the increased feeding induced by buspirone, gepirone and ipsapirone were investigated. 2. All three compounds induced dose-dependent increases in food intake when administered subcutaneously to free feeding rats. Buspirone was effective over a narrower dose range than either gepirone or ipsapirone, and the maximal effect observed was smaller than the effects elicited by gepirone and ipsapirone. 3. Depletion of brain 5-HT with parachlorophenylalanine (PCPA) prevented the effects of equi-effective doses of gepirone (2.5 mg kg-1) and ipsapirone (2.5 mg kg-1), but failed to prevent buspirone (1 mg kg-1)-induced eating. Thus buspirone does not appear to interact with 5-HT systems to elicit feeding. 4. Gepirone (0.2 micrograms) and ipsapirone (0.04 and 0.2 micrograms) increased food intake when injected into the dorsal raphé nucleus (DRN), presumably by inhibiting the activity of DRN 5-hydroxytryptaminergic afferents. Buspirone (0.04-5 micrograms) was ineffective when injected into the DRN. 5. Pretreatment with haloperidol (0.1 mg kg-1, 30 min) significantly attenuated the effects of equi-effective doses of buspirone, gepirone and ipsapirone, indicating that these drugs interact with dopaminergic systems to increase feeding. 6. Previously it has been shown that each of these drugs increases striatal dopamine activity. Increased dopaminergic neurotransmission in the striatum induces a general behavioural activation, which under certain conditions facilitates feeding. It is possible that this mechanism underlies the behavioural effects of buspirone, gepirone and ipsapirone. The effects of gepirone and ipsapirone probably involve an indirect action to inhibit the activity of DRN 5-hydroxytryptaminergic afferents, whereas buspirone interacts directly with dopaminergic systems.

Ipsapirone and 1-(2-pyrimidinyl)-piperazine increase rat locus coeruleus noradrenergic activity

The effects of systemically administered ipsapirone, an aryl-piperazine compound, and its major metabolite 1-(2-pyrimidinyl)-piperazine (1-PP), on locus coeruleus (LC) noradrenergic activity was investigated. On an equimolar basis both ipsapirone and 1-PP were approximately equipotent in increasing LC neuronal activity. However, pretreatment with 1-PP caused a significantly greater parallel shift to the right of the dose response curve for the inhibitory action of the LC alpha 2-receptor agonist clonidine compared to ipsapirone. Biochemically, pretreatment with SKF 525A, a compound which prevents the formation of 1-PP from ipsapirone, diminished the ipsapirone-induced increase in MOPEG-SO4 levels in the brainstem and cortex. These data, together with the findings that 1-PP is more potent than ipsapirone in displacing 3H-clonidine from cerebral cortical membranes, suggest that the parent drug influences LC neuronal activity via the action of I-PP on LC alpha 2-adrenoceptors.

Antidepressant-anxiolytic interactions: involvement of the benzodiazepine-GABA and serotonin systems

1. Recent studies have demonstrated that antidepressant drugs are actually more effective than BZ's in the treatment of anxiety states. The role of two major neurochemical substrates that may be implicated in the anxiolytic activity of antidepressants, the benzodiazepine (BZ)-GABA receptor chloride ionophore complex and central serotonergic pathways, are focused on in this review. 2. A wide range of antidepressants elicit a reduction in BZ receptors and display anxiolytic effects within a conflict paradigm. 3. The anxiolytic activity of antidepressants, however, does not appear to be mediated via the BZ receptor, but possibly via another component of the complex such as the chloride channel-associated with the GABAA receptor. 4. Additionally, as possible candidates for the mechanism of anxiolytic activity of these compounds, results of pharmacological, behavioral and clinical studies point to the importance of serotonin (5-HT)1A receptors and 5-HT transporter sites as targets for the action of antidepressants, triazolobenzodiazepines and anxioselective piperazine derivatives.

Antidepressant-like activity of ipsapirone, buspirone and gepirone in the forced swimming test in rats pretreated with proadifen

The antidepressant-like activity of ipsapirone, buspirone and gepirone was studied in rats in the forced swimming test (behavioural despair test). lpsapirone and buspirone administered in single doses (5-20 mg/kg) did not affect the immobility time in this test. When administered in the same doses in a three-injection course in 24 h, buspirone was also inactive, while ipsapirone slightly but significantly reduced the immobility time only after a dose of 5 mg/kg. On the other hand, gepirone administered both in single doses (2.5-20 mg/kg) and in a three-injection course (5-20 mg/kg) potently and dose-dependently shortened the immobility time. 1-(2-Pyrimidinyl)-piperazine (1-PP; 5-20 mg/kg), a common metabolite of all the three drugs, administered in single doses or in a three-injection course, was inactive in the forced swimming test. In rats pretreated with proadifen (50 mg/kg), a non-selective drug metabolism inhibitor, both ipsapirone and buspirone administered in single doses (5-20 mg/kg) reduced the immobility time in a dose-dependent manner. Proadifen also potentiated the anti-immobility effect of gepirone (5 and 10 mg/kg). The anti-immobility effect of single doses (20 mg/kg) of ipsapirone, buspirone and gepirone in proadifen-pretreated animals was completely abolished by 1-PP (4 mg/kg). These results indicate that the antidepressant-like activity of the examined drugs in the behavioural despairtest is masked (ipsapirone, buspirone) or attenuated (gepirone) by their metabolite 1-PP.

Central serotonergic function in parasuicide

1. Central 5-HT is thought to be involved in neuronal inhibition and as such as a modulating influence in restraining the organism from responding to (e.g., especially adverse) stimuli. 2. Evidence for a role of central 5-HT in suicide arises from reduced concentrations of brain 5-HT or 5-HIAA in brain stem, reduced binding of [3-H]-IMI in brain tissue of frontal cortex/hypothalamus, and increased binding of radioligands to 5-HT-2 receptors in the frontal cortex. 3. Evidence for a role of central 5-HT in parasuicide arises from reduced concentrations of lumbar CSF 5-HIAA, reduced PRL responses to d,l-fenfluramine challenge, and increased CORT responses to 5-HTP challenge. 4. Since reduced central 5-HT activity appears to be consistently associated with impulsive aggression, it is possible that suicidal and parasuicidal acts in individuals with evidence of reduced central 5-HT activity are a manifestation of reduced impulse control. 5. Agents which enhance central 5-HT function and/or diminish the activity of neuronal systems involved in arousal (e.g. norepinephrine or dopamine) should be efficacious in reducing parasuicidal behavior.

Quantitative autoradiographic distribution and pharmacological characterization of (3H)buspirone binding to sections from rat, bovine and marmoset brain

(3H)Buspirone binds with high affinity (KD = 11 nM) to sections from rat striatum. Spiroperidol, chlorpromazine, (+)-butaclamol and apomorphine are the most potent inhibitors of (3H)buspirone binding. Ketanserin, SCH 23390, serotonin and phentolamine are clearly less active. The regional distribution of (3H)buspirone binding in rat and marmoset brain is characterized by high silver grain densities in the olfactory tubercle, nucleus accumbens and striatum. In the hypophysis, the pars intermedia is strongly labeled. Within the hippocampal formation, slightly higher binding site densities are found in the dentate gyrus. The distribution pattern of binding sites in the dentate gyrus varies according to the species investigated. The data presented in this study permit the conclusion that (3H)buspirone binds with high affinity to dopamine 2 receptors but do not exclude additional binding to other types of receptors, e.g. 5-HT1 receptors. The interaction of buspirone with dopamine 2 receptors may be mainly responsible for its pharmacological profile.

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.

Effects of the putative anxiolytic SM-3997 on central monoaminergic systems

The effects of SM-3997 on central monoaminergic systems were evaluated by ex vivo measurement of monoamines and their metabolite levels in rat brain after intraperitoneal treatment of drugs and by in vitro measurement of monoamine uptake into rat brain slices. The effects of SM-3997 were also compared with those of other new nonbenzodiazepine anxiolytic compounds. SM-3997, buspirone, gepirone and ipsapirone showed no effects on serotonin uptake and dopamine uptake, and a weak inhibition of norepinephrine uptake at the concentration of 100 microM. SM-3997 decreased the serotonin metabolite (5-hydroxyindole-3-acetic acid) level without changing the serotonin level in hippocampus and increased dopamine metabolite (3,4-dihydroxyphenylacetic acid, homovanillic acid) level with no effect on the dopamine level in striatum. SM-3997 also produced an increase in the norepinephrine metabolite (3-methoxy-4-hydroxyphenylglycol) level with a decrease in the norepinephrine levels in hippocampus. Similar effects on serotonin metabolites and norepinephrine metabolites were observed in several other regions. Although the serotonergic effect of SM-3997 was similar to that of buspirone, gepirone and ipsapirone, the dopaminergic effect of SM-3997 was much weaker than that of buspirone.

Effects of microgravity on brain neurotransmitter receptors

Neurotransmitter receptor binding and Na+, K+-ATPase activity were examined in the brains of six rats exposed to 7 days of microgravity during the flight of Spacelab 3. The same variables were examined in a group of six ground control rats. 5-HT1 receptor number in the hippocampus was significantly elevated by exposure to the microgravity environment, and cortical sodium-potassium pump activity was significantly depressed. A marginal depression in dopamine D-2 binding in the striatum was noted. Dopamine and 5-HT binding in a wide variety of other central regions, in addition to GABAA, muscarinic acetylcholine, adenosine A1, and opiate receptor binding, and adrenoceptor binding, was unaffected by microgravity exposure.

5-HT1 agonists reduce 5-hydroxytryptamine release in rat hippocampus in vivo as determined by brain microdialysis

1. An intracerebral perfusion method, brain microdialysis, was used to assess changes of 5-hydroxytryptamine (5-HT) release in the ventral hippocampus of the chloral hydrate-anaesthetized rat in response to systemic administration of a variety of 5-HT1 receptor agonists. 2. A stable output of reliably detectable endogenous 5-HT was measured in dialysates collected from ventral hippocampus with the 5-HT reuptake inhibitor, citalopram, present in the perfusion medium. 3. Under these conditions the putative 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) caused a dose-dependent (5-250 micrograms kg-1, s.c.) reduction of 5-HT in hippocampal dialysates. 4. Similarly, the putative 5-HT1A agonists gepirone (5 mg kg-1, s.c.), ipsapirone (5 mg kg-1, s.c.) and buspirone (5 mg kg-1, s.c.) markedly reduced levels of 5-HT in hippocampal perfusates whereas their common metabolite 1-(2-pyrimidinyl) piperazine (5 mg kg-1, s.c.), which does not bind to central 5-HT1A recognition sites, had no effect. 5. 5-Methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969), a drug with reported high affinity for brain 5-HT1B binding sites, also produced a dose-dependent (0.25-5 mg kg-1, s.c.) decrease of hippocampal 5-HT output. 6. These data are direct biochemical evidence that systemically administered putative 5-HT1A and 5-HT1B agonists markedly inhibit 5-HT release in rat ventral hippocampus in vivo.

Effects of classical and atypical antipsychotic drugs on isolation-induced aggression in male mice

A series of classical, atypical and putative antipsychotic drugs were compared for their ability to inhibit isolation-induced intraspecies aggression with affinity for D-2 dopamine receptors and induction of akinesia. The majority of drugs tested significantly inhibited aggressive behavior only after doses that greatly decreased the ability of mice to move. Even though akinesia seemed to account for inhibition of aggression there was no apparent correlation with binding to striatal D-2 receptors.