A possible olfactory component in the effects of diazepam on social behavior of mice

Effects of anesthetic agents on socially transmitted olfactory memories in mice

Mice can learn a food preference from odor cues transmitted on the breath of a conspecific, even if the "demonstrator" is anesthetized. To our knowledge there are no studies examining the effect of anesthetizing the "observer" on development of memory for socially transmitted food preferences (STFP). In Experiment 1 we found that 2-4 month-old F2 C57Bl/6x129sv male and female mice demonstrated a STFP after a 5min exposure to an anesthetized demonstrator mouse when tested 24h later. In Experiment 2, observer mice anesthetized with Sagatal (60 mg/kg) prior to the "social interaction" preferentially avoided the cued food when tested 24h later. This aversion was not due to any overt aversive effects of this dose of Sagatal because mice that ate the food and were then anesthetized, or could only smell the food for 5 min while anesthetized, showed no preference or aversion. In a third experiment we found that the Sagatal-induced aversion was not a general property of anesthesia because there were varied results produced by observer mice treated with anesthetic drugs with different mechanisms of action. Vetalar (200mg/kg) and Rompun (10 mg/kg) treated animals ate similar amounts of cued and non-cued food at test, indicating an absence of learning. Hypnorm (0.5 ml/kg) treated animals showed a preference for the cued food whereas those treated with Hypnovel (2.5 ml/kg) showed an aversion to the cued food. These results show that the food aversion observed with Sagatal is not a general property of anesthetic agents, but appears to be restricted to those acting primarily on the GABAergic system. Thus, we have shown that under certain conditions it is possible for an anesthetized observer mouse to learn a preference or aversion of a socially-linked olfactory cue.

Mean genes and the biology of aggression: a critical review of recent animal and human research

Recent genetic work has suggested that abnormalities in serotonin biochemistry are directly causally linked to aggressive behavior, and there appears to be a consensus in the psychiatric literature that low levels of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid are specifically associated with impulsive violent behavior. We review the limitations of the genetic studies and conduct a meta-analysis of 39 studies linking 5-HIAA to aggression in humans. No differences in mean 5-HIAA levels were found between groups of violent impulsive psychiatric patients and groups of subjects diagnosed with other psychiatric or medical conditions not considered to involve violence once these levels had been corrected for three nonpsychiatric sources of variation (age, sex and height). However, mean 5-HIAA levels in both of these groups were lower than the mean corrected level in groups of normal healthy volunteers. The results confirm an association between low 5-HIAA levels and psychiatric disorders, but fail to support any specific relationship between low 5-HIAA levels and impulsive aggression or criminality. It is premature and misleading to speak of "mean genes" (Hen 1996) or a specific neurochemistry of aggressive behavior.

Effects of acute and chronic administration of the antidepressants, imipramine, phenelzine and mianserin, on the social behaviour of mice

Effects of imipramine, phenelzine and mianserin on the behaviour of male CDl mice were examined after a single intraperitoneal injection (imipramine, 15.8 and 63.2 mumol/kg; phenelzine, 1 and 8 mumol/kg); mianserin, 0.12 and 0.48 mumol/kg) and after administration for 12-16 days in the drinking fluid (mean daily intake; imipramine, 15.8 and 63.2 mumol/kg; phenelzine, 1 and 8 mumol/kg; mianserin, 0.12, 0.48 and 1.92 mumol/kg). Behaviour was examined by ethological procedures during 5 min encounters with an untreated partner in a familiar situation, the animal's home cage, and in the more aversive environment of an unfamiliar cage. At 30 min after injection, the higher doses of acutely administered imipramine and mianserin decreased aggressive behaviour in the unfamiliar cage. In the home cage, effects of mianserin were only slight, whereas imipramine reduced social investigation at the larger dose and in both test environments decreased digging. Phenelzine increased social investigation in both environments. After chronic administration, each of the drugs increased social investigation in the neutral cage and home cage at some of the dose levels, indicating potential anxiolytic efficacy. Mianserin showed the additional effect of enhancing digging during tests in the neutral cage, which may correlate with its anxiolytic actions. Phenelzine was the only antidepressant to increase aggression during encounters in the neutral cage after chronic administration. The significance of these findings is discussed.

Effects of eltoprazine hydrochloride on reactivity to conspecific or novel odors and activity

Treatment with eltoprazine (DU 28853) increased the number of entries by male mice into compartments containing the odors of male and female conspecifics. This effect was most pronounced when odors were provided by previously defeated males. In contrast, the drug had no effect upon responsiveness to the odors of cinnamon and chocolate. The results suggest that eltoprazine may selectively increase reactivity to conspecific odors and that this effect is further enhanced by agonistic experience. Eltoprazine also substantially increased activity levels in all experiments. Since hyperactivity occurred both in the presence and absence of conspecific odors, however, the drug's effects on activity and olfaction seem to be largely independent. The results suggest that the aggression-modulating effects of eltoprazine, as well as other drugs, may be mediated in part by their effects on normal olfactory function.

Effects of yohimbine on isolation-induced aggression, social attraction, and conspecific odor preference in mice

Yohimbine treatment inhibited isolation-induced attack in mice but had no effect on defense. The drug also increased social distances and produced a transient decrease in preference for conspecific male odors. The antiaggressive actions of yohimbine parallel those reported for the anxiogenic beta-carbolines and for phenylpiperazine "serenic" agents. The results emphasize the importance of supplementing conspecific agonistic encounters with additional behavioral measures such as nonagonistic social attraction in evaluating antiaggressive drugs. The decreased responsiveness to conspecific odors seen in Experiment 3 also suggests that increased conspecific avoidance may be mediated, in part at least, by altered olfactory processes.

Ethopharmacology: a historical perspective

Ethopharmacology can be defined as the study of behavioral and other effects of drugs through the use of ethological concepts. The study of drug effects on natural action patterns (motor acts and postures listed in ethograms), with respect to natural settings and to behavior as a whole (all identifiable behaviors occurring during the measurement) represents the basic concepts of ethopharmacology. Although pioneers drew attention to the potential of the ethological approach in pharmacology in the early 1960s, the number of publications utilizing this approach has steadily grown only since the mid-1970s. In the 1980s, modern technology, such as videorecorders, microcomputers and software, has been more widely applied in ethopharmacological experiments, greatly facilitating the observation and quantitative analysis of multiple data. Ethopharmacology is not "another" behavioral pharmacology, but an integral part of it. Rather, it represents one of the tools which can be useful (and sometimes even indispensable) in achieving a better understanding of the behavioral effects of drugs. It is to be hoped that it will be used in concert with other approaches in the future.

An ethological study of the effects of buspirone and the 5-HT3 receptor antagonist, BRL 43694 (granisetron) on behaviour during social interactions in female and male mice

Buspirone (12.8 mg/l; 2.3-2.6 mg/kg daily) and the 5-HT3 receptor antagonist, BRL 43694 (granisetron) (40 micrograms/l; 10 micrograms/kg daily), were each given in drinking fluid to male and female DBA/2 mice for 5-10 days. Controls received tap water. Effects on behaviour were examined by ethological procedures during 5 min encounters with unfamiliar BKW partners. One group of DBA/2 males acted as intruders in a resident-intruder paradigm and another group encountered oestrous females in a neutral cage. The DBA/2 females each encountered a group-housed male in a neutral cage. Both buspirone and BRL 43694 decreased flight in females and increased the duration of their active social investigation. In females, BRL 43694 also reduced the occurrence of "scan" and prolonged the bout length of exploration. In male mice, buspirone increased social investigation, including the specific elements "sniff" and "follow" in encounters with female partners, but its only effect on behaviour during encounters with isolated resident males, was to decrease duration of the element, "attend". In males, BRL 43694 did not significantly affect behaviour in heterosexual encounters and had only a slight effect on behaviour during encounters with resident males, decreasing the occurrence of "eat". Overall, these results suggest that records of effects of drugs on flight responses of female mice, in encounters with male partners, may provide a sensitive index of the anxiolytic profile of novel compounds.

Opposite effects of agonist and inverse agonist ligands of benzodiazepine receptor on self-defensive and submissive postures in the rat

The effects of benzodiazepine receptor ligands on different types of defensive behaviours were examined in intruder male rats confronted with offensive residents. Chronic administration, via a subcutaneous silastic pellet, of a full agonist (diazepam) for 15 days increased self-defensive postures as well as social and non-social behaviour whereas submissive postures and flight were reduced. Acute administration of a partial agonist (ZK 91296) resulted in a similar increase in self-defensive postures and a decrease of submission and non-social elements. Acute administration of a partial inverse agonist (FG 7142) reduced defensive postures and social behaviour whereas submissive postures were increased. These results show that activation of benzodiazepine receptors by full or partial agonists increased self-defensive responses to attacks by a conspecific, while decreasing submissive postures. On the contrary, "inverse activation" of these receptors by an inverse agonist increased submissive postures while decreasing self-defensive responses. These data suggest that benzodiazepine receptors are involved in the control of the animal's strategy to respond to an attack of another rat.

Behavioural pharmacology of the serenic, eltoprazine

In this paper the effects of serenics (eltoprazine and fluprazine) are described in several animal models for offensive agonistic, defensive agonistic and predatory behaviour. They are compared with the effects of a number of other putative anti-aggressive compounds or drugs used clinically in order to ameliorate aggressive behaviour of psychiatric patients. In isolation-induced offensive aggression in mice, eltoprazine has a marked and potent anti-aggressive activity, although numerous other psychoactive drugs also exert anti-aggressive effects. The behavioural specificity of this anti-aggressive profile was investigated using an ethologically derived animal model, social interaction in male mice. In this model, eltoprazine has a very specific anti-aggressive (serenic) profile, inhibiting aggression while social interaction and exploration are not decreased but even enhanced; inactivity, a measure for sedation, is not affected. Such a profile contrasts sharply with that of neuroleptics (chlorpromazine, haloperidol), psychostimulants (d-amphetamine) or benzodiazepines (chlordiazepoxide), which exert severe sedation (neuroleptics) or even aggression-enhancing effects (BDZ). After subchronic treatment no tolerance for the anti-aggressive effects of eltoprazine occurred. The specific anti-aggressive effects of eltoprazine were also found in rat models of offensive agonistic behaviour. In one such model - resident-intruder aggression - eltoprazine reduced offensive behaviour specifically, leaving social interactions and exploration intact, and did not induce sedation or other unwanted side-effects. The neuroleptic haloperidol was very sedative in this model, as was the 5-HT1A-agonist buspirone. Benzodiazepines (chlordiazepoxide) have a biphasic effect in this paradigm, enhancing offence at low doses and decreasing it at higher doses, due to muscle relaxation. In another offensive model, colony-aggression, in which a dominant and subordinate male in a colony are confronted with a male intruder, eltoprazine reduced offensive behaviour of both the dominant and the subordinate against the intruder. In contrast, chlordiazepoxide enhanced aggression, at least at lower doses, whereas alcohol had, up to very high doses, no effect on the offensive behaviour. In a brain-stimulation induced offensive model--hypothalamically-induced aggression in rats--eltoprazine specifically reduces offence. Locomotion, a measure for sedation, was either unaffected or even somewhat enhanced, indicating the absence of any sedatory activity of this serenic compound. In contrast, haloperidol heavily sedated animals, making them incapable of aggression.(ABSTRACT TRUNCATED AT 400 WORDS)

The potential anxiolytic activity of GR38032F, a 5-HT3-receptor antagonist

1. The highly selective 5-HT3-receptor antagonist, GR38032F, has been tested in five animal models predictive for anxiolytic activity. 2. In the social interaction test in the rat and in a light/dark exploration test in the mouse, GR38032F dose-dependently released suppressed behaviour without modifying locomotor activity. 3. In the cynomolgus monkey and the marmoset, GR38032F reduced anxiety-related symptoms without causing sedation. In the marmoset, the effects were clearly dose-related. 4. GR38032F did not have any detectable activity in the water-lick conflict test in the rat. 5. We conclude that GR38032F is potentially a very potent anxiolytic agent without sedative, anticonvulsant or hypnotic activity.

Agonistic behavior patterns in mice with streptozotocin-induced diabetes mellitus

To examine the effects of the altered metabolic and hormonal state of diabetes mellitus on rodent social behavior, male Swiss Webster mice made diabetic with streptozotocin were tested in a resident-intruder encounter. Isolated diabetic and control mice were introduced as intruders into the home cages of aggression-trained resident mice. The encounters were videotaped and analyzed for frequencies and durations of agonistic behavior. Diabetic mice responded to the aggression of resident mice with significantly less investigation and aggression and significantly more static defense and escape behaviors than did control mice. Resident mice responded to less aggressive diabetic mice with more aggression and social investigation. Plasma corticosterone levels were significantly higher in diabetic mice compared to controls and positively correlated with submissive behavior in diabetic mice. These findings indicate that social behavior is altered in male diabetic mice and support the hypothesis that elevated pituitary-adrenal cortical activity and/or metabolic changes affect behavior in male diabetic mice.

Benzodiazepines and their antagonists: a pharmacoethological analysis with particular reference to effects on "aggression"

A review of the literature on chlordiazepoxide indicates that the traditional view of benzodiazepines as antiaggressive drugs represents an inaccurate generalization. In fact, highly variable findings have been reported with the most significant factor in the variability being the type of aggression studied. Furthermore, considerable controversy surrounds the nature of chlordiazepoxide's influence on social conflict in rodents, with opinion divided regarding the selectivity of its inhibitory effect on offensive responding. It is argued that inappropriate behavioural methodology may have substantially contributed to this controversy. A pharmacoethological approach to the analysis of drug effects on social behaviour is described and exemplified by new data on chlordiazepoxide and midazolam. Both agents inhibit offense at doses which do not result in general response inhibition, yet their overall behavioural profiles are somewhat different. Evidence is also presented indicating low dose behavioural activity of the benzodiazepine antagonist Ro15-1788 in two test situations and suggesting possible differences in the effects of Ro15-1788 and CGS8216 on novelty-related responding. Several avenues of research are discussed which may yield insights into the manner whereby benzodiazepines influence social patterns and the significance of benzodiazepine-GABA interactions in such processes.

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

Animal models for the study of anxiolytic agents are reviewed and evaluated according to pharmacological and behavioral criteria. Although there are important exceptions, in general, most early animal models have not provided a reliable basis for identifying compounds with potential anxiolytic action, or for delineating the mechanisms of anxiolytic drug action. The possibility that phylogenetically 'prepared' forms of defensive learning might serve as a basis for the study of anxiolytic agents is introduced.

Effects of the benzodiazepine antagonist Ro 15-1788 on social and agonistic behaviour in male albino mice

In view of recently reported low-dose behavioural activity of Ro 15-1788, the present study examined the effects of this benzodiazepine antagonist on social and agonistic behaviours in adult male albino mice. Using a resident-intruder paradigm, independent pharmacological manipulation of interactants and pharmaco-ethological analysis, our data demonstrate significant behavioural effects of Ro 15-1788 in benzodiazepine-naive animals. In residents, treatment with the antagonist (1.25, 2.5, 10 and 20 mg/kg, IP) resulted in dose-related increases in offensive threat behaviour and reduced olfactory investigation. However, 5 mg/kg exerted no detectable behavioural action in these animals. In intruders, behavioural effects were observed only with 1.25 mg/kg Ro 15-1788, and consisted of a profile suggestive of reduced defensiveness. In both experiments, the behaviour of untreated opponents confirmed the existence of drug-induced behavioural changes in their partners. It is argued that present data are not inconsistent with the existence of putative endogenous benzodiazepine-like ligands and that the differential effects of Ro 15-1788 in residents (singly-housed) and intruders (grouped) suggest one possible explanation for previous failures to detect low-dose behavioural activity with this compound.

Heightened aggressive behavior by animals interacting with alcohol-treated conspecifics: studies with mice, rats and squirrel monkeys

Drug-free mice, rats and squirrel monkeys showed more aggression toward alcohol-treated conspecifics than under control conditions. Quantitative ethological analysis was used to assess the dose-dependent effects of ethyl alcohol on a range of aggressive, submissive, defensive, escape responses as well as on non-agonistic behavior such as associative responses, grooming, and locomotor activities. Two experimental situations were studied: resident-intruder confrontations in mice and rats, and interactions between members of established groups of squirrel monkeys. After PO administration of ethyl alcohol to intruder mice and rats, the non-drugged resident mice and rats attacked, threatened, and pursued intruders at higher frequencies during 5-min encounters. Similarly, subordinate squirrel monkeys who were members of three established groups, when given alcohol, were grasped, displaced, and displayed to more frequently by non-drugged group members than after water control injections during the first 40 min after injection. This change in aggressive behavior by non-drugged animals was related to the alcohol dose given to the intruder or subordinate animal; near-ataxic alcohol doses (3.0 g/kg in mice, 1.7 g/kg in rats, 1.0 g/kg in squirrel monkeys) altered the behavior of animals whose prevalent pattern is defensive and submissive so that they were the subject of most frequent and intense aggression.

Prenatal treatment with clomipramine: effects on the behaviour of male and female adolescent rats

The tricyclic anti-depressant clomipramine (7.5 or 15 mg/kg/day) was administered to pregnant rats between days 8 and 21 of gestation. Between postnatal days 31 and 47, both male and female offspring received three behavioural test. Prenatal clomipramine (15 mg/kg/day) increased baseline acoustic startle in females, but not in males; both sexes showed greater between-day response decrements if they had received clomipramine. In the social interaction test of anxiety, males prenatally exposed to clomipramine (both dosages), and females prenatally exposed to 7.5 mg/kg/day, revealed a similar profile to that seen after chronic administration of benzodiazepines in the adult. The likelihood that differences in within-session habituation could underlie the changes in social interaction that have been found in this and other studies is assessed.

Sodium valproate: effects on social behaviour and physical development in the mouse

Sodium valproate given in drinking fluid at 600 mg/l (160-180 mg/kg daily) to breeding mice did not affect fertility, birth weights or physical development of pups. Postnatal and postweaning administration of this dose also had no effects upon development or weight gain. The offspring ingested 103-158 mg/kg valproate daily after weaning. Behaviour was examined in a neutral enclosure by ethological methods. Offspring exposed to valproate in utero and throughout postnatal life showed no behavioural changes at 5 weeks, although at 15 weeks Immobility was reduced in females and Social Investigation increased. At 25 weeks when encountering mice of the opposite sex, treated males showed increase in Social Investigation and treated females increases in Other Non-social Activity. Postnatal and postweaning treatment with valproate caused behavioural changes both in juveniles and adults. After postnatal exposure, reduced Immobility with increased Social Investigation and Explore and Scan occurred at 5 and 15 weeks, at 25 weeks valproate increased Social Investigation in males encountering females and at 30 weeks enhanced Aggression in pair-housed males. Stimulation of Social Investigation was the only significant behavioural effect after postweaning exposure. Overall valproate appears to enhance behaviour stimulated by the test situation; urinary pheromones do not appear to play a part in this behavioural action.

Habituation of aggression in mice: pharmacological evidence of catecholaminergic and serotonergic mediation

A pharmacological study was undertaken to evaluate the role of catecholamines and serotonin in the mediation of aggression. The dose-effect relationship of d-amphetamine, apomorphine, methysergide, lisuride, and the time-dependent effects of 10 mg/kg p-chloroamphetamine (PCA) were determined on aggressive behavior in a habituation paradigm. The frequency of attacks and sideways threats exponentially declined in ten consecutive confrontations between resident and intruder mice, and recovered when a new intruder was introduced. d-Amphetamine (0.1-5.0 mg/kg) and apomorphine (0.03-1.0 mg/kg), administered IP 5 min before the first confrontation, attenuated the usual decline of attack and threat in subsequent trials. PCA enhanced attack, sideways threat, and locomotion at day 1 after injection. Methysergide (1, 3, 10 mg/kg) and lisuride (0.03, 0.3, 1.0 mg/kg) suppressed all activity, including locomotion and aggression. The data support the hypothesis that catecholamines mediate the activation of aggression, but do not indicate an inhibitory role for serotonin. Aggression in the resident-intruder paradigm appears to require intact serotonin activity.