Ethopharmacological studies on the effects of antihormones on rodent agonistic behavior with especial emphasis on progesterone.

The effects of a range of antiandrogens and antiestrogens on conflict behaviors in laboratory rats and mice are reassessed in the light of recent studies applying ethophamacological analyses (recording the full spectrum of behaviors) to such investigations. It is argued that any antihostility properties of the antiandrogen cyproterone acetate are largely a consequence of indirect actions on odor communication, whereas antiestrogens (e.g., tamoxifen and CI 680) seem to have more fundamental motivational effects in addition to communicatory actions. A detailed example of the approach is provided in which progesterone (which can be antiandrogenic) is given to rats paired in different ways. The type of pairing has a very substantial effect on the actions seen after treatment, and the ethopharmacological approach generates a better picture of antihormone effect than traditional psychopharmacological tests.

A brief review comparing the effects of sex steroids on two forms of aggression in laboratory mice.

This brief review examines the roles of sex steroids in two forms of "aggression" in laboratory mice. The social conflict induced in male mice by individual housing or reproductive experience was contrasted with the attack shown by small groups of female mice on lactating intruders. Gonadectomy of males largely abolishes the former response but actually augments the latter activity in male subjects. Testosterone, estradiol and 5 alpha-dihydrotestosterone all restore social conflict in gonadectomized male mice but these sex steroids inhibit attack on lactating female intruders by gonadectomized males. The data clearly confirm that there is no simple relationship between a particular hormone and "aggression." These forms of attack may serve very different functions even though they involve similar action patterns and distributions of bites on the attacked animal. A tentative discussion is included about the roles of these activities.

The effects of 5-HT receptor ligands on ultrasonic calling in mouse pups.

The influence of a range of drugs acting at various 5-HT receptor sites on the ultrasonic calling of mouse pups was assessed. Calling was decreased by the novel anxiolytics buspirone, ipsapirone and gepirone, and by TFMPP, spiperone, ritanserin and GR 38032F. In contrast, 8-OH-DPAT, DOI and quipazine increased the rate of calling. These effects on ultrasonic calling were independent of sedative or thermoregulatory actions of these drugs. Present data provide further support for the view that ultrasonic calling can be used to assess novel compounds for possible anxiolytic or anxiogenic properties.

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

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

Comparison of the influence of the opiate delta receptor antagonist, ICI 154,129, and naloxone on social interaction and behaviour in an open field.

The influence of a novel opiate delta receptor antagonist, ICI 154,129, and naloxone on social interaction and on behaviour in an open field were compared. At a dose thought to optimally block the delta receptor, ICI 154,129 produced open field behaviour typical of a non-emotional animal: this drug decreased social investigation and the latency to attack. In contrast, naloxone was largely without effect in these tests.

Hormonal and neurochemical correlates of various forms of animal "aggression".

The majority of studies attempting to evaluate the roles of hormones and neurochemicals in "aggression" concern laboratory rodents, notably rats and mice, with fewer investigations on infrahuman primates. Studies suggest that situations used to assess aggression (e.g., social conflict tests, parental attack, predatory behavior, use of unavoidable electroshock) actually tap a diverse range of motivations whose functions include offense, defense and predation. It is also apparent that ethoexperimental techniques, i.e., those applying ethological methodologies and concepts to laboratory situations, have advantages in assessing the direct and indirect consequences of chemical treatments. In this review, the impacts of hormonal manipulation (by surgery and/or application) and varying neurotransmitters (studied in terms of regional changes and as consequences of drug treatments) on a variety of forms of behavior are assessed. Different tests do show varying responses to common treatments, confirming the heterogeneity of the available paradigms. A brief discussion is provided of which tests are likely to prove most relevant to clinical studies.

Relating testosterone levels and free play social behavior in male and female preschool children.

This study assessed potential relationships between a series of behavioral measures seen in the interactions of preschool children with their peers (particularly aggressive behavior) and testosterone levels. 28 boys and 20 girls of preschool age were videotaped in free play interactions. Their behavior was then evaluated with particular emphasis on aggression and affiliation in play and social interactions. Testosterone levels were measured using radioimmunoassay in saliva samples. Correlation analysis revealed a positive relationship in boys between testosterone and giving and receiving aggression in the context of 'social interactions' (serious aggression), but not in the context of play (playful aggresstion). Testosterone can be a useful biological marker for serious aggression (and behavioral patterns reflecting different levels of sociability) in preschool boys.

Effects of chronic mild stress (CMS) and imipramine administration, on spleen mononuclear cell proliferative response, serum corticosterone level and brain norepinephrine content in male mice.

There is increasing evidence that stress and emotional reactions produce changes in various immune processes. These changes may be due to alterations of the stress responses endocrine and for autonomic mediating mechanisms. In order to study such effects, the impact of chronic mild stress (CMS) application, and of subsequent imipramine administration were studied on the spleen mononuclear cell proliferative response period. OFI strain male mice were subjected to 4 or 7 weeks of CMS. The effects of these treatments on serum corticosterone levels and hypothalamic and hippocampal norepinephrine (NE) contents were also assessed. Subjects submitted to CMS had a higher spleen mononuclear cell proliferative response after either treatment duration. Imipramine treatment diminished this response enhancement in CMS exposed animals, but did not alter the proliferative responses of control subjects. Serum corticosterone levels, as well as hypothalamic and hippocampal nonrepinephrine contents did not significantly vary between groups. Taken together, these results suggest that CMSs effects on immune reactivity are not related to serum glucocorticoids or NE changes in these locations associated with the hypothalamic-pituitary- adrenocortical (HPA) axis.

Comparison in the mouse of the effect of the opiate delta receptor antagonist ICI 154129 and naloxone in tests of extinction, passive avoidance and food intake.

The effects of 30 and 80 mg/kg ICI 154,129, an opiate delta receptor antagonist, were compared with those of 0.1 and 10 mg/kg naloxone using tests of food-intake, passive avoidance and extinction in mice. Whereas naloxone depressed food intake and facilitated extinction, ICI 154,129 failed to affect food intake, passive avoidance or extinction although the mice reared significantly more during the test of food intake.

Attenuation of sucrose consumption in mice by chronic mild stress and its restoration by imipramine.

Chronic exposure to mild unpredictable stressors (CMS) has previously been found to reduce the consumption of palatable, sweet solutions in rats. In the present study, the utility of this procedure was assessed in mice. Male AP mice subjected to CMS showed reduced consumption of a 2% or 4% sucrose solution. This effect was reversed by chronic (3 weeks) treatment with the tricyclic antidepressant imipramine (20 mg/kg per day). These results extend previous reports of a generalized decrease in sensitivity to reward (anhedonia) in rats caused by CMS and the efficacy of antidepressant treatment in this paradigm. Chronic unpredictable mild stress in mice appears to provide a realistic animal model of depression.

Preferential occupation of mineralocorticoid receptors by corticosterone enhances glutamate-induced burst firing in rat midbrain dopaminergic neurons.

Sensitisation to the behavioural effects of amphetamine, a phenomenon which appears to involve the potentiation of excitatory amino acid (EAA)-mediated transmission at the level of dopaminergic (DA) neurons in the ventral tegmental area (the A10 cell group), is known to be affected by corticosteroid manipulations. Since there is evidence that corticosteroid manipulations can also influence unpotentiated EAA-mediated transmission elsewhere in the brain, the possibility was examined that the same may be true for midbrain DA neurons. The effect of iontophoretically administered glutamate on the activity of A10 DA neurons was investigated in adrenalectomised animals given a low dose of corticosterone intravenously (equivalent to 13.4 micrograms/100 ml plasma - likely to preferentially occupy the mineralocorticoid subtype of corticosteroid receptor) at least 45 min (median 132.5) prior to recording. Cells from these animals were compared to those from adrenalectomised and sham operated animals administered saline. Adrenalectomy significantly reduced the firing rate of A10 cells, and this effect was reversed by corticosterone replacement. Adrenalectomy did not affect basal burst firing. However, in those cells which could be classified as "bursting' under basal conditions, cells from animals administered corticosterone showed enhanced glutamate-induced bursting relative to the other two groups. The degree of enhancement was strictly determined by the basal bursting level of the cell. Since the distinction between "bursting' and "non-bursting' DA neurons is probably not related to differences at the level of the EAA receptor/effector mediating bursting, it is argued that corticosterone's facilitation of glutamate-induced bursting is not produced at this level, but rather at the level of an intrinsic membrane property which modulates bursting.

Prenatal caffeine exposure modifies behavioural responses in mice.

Caffeine was given to pregnant mice subcutaneously at doses of 10 and 40mg/kg body weight, on the last four days of pregnancy. Subsequently, effects on the behaviour of their cross-fostered male offspring were studied using the "standard opponent" test. Significant decreases in threat, attack, displacement and number of fights, as well as an increase in latency to attack, were observed in the offspring exposed to the higher dose. Thus, excessive consumption of caffeine during pregnancy appears to have a lasting influence on the behaviour of offspring via a direct in utero action.

The effects of compounds acting at the benzodiazepine receptor complex on the ultrasonic calling of mouse pups.

The influence of a range of drugs acting at the benzodiazepine - GABA receptor - chloride ion complex on the ultrasonic calling of mouse pups was examined. Five benzodiazepine agonists decreased, and four inverse agonists increased, the rate of calling; both effects were blocked by the benzodiazepine antagonist RO 15-1788. Muscimol and baclofen, that act via the GABA receptor, both decreased calling, whereas pentylenetetrazole that directly affects the chloride channel increased the rate of calling. It was concluded that the monitoring of ultrasonic calling is a useful means of screening for the effects of benzodiazepines.

An ethological analysis of the effects of diazepam and nitrazepam on the responses of female mice to anosmic males encountered in a novel arena.

The effects of acutely administered benzodiazepines have largely been validated in male animals, in spite of the fact that the majority of anti-anxiety drugs are prescribed for female patients. A study was carried out assessing the potential of female mice in the testing of the anxiolytic properties of drugs. Three doses (0.5, 1.0 and 2.0mg/kg) of the benzodiazepines diazepam and nitrazepam were given to individually-housed female Swiss mice before dyadic encounters with anosmic, group-housed males. Videotape analysis of the encounters, using an ethopharmacological technique, revealed suppressive effects of diazepam (1.0 and 2.0mg/kg) and nitrazepam (all doses) on avoidance/flee, confirming the anxiolytic properties of these drugs. However, some doses of diazepam (2.0mg/kg) and nitrazepam (1.0mg/kg), greatly increased immobility with little effect on active behavioural elements. It is suggested that "immobility" does not simply measure sedation.

Steroid hormone-induced effects on membrane fluidity and their potential roles in non-genomic mechanisms.

Steroid hormones are lipophilic suggesting they intercalate into the bilayer of target cell plasma membranes, potentially altering the fluidity and function of the membrane. The present study measured the effects of steroidal exposure on both phospholipid fluidity and integral protein mobility. Studies were performed on the effects of a variety of steroids on phosphatidylcholine liposomes, synaptosomal plasma membranes and sarcoplasmic reticulum membranes. Progesterone decreased the lipid fluidity, whereas testosterone had no effect on lipid movement. The estrogen, 17 beta-estradiol, an aromatised metabolite of testosterone, increased lipid mobility. In each case, the steroid action was concentration-dependent. The steroids all increased the activity of the Ca2+ ATPase of SR membrane, in keeping with their effects on this enzyme's aggregation state. The results suggest that, although lipid fluidity is a factor influencing protein activity, their mobility within the bilayer is the primary determinant of enzyme activity in the membrane for most proteins.

The effects of differential housing, castration and steroidal hormone replacement on attacks directed by resident mice towards lactating intruders.

Group-housed castrated (but not intact) males show high incidences of attack on lactating (but not non-lactating) female intruders. In Experiment 1, responses by isolated and group (in 3's)-housed intact and castrated males to lactating intruders were studied. The latter males were given sham, testosterone (T) or estradiol (E2) implants before testing. Castration augmented attack by animals in both housing conditions, confirming that intra-group fighting could not account for androgen-related changes in fighting behaviour in group-housed animals. Both T and E2 implants suppressed attack in animals in both housing conditions. Consequently, Experiment 2 evaluated the influence of three dose levels of T, E2 and DHT (dihydrotestosterone), in attack by castrated group-housed male residents on lactating intruders. Treatment of castrated males with T or E2 (but not DHT) inhibited attack in these animals. These findings provide support for the idea that aromatization is also a prerequisite for the inhibitory action of T on male aggression towards lactating females.

Effect of predatory stress on sucrose intake and behavior on the plus-maze in male mice.

In this study, the effect of the exposure of male mice to sensory stimuli from rats was assessed on both sucrose intake and the elevated plus-maze tests. CDl male mice were trained in the sucrose intake task (the prestress phase) and, subsequently, distributed into two groups. The stressed group was accommodated in the same room as rats and the control group with mice (the stress phase). After being transferred, animals were tested on sucrose intake and the plus-maze (acute tests) and retested three times a week for sucrose intake and once on plus-maze on the last day (chronic tests). After acute exposure to the predator, the only difference between stressed and control animals was a higher number of fecal boli left on the plus-maze by the former. During the chronic phase, stressed animals showed a lower level of sucrose intake and higher level of anxiety than controls. In conclusion, this study shows that chronic exposure of male mice to stimuli from rats reduces the sensitivity to the rewarding properties of sucrose and prevents the habituation to the plus-maze observed in controls. Thus, this study suggests that exposure of mice to sensory stimuli from rats may provide an animal model of stress, and that these species should not be routinely housed together.

Comparisons of the influence of morphine sulphate, morphine-3-glucuronide and tifluadom on social encounters in mice.

The influences of morphine sulphate, morphine-3-glucuronide and tifluadom on social encounters were compared in male and female mice that were allowed to interact with an anosmic male partner. The drugs were compared, as morphine sulphate is thought to act via mu, and tifluadom via kappa opiate receptors; morphine-3-glucuronide is the breakdown product of morphine. Neither morphine sulphate nor morphine-3-glucuronide significantly influenced inter-male social encounters. However, tifluadom increased non-social and decreased social behaviour, while increasing timid/defensive activities. Tifluadom did not significantly influence the behaviour of female mice in this social encounter: in contrast both morphine sulphate and morphine-3-glucuronide decreased timid/defensive behaviour and stimulated non-social behaviour. It was concluded that the results could be explained by suggesting that morphine sulphate decreases whereas tifluadom increases timidity.

Aggression in female mice: contrasting effects of amiflamine (FLA 336), a selective and reversible MAO-type A inhibitor.

The effects of FLA 336 on the attack by resident groups of female mice on strange female intruders were assessed. This MAO-type A inhibitor clearly suppressed attack in treated subjects without producing major alterations in other activities but there was no clear dose-response relationship. The substance also increased attack on treated animals, an effect largely mediated via changes in the odor characteristics of the urine. The data emphasize the need for appropriate controls in studies with psychoactive compounds to distinguish direct (CNS-mediated) from indirect (mediated via changed signalling or perception) actions.

Substrate soiled by an unfamiliar conspecific modifies opioid activity in mice placed in novel environments.

Naloxone induces behavioural changes in rodents exposed to novel environments, indicating the involvement of endogenous opioid mechanisms in these situations. The present study investigated whether soiled sawdust substrate from the cage of an unfamiliar, isolated, male conspecific modifies the effect of naloxone (0.5 or 12.5 mg/kg) upon behaviour of mice in an open field test situation. There was little difference between the effects of naloxone upon the frequency of acts or postures shown in the soiled and unsoiled environments. Cluster analysis of the activities according to their position and frequency in behavioural sequences, revealed variations in behavioural organisation in these two situations in control animals, and differential responses to naloxone administration. The data are discussed in terms of an involvement in behaviour of opioid mechanisms which can be modified by non-painful, biologically-relevant, aversive stimuli such as unfamiliar, conspecific-soiled substrates.