Effects of acute and subchronic administration of propranolol on the social behaviour of mice; an ethopharmacological study

Maternal defense is modulated by beta adrenergic receptors in lateral septum in mice

Maternal defense (offspring protection) is a critical and highly conserved component of maternal care in mammalian systems that involves dramatic shifts in a female's behavioral response to social cues. Numerous changes occur in neuronal signaling and connectivity in the postpartum female, including decreases in norepinephrine (NE) signaling in subregions of the CNS. In this study using a strain of mice selected for maternal defense, we examined whether possible changes in NE signaling in the lateral septum (LS) could facilitate expression of maternal aggression. In separate studies that utilized a repeated measures design, mice were tested for maternal defense following intra-LS injections of either the β-adrenergic receptor agonist isoproterenol (10 μg or 30 μg) or vehicle (Experiment 1), the β-adrenergic receptor antagonist propranolol (2 μg) or vehicle (Experiment 2), or the β1-receptor antagonist, atenolol (Experiment 3). Mice were also evaluated for light-dark performance and pup retrieval. Thirty micrograms of the agonist isoproterenol significantly decreased number of attacks and time aggressive relative to vehicle without affecting pup retrieval or light-dark box performance. In contrast, the antagonist propranolol significantly increased maternal aggression (lowered latency to attack and increased total attack time) without altering light-dark box test. The β1-specific antagonist, atenolol, significantly decreased latency to attack (1 μg vs. vehicle) without altering other measures. Although the findings were identified in a unique strain of mice, the results of these studies support the hypothesis that changes in NE signaling in LS during the postpartum period contribute to the expression of offspring protection.

Social isolation and expression of serotonergic neurotransmission-related genes in several brain areas of male mice

Early-life events influence brain development and evoke long-lasting behavioral consequences. Postweaning social isolation in rodents induces emotional and neurochemical alterations similar to those observed among some human psychopathologies. Central serotonergic neurotransmission is intimately involved in the observed adjustments, but the impact of social deprivation on serotonergic gene expression is unknown. We investigated the effects of prolonged early social isolation on emotion-related behaviors and 5-hydroxytryptamine (5-HT)-related gene transcription in mice. After weaning, male C57BL/6J mice were reared singly or in groups of four for 6 weeks. Gene expression of 5-HT(1A), 5-HT(1B), 5-HT(2A), 5-HT(2C), 5-HT(3A), 5-HT(6) and 5-HT(7) receptors and of 5-HT transporter and tryptophan hydroxylase-2 was determined by quantitative real-time polymerase chain reaction in distinct brain areas. Single-housed mice were hyperactive in a novel environment and showed signs of aggressive behavior. Housing condition did not alter weight gain or body temperature. Isolation markedly reduced transcription of all postsynaptic 5-HT receptors in the prefrontal cortex and reduced 5-HT(1B), 5-HT(2A) and 5-HT(2C) in both hypothalamus and midbrain. In contrast, the only alteration in the hippocampus was 5-HT(6) overexpression. Neither 5-HT transporter nor synthetic enzyme gene transcription differed between housing conditions. In conclusion, early social isolation in mice induces robust changes in postsynaptic 5-HT receptors gene transcription, motor hyperactivity and behavioral disinhibition. The overall pattern of decreased gene expression in the prefrontal cortex highlights its high vulnerability to environment. Furthermore, this is the first study to present a general representation of 5-HT-related gene expression in specific brain areas after social isolation and identifies novel candidates that may be critical for underlying molecular mechanisms.

Adrenergic transmission facilitates extinction of conditional fear in mice

Extinction of classically conditioned fear, like its acquisition, is active learning, but little is known about its molecular mechanisms. We recently reported that temporal massing of conditional stimulus (CS) presentations improves extinction memory acquisition, and suggested that temporal spacing was less effective because individual CS exposures trigger two opposing processes: (1) fear extinction, which is favored by CS massing, and (2) fear incubation (increase), which is favored by spacing. We here report the effects of manipulating the adrenergic system during massed or spaced CS presentations in fear-conditioned mice. We administered yohimbine (5 mg/kg), an alpha(2)-receptor antagonist, or propranolol (10 mg/kg), a beta-receptor antagonist, systemically prior to CS presentation sessions and recorded both short- and long-term changes in conditional freezing. Yohimbine treatment facilitated extinction of both cue and context fear with massed protocols. When given before spaced CS presentations, propranolol led to a persistent incubation of cue fear, whereas yohimbine led to persistent extinction, compared with vehicle-treated animals, which showed no change in fear. These results suggest that norepinephrine positively modulates the formation of fear extinction memories in mice. They also provide clear evidence that spaced CS presentations trigger both fear-reducing (extinction) and fear-increasing (incubation) mechanisms.

Measurement of anxiety in transgenic mice

A wide range of approaches has been used to study anxiety in mice. All presuppose that aversive stimuli, such as foot shock or novelty, induce a central state of fear, which can be quantified through specific behavioural and physiological measures. This review discusses the validity of the various approaches in terms of their similarity to different human anxiety disorders, their ability to detect compounds which modulate human anxiety, and their relevance to animal defensive processes. The most commonly used models of anxiety suitable for screening transgenic and knockout mice are discussed, with an emphasis placed on controlling for factors which could confound results. As all models used to date have limitations and no single paradigm adequately models all aspects of anxiety, this review recommends the use of a broad range of anxiety models in order to provide a comprehensive characterisation of the behavioural phenotype of transgenic mice.

Pharmacological evaluation of a modified open-field test sensitive to anxiolytic drugs

In a recent study it has been shown that benzodiazepine receptor agonists attenuate novelty-induced suppression of feeding and increase the percentage of animals feeding in the open field. Food-deprived rats were placed in one corner of the open field containing food in the center. The number of rats beginning to eat in the first 5 min was recorded. In the present study this test was validated pharmacologically using known "anxiolytic" or "nonanxiolytic" drugs. The following substances (effective doses, given IP) increased the number of rats feeding within 5 min in the center of the open field: meprobamate (30.0-300 mg/kg), 8-OH-DPAT (10 and 30 microg/kg), ipsapirone (1.0 and 2.0 mg/kg), ritanserin (0.125-0.5 mg/kg), tropisetron (0.1-10.0 microg/kg), ondansetron (0.3-3.0 microg/kg), lisuride (0.28-0.55 mg/kg), morphine (0.3 and 1.0 mg/kg), propranolol (0.3 and 1.0 mg/kg), clozapine (1.0 mg/kg). Drugs without "anxiolytic" effects in other animal models or in humans, including amphetamine, apomorphine, haloperidol, sulpiride, and mCPP did not increase the incidence of food intake in this test. Ethanol and hexobarbital, in nonsedative doses, had no effect in this paradigm. Drugs and doses effective in the modified open-field test caused no increase in food intake in an independent food consumption test using food-deprived rats staying in the familiar cages. The results suggest that the modified open-field test can detect "anxiolytic" drug properties and is valid for the assessment of "anxiolytic" effects from different classes of drugs.

5-Hydroxytryptamine-interacting drugs in animal models of anxiety disorders: more than 30 years of research

An overview of the behavioral data arising from the vast literature concerning the involvement of 5-hydroxytryptamine (5-HT) neurotransmission in the regulation of anxiety is presented. More than 1300 experiments were carried out in this area and they provide evidence that: (1) results obtained in ethologically based animal models of anxiety with drugs stimulating 5-HT transmission are most consistent with the classic 5-HT hypothesis of anxiety in that they show an increase in animals' emotional reactivity; (2) no category of anti-anxiety models are selectively sensitive to the anxiolytic-like effects of drugs targetting 5-HT1A, 5-HT2A or 5-HT2C receptor subtypes; (3) anxiolytic-like effects of 5-HT3 receptor antagonists, in the great part, are revealed by models based on spontaneous behaviors. Taken together, these observations lead to the conclusion that different 5-HT mechanisms, mediated by different receptor subtypes, are involved in the genesis of anxiety.

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.

Ethological study of the effects of tetrahydroaminoacridine (THA) on social recognition in rats

Two major difficulties confront ethopharmacological investigations on cognitive abilities such as social recognition in drug-treated animals involved in free social interactions. The first concerns the choice of the most relevant behaviours, those reflecting the cognitive abilities attributed to the animals and assessing the specificity of the drug activity, and those reflecting non-specific drug effects. The second refers to the experimenter's awareness that in contrast to physical objects, social stimuli respond to drug-treated subjects and that their own level of responsiveness may influence the changes of drug-treated subjects' social interest. In addition, their contribution may vary according to the different treatments the drug-treated subjects receive. In examining the effects of tetrahydroaminoacridine (THA) at doses of 0.3, 1 and 3 mg/kg on the ability of adult male rats to recognize previously encountered conspecifics, we attempted to take into consideration such difficulties. A detailed behavioural profile of drug-treated rats was reported to separate specific from non-specific effects of THA. In addition, rats were assigned an index of responsibility for contact which takes into account the interactive dimension of each dyad and allows relevant comparisons between different treatments. The doses of THA which were found to decrease the duration of exploration of a familiar juvenile were also found to decrease the number of contacts initiated by the drug-treated subjects. THA induced a relative increase in body care by comparison to saline treatment. However, it had no effect of locomotor activity and rearing of the subjects. These findings enable dissociation of the effects of THA on cognitive versus non-cognitive processes.

Buspirone increases social investigation in pair-housed male mice; comparison with the effects of chlordiazepoxide

Effects of buspirone (1, 5 and 10 mg/kg, i.p.) on the behaviour of adult male CD1 mice have been compared with those of chlordiazepoxide (1, 4 and 8 mg/kg, i.p.). Commencing at 30 min after injection, the behaviour of each mouse was examined by ethological procedures during 5 min social encounters with an untreated partner in the animal's home cage and in the more aversive situation of an unfamiliar neutral cage. In both test environments, buspirone at 1 and 5 mg/kg and chlordiazepoxide (CDP) at 1 and 4 mg/kg increased social investigation and some of its constituent elements, while decreasing non-social activity and the element, "explore" (and for CDP, of "scanning" also). In both test environments, the increase of social investigation by buspirone and CDP was less marked at 10 and 8 mg/kg, respectively. For CDP, although not for buspirone, this effect was related to dose-dependent increases of immobility coupled with reductions of exploratory non-social activity and scanning below those occurring at the intermediate dose level. Buspirone at 5 mg/kg increased social investigation to a greater extent in the home cage (P < 0.01) than in the unfamiliar neutral cage (P < 0.05), whereas CDP was approximately equipotent in the two test situations. In the neutral cage, buspirone at all dose levels showed an additional effect of increasing the time spent by the mice in digging, whereas chlordiazepoxide dose-dependently increased aggression. These results indicate anxiolytic activity by both compounds after acute administration, and identify certain differences in the profile of their other effects on social behaviour.

Effects of quinpirole on the behaviour shown by mice in the light-dark box and during social interactions

Quinpirole (0.25, 0.5 and 1.0 mg/kg) was administered by intraperitoneal injection to pair-housed adult DBA/2 mice. Controls received injections of physiological saline. Effects on behaviour during 5 min social encounters with untreated partners were examined by ethological procedures, commencing at 30 min after injection. Behaviour was examined in an aversive and less aversive situation, an unfamiliar neutral cage and the home cage. Behavioural effects were then assessed in a two-compartment black and white test box. Quinpirole dose-dependently increased the frequency and duration of flight, including the specific element "retreat". At 0.5 mg/kg, the element, "freeze", was also increased during encounters in the neutral cage. Immobility (a flaccid sitting posture) and sniffing of the substrate were increased by quinpirole to a similar extent at all dose levels, while non-social activity and social investigation were reduced. The significance of the effects of quinpirole in the home cage and neutral cage were qualitatively similar; the only quantitative differences were a greater enhancement of the duration of immobility and the frequency of substrate sniffing in the home cage. In the light-dark box, quinpirole reduced the number of transitions between light and dark compartments and decreased line crossings and scans/unit time in the light compartment, although it increased the amount of time in the light compartment into which mice had been originally placed. The induction of immobility and decrease of several active behavioural responses may arise from a D2 autoreceptor inhibition of locomotor activity.(ABSTRACT TRUNCATED AT 250 WORDS)