Psychotropic effects of adrenergic beta-blockers on agonistic behavior between resident and intruder mice

Selective increase of dark phase water intake in neuropeptide-Y Y2 and Y4 receptor knockout mice

Neuropeptide-Y (NPY) is involved in the regulation of ingestive behaviour and energy homeostasis. Since deletion of the NPY Y2 and Y4 receptor gene increases and decreases food intake, respectively, we examined whether water intake during the light and dark phases is altered in Y2 and Y4 receptor knockout mice. The water consumption of mice staying in their home cages was measured by weighing the water bottles at the beginning and end of the light phase during 4 consecutive days. Control, Y2 and Y4 receptor knockout mice did not differ in their water intake during the light phase. However, during the dark phase Y2 and Y4 receptor knockout mice drank significantly more (46-63%, P<0.05) water than the control mice. The total daily water intake over 24 h was also enhanced. The enhanced water intake during the dark phase was not altered by the beta-adrenoceptor antagonist propranolol or the angiotensin AT1 receptor antagonist telmisartan (each injected intraperitoneally at 10 mg/kg). These data indicate that NPY acting via Y2 and Y4 receptors plays a distinctive role in the regulation of nocturnal water consumption. While beta-adrenoceptors and angiotensin AT1 receptors do not seem to be involved, water intake in Y2 and Y4 receptor knockout mice may be enhanced because presynaptic autoinhibition of NPY release and inhibition of orexin neurons in the central nervous system are prevented.

Neuropharmacology of brain-stimulation-evoked aggression

Evidence is reviewed concerning the brain areas and neurotransmitters involved in aggressive behavior in the cat and rodent. In the cat, two distinct neural circuits involving the hypothalamus and PAG subserve two different kinds of aggression: defensive rage and predatory (quiet-biting) attack. The roles played by the neurotransmitters serotonin, GABA, glutamate, opioids, cholecystokinin, substance P, norepinephrine, dopamine, and acetylcholine in the modulation and expression of aggression are discussed. For the rat, a single area, largely coincident with the intermediate hypothalamic area, is crucial for the expression of attack; variations in the rat attack response in natural settings are due largely to environmental variables. Experimental evidence emphasizing the roles of serotonin and GABA in modulating hypothalamically evoked attack in the rat is discussed. It is concluded that significant progress has been made concerning our knowledge of the circuitry underlying the neural basis of aggression. Although new and important insights have been made concerning neurotransmitter regulation of aggressive behavior, wide gaps in our knowledge remain.

The antiaggressive potency of (-)-penbutolol involves both 5-HT1A and 5-HT1B receptors and beta-adrenoceptors

The relative importance of 5-HT1A and beta-adrenergic activities in the antiaggressive effects of (-)-penbutolol was studied in male mice. (-)-Penbutolol had high affinity for 5-HT1A receptors and beta-adrenoceptors, and antagonized the 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)-induced 5-HT syndrome and the 8-hydroxy-2-(di-n-propylamin)tetralin (8-OH-DPAT)-induced discriminatory stimulus in rats. (-)-Penbutolol abolished aggressive behaviour (ED50 = 56 mumol/kg), and reversed the antiaggressive effects of 8-OH-DPAT and 1-(3-trifluoromethylphenyl)piperazine (TFMPP) (ED50 = 8.1 and 2.1 mumol/kg, respectively). (N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl-N-(2-pyridinyl) cyclohexanecarboxamide (WAY 100635) reversed the antiaggressive effects of 8-OH-DPAT (ED50 = 0.012 mumol/kg), but did not affect the antiaggressive effects of TFMPP. The antiaggressive effect of a submaximal dose of 8-OH-DPAT was markedly potentiated by beta-adrenoceptor antagonists without 5-HT1A receptor affinity, whereas (-)-penbutolol was effective at only one dose (4.5 mumol/kg). In conclusion, the 5-HT1A receptor antagonistic potency of (-)-penbutolol in aggressive mice is attenuated by beta-adrenoceptor-induced facilitation of serotonergic neurotransmission.

D-cycloserine enhances social behaviour in individually-housed mice in the resident-intruder test

D-Cycloserine (DCS) has been reported to affect the central nervous system in man. To investigate whether the compound produces specific behavioural effects, DCS was administered to male mice in a resident-intruder situation and the behaviour of the interacting mice assessed using ethological analysis. Resident mice given DCS (32.0-320.0 mg/kg PO, 60 min before testing) showed dose-dependent increases in social investigation, smaller increases in sexual behaviour and decreased aggressiveness. Defensive and flight behaviour were not affected. Intruder mice showed slight increases in sexual behaviour that were not dose-dependent, and small increases in social investigation. The increases in social investigation induced by DCS (320.0 mg/kg) in resident mice were not reversible with R-HA 966 (32.0 mg/kg IP, 30 min before testing), a blocker of the strychnine-insensitive glycine modulatory site associated with the N-methyl-D-aspartate receptor, but were blocked by the GABA antagonist bicuculline (0.56 mg/kg IP, 5 min before testing). The small DCS-induced increase in sexual behaviour in residents was reversed by R-HA 966. Within the parameters of the resident-intruder situation, DCS exerts socio-sexual behaviour-enhancing effects which are dependent upon the role of the interactant, and which are mediated by an action upon multiple substrates. DCS may be regarded as another example of a sociotropic (approach-promoting) agent.

Propranolol-induced increases in target-biting attack

The effect of a beta-adrenoreceptor blocking agent on defensive aggression in mice was evaluated. Acute doses of d,l-propranolol (0.2, 0.4, 0.8, 1.6, 3.2, 6.4, and 12.8 mg/kg) were administered to male Rockland-Swiss mice prior to testing in a target-biting paradigm. Baseline conditions established a high target-biting rate low biting rate during a 15-s tone stimulus preceding the next shock. Every dose of propranolol increased target-biting rates above baseline during each interval with one exception: 0.4 mg/kg decreased the biting rate immediately after delivery of the tail shock. The overall increase in aggression observed following dosing with propranolol was not expected from a review of the clinical literature. These results are discussed in reference to propranolol's known effects on the brain serotoninergic systems and the use of an animal model of defensive aggression.

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

The effects of dl-propranolol on the behaviour of adult male CD1 mice were examined after acute intraperitoneal injection (1.5 and 6 mg/kg) and after administration for 10-13 days in the drinking fluid at 12.4 mg/l (1.9 mg/kg daily) and 24.9 mg/l (4.6 mg/kg daily). The behaviour of each mouse was examined by ethological procedures during 5 min social encounters with an untreated partner in an aversive and a less aversive situation, an unfamiliar neutral cage and the animals' home cage. The behaviour of each mouse also was monitored for 5 min in the light-dark box. In the acute studies, behavioural observations commenced at 30 min after the injection. In the light-dark box, propranolol, after acute administration, increased the number of transitions between the light and dark compartments and increased scanning in the light area but propranolol had no significant effect after subchronic administration. In the home cage, propranolol significantly increased social investigation during social encounters and reduced exploratory activity at all doses tested, after both acute and subchronic administration. In the neutral cage, propranolol, after acute administration, increased digging of the sawdust and decreased exploratory activity at both dose levels, while at the largest dose it also increased social investigation. In the neutral cage, propranolol, given by subchronic administration, increased aggressive behaviour as well as social investigation and digging of the sawdust at both dose levels, while reducing non-social exploratory activity. The largest dose of propranolol also increased investigation of the substrate. These results indicate that propranolol increased reactivity to normal environmental and social stimuli, in addition to its anxiolytic profile of behavioural effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethopharmacology of copulatory disorder induced by chronic social conflict in male mice

The present study was designed to investigate how the experience of fighting affects copulatory behavior in male mice and also to determine the effect of naloxone on the interaction between social conflict and copulatory disorder. To generate intraspecific fighting a resident-intruder paradigm was employed. Agonistic confrontations were terminated after 10 or 20 attack bites, and were repeated for 5 consecutive days. Twenty-four hours after the last confrontation test, both resident and intruder mice were tested with estrus females for 10 min. Compared to the control group without agonistic confrontation, intruder mice that had been attacked repeatedly showed a significant reduction of copulatory behavior. In contrast, attacking resident mice showed a significant increase in copulatory behavior. Pretreatment with naloxone (1 and 3 mg/kg, IP) prior to daily fighting failed to antagonize defeat-induced copulatory disorder. It would, therefore, appear that endogenous opioid mechanism may not participate in this phenomenon.

Ethology and pharmacology of hypothalamic aggression in the rat

Stimulation of a restricted area of the rat's hypothalamus elicits unprovoked violent attacks of a species-specific and strain-specific nature. Serotonergic drugs affecting 5HT1 receptors, propranolol, the 5HT re-uptake inhibitor fluvoxamine, and the anxiolytic oxazepam, inhibit hypothalamic attack selectively. However, hypothalamic attack is extremely unsensitive for many drugs that do affect attack provoked by natural stimuli. The pharmacology, the form, the impulsive nature, the absence of preliminaries, the insensitivity for contexts and ultimate aims of aggressive behaviour, suggest that a mechanism with the limited function of damaging adversaries of any kind is activated in the hypothalamus. This hypothalamic attack release mechanism (harm) requires specific sensory input for the expression of specific motor components, such as biting and kicking. The back and dorsal part of the opponent's head are the important attack releasing and directing stimuli. Attacks of this nature are part of the "aggressive" repertoire of the rat in natural settings. "Lateral" or "sideways" postures, specific for intermale fighting cannot be induced by hypothalamic stimulation. Drug, lesion, and stimulation studies suggest that attack and "sideways" postures are under the control of different central mechanisms. These results suggest new ways to describe the patterning of aggressive behaviour. There are interesting ethopharmacological similarities between hypothalamic responses and obsessive compulsive disorders (OCD) in man. It is suggested that further study of the ethopharmacology of hypothalamic responses may shed light on the pathophysiology of impulsive behavioural symptoms which in man seem to be beyond the control of appraisal or context.

Alteration in hypnotic effect of pentobarbital following repeated agonistic confrontations in mice

We investigated how repeated agonistic confrontations affect the hypnotic effect of pentobarbital (PB) in male mice, using a resident-intruder paradigm. PB concentrations in the cortex, midbrain and brainstem were determined. Agonistic confrontations were terminated after 10 or 20 attack bites, and were repeated for 5 consecutive days. Immediately after the last encounter, PB (55 mg/kg, IP) was administered to both resident and intruder mice. Compared to the control group, intruders exposed to 20 daily attack bites showed a significant prolongation of the latency to sleep and a shortening of the duration of sleeping time. At the stage of induction, no significant difference in brain PB levels was found between the "defeated" and control intruders. At the stage of recovery, however, the "defeated" intruders showed a significantly low level of PB in all brain areas. In contrast, attacking resident mice did not show any significant changes in either the hypnotic effect or regional brain concentration of PB. Because pretreatment with naloxone prior to daily agonistic confrontation antagonized the alteration in PB-induced hypnosis, it seems that endogenous opioid mechanisms may participate in this phenomenon. The present study indicates that susceptibility to a hypnotic drug can be altered by chronic social conflict experience.

Psychotropic effects of ginseng saponins on agonistic behavior between resident and intruder mice

The psychotropic actions of crude ginseng saponins, pure ginsenoside Rb1 (GS-Rb1) and ginsenoside Rg1 (GS-Rg1) obtained from the root of Panax ginseng, were evaluated from their effects on agonistic behavior in mice. A resident-intruder test situation was used. When the resident mouse was treated with crude ginseng saponins (25, 50 and 100 mg/kg i.p.), aggressive episodes (offensive sideways posture and attack bite) were significantly suppressed in a dose-dependent manner. However, the agonistic behavior was not altered when the intruder was treated with crude ginseng saponins. GS-Rb1 (2.5, 5 ad 10 mg/kg i.p.) also significantly suppressed aggressive episodes when given to the resident, whereas GS-Rg1 (2.5, 5 and 10 mg/kg i.p.) was ineffective. Neither GS-Rb1 nor GS-Rg1 given to the intruder caused any significant changes in the behavior of the resident. Although the highest dose of crude ginseng saponins suppressed locomotion frequency, it appears that both crude ginseng saponins and GS-Rb1 possess a specific psychotropic action on agonistic behavior.