Gabaergic modulation of mouse-killing in the rat

GABA and behavior: the role of receptor subtypes

The discovery of different GABA receptor subtypes has stimulated research relating this neurotransmitter to a variety of behavioral functions and clinical disorders. The development of new and specific GABAergic compounds has made it possible to try to identify the specific functions of these receptors. The purpose of the present review is to evaluate the data regarding the functions of the GABA receptor subtypes in different behaviors such as motor function, reproduction, learning and memory, and aggressive-defensive behaviors. A description of GABAergic functions (stress, peripheral effects, thermoregulation) that might directly or indirectly affect behavior is also included. The possible involvement of GABA in different neurological and psychiatric disorders is also discussed. Although much research has been done trying to identify the possible role of GABA in different behaviors, the role of receptor subtypes has only recently attracted attention, and only preliminary data are available at present. It is therefore evident that still much work has to be done before a clear picture of the behavioral significance of these receptor subtypes can be obtained. Nevertheless, existing data are sufficient to justify the prediction that GABAergic agents, in the near future, will be much used in the field of behavioral pharmacology. It is hoped that the present review will contribute to this. Some specific suggestions concerning the most efficient way to pursue future research are also made.

The aggression theory of schizophrenia: revisited

The aggression theory of schizophrenia is a psychoanalytic theory which proposes that schizophrenia results from uncontrolled, deprivation-induced aggressive impulses. An animal model of the aggression theory is presented using predatory aggression as the source of arousal. Although neurochemical control of predatory aggression is nonspecific, anatomic control is located in the lateral hypothalamus across species. The lateral hypothalamus also controls schedule-induced polydipsia which has been implicated in schizophrenia. The aggression theory could be empirically evaluated by determining if schizophrenics respond differently than normals to scheduled feedings. Implications of the aggression theory are discussed.

Increased GABAA-dependent chloride uptake in mice selectively bred for low aggressive behavior

Selective breeding for aggressive behavior alters GABA-dependent chloride uptake and behavioral response to benzodiazepine treatment. Pharmacological and biochemical studies examined subjects from three lines of adult male ICR mice selectively bred for either high levels or low levels of aggressive behavior, as well as unselected controls. Selective breeding produced two lines of behaviorally distinct males. During 5-min dyadic confrontations with an outbred stimulus animal, untreated low-aggressive mice spent more time in walking, rearing, and social interaction than untreated high-aggressive mice. The three lines also showed different responsiveness to the aggression increasing and decreasing effects as well as the sedative effects of benzodiazepine treatment. High doses of chlordiazepoxide (17, 30 mg/kg) reduced motor behaviors (walk, rear and groom) in the low-aggressive line without altering these behaviors in the high aggressive line. In the high-aggressive line, the same doses of chlordiazepoxide (17, 30 mg/kg) produced a behavioral shift; aggressive behaviors were reduced while social behaviors increased to levels similar to the untreated low-aggressive line. In contrast, only the unselected line pursued and threatened more after a low dose of chlordiazepoxide (3 mg/kg). The three lines also showed alterations at the GABAA-benzodiazepine receptor complex. Specific uptake of [3H]Ro-15-1788 was increased in cerebral cortex, hypothalamus and hippocampus in the low-aggressive line, and was reduced in these areas in high-aggressive line when compared with unselected controls. Similarly, GABA-dependent chloride uptake in cortical synaptoneurosomes was augmented in low-aggressive mice and decreased in high-aggressive mice when compared to unselected controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential and limitations of the offense-defense dichotomy in aggression research, considering the complex and evolving interactions of biological, psychological and social determinants of aggression

The offense-defense dichotomy undeniably proved to be of heuristic interest in that it allowed relevant distinctions between specific behaviour patterns, to establish correlations between situations in which either "offensive" or "defensive" patterns are likely to be displayed, and to uncover differential drug effects on those distinct behavior patterns. But for a number of reasons, the author is led to conclude that even though the offense-defense dichotomy indeed helps in many instances to describe and to distinguish, it has rather limited potential really to explain in depth what it distinguishes at a phenomenological level of investigation.

Evidence that activation of GABA receptors in the substantia nigra suppresses spontaneous spike-and-wave discharges in the rat

The involvement of intranigral gamma-aminobutyric acid (GABA) receptors in the control of generalized non-convulsive epilepsy was investigated in a genetically determined model of petit mal epilepsy in the rat. Bilateral intranigral injection of muscimol (2 ng/0.2 microliter/side), a GABA agonist, significantly suppressed EEG-recorded spike-and-wave discharges for about 80 min, both at the cortical and thalamic levels. This suppressive effect was shown to be dose-dependent, reproduced by bilateral intranigral injections of 4,5,6,7-tetrahydro-isoxazolo [5,4-c]pyridin 3-ol (THIP), another GABA agonist, and reversed by a subsequent intranigral injection of bicuculline methiodide, a GABA antagonist. In addition, the anti-absence effects of bilateral intranigral injections of muscimol were well localized to the substantia nigra. Bilateral intranigral injections of GABA antagonists per se had no effects on the discharges. These results demonstrate that activation of GABA receptors in the substantia nigra suppresses the occurrence of spike-and-wave discharges in an animal model of generalized non-convulsive epilepsy. The results are compared to data obtained in models of generalized convulsive epilepsy and the hypothesis of nigral GABAergic mechanisms as a control system for generalized epilepsies is discussed.

Effects of the potentiation of the GABAergic neurotransmission in the olfactory bulbs on mouse-killing behavior

Intra olfactory bulb administration of three classes of GABA-mimetics (GABAa agonists, inhibitors of reuptake, inhibitors of GABA degradation) clearly inhibit mouse-killing behavior, without sedation. A linear correlation is observed between GABA levels increase in the olfactory bulbs and muricidal inhibition following local injection of valproic acid and gamma-vinyl GABA, two GABA-T inhibitors; the differences observed between these two compounds may be due to the differences in their mechanism of action on GABA-T activity and to the different pool of GABA on which they act. No diffusion to extra bulbar sites were observed after local administration of gamma-vinyl GABA. This evidence suggests an inhibitory role of GABA from olfactory bulbs in the modulation of mouse-killing behavior.

Effect of GABAergic drugs in the behavioral 'despair' test in rats

Aminooxyacetic acid (AOAA, 25 mg/kg i.p.), muscimol (2 mg/kg i.p.) and 4,5,6,7-tetrahydroisooxazol-[4,5-c]-pyridin-3-ol (THIP, 5 and 10 mg/kg s.c.), but not baclofen (10 mg/kg i.p.) administered three times (24, 5 and 1 h before the test) decreased the immobility time of rats in the behavioral 'despair' test. At these doses, AOAA, muscimol and THIP reduced motor activity. Muscimol (2 mg/kg) and THIP (5 and 10 mg/kg) exerted the antiimmobility effect even after single dosing 1 h before the test. Picrotoxin (1 and 2 mg/kg i.p.), but not bicuculline (2 mg/kg i.p.), prevented the effect of both muscimol and THIP in the behavioral 'despair' test.

Elicitation of conspecific attack or defense in the male rat by intraventricular injection of a GABA agonist or antagonist

The involvement of central GABAergic mechanisms in the control over offensive and defensive behaviours in the rat was studied using intracerebroventricular injections (5 microliter) of a GABA agonist (THIP) or a GABA antagonist (bicuculline methiodide). Intracerebroventricular injections of THIP (1.25 and 2.5 micrograms) induced attacks and offensive sideways towards an untreated partner, in animals placed in a neutral area where no aggressive reactions occur in controls. Social approach behaviours (partner investigation, allogrooming) were also increased in both attacking and non-attacking animals, whereas individual behaviours (cage exploration, autogrooming, immobile posture) were decreased. Inversely, intracerebroventricular injections of bicuculline methiodide (62.5 and 125 ng) suppressed offensive items (attacks, offensive sideways, upright postures) in resident animals confronted with untreated intruders and increased occurrence of defensive sideways. This treatment also decreased reactions oriented towards the partner (investigation, allogrooming and crawl under/over), while increasing individual behaviours (cage exploration, immobile posture). These data demonstrate that activation of central GABA receptors elicits intraspecific offensive behaviours in the rat. On the contrary, blockage of these receptors induces defensive reactions and suppresses offensive behaviours. The involvement of these receptors in the neural control over aggressive behaviour in the rat is discussed.