AGGRESSIVE EXPERIENCE AFFECTS THE SENSITIVITY OF NEURONS TOWARDS PHARMACOLOGICAL TREATMENT IN THE HYPOTHALAMIC ATTACK AREA

Early investigators of brain stimulation-evoked complex behaviours (at tack, escape, feeding, self-grooming, sexual behaviour) reported that experience may affect the behavioural outcome of brain stimulation. Th is intriguing example of functional neuronal plasticity was later tota lly neglected. The present experiment investigated the behavioural out come of in vivo microdialysis perfusion of the glutamate agonist kaina te and/or the GABA(A) antagonist bicuculline into the hypothalamic att ack area (HAA) of (1) animals naive to dyadic encounters; (2) animals with a recent aggressive experience (the probe being implanted 6-24 h after the last of a series of dyadic encounters); and (3) animals with an earlier aggressive experience (probe being implanted 2 weeks after the last aggressive experience). On the experimental day, rats receiv ed two 5-min infusions during a dyadic encounter lasting 35 min with a n unknown opponent. Flow rate was 1.5-2 mu l/min, drug concentrations were 1.8 x 10(-5) and 1.5 x 10(-5) M for kainate and bicuculline, resp ectively. Behaviour,vas analysed before, during and after perfusions. Only the combined kainate + bicuculline treatment had significant effe cts on behaviour at the doses studied. A significant increase in aggre ssive behaviour was elicited only in animals with a recent aggressive experience, while naive animals and animals with an earlier experience responded to the treatments by grooming. These results appear to supp ort early observations indicating that one important aspect of brain s timulation effects is previous experience. Behav Pharmacol 1998; 9:469 -475 (C) 1998 Lippincott Williams & Wilkins.