BEHAVIORAL-RESPONSES OF BICUCCULLINE METHIODIDE INJECTIONS INTO THE VENTRAL HYPOTHALAMUS OF FREELY MOVING, SOCIALLY INTERACTING RATS

Several studies, using electrical stimulation of parts of the hypothal amus, have shown, that different parts of the hypothalamus yield diffe rent behavioural responses upon stimulation. In order to differentiate between stimulation of neuronal cell bodies and passing fibres and to investigate the role of GABA in hypothalamically elicited behaviour, 25 local injections with bicucculline methiodide, a GABA antagonist, ( 35 ng/0.2 mul) were performed in the ventral parts of the hypothalamus of 16 freely moving rats in a social environment. A cannula system wa s used that allowed injection without interruption of the ongoing soci al interactions. Digging, gnawing, drinking and attack behaviour were elicited in different animals. By plotting the behavioural responses o f the animals into a detailed hypothalamic atlas, we assessed the hypo thalamic distribution of the elicited behavioural responses. A number of injections elicited a combination of two or three different respons es, probably due to diffusion of the substance, thus disinhibiting mor e than one behavioural system. Our results are in general agreement wi th previous electrical stimulation data and show that, in an overlappi ng pattern, different populations of neurons are involved in the elici tation of digging, gnawing, drinking and attack behaviour. In the hypo thalamus, a tonic GABAergic inhibition of neurons involved in the disp lay of these types of behaviour appears to exist.