Behavioural responses of bicucculline methiodide injections into the ventral hypothalamus of freely moving, socially interacting rats.

Several studies, using electrical stimulation of parts of the hypothalamus, have shown, that different parts of the hypothalamus yield different 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 microliter) were performed in the ventral parts of the hypothalamus of 16 freely moving rats in a social environment. A cannula system was used that allowed injection without interruption of the ongoing social interactions. Digging, gnawing, drinking and attack behaviour were elicited in different animals. By plotting the behavioural responses of the animals into a detailed hypothalamic atlas, we assessed the hypothalamic distribution of the elicited behavioural responses. A number of injections elicited a combination of two or three different responses, probably due to diffusion of the substance, thus disinhibiting more than one behavioural system. Our results are in general agreement with previous electrical stimulation data and show that, in an overlapping pattern, different populations of neurons are involved in the elicitation of digging, gnawing, drinking and attack behaviour. In the hypothalamus, a tonic GABAergic inhibition of neurons involved in the display of these types of behaviour appears to exist.