Responses evoked by stimulation of points in the diencephalon of unrestrained rabbits

Behavioural responses were obtained from unanaesthetized rabbits by stimulating the diencephalon through implanted electrodes (10--250 micro A, 1 msec, 60 Hz). Mild arousal and related effects were evoked from widespread sites between stereotaxic planes P 1.5--P 4.5 and 0.1--3.5 mm from the midline. Stimulation readily evoked vigorous running responses, together with other responses suggestive of agitation with escape and concealment behaviour, at sites in the hypothalamus within 2 mm of the midline near or just caudal to the mammillothalamic tracts. Signs of rage or aggression were infrequently seen. When the centre of this hypothalamic zone was stimulated after re-anaesthetizing the animals, bradycardia was obtained. The results are interpreted as suggesting that stimulation in this area, which is known to evoke cardiovascular responses different from the carnivore, also evokes a modified form of "Defence Reaction" appropriate to a species that is preyed upon.