Central gray and medial hypothalamic stimulation: correlation between escape behavior and unit activity

A chronic experiment and an acute one were carried out in the same rat in order to get information on the neuronal events correlated with the escape latency (EL) induced by an electrical stimulation in the mesencephalic central gray (CG) or in the medial hypothalamus (MH). Escape latencies as well as unitary MH and CG neuronal responses (104 units in 25 rats) were studied as functions of the intensity and the pulse duration of a 50 pulses/sec stimulation train. The CG and/or the MH neuronal firing rate was either synchronized or diffusely altered, either inhibited or activated, by the CG or the MH stimulations. Many neuronal firing rate alterations were highly correlated with the escape speed (ES = 1/EL) induced by the same stimulation. Intensity duration trade-off functions were computed from both the EL and the unit recordings. Chronaxie determinations were performed from these data: the behaviorally determined chronaxies did not differ from the unitary ones (limit values: 0.05-0.42 msec). The discussion bear on the possible role of the observed neuronal alterations induced by CG or MH stimulations in relation to their behavioral effects.