Time course effects of uncontrollable stress in locus coeruleus neuronal activity.

The animals exposed to inescapable shock (IS) showed a behavioral depression which was assessed by the increased number of escape failures on an avoidance escape test, either 24 or 48 hours after. The number of noradrenergic (NA) spontaneously active cells of locus coeruleus (LC) appear to be increased 24 and 48 h later (IS) compared to control animals. On the other hand the firing rate at 24 and 48 hours was continuously decreased. The dose-response curve to inhibitory effect of clonidine (CLON) on firing rate of locus coeruleus (LC) neurons showed a clear shift to the right. These results are discussed in terms of the subsensitivity of alpha-2 adrenoceptor and a calcium-activated potassium current (IK(Ca)) controlling the firing rate of LC neurons and the increased release of noradrenaline induced by IS 24 or 48 h before.