Patterns of activity in sympathetic postganglionic nerves to skeletal muscle, skin and kidney during stimulation of the medullary raphe area of the rat.

In chloralose/urethane anaesthetised rats multi and single fibre activity was recorded in renal sympathetic nerves and in sympathetic nerves to skeletal muscle and to the skin of the hind limb. The activity was pulse-modulated and inhibited by stimulating baroreceptors with an increase in blood pressure following i.v. phenylephrine. The study investigated the effect of stimulating medial regions of the lower brainstem on activity in these sympathetic nerves. Comparing renal nerve and skin sympathetic nerve activity two main patterns of response were seen, either an inhibition of both or excitation of both. In contrast when comparing renal nerve activity with muscle sympathetic nerve activity a third pattern was evoked from a few sites located in nucleus raphe obscurus, an inhibition of renal nerve activity and excitation of muscle sympathetic activity. The latter is the same pattern as that evoked in the cat. Unlike the cat, however, the decerebrate rat was not observed to generate this differential pattern of activity either spontaneously or following the administration of physostigmine. It is argued that the activation of cell bodies located in raphe obscurus is responsible for inducing a pattern of sympathetic activity similar to that occurring during paradoxical sleep in other animals.