ABSTRACT
Blood pressure changes were evoked in the anaesthetized rabbit and rat by stimulating electrically within the caudal raphe nuclei. The responses evoked in the two species were very different, mainly pressor in the rat (85% pressor, 5% depressor) compared with approximately similar proportions of depressor and pressor in the rabbit (29% and 27%, respectively). The responses evoked from a particular site could not be reversed by changing the stimulus strength. It is proposed that the haemodynamic responses evoked in the rabbit and the rat, in response to stimulation within raphe, are related to differences in the central organization of these nuclei and/or their connexions. These results are then discussed in relation to the observation that the tonic phase of desynchronized sleep is accompanied by hypotension in the rabbit and hypertension in the rat. Finally, it is suggested that the haemodynamic differences observed during desynchronized sleep in these two species are caused by differences in central nervous regulation which involve the caudal raphe nuclei, magnus, pallidus and obscurus