[The effects of stimulation of nucleus raphe obscurus on Fos-expression evoked by activiting dorsal periaqueductal gray and unit discharge in ventral periaqueductal gray in rat].

Experiments were carried out on rats anaesthetized with sodium pentobarbital or urethane and alpha-chloralose. Nucleus raphe obscurus (NRO) and dorsal periaqueductal grey (dPAG) were stimulated singly or simultaneously by square-wave pulses to induce the Fos-expression in midbrain and medulla oblongata. During the period of NRO stimulation, the basal blood pressure was increased (P < 0.05), the defensive pressor response to stimulation of dPAG was attenuated (P < 0.01). When both NRO and dPAG were stimulated, Fos- like immunoreactive (FLI) cells in the ventral periaqueductal grey (vPAG) and paragigantocellularis lateralis (PGL) were increased as compared with cases in which the stimulation was only delivered to dPAG, i.e., reaching a FLI cell count value of 66.5 +/- 8.3 and 10.8 +/- 1.5 respectively. Stimulation of the NRO with single or paired stimulus evoked both excitatory (84%) and inhibitory (16%) responses of the units in vPAG. Bilateral microinjection of lidocaine (2 micrograms in 0.1 microliter/side) into vPAG attenuated the depressor responses induced by stimulation of NRO, but little change in basal blood pressure (P > 0.01). It is suggested that there exist different types of neurons possessing different functions in the ventral lateral medulla (VLM) and NRO and that an excitatory projection from the NRO to vPAG may mediate the sympathoinhibitory effect of the nucleus.