Interaction between central gray and nucleus raphe magnus: role of norepinephrine.

Recordings were made from single cells in the nucleus raphe magnus (NRM) of the rat. The response of these cells to electrical stimulation of the periaqueductal gray (PAG) was correlated with their response to iontophoretically applied norepinephrine (NE). It is shown that NE can cause excitation as well as inhibition of NRM neurons, although excitatory response was obtained more often than an inhibitory response. No correlation between the response to PAG stimulation and to NE was obtained. It is concluded that NE is not the transmitter that mediates the interaction between the PAG and NRM.