Spontaneous and synaptic excitation of paramedian reticular neurones in the decerebrate cat.

1. In decerebrate cats neurones in the region of the paramedian reticular nucleus were identified by responses to stimulation of implanted cerebellar electrodes. Approximately one half were antidromically activated and one half orthodromically. 2. Somatic stimulation and electrical stimulation of both hind limb and cranial nerves activated many of these cells. There was no correlation between the effects of these stimuli on cell firing and on blood pressure. 3. A number of rhythms in spontaneous firing were observed. One fifth of cells fired with the rhythm of efferent activity in the recurrent laryngeal nerve. In animals showing cycles of stability and instability in blood pressure corresponding phases of activity and inactivity in the firing of paramedian reticular neurones were observed. 4. Most paramedian reticular cells showed bursts of firing preceding abrupt rises in blood pressure but this was also observed with cells lateral to this area. 5. One third of cells studied showed changes in firing rate correlated with the changes in blood pressure which followed I.V. acetylcholine and noradrenaline. 6. Bilateral carotid artery occlusion, which always produced a rise in blood pressure, had little effect on cell firing.