The effects of electrical stimulation of lobule IXb of the posterior cerebellar vermis on neurones within the rostral ventrolateral medulla in the anaesthetised cat.

This study was designed to investigate the effects of electrical stimulation of sublobule IXb of the posterial cerebellar vermis (the uvula) on the activity of neurones in the rostroventral medulla (RVLM) of anaesthetised cats. The ongoing activity of 38 RVLM neurones was studied in detail. One group consisted of 22 neurones that had axons projecting to the spinal cord (Group A, 22 neurones), the second had only an excitatory synaptic input from the spinal cord (Group B, 14 neurones) and the last were inhibited by equivalent spinal cord stimulation (Group C, 2 neurones). In Group A 16 neurones were excited, 2 inhibited and the other 5 showed a biphasic response involving excitation followed by inhibition, to lobule IXb stimulation. In Group B, lobule IXb stimulation excited 9 cells, inhibited 2 and evoked a biphasic response in 3 neurones. In Group C both cells were inhibited on cerebellar stimulation. Some cells in Group A and B were affected by electrical stimulation of the carotid sinus nerve--the predominant effect being an excitation. Specific baroreceptor stimulation invariably caused inhibition and several neurones had pulse modulated discharge. These data indicate that stimulation of sublobule IXb has marked influences on RVLM neuronal activity including a proportion of those neurones that have axons descending to the spinal cord that has been described as presympathetic 'vasomotor' neurones. A striking finding is the more widespread action of sublobule IXb, baroreceptor and sinus nerve inputs on other neurones of the RVLM, and the implications of this for the integration of cardiovascular control are discussed.