Activation of bulbar reticular neurons by visceral afferents

Conclusion Synaptic activation of reticular neurons of the bulbar gigantocellular nucleus has been investigated with stimulation of the left greater splanchnic nerve, Synaptic activation of these neurons has been shown to be produced by ascending pathways formed by somatic and visceral afferents, running in the ventro-lateral part of the lateral, and the ventral, columns of the spinal cord. Synaptic processes arising in reticular neurons are uniform and differ only temporally. The pattern of development of synaptic processes in reticular neurons suggests that transmission of visceral impulses into the bulbar reticular formation takes place along two pathways. One of these, formed by the spinoreticular fibers of the lateral columns, activates neurons after a short latency (8–10 msec). Besides this there are also polysynaptic, nonspecific fibers in the ventrolateral and ventral columns, organized on the principle of long sensory tracts and including an intermediate link in the segmental interneurons. Synaptic processes in reticular neurons evoked by the polysynaptic pathways develop after 10–20 msec and originate from excitation of somatic and visceral afferents possessing lower excitability and a lower conduction velocity.Division of afferent fibers of the splanchnic nerve running in the dorsal columns and dorsolateral part of the lateral columns of the spinal cord has no significant influence on synaptic processes in reticular neurons.