Pre- and postganglionic sympathetic activity in splanchnic nerves of rats

Integrated sympathetic activity was recorded on anterior or posterior divisions of the greater splanchnic nerve (GSN) in anesthetized, acutely spinalized, artificially respired Wistar rats before and after ganglionic blockade by hexamethonium. Focal electrical stimulation of spinal sympatho-excitatory pathways elicited large increases in splanchnic sympathetic activity. Ganglionic blockade showed that the anterior and posterior divisions of the GSN are pedominantly preganglionic and postganglionic, respectively. Histological examinations of excised splanchnic nerves and sympathetic chains indicated that splanchnic postganglionic cell bodies must lie in the chain ganglia rather than within the GSN. Postganglionic responses were calculated for each rat by subtracting responses recorded after ganglionic blockade from responses recorded before ganglionic blockade. As expected, post-ganglionic responses exhibited longer onset latencies than pre-ganglionic responses. However, evoked activity increased and decreased more rapidly in postganglionic fibers than in preganglionic fibers. Responses to stimulus trains were also better maintained in postganglionic than in preganglionic fibers.