Integrative properties of the major pelvic ganglion in the rat.

The integrative properties of the major pelvic ganglion were investigated in the male rat on an in vitro preparation consisting of the ganglion connected to the hypogastric, pelvic and cavernous nerves. The electrical activity of ganglionic neurones was recorded using intracellular recording techniques. The neurones never displayed any spontaneous activity and were found to be only of the phasic type. Fast synaptic activation could be evoked in the same neurone by stimulating the hypogastric, pelvic and cavernous nerves with a single pulse. This activation was not affected by hexamethonium plus D-tubocurarine but was abolished by mecamylamine. During nerve stimulation with a train of pulses, a gradual depression of the fast synaptic responses occurred. This phenomenon increased with the frequency of stimulation. Our results show that the neurones of the major pelvic ganglion can integrate central inputs from both the sympathetic and parasympathetic systems as well as peripheral inputs. This activation is modulated by a rate limiting mechanism. Thus the major pelvic ganglion should not be considered as a simple relay but as a true integrative nervous centre which opens new perspectives concerning its role in the nervous control of the urogenital and gastrointestinal tracts.