Transmission from Pregnanglionic Fibres in the Hypogastric Nerve to Peripheral Ganglia of Male Guinea-pigs

1. Intracellular records were obtained from ganglion cells of the pelvic plexus of male guinea-pigs.2. The input resistance of cells which responded to intracellular stimulation varied from 40 to 150 MOmega. Slope resistance decreased when the membrane was hyperpolarized. Time constants varied from 5 to 200 msec. Resting membrane potentials ranged from 40 to 70 mV.3. Action potentials in response to direct stimulation were followed by a prolonged phase of after-hyperpolarization.4. A second type of cell was also impaled which did not respond to electrical stimulation. These cells had resting membrane potentials in the range 60-70 mV, input resistances of less than 20 MOmega and time constants of less than 3 msec.5. In most ganglion cells, stimulation of the hypogastric nerve evoked action potentials which were often followed by a secondary phase of depolarization indicating continuing transmitter action.6. Orthodromic responses were generally ;all-or-nothing' and could not be graded with changes in stimulus strength. The latency of orthodromic responses indicated that ganglion cells were innervated by both B and C fibres in the hypogastric nerve.7. Orthodromic responses were blocked by tubocurarine, 5 x 10(-5) g/ml., and dihydro-beta-erythroidine, 10(-5) g/ml.8. Spontaneous, excitatory post-synaptic potentials of up to 4.8 mV in amplitude were observed. The frequency of their discharge was greatly increased by repetitive stimulation of the hypogastric nerve.9. The ultrastructure of the pelvic ganglia was studied by electronmicroscopy. Two types of ganglion cell process were observed, fine (0.1 mu) branching tufts thrown up from the soma within the surrounding capsule and longer, thicker (1 mu) extracapsular processes. Synapses were found to occur most frequently between the varicose terminal segments of preganglionic axons and the small intracapsular processes.10. Similarities between the properties of the pelvic ganglia innervated by the hypogastric nerve and those of the parasympathetic division of the autonomic nervous system are discussed.