Synaptic innervation of sympathetic ganglion cells in the bullfrog

The synaptic innervation of the ganglion cells in the ninth and tenth paravertebral sympathetic ganglia of the bullfrog was investigated by histochemical and electron microscopic techniques and by intracellular recording. The neurons were unipolar and most ganglion cells were innervated by a single preganglionic axon. The preganglionic fiber stained for acetylcholinesterase and was observed to spiral around the axon hillock of the ganglion cell before arborizing and making synaptic contact with the neuron. Most synapses were located on the soma near the axon hillock region, with features typical for cholinergic junctions. The axosomatic location of the synapses was manifested physiologically by a decrease in membrane resistance (increased conductance) at the peak of the fast EPSP (excitatory postsynaptic potential) and by a demonstrable reversal potential for the fast EPSP.