The synaptology of two types of neurons in the sympathetic ganglia of the frog

Abstract

Nishi et al. [9] described two types of neurons on physiological grounds in the sympathetic ganglia of the frog: B neurons, with an axonal nerve impulse conduction rate of several m/sec and innervated by B fibers, and C neurons, with an axonal nerve impulse conduction rate of less than 0.5 m/sec and innervated by preganglionic C-type fibers. These neurons have different time characteristics for synaptic transmission: the latent period of B-neuron synapses is short, while that of Cneuron synapses is much longer, lqaese data were supported by studies on the frog Rana esculenta [1].The aim of the present work was to study the morphological differences between the two types of cholinergic synapses--B and C--and to determine the extent to which these contacts are specific, i.e., to determine how much the fibers of one type can be substituted by fibers of the other. MATERIALS AND METHODSThe frog sympathetic nervous system present was selected for the present studies for the following reasons.In 1910, Langley and Orbeli [5] showed that all preganglionic fibers innervating the last two abdominal gangfia (VI/I and IX) run within the connecting branches (CB) of ganglion VII and above. This means that the CB of the last two ganglia contain only postganglionic fibers directed to the lumbosacral plexus, and that complete deafferentation of these occurred when the