Reinnervation of frog sympathetic ganglia after selective denervation of B or C neurons

Abstract

Selective transection of the B or C preganglionic nerve fibres respectively innervating the B and C sympathetic neurons was carried out on the last two ganglia of the sympathetic chain of the frog Rana esculenta. At different times thereafter, the cross-reinnervation of one type of denervated neuron by nerve endings sprouting within the ganglia from intact fibres innervating the other type was investigated by both the quantitative morphology of the synaptic contacts and related structures and electrophysiological recordings of ganglionic transmission. As there are no fine ultrastructural criteria for distinguishing B from C neurons, the overall density of synapse, simple contact, and 'vacated' postsynaptic differentiation profiles was measured in the two cases of selective section and compared with the values for normal ganglia, therefore permitting the progress of cross-reinnervation with time for each type of neuron to be followed. At ten days after section of the C preganglionic fibres, immunocytochemistry showed that there were no anti-LH-RH-like peptide containing fibres within the ganglia. The B myelinated preganglionic fibres were able to reinnervate the denervated C neurons, with return to normal values of synaptic density and fully efficient transmission at two months in all tested C neurons. However, the latency of orthodromic action potentials was close to that of normally innervated B neurons. In contrast, the C non-myelinated preganglionic fibres reinnervated the denervated B neurons with limited efficiency, the synaptic density being two-thirds the normal value after five months, while subthreshold excitatory postsynaptic potentials or action potentials were only recorded in 44% of the tested B neurons. The latency of these orthodromic responses was close to that of normally innervated C neurons. It is postulated that the poor cross-reinnervation of B neurons could be due to insufficient sprouting of C fibres and/or lack of 'affinity' between C fibres and B neurons. In addition, these experiments demonstrated that the subsynaptic apparatus, fairly characteristic of frog ganglionic synapses, is present in both types of sympathetic neurons, although predominantly in B neurons.

Morphological changes of cholinergic nerve fibers in the urinary bladder after establishment of artificial somatic-autonomic reflex arc in rats

“…It also indicated that the efferent motor branches of somatic nerves can grow into the parasympathetic fibers of autonomic nerves through axonal regeneration, similar to the results of de Castro et al [14] and Eugene et al [15] . In the new reflex, somatic motor excitation evoked by the cutaneous stimuli is probably transmitted to the bladder through those anastomosed efferent motor nerves, resulting in the autonomic bladder contraction.…”

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

“…Thus, each simple contact could serve as an indicator of the appearance of a synapse. Regeneration in sectioned preganglionic fibers was blocked [2], so the only cause of variation of SI + ISC values was branching of fibers already present in the ganglia, as observed by the pioneer of this type of experiment, Feldman [3]. N e u r o n types were identified by antidromal stimulation.…”

“…By 7-10 days after denervation, when C neurons were reinnervated with ]3 fibers, the value of SI + ISC was twice that in the situation of innervation of B neurons with C fibers. Then over the next month, there was an unexpected reduction in this parameter, which was especially paradoxical in relation to C fibers, since all active C neurons were involved in synaptic transmission of type B [2].…”

“…Reformed synapses were studied by intracellular recording of potentials. It was noted that the time characteristics of synaptic transmission in C neurons was identical to that in B neurons and vice versa [2,8]. Synaptic transmission was found to depend not on the internal properties of neurons, but on the type of preganglionic fiber.…”