Incoming synapses and size of small granule‐containing cells in a rat sympathetic ganglion after post‐ganglionic axotomy.

Abstract

SUMMARY1. A quantitative ultrastructural study has been made of the reaction of the incoming synapses of small granule-containing cells after axotomy of the major post-ganglionic branches of the superior cervical ganglion of the young adult rat. These cells are intrinsic and interneurone-like in this ganglion, receiving a preganglionic input and giving outgoing synapses to principal post-ganglionic neurones.2. Unlike their outgoing synapses, which are lost after post-ganglionic axotomy (Case & Matthews, 1986), the incoming synapses of the small granule-containing cells in axotomized ganglia increased in incidence post-operatively. The increase first became clearly evident 5-7 days post-operatively and was greater, being both more sustained and progressive, after bilateral than after unilateral axotomy. After bilateral axotomy the incidence of incoming synapses rose to more than four times that of normal ganglia and was still elevated at 128 days post-operatively, but was within normal limits at 390 days.3. After a unilateral lesion, increases of similar extent and time course to those in the axotomized ganglia were seen in the incoming synapses of small granulecontaining cells in the uninjured contralateral ganglia.4. The incoming synapses of the small granule-containing cells are multifocal, i.e. show several points or active foci of synaptic specialization. The increase in synapses expressed itself both through an increased incidence of these synaptic active foci per nerve terminal and through an increase in the number of~presynaptic nerve terminal profiles associated with the cells.5. Control observations indicated that the increase in synapses was not due to surgical stress, nor was it attributable solely to post-operative ageing.6. The nerve terminals which were presynaptic to the small granule-containing cells post-operatively were all ofpreganglionic origin: no incoming synapses or presynaptic nerve terminals remained at 2 days after a preganglionic denervation of axotomized or contralateral ganglia, at whatever stage this was performed throughout the range of survival intervals.7. There was some evidence that the synapses had increased by sprouting, including terminal sprouting, of the preganglionic nerve fibres. In the shorter term * To whom correspondence should be sent.PHY 374 2 C. P. CASE AND M. R. MATTHEWS there was an increase in the proportion of small nerve terminal profiles. In the longer term the mean size of the terminal profiles increased, and very large terminals of unusual form were seen.8. After post-ganglionic axotomy, and in particular after a bilateral lesion, the small granule-containing cells became hypertrophied. The size of the small granulecontaining cells was directly correlated with both the incidence and the collective size of the preganglionic nerve terminals which innervated them. Both the small granule-containing cells and their incoming innervation thus display a considerable capacity for expansion, such as is found to be inherent also in other neuronal systems.9. These inte...

Small, intensely fluorescent cells and the paraneuron concept

“…The same phenomenon is seen in relation to the outgoing synapses of the SIF cells in these axotomized ganglia: the synapses decrease in incidence and later reappear, with a time course similar to that shown by the preganglionic synapses to the principal neurones, thus suggesting that the injured principal neurones are the recipient also of the SIF cell synapses (Case and Matthews, 1986a). In the course of this study, we were surprised to find that the incoming preganglionic innervation of the SIF cells in these axotomized ganglia did not remain unchanged but instead increased up to fourfold (Case and Matthews, 1986b). The increase was greatest if both SCGs had been axotomized.…”

The neuroimmunology of degeneration and regeneration in the peripheral nervous system

“…Electrophysiological studies in which synaptic potentials were recorded have confirmed the occurrence of synaptic stripping following axotomy of facial or hypoglossal motor neurons (Yamada et al, 2008; Yamada et al, 2011). The impaired recovery of function fine muscle observed following facial nerve trauma in humans and in SCG axotomy in rats has been attributed to synaptic stripping and its incomplete reversibility after regeneration (Case and Matthews, 1986; Graeber et al, 1993). Along with synaptic stripping observed in the SCG following axotomy, it is interesting to note that a significant reduction in the mRNA of the α3, α5, α7, and β4 subunits of the postsynaptic nicotinic acetylcholine receptors is observed 48 h post-injury (Zhou et al, 1998).…”

Outgoing synapses of small granule‐containing cells in the rat superior cervical ganglion after post‐ganglionic axotomy.

“…1 B and 2B and D), suggests the local depletion of the large cored vesicles and implies that these morphologically distinct synapses are also functional. A reflexly increased drive from the preganglionic fibres could be a factor influential in producing this effect post-operatively (Case & Matthews, 1986). Synapses between small granule-containing cells in ganglia which have been subjected to postganglionic axotomy.…”

“…The increasing separation of the small granule-containing cells post-operatively, noted in the present experiments and by Soinila & Eranko (1980), might be involved in this. Some of the cells show an increase in volume post-operatively, which includes an extension of their processes (Case & Matthews, 1986).…”