The selective innervation of guinea-pig superior cervical ganglion cells by sprouts from intact preganglionic axons.

If the guinea-pig superior cervical ganglion is partially denervated in a way which spares some preganglionic axons arising from each of the spinal cord segments which normally innervate this ganglion (C8-T7), sprouting of the intact preganglionic axons occurs without a loss of selective end-organ responses to stimulation of individual ventral roots (Maehlen & Njå, 1981). In the present work we examine the selective innervation of individual ganglion cells by ventral roots after sprouting and compare it to that in normal ganglia. After sprouting the pattern of ganglion cell innervation by the intact preganglionic axons shows some of the features typical of normal ganglia. Thus each ganglion cell is strongly innervated by one or two neighbouring spinal cord segments, with the adjacent segments contributing a synaptic influence which diminishes with distance from the dominant one. Acutely after the partial denervation there is a tendency for the rostral segments to innervate ganglion cells more strongly than do caudal segments, compared to the situation in normal ganglia. The same is true following sprouting. The pattern of ganglion cell innervation observed after sprouting can be explained if the affinities of ganglion cells for innervation from particular spinal levels are assumed to be unchanged and the shift in the relative availability of different preganglionic axons, caused by the partial denervation, is taken into account. This view was substantiated by statistical analysis based on a model of selective synapse formation in the guinea-pig superior cervical ganglion. We conclude that the ability of individual ganglion cells to distinguish preganglionic axons arising from different spinal levels is maintained during sprouting. Moreover, the way in which selective recognition and the availability of different preganglionic axons combine to produce particular patterns of innervation appears to be similar in normal development and after partial denervation in maturity.