REGULATION OF NACHR SUBUNIT GENE-EXPRESSION RELATIVE TO THE DEVELOPMENT OF PRESYNAPTIC AND POSTSYNAPTIC PROJECTIONS OF EMBRYONIC CHICK SYMPATHETIC NEURONS

Previous work has established that synaptic input influences the differentiation of muscle and glandular targets and that these targets reciprocally influence the differentiation of the innervating neurons. In contrast, there is little information on the impact of pre- vs postsynaptic contact on the differentiation of neuronal targets. We have delineated the timing of presynaptic projections to lumbar sympathetic neurons as well as the timing of the projections from these neurons to their targets during normal embryonic development. A combination of anterograde and retrograde labeling techniques and immunohistochemical approaches reveal that the establishment of significant synaptic input to chick sympathetic ganglia is a rather protracted process spanning late embryonic development. Although target contact in the periphery also occurs over mid to late embryogenesis, significant target projections appear to be established prior to the evolution of a comparable level of presynaptic input. Analysis of concurrent changes in the pattern and levels of expression of genes encoding neuronal nicotinic receptor (nAChR) subunits are consistent with both presynaptic input and target contact regulating nAChR expression during embryogenesis. These studies also suggest that retrograde influences of target contact on receptor expression may be more substantial than previously appreciated. (C) 1994 Academic Press, Inc.