Axotomy and nerve growth factor regulate levels of neuronal nicotinic acetylcholine receptor alpha 3 subunit protein in the rat superior cervical ganglion

Neuronal nicotinic acetylcholine receptors (nAChRs) play a significant role in sympathetic transmission in the superior cervical ganglia (SCG), with m ost of the signal carried by a nAChR containing an alpha3 subunit. Work has shown that transection of the postganglionic nerves (axotomy) of the SCG r esults in a decrease in mRNA transcripts for alpha3, alpha5, alpha7 and bet a4 and in protein expression of alpha7 and beta4. To evaluate effects of ax otomy on alpha3 protein in the SCG, quantitative immunoblotting was used to demonstrate a dramatic decrease (> 80%) in the levels of this subunit 4 da ys after axotomy. Similarly, immunocytochemistry showed a marked decline in the number and the intensity of stained neurons for the alpha3 subunit as well as tyrosine hydroxylase. Ganglia explanted into culture for 4 days als o showed a substantial decrease in alpha3 subunit protein. This decrease wa s partially prevented by the addition of nerve growth factor (NGF) to the c ulture medium at the time of explantation. Additionally, this decrease was reversed by the addition of NGF to the culture medium following 4 days in c ulture in the absence of NGF. These findings suggest that the loss of alpha 3 subunit contributes to the reported decrease in ganglionic synaptic trans mission that follows axotomy, and that NGF plays an important role in regul ating the expression of alpha3-containing nAChRs in the SCG.