ALTERATION IN NICOTINIC AND MUSCARINIC RESPONSES OF RABBIT SUPERIOR CERVICAL GANGLION-CELLS AFTER CHRONIC PREGANGLIONIC DENERVATION

The effect of chronic preganglionic denervation on the cholinergic responses of the rabbit superior cervical ganglion cells was investigated with intracellular microelectrode techinques in vitro. The nicotinic depolarization of the sympathetic ganglion cells induced by the nicotinic action of acetylcholine [ACh] and carbachol was substantially decreased after chronic denervation, whereas the muscarinic depolarization of the denervated ganglion cells elicited by the muscarinic action of ACh, carbachol and methacholine was markedly increased. The enhanced muscarinic response of the denervated ganglion cells could be completely blocked by atropine (5 .times. 10-5 M). The equilibrium potential of the nicotinic subsynaptic membrane determined by iontophoretically applied Ach appeared to be the same before and after denervation. The ratio of Na and K conductance change (.DELTA.gNa/.DELTA.gK) was not changed appreciably after denervation. The dissocation constant (Ka) of drug-receptor complex, extrapolated from the double reciprocal plots for nicotinic or muscarinic response was not altered and the ratio of ACh molecule attached to a single nicotinic or muscarinic receptor, which was 1:1, remained unchanged after denervation.