The effect of guanethidine pretreatment on transmission in the superior cervical ganglion.

Abstract

Abstract:Isolated superior cervical ganglia from rats pretreated with guanethidine sulphate intraperitoneally in single daily doses of 20‐40 mg/kg for 5‐21 days showed transmitted action potentials of normal form but diminished amplitude following single or repetitive stimulation of the preganglionic nerve. Curves relating the relative reduction in ganglionic action potential height with increasing frequency of stimulation were similar in preparations from control and guanethidine pretreated rats. Ganglia from guanethidine pretreated rats had the same sensitivity to exogenous acetylcholine as those from the controls as judged by doseidepolarization response curves. The absolute values of depolarization were, however, diminished. No impairment of the conduction of impulses in the preganglionic nerve or of the effect of antidromic stimulation was observed. The addition of guanethidine to the bath fluid resulted in an acute reversible ganglion block. A 50 % reduction of the ganglionic action potentials following single stimuli was observed at a concentration of 2 × 10−5M. At guanethidine concentrations of 5 × 10−5M maximum depolarizations obtained with acetylcholine or carbachol were reduced by approximately 50 % but the doselresponse curves were not shifted. Recovery was complete after washing. Retractions of the cat nictitating membrane following repetitive stimulation of the preganglionic nerve after pretreatment with guanethidine 5‐40 mg/kg for 14 days were preferentially decreased at low stimulus frequencies. The nictitating membrane was hypersensitive to intravenous adrenaline or noradrenaline. Contralateral ganglia from both rats and cats exhibited profound structural changes consisting of chromatolysis of the nerve cells and infiltration of small cells. The effects of guanethidine on the neurophysiological parameters are probably the result of a dose dependent inactivation of the majority of the ganglion cells.