THE EFFECT OF NICOTINE ON SYNAPTIC TRANSMISSION IN THE SYMPATHETIC GANGLION

¹ Department of Physiology, The Australian National University, Canberra, Australia

The superior cervical ganglia excised from rabbits were used in a pharmacological investigation of the effects of nicotine before and after the addition of curarizing agents.

Measurement of the potential difference between the ganglion and the postganglionic trunk showed that addition of nicotine caused the ganglion to become negative. This negativity, or depolarization, reached a maximum in about ten minutes and seemed to remain constant.

In the uncurarized ganglion nicotine steadily increased the size of the positive potentials following a spike potential to reach a maximum in about ten minutes and this was maintained for as long as records were taken, i.e. up to 3 hours. This was explained by the depolarizing action of nicotine.

Extrinsically generated hyperpolarizing currents applied to ganglia soaked in nicotine produced a delay in the onset of these increased positive potentials but there was no significant effect on their size.

In curarized ganglia nicotine in low concentration reduced the time of decay of the synaptic potential, which presumably was due to a diminution of the time constant of the membrane. Nicotine in higher concentrations produced a decrease in size as well as time course of the synaptic potential. The shortening of the time constant of the membrane was probably due to an increase in its ionic conductance.