POST-TETANIC ENHANCEMENT OF STIMULUS-INDUCED MUSCARINIC AFTERDISCHARGE IN RAT SUPERIOR CERVICAL GANGLION

  • 1 January 1978
    • journal article
    • research article
    • Vol. 207  (1) , 72-82
Abstract
The enhancement of asynchronous muscarinic ganglionic firing which followed a preganglionic nerve stimulus volley by high frequency repetitive conditioning stimuli was studied in the rat isolated superior cervical ganglion. Muscarinic afterdischarge which occurred in chlorisondamine-blocked ganglia was enhanced for up to 1 hr after a 40 Hz conditioning volley lasting 7.5-30 s. Enhancement did not occur when release of acetylcholine was blocked by reducing the Ca in the modified Krebs'' solution or when Mg or Mn chlorides were added to the saline during the conditioning period. Metabolic inhibitors, dinitrophenol, sodium azide and ouabain, blocked the enhancement process but not the asynchronous muscarinic firing. Phenytoin, 10-6 M, did not reduce the enhancement of firing. Dopamine, 5 .times. 10-5 M, had no effect on muscarinic afterdischarge, but dibutyryl cyclic[c] AMP, 5 and 10 .times. 10-3 M, caused a 43 and 53% increase in the maximum amplitude of afterdischarge. Dibutyryl GMP had no effect on post-tetanic enhancement or afterdischarge in concentrations up to 1 .times. 10-3 M. Following a conditioning stimulus, a prolonged postsynaptic change occurred which resulted in an increased responsiveness to muscarinic agonists, and this change probably involved a metabolic reaction since it was reduced by metabolic inhibitors. That dopamine might be a modulator of enhancement in the rat superior cervical ganglion was not supported.