Suppressing effects of pentobarbital on synaptic transmission in bullfrog sympathetic ganglia.

Abstract

Abstract:Compound action potentials (CAP) in response to orthodromic stim ulation of the nerve trunk were extracellularly recorded from bullfrog sympathetic ganglia . Application of pentobarbital (PB) significantly suppressed the CAP-amplitude . The mode of inhibition of PB on the synaptic transmission was apparently competitive when examined under the condition of lowered transmitter r elease by low Ca21+-solutions and analyzed by dose-inhibition curves . However, the mode of inhibition by PB was noncompetitive when examined under increased transmitter release by 3 , 4-diaminopyridine (3, 4-DAP). Furthermore, acetylcholine (ACh) -induced depolarizing response , intracellularly recorded from a sympathetic ganglion cell, was markedly suppressed by PB . The mode of inhibition by PB on the ACh-induced response was noncompetitive when analyzed in low Ca2+-solutions . These results suggest that PB suppresses both of the transmitter release from the presynaptic terminal and ACh -receptor activation at the postsynaptic membrane, and that the latter effect of PB is dominant in normal Ringer's soluti on to suppress the synaptic transmission at the sympathetic ganglia .