Suppressing effects of pentobarbital on synaptic transmission in bullfrog sympathetic ganglia

Abstract

Compound action potentials (CAP) in response to orthodromic stimulation 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 release by low Ca²⁺-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.