Effects of ganglion blocking agents on post-train facilitation in the rabbit superior cervical ganglion

The effect of ganglion blocking agents, hexamethonium and tubocurarine, on post-train facilitation and ganglionic transmission was studied and compared in isolated superior cervical ganglion of the rabbit, using electrophysiological technique--the conditioning-testing methodology. The preganglionic nerve trunk was stimulated, with either a single unconditioned stimulus (UR)-or a train of conditioning stimuli at 10 or 30 Hz, followed by a post-train test stimulus (PTR). The transmitted postganglionic, compound action potential (PCAP) was recorded following single and trains of stimuli, in the presence and absence of ganglion blocking drugs, hexamethonium (1-100 microM) and tubocurarine (1-100 microM). Hexamethonium and tubocurarine produced concentration-dependent reduction in the amplitude of the transmitted PCAP, increased post-train facilitation values and proportionately reduced those of the subliminal fringe (SF). The mean IC50 values (concentration to produce 50% block of PCAP) of hexamethonium and tubocurarine-induced blockade of the single unconditioned response were 15 +/- 1 microM and 26 +/- 2 microM (n = 6, P less than 0.01) respectively. A dose-ratio (tubocurarine)/hexamethonium) of 1.7 was obtained.