Hexamethonium produces both twitch and tetanic depression without fade in common African toad (Bufo regularis)

Abstract

The study was designed to investigate the nature of the cholinoceptors at the sciatic nervegastrocnemius muscle junction of the common African toad (Bufo regularis). Using myographic technique, the twitch properties of the sciatic-gastrocnemius muscle preparation of the common African toad was studied. Both the twitch height and peak tetanic height were measured as a percentage of control. Hexamethonium at a concentratration of 0.1mM significantly (P<0.05) reduced the mean twitch height from 2.62cm to 1.0cm and mean peak tetanic height from 5.38cm to 4.32cm. Hexamethonium, however does not produce tetanic fade at the same concentration. We hypothesized that the cholinoceptors of the neuromuscular junction of the common African toad (Bufo regularis) resemble the developing synapse of African clawed toad (Xenopus laevis) and may contain muscarinic M1 autoreceptors at the pre juntional membrane.

Keywords: Hexamethonium, Tetanic fade, Bufo regularis, Cholinoceptors