The effects of a number of agonists, antagonists and local
anaesthetics on electrical activity in fibres of the rabbit
saphenous nerve in situ, and. on the surface potential of the
isolated superior cervical ganglion of the rat have been studied.
Acetylcholine, carbachol, methacholine, pilocarpine, Mcl A343,
nicotine, tetramethylammonium, dimethylphenylpiperazinium, histamine,
5- hydroxytryptamine, bradykinin and angiotensin induced an afferent
discharge in fibres of the rabbit saphenous nerve on intra- arterial
injection into the skin. The same compounds depolarized the isolated . ganglion, although the rank orders of potency differed somewhat in
the two preparations. The use of the appropriate agonists and. antagonists showed. that the cholinoceptive sites could be subdivided. into muscarinic and nicotinic receptors, the latter
predominating in both tissues.
Adrenaline and noradrenaline first augmented and then depressed.
the acetylcholine -induced. discharge in the saphenous nerve; these
effects were mediated via a- adrenoreceptors. Isoprenaline produced
a prolonged small. increase in the acetylcholine -induced. discharge
and this effect was mediated via ß- adrenoreceptors. In the isolated
ganglion, adrenaline and. noradrenaline produced. a weak, a- receptormediated, hyperpolarization.
Drugs possessing a nicotinic action gave rise to a secondary
hyperpolarization of the ganglion cells which followed the initial
depolarization on washing the tissue. Some evidence was obtained
suggesting that this hyperpolarization was not a rebound phenomenon
consequent upon the initial depolarization, but was due to the
release of catecholamine within the ganglion. Drugs with a muscarinic action gave rise to a late post-washing depolarization
which appeared to be mediated via muscarinic receptors.
Guanethidine blocked. the action of acetylcholine on the
saphenous nerve and. on the ganglion, but only in the former
preparation did the effect resemble the adrenergic neurone
blocking action of the drug in being reversed by d.examphetamine.
No evidence was forthcoming to support the concept of the
existence of a synaptic gap associated. with sensory endings:
natural touch responses were still present at a time when drug - induced discharges had, been extinguished by antagonistic agents.
A brief study was made of the effect of local anaesthetics
and. drugs with local anaesthetic properties upon both preparations.
It is suggested. that the rabbit saphenous nerve preparation may
provide an additional means of assessing the potency and. durability
of local anaesthetic agents.
The results are discussed. in relation to the effects of the
drugs on other non-myelinated neuronal membranes.