Postganglionic sympathetic neurones supplying skeletal muscle and skin can be activated from the preganglionic site via cholinergic nicotinic, muscarinic and noncholinergic synaptic mechanisms. The experiments described in this paper were designed in order to show that postganglionic vasoconstrictor neurones supplying skeletal muscle can be activated by the naturally occurring discharge pattern in preganglionic axons when the nicotinic transmission is blocked. For this purpose, the activity was recorded simultaneously from postganglionic vasoconstrictor axons supplying skeletal muscle and vasoconstrictor axons supplying hairy skin. The preganglionic neurones were driven reflexly by stimulation of the arterial chemoreceptors. 1) During blockade of nicotinic transmission muscle vasoconstrictor neurones were activated via the CNS during stimulation of arterial chemoreceptors. This activation is either generated by muscarinic action of released acetylcholine or by a noncholinergic synaptic mechanism. 2) Postganglionic cutaneous vasoconstrictor neurones were inhibited during stimulation of arterial chemoreceptors. During blockade of cholinergic nicotinic transmission these neurones were not activated reflexly by stimulation of arterial chemoreceptors although they received inputs via cholinergic muscarinic and noncholinergic synaptic mechanisms. 3) The results illustrate that postganglionic vasoconstrictor neurones supplying skeletal muscle can not only be activated via non-nicotinic synaptic mechanisms through synchronous repetitive electrical stimulation of preganglionic axons but also by the discharge pattern produced in preganglionic neurones during stimulation of arterial chemoreceptors.

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Activity in postganglionic neurones supplying skeletal muscle and hairy skin of the cat hindlimb was measured after single and repetitive stimulation of preganglionic axons in the lumbar sympathetic trunk at variable stimulation strengths. Simultaneously the compound action potentials were measured in one of the lumbar white rami L2 or L3. Early short latency ("nicotinic") responses were obtained in the postganglionic neurones when preganglionic axons conducting at 8.9 +/- 3.44 m/s (n = 12) or less were stimulated. Late, long-latency non-nicotinic responses were elicited in the postganglionic neurones when preganglionic axons conducting at 1.52 +/- 0.94 m/s (n = 12) or less were stimulated.