Figure 1. Muscarinic and non-cholinergic responses elicited in postganglionic vasoconstrictor neurones (skin (CVC), muscle (MVC)) projecting to the cat hindlimb by activation of preganglionic neurones.
A, experimental set-up. B, electrical stimulation of preganglionic axons in the lumbar sympathetic trunk (LST) suprathreshold for all fibres with 50 stimuli at 25 Hz in a decentralized preparation (preganglionic axons cut). Afterdischarges in 2 CVC neurones before and after atropine. C, preganglionic axons intact. Long-lasting enhancement of activity in a CVC neurone following suprathreshold electrical stimulation of all preganglionic fibres in the LST. Inset: Original activity. D, reflex activation of a postganglionic MVC neurone to stimulation of arterial chemoreceptors by ventilating the cat with a hypoxic gas mixture during complete block of cholinergic transmission (26 mg kg−1 hexamethonium (C6) infused into the iliac artery in the presence of atropine (1 mg kg−1). Inset: response of the MVC neurone to repetitive stimulation of the preganglionic axons in the LST (50 stimuli at 25 Hz) under complete block of cholinergic transmission. E, myelinated preganglionic fibres conducting at > 3 m s−1 generate only nicotinic responses in VC neurones. Repetitive stimulation of unmyelinated and some small diameter myelinated preganglionic axons (conduction velocity < 3 m s−1) may generate, in addition to nicotinic reponses, non-nicotinic (muscarinic or non-cholinergic (possibly peptidergic)) responses. Most muscarinic and non-cholinergic receptors probably are located extrajunctionally. B from Hoffmeister et al. (1978); C from Blumberg & Jänig (1983); D from Jänig et al. (1983).