Synaptic and antidromic potentials of visceral neurones in ganglia of the lumbar sympathetic chain of the cat.

Intracellular recordings were obtained in vitro from two hundred and twenty post-ganglionic neurones of the fourth and fifth lumbar paravertebral ganglia of cats. Thirty-seven percent of neurones tested evoked antidromic responses during electrical stimulation of post-ganglionic fibres in the inferior lumbar splanchnic nerves. Twenty-seven percent of neurones tested evoked antidromic responses during electrical stimulation of post-ganglionic fibres in the lumbar sympathetic chain. Twenty-four percent of neurones tested evoked convergent antidromic responses during electrical stimulation of post-ganglionic fibres in separate inferior lumbar splanchnic nerves or lumbar sympathetic chain, and by inferior lumbar splanchnic nerves and lumbar sympathetic chain. Eighty-six percent of paravertebral post-ganglionic fibres which project to the inferior lumbar splanchnic nerves or lumbar sympathetic chain were composed of B fibres with maximal conduction velocities ranging from above 2.0 to 16.0 m/s. Fourteen percent of post-ganglionic fibres were composed of C fibres with maximal conduction velocities ranging from 0.2 to 2.0 m/s. Synaptic responses of neurones were recorded intracellularly during electrical stimulation of preganglionic fibres in inferior lumbar splanchnic nerves, lumbar white rami communicantes and lumbar sympathetic chain located one to three segments above the fourth and fifth lumbar ganglia and one to two segments below. Synaptic responses consisting of excitatory post-synaptic potentials and action potentials were mediated via nicotinic receptors. Twenty-seven percent of neurones tested received synaptic input from only one or two segments of the lumbar sympathetic chain. Seventy-three percent of neurones tested received convergent synaptic input from one or two segments of the lumbar sympathetic chain, lumbar white rami communicantes and inferior lumbar splanchnic nerves. It is concluded that central preganglionic fibres which project to inferior lumbar splanchnic nerves also project to the lumbar sympathetic chain to innervate neurones in the L4 and L5 ganglia. Synaptic responses of neurones during electrical stimulation of preganglionic fibres in the lumbar sympathetic chain and in the inferior lumbar splanchnic nerves were reduced in a chronic isolated segment of the sympathetic chain devoid of central preganglionic inputs. It is concluded that synaptic responses elicited in neurones during electrical stimulation of inferior lumbar splanchnic nerves and lumbar sympathetic chain were mediated in part via collaterals of central preganglionic axons and in part via axons whose cell bodies were located in the periphery.(ABSTRACT TRUNCATED AT 400 WORDS)