Axons of peripheral origin preferentially synapse with tonic neurones in the guinea pig coeliac ganglion.

Intracellular recordings from a population of guinea pig coeliac neurones projecting in the coeliac nerves were used to define their central and peripheral synaptic input. The neurones were classified as 'phasic' or 'tonic' by their discharge in response to depolarizing current. Stimuli applied to the greater splanchnic nerves evoked suprathreshold responses in 89% of phasic neurones, but in less than half the tonic neurones. In contrast, coeliac nerve stimulation evoked only small subthreshold responses in 11% of phasic neurones, but multiple synaptic potentials in 92% of tonic neurones. This suggests that peripheral intestinal reflexes involve only one sympathetic neurone type.