Ganglionic neuronal mechanisms involved in circulatory control system.

Intracellular tonic activity and responses to orthodromic stimuli were recorded from the neurones of rabbit superior cervical ganglion and compared with those recorded from the nerves containing pre- and postganglionic nerve fibres, with the use of a coherent recording technique. It was found that: (1) firing of each ganglion neurone is triggered by two presynaptic inputs, single and multiple, formed by a single preganglionic nerve fibre whose discharges evoke the postsynaptic spikes correlated with cardiac rhythm, and by a few converging preganglionic nerve fibres which evoke the postsynaptic spikes, either correlated with cardiac rhythm or irregular, only if two or more of them discharge together, correspondingly; (2) about 240 neurones of the ganglion, on the average, fire synchronously during their tonic activity, being driven by only three preganglionic nerve fibres; (3) only about 9% of a "neural unit", the number of the ganglion neurones receiving innervation from the same preganglionic nerve fibre, are discharged during their tonic activity through a single input, while the rest of neurones are either discharged through a multiple input (17%), or generate only the excitatory postsynaptic potentials subthreshold for spike generation (73%). The results obtained suggest that the ganglionic neuronal mechanisms responsible for vasomotor control involve much more complex ganglionic integrative processes than it has been commonly thought.