On the occurrence and physiological effect of somatostatin in the ciliary ganglion of cats.

Somatostatin-like immunoreactive nerve fibers occurred among and around ganglion cells in the form of punctate structures or varicose processes in the cat ciliary ganglion. The density of the fibers varied greatly from region to region and approximately 25% of the whole population of neuronal soma that appeared in a single section were surrounded by immunoreactive fibers. No somatostatin-positive cell bodies were observed. Application of somatostatin to this ganglion in vitro by superfusion induced membrane hyperpolarization in approximately 60% of the neurons examined. The hyperpolarization was preserved in a low Ca/high Mg medium. This response was associated with a decrease in input membrane resistance and was reversed in polarity at nearly --90 mV. The present findings suggest that somatostatin may play a role as a neurotransmitter or modulator in this parasympathetic ganglion.