Somatostatin enhances neurite outgrowth and electrical coupling of regenerating neurons in Helisoma.

The present study tested the ability of 3 peptides (somatostatin, arginine-vasopressin (AVP) and arginine-vasotocin (AVT)) to enhance neurite outgrowth from regenerating Helisoma neurons. The buccal ganglia from Helisoma were incubated either short-term in saline or longer-term (2-5 days) in medium and the extent of neurite outgrowth (induced by nerve crush) by a buccal neuron (neuron 5) was determined. Neurite outgrowth was consistently enhanced by both somatostatin and its extended analog somatostatin, but was unaffected by either AVT or AVP. The enhanced outgrowth due to somatostatin was associated with stronger electrical synapse formation between the two neurons 5, this being attributable to lower coupling resistance rather than a change in non-junctional resistance. Both the enhancement of neurite outgrowth and the increased efficacy of electrical coupling due to somatostatin were prevented by a somatostatin inhibitor. An immunohistochemical survey produced evidence for neurons containing a somatostatin-like peptide in both the cerebral ganglia and the enteric nervous system of Helisoma. It is concluded that somatostatin can act neurotrophically in the nervous system.