Electrophysiological effects of somatostatin-14 and somatostatin-28 on mammalian central nervous system neurons.

Somatostatin (SOM) exists in at least two active forms in the central nervous system (CNS): SOM-14 and SOM-28. These peptides have multiple actions on neurons in the CNS and these actions appear to be mediated by different receptors. Thus, SOM-14 can enhance voltage-dependent K currents, whereas SOM-28 inhibits these same currents, sometimes even in the same neurons. These effects are not mediated via cAMP, but do seem mediated by GTP-binding proteins. On the other hand, both forms of SOM inhibit a voltage-dependent Ca current, again via a GTP-binding protein. SOM can also interact with the GABA(A) receptor to modulate responses to this inhibitory transmitter. The physiological effects of SOM in an integrated circuit within the CNS will depend on the form of SOM released, the kinds and numbers of receptors present on the postsynaptic neurons, and the presence of other neurotransmitters.