Somatostatin(14) and -(28) but not somatostatin(1-12) hyperpolarize CA1 pyramidal neurons in vitro.

The three major prosomatostatin-derived peptides found within CNS neurons are a 28-amino acid peptide (SS28), a cyclic 14 amino acid peptide (SS14) and a 12 amino acid peptide (SS1-12). Immunohistochemical studies demonstrate a differential distribution of these related forms of somatostatin within CNS neurons and have led to the suggestion that SS1-12 may represent the predominant neurotransmitter form of this family of peptides. Intracellular recordings from CA1 pyramidal neurons in the in vitro rat hippocampal slice revealed that application of SS14 and SS28 in nanomolar concentration produced neuronal hyperpolarization; synaptic responses, recorded extracellularly, were also reduced. In contrast, we were unable to demonstrate a pre- or postsynaptic action of SS1-12 on these neurons. These results do not support the hypothesis that SS1-12 functions as a central neurotransmitter in area CA1 of the hippocampus.