Somatostatin selectively enhances acetylcholine-induced excitations in rat hippocampus and cortex.
The neuronal effects of somatostatin-14 (SS-14) and its influence on responses to acetylcholine (AcCho) were studied in vivo in the rat parietal cortex and dorsal hippocampus, using single-unit recording and microiontophoresis. SS-14 inhibited spontaneous firing of nearly all cells tested, while AcCho facilitated their firing. In contrast to its direct slowing effect, sustained iontophoretic application of SS-14 enhanced AcCho-induced excitations in 78% of all cells tested. This AcCho-enhancing effect of SS-14 was dose dependent. SS-14 did not enhance the responsiveness to pulses of the excitatory amino acid glutamate. Neurons tonically driven by iontophoretic currents of AcCho responded to concurrent pulses of SS-14 with an increase in firing. Thus, iontophoretic application of SS-14 can produce qualitatively different effects on the spontaneous activity of its target cells depending on the simultaneous effects of other chemical messengers. These condition-dependent interactions may explain the diverse neuronal effects of SS-14 reported in the literature.
D000109:Acetylcholine / Q000494:pharmacology*; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D004357:Drug Synergism; D005971:Glutamates / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D011712:Pyramidal Tracts / Q000187:drug effects; D051381:Rats; D013004:Somatostatin / Q000494:pharmacology*; D013570:Synaptic Membranes / Q000187:drug effects
D005971:Glutamates; D013004:Somatostatin; D000109:Acetylcholine