Effects of somatostatin-28 on rat locus coeruleus neurons

The effects of somatostatin-28 (SS-28) on rat locus coeruleus (LC) neurons were investigated with techniques of brain slice and intracellular recording. SS-28 was applied by micropressure ejection through a micropipette. SS-28 (500 microM, 10 or 20 psi, 1 msec - 5 sec) reversibly decreased the firing rate of all neurons of the locus coeruleus tested. In addition to inhibition of spontaneous firing, larger concentrations of SS-28 also hyperpolarized the neurons of the locus coeruleus and simultaneously decreased the input resistance. At the greatest concentration (20 psi x 5sec) applied, SS-28 produced complete inhibition of firing of all neurons tested; the inhibition was associated with a 11-mV hyperpolarization and decreased input resistance 9 percent. The voltage-current relationship of the resting cell revealed an inward-going rectification that became enhanced after the pressure application of SS-28. The reversal potential for the SS-28-induced hyperpolarization was -116 mV, which is approximately the potassium equilibrium potential. The results also showed that BaCl2 blocked the SS-28-induced hyperpolarization, but apamin did not. We conclude that the inhibitory actions of SS-28 are due to opening the inward-going rectification potassium channels and that SS-28 and somatostatin-14 exert similar electrophysiological actions on LC neurons.