Nitric oxide inhibits electrically active units in the rat pineal gland

Extracellular multiple unit recordings were performed in isolated rat pineal glands to determine a possible effect of nitric oxide (NO) on the spontaneous electrical activity of pinealocytes. Spontaneously active cells forming clusters of 3-5 cells fell into two categories: more or less regularly firing clusters (REG, 64%) and irregularly discharging clusters with periodically repeated bursts (RHY, 36%). The NO-donor sodium nitroprusside (SNP) reduced the discharge rate of the great majority of REG clusters and of all the RHY clusters examined. Moreover, the burst activity of RHY clusters was abolished. These results could be completely reproduced by using another NO-donor, S-nitroso-N-acetyl-penicillamine (SNAP). The NO synthase inhibitor NMLA had no effect on REG and RHY clusters. The results show that spontaneous electrical activity is an intrinsic function of the rat pineal gland. NO can modulate the electrical activity affecting discharge rate and discharge pattern.