Electrical responses of pineal cells to thyroid hormones and parathormone. A microelectrophoretic study

The effects of microelectrophoretic application of thyroxin, thyrocalcitonin and parathormone on pineal cells of urethane anesthetized guinea pigs were evaluated. A total of 162 cells were tested with thyroxin, 122 of these units also being subjected to the microelectrophoresis of the indolamine melatonin. 68 cells were excited by the administration of thyroxin, 63 were inhibited while the remaining cells did not respond. 79% of the cells tested with both thyroxin and melatonin responded in a similar way to two substances. The responses to thyroxin varied significantly depending on whether the cells were tested during the day or at night. 104 pineal cells were tested with thyrocalcitonin, 20 U exhibiting an increased firing frequency, 58 showing an inhibitory response and the remaining 26 being unresponsive. Parathormone was applied to 64 pineal cells. Of the 43 cells responding to the hormone, 29 were excited and 14 showed decreased activity. In general, these results suggest that pineal cells may be subject to feedback control by the hormones of the thyroid and parathyroid glands.