Effects of reserpine and p-chlorophenylalanine on the circadian rhythm of granulated vesicles in the pinealocytes of mice.

The number of granulated vesicles in mouse pinealocytes exhibit a distinct circadian rhythm which is abolished by superior cervical ganglionectomy. Since melatonin treatment markedly effects the number of pinealocytic granulated vesicles, it was suggested that a relationship may exist between norepinephrine, melatonin, and the synthesis and/or secretion of pinealocyte granulated vesicles. The present study was undertaken in an attempt to clarify this relationship. Mice were housed in an environmental chamber under controlled lighting (12L/12D), and were treated with either reserpine, a drug which depletes serotonin and norepinephrine, or p-chlorophenylalanine (p-CPA), an inhibitor of serotonin synthesis. They were sacrificed at various times over a twenty-four hour period, and granulated vesicles present in the pinealocytes were quantitated in thin cross sections through pericapillary areas. Reserpine treatment resulted in a marked increase in the number of granulated vesicles during the dark, but led to a slight decrease during the photoperiod. Treatment with p-CPA produced no significant effect. The results of this study do not support our previous theory that melatonin plays an important role in the regulation of the pinealocyte secretory process, but instead points more directly to the significant role that norepinephrine has in controlling pinealocyte secretion.