Adrenergic Regulation of “Synaptic” Ribbon Populations in the Rat Pinealocyte

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“Synaptic” ribbons (SR) are functionally enigmatic organelles characteristic of a number of neuroreceptor cells including the mammalian pinealocyte. SR appear to be responsive to a number of physiological stimuli, both normal and experimental. During the first days after birth, an initial, non-rhythmic rise in SR numbers nocturnally and diurnally (King and Dougherty, 1980) appeared to reflect a similar non-rhythmic increase in norepinephrine (NE) content in the neonatal rat (Moore and Smith, 1969). During the second postnatal week, both SR numbers (fig. 1) and NE content developed circadian rhythms, being high nocturnally and low diurnally. Our observations suggested that the circadian rhythm in SR numbers is regulated or influenced directly by an adrenergic mechanism via the superior cervical ganglia. Morphometric analyses of SR populations in female rat pinealocytes were performed to determine changes related to (1) continuous light, (2) continuous darkness, (3) isoproterenol, isoproterenol-propranolol and isoproterenol-phentolamine administration and (4) bilateral superior cervical ganglionectomy (SCGx) and SCGx-isoproterenol administration. Comparison of this data to that obtained from SR populations during the course of so-called “normal” 12 hours light:12 hours darkness cycles was made (fig. 2).