The effects of short pulses of light at night on numbers of pineal ?synaptic? ribbons and serotonin N-acetyltransferase activity in male Sprague-Dawley rats

Abstract

To characterize further the functionally enigmatic "synaptic" ribbons (SR) of the mammalian pineal gland and to study possible relationships to melatonin synthesis, in the present investigation rats were exposed to short pulses of light at night when both SR numbers and serotonin N-acetyltransferase (NAT) activity are high in comparison to day-time values. Male Sprague-Dawley rats were killed at 13:00 and 01:00 h, respectively, and at 01:10 and 02:00 h after exposure to light for 10 and 60 min, respectively. The pineals were rapidly taken out and cut sagittally in half. One half was processed for electron-microscopic quantitation of SR numbers and the other half for NAT determinations. It was found that both SR numbers and NAT activity decreased significantly when the animals were exposed to light at night. Although both parameters showed corresponding changes, there was no clear-cut correlation between SR numbers and NAT activity in individual animals within a group, except after exposure to light for 60 min when a positive correlation (R = 0.939; p less than 0.05) existed. After exposure to light the electron-lucent vesicles of the SR decreased in number, but the length of the SR was unchanged. These results show that numbers of pineal SR can be easily and quickly manipulated and that the presently used model may be ideal in studying the poorly understood mode in which degradation of SR occurs.

Plasticity of retinal ribbon synapses

“…Short pulses of light given at night decrease SR numbers (Karasek et al, 1988b;Maitra et al, 1986). Acute extension of the dark phase results in high SR numbers, whereas extension of the light phase decreases SR numbers (Vollrath and Howe, 1976).…”

‘Synaptic’ Bodies in the Pineal Glands of the Cow, Sheep and Pig

“…In the pineal gland they are thought to play an important role in the communication between adjacent cells [2,3] or to regulate the number of (^-adrenergic receptors (4). Sev eral studies suggest that SR are influenced by (1-adrcncrgic mechanisms [5][6][7], SR have been extensively studied in the rat [8][9][10], guinea pig [3, 11. 12] and Djungarian hamster [13.…”

Pinealocyte synaptic ribbons and neuroendocrine function

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