Abstract
Nerve endings on adrenaline cells in male rat adrenal medullas were investigated by quantitative electron microscopy, with sampling at 8 times during a standard light: dark (12:12) photoperiod. Number (N) per unit area of 2 vesicle types (small clear vesicle, SCV; large granular vesicle, LGV) and % of LGV per total vesicle N were determined. Normal (non-operated) animals showed a circadian rhythm (p less than 0.005) in mean SCVN and one with nearly opposite phase relations in % LGVN. Doubly sham-operated animals had a similar rhythm in %LGVN but diminished circadian change in SCVN. Pinealectomized animals had a circadian pattern in SCVN, but this differed from that of normals in having a 2nd peak, a delay or phase shift of the primary peak, and an increased amplitude of the rhythmic changes.
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