Observations on the Secretions of the Subcommissural Organ and the Pineal in the Adult Brush-Tailed Possum (Trichosurus vulpecula)

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Abstract
Secretory functions of the subcommissural organ (SCO) were investigated using mainly transmission and scanning electron microscopes, in 40 adult (19 males, 21 females) T. vulpecula which were caught in different seasons over several years. There was clear evidence of apical secretion, Reissner''s fiber (RF), a presumptive basal secretory material with associated perivascular space and labyrinthine basal lamina. Secretory function did not appear to be related to the sex of the animal or to the season when they were investigated. Radioimmunoassay of blood, SCO and pineal gland (PIN) for melatonin (MEL) was carried out in 18 adult animals in summer and winter. Gonads were histologically examined. The SCO showed very little MEL. The PIN of this animal apparently has a low capacity to store and secrete MEL. There was no evidence for the increased storage or secretion of MEL during darkness, and more specifically at midnight. Other indoles such as methoxytryptophol or pineal peptides may elicit the physiological effects of PIN.