Observations on the secretions of the subcommissural organ and the pineal in the adult brush-talled possum (Trichosurus vulpecula).

Secretory functions of the subcommissural organ (SCO) were investigated using mainly transmission and scanning electron microscopes, in 40 adult (19 males, 21 females) Trichosurus vulpecula which were caught in different seasons over several years. There is clear evidence of apical secretion, Reissner's fiber (RF), a presumptive basal secretory material with associated perivascular space and labyrinthine basal lamina. Secretory function does 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 also histologically examined. The SCO showed very little MEL. Findings suggest that the PIN of this animal has a low capacity to store and secrete MEL. Further, there is no evidence for the increased storage or secretion of MEL during darkness, and more specifically at midnight. The present investigators support the view that other indoles such as methoxytryptophol or pineal peptides may elicit the physiological effects of PIN.