Neural elements associated with the subcommissural organ of the brush-tailed possum (Trichosurus vulpecula)

Abstract

By means of various techniques and on the basis of a large sampling of the brush-tailed possum, Trichosurus vulpecula, a detailed description is given of the morphology of the neural elements associated with the subcommissural organ (SCO) and the leptomeninges on the dorsal surface of the midbrain. It is shown that the SCO of the possum is richly innervated, the nerves reaching the cerebral aqueduct by passing through the organ; there is, however, no evidence of a neural link between the SCO and the pineal gland. No typical axo-glandular synapses were found; however, many axo-glandular synaptoid junctions between axons and secretory cells of the SCO were demonstrable within the parenchyma of the SCO and on the aqueductal surface of the organ. The possible functional implications of the findings are: (1) The secretory activity of the SCO may be modified by nerves associated with it; this is in accord with some recently published experimental studies. (2) The nerves that innervate the SCO may also be responsible for ciliary activity on the aqueductal surface of the SCO, thus directing the apical secretory product of the SCO and debris flowing caudally in the cerebrospinal fluid into the poorly ciliated median groove where Reissner's fibre is found.

Central innervation of the rat ependyma and subcommissural organ with special reference to ascending serotoninergic projections from the raphe nuclei

“…The close relationships of the secretory cells of the organ with both blood vessels and the cerebrospinal fluid (CSF), as demonstrated by using classical neurosecretory stains or conventional electron microscopy, indicate that the SCO is involved in neurohumoral regulation (Oksche, 1969;Tulsi, 1983;Rodriguez et al, 1984a,b) or in regulation of the flow of CSF (Cifuentes et al, 1994). Support for the latter opinion comes from indirect evidence that the SCO is lacking or degenerating in animal models with hydrocephalus (Takeuchi et al, 1987;Irogini et al, 1990).…”