Structural changes in the pars intermedia of the cichlid teleost Sarotherodon mossambicus as a result of background adaptation and illumination

van Eys, GJJM.; Wendelaar Bonga, SE.

Cell and Tissue Research 2203: 561-571

1981


ISSN/ISBN: 0302-766X
DOI: 10.1007/bf00234176
Accession: 017141670

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Abstract
The MSH producing cells in the pars intermedia of S. mossambicus are involved in background adaptation processes. Reflected light received by the eyes affects the activity of these cells. The hypothesis was tested that the pineal organ, as a 2nd photoreceptor, is also involved in regulation of the metabolic activity of the MSH cells. The pineal organ appears to contain to photoreceptor cells and is considered to be capable of transferring information about light conditions to the animal. Removal of the pineal organ of fish kept on a black background has no effect on activity of MSH cells, whereas the activity of these cells in fish kept in darkness is increased. Thus it seems that the pineal organ exercises its influence on MSH cells only in darkness and that this influence results in a reduced activity of these cells. The metabolic activity of MSH cells is inhibited not only be reflected light received by the eyes, but also by the action of the pineal organ as a result of the absence of illumination. No structural signs of secretory activity can be observed in the pineal, which might indicate synthesis or release of substances like melatonin. Administration of melatonin reduces the activity of MSH cells. Neither pinealectomy nor treatment with melatonin has any influence on the 2nd cell type of the pars intermedia, the periodic acid-Schiff positive cells.

Structural changes in the pars intermedia of the cichlid teleost Sarotherodon mossambicus as a result of background adaptation and illumination