Experimental Studies on the Hypothalamic Control of the Pars Intermedia Activity of the Frog, Rana Nigromaculata

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Abstract
In the hypothalamo-hypophysial (HH) tract-transected frog, Rana nigromaculata, the physiological activity in the pars intermedia was studied by means of melanophore-stimulating hormone (MSH) assay and electron microscopy. The MSH assay presented evidence that the MSH content of single pars intermedio-posterior greatly decreases. The electron micrographs revealed that a numerical diminution of secretory granules and an increase of rough-surfaced endoplasmic reticulum are prominent in the pars intermedia cells. The above results suggest that, not only the release of MSH from the pars intermedia cells, but also the synthesis of this hormone is increased in the cells after transection of the HH tract. Furthermore, it is assumed that the function of the pars intermedia cells is controlled by inhibitory nerves from the hypothalamus.