Onset of Melanophore-stimulating Substances by the Pars Distalis and Pars Intermedia of the Pituitary Body of Ambystoma tigrinum melanostictum

Abstract

It has been shown that the hypothalamus, pars distalis and pars intermedia are separate sources of melanophore-stimulating substances in the tiger salamander, Ambystoma tigrinum melanostictum (Thurmond, 1967). In light of these findings, previous reports that intermedin could first be detected in extracts of heads of tailbud embryos should be re-examined. In fact, recent studies have shown that it is the hypothalamus of the late tailbud embryo (stages 37-38) that possesses melanophore-stimulating activity and only at young larval stages 39-40 does the adenohypophysis evoke a pigment response (Thurmond, 1967). The present study was undertaken to determine if the initial melanophore-stimulating activity of the adenohypophysis was pars intermedia or pars distalis in origin. Project Number 122.