Further observations on the distribution and properties of teleost melanin concentrating hormone

Abstract

The distribution of melanocyte concentrating hormone (MCH) bioactivity was mapped in the trout brain from cryostat sections cut in several planes. Most of the bioactivity occurred in the ventral third of the hypothalamus, with about 30% of the activity in the dorsal hypothalamus. The bioactivity was rapidly lost if the hypothalami were extracted in dilute acid, with a final extraction pH of 5.2. This loss, which can be avoided if the extract is heated, is presumed to be the result of hypothalamic enzyme activity. Preliminary chemical characterisation indicates that the molecule is a small basic peptide, of less than 2000 daltons (Da) and with an isoelectric point greater than 9.5. MCH bioactivity was also found in the hypothalamus but not the pituitary of Lampetra, Rana, Xenopus, and the rat. The activity from Xenopus and Lampetra had a similar Rf value to MCH from trout during polyacrylamide gel electrophoresis. Partially purified MCH of trout origin, free from MSH bioactivity, induced melanin concentration in eel melanophores but Xenopus melanophores failed to respond.