Coat color in intact and neurointermediate lobe-grafted agouti mice: effect of dopamine agonists and antagonists

The natural variation in the coat color of agouti C3H Avy mice was observed and reflectometrically recorded during the first 6 months of life. Three well-defined color stages were detected: (a) yellow coat from birth to the 6th week; (b) dark-gray coat from the 8th week to the 6th month, and (c) from the 6th month onward a yellow coat prevailed. To clarify the role played by the pituitary pars intermedia on these coat color variations, pimozide or d-butaclamol were chronically administered to newborn and 6-month-old mice. These drugs produced an intense darkening in the color of the growing hairs in newborn mice and in the color of the newly grown hair of adult preplucked mice. Pituitary pars intermedia grafted in adult yellow mice also produced an intense coat darkening of newly grown hair. Dopaminergic agonists, administered either subcutaneously or close to the grafts, prevented this darkening effect. It is suggested that pars intermedia peptides might be responsible for the hair color cycle in this mouse strain and that peptide secretion is controlled by a tonic inhibitory dopaminergic mechanism which operates from the first days of life.