The Effect of Apomorphine and Ergocriptine on the Release of MSH by the Pars intermedia of Rana pipiens

Abstract

In an attempt to further characterize the nature of the innervation controlling melanophore-stimulating hormone (MSH) release from the pars intermedia (PI), pellets containing either apomorphine or ergocriptine were implanted in contact with the PI of the frog, and the effect on the animal’s coloration was observed. Frogs with apomorphine implants exhibited skin pallor for several hours and those with ergocriptine implants were pallid for a few days. Hypophysectomized (HX) frogs which had been darkened with MSH regained their pallor no sooner when given an injection of apomorphine than with the vehicle. However, intact dark frogs lightened when injected with apomorphine. Frogs darkened by autotransplantation of the PI to the dorsal lymph sac were lightened by an injection of apomorphine. Frogs lightened by an ergocriptine implant on the PI and then darkened by MSH did not lighten sooner than HX frogs given an injection of MSH. Ergocriptine-containing pellets implanted in the thigh took longer to produce the same effect than those implanted in contact with the PI. Since apomorphine is known to stimulate dopamine receptors in the central nervous system, and there is some evidence that ergocriptine does also, the above evidence supports the hypothesis that dopamine receptors are present in the PI.

Biosynthesis, processing, and control of release of melanotropic peptides in the neurointermediate lobe of Xenopus laevis.

“…The catecholamine in Xenopus pars intermedia has been identified as dopamine (Terlou and Van Kooten, 1974). The results of various pharmacological studies (Tanzer and Thoenen, 1968;Smith, 1975;DeVolcanes and Weatherhead, 1976) have lent support to the hypothesis that the release of MSH is under inhibitory control by dopamine. The effect of dopamine to inhibit release raises the question of whether there is an inhibition of the biosynthesis of MSH by dopamine.…”

Dopamine and background adaptation in bullfrog tadpoles (Rana catesbeiana): A pharmacological and histofluorescence study.

“…This suggests that the agent acted directly on the MSH producing cells to inhibit its release as reported by Smith (1975) and Morgan and Hadley (1976). On the other hand, pimozide, a specific dopamine antagonist (Janssen et al, 1968;Anden et al, 1970) …”

Alteration of the Agouti Mouse Coat Color Pattern by Bromoergocryptine. Possible Involvement of MSH

“…One approach to testing this hypothesis was to inhibit MSH secretion and observe changes in the normal develop ment of the coat color. Ergocryptine was cho sen for this study, since it has been reported to inhibit the secretion of MSH [11,16,19].…”