Dopamine and melatonin interactions in the intact chicken eye. Electrooculographic and biochemical study

Electrophysiological and biochemical techniques were used to investigate the interactions between dopamine (DA) and melatonin (MEL) in the intact chicken eye. Endogenous DA depletion induced by intraocular administration of alpha-methyl-para-tyrosine (alpha-MPT), a selective tyrosine hydroxylase inhibitor, decreases the transepithelial potential (TEP) of the retinal pigment epithelium and reduces the light peak (LP) recorded by an indirect electro-oculographic (EOG) method. An intraocular injection of MEL also reduces the TEP but does not reduce the LP. Retinal MEL is increased after endogenous DA depletion and a tight inverse correlation between DA and MEL contents was found. The present data, together with other findings support the hypothesis (1) that in the intact chicken eye, DA and MEL play respectively a role of light and dark signals on the TEP, and (2) that a balance between these two neurohormones may be responsible for the regulation of RPE events which are dependent on light-dark conditions.