Regulation of retinal dopamine biosynthesis and tyrosine hydroxylase activity by light

Fed Proc. 1984 Sep;43(12):2709-13.


Dopamine (DA)-containing neurons of the rat retina are apparently activated transsynaptically by photic stimulation. Exposure of dark-adapted rats to light increases retinal DA biosynthesis and metabolism. Associated with the light-evoked increase of DA biosynthesis is a rapid activation of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine biosynthesis. The activation of TH is characterized by an increased affinity of the enzyme for the pteridine cofactor. Because TH in dark-adapted retinas is apparently not saturated with cofactor, the light-evoked increase of affinity is probably responsible for the observed stimulation of DA biosynthesis. Cyclic AMP (cAMP)-dependent protein phosphorylation in vitro activates TH extracted from dark-adapted retinas, and phosphorylation-induced TH activation is very similar and not additive with light-evoked activation of the enzyme. Incubation of viable cell suspensions of dissociated retinas with 8-bromo cAMP also activates TH, which indicates the availability of sufficient cAMP-dependent protein kinase in the proper subcellular compartment to regulate the enzyme in situ. The DA-containing neurons of the rat retina are tonically inhibited in darkness, and evidence is presented that this tonic inhibition involves direct synaptic input to the DA neurons from gamma-aminobutyric acid-containing amacrine cells. The DA-containing neurons are also subject to feedback inhibition through DA receptors, and to modulation by alpha 2-adrenergic receptors.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Dopamine / biosynthesis*
  • Enzyme Activation
  • Light
  • Phosphorylation
  • Protein Kinases / metabolism
  • Rats
  • Retina / metabolism*
  • Retinal Ganglion Cells / enzymology
  • Tyrosine 3-Monooxygenase / metabolism*
  • gamma-Aminobutyric Acid / pharmacology


  • gamma-Aminobutyric Acid
  • Tyrosine 3-Monooxygenase
  • Protein Kinases
  • Dopamine