Subject(s)
Light , Melatonin/biosynthesis , Nitric Oxide/physiology , Photoreceptor Cells/metabolism , Animals , Arylamine N-Acetyltransferase/antagonists & inhibitors , Arylamine N-Acetyltransferase/metabolism , Chickens , Circadian Rhythm , Cyclic GMP/metabolism , Dark Adaptation , Dibutyryl Cyclic GMP/pharmacology , Dopamine Agonists/pharmacology , Nitroprusside/pharmacology , Photoreceptor Cells/drug effects , Photoreceptor Cells/radiation effects , Radioimmunoassay , Tetrahydronaphthalenes/pharmacology , Vasodilator Agents/pharmacologyABSTRACT
Nitric oxide synthase (NOS) activity, as measured by the formation of L-[3H]citrulline from L-[3H]arginine, was blocked by micromolar concentrations of NOS inhibitors in retinal homogenates, but concentrations approximately 20-3000 times higher were needed in intact retina. The higher concentrations could be related to transport of the NOS inhibitors into neuronal cells and/or their sequestration within glial cells. NG-monomethyl-L-arginine and N-iminoethyl-L-ornithine significantly inhibited L-[3H]arginine uptake, whereas N omega-nitro-L-arginine methyl ester and N omega-nitro-L-arginine had little or no effect on L-[3H]arginine uptake. The high concentrations of the inhibitors needed to inhibit nitric oxide production in intact tissue and their different interactions with arginine uptake systems may explain some of the conflicting results on the activity of NOS inhibitors on a range of physiological parameters in vivo.
Subject(s)
Blood-Retinal Barrier/physiology , Chickens/physiology , Enzyme Inhibitors/pharmacology , Neurons/physiology , Nitric Oxide Synthase/antagonists & inhibitors , Retina/enzymology , Animals , Arginine/analogs & derivatives , Arginine/pharmacology , Citrulline/metabolism , In Vitro Techniques , NG-Nitroarginine Methyl Ester , Nitric Oxide Synthase/metabolism , Ornithine/analogs & derivatives , Ornithine/pharmacology , Pigment Epithelium of Eye/drug effects , Pigment Epithelium of Eye/metabolism , Retina/cytology , omega-N-MethylarginineABSTRACT
The functional state of the amacrine cells which contain enkephalin-, neurotensin- and somatostatin-like immunoreactivity of the chicken retina was monitored by measuring the rate of change in the levels of [Leu]enkephalin-like immunoreactivity in the retina. Dark-adapted birds were exposed to lights of different intensities for 12 h. At light levels of < or = 0.03 microW/cm2, the ENSLI amacrine cells were highly active but, by 0.08 microW/cm2, they reached a state of maximum inactivation. Thus, the ENSLI amacrine cells act as flip-flop devices, inactivated by critical levels of light, which correspond to those which inactivate pineal melatonin synthesis. They may, therefore, be involved in retinal pathways which signal the difference between day and night.