Retina nitric oxide

Moreover in the retina, iron is a cofactor of a number of other enzymes, including nitric oxide synthase, (i-carotene monooxygenase, and RPE65-isomerohydrolase converting all-tranx-retinol to 11 -m -retinol in the visual cycle. 

In the rat retina, ischemia upregulates expression of the neuronal nitric oxide synthase and cyclo-oxygenase-2 these effects can be effectively inhibited by lutein (Choi et al., 2006). 

High levels of nitric oxide have also been shown to cause destruction of photoreceptor cells in the retina. This is believed to be due to a prolonged increase in cGMP formation. Finally, nitric oxide and cGMP have been reported to have a role in epileptic seizures. 

Broillet MC, Firestein S (1997) Beta subunits of the olfactory cyclic nucleotide-gated channel form a nitric oxide activated Ca2+ channel. Neuron 18 951-8 Bugnon O, Schaad NC, Schorderet M (1994) Nitric oxide modulates endogenous dopamine release in bovine retina. Neuroreport 5 401—4... 

Sharma RK, Perez MT, Ehinger B. 1997. Immunocytochemical localisation of neuronal nitric oxide synthase in developing and transplanted rabbit retinas. Histochem Cell Biol 107 449-458. 

Sharma RK, Warfidnge K, Ehinger B. 2001. Expression of nitric oxide synthase during the development of RCS rat retinas. Ophthalmologica 215 222-228. 

NO is an important neuromodulator in the retina, and is implicated in many physiological processes (Goldstein et al., 1996). NO is synthesized from arginine via the action of nitric oxide synthase (NOS). Three distinct isoforms of NOS have been identified. Neuronal NOS (nNOS) and endothelial NOS (eNOS) are Ca -dependent. nNOS is constitutively expressed by certain types of amacrine cells in the retina. These cells often have long projections in the irmerplexiform layer (Sharma et al., 1997 Sharma et al., 2001). eNOS is expressed by the endothelial cells of blood vessels (Cheon et al., 2003). iNOS is Ca -independent and expressed in Muller and RPE cells in response to certain stimuli (Lopez-Costa et al., 1997). Activation of the NMDA receptor leads to an increase in intracellular calcium levels, which can induce expression of, and activate NOS isoforms, either directly (nNOS) or via the activation of calcium-dependent protein kinase C (PKC) (Lipton, 1999) (O Figure 3-6). 

Cheon EW, Park CH, Kang SS, Cho GJ, Yoo JM, et al. 2002. Nitric oxide synthase expression in the transient ischemic rat retina Neuroprotection of betaxolol. Neurosci Lett 330 265-269. 

Lopez-Costa JJ, Goldstein J, Saavedra JP. 1997. Neuronal and macrophagic nitric oxide synthase isoforms distribution in normal rat retina. Neurosci Lett 232 155-158. 

Dighiero, P., Reux, I., Hauw, J.-J., Fillet, A. M., Courtois, Y., and Goureau, O. (1994). Expression of inducible nitric oxide synthase in cytomegalovirus-infected glial cells of retinas from AIDS patients. Neurosci. Lett. 166, 31-34. 

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