Enhanced expression of nitric oxide synthase by rat retina following pterygopalatine parasympathetic denervation

Removal of the pterygopalatine ganglion enhanced the expression of nitric oxide synthase (NOS) in the ipsilateral rat retina and optic nerve by immunohistochemical and biochemical criteria. The denervation procedure did not alter the apparent histochemical reactivity of retinal cells normally immunoreactive for NOS but did induce expression in retinal ganglion cells and their axons in the retinal nerve fiber layer and optic nerve. After denervation, the induced NOS immunohistochemical reactivity was consistently visualized by day 7, reached a maximum intensity during days 14 to 28, and thereafter gradually attenuated to become barely detectable by microscopy at 10 weeks. Biochemical assays performed two weeks after pterygopalatine denervation confirmed the immunohistochemical observations, especially with regard to the optic nerve. The induced enzyme activity in both retina and optic nerve showed calcium dependency. These results point towards interactions of the ocular parasympathetic innervation and the retina, between which no known neuronal connections exist.