SYMPATHETIC INNERVATION OF THE RAT CHOROID - AN AUTORADIOGRAPHIC TRACING AND IMMUNOHISTOCHEMICAL STUDY

The sympathetic innervation of the choroid was investigated by means o f the anterograde tracer H-3-leucine, injected into the rostral part o f the superior cervical ganglion. The tracer was autoradiographically visualized at the light- and electron-microscopic levels. Labelled unm yelinated fibres were found in the choroid and labelled terminals were observed in close proximity to the smooth muscle cells of arterioles. The labelled terminals contain granular vesicles of different size an d clear vesicles; the mitochondria were of the electron-dense type and no cell-to-cell synaptic contacts were observed. In addition, tyrosin e hydroxylase immunocytochemistry was performed. Immunostained termina ls found in the choroid show ultrastructural features similar to those found in the tracing experiments: granular vesicles of different size , clear vesicles and electron-dense mitochondria. On the basis of prev ious studies and the present observations, it is concluded that the ch oroid has a dual innervation, a parasympathetic innervation from the p terygopalatine ganglion and a sympathetic innervation from the superio r cervical ganglion. The dual innervation is most likely involved in m aintaining the homeostasis of vasodilatation and vasoconstriction in t he choroid.