Dorsal raphe serotonergic projection to the retina. A combined peroxidase tracing-neurochemical/high-performance liquid chromatography study in the rat.

The existence of retinopetal neurons in the rat was verified using a morphological and neurochemical approach. Horseradish peroxidase injected into the posterior chamber of the eye labeled polygonal, ovoid, fusiform and small multipolar neurons in the lateral cell groups of the dorsal raphe nucleus. Very small electrolytic lesions of this region produced after several days of survival a significant decrease in the serotonin content of the retina. These results demonstrate the existence of a centrifugal projection to the retina from the lateral cell groups of the dorsal raphe nucleus and show its probable serotonergic nature. Besides, they also provide a new possibility to explain the presence of serotonin in the retina.