CENTRAL PROJECTIONS FROM THE GOLDFISH PINEAL ORGAN TRACED BY HRP-IMMUNOCYTOCHEMISTRY

Pineal efferent projections have been traced in the brain of the goldf ish (Carassius auratus) by administration of a concentrated solution o f horseradish peroxidase onto the pineal organ. After different surviv al times, fish were sacrificed and the administered peroxidase was rev ealed by immunocytochemistry on paraffin sections using an anti-horser adish peroxidase antiserum. Immunoreactive fibres were seen in the ant erior hypothalamus, habenula, dorsal thalamus, ventral thalamus, optic tectum, torus longitudinalis, area pretectalis, torus semicircularis and dorsal tegmentum. No immunoreactive cell bodies were visualized in the central nervous system, thus suggesting the absence of central pi nealopetal innervation. Since all areas showing pineal labelled fibres are also known to receive retinal inputs, it can be suggested that an overlapping of information from retinal and extraretinal photorecepto rs may be important to processes depending on photic stimulation such as entrainment of circadian rhythms or photoneuroendocrine responses.