A second hypothalamic nucleus receiving retinal input in man: the paraventricular nucleus.

A retinofugal projection to the suprachiasmatic nucleus of the hypothalamus has been described in man by means of a newly developed staining technique (PPD) for tracing degenerated fibers in the human brain. We applied the PPD method to the chiasmal/hypothalamic area of human autopsy brains from patients who had incurred prior optic nerve damage. We followed degenerated fibers from the optic nerve through the optic chiasm and the optic tract. At the optic chiasm/tract junction, some fibers were seen to diverge and to form an optic fascicle which traversed the lateral preoptic-anterior hypothalamic area towards the third ventricle. These degenerated fibers terminated in the paraventricular nucleus of the hypothalamus. We suggest that there are at least two retinohypothalamic pathways in man. Some of the neuroendocrine imbalances in blind persons may be attributed to the disruption of the retinal input to the paraventricular and suprachiasmatic nuclei of the hypothalamus. These retinohypothalamic pathways may be the anatomical substrates for light/dark entrainment of human neuroendocrine and autonomic regulatory processes.