Direct projections from the anterior and tuberal regions of the lateral hypothalamus to the rostral part of the pineal complex of the rat. An anterograde neuron-tracing study by using Phaseolus vulgaris leucoagglutinin.

The anterograde tracer, Phaseolus vulgaris leucoagglutinin, was injected into the lateral hypothalamic division of the Wistar rat. After 7 days of survival the animals were fixed by perfusion, and cryostat sections processed for visualization of the tracer by immunohistochemistry. Injections into the anterior and tuberal regions of the lateral hypothalamic division labeled neurons which projected caudally to the rostral part of the pineal complex, e.g. the deep pineal gland and the pineal stalk. Labeled fibers were in this study not observed in the superficial pineal gland. Due to the direct innervation of the lateral hypothalamic region from the retina and the involvement of this area in circadian rhythmicity, the projections, demonstrated in this study, from the lateral hypothalamic region to the pineal gland are suggested to transmit impulses which modulate the circadian activity of the rat pineal gland.