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Abstract
The organization of retinohypothalamic tract (RHT) projections in the rat and hamster
was studied using anterograde transport of cholera toxin conjugated to HRP (CT-HRP).
In both species the major RHT projections lead to the suprachiasmatic nuclei (SCN).
This projection begins in the rostral SCN as a loose plexus in the hamster and a a
dense aggregation of terminals along the chiasmal border in the rat. Through the remainder
of the SCN there is a very dense terminal plexus in the ventral and lateral part of
the nucleus with fewer terminals present medially. The RHT projection to the SCN is
greater contralaterally in the rat whereas in the hamster the contralateral and ipsilateral
projections are approximately equal. In addition to projections to the SCN, the RHT
projects to the anterior hypothalamic area, the retrochiasmatic area and lateral hypothalamic
area in both species. The anterior hypothalamic projections are more extensive in
the hamster than in the rat and extend into the perifornical region, the dorsal hypothalamus
and zona incerta. The SCN and anterior hypothalamic projections are continuous with
a projection to the retrochiasmatic area and, in the hamster, with a projection extending
into the subparaventricular zone with some axons and terminals continuing into the
paraventricular nucleus. In contrast to these, the lateral hypothalamic projection
in the rat is more extensive than in the hamster. Albino and pigmented rats show identical
projections. In addition to the hypothalamic projections, there is in the hamster
a small projection along the base of the telencephalon to the anterior amygdaloid
area and cortical amygdaloid nucleus and a very sparse projection to the anterior
thalamic nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)