Retinal input to the sleep-active ventrolateral preoptic nucleus in the rat

Light-dark periodicity and luminance play important roles in regulating sle ep-wake cycles. We recently identified a discrete cluster of sleep-active c ells in the ventrolateral preoptic nucleus that we hypothesize plays a cent ral role in sleep regulation. These ventrolateral preoptic nucleus neurons are GABAergic and galaninergic and innervate the monoaminergic cell groups that contribute to the ascending arousal system. To determine whether there are retinal inputs to sleep-active ventrolateral preoptic nucleus neurons, we injected 5 mu l of 1% cholera toxin B subunit into one eye in a series of rats. We found anterogradely labeled axons in the ventrolateral preoptic nucleus bilaterally, with a contralateral predominance. Using Fos to ident ify sleep-active neurons, we found that the cholera toxin B subunit-labeled retinal fibers gave rise to terminals that were distributed among the Fos- positive, sleep-active ventrolateral preoptic nucleus neurons. Combining ch olera toxin B subunit staining with galanin immunoreactivity, we found that the retinal terminals formed appositions with the cell bodies and proximal dendrites of galaninergic ventrolateral preoptic nucleus neurons. Followin g Fluorogold injection into the ventrolateral preoptic nucleus region. we f ound retrogradely labeled neurons in the superior part of the peripheral re tina contralateral to the injection site and in the superior temporal quadr ant of the peripheral retina ipsilateral to the injection site. The size of labeled retinal ganglion cells suggested that they belonged to the type II I or W type, which provide luminance input, e.g., to the suprachiasmatic nu cleus. The retinal projection to the ventrolateral preoptic nucleus may pro vide an anatomical substrate by which luminance levels may directly influen ce sleep. (C) 1999 IBRO. Published by Elsevier Science Ltd.