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J. Hannibal, L. Kankipati, P. D. Gamlin; Central Projections of Intrinsically-photosensitive Retinal Ganglion Cells in the Macaque Monkey. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5028.
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Circadian rhythms generated by the suprachiasmatic nucleus (SCN) are entrained to the environmental light/dark cycle via retinal projections which, in rodents, originate primarily from melanopsin expressing intrinsically photosentisitive retinal ganglion cells (ipRGCs). This pathway, known as the retinohypothalamic tract (RHT), is also involved in non-image-forming photoreceptions such as the pupillary light reflex and masking behaviour. In rodents and in humans, the melanopsin containing ipRGCs contains the neurotransmitter pituitary adenylate cyclase activating polypeptide (PACAP). To study the central projection of ipRGCs in the monkey brain, we examined the retinal target areas in the brain containing PACAP and an anterograde tracer Cholera Toxin subunit B (CtB).
Two macaque monkeys were anesthetized and received a unilateral intravitreal injection of 100 µl of 1 % CtB. After 7-10 days’ survival, the animals were transcardially perfused during pentobarbital anaesthesia and the brains were removed, cryoprotected and sectioned at 40 µm free-floating sections through the SCN, the lateral geniculate nucleus, and the pretectum. Sections were stained using a well-characterized mouse monoclonal anti-PACAP antibody and a goat anti-CtB antibody, and fluorescence images were obtained by confocal microscope.
Bilateral retinal projections containing CtB immunostaining were identified in the SCN, the lateral geniculate complex including the pregeniculate nucleus (PrGC), the olivary pretectal nucleus (PON), the nucleus of the optic tract (NOT) and in the superior colicullus (SC). Co-localization of PACAP and CtB was found in retinal nerve terminals of the rostral and mid SCN. In the caudal SCN CtB nerve fibres, not co-storing PACAP were demonstrated. Co-localization was also found in retinal projections in the PrGC. In the PON and in the NOT, a relatively sparse amount of CTB containing fibres co-stored PACAP immunoreactivity.
IpRGCs of the macaque monkey project to the SCN, the pregeniculate nucleus, the PON and the NOT.
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