Optic afferents to the parabrachial nucleus.

Following intraocular injection of cholera toxin subunit B (CTB), optic afferents to the dorsal pontine region were observed in Mongolian gerbils, Chilean degus, and laboratory rats. CTB-positive optic axons emerge at the caudal pole of the superior colliculus, descend through the periaqueductal gray, and innervate the lateral parabrachial nucleus. This projection appears to be a continuation of the retinal pathway that innervates the dorsal raphe nucleus in these same species.