Kokel et al. claim to have discovered the first known light sensitive circuit in the vertebrate (zebrafish) hindbrain that drives motor behavior. On the contrary, a photosensitive region in an in vitro preparation of the turtle hindbrain that produces a neural correlate of a blink response when stimulated was reported by us in 1998 (Anderson and Keifer, 1998). In fact, there is an interesting literature on "extraoptic...
Kokel et al. claim to have discovered the first known light sensitive circuit in the vertebrate (zebrafish) hindbrain that drives motor behavior. On the contrary, a photosensitive region in an in vitro preparation of the turtle hindbrain that produces a neural correlate of a blink response when stimulated was reported by us in 1998 (Anderson and Keifer, 1998). In fact, there is an interesting literature on "extraoptic" or "extrapineal" photoreceptors in vertebrates that we review briefly in our paper. Like the response reported by Kokel et al., the photosensitive region in turtle is most responsive to blue or magenta wavelengths (< ~550 nm). In our case, we localized the region to the locus coeruleus and isthmo-optic nucleus in the caudal mescencephalon, near the surface of the fourth ventricle. Furthermore, pharmacological analysis indicated that the light-evoked blink response is mediated by serotonin, suggesting the isthmo-optic nucleus is the origin of the response. The region of the isthmo-optic nucleus in reptiles and birds appears to send efferent projections to the retina and saccade-related signals have been reported there. However, the anatomical projections of this region are poorly understood. The function of nonvisual photosensitive regions in brain and why they may be linked with motor centers remains a mystery.
References
Anderson CW and Keifer J (1998) Evidence for a photosensitive region in the caudal mesencephalon of the turtle brain. Exp. Brain Res.119: 453-459.
None declared