We have isolated a cDNA clone encoding a deep brain photoreceptive molecule from the hypothalamic cDNA library of the toad, Bufo japonicus. The deduced amino acid sequence showed the highest similarity to that of pinopsin (75-76%) among vertebrate retinal opsins, indicating the expression of toad pinopsin in the deep brain. Antibodies raised against the C-terminal tail of toad pinopsin stained cell bodies and the knob-like structures of the cerebrospinal fluid-contacting neurons in the anterior preoptic nucleus. This region is known to play an important role in breeding behavior, suggesting that toad pinopsin acts as a photosensor for the photoperiodic gonadal response.
Yoshikawa, T., Okano, T., Oishi, T., & Fukada, Y. (1998). A deep brain photoreceptive molecule in the toad hypothalamus. FEBS Letters, 424(1–2), 69–72. https://doi.org/10.1016/S0014-5793(98)00139-2