Appearance of Crypt Neurons in the Olfactory Epithelium of the Skate Raja clavata During Development

Crypt neurons are olfactory receptor cells located in the olfactory epi- thelium of fishes. They exhibit a peculiar and well-recognizable morphol- ogy, although their odorant specificity is still unknown. Data on their appearance during development are few and far between. This study set out to identify the time at which crypt neurons appeared in the skate, Raja clavata, using histological and immunohistochemical methods. For this purpose, embryos and juveniles at different stages of development, from 13 weeks after laying (11 weeks before hatching) to 24 weeks after hatching, were examined. The crypt neurons were identified on a morpho- logical basis. An anti–a-tubulin antibody and two lectins (wheat germ agglutinin and peanut agglutinin) were used to highlight morphological details. The olfactory marker protein was detected by immunohistochem- istry, because this protein is a marker of neuronal maturity in verte- brates. The crypt neurons could be detected by their morphology at 15 weeks after laying and became strongly olfactory marker protein immu- noreactive 22 weeks after laying. Although involvement of crypt neurons in reproductive behavior has been inferred in various studies on bony fishes, their early presence in skate embryos and juveniles may suggest that they are not exclusively involved in sexual behavior.