The morpho-anatomy and histology of the pineal complex in a major Indian XXXX , @entity67990 : identification of the pineal photoreceptor cells and their responsiveness to constant light and constant darkness during different phases of the annual reproductive cycle.

@entity67990 @entity7136 @entity1 @entity336
In contrast to mammals in which the pineal gland is a discrete structure situated dorsally in the brain, the "pineal gland" in teleost fishes is composed of a number of separate but connected constituent parts, collectively described as the "pineal complex." In this paper, we have described the pineal complex in a common Indian @entity7136 , @entity67990 , which exhibits an annual reproductive cycle. Attempts have been made to (a) provide an in-depth description of the structure of the pineal complex; and (b) identify the photoreceptor cells of the pineal, by exposing the animals to constant light (LL) and constant darkness ( @entity336 ). Furthermore, we examined any possible influence of the reproductive status of the fish on the responsiveness of the pineal photoreceptor cells in @entity67990 following exposure to LL and @entity336 . To this end, a total of four experiments were carried out during the four different phases of the annual reproductive cycle that is characteristic of this species. Each of these four experiments was carried out for a period of 30 days after which the fishes were sacrificed, different parts of the pineal complex were dissected out, and processed for histological and karyometric studies. Our results showed that the pineal complex in this species is composed of three separate but connected parts, (a) an end vesicle (EV); (b) a dorsal sac (DS); and (c) a long and thin pineal stalk (PS) that attaches the EV to the DS. Detailed karyometric and histo-morphologic studies following exposure of the animals to @entity336 and LL showed that constant darkness led to a stimulatory effect on the pineal photoreceptor cells of the EV as evident from a significant increase in the nuclear diameter. In contrast, the nuclear diameter of the photoreceptor cells in animals subjected to constant light showed a significant reduction. Furthermore, the observed cellular changes in the EV of fish exposed either to LL or @entity336 were independent of the stage of the gonadal cycle. The apparent lack of any cellular responses either in the PS, or in the DS, following exposure to LL and @entity336 , suggests that in @entity67990 the photoreceptor cells are located only within the epithelial lining of the EV and that these cells respond in a manner similar to @entity1 pinealocytes when subjected to comparable photoperiod-induced experimental conditions.
