Cerebrospinal fluid-contacting area of the deep pineal: effects of photoperiod.

The surface of the pineal recess of the Syrian hamster demonstrates three morphologically distinct zones that are classified as the peripheral, transitional, and central zones. The central zone is the most remarkable because of the number of distinguishable morphological specializations in this region that appear to indicate interaction between the cerebrospinal fluid (CSF) and associated ventricular structures and the deep pineal gland. CSF-contacting pinealocytes are present in the central zone and have a relatively indistinct ventricular surface except for the presence of surface blebs and pinealocyte processes that course on the surface of the deep pineal. Supraependymal neurons and neuronal processes appear to converge on the central zone, occasionally having presumptive terminals that are associated with the cells of the central zone. When the hamsters were maintained in a short photoperiod (LD 8:16), the CSF-contacting area of the pineal recess was significantly larger in those hamsters killed 2 hours before lights off compared to those killed 2 hours before lights on (P less than 0.01). There were no significant differences in the CSF-contacting area when comparing two groups of hamsters maintained in a long photoperiod (LD 14:10, killed 2 hours before lights on and lights off, respectively). There was statistically significant interaction (P less than 0.05) between the lighting cycle and the time of day of death on the appearance of CSF-contacting pinealocytes. The hamsters maintained in LD 8:16 had significantly reduced testicular weights when compared to those maintained in LD 14:10. The plasticity of the central zone and the associated CSF-contacting pinealocytes of the pineal recess of the hamster are evidence that this region demonstrates morphological changes that are dependent upon the physiological state of the animal.