QUANTITATIVE LIGHT-MICROSCOPIC STUDY ON THE HETEROGENEITY IN THE SUPERFICIAL PINEAL-GLAND OF THE RAT

Background The previous results regarding regional and day-night diffe rences in pinealocyte size in rats are conflicting, The relationships between these differences and the vascularity and sympathetic innervat ion have scarcely been investigated, Methods: Wistar-King rats, kept u nder light/dark 12:12, were killed at midday or midnight in October, T he nuclear density of pinealocytes in the superficial pineal was measu red on the dorsoperipheral, dorsocentral, ventroperipheral, and ventro central regions at distal, middle, and proximal levels at daytime and nighttime, The total area of blood vessels per unit area at daytime an d nighttime and total length of tyrosine hydroxylase (TH)-immunoreacti ve fibers per unit area at daytime were determined on the same regions at the same levels, Results: Pinealocyte size was larger toward the d istal levels and in the periphery than in the center at any level, The area of blood vessels and length of TH fibers were also larger toward the distal levels; the former in the ventral region and the latter in the dorsal and ventral regions were larger in the periphery than in t he center, Ventral pinealocytes, but not dorsal ones, showed day-night changes in size, Prominent day-night rhythms in area of blood vessels occurred in the ventral region, where TH fibers were more abundant th an in the dorsal region, Conclusions: Pinealocyte size shows the dista l to proximal and peripheral to central gradients, which may be relate d to the differential distribution of blood vessels and sympathetic fi bers, Since pinealocytes and blood vessels, showing prominent day-nigh t changes in size, are localized in the more richly innervated regions , sympathetic fibers may play an important role in controlling these r hythms. (C) 1998 Wiley-Liss, Inc.