Quantitative light microscopic study on the heterogeneity in the superficial pineal gland of the rat

Abstract

Background: The previous results regarding regional and day-night differences in pinealocyte size in rats are conflicting. The relationships between these differences and the vascularity and sympathetic innervation have scarcely been investigated. Methods: Wistar-King rats, kept under light/dark 12:12, were killed at midday or midnight in October. The nuclear density of pinealocytes in the superficial pineal was measured on the dorsoperipheral, dorsocentral, ventroperipheral, and ventrocentral regions at distal, middle, and proxi-mal levels at daytime and nighttime. The total area of blood vessels per unit area at daytime and nighttime and total length of tyrosine hydroxy-lase (TH)-immunoreactive fibers per unit area at daytime were determined on the same regions at the same levels. Results: Pinealocyte size was larger toward the distal 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 the 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 than in the dorsal region. Conclusions: Pinealocyte size shows the distal to proximal and peripheral to central gradients, which may be related to the differential distribution of blood vessels and sympathetic fibers. Since pinealocytes and blood vessels, showing prominent day-night changes in size, are localized in the more richly innervated regions, sympathetic fibers may play an important role in controlling these rhythms. Anat. Rec. 250:80-94, 1998. 1998 Wiley-Liss, Inc. The unequivocal morphological evidence for a circa-dian rhythmicity in the pineal gland of mammals was first described by Quay and Renzoni (1966), who demonstrated that the nuclear and nucleolar sizes of the pinealocytes of the rat show similar rhythms, with maximums at midday and low values during the night-time, and that the nuclear and nucleolar sizes are similar between peripheral (cortical) and central (med-ullary) regions. Thereafter, determinations of the size of the pinealocytes in the peripheral and central regions at various time points during a 24-h period in rats have been repeated by many investigators (Diehl, 1981; Becker and Vollrath, 1983; Diehl et al., 1984; Lew et al., 1984; Karasek et al., 1990). However, the original findings by Quay and Renzoni (1966) have not always been reproducible. It is therefore an open question whether the size of pinealocytes differs in different regions and whether 24-h rhythms in the size of pinealocytes exist in different regions in the pineal gland of the rat. Our previous studies revealed that the size of pinealo-cytes of mice (Matsushima et al., 1989) and Chinese hamsters (Matsushima et al., 1983; Sakai et al., 1986; Hira et al., 1989) exhibited a 24-h rhythm similar to that described ...

Regional heterogeneity in immunoreactive macrophages/microglia in the rat pineal gland

“…antigen and it was suggested that the more strongly stained cells, being concentrated distally, were under sympathetic control. A similar gradient change was also found in terms of the pinealocyte size, area of blood vessels and length of tyrosine hydroxylase (TH) 5 fibers that were larger toward the distal level [23]. All the above-mentioned findings suggest a regional heterogeneity and differential gradient of pineal elements.…”

“…Previous study further showed that norepinephrine was the potent inhibitor of MHC class II expression on isolated microglia after IFN‐gamma stimulation [29]. In this regard, the sparse distribution of MHC class II positive PMM in the distal portion of the pineal gland may be attributed to a richer sympathetic innervation in the same area [23].…”

“…Hira et al. [23] have also demonstrated a clear dorso‐ventral difference in the density of TH fibers. It would appear, therefore, that in addition to the cortex and medulla, there may be present a dorsal and ventral arrangement of rat pineal for PMM with distinctive immunophenotypes.…”

“…Hira et al. [23] have demonstrated that rat pinealocytes vary in size – a feature that may be related to the differential distribution of blood vessels and sympathetic fibers. Whether this regional difference also occurs in the PMM is unclear.…”

“…To this end, an immunostaining study has shown that the central zone of the pineal gland was more densely occupied by GFAP-labeled fibers than the periphery [22]. Hira et al [23] have demonstrated that rat pinealocytes vary in size -a feature that may be related to the differential distribution of blood vessels and sympathetic fibers. Whether this regional difference also occurs in the PMM is unclear.…”