Morphological evaluation of the pineal gland of mares in reproductive activity and in physiological anestrus

Abstract

The pineal gland (PG), part of the epithalamus, is sensitive to light and, in vertebrates, secretes melatonin, in the absence of light. This hormone seems to interfere in the adaptation of reproductive functions to light conditions, especially in animals that reproduce seasonally, such as horses, allowing birth in times of warmer weather and favorable to the availability of food. Therefore, the objective of this study was to evaluate and describe the ultrastructural components of the PG of 24 mares, distributed in two phases: breeding season and physiological anestrus, each one with 2 groups (3-8 and 15-20 years of age). The PG was removed after the animals were slaughtered, and processed in stages of fixation, histological sections and staining. The analysis of the processed material was performed using light and transmission microscopy, and the data were subjected to statistical analysis. The PG was found in the midsagittal plane, dorsocaudal to the interthalamic adhesion and ventrally to the splenium of the corpus callosum, presenting ovoid or piriform shape. It was surrounded by a connective tissue capsule, from which septa depart from and, accompanied by blood vessels, divide the parenchyma into lobules. The main glandular components were pinealocytes and astrocytes. Calcareous concretions were evidenced in the nucleus and cytoplasm of pinealocytes, as well as in the extracellular space of all PGs, regardless of age and/or reproductive stage. On the other hand, mares in physiological anestrus had a higher number of pinealocytes.