Topographic morphometry of the pineal gland of the rat. A 24-hours period, light-dark cycle and seasonal study

Classical studies pointed out to a possible division of rodents' pineal parenchyma in various regions and layers, also observing variations in nuclear sizes that could depend on luminosity cycles. The aim of this study is to analyze the morphological changes of nuclear sizes of pinealocytes that occur in the pineal gland of albino rats during different hours of the day, seasons and photoperiods, taking into account the different layers and regions. We studied differences on karyometric indices of pinealocytes of the peripheral (cortical) and central (medullary) layers of pineal gland in order to analyze the circadian and seasonal modifications, and establish wheth- er these are indicative of functional differences between proximal, intermediate, and distal por- tions. Results showed that the total karyometric values of the distal area are clearly higher than those of the other two areas, and in turn those of the intermediate area are also significantly higher than those of the pars proximalis; and also, that there are significant differences between the pe- ripheral and central karyometric indices of all the pineal regions analyzed. Moreover, there are significant evolutionary circadian, photophasic and seasonal differences between regions and the pi- neal layers analyzed.