Characterization of the rat pituitary capsule: Evidence that the cerebrospinal fluid filled the pituitary cleft and the inner side of the capsule.

In humans, the pituitary gland is covered by a fibrous capsule and is considered a continuation of the meningeal sheath. However, in rodents some studies concluded that only the pars tuberalis (PT) and pars nervosa (PN) are enwrapped by the pia mater, while others showed that the whole gland is covered by this sheath. At PT the median eminence subarachnoid drains cerebrospinal fluid (CSF) to its cisternal system representing a pathway to the hypothalamus. In the present study we examined the rat pituitary capsule to elucidate its configuration, its physical interaction with the pituitary border and its relationship with the CSF. Furthermore, we also revisited the histology of the pituitary cleft and looked whether CSF drained in it. To answer such questions, we used scanning and transmission electron microscopy, intracerebroventricular infusion of Evan´s blue, fluorescent beads, and sodium fluorescein. The latter was measured in the pars distalis (PD) and various intracranial tissues. We found a pituitary capsule resembling leptomeninges, thick at the dorsal side of the pars intermedia (PI) and PD, thicker at the level of PI in contiguity with the PN and thinner at the rostro-ventral side as a thin membrane of fibroblast-like cells embedded in a fibrous layer. The capsule has abundant capillaries on all sides. Our results showed that the CSFs bathe between the capsule and the surface of the whole gland, and ciliate cells are present in the pituitary border. Our data suggest that the pituitary gland intercommunicates with the central nervous system (CNS) through the CSF.

Physiological changes of growth hormone during lactation in pup rats artificially reared.

During the lactation period, rat pups are fed by the dam, and the patterns of mother-pup interaction change during this period. Additionally, there are changes in feeding; first, mother´s milk is the only food needed for sustenance, and later, it is combined with solid food and water. GH serum concentrations depend on both maternal-pup interaction and energy metabolism. In the artificial rearing (AR) procedure, pups are deprived of mother-pup interaction, and the feeding pattern is controlled. This rearing paradigm has been used in rats to analyze the effects of maternal deprivation on social behavior. In the present study, we analyzed the variation in GH, acylated ghrelin and IGF-1 serum concentrations throughout the lactation period in AR pups. At pnd7, the maternal rearing (MR) pups responded to a 4 h fast with a drop in GH serum concentration, which is a well-known response to maternal deprivation. GH serum levels in the AR pups did not change, suggesting an adaptation phenomenon. A dopamine inhibitory effect of GH secretion was observed in pnd7 cultured somatotropes, suggesting dopamine regulation of GH secretion at this age. Acylated ghrelin serum levels in the AR pups showed an inverted pattern compared to that in the MR pups, which was related to the artificial feeding pattern. IGF-1 serum levels were lower in the AR pups than in MR pups, which was associated with hepatic GH resistance and with low Igf1 mRNA expression at pnd7. Interestingly, at pnd14, both pup groups showed high hepatic Igf1 mRNA expression but low IGF-1 serum levels, and this was inverted at pnd21. However, serum glucose levels were lower in the AR pups at pnd14 but reached the same levels as the MR pups at pnd21. Moreover, hepatomegaly and higher hepatic GH-receptor levels were observed in the AR pups at pnd21, which was in agreement with an absence of a solid food meal. During AR, the pups lost the maternal interaction-stimulated GH secretion, which correlated with lower IGF-1 serum levels during the first week of postnatal development. Later, the AR pups exhibited hepatic responses, in order to satisfy the metabolic demand for the normal weaning, with low carbohydrates levels in their meal.