Calbindin-D28k- and astroglial protein-immunoreactivities, and ultrastructural differentiation in the prenatal rat cerebral cortex and hippocampus are affected by maternal adrenalectomy

Simultaneous glutamate and GABA(A) receptor agonist administration increases calbindin levels and prevents hippocampal damage induced by either agent alone in a model of perinatal brain injury

Perinatal brain injury is associated with the release of amino acids, principally glutamate and GABA, resulting in massive increases in intracellular calcium and eventual cell death. We have previously demonstrated that independent administration of kainic acid (KA), an AMPA/kainate receptor agonist, or muscimol, a GABA(A) receptor agonist, to newborn rats results in hippocampal damage [Hilton, G.D., Ndubuizu, A., and McCarthy, M.M., 2004. Neuroprotective effects of estradiol in newborn female rat hippocampus. Dev. Brain Res. 150, 191-198; Hilton, G. D., Nunez, J.L. and McCarthy, M.M., 2003. Sex differences in response to kainic acid and estradiol in the hippocampus of newborn rats. Neuroscience. 116, 383-391; Nunez, J.L. and McCarthy, M.M., 2003. Estradiol exacerbates hippocampal damage in a model of preterm infant brain injury. Endocrinology. 144, 2350-2359; Nunez, J.L., Alt, J.J. and McCarthy, M.M., 2003. A new model for prenatal brain damage. I. GABA(A) receptor activation induces cell death in developing rat hippocampus. Exp. Neurol. 181, 258-269]. We now report that KA or muscimol alone administered to immature hippocampal neurons in culture induces significant cell death as evidenced by TUNEL assay. Surprisingly, simultaneous administration of equimolar quantities of these two agonists blocks the effect of either one alone. Moreover, treatment of newborn pups results in less damage compared to either muscimol or KA alone. We further observed that immunoreactivity for the calcium-binding protein, calbindin D(28K), is increased in the brains of pups simultaneously administered KA and muscimol as compared to either alone.

Effects of maternal bilateral adrenalectomy on fetal rat cerebral cortex

We investigated the effects of maternal bilateral adrenalectomy (ADX) on fetal rat cerebral cortices by assessing morphological and morphometrical parameters in light and electron microscopy studies. Pregnant adult rats underwent ADX on day 4 of gestation. Embryonic brain tissue from control and ADX groups were examined at each of the 10 embryonic stages, days 11 through 20 (E11-E20). Control and adrenalectomized pregnant females were sacrificed at each fetal stage, fetuses were removed from the uterine horns, and their brain tissue was processed for light and electron microscopy examination. In the ADX fetuses, the cortical laminae were thicker and overall cortex thickness was greater, but structural differentiation in the primitive cortical layers was delayed compared with that observed in controls. Apart from the differences in embryonic cell development noted at the structural level, we found no noticeable ultrastructural differences between the cerebral cortices of ADX and control fetuses at any of the stages studied. Overall, the ADX group's cortical tissue exhibited a greater degree of cell migration, an extended proliferative period in the cortical layers with the highest proportion of mitotic activity, and a greater thickness than that of control specimens. We believe that by eliminating the inhibitor effects of glucocorticoids, ADX effectively induces mitotic activity and extends the proliferative periods in developing cerebral cortex.

Effects of endogenous and exogenous glucocorticoids on liver differentiation

The effects of maternal bilateral adrenalectomy on day 1 of gestation and betamethasone treatment on fetal liver development were compared, in terms of biochemical and morphological parameters. For fetuses 20 days old (E20), absence of maternal glucocorticoids during gestation caused an increase in the number of nuclei in whole livers, and a significantly decrease of both body weight and protein content per nucleus, in comparison with the control group (C). Betamethasone injection on days 15, 16 and 17 of gestation into adrenalectomized pregnant rats (ADX + BET) did not completely prevent these effects. The electron microscopic analysis of the ADX fetal liver (E20) showed some hepatocyte lesions such as loss of cytoplasmic organelles, increase in hematopoietic cell number as well as a lower cellular maturation in comparison with the control group. The fetal liver from ADX + BET mothers 20 days after gestation displayed a noticeable involution of the hematopoietic component in spite of its relatively immature stage. However, there was no significant change in the degree of fetal hepatocyte lesions. Therefore, supply of maternal glucocorticoids from the beginning of gestation is essential for maintenance of the integral structure of the rat fetal hepatic parenchyma, for the correct maturation of the blood strains and for the beginning of involution of the hematopoietic tissue at the end of gestation.

Maternal adrenalectomy at the early onset of gestation impairs the postnatal development of the rat hippocampal formation: effects on cell numbers and differentiation, connectivity and calbindin-D28k immunoreactivity

The possible role of the maternal glucocorticoids on the postnatal development of the hippocampus was tested with bilateral adrenalectomy of pregnant rats. Surgery was performed 24 hr after sperm-positiveness was determined. The offspring from adrenalectomized mothers, compared with animals from control sham-operated mothers, showed decreased body weight and increased brain weight. The CA1 field of the hippocampus of these animals showed lower number of both Nissl-stained and Calbindin-immunoreactive cells, whereas the granule cell layer of the dentate gyrus showed higher number of both populations. Both types of cell numbers were statistically similar from postnatal Day 21, however, suggesting some compensatory mechanism. The neuronal populations of adrenalectomized animals appeared with a delay in the development of their dendritic trees, cytoplasmic differentiation, and synaptic connections. In the same way, both septohippocampal and hippocamposeptal projections appeared delayed in the adrenalectomized animals with respect to control ones by several days, mainly with regard to regressive events typical of the first 8 days of age. The ultrastructural study showed that every ADX postnatal group appeared more immature than the corresponding control group. These results suggest that gestational levels of maternal glucocorticoids (that were removed by adrenalectomy) influence the normal postnatal development of the hippocampus as reflected in neuron numbers and cell maturation, as well as in the developmental timing of the pattern of connectivity, and that this effect must be accomplished both in neuroepithelium and post-mitotic cells before the endogenous fetal hormones are secreted and reach concentrations capable to produce a response.

Differential expression of S100B and S100A6(1) in the human fetal and aged cerebral cortex

S100B and S100A6 (calcylin) are two members of the S100 Ca(2+)-binding protein family and have been localized in the mammalian nervous system. However, information on their distribution in the human nervous system, especially in the developing human fetal brain, is scarce. In the present study, an immunocytochemical method was used to examine the spatio-temporal protein expression patterns of S100B and S100A6 in normal human fetal hippocampus, entorhinal cortex and occipital cortex. Normal aged adult human brain specimens were also included for comparison. From week 15 onwards, an increase with advancing gestation age in both the number and staining intensity of S100B positive, astrocyte-like cells was found in the pyramidal layer of the hippocampus, while both the molecular and polymorphic layers showed similar S100B immunoreactivities at all stages examined. A decrease in the immunoreactivities was found in the molecular layer of the aged adult hippocampus while other layers exhibited immunoreactivities similar to those of the late fetus. At week 15, the molecular, pyramidal and ganglionic/multiform layers of the entorhinal cortex also showed positive S100B immunoreactivities which were maintained throughout the rest of the gestation and in adult specimens. In the occipital cortex, the numbers of positive cells for all layers were about twofold higher than those found in the hippocampus and entorhinal cortex, and immunoreactivities detected in the granular layer increased from week 21, reaching a plateau at around week 27. S100B positive fibers were also found at week 30 but were not observed in aged adult specimens. S100A6 positive cells were on the whole fewer in number than those of S100B in the brain regions examined. The S100A6 immunoreactivities which were localized in some pyramidal neuron-like and some glial-like cells of the pyramidal and molecular layers of the hippocampus increased by midgestation and became weak in the late fetus and in aged adult specimens. Weakly stained S100A6 positive cells were also observed in the entorhinal cortex throughout the gestation and in aged adult cortex. S100A6 immunoreactivities were weak in the fetal occipital cortex. They were also localized in the glial-like cells of the aged adult occipital cortex. The differential spatio-temporal expression of S100B and S100A6 proteins suggests that the proteins play different roles in different brain regions during development and in adulthood.