Cytology of the Pituitary Gonadotrophs, Histological Characteristics of Interrenal and Chromaffin Cells in Relation to Testicular Activities in Mystus Vittatus (Siluriformes, Bagridae) During Growth, Maturation and Spawning Phases

The histological changes observed in the pituitary corticotrophs, gonadotrophs, adrenocortical tissues and testicular cells in M. vittatus (Bloch, 1794) have been studies during growth, maturation and spawning phases. The studies based on the changes observed in the cell types, shape and size of the cells of the adrenocortical tissues, testes and the overall percentage of gonadotroph (GTH) and thyrotroph (TSH) cells of the pituitary. However, during growth phase, in proximal pars distalis (PPD) the considerable increment of GTH and TSH have been observed having intense aniline blue stain. The corticotrophs (ACTH) also showed significant accumulation of fuchsinophilic cytoplasmic granules. The cytoplasmic features and the architecture of the interrenal cells were well coincident with the increase of different spermatogenic cells. During the maturation phase dense granulation in the GTH and TSH cells appeared to be concomitant with the spermiation. The amount of cytoplasmic granules of the interrenal cells increased than chromaffin cells and was well coincidence with the increase of spermatids and spermatozoa. The hyperactive and vacuolated features of the interrenal cells during spawning phase appeared to be concomitant with the final process of spermiation.

Increased avidity for Dpp/BMP2 maintains the proliferation of eye progenitors in Drosophila

During normal organ development, the progenitor cell state is transient: it depends on specific combinations of transcription factors and extracellular signals, that cooperate to sustain the proliferative potential and undifferentiated status of organ progenitor cells. Not surprisingly, abnormal maintenance of progenitor transcription factors may lead to tissue overgrowth, and the concurrence of specific signals from the local environment is often critical to trigger this overgrowth. Therefore, the identification of the specific combinations of transcription factors and signals that promote or oppose proliferation in progenitor cells is essential to understand normal development and disease. We have investigated this issue by asking what signals may promote the proliferation of eye progenitors in Drosophila. Two transcription factors, the MEIS1 homologue homothorax (hth) and the Zn-finger teashirt (tsh) are transiently expressed in eye progenitors causing the expansion of the progenitor pool. However, if their co-expression is maintained experimentally, cell proliferation continues and differentiation is halted. Here we show that Hth+Tsh-induced tissue overgrowth requires the BMP2 ligand Dpp and the activation of its pathway. In Hth+Tsh cells, the Dpp pathway is abnormally hyperactivated. Rather than using autocrine Dpp expression, Hth+Tsh cells increase their avidity for Dpp, produced locally, by upregulating extracellular matrix components. During normal development, Dpp represses hth and tsh ensuring that the progenitor state is transient. However, cells in which Hth+Tsh expression is maintained use Dpp to enhance their proliferation.

Dexamethasone treatment during pregnancy influences the number of TSH cells in rat fetuses

Glucocorticoids and thyroid hormones control many aspects of fetal development. Using immunohistochemistry and stereology, in the present study we investigated the effects of dexamethasone (Dx) administration during pregnancy on pituitary TSH cells of 19-day-old fetuses. Doses of 1.0, 0.5, and 0.5 mg Dx/kg bw/day were given to the dams on three consecutive days starting on day 16 of gestation. Administration of Dx to pregnant rats induced a significant decline of fetal TSH cell number per unit of area and their volume density in comparison with the corresponding controls. Our results showed that maternal Dx administration inhibited multiplication of TSH cells in 19-day-old fetuses.

Pituitary thyrotropic cells are affected by steroid hormones

The pituitary gland is a heterogeneous tissue comprised of several hormone-secreting cells most of which are targeted by sex steroids. Our long-term studies were concentrated on the response of rat pituitary TSH cells to gonadal steroids applied to animals of different age. With this goal, we examined immunoreactive and morphometric, as well as subcellular organization of pituitary TSH cells in rats of both sexes after neonatal and perinatal estradiol-dipropionate (EDP) treatment. The results undoubtedly indicated persistent EDP-related inhibitory changes of tyrotrophs up to the adulthood. At the subcellular level, a delayed differentiation of TSH cells was noticed. Besides, a special attention has been paid to the changes in the structure of immunoreactive TSH cells of middle-aged (14-month-old) rat females, chronically treated with EDP, calcium (Ca) or a combination of EDP and Ca. Based on our results it can be concluded that both EDP and Ca act inhibiting the thyrotrophs under the applied experimental conditions.