Gonadotropin-releasing hormone agonist administration affects the thymopoiesis in adult female rats independently on gonadal hormone production

The compensatory expression of reproductive hormone receptors in the thymus of the male rat following active immunization against GnRH

To determine whether hormone-receptor signaling pathways in the thymus are altered by active immunization against gonadotrophin-releasing hormone I (GnRH), 3-week-old Sprague-Dawley male rats received GnRH-tandem-OVA peptides (200 μg/ml), and the effects were compared to a control group. Serum testosterone, LH and FSH concentrations were markedly reduced, with severe testicular atrophy, compared to controls, demonstrating effective blockade of the pituitary-gonadal axis. The reduction in LH and FSH concentrations in the thymus of immunized animals was lower than that observed in the serum, where a significant difference (P<0.001) in concentration was observed between both groups. Concentrations of GnRH were increased in the thymus of immunized rats. In thymic tissue, GnRHR, FSHR and LHR demonstrated stronger immunostaining, and AR weaker staining, in the immunized group compared to controls. Reproductive hormone receptor mRNA expression was consistent with protein variations in the immunized thymus. Compared to controls, GnRHR gene levels were significantly increased (P<0.05), however, AR mRNA expression were greatly decreased with immune week-age (P<0.05). Both FSHR and LHR mRNA expression levels were significantly higher in the treated group than in controls in the first three samples (P<0.05). When GnRHR was blocked by an antagonist in thymocytes, all reproductive hormone receptor gene expressions were significantly increased (P<0.001). In summary, these findings suggest that active immunization against GnRH can up-regulate GnRH receptor and gonadotropin receptor signaling, by stimulating thymic autocrine and paracrine function, whereas the androgen receptor is down-regulated due to a lack of testosterone secretion in the thymus.

Role of gonadal hormones in programming developmental changes in thymopoietic efficiency and sexual diergism in thymopoiesis

There is a growing body of evidence indicating the important role of the neonatal steroid milieu in programming sexually diergic changes in thymopoietic efficiency, which in rodents occur around puberty and lead to a substantial phenotypic and functional remodeling of the peripheral T-cell compartment. This in turn leads to an alteration in the susceptibility to infection and various immunologically mediated pathologies. Our laboratory has explored interdependence in the programming and development of the hypothalamo-pituitary-gonadal axis and thymus using experimental model of neonatal androgenization. We have outlined critical points in the complex process of T-cell development depending on neonatal androgen imprinting and the peripheral outcome of these changes and have pointed to underlying mechanisms. Our research has particularly contributed to an understanding of the putative role of changes in catecholamine-mediated communications in the thymopoietic alterations in adult neonatally androgenized rats.

Beta-adrenoceptor blockade ameliorates the clinical course of experimental allergic encephalomyelitis and diminishes its aggravation in adrenalectomized rats

As glucocorticoids influence both catecholamine synthesis and adrenoceptor expression by immune cells, the current study was undertaken to distinguish their direct effects on the development of experimental allergic encephalomyelitis from those induced by alteration of catecholamine signaling. We examined the influence of 16-day-long beta-adrenoceptor blockade with propranolol (0.40 mg/100 g body weight/day, s.c.) beginning 3 days before immunization on the development of experimental allergic encephalomyelitis in adrenalectomized (7 days before immunization) and in non-operated male Dark Agouti rats. Adrenalectomy aggravated the clinical course of experimental allergic encephalomyelitis. In contrast, propranolol attenuated both the clinical signs of the disease and decreased the number of lesions in the spinal cord. Furthermore, propranolol prevented adrenalectomy-induced aggravation of the disease course without affecting mortality. We also found that the percentage of CD4(+)CD25(+) T lymphocytes (recently activated or regulatory cells) was increased in peripheral blood of experimental allergic encephalomyelitis rats over that in the corresponding non-immunized and bovine serum albumin immunized rats. However, the percentage of these cells was reduced in adrenalectomized and/or propranolol-treated experimental allergic encephalomyelitis rats compared to control experimental allergic encephalomyelitis rats. Our findings, coupled with the clinical course of the disease and the underlying pathomorphological changes, clearly suggest that differential mechanisms were responsible for the changes in the percentage of CD4(+)CD25(+) T lymphocytes in propranolol-treated adrenalectomized rats and only propranolol-treated rats with experimental allergic encephalomyelitis. Our results, when viewed globally, indicate that: i) beta-adrenoceptor-dependent mechanisms are involved in the immunopathogenesis of experimental allergic encephalomyelitis, ii) experimental allergic encephalomyelitis has a more severe course in adrenalectomized rats and iii) beta-adrenoceptor-mediated mechanisms operate in adrenalectomy-induced aggravation of the disease.

Age-associated changes in CD90 expression on thymocytes and in TCR-dependent stages of thymocyte maturation in male rats

To elucidate the effects of ageing on T-cell-maturation, in 3- and 18-month-old rats, we analysed the expression of: (i) CD4/CD8/TCRalphabeta and (ii) Thy-1, which is supposed to be a regulator of TCRalphabeta signalling, and thereby the thymocyte selection thresholds. Since an essential role for TCRalphabeta signalling in the development of CD4+25+T(reg)-cells was suggested, the frequency of these cells was also quantified. We demonstrated that, as for mice, early thymocyte differentiational steps within the CD4-8- double negative (DN) developmental stage are age-sensitive. Furthermore, we revealed that TCRalphabeta-dependent stages of T-cell development are affected by ageing, most likely due to an impaired expression of Thy-1 on TCRalphabeta(low) thymocytes entering selection processes. The diminished frequency of the post-selection CD4+8+ double positive (DP) cells in aged rats, together with an overrepresentation of mature single positive (SP) cells, most probably suggests more efficient differentiational transition from the DP TCRalphabeta(high) to the SP TCRalphabeta(high) developmental stage, which is followed by an increase in pre-migration proliferation of the mature SP cells. Moreover, the study indicated impaired intrathymic generation of CD4+25+T(reg)-cells in aged rats, thus providing a possible explanation for the increased frequency of autoimmune diseases in ageing.