Influence of melatonin and sexual hormones on the expression of proliferating cell nuclear antigen in the adrenal cortex of a seasonal breeder (Lagostomus maximus).

The viscacha (Lagostomus maximus) is a rodent of nocturnal habits, whose physiology and behavior vary according to modifications of environmental signals. The objective of this study is to assess the influence of melatonin and sexual hormones on the viscacha adrenal cortex proliferative activity through the immunohistochemical detection of proliferating cell nuclear antigen (PCNA) along with hormonal determinations. PCNA expression was studied in male viscachas to assess the effect of melatonin administration, castration, and the annual reproductive cycle. In female viscachas, PCNA was studied in nonpregnant and pregnant viscachas. PCNA expression was observed in adrenocortical cells (PCNA-A) and endothelial cells (PCNA-E). Melatonin-administered animals showed a significantly lower number of PCNA-A compared to the control group. No significant difference could be established in the number of PCNA-A and PCNA-E between castrated and control animals. However, the morphometric analysis showed an increase in the size of the cortex of castrated animals, along with other cytological features. Significant differences in serum testosterone levels were observed during the male viscacha reproductive cycle, with the lowest levels encountered during the regression period (winter). Male viscachas exhibited a significantly high number of PCNA-A during late autumn and a high number of PCNA-E during winter. In females, hormonal determinations showed a peak of progesterone and estrogen during mid-pregnancy, along with a notably high number of PCNA-A and an increase in the number of PCNA-E. Our results suggest that proliferation in the adrenal cortex of the viscacha varies in relation to melatonin, sexual hormones, and environmental conditions.

Interstitial Cells in the Pineal Gland of Pregnant and Nonpregnant Viscachas (Lagostomus maximus maximus): A Morphometric and Biochemical Study.

The pineal gland of mammals undergoes morphological and biochemical changes throughout the gestation period. In viscachas, a seasonal breeding rodent, pregnancy lasts approximately 154 days and 3 stages can be defined, i.e., early, mid, and late pregnancy. The purpose of this study is to analyze morphometric variations in the expression of S-100 protein, glial fibrillary acidic protein (GFAP), and vimentin in the interstitial cells (IC) in pregnant and nonpregnant viscachas by immunohistochemistry (IHC). We also aim to evaluate a probable relation between glandular activity and pregnancy. The immunopositive percentage area (%IA) for the studied proteins and the number of immunoreactive cells against the S-100 protein with a visible nucleus (nº IC-S-100) were analyzed. Estradiol and progesterone serum levels were also determined by RIA. Variations in the expression of the S-100 protein and GFAP, as well as changes in the nº IC-S-100 related to serum hormone levels, were found between pregnant and nonpregnant viscachas. Viscachas in mid pregnancy exhibited the highest values of %IA for the analyzed proteins, followed by females in late and early pregnancy, while the nonpregnant ones showed the lowest values for all of the groups studied. Likewise, the nº IC-S-100 also varied following the same pattern. Thus, these variations seem to indicate a direct relationship between glandular activity and gonadal hormone levels. On these grounds, we may conclude that IC undergo changes in relation to ovarian hormone levels and participate in the regulation of glandular activity during pregnancy. However, further research is necessary to elucidate this relationship.

Immunomorphometric variations of sustentacular cells of the male viscacha adrenal medulla during the annual reproductive cycle. Effects of androgens and melatonin.

The adrenal medulla is crucial for the survival of species facing significant environmental changes. The parenchyma is composed mainly of chromaffin cells, ganglion cells and sustentacular cells (SC). The male viscacha exhibits seasonal variations of gonadal activity and other metabolic functions. The aim of this work was to investigate the influence of the reproductive conditions on the morphology of SC of this rodent. In addition, the effects of testosterone and melatonin on these cells were studied. Immunoexpression of S100 protein, GFAP and vimentin were analyzed. Furthermore, the distribution of adrenergic and noradrenergic chromaffin cells subpopulations was studied for the first time in this species. SC present long cytoplasmic processes in contact with chromaffin cells, probably generating an intraglandular communication network. Significant differences (p < 0.05) in the %IA (percentage of immunopositive area) for the S100 protein were observed according to winter (4.21 ±â€¯0.34) and summer (3.51 ±â€¯0.15) values. In castrated animals, the %IA (6.05 ±â€¯0.35) was significantly higher in relation to intact animals (3.95 ±â€¯0.40). In melatonin-treated animals the %IA (3.62 ±â€¯0.23) was significantly higher compared to control animals (2.65 ±â€¯0.26). GFAP immunoexpression was negative and no noradrenergic chromaffin cells were detected suggesting an adrenergic phenotype predominance. Vimentin was observed in SC, endothelial cells and connective tissue. Results indicate that SC exhibit variations along the annual reproductive cycle, along with castration and the melatonin administration. Our results suggest that in this rodent SC are not only support elements, but also participate in the modulation of the activity of the adrenal medulla; probably through paracrine effects.