Effects of early and late adverse experiences on morpho-quantitative characteristics of Sprague-Dawley rat spleen subjected to stress during adulthood.

Morpho-quantitative studies of the spleen indicate that the proportions of the compartments and sub-compartments are stable in normal conditions. However, disorders due to stress can influence the number and function of the immune cells in this organ. The aim of this study was to determine, through the model of altering the early mother-infant bond and altering the late social bond through isolation, the effect on the morpho-quantitative characteristics of the spleen in adult Sprague-Dawley rats subjected to intermittent chronic stress in adulthood. Twenty-five newborn female rats were used, kept under the standardized lactation and feeding conditions. The rats were assigned randomly to 2 control groups (C1 and C2) and 3 experimental groups, exposed to early (E1), late (E2) or early-late (E3) adverse experiences and then subjected to intermittent chronic stress in adulthood (C2, E1, E2 and E3). The spleen of each animal was isolated and its morphometric characteristics were determined: volume density (Vv) of the red pulp, white pulp, marginal zone, splenic lymph nodule, periarterial lymphatic sheath and germinal center; areal number density (Na), surface density (Sv), number density (Nv), diameter (D) and total number of splenic lymph nodules. The mass of each compartment was also determined. A one-way analysis of variance (ANOVA) and Scheffé's post hoc test were used for the statistical analysis. The p values were considered significant when they were less than 0.05 (*) and very significant at less than 0.025 (**). There were significant differences in the Vv of the red pulp, white pulp and their sub-compartments between the control and experimental groups. The white pulp increased significantly (P = 0.000) in E1, E2 and E3 compared to C1 and C2. The average Na and D values of the splenic lymph nodules were also higher in the experimental groups. The ANOVA for the mass of the spleen and the red pulp revealed no differences between the groups. The mass of the white pulp and its subcompartments was greater in the experimental groups. A higher proportion of white pulp in the experimental groups could be associated with an increase in spleen immune activity, with alterations depending on certain cell subsets. The chronic stress produced morpho-quantitative changes in the rat spleen, and these depended on the animal's history of stress, whether it had been previously stressed or not, with further exposure to stress in adulthood.