Changes in NGF/c-Fos double staining in the structures of the limbic system in juvenile and aged rats exposed to forced swim test.

This study aimed to investigate the influence of acute (a single 15 min) and chronic (15 min daily for 21 days) exposure to forced swim (FS) test on nerve growth factor (NGF)/c-Fos cells in hypothalamic paraventricular (PV) and supraoptic (SO) nuclei, the central (CeA) and medial (MeA) amygdaloid nuclei and CA3-hippocampus in juvenile (P28) and aged (P360) rats. The double-immunofluorescence (-ir) method was used to detect NGF-ir and c-Fos-ir cells. The amount of NGF/c-Fosir cells in relation to all NGF-ir cells is shown as a percentage. In the acute FS test an increase in NGF/c-Fos-ir cells (P<.05) was observed in all studied structures of juvenile rats and in the PV and SO of the aged individuals. After chronic FS stress, the NGF/c-Fos-ir ratio remained unaltered (except in the SO) in P28, but it increased (P<.05) in all investigated regions in P360 compared with the controls. The findings may reflect the state of molecular plasticity within the limbic hypothalamicpituitary- adrenocortical (HPA) axis in both age groups, yet the phenomenon of habituation in NGF/c-Fos-ir after chronic FS exposure was observed only in juvenile animals.