Exposure to mild stress and brain derived neurotrophin factor (BDNF) immunoreactivity in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei: Comparison between aged and adult rats

It seems that age-dependent changes in stress response may be correlated with alterations in the hypothalamic brain derived neurotrophin factor (BDNF). Two hypothalamic nuclei, ie. paraventricular (PVN) and supraoptic (SON) are closely related to the stress response. Therefore, the aim of our study was to explore the influence of acute and chronic high-light open field (HL-OF) or forced swim (FS) stimulation on the density of BDNF immunoreactive (ir) neurons in the PVN and SON in adult (postnatal day 90; P90) and aged (P720) Wistar Han rats. Our data demonstrated that in comparison with non-stressed rats, neither acute nor chronic FS caused significant changes in the density of BDNF-ir neurons of PVN and SON in P90 or P720 rats. However, a significant increase in the density of BDNF-ir neurons in the SON of P90 and a decrease in the PVN of the P720 rats were noted after acute HL-OF. Despite the lack of change in the density of BDNF-ir neurons between P90 and P720 non-stressed and FS stressed rats, there was an age-dependent decrease in the BDNF-ir cells of HL-OF stressed rats, especially in the PVN. We may conclude that in terms of its influence on the BDNF-ir neurons in PVN and SON, acute HL-OF was the factor inducing changes in the density of BDNF-ir neurons in the hypothalamic nuclei of adult or aged rats. Furthermore, ageing involutional processes, which can impair hypothalamic-pituitary-adrenal axis functioning, may have been able to cause an age-related decrease in the BDNF-ir PVN and/or SON neurons in HL-OF stressed rats.