Glial Fibrillary Acidic Protein Immunoreactivity in the Prefrontal Cortex Distinguishes Younger from Older Adults in Major Depressive Disorder

Background: Recent postmortem studies in major depressive disorder (MDD) provide evidence for a reduction in the packing density and number of glial cells in different regions of the prefrontal cortex; however, the specific types of glia involved in those morphologic changes are unknown.

Methods: The territory occupied by the astroglial marker glial fibrillary acidic protein (GFAP) was measured as an areal fraction in cortical layers III, IV, and V in sections from the dorsolateral prefrontal cortex (dlPFC) of MDD and control subjects. In addition, the packing density of GFAP-immunoreactive somata was measured by a direct three-dimensional cell counting method.

Results: The mean areal fraction and packing density of GFAP-immunoreactive astrocytes in the dlPFC of MDD subjects were not significantly different from those in control subjects; however, in MDD there was a significant strong positive correlation between age and GFAP immunoreactivity. When the MDD group was divided into younger (30-45 years old) and older (46-86) adults, in the five younger MDD adults, areal fraction and packing density were smaller than the smallest values of the control subjects. In contrast, among older MDD subjects these parameters tended to be greater than in the older control subjects.

Conclusions: The present results suggest that the GFAP-immunoreactive astroglia is differentially involved in the pathology of MDD in younger compared with older adults.