Changes in dendritic spine density on layer 2/3 pyramidal cells within the cingulate cortex of late pregnant and postpartum rats.

A rapid upregulation of astrocytic protein expression within area 2 of the cingulate cortex (Cg2) of the maternal rat occurs within 3h postpartum and persists throughout lactation. Previous studies have shown that similar changes in astrocytic proteins can signal changes in local synapses and dendritic spines. Thus, here we used the Golgi-Cox impregnation technique to compare spine density in layer 2 and 3 pyramidal cells of Cg2, the CA1 region of the hippocampus and the parietal cortex (ParCx) among metestrus, late pregnant (LP), 3-hour postpartum (3H PP) and 16-day postpartum rats (D16 PP). Rats in the 3H PP group had higher numbers of dendritic spines/10 μm on the apical dendrites of pyramidal neurons in both Cg2 and CA1 than the other groups, which did not differ. A similar pattern was observed in basilar dendrites but this failed to reach significance. In Cg2, Sholl analysis revealed that rats in the D16 PP group had a significantly greater extent of dendritic arborization in the basilar region than any other group. These data suggest that the changes in astrocytic proteins that occur in Cg2 in the postpartum period are associated with neuronal plasticity in pyramidal layers 2 and 3.