The effect of ovariectomy on learning and memory and relationship to changes in brain volume and neuronal density

The loss of sex hormones in postmenopausal women has been suggested to be involved in cognitive degenerative diseases, such as Alzheimer's disease. In the present study, ovariectomized (OVX) and control rats were tested for 4 months in a Morris water maze (MWM) task to track their memory status. Thereafter, postmortem frozen brain sections were analyzed to determine if changes in brain area volumes and neuronal density were related to changes in cognitive ability. A modified artificial-land-mark-based method was used to assure the fidelity of the three dimensions (3D) reconstructed structures. Volumetric areas of the hippocampus, cortex, caudate putamen (cpu), and cerebellum were estimated from the reconstructions, and neuron densities of CA1 and CA3 subregions of the hippocampus were measured in an adjacent second series of Nissl-stained sections. Compared to the control rats, OVX rats displayed memory impairments, beginning in the second month after the ovariectomy (p < .05). Assessments at the end of the study demonstrated that OVX (compared to control) rats displayed reduced brain volume in the hippocampus and neocortex and in the brain as a whole. In contrast, when compared to controls, the volumes of cpu and cerebellum of OVX rats increased slightly. CA3 neuron density of OVX (compared to controls) rats was significantly lower, but the CA1 neuron density was significantly higher. In conclusion, ovariectomy impaired spatial memory and led to morphological changes in cognitive centers of rat brain. The results demonstrate that the 3D reconstructed method is useful for the study of brain morphological abnormality in rats.