Longitudinal metabolic changes in the hippocampus and thalamus of the maternal brain revealed by proton magnetic resonance spectroscopy

- Metabolic changes during pregnancy and motherhood were investigated by 1H MRS.
- NAA levels were increased in the hippocampus and thalamus of late pregnant rats.
- Higher NAA may arise from higher density of dendritic spines, synapses or neurons.
- These neurochemical changes may underlie maternal behavioral modifications.

Pregnancy is accompanied by dramatic hormonal changes, which are essential for the display of maternal behaviors. Reproductive hormones have been shown to remodel the neuronal structure and function of the female brain. However, most previous studies have examined the structural and functional changes elicited by transient fluctuations in reproductive hormones. The impact of naturally elevated and more sustained hormonal alterations during pregnancy and lactation are not fully understood. Further alterations in neurochemistry, which may result in substantial changes in the structure and function of neurons that are associated with behavioral modifications in the maternal female, are difficult to capture in a longitudinal and non-invasive manner. In this study, neurobiological alterations during pregnancy and motherhood were investigated longitudinally using non-invasive proton magnetic resonance spectroscopy (1H MRS) at 7T in regions related to learning and memory, such as the hippocampus, and in structures involved in alertness and attention, such as the thalamus. Pregnant primiparous rats (N = 15) were studied at three days before mating, gestational day 17, lactation day 7 and post-weaning day 7. Age-matched nulliparous female rats (N = 9) served as non-pregnant controls. Significantly higher N-acetylaspartate (NAA) levels were observed in the hippocampus and thalamus of rats at gestational day 17. These increases may be associated with increased dendritic sprouting, synaptogenesis or neurogenesis, thereby facilitating supporting behaviors that involve spatial learning and memory and alleviating fear and stress. The 1H MRS detection of ongoing neurochemical changes induced by pregnancy, especially in the hippocampus, can shed light on the neurochemical underpinnings of behavioral modifications, including the improvement in spatial learning and memory, during pregnancy.