Late post‐natal neurometabolic development in healthy male rats using 1 H and 31 P Magnetic Resonance Spectroscopy

Brain metabolism evolves rapidly during early post‐natal development in the rat. While changes in amino acids, energy metabolites, antioxidants or metabolites involved in phospholipid metabolism have been reported in the early stages, neurometabolic changes during the later post‐natal period are less well characterized. Therefore, we aimed to assess the neurometabolic changes in male Wistar rats between post‐natal days 29 and 77 (p29‐p77) using longitudinal magnetic resonance spectroscopy (MRS) in vivo at 9.4 Tesla. 1H MRS was performed in the hippocampus between p29‐p77 at one‐week intervals (n=7) and in the cerebellum between p35‐p77 at two‐week intervals (n=7) using the SPECIAL sequence at ultra‐short echo‐time. NOE enhanced and 1H decoupled 31P MR spectra were acquired at p35, p48 and p63 (n=7) in a larger voxel covering cortex, hippocampus and part of the striatum. The hippocampus showed a decrease in taurine concentration and an increase in glutamate (with more pronounced changes until p49), seemingly a continuation of their well described changes in the early post‐natal period. A constant increase in myo‐inositol‐ and choline‐containing compounds in the hippocampus (in particular glycero‐phosphocholine as shown by 31P MRS) was measured throughout the observation period, probably related to membrane metabolism and myelination. The cerebellum showed only a significant increase in myo‐inositol between p35‐p77. In conclusion, the present study showed important changes in brain metabolites in both the hippocampus and cerebellum in the later post‐natal period (p29/p35‐p77) of male rats, something previously unreported. Based on these novel data, changes in some neurometabolites beyond p28‐35, conventionally accepted as the cut off for adulthood, should be taken into account in both experimental design and data interpretation in this animal model.