Changes in brain phosphorus metabolites during the post‐natal development of the rat.

Changes in brain phosphorus metabolites during the post‐natal development of the rat and in neonatal and adult guinea‐pigs have been studied in vivo using 31P nuclear magnetic resonance spectroscopy (n.m.r.s.). The brain spectra showed clear differences with age, particularly during the first 3 weeks post‐partum. The spectra from 4‐day‐old rats resembled those of new‐born human infants. We suggest that the differences between human and animal brains seen in previously published spectra arise because of an age difference rather than a species difference. The phosphocreatine (PCr) to nucleoside triphosphate (NTP) ratio increased from around 1.0 in 3‐day‐old rats to 1.8 in adult animals. The adult ratio is larger than that previously reported from in vitro chemical analyses. An unknown compound in the phosphomonoester (PME) region of the spectra predominated in young animals, but decreased in concentration relative to NTP with age and reached adult values by around 2 weeks post‐partum. Neonatal guinea‐pigs, which are much more developed at birth than the rat, had a significantly greater PCr/NTP ratio than the neonatal rat, but their brain spectra also contained the large PME peak. The intracellular pH of cerebral tissue was estimated to be 7.21 +/‐ 0.02 and did not show any change with age. The changes we find in the phosphorus compounds in the brain may be of importance in post‐natal development, and the possible functional significance of these results is discussed.