Effects of postnatal undernutrition on the catecholamine and serotonin contents of suckling rat brain.

The effect of postnatal undernutrition on the catecholamine and serotonin contents of various parts of the brain of suckling rats was examined. Undernourishment was induced by increasing the litter size to 18 pups from day 1 to 21 after birth. In control pups, the total amounts of norepinephrine and dopamine in the whole brain increased greatly during the suckling period (norepinephrine: 17.7 ng at birth, 154 ng on day 10, and 420 ng on day 21; dopamine: 12.6 ng at birth, 269 ng on day 10, and 1,022 ng on day 21). Similar, but less marked increases in the norepinephrine and dopamine contents of the brain were observed in malnourished pups. The norepinephrine contents of the forebrain, cerebellum, and brain stem of malnourished pups were comparable with those of normal pups on day 10 but the contents of the cerebellum and brain stem were significantly less than those of normal pups on day 21. Postnatal malnutrition also led to a significant decrease in the dopamine content of the forebrain. In contrast, the serotonin content of the brain of undernourished pups was significantly higher than that of controls. The control pups at the end of suckling period were significantly higher than those of undernourished pups (forebrain: 18.3 pmol in controls and 11.5 pmol in malnourished pups; brain stem: 12.3 pmol in controls and 9.8 pmol in malnourished pups). The tyrosine hydroxylase activity (pmol/g) correlated more closely with the norepinephrine content than with the dopamine or norepinephrine plus dopamine content. The tyrosine and phenylalanine contents of the brain were similar in the two groups. It is concluded from these findings that the catecholamine content of the brain is regulated by the enzyme activity rather than the levels of precursor amino acids.