Abstract
The fetus is sensory deprived and some of its behavioural functions are inhibited. This inhibited state is immediately reversed at birth, the newborn infant is awake and aroused. We now wanted to study how the noradrenergic activity in the brain is related to this excitation at birth.
Noradrenalin (NA)-turnover was studied in the cortex and pons-medulla of rat fetuses and pups. The ratio between the NA-metabolite 3-methoxy-4-hydroxy-penylethylene glycol (MHPG) and NA was determined by HPLC and used as an index of NA-turnover.
Results: The MHPG/NA-ratio was 0.094 in the pons-medulla of fetuses and 0.27 (p < 0.05) in the one day old pups. The cortex ratio increased from 0.082 to 0.30 (p < 0.05). The index of NA turnover increased significantly already one hour after birth when the pups were exposed to air. If the pups were kept in hypoxic environment, the NA-turnover increased less.
We conclude that the NA-turnover is considerably enhanced after birth if the pups are born in normoxic environment but not in hypoxia. This reflects the activation of the noradrenergic nerves in the brain, which to a large extent originate from the locus coeruleus in the brain stem. We believe that in this way the brain is aroused to new stimuli, e.g. the extra-uterine environment.
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Lagercrantz, H., Pequignot, JM. ACTIVATION OF THE NORADRENERGIC SYSTEM IN THE RAT BRAIN AT BIRTH. Pediatr Res 32, 633 (1992). https://doi.org/10.1203/00006450-199211000-00169
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DOI: https://doi.org/10.1203/00006450-199211000-00169