BIRTH-RELATED CHANGES OF EXPRESSION AND TURNOVER OF SOME NEUROACTIVE AGENTS AND RESPIRATORY CONTROL

Respiratory movements are partially inhibited before birth and central and peripheral chemoreceptors are probably less sensitive. The transi tion to continuous breathing might be due to the switch-off of inhibit ory neuromodulators and the switch-on of excitatory neuroactive agents . This hypothesis has been explored mainly in rats. One example is dop amine which was found to have a high turnover in carotid bodies in new born pups prior to decreasing rapidly. It is suggested to inhibit the carotid bodies before birth. In the brain, the noradrenergic system ha s been found to be activated at birth, possibly promoting neural trans mission and arousal. Increased expressions of mRNA for c-fos, tyrosine hydroxylase and some neuropeptides have also been found.