THE DEVELOPMENT OF THE NERVE NETWORK IN THE FETAL HUMAN CAROTID-BODY AND ITS SUBSEQUENT FUNCTION IN CARDIAC DISEASE

Carotid bodies from 17 human fetuses of gestational age ranging from 1 0 weeks to full term were examined in histological sections stained by the Bodian silver protargol method to demonstrate nerve axons. At 10 weeks gestation the carotid body was contacted by a single nerve bundl e at its apical pole but by the 13th week a second bundle bad also rea ched the proximal pole. Thin, pale nerve axons extended from these bun dles and surrounded the carotid body to form a plexus from which sever al small groups of axons entered its superficial regions. With increas e of gestational age beyond this point there was a progressive influx of axons to penetrate the innermost areas of glomic tissue by the 19th week. Nerve endings were not identified until 23 weeks gestation when occasional small boutons, and rarely calyces, were seen to terminate on fetal chief cells. Thus there was by this age a well-developed nerv e link between glomus and brain consistent with the view that from thi s stage of development the carotid bodies are able to function as chem oreceptors. However, results of previous research work in our Departme nt and in the literature lead us to believe that the fully anatomicall y developed nerve network of the carotid body depends on its cellular and biochemical environment to ensure that it functions efficiently as a chemoreceptor. Thus, reduction of dopamine-turnover or attenuation of chief cells in the carotid bodies is associated with increased chem osensitivity, as in the days following birth and in systemic hypertens ion in later life. Increase in chief cells, and probably in dopamine-t urnover, is associated with depression of chemosensitivity as in nativ e highlanders and cyanotic congenital heart disease.