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 10 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 bundle at its apical pole but by the 13th week a second bundle had also reached the proximal pole. Thin, pale nerve axons extended from these bundles and surrounded the carotid body to form a plexus from which several small groups of axons entered its superficial regions. With increase 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 nerve link between glomus and brain consistent with the view that from this stage of development the carotid bodies are able to function as chemoreceptors. However, results of previous research work in our Department and in the literature lead us to believe that the fully anatomically 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 chemosensitivity, as in the days following birth and in systemic hypertension in later life.(ABSTRACT TRUNCATED AT 250 WORDS)