Reciprocal modulation of tyrosine hydroxylasea activity in rat carotid body

The carotid body is an arterial chemoreceptor organ responsive to blood levels of pO2, pCOe and pH 13. The parenchymal tissue of the carotid body is composed mainly of two cell types: the glomus or Type I cells, which are disposed together in groups or glomeruli, and the sustentacular or Type II cells, which appear as glial-like elements enclosing the glomeruli in capsular fashion 3,4. The Type I cells, which have abundant dense-cored vesicles and are known to contain catecholaminesl, 2,11,15, receive a sensory innervation from afferent fibers of the carotid sinus nerve 3. Recent studies have also shown the presence of reciprocal synapses at these junctions between afferent nerve terminals and Type I cells TM. In addition, these cells receive an efferent innervation from both preganglionic and postganglionic sympathetic fibers which reach the carotid body from the superior cervical ganglion 1