Modulators of Cat Carotid Body Chemotransduction

The Carotid Body (CB) senses hypoxia, hypercapnia, and acidosis in the arterial blood. The resulting increase in CB neural output (CBNO) to the nucleus tractus solitarius in the medulla promotes reflex responses in the respiratory, circulatory, renal, and endocrine systems. Increases in CBNO are commonly thought to be due to the release of neurotransmitters from glomus cells in the CB. Additional to the action of these released transmitters on the postsynaptic afferent neurons which abut on the glomus cells the transmitters act presynaptically on glomus cell autoreceptors. Among the several transmitters contained in the glomus cells there now exists considerable evidence supporting excitatory roles for both acetylcholine (ACh) and ATP and an inhibitory role for dopamine (DA) and norepinephrine (NE) (Fitzgerald, 2000). The release of ACh (Fitzgerald et al., 1999; Kim et al., 2004) and catecholamines (Wang and Fitzgerald, 2002) appears to be influenced by modulators. The present study investigated the action of adenosine (ADO) on the release of ACh, DA, and NE since it has been reported that ADO influences CBNO (McQueen and Ribeiro, 1981) and CB-mediated increases in ventilation (Monteiro and Ribeiro, 1987). The study further investigated the action of nitric oxide (NO) on the release of ACh since NO has been reported to reduce the hypoxia-induced increase in CBNO (Wang, et al., 1994).