02-Sensing Mechanisms in Efferent Neurons to the Rat Carotid Body

Abstract02-sensing by mammalian cells is a fundamental process that is important for adaptation to variable physiological situations. The mammalian carotid bodies (CB) are peripheral chemoreceptors which monitor blood levels of Po2, Pco2and pH (Gonzalezet al., 1994; Prabhakar, 2000; López-Barneoet al., 2001). As a result they can initiate or modify respiratory reflexes in order to maintain P02homeostasis. Inhibition of K+channels appears to be an important step in CB chemotransduction during hypoxia (Peers, 1997; López-Barneoet al., 2001). It is known that under certain conditions the responses of the CB to specific stimuli can be altered. Chemoreceptor inhibition is the mechanism by which the CB responses are reduced during chemical stimulation, leading to an inhibition of chemoreceptor discharge. Nitric oxide (NO) has been implicated as an important neurotransmitter in the efferent inhibition of rat CB chemoreceptors during hypoxia (Wanget al. 1993; 1994a & b; 1995a & b; Hö hleret al. 1994). An extensive plexus of NO synthase (NOS)-containing nerve fibers projects to the CB and is formed by sensory fibers from the petrosal ganglion and autonomic fibers from neurons located near the junction of the glossopharyngeal (GPN) and carotid sinus (CSN) nerves (WangeM/., 1993).