Responses induced by acetylcholine and ATP in the rabbit petrosal ganglion
Introduction
The carotid body (CB) is the principal arterial chemoreceptor organ, constituted by specific parenchymal cells: the receptor (glomus, type-I) cells and the glial-like (sustentacular, type-II) cells. The glomus cells are innervated, through the carotid (sinus) nerve, by sensory neurons whose perikarya are located in the petrosal ganglion (PG). The most accepted paradigm of CB chemoreception states that, as a result of the transduction mechanism, the glomus cells release one or more transmitters that, acting on postsynaptic receptors located on the nerve terminals of PG neurons, generate or maintain the afferent activity (Eyzaguirre and Zapata, 1984, González et al., 1994, Prabhakar, 2000). There are several transmitter molecules present in the CB, but their exact participation in the generation of the chemo-afferent activity is still controversial. Part of the controversy arises from conflicting results obtained from different species and preparations.
Acetylcholine (ACh) was one of the first molecules postulated as a transmitter in the CB (see Heymans, 1955). ACh and its metabolic synthesis and degradation pathways are present in the CB of cats (Fidone et al., 1976, Wang et al., 1989), rabbits (Wang et al., 1989, Kim et al., 2004) and in the rat CB-PG reconstituted system in vitro (Nurse and Zhang, 1999). ACh is released from the cat CB during electrical (Eyzaguirre and Zapata, 1968) and hypoxic stimulation (Fitzgerald et al., 1999, Fitzgerald, 2000), but ACh release from the rabbit CB is reduced during hypoxic stimulation (Kim et al., 2004). The exogenous application of ACh to the cat CB increases the carotid nerve frequency of discharge (Eyzaguirre and Zapata, 1968), while its effect is mainly inhibitory in the rabbit CB (Docherty and McQueen, 1979, Monti-Bloch and Eyzaguirre, 1980). However, application of nicotine to the CB increases the carotid nerve frequency of discharge both in the cat (Eyzaguirre and Zapata, 1968, Reyes et al., 2007) and in the rabbit (Monti-Bloch and Eyzaguirre, 1980, Jonsson et al., 2004), effects blocked by nicotinic ACh receptor antagonists (Eyzaguirre and Zapata, 1968, Jonsson et al., 2004, Reyes et al., 2007). On the other hand, muscarinic ACh receptor subtypes M1 and M2 have been described in the cat CB (Shirahata et al., 2004). However, muscarinic antagonists have no effect on the cat chemosensory activity but depressed the carotid nerve frequency of discharge on the rabbit (Monti-Bloch and Eyzaguirre, 1980). In the rabbit CB, atropine antagonizes the inhibitory effects of muscarinic ACh receptor agonists on the carotid nerve frequency of discharge (Monti-Bloch and Eyzaguirre, 1980), increases basal ACh release and revert the reduction of ACh release induced by hypoxia to an increased release (Kim et al., 2004). Thus, the available data indicate that ACh appear to be excitatory in the cat CB, but may have both excitatory and inhibitory actions in the rabbit, mediated by nicotinic and muscarinic ACh receptors, respectively. However, the exogenous application of ACh to the CB may involve activation of both presynaptic and postsynaptic receptors (Kim et al., 2004, Shirahata et al., 2007).
Currently, is accepted that both ATP and adenosine (Buttigieg and Nurse, 2004, Conde and Monteiro, 2004, Conde and Monteiro, 2006a) are released from the rat CB by hypoxia (see Conde and Monteiro, 2006b). ATP increases the carotid nerve frequency of discharge when applied to the rat CB in situ and in vitro (McQueen and Ribeiro, 1981, Spergel and Lahiri, 1993), although the action of ATP through its metabolites AMP (McQueen and Ribeiro, 1983) or adenosine (Runold et al., 1990) has been suggested. In the rat CB preparation in vitro, adenosine appears to participate in the response to an hypoxic challenge, acting both on PG and CB cells trough A2A and A2B receptors, respectively (Conde et al., 2006). On the other hand, using the cat PG preparation in vitro we found that the application of ATP increases the carotid nerve frequency of discharge in a dose-dependent manner, effect that is only marginally mimicked by AMP (Alcayaga et al., 2000a, Alcayaga et al., 2000b). These data suggest that ATP increases the chemosensory activity in the rat and cat at the postsynaptic level in the PG neurons, but there is no information on the effects of ATP on the rabbit carotid chemosensory afferents.
Both ACh and ATP have been proposed to participate in the generation of the afferent chemosensory activity by acting on specific receptors located on the PG terminals in the CB of cats and rats (Prasad et al., 2001, Iturriaga and Alcayaga, 2004, Nurse, 2005). However, in the rabbit the effect of ACh is controversial and little or no information about the effect of ATP is available (see Alcayaga et al., 2006, Iturriaga et al., 2007). Thus, we studied the responses evoked by ACh and ATP on the rabbit PG neurons that project through the carotid nerve, using an isolated PG preparation (Alcayaga et al., 1998).
Section snippets
Animals
Experiments were performed on 24 male adult White New Zealand rabbits (2.30 ± 0.11 kg; mean ± SEM). The protocol was approved by the Ethical Committee of the Facultad de Ciencias of the Universidad de Chile, and meets the guidelines of the National Fund for Scientific and Technological Research (FONDECYT), Chile, and the Guiding Principles for the Care and Use of Animals of the American Physiological Society.
Surgical procedures and recording of nerve activity
The PGs were obtained from animals anaesthetized with an intramuscular injection of a
Electrical stimulation
Electrical stimulation of the PG elicited an antidromic compound action potential in both the carotid nerve and the glossopharyngeal branch of the glossopharyngeal nerve. Fig. 1 shows representative compound action potentials recorded from the peripheral branches of the glossopharyngeal nerve. The compound action potential recorded in the glossopharyngeal branch was dominated by components attributable to fast conducting fibers (Fig. 1A), while the compound action potential evoked in the
General
One main finding of this study is that application of ACh to the rabbit PG increases carotid nerve frequency of discharge, effect blocked by hexamethonium (10 μM) and mimicked by nicotine (0.1–1000 μg) but not by bethanechol (0.1–1000 μg). Acetylcholine-induced responses were transiently reduced by prior application of bethanechol (500–1000 μg), but were enhanced during atropine (10 μM) treatment. Similarly, ATP increases carotid nerve frequency of discharge, responses that were reversibly blocked
Acknowledgement
This work was supported by grants 1040638 and 1090157 from the National Fund for Scientific and Technological Development (FONDECYT) of Chile.
References (59)
- et al.
Selective activation of carotid nerve fibers by acetylcholine applied to the cat petrosal ganglion in vitro
Brain Res.
(1998) - et al.
Adenosine triphosphate-induced peripheral nerve discharges generated from the cat petrosal ganglion in vitro
Neurosci. Lett.
(2000) - et al.
ATP- and ACh-induced responses in isolated cat petrosal ganglion neurons
Brain Res.
(2007) - et al.
Developmental profile of cholinergic and purinergic traits and receptors in peripheral chemoreflex pathway in cats
Neuroscience
(2007) - et al.
Detection of hypoxia-evoked ATP release from chemoreceptors cells of the rat carotid body
Biochem. Biophys. Res. Comm.
(2004) - et al.
Muscarinic receptor localization and function in rabbit carotid body
Brain Res.
(1991) - et al.
Autoradiographic localization of muscarinic receptors in rabbit carotid body
Brain Res.
(1986) - et al.
Loss of functional neuronal nicotinic receptors in dorsal root ganglion neurons in a rat model of neuropathic pain
Neurosci. Lett.
(2005) Oxygen and carotid body chemotransduction: the cholinergic hypothesis—a brief history and new evaluation
Respir. Physiol.
(2000)- et al.
Acetylcholine release from cat carotid bodies
Brain Res.
(1999)
Inhibitory M2 muscarinic receptors are upregulated in both axotomized and intact small diameter dorsal root ganglion cells after peripheral nerve injury
Neuroscience
Characterization of nicotinic acetylcholine receptors in cultured arterial chemoreceptor cells of the cat
Brain Res.
Neurotransmission in the carotid body: transmitters and modulators between glomus cells and petrosal ganglion nerve terminals
Brain Res. Rev.
Electrical and pharmacological properties of petrosal ganglion neurons that innervate the carotid body
Respir. Physiol. Neurobiol.
Neuromuscular blocking agents block carotid body neuronal nicotinic acetylcholine receptors
Eur. J. Pharmacol.
A comparative physiological and pharmacological study of cat and rabbit carotid body chemoreceptors
Brain Res.
Neurotransmission and neuromodulation in the chemosensory carotid body
Auton. Neurosci.
Acetylcholine contributes to hypoxic chemotransmission in co-cultures of rat type 1 cells and petrosal neurons
Respir. Physiol.
Effects of combined cholinergic–purinergic block upon cat carotid body chemoreceptors in vitro
Respir. Physiol. Neurobiol.
Effect of adenosine on isolated and superfused cat carotid body activity
Neurosci. Lett.
Presence of chemoreceptor and baroreceptor C-fibers in the carotid nerve of the cat
Brain Res.
Presence of nicotinic acetylcholine receptors in cat carotid body afferent system
Brain Res.
Identification of M1 and M2 muscarinic acetylcholine receptors in the cat carotid body chemosensory system
Neuroscience
Role of acetylcholine in neurotransmission of the carotid body
Respir. Physiol. Neurobiol.
Acetylcholine sensitivity in primary sensory neurons dissociated from the cat petrosal ganglion
Brain Res.
ACh and ATP mediate excitatory transmission in identified cat carotid body chemoreceptor units in vitro
Brain Res.
Electrophysiological characterization of nicotinic acetylcholine receptors in the cat petrosal ganglion neurons in culture. Effects of cytisine and its bromo derivatives
Brain Res.
Immunocytochemical localization of choline acetyltransferase in the carotid body of the cat and rabbit
Brain Res.
Nicotinic acetylcholine sensitivity of rat petrosal sensory neurons in dissociated cell culture
Brain Res.
Cited by (6)
Petrosal ganglion responses to acetylcholine and ATP are enhanced by chronic normobaric hypoxia in the rabbit
2013, Respiratory Physiology and NeurobiologyCitation Excerpt :Similar responses have been recorded in co-cultures of rat petrosal ganglion neurons and carotid body tissue (Nurse and Zhang, 1999; Prasad et al., 2001; Zhang et al., 2000). These responses are mediated by receptors located on the petrosal ganglion neurons (Alcayaga et al., 1998, 2000, 2007; Prasad et al., 2001; Shirahata et al., 1998; Soto et al., 2010; Zhang et al., 2000). Both the basal discharge and the responses to acute hypoxia are increased in the peripheral chemoreceptors after HVA, indicating an increased sensibility, but the mechanisms underlying this increased sensibility are still not fully understood.
Role of ATP and adenosine on carotid body function during development
2013, Respiratory Physiology and NeurobiologyCitation Excerpt :This effect likely involves the homomeric P2X2 and P2X1 or the heteromeric P2X2/P2X3 receptor, and is not affected by age in rats less than 12 days old (Nunes et al., 2012; Niane et al., 2011). It has been hypothesized that the co-release of ACh and ATP from chemoreceptor cells is important for neural transmission in the adult carotid body, at least in cats, rats and rabbits (Zhang et al., 2000; Zapata, 2007; Fitzgerald et al., 2009; Nurse, 2010; Soto et al., 2010). In newborn subjects, data on this eventual co-transmission is still scarce.
CAROTID BODY CHEMORECEPTORS: PHYSIOLOGY, PATHOLOGY, AND IMPLICATIONS FOR HEALTH AND DISEASE
2021, Physiological ReviewsPurines and carotid body: New roles in pathological conditions
2017, Frontiers in PharmacologyPetrosal ganglion: A more complex role than originally imagined
2014, Frontiers in PhysiologyExpanding role of ATP as a versatile messenger at carotid and aortic body chemoreceptors
2013, Journal of Physiology
- 1
Present address: Programa de Doctorado en Ciencias, mención Neurociencia, Universidad de Valparaiso, Gran Bretaña 1111 Playa Ancha, Valparaiso, Chile.
- 2
Present address: Programa de Doctorado en Ciencias Biológicas, mención Ciencias Fisiologicas, P. Universidad Católica de Chile, Facultad de Ciencias Biológicas, Portugal 49, Casilla 114-D, Santiago, Chile.