Localization of Dopamine D2 Receptor mRNA in the Rabbit Carotid Body and Petrosal Ganglion by in situ Hybridization

Abstract

The carotid body (CB) of mammals is known to contain large amounts of catecholamines and it has been demonstrated that dopamine (DA) is predominant in this structure among several species (rat, rabbit, human…, see Fidone et al., 1983). There is no doubt that DA is localized to the glomus (type I) cells but the role of DA in chemoreception processes is controversial. Both inhibitory and excitatory effects on the chemoafferent activity have been reported, depending on the dose, species and experimental technique used. Pharmacological studies with specific agonists and antagonists have established that DA-receptors exist in the CB (Zapata et al., 1983), some of them belonging to the D2 subtype (McQueen and Mir, 1984; Mir et al., 1984) which are not linked to adenylate cyclase activation (Kebabian and Calne, 1979). To better understand the role of DA in chemoreception, it appears to be essential to define the distribution and the precise localization of DA receptors in the CB. Until now, only indirect data have been obtained on this issue. Binding studies, using tritiated spiroperidol or domperidone (Dinger et al., 1981; Mir et al., 1984) have suggested that most of DA receptors in the CB are linked to the afferent innervation but the location of the other receptors remains unknown (glomus cells? blood vessels? sympathetic nerve fibers?). However, some data have shown that DA can modify the resting electrical parameters of glomus cells, suggesting that DA-receptors (autoreceptors) are present on these cells (Goldman and Eyzaguirre, 1984; Benot and Lopez-Barneo, 1990).