Characterization of opioid receptors in the cat carotid body involved in chemosensory depression in vivo

Abstract

1 The effects of selective opioid receptor agonists and antagonists on neural discharge recorded from carotid body arterial chemoreceptors in vivo were studied in anaesthetized cats. immediately before and after injecting ICI 174864 (0.1-0.2 mg kg-' i.c.) showed a significant increase in discharge in one experiment, but in four others discharge was either unaffected or decreased after the antagonist, which argues against a toxic depression of chemosensors by endogenous opioids under resting conditions in our preparation. 5 Sensitivity of the carotid chemoreceptors to hypoxia (ventilating with 10% 02) was increased significantly after ICI 174864, which could be taken as evidence that endogenous opioids depress chemosensitivity during hypoxia. In contrast, responsiveness to hypercapnia was reduced after the antagonist, implying that endogenous opioids may potentiate chemoreceptor sensitivity during hypercapnia.6 The results obtained using 'selective' agonists and antagonists provide evidence that depression of chemosensory discharge caused by injected opioids involves a 6 type of opioid receptor within the cat carotid body. Endogenous opioids may modulate arterial chemoreceptor sensitivity to physiological stimuli such as hypoxia and hypercapnia.

Immunohistochemical distribution and colocalization of regulatory peptides in the carotid body

“…In contrast to the tachykinins, however, opioids depress chemoreceptor activity in cat. This effect was demonstrated in sinus nerve preparations both in vivo (Kirby and McQueen, 1986;McQueen and Ribeiro, 1980) and in vitro (Monti-Bloch and Eyzaguirre, 1985) and is mediated via the 6-subtype of opioid receptors (Kirby and McQueen, 1986).…”

Effects of Anesthetics, Sedatives, and Opioids on Ventilatory Control

“…Injection of -opioid receptor agonists into the CB of anesthetized cats depressed the HVR, suggesting the presence of these receptors (337). On the other hand, injection of selective -antagonists during normoxia produced no clear change in MV, although -antagonists enhanced the HVR, suggesting some minor endogenous opioid effect may be present at baseline.…”

“…On the other hand, injection of selective -antagonists during normoxia produced no clear change in MV, although -antagonists enhanced the HVR, suggesting some minor endogenous opioid effect may be present at baseline. μ-agonists had no effect on the CB response (337). Since all clinically used opioids are highly selective μ-agonists, especially at clinically relevant concentrations, the effect of opioids on the CB-mediated HVR should be negligible for clinical purposes.…”

“…Opioid receptors are widely distributed in the spinal cord (735), the central nervous system (CNS) (93,130,223,227,407,408,465,527,542,633,733,734), including the respiratory nuclei (242,357,389,390,466,594), and the peripheral nervous system including the peripheral chemoreceptors (337). The role of endogenous opiates in the control of respiration remains ill defined (241,597) compared to the wellknown respiratory depressant effects of μ-opioid agonists in clinical use.…”

Arterial chemoreceptor involvement in salicylate‐induced hyperventilation in rats

“…An alternative, therefore, would be to reduce the elevated chemosensory discharge pharmacologically, without producing nonselective depression of the CNS. Drugs which could do this include dopamine or dopamine D2-receptor agonists (Mir et al, 1984) and b-opioid receptor agonists (Kirby & McQueen, 1986).…”