Selective distribution of μ-opioid receptors in C1 adrenergic neurons and their afferents
Journal of Comparative Neurology
Agonists of the μ-opioid receptor (MOR) have profound effects on blood pressure, heart rate, and respiration that may be mediated by C1 adrenergic neurons in the rostral ventrolateral medulla (RVL). C1 neurons are sympathoexcitatory and are involved in both tonic and reflex regulation of sympathetic outflow. This study was designed to determine whether C1 neurons, or their afferents, contain MOR. C1 neurons were identified by using an antibody against the epinephrine synthesizing enzyme phenylethanolamine-N-methyl transferase (PNMT), whereas MOR was localized by using an antipeptide antibody that recognizes the cloned MOR, MOR1. Combined immunoperoxidase and immunogold methods were used to examine the cellular distribution of MOR1 relative to PNMT-containing neurons in the RVL. MOR1 was found in 22% of PNMT-containing dendrites (n = 392), whereas MOR1-containing axons or axon terminals contacted 14% of PNMT-containing dendrites. This distribution was heterogenous with regard to dendritic size: PNMT-labeled dendrites containing MOR1 were usually large (60% were >1.2 μm), whereas PNMT-containing dendrites that received MOR1-labeled afferents were usually small (79% were
Higgs, Dennis M. and Burd, G. D., "Selective distribution of μ-opioid receptors in C1 adrenergic neurons and their afferents" (2001). Journal of Comparative Neurology, 433, 1, 23-33.