Mu-opioid receptor trafficking on inhibitory synapses in the rat brainstem.
Whole-cell recordings were made from identified gastric-projecting rat dorsal motor nucleus of the vagus (DMV) neurons. The amplitude of evoked IPSCs (eIPSCs) was unaffected by perfusion with met-enkephalin (ME) or by mu-, delta-, or kappa-opioid receptor selective agonists, namely D-Ala2-N-Me-Phe4-Glycol5-enkephalin (DAMGO), cyclic [D-Pen2-D-Pen5]-enkephalin, or trans-3,4-dichloro-N-methyl-N-[2-(1-pyrolytinil)-cyclohexyl]-benzeneacetamide methane sulfonate (U50,488), respectively. Brief incubation with the adenylate cyclase activator forskolin or the nonhydrolysable cAMP analog 8-bromo-cAMP, thyrotropin releasing hormone, or cholecystokinin revealed the ability of ME and DAMGO to inhibit IPSC amplitude; this inhibition was prevented by pretreatment with the mu-opioid receptor (MOR1) selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2. Conversely, incubation with the adenylate cyclase inhibitor dideoxyadenosine, with the protein kinase A (PKA) inhibitor N-[2-(p-Bromocinnamyl-amino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H89), or with the Golgi-disturbing agent brefeldin A, blocked the ability of forskolin to facilitate the inhibitory actions of ME. Immunocytochemical experiments revealed that under control conditions, MOR1 immunoreactivity (MOR1-IR) was colocalized with glutamic acid decarboxylase (GAD)-IR in profiles apposing DMV neurons only after stimulation of the cAMP-PKA pathway. Pretreatment with H89 or brefeldin A or incubation at 4 degrees C prevented the forskolin-mediated insertion of MOR1 on GAD-IR-positive profiles. These results suggest that the cAMP-PKA pathway regulates trafficking of mu-opioid receptors into the cell surface of GABAergic nerve terminals. By consequence, the inhibitory actions of opioid peptides in the dorsal vagal complex may depend on the state of activation of brainstem vagal circuits.
Department of Internal Medicine-Gastroenterology, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA.
Kirsteen N
KN
Browning
Alexander E
AE
Kalyuzhny
R Alberto
RA
Travagli
D000818:Animals; D001933:Brain Stem / Q000502:physiology*; D020126:Brefeldin A / Q000494:pharmacology; D005576:Colforsin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005071:Evoked Potentials; D041981:Gastrointestinal Tract / Q000294:innervation; D007150:Immunohistochemistry; D007700:Kinetics; D009046:Motor Neurons / Q000502:physiology; D009433:Neural Inhibition; D018847:Opioid Peptides / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D011957:Receptors, Opioid / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects; D014630:Vagus Nerve / Q000166:cytology / Q000502:physiology*
D018847:Opioid Peptides; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D005576:Colforsin; D020126:Brefeldin A; D000242:Cyclic AMP