title: Mu opioid receptor activation inhibits GABAergic inputs to basolateral amygdala neurons through Kv1.1/1.2 channels.
abstract: The basolateral amygdala (BLA) is the major amygdaloid nucleus distributed with mu opioid receptors. The afferent input from the BLA to the central nucleus of the amygdala (CeA) is considered important for opioid analgesia. However, little is known about the effect of mu opioids on synaptic transmission in the BLA. In this study, we examined the effect of mu opioid receptor stimulation on the inhibitory and excitatory synaptic inputs to CeA-projecting BLA neurons. BLA neurons were retrogradely labeled with a fluorescent tracer injected into the CeA of rats. Whole cell voltage-clamp recordings were performed on labeled BLA neurons in brain slices. The specific mu opioid receptor agonist, (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin (DAMGO, 1 microM), significantly reduced the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in 77% of cells tested. DAMGO also significantly decreased the peak amplitude of evoked IPSCs in 75% of cells examined. However, DAMGO did not significantly alter the frequency of mEPSCs or the peak amplitude of evoked EPSCs in 90% and 75% of labeled cells, respectively. Bath application of the Kv channel blockers, 4-AP (Kv1.1, 1.2, 1.3, 1.5, 1.6, 3.1, 3.2), alpha-dendrotoxin (Kv1.1, 1.2, 1.6), dendrotoxin-K (Kv1.1), or tityustoxin-Kalpha (Kv1.2) each blocked the inhibitory effect of DAMGO on mIPSCs. Double immunofluorescence labeling showed that some of the immunoreactivities of Kv1.1 and Kv1.2 were colocalized with synaptophysin in the BLA. This study provides new information that activation of presynaptic mu opioid receptors primarily attenuates GABAergic synaptic inputs to CeA-projecting neurons in the BLA through a signaling mechanism involving Kv1.1 and Kv1.2 channels.
authors.affiliation: Department of Anesthesiology , Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey Pennsylvania, USA.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Finnegan
authors.forename: Shao-Rui
authors.initials: SR
authors.lastname: Chen
authors.forename: Hui-Lin
authors.initials: HL
authors.lastname: Pan
mesh_terms: D000679:Amygdala / Q000737:chemistry / Q000502:physiology*; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004546:Elapid Venoms / Q000494:pharmacology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D051662:Kv1.1 Potassium Channel / Q000032:analysis / Q000187:drug effects / Q000502:physiology*; D051663:Kv1.2 Potassium Channel / Q000032:analysis / Q000187:drug effects / Q000502:physiology*; D008032:Limbic System / Q000502:physiology; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000502:physiology*; D012604:Scorpion Venoms / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D016708:Synaptophysin / Q000032:analysis; D005680:gamma-Aminobutyric Acid / Q000502:physiology*; D000094942:Nociceptin Receptor
chemical_list: D000701:Analgesics, Opioid; D001640:Bicuculline; D004546:Elapid Venoms; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D051662:Kv1.1 Potassium Channel; D051663:Kv1.2 Potassium Channel; D010455:Peptides; D026902:Potassium Channel Blockers; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D012604:Scorpion Venoms; D016708:Synaptophysin; D005680:gamma-Aminobutyric Acid; D000094942:Nociceptin Receptor; C081506:dendrotoxin K; C003609:tityustoxin; C020273:dendrotoxin; C000722285:Oprl1 protein, rat