Opioids Inhibit Lateral Amygdala Pyramidal Neurons by Enhancing a Dendritic Potassium Current

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Abstract
Pyramidal neurons in the lateral amygdala discharge trains of action potentials that show marked spike frequency adaptation, which is primarily mediated by activation of a slow calcium-activated potassium current. We show here that these neurons also express an α-dendrotoxin- and tityustoxin-Kα-sensitive voltage-dependent potassium current that plays a key role in the control of spike discharge frequency. This current is selectively targeted to the primary apical dendrite of these neurons. Activation of μ-opioid receptors by application of morphine ord-Ala2-N-Me-Phe4-Glycol5-enkephalin (DAMGO) potentiates spike frequency adaptation by enhancing the α-dendrotoxin-sensitive potassium current. The effects of μ-opioid agonists on spike frequency adaptation were blocked by inhibiting G-proteins withN-ethylmaleimide (NEM) and by blocking phospholipase A2. Application of arachidonic acid mimicked the actions of DAMGO or morphine. These results show that μ-opioid receptor activation enhances spike frequency adaptation in lateral amygdala neurons by modulating a voltage-dependent potassium channel containing Kv1.2 subunits, through activation of the phospholipase A2–arachidonic acid–lipoxygenases cascade.