Hypocretin/orexin and nociceptin/orphanin FQ coordinately regulate analgesia in a mouse model of stress-induced analgesia
Xinmin Xie, … , Lawrence Toll, Thomas S. Kilduff
Xinmin Xie, … , Lawrence Toll, Thomas S. Kilduff
Published June 12, 2008
Citation Information: J Clin Invest. 2008;118(7):2471-2481. https://doi.org/10.1172/JCI35115.
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Research Article Neuroscience

Hypocretin/orexin and nociceptin/orphanin FQ coordinately regulate analgesia in a mouse model of stress-induced analgesia

Abstract

Stress-induced analgesia (SIA) is a key component of the defensive behavioral “fight-or-flight” response. Although the neural substrates of SIA are incompletely understood, previous studies have implicated the hypocretin/orexin (Hcrt) and nociceptin/orphanin FQ (N/OFQ) peptidergic systems in the regulation of SIA. Using immunohistochemistry in brain tissue from wild-type mice, we identified N/OFQ-containing fibers forming synaptic contacts with Hcrt neurons at both the light and electron microscopic levels. Patch clamp recordings in GFP-tagged mouse Hcrt neurons revealed that N/OFQ hyperpolarized, decreased input resistance, and blocked the firing of action potentials in Hcrt neurons. N/OFQ postsynaptic effects were consistent with opening of a G protein–regulated inwardly rectifying K+ (GIRK) channel. N/OFQ also modulated presynaptic release of GABA and glutamate onto Hcrt neurons in mouse hypothalamic slices. Orexin/ataxin-3 mice, in which the Hcrt neurons degenerate, did not exhibit SIA, although analgesia was induced by i.c.v. administration of Hcrt-1. N/OFQ blocked SIA in wild-type mice, while coadministration of Hcrt-1 overcame N/OFQ inhibition of SIA. These results establish what is, to our knowledge, a novel interaction between the N/OFQ and Hcrt systems in which the corticotropin-releasing factor and N/OFQ systems coordinately modulate the Hcrt neurons to regulate SIA.

Authors

Xinmin Xie, Jonathan P. Wisor, Junko Hara, Tara L. Crowder, Robin LeWinter, Taline V. Khroyan, Akihiro Yamanaka, Sabrina Diano, Tamas L. Horvath, Takeshi Sakurai, Lawrence Toll, Thomas S. Kilduff

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Figure 1

N/OFQ-containing fibers innervate Hcrt neurons, and N/OFQ inhibits Hcrt neuronal activity.

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N/OFQ-containing fibers innervate Hcrt neurons, and N/OFQ inhibits Hcrt ...
(A) Left panel shows confocal image of N/OFQ-immunoreactive fibers in the vicinity of, and in putative contact with, Hcrt-immunoreactive neurons in the PLH of WT mice. N/OFQ (green) fibers are in close proximity to Hcrt-immunoreactive (red) cells. The arrow indicates the N/OFQ innervation of an Hcrt cell body. Middle panel shows light micrograph of a light brown immunolabeled Hcrt neuron contacted by a dark black bouton (arrow) representing immunolabeling for N/OFQ. Right panel shows electron micrograph taken from ultrathin sections of the same labeled terminal and dendrite shown in the light micrograph in the middle panel. Black arrow indicates the N/OFQ-immunolabeled axon terminal in synaptic contact (red arrowhead) with the dendrite of the Hcrt cell. Scale bars: 10 μm (left and middle panels); 1 μm (right panel). (B) Under current clamp, bath application of N/OFQ (1 μM) hyperpolarized Hcrt neurons, decreased input resistance, and blocked spontaneous firing of action potentials. The resting potential of this cell was –54 mV and was manually adjusted to –60 mV with DC current. Membrane resistance was monitored using hyperpolarizing current pulses (–0.3 nA, 800 ms) delivered every 5 seconds throughout the experiment. (C) Under voltage-clamp mode at a Vh of –60 mV, N/OFQ (1 μM) induced an outward current (–53 pA) in an Hcrt neuron. Notice that the frequency but not the amplitude of the miniature synaptic currents (inward currents) recorded in the presence of TTX (0.5 μM) was also reduced.