Dataset Information

N-arachidonyl-glycine modulates synaptic transmission in superficial dorsal horn.

ABSTRACT:

Background and purpose

The arachidonyl-amino acid N-arachidonyl-glycine (NAGly) is an endogenous lipid, generated within the spinal cord and producing spinally mediated analgesia via non-cannabinoid mechanisms. In this study we examined the actions of NAGly on neurons within the superficial dorsal horn, a key site for the actions of many analgesic agents.

Experimental approach

Whole cell patch clamp recordings were made from lamina II neurons in rat spinal cord slices to examine the effect of NAGly on glycinergic and NMDA-mediated synaptic transmission.

Key results

N-arachidonyl-glycine prolonged the decay of glycine, but not β-alanine induced inward currents and decreased the amplitude of currents induced by both glycine and β-alanine. NAGly and ALX-1393 (inhibitor of the glycine transporter, GLYT2), but not the GLYT1 inhibitor, ALX-5407, produced a strychnine-sensitive inward current. ALX-5407 and ALX-1393, but not NAGly prolonged the decay phase of glycine receptor-mediated miniature inhibitory postsynaptic currents (IPSCs). NAGly prolonged the decay phase of evoked IPSCs, although to a lesser extent than ALX-5407 and ALX-1393. In the presence of ALX-1393, NAGly shortened the decay phase of evoked IPSCs. ALX-5407 increased and NAGly decreased the amplitude of evoked NMDA-mediated excitatory postsynaptic currents.

Conclusions and implications

Our results suggest that NAGly enhanced inhibitory glycinergic synaptic transmission within the superficial dorsal horn by blocking glycine uptake via GLYT2. In addition, NAGly decreased excitatory NMDA-mediated synaptic transmission. Together, these findings provide a cellular explanation for the spinal analgesic actions of NAGly.

SUBMITTER: Jeong HJ

PROVIDER: S-EPMC2992905 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

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Publications

N-arachidonyl-glycine modulates synaptic transmission in superficial dorsal horn.

Jeong Hyo-Jin HJ Vandenberg Robert J RJ Vaughan Christopher W CW

British journal of pharmacology 20101001 4

<h4>Background and purpose</h4>The arachidonyl-amino acid N-arachidonyl-glycine (NAGly) is an endogenous lipid, generated within the spinal cord and producing spinally mediated analgesia via non-cannabinoid mechanisms. In this study we examined the actions of NAGly on neurons within the superficial dorsal horn, a key site for the actions of many analgesic agents.<h4>Experimental approach</h4>Whole cell patch clamp recordings were made from lamina II neurons in rat spinal cord slices to examine t ...[more]

PMID: 20860669

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Project description:BackgroundNeurons in superficial (SDH) and deep (DDH) laminae of the spinal cord dorsal horn receive sensory information from skin, muscle, joints and viscera. In both regions, glycine- (GlyR) and GABAA-receptors (GABAARs) contribute to fast synaptic inhibition. For rat, several types of GABAAR coexist in the two regions and each receptor type provides different contributions to inhibitory tone. Recent work in mouse has discovered an additional type of GlyR, (containing alpha 3 subunits) in the SDH. The contribution of differing forms of the GlyR to sensory processing in SDH and DDH is not understood.Methods and resultsHere we compare fast inhibitory synaptic transmission in mouse (P17-37) SDH and DDH using patch-clamp electrophysiology in transverse spinal cord slices (L3-L5 segments, 23 degrees C). GlyR-mediated mIPSCs were detected in 74% (25/34) and 94% (25/27) of SDH and DDH neurons, respectively. In contrast, GABAAR-mediated mIPSCs were detected in virtually all neurons in both regions (93%, 14/15 and 100%, 18/18). Several Gly- and GABAAR properties also differed in SDH vs. DDH. GlyR-mediated mIPSC amplitude was smaller (37.1 +/- 3.9 vs. 64.7 +/- 5.0 pA; n = 25 each), decay time was slower (8.5 +/- 0.8 vs. 5.5 +/- 0.3 ms), and frequency was lower (0.15 +/- 0.03 vs. 0.72 +/- 0.13 Hz) in SDH vs. DDH neurons. In contrast, GABAAR-mediated mIPSCs had similar amplitudes (25.6 +/- 2.4, n = 14 vs. 25. +/- 2.0 pA, n = 18) and frequencies (0.21 +/- 0.08 vs. 0.18 +/- 0.04 Hz) in both regions; however, decay times were slower (23.0 +/- 3.2 vs. 18.9 +/- 1.8 ms) in SDH neurons. Mean single channel conductance underlying mIPSCs was identical for GlyRs (54.3 +/- 1.6 pS, n = 11 vs. 55.7 +/- 1.8, n = 8) and GABAARs (22.7 +/- 1.7 pS, n = 10 vs. 22.4 +/- 2.0 pS, n = 11) in both regions. We also tested whether the synthetic endocanabinoid, methandamide (methAEA), had direct effects on Gly- and GABAARs in each spinal cord region. MethAEA (5 muM) reduced GlyR-mediated mIPSC frequency in SDH and DDH, but did not affect other properties. Similar results were observed for GABAAR mediated mIPSCs, however, rise time was slowed by methAEA in SDH neurons.ConclusionTogether these data show that Gly- and GABAARs with clearly differing physiological properties and cannabinoid-sensitivity contribute to fast synaptic inhibition in mouse SDH and DDH.

Project description:Vesicular glutamate transporter-2 (VGluT2) mediates the uptake of glutamate into synaptic vesicles in neurons. Spinal cord dorsal horn interneurons are highly heterogeneous and molecularly diverse. The functional significance of VGluT2-expressing dorsal horn neurons in physiological and pathological pain conditions has not been explicitly demonstrated. Designer receptors exclusively activated by designer drugs (DREADDs) are a powerful chemogenetic tool to reversibly control neuronal excitability and behavior. Here, we used transgenic mice with Cre recombinase expression driven by the VGluT2 promoter, combined with the chemogenetic approach, to determine the contribution of VGluT2-expressing dorsal horn neurons to nociceptive regulation. Adeno-associated viral vectors expressing double-floxed Cre-dependent Gαq-coupled human M3 muscarinic receptor DREADD (hM3D)-mCherry or Gαi-coupled κ-opioid receptor DREADD (KORD)-IRES-mCitrine were microinjected into the superficial spinal dorsal horn of VGluT2-Cre mice. Immunofluorescence labeling showed that VGluT2 was predominantly expressed in lamina II excitatory interneurons. Activation of excitatory hM3D in VGluT2-expressing neurons with clozapine N-oxide caused a profound increase in neuronal firing and synaptic glutamate release. Conversely, activation of inhibitory KORD in VGluT2-expressing neurons with salvinorin B markedly inhibited neuronal activity and synaptic glutamate release. In addition, chemogenetic stimulation of VGluT2-expressing neurons increased mechanical and thermal sensitivities in naive mice, whereas chemogenetic silencing of VGluT2-expressing neurons reversed pain hypersensitivity induced by tissue inflammation and peripheral nerve injury. These findings indicate that VGluT2-expressing excitatory neurons play a crucial role in mediating nociceptive transmission in the spinal dorsal horn. Targeting glutamatergic dorsal horn neurons with inhibitory DREADDs may be a new strategy for treating inflammatory pain and neuropathic pain.

Dataset Information

N-arachidonyl-glycine modulates synaptic transmission in superficial dorsal horn.

Background and purpose

Experimental approach

Key results

Conclusions and implications

Publications

N-arachidonyl-glycine modulates synaptic transmission in superficial dorsal horn.

Similar Datasets

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