The role of Cx36 and Cx43 in 4-aminopyridine-induced rhythmic activity in the spinal nociceptive dorsal horn: an electrophysiological study invitro.

Christopher W P Kay,Emanuele Sher,Anne E King,Daniel Ursu

doi:10.14814/phy2.12852

Christopher W P Kay, Emanuele Sher + Show 2 more

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https://doi.org/10.14814/phy2.12852

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Abstract

Connexin (Cx) proteins and gap junctions support the formation of neuronal and glial syncytia that are linked to different forms of rhythmic firing and oscillatory activity in the CNS. In this study, quantitative reverse transcription polymerase chain reaction (RT‐qPCR) was used to profile developmental expression of two specific Cx proteins, namely glial Cx43 and neuronal Cx36, in postnatal lumbar spinal cord aged 4, 7, and 14 days. Extracellular electrophysiology was used to determine the contribution of Cx36 and Cx43 to a previously described form of 4‐aminopyridine (4‐AP)‐induced 4–12 Hz rhythmic activity within substantia gelatinosa (SG) of rat neonatal dorsal horn (DH) in vitro. The involvement of Cx36 and Cx43 was probed pharmacologically using quinine, a specific uncoupler of Cx36 and the mimetic peptide blocker Gap 26 which targets Cx43. After establishment of 4–12 Hz rhythmic activity by 4‐AP (25 μmol/L), coapplication of quinine (250 μmol/L) reduced 4‐AP‐induced 4–12 Hz rhythmic activity (P < 0.05). Preincubation of spinal cord slices with Gap 26 (100 μmol/L), compromised the level of 4‐AP‐induced 4–12 Hz rhythmic activity in comparison with control slices preincubated in ACSF alone (P < 0.05). Conversely, the nonselective gap junction “opener” trimethylamine (TMA) enhanced 4–12 Hz rhythmic behavior (P < 0.05), further supporting a role for Cx proteins and gap junctions. These data have defined a physiological role for Cx36 and Cx43 in rhythmic firing in SG, a key nociceptive processing area of DH. The significance of these data in the context of pain and Cx proteins as a future analgesic drug target requires further study.

Highlights

Gap junctions support electrical signaling and permit rapid intercellular exchange of small molecules including ions, second messengers, nutrients, and metabolites (Sohl et al 2005)
Identification and characterization of a family of 20 Cx genes has given an improved understanding of their roles in the immature and adult central nervous system (CNS), highlighting diverse functions ranging from formation of neuron-glial syncytia to facilitation of rhythmic neuronal firing or distributed network synchrony (Sohl et al 2004)
Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society

Summary

Introduction

Gap junctions support electrical signaling and permit rapid intercellular exchange of small molecules including ions, second messengers, nutrients, and metabolites (Sohl et al 2005). The presence of heterogeneous Cx subtypes in spinal cord dorsal and ventral horn raises the question of their potential physiological significance and whether gap junction connectivity could influence sensory or motor functions. For the latter, a role for gap junctions in coordinating and a 2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society

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