Experimental Protocols and Analytical Procedures for Studying Synaptic Transmission in Rodent Spinal Cord Dorsal Horn

Abstract

Synaptic modulation and plasticity are key mechanisms underlying pain transmission in the spinal cord and supra‐spinal centers. The study and understanding of these phenomena are fundamental to investigating both acute nociception and maladaptive changes occurring in chronic pain. This article describes experimental protocols and analytical methods utilized in electrophysiological studies to investigate synaptic modulation and plasticity at the first station of somatosensory processing, the spinal cord dorsal horn. Protocols useful for characterizing the nature of synaptic inputs, the site of modulation (pre‐ versus postsynaptic), and the presence of short‐term synaptic plasticity are presented. These methods can be employed to study the physiology of acute nociception, the pathological mechanisms of persistent inflammatory and neuropathic pain, and the pharmacology of receptors and channels involved in pain transmission. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Spinal cord dissection and acute slice preparation Basic Protocol 2: Stimulation of the dorsal root and extracellular recording (compound action potentials and field potentials) Basic Protocol 3: Patch‐clamp recording from dorsal horn neurons: action potential firing patterns and evoked synaptic inputs Basic Protocol 4: Analysis of parameters responsible for changes in synaptic efficacy Basic Protocol 5: Recording and analysis of currents mediated by astrocytic glutamate

Modulation of NMDA receptor activity by CR4056, an imidazoline-2 receptor ligand with analgesic properties

“…To determine whether the effect of CR4056 on NMDA EPSCs was due to a decrease of glutamate release from primary afferents or to a modulation of NMDARs, we recorded extracellular field potentials evoked by dorsal root stimulation ( Figure 4E ). As shown in previous studies, field potentials recorded from spinal cord dorsal horn are mainly mediated by AMPARs ( 25 , 26 ). Application of CR4056 did not affect field potential area in 6 tested slices ( Figure 4F ), suggesting a postsynaptic effect of the compound on NMDARs.…”

“…NMDA receptors are key elements in pain transmission, indeed in pathological situations, such as neuropathic pain, an overactivation of these receptors was demonstrated ( 26 ).…”