Brain‐derived neurotrophic factor drives the changes in excitatory synaptic transmission in the rat superficial dorsal horn that follow sciatic nerve injury

Abstract

Peripheral nerve injury can promote neuropathic pain. The basis of the 'central sensitization' that underlies this often intractable condition was investigated using 14-20-day chronic constriction injury (CCI) of the sciatic nerve of 20-day-old rats followed by electrophysiological analysis of acutely isolated spinal cord slices. In addition, defined-medium organotypic spinal cord slice cultures were exposed for 5-6 days to brain-derived neurotrophic factor (BDNF, 200 ng ml −1 ) or to medium conditioned with activated microglia (aMCM). Since microglial activation is an early consequence of CCI, the latter manipulation allowed us to model the effect of peripheral nerve injury on the dorsal horn in vitro. Using whole-cell recording from superficial dorsal horn neurons, we found that both BDNF and CCI increased excitatory synaptic drive to putative excitatory 'radial delay' neurons and decreased synaptic excitation of inhibitory 'tonic islet/central' neurons. BDNF also attenuated synaptic excitation of putative GABAergic neurons identified by glutamic acid decarboxylase (GAD) immunoreactivity. Intrinsic neuronal properties (rheobase, input resistance and action potential discharge rates) were unaffected. Exposure of organotypic cultures to either BDNF or aMCM increased overall excitability of the dorsal horn, as seen by increased cytoplasmic Ca 2+ responses to 35 mm K + as monitored by confocal Fluo-4AM imaging. The effect of aMCM was attenuated by the recombinant BDNF binding protein TrkBd5 and the effect of BDNF persisted when GABAergic inhibition was blocked with SR95531. These findings suggest that CCI enhances excitatory synaptic drive to excitatory neurons but decreases that to inhibitory neurons. Both effects are mediated by nerve injury-induced release of BDNF from microglia.

The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice

“…It was used to study morphological changes in myelinated and unmyelinated fibers 6,29 , and functional changes in sensory neurons, primary afferents and spinal neurons 19,21,22,[30][31][32][33][34][35] . It allowed demonstration that glial activation and a central shift in neuronal anion gradient participate in changes in the activity and in the responses of spinal nociceptive neurons and in neuropathic allodynia 24,[36][37][38] .…”

Analysis of the long-term actions of gabapentin and pregabalin in dorsal root ganglia and substantia gelatinosa

“…This was done by culturing DMOTC slices with 200 ng/ml BDNF for 5-6 days (Lu et al 2007(Lu et al , 2009a. This led to a significant increase in the amplitude (P Ͻ 0.05) but not the AUC of the Ca 2ϩ response to 35 mM K ϩ solution (Fig.…”

“…We therefore examined the overall effects of gabapentinoids on excitability of the dorsal horn by confocal Ca 2ϩ imaging. Challenge with high-K ϩ solution (20 or 35 mM) produces robust increases in the concentration of intracellular Ca 2ϩ in dorsal horn neurons in DMOTC (Biggs et al 2012;Lu et al 2009a). Typical recordings are illustrated in Fig.…”

“…sensitization that contributes to the establishment of neuropathic pain (Biggs et al 2010;Coull et al 2005;Liu and Sandkuhler 1997;Lu et al 2007Lu et al , 2009aMerighi et al 2008;Smith 2014;Wang et al 2009), we examined actions of GBP on neuropathic slices in which the extracellular environment of spinal neurons may resemble that seen following peripheral nerve injury in vivo. This was done by culturing DMOTC slices with 200 ng/ml BDNF for 5-6 days (Lu et al 2007(Lu et al , 2009a.…”

“…Age-matched untreated DMOTC slices served as controls. In some experiments, cultures were exposed to brain-derived neurotrophic factor (BDNF; 200 ng/ml; Alomone Labs, Jerusalem, Israel) for 4 -5 days (Lu et al 2007(Lu et al , 2009a. Other cultures were exposed acutely (for 90 s) to ATP (100 M), (Ϯ)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD; 25 M; Tocris), or epinephrine (25 M).…”