Time Course of Immediate Early Gene Protein Expression in the Spinal Cord following Conditioning Stimulation of the Sciatic Nerve in Rats

Abstract

Long-term potentiation induced by conditioning electrical stimulation of afferent fibers is a widely studied form of synaptic plasticity in the brain and the spinal cord. In the spinal cord dorsal horn, long-term potentiation is induced by a series of high-frequency trains applied to primary afferent fibers. Conditioning stimulation (CS) of sciatic nerve primary afferent fibers also induces expression of immediate early gene proteins in the lumbar spinal cord. However, the time course of immediate early gene expression and the rostral-caudal distribution of expression in the spinal cord have not been systematically studied. Here, we examined the effects of sciatic nerve conditioning stimulation (10 stimulus trains, 0.5 ms stimuli, 7.2 mA, 100 Hz, train duration 2 s, 8 s intervals between trains) on cellular expression of immediate early genes, Arc, c-Fos and Zif268, in anesthetized rats. Immunohistochemical analysis was performed on sagittal sections obtained from Th13- L5 segments of the spinal cord at 1, 2, 3, 6 and 12 h post-CS. Strikingly, all immediate early genes exhibited a monophasic increase in expression with peak increases detected in dorsal horn neurons at 2 hours post-CS. Regional analysis showed peak increases at the location between the L3 and L4 spinal segments. Both Arc, c-Fos and Zif268 remained significantly elevated at 2 hours, followed by a sharp decrease in immediate early gene expression between 2 and 3 hours post-CS. Colocalization analysis performed at 2 hours post-CS showed that all c-Fos and Zif268 neurons were positive for Arc, while 30% and 43% of Arc positive neurons were positive for c-Fos and Zif268, respectively. The present study identifies the spinal cord level and time course of immediate early gene (IEGP) expression of relevance for analysis of IEGPs function in neuronal plasticity and nociception.

Pharmacology, pharmacokinetics, and metabolism of the DNA-decoy AYX1 for the prevention of acute and chronic post-surgical pain

“…EGR1 induction is detectable within ∼30 to 60 min following a noxious stimulation. 12 , 13 The histologic visualization of a fluorescent conjugate of AYX1 in the lumbar spinal cord and DRG 30 min following an IT injection shows that AYX1 is already present in cell nuclei ( Figure 4 ), where it can compete with the newly induced EGR1. EGR1 induction is known to continue for at least 720 min following the initial stimulation, as illustrated in the spinal cord.…”

“…Prior studies in the spinal cord have shown that EGR1 induction is detectable from 30 to 60 min up to at least ∼12 h following a noxious or sensitizing stimulus. 12 , 13 The pharmacokinetic properties of single strand oligonucleotides are just beginning to be understood 14 – 17 and to the best of our knowledge, no information is publicly available regarding IT injection of DNA-decoys as a class of molecules. We characterized AYX1 local pharmacokinetics (PK) and metabolism features driving AYX1 exposure in the lumbar cerebrospinal fluid (LCSF), DRG, and spinal cord during that timeframe.…”

Genotype-dependent responsivity to inflammatory pain: A role for TRPV1 in the periaqueductal grey

“…Modulation of the activity of dorsal horn neurons is a key outcome/endpoint following activation of the descending pain pathway (Bojovic et al, 2015;Gao and Ji, 2009). The fact that the behavioural effects of the drugs administered are not accompanied by drug-induced effects on c-Fos expression in the dorsal horn may suggest that the behavioural effects of pharmacological manipulation of TRPV1 in the DLPAG are not mediated by modulation of the descending pain pathway.…”

Intercellular Arc signaling regulates vasodilation

“…Among the transcripts with significant increases in translation was the immediate early gene Arc ( Figure 1G). While Arc is expressed in the spinal cord, it is unclear if it is present in DRG neurons (Bojovic et al, 2015;Hossaini et al, 2010;Minatohara et al, 2015;Plath et al, 2006). To validate if Arc is translated in response to inflammatory mediators, we conducted immunoblots on cultured DRG exposed to NG/IL-6 ( Figure 1H).…”