Stereological Analysis of Early Gene Expression Using Egr-1 Immunolabeling After Spreading Depression in the Rat Somatosensory Cortex

Abstract

Early growth response-1 (Egr-1), defined as a zinc finger transcription factor, is an upstream master switch of the inflammatory response, and its expression can be used to investigate the spatial and temporal extent of inflammatory changes in the brain. Cortical spreading depression (CSD) is characterized as a slowly propagating (2–5 mm/min) depolarization wave through neurons and astrocytes in humans that contributes to migraines and possibly to other brain pathologies. In rodents, CSD can be induced experimentally, which involves unilateral depolarization that is associated with microglial and astrocyte responses. The impact of CSD on structures beyond the affected hemisphere has not been explored. Here, we used an optical fractionator method to investigate potential correlations between the number of and period of the eletrophysiologic record of CSD phenomena and Egr-1 expression in ipsilateral and contralateral hemispheres. CSD was elicited by the restricted application of a 2% KCl solution over the left premotor cortex. Electrophysiological events were recorded using a pair of Ag/AgCl agar-Ringer electrodes for 2 or 6 h. An optical fractionator was applied to count the Egr-1 positive cells. We found that CSD increased Egr-1 expression in a time- and event-dependent manner in the ipsilateral/left hemisphere. Although CSD did not cross the midline, multiple CSD inductions were associated with an increased number of Egr-1 positive cells in the contralateral/right hemisphere. Thus, repeated CSD waves may have far reaching effects that are more global than previously considered possible. The mechanism of contralateral expression is unknown, but we speculate that callosal projections from the depolarized hemisphere may be related to this phenomenon.

Deep Brain Stimulation of the Medial Septal Area Can Modulate Gene Expression in the Hippocampus of Rats under Urethane Anesthesia

“…After induction, spreading depression will travel along the longitudinal axis of the hippocampus and will not be induced in the contralateral hemisphere. It was previously shown that in the neocortex, spreading depression increases the expression of c-fos [ 32 ], arc [ 33 ], egr1 [ 34 ], npas4 [ 35 ], bdnf [ 33 ], il1b [ 36 ], and tnf [ 36 ]. Our data are in agreement with these observations because in our case, the expression of all these genes, except il1b , increased in the right ventral hippocampus compared to the left ventral hippocampus.…”

Detecting Abnormal Neuronal Activity in a Chronic Migraine Model by Egr1-EGFP Transgenic Mice

“…Egr1-enhanced green fluorescent protein (EGFP) transgenic mice were used to apply the endogenous fluorescent signal to indicate neural activity in the brain at cellular resolution (Xie et al, 2014). Previous study has demonstrated that cortical spreading depression (CSD), which might be involved in the biological process of migraine attack, up-regulated Egr1 expression in the somatosensory cortex (Sosthenes et al, 2019). However, there is no research on the expression of Egr1 in the whole brain of CM model.…”

Genome-wide DNA methylation analysis in an antimigraine-treated preclinical model of cortical spreading depolarization

“…At the transcriptomic level, several studies have confirmed that CSD modulates gene expression in the cerebral cortex of rodents. Specifically, CSD has been shown to modulate the expression of genes involved in inflammatory processes (30), in sleep homeostasis (31), in neuroprotection (32) and in stress responses (33), amongst others. In agreement with this, our group showed in a previous study that CSD induction in the same samples used in this study modulates the expression of genes related to hormone stimulus, apoptosis, synaptic transmission and interleukin signaling, without differences between the animals pre-treated or not with TPM or VPA (34).…”