Gene Expression in the Rat Thalamus following Chronic Neuropathic Pain Development: mRNA sequencing analysis

Chronic pain afflicts roughly 44% of Service Members returning from Iraq and Afghanistan, and it is estimated that 100 million Americans suffer from this condition. The underlying molecular mechanisms of chronic pain development have remained elusive. The broad objective of this study is to identify molecular signals and indications of chronic pain in key brain regions during the onset and progression of neuropathic pain, in a rodent model. For this experiment, we collected tissue from five brain regions (thalamus, amygdala, cingulate cortex, insular cortex, and somatosensory cortex), as well as the L4–L6 spinal cord and L5 dorsal root ganglia, from rats subjected to the spared nerve injury (SNI) protocol, a model for chronic neuropathic pain. Tissue was collected at 1, 3, 7, 14 and 21 days post‐injury from each tissue and RNA extracted for mRNA sequencing (TruSeq total RNA protocol and Illumina HISCAN‐SQ platform). We present here the detailed mRNA sequencing workflow (pipeline) customized to provide the full complement of mRNA data (transcriptome) for multiple brain regions over the time course of the SNI protocol. In our initial analysis we focused on the assessment of the transcriptome of the thalamus, which is an important center of pain processing in the brain. We focused in particular on the 21 day time point, which is when the mechanical allodynia reaches its peak and therefore the most severe alterations in transcription are expected. In rats experiencing chronic pain relative to controls, we observed a reduction in the expression of several neurotransmitter receptors, such as CHRM4, CHRNB3, CHRNA5, CHRNB4, CNR1, ADORA2A, GPR85, BDKRB2, MC5R, DRD1, DRD2, and associated G proteins, such as GPR85, GNAT2, GNB3, GNG7, as well as the neurotransmitter TAC1. These findings suggest a global desensitization of neural signaling in the thalamus corresponding to chronic pain. Analysis of all time points and brain regions is underway and will provide a comprehensive picture of gene expression changes during the onset and progression of chronic pain. Research was conducted in compliance with the Animal Welfare Act, and all other Federal requirements. The views expressed are those of the authors and do not constitute endorsement by the U.S. Army. Support or Funding Information This work was supported by funding from the United States Army Medical Research and Material Command. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .