Sigma 1 receptor (σ1R) is a non-opioid receptor that modulates pain perception and is strongly expressed in dorsal root ganglion (DRG) neurons. We studied the changes in the expression of σ1R in different subpopulations of DRG neurons during the first 48 hr in a carrageenaninduced inflammation rat model, with σ1R being a possible base for the development of neuropathic pain after inflammation. Twenty Sprague Dawley rats were divided into five groups (N = 4 in each group): the control (C) group was sacrificed immediately; all other animals received an intraplantar injection of 0.1 mL 2% carrageenan and were sacrificed in 6, 12, 24 or 48 hr after the injection and DRGs were collected and processed for immunohistochemistry. σ1R fluorescence intensity decreased slightly but significantly in up to 24 hr post-carrageenan injection in all subpopulations of DRG neurons (ib4+; ib4− medium, ib4− large and ib4− in total; P < 0.05 -P < 0.001), with the exception of the ib4− small neurons (<25 μm; P > 0.05). This decrement was followed by a subsequent increase in σ1R fluorescence intensity 48 hr after the plantar carrageenan injection (P < 0.05 -P < 0.0001). The same trend was also observed in the CGRP+ population of the DRG neurons, in the total population as well as in the CGRP+ small (<25 μm) and larger CGRP (>25 μm) sub-populations (P < 0.05 -P < 0.001). The presented results may contribute to further understanding of role of σ1R in the development of peripheral sensitization during inflammation. They may also be valuable for the therapeutic application of σ1R antagonists, particularly in the adjustment of the ABBREVIATIONS: CCI = chronic constriction injury; CFA = complete Freund adjuvant; CGRP = calcitonin gene-related peptide; DRG = dorsal root ganglion; ER = endoplasmic reticulum; ib4 = isolectin B4; IP3 = inositol 1,4,5-triphosphate; KO = knockout; PBS = phosphate-buffered saline; SNL = spinal nerve ligation; σ1R = sigma 1 receptor Grant sponsor: Ministarstvo Znanosti, Obrazovanja i Sporta.

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