Anat Cell Biol.  2011 Mar;44(1):60-68. 10.5115/acb.2011.44.1.60.

The expression of corticotropin-releasing factor and its receptors in the spinal cord and dorsal root ganglion in a rat model of neuropathic pain

• Kim EH
• Ryu DH
• Hwang S

• KMID: 2168869
• DOI: http://doi.org/10.5115/acb.2011.44.1.60

Abstract

Corticotropin-releasing factor (CRF) is a peptide involved in the activation of the hypothalamic-pituitary-adrenal (HPA) axis. CRF is distributed not only along the HPA axis but also throughout pain-relevant anatomical sites. CRF elicits potent antinociception at the three main levels of pain transmissions: namely, the brain, spinal cord, and peripheral sensory neurons. The widespread distribution of CRF receptors 1 and 2 in the brain offers several targets wherein CRF could alter pain, some of which may be independent of the HPA axis. In this study, we assessed the expression of CRF and its receptors, CRF receptor type (CRFR)1 and CRFR2, in the spinal dorsal horn and dorsal root ganglion (DRG) in a rat model of neuropathic pain induced by spinal nerve injury (SNI). CRF was expressed in a few DRG neurons and primary afferent fibers in the dorsal horns of nasmall yi, Ukrainianve rats, and the CRF-positive neurons in DRG and fibers in the spinal dorsal horn were found to have increased after SNI. CRFR1 was not expressed in DRG or the dorsal horn and CRFR2 was expressed weakly in the small neurons in DRG in the nasmall yi, Ukrainianve rats. After SNI, CRFR1 was expressed in the activated microglia in the ipsilateral dorsal horn, and immunoreaction for CRFR2 was increased in the contralateral DRG following SNI. Consequently, it has been suggested that the increased expression of CRF and CRFR2 in DRG neurons and primary afferent fibers in dorsal horn, and CRFR1 in the activated microglia, may be involved in the mediation of stress responses as well as in microglial activation in the neuropathic pain state following SNI.

Keyword

Corticotropin-releasing hormon; Corticotropin-releasing hormon receptor; Spinal cord; Neuralgia; Dorsal root ganglion

MeSH Terms

Animals
Axis, Cervical Vertebra
Brain
Corticotropin-Releasing Hormone
Diagnosis-Related Groups
Ganglia, Spinal
Horns
Microglia
Negotiating
Neuralgia
Neurons
Rats
Receptors, Corticotropin-Releasing Hormone
Sensory Receptor Cells
Spinal Cord
Spinal Nerve Roots
Spinal Nerves
Corticotropin-Releasing Hormone
Receptors, Corticotropin-Releasing Hormone

Figure

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  Fig. 1 Von Frey test for the assessment of mechanical hyperalgesia in the sham control (sham) and spinal nerve injury (SNI) rats. The SNI rats evidenced reductions in the paw withdrawal threshold relative to the sham control group. One-way ANOVA (n=5, *P<0.005 vs. Con, #P<0.005 vs. sham).

• 

  Fig. 2 Corticotropin-releasing factor (CRF) and transient receptor potential vanilloid 1 receptor (TRPV1) expression in the L5 dorsal root ganglion (DRG) of the naїve and spinal nerve injury (SNI) rats. (A) In the DRG of naїve rats, CRF was expressed in a few small neurons, and the majority of CRF-positive neurons also expressed TRPV1 (arrows). (B) After SNI, virtually all immunoreactivity for CRF and TRPV1 disappeared in the ipsilateral (ipsi) DRG. (C) In the contralateral (contra) DRG of the SNI group rats, the levels of CRF-positive neurons were increased relative to that of naїve rats. (D) The number of CRF-positive neurons in ipsilateral and contralateral DRGs in naїve rats and SNI group rats. One-way ANOVA (n=5, *P<0.05 vs. naїve). Scale bar=20 µm.

• 

  Fig. 3 Corticotropin-releasing factor (CRF) expression in the spinal dorsal horn in the naїve and spinal nerve injury (SNI) group rats. (A) In the spinal cords of naїve rats, CRF-immunoreactive fibers and puncta were noted in the superficial laminae of the dorsal horn. (B, C) CRF immunoreactive fibers and puncta were increased in lamina I, II of the contralateral (contra) dorsal horn after SNI. Ipsi, ipsilateral. Scale bars=500 µm (left column), 200 µm (middle column).

• 

  Fig. 4 Corticotropin-releasing factor receptor type 1 (CRFR1) expression in the Iba1-positive microglia in the spinal dorsal horn. (A) Immunoreactivity for CRFR1 was not noted in the dorsal horn of the naїve animals. (B) Immoreactivity for CRFR1 was noted in the activated microglia in the laminae III-V, but not in the lamina I-II (asterisk), of the ipsilateral (ipsi) dorsal horn at 7 days after spinal nerve injury (SNI). (C) At 14 days after SNI, CRF expression was weaker relative to that observed 7 days after SNI. (D) Confocal microscopy for CRFR1 and Iba1 expression in the ipsilateral dorsal horn at 14 days after SNI. CRFR1-positive cells in the ipsilateral dorsal horn were also stained for Iba1 (arrows) in the deeper laminae. Contra, contralateral. Scale bars=500 µm (A-C), 50 µm (D).

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  Fig. 5 Expression of corticotropin-releasing factor receptor type 2 (CRFR2) in the L5 dorsal root ganglion (DRG) of the sham control and spinal nerve injury (SNI) group rats. (A, B) In the sham control rats, weak immunoreactivity for CRFR2 was noted in the majority of DRG neurons. (C, D) The increase in CRFR2 immunoreactivity was observed in the neurons (arrows) of the contralateral (contra) DRG after SNI. Ipsi, ipsilateral. Scale bar=200 µm.

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