The Relationship between the expression of the TrkA Receptors and the Occurrence of Neuropathic Pain

1998 Fiscal Year Final Research Report Summary

• Project/Area Number: 09671575
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Anesthesiology/Resuscitation studies
• Research Institution: Miyazaki Medical College
• Principal Investigator: UNO Takeshi Miyazaki Medical College, Medical Department, Associate Professor, 医学部, 助教授 (70038842)
• Co-Investigator(Kenkyū-buntansha): KOSAI Kazuko Miyazaki Medical College, Medical Department, Instructor, 医学部, 助手 (00234740) ; NISHIMORI Toshikazu Miyazaki Medical College, Biology, Professor, 医学部, 教授 (20112211)
• Project Period (FY): 1997 – 1998
• Keywords: Neuropathic Pain / Nerve Growth Factor / γ-aminobutyric acid

Research Abstract

We observed the expression of the TrkA receptors which have high affinity to couple with nerve growth factor (NGF) on ligated sciatic nerve and dorsal root ganglion (5th and 6th lumbar vertebral level) by using immunohistological staining. But, we could not detect any Trk receptors on those specimen. The antidody to TrkA receptor with high titer is not available during the study period, so that we decided to study the effect of NGF on the inhibitory interneuron containing γ-aminobutyric acid (GABA) which might decrease in neuropathic pain model.
Methods : Male Sprague-Dawley rats weighing 150〜280g at the beginning of the experiment were used. The rats were anesthetized with sodium pentobarbital (50mg/kg,i.p.), and the right sciatic nerve was ligated with 4-0 chromic gut suture under microscopic observation. At the level of the mid-thigh, four loose ligatures were done just proximal to its trifurcation with 1-2mm distance between each ligature. We divided it to three groups - ligated, li gated plus NGF and sham. In ligated plus NGF group, osmotic minipump connected to silicone tube was implanted subcutaneously in the back for the continuous infusion of NGF (human recombinant NGF, 1μg/day) for 2 weeks. Two weeks after sciatic nerve ligation, rats were deeply anesthetized and perfused with 0.9%saline and paraformaldehyde. Then, spinal cord (3rd to 5th lumbar level) was removed and frozen to make serial cutted specimen. After the pretreatment with goat antiserum, those were incubated with the antibody to GABA and the rabbit IgG labelled with fluorescence. After washing, those were putted and enclosed on slide glasses. Then, GABA positive neurons were measured by using fluorescent microscopy.
Results : In ligated group, GABA positive neurons decreased at ligated side (13.9±9.7) as compared to sham group (27.1±7.7). In ligated and NGF group, those number were restored (26.3±9.7). Among three groups, there were no differences at the not-ligated side.
Conclusion : NGF could protect the inhibitory interneuron containing GABA which is susceptible transsynaptic degeneration due to nerve injury. Hence, strategy to increase NGF at the injured site might be useful to lower the occurrence of neuropathic pain.