Effect of capsaicin on calcitonin gene-related peptide and nitric oxide synthase-positive nerve fiber in rat facial skin

Jigu DING; Liqiang RU

ABSTRACT

BACKGROUND:

The effect of external application of capsaicin in the treatment of superficial pain has been recognized, but its effect against trigeminal neuralgia by direct action on the nerve ending or nerves in the hypodermis or deep tissues awaits intensive investigation.

OBJECTIVE:

To observes the effect of subcutaneous injection of capsaicin on calcitonin gene-related peptide (CGRP) and nitric oxide synthase(NOS)-positive nerve fibers in rat facial skin.

SETTING:

Teaching and Research Division of Anatomy, Xianning Medical College, and Department of Neurobiology, Tongji Medical College of Huazhong University of Science and Technology.MATERIALS This experiment was conducted in the Laboratory of Neurobiology, Tongji Medical College, between October and December 2003.Twenty healthy Wistar rats of either sex with body mass of 120-170 g were used.

METHODS:

The rats received subcutaneous injection of capsaicin for treatment of the suborbital branch of the trigeminal nerve on the right side,with the left side serving as the control side. According to the doses of capsaicin applied, the rats were divided into 4 groups, namely 20, 30, 50and 100 μL capsaicin groups with 5 rats in each group. Twenty-four hours after the injections, samples were obtained and cut into slices for microscopic observation and the expressions of CGRP and NOS were examined immunohistochemically.MAIN OUTCOME

MEASURES:

[1] Changes of CGRP and NOS-positive nerve fibers on the experimental side and image analysis of the mean absorbance of CGRP and NOS; [2] changes of characteristic behaviors and body signs of the rats.

RESULTS:

Totally 20 rats entered the result analysis. [1] Behavioral change A few minutes after subcutaneous injection of capsaicin, the rats exhibited a series of characteristic behavioral and symptomatic changes,which gradually diminished or even vanished with the increase of the doses. [2] Microscopic changes On the experimental side, no obvious difference was noted in the expression of CGRP and NOS-positive nerve fibers between the groups. [3] Imaging analysis of the mean absorbance of CGRP and NOS For CGRP, the mean absorbance was 0.984±0.056 on the control side and 0.947±0.025, 0.852±0.042, 0.756±0.028 and 0.730±0.016 in 20,30, 50 μL and 100 μL capsaicin groups, respectively. As for NOS, the mean absorbance was 0.151±0.009 on the control side, and was 0.148±0.007,0.132±0.012, 0.111±0.067 and 0.107±0.006 in 20, 30, 50 μL and 100 μL capsaicin groups. Analysis of variance revealed significant differences between the groups (P ＜ 0.01).

CONCLUSION:

CGRP and NOS participate in the processing of nociceptive information and modulate pain and analgesia. Capsaicin executes analgesic effect by exhausting massive neurotransmitters.