Evaluation of the brain functional activities in rats various location-endometriosis pain model

Abstract

Background: Endometriosis (EM) is a common gynecological disease in women of reproductive age. These patients in approximately 80% suffer the various degree pain. This study will investigate synergistically the mechanism of the higher-position central sensitization and offer a pre-clinical experiment evidence for treatment of various location-EM patients with pain.

Methods: Twenty Sprague-Dawley rats were induced three types EM including abdominal EM (n=5), gastrocnemius EM (n=5) and ovary EM group (n=5) and one sham control group (n=5). All groups were measured the pain sensitization by hotplate test, then scanned by the functional magnetic resonance imaging (fMRI). The resting-state fMRI (rs-fMRI) date was analyzed using regional homogeneity (ReHo) approach to find out the abnormal functional activity brain regions. Nissl staining method observed the state of neurons in aberrant ReHo signal brain regions.

Results: Rats with EM pain sensitization were increased in abdominal EM and gastrocnemius EM than ovary EM group and sham control. The ReHo value is decreased in gastrocnemius EM in right thalamus and left olfactory tubercle compared with other three groups. The number of neurons was decreased; cavitation around nucleus, and pyknotic homogenous nuclei. Nissl bodies were stained deeply, and the shape was irregular in gastrocnemius EM by Nissl staining in right thalamus. In left olfactory tubercle, there was no significant difference in 4 groups.

Conclusions: The thalamus may be the potential key brain region for the central sensitization mechanism of various location-EM pain. The oxidative activation may be weakened in thalamus in gastrocnemius EM group with more severe pain. This finding could lend support for future research on the imageology and pathology of various location-EM pain.

Keywords: Various location-endometriosis; brain functional activities; central sensitization; models; pain; regional homogeneity (ReHo); resting-state functional magnetic resonance imaging (rs-fMRI).

Figure 1

The endometriosis (EM)-like lesions in EM groups were checked at 2 weeks after the operation. (A) A vesicular cyst (arrow) at the inner side of abdominal wall; (B) a vesicular cyst (arrow) at the mesenterium; (C) a vesicular cyst (arrow) at gastrocnemius muscle; (D) a vesicular cyst at ovary.

Figure 2

Rats with endometriosis (EM) pain sensitization were tested by the hotplate test at pre-surgery and at 4, 8, 12 weeks after surgery.

Figure 3

The brain regions in right thalamus and left olfactory tubercle emerged higher functional activity signals than the whole-brain average by ReHo analysis after resting-state fMRI scanning among the four groups. ReHo, regional homogeneity; fMRI, functional magnetic resonance imaging.

Figure 4

The comparison of ReHo average values in various groups. (A) In the right thalamus, there were significant differences between the abdominal EM and gastrocnemius EM group, the ReHo average values in abdominal EM group increased than gastrocnemius EM (**, P<0.001); (B) ReHo value in ovary EM also was higher than gastrocnemius EM in the right thalamus, (**, P<0.001); (C) in the right thalamus, the ReHo value was increased than gastrocnemius EM compared with sham control (**, P<0.001); (D) in left olfactory tubercle, the ReHo value in gastrocnemius EM decreased than ovary EM(**, P<0.001). ReHo, regional homogeneity; EM, endometriosis.

Figure 5

In the right thalamus, a large number of neurons and bigger cell volume, the Nissl body was stained and the number and shape showed normal in abdominal EM, ovary EM and sham control groups (see Figure 5A,B,C). However, in the gastrocnemius EM group, the number of neurons was decreased; cavitation around nucleus, and pyknotic homogenous nuclei. Nissl body was stained deeply, and the shape was irregular (Figure 5D). In left olfactory tubercle, there was no significant difference in the number, volume and morphology of neurons and significant in the four groups although variety in ReHo values between them. Magnification, 400×.

Figure 6

In left olfactory tubercle, there was no significant difference in the number, volume and morphology of neurons and significant in the four groups although variety in ReHo values between them. Magnification, 400×.

Figure 7

The endometriosis-like lesions in various locations. (A) An ectopic endometrial cyst at the inner side of abdominal wall (HE, 20×); (B) an ectopic endometrial cyst at the mesenterium (HE, 10×); (C) an ectopic endometrial cyst at gastrocnemius muscle (HE, 20×); (D) an ectopic endometrial cyst at ovary (HE, 20×).