Experimental animals
In all, 70 healthy adult male SD rats weighing 250–300 g were provided by Qinglongshan Animal Breeding Farm in Jiangning District, Nanjing City (certificate number: SCXK (Su) 2018-0001).The experimental operation process complies with the experimental animal ethics requirements of Shanghai University of Traditional Chinese Medicine (ethics approval number: SZY201807016).
Model building and grouping
Thirty male SD rats weighing 280–300 g were sacrificed by grabbing the head of the rats with one hand and the tail of the rats with the other, and pulling with both hands at the same time until their cervical spines were broken, and the lower abdomen skin was disinfected. The prostate tissue was stripped and fully washed with cold physiological saline and a physiological saline solution (containing 0.5% TritonX-100,American Sigma). The prostate tissue was then homogenized (with the lower part of the glass homogenizer in ice) and centrifuged at 3000 ×g for 30 min at 4°C; The centrifuged supernatant was extracted, and the biuret method was used to determine the protein concentration (Biuret kit,Nanjing Jiancheng Technology Co., Ltd.). The prostate protein solution was diluted to 40 g/L with 0.1 mol/L PBS (pH 7.4) for subsequent use.
Forty male SD rats weighing 250–280 g were randomly divided into four groups: one control group and three model groups (45 days [d], 60 d, and 90 d), with 10 rats in each group. On days 0 and 30, animals in each group were anesthetized with ether. The model groups were injected intraperitoneally with 0.5 mL of diazepam vaccine (Wuhan Institute of Biological Products), while intradermal injections of 1 ml Freund's Complete Adjuvant (American Sigma) at a ratio of 1:1 and a suspension of prostate protein extract. The control group was injected with the same volume of saline.
Detection of paw withdrawal threshold (PWT)
The PWT was measured by Chaplan et al’s method[8].All rats were placed in a translucent glass cage, and Von Frey filaments were used to stimulate the midfoot of the rats’ hind limbs. The slight bending of the cilia was used as the complete force standard to bend the fibers into an S shape for 6–8 s, use fiber filaments to stimulate 2, s, 6, 8, 8, 10, 15, 26 g for 2 s in sequence, at intervals of 15 s, for 5 consecutive times. The minimum number of grams that caused 3/5 leg lifts was defined as PWT. The PWT was measured at 45, 60, and 90 days after the start of modeling.
Light microscopy, transmission electron microscopy, and SP and NK-1R immunohistochemistry
On days 45, 60, and 90 after modeling,the rats died of torn cervical spine, and the prostate tissue of each rat from all the groups was collected. Part of the prostate tissue was fixed with 4% neutral formaldehyde solution at room temperature for 24 h, followed by dehydration in a graded series of ethanol, and xylene treatment. After being embedded in paraffin, the tissues were sectioned into 4-μm-thick slices, stained with hematoxylin-eosin (HE), and observed under a light microscope(Japan Olympus Optical Ltd). The remaining part of the prostate tissue was cut into small pieces measuring 1 mm×1 mm×1 mm, submerged in 4.9% glutaraldehyde and 1% acetic acid (pH 7.4) solution for double fixing, dehydrated with ethanol and acetone, embedded in Epon 812 epoxy resin, and sectioned. Ultrathin sections were stained with uranium acetate and lead citrate, and the microstructure was observed by transmission electron microscopy(Japan HITACHI company).
The spinal cord was removed and fixed in 4% paraformaldehyde phosphate buffer and kept in the refrigerator 4°C overnight. The L5-S2 spinal cord segment was isolated, and continuous cross-sections were obtained using a vibrating microtome, and floating immunohistochemistry on freely floating fixed tissue sections (American Sigma) was performed to detect the optical density (OD) values of SP and NK-1R immunopositive reactions.
Determination of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-2 (IL-2), and interleukin-10 (IL-10) in prostate tissues
Briefly, 1 mL of 0.5% TritonX-100 normal saline per 100 mg of prostate tissue was added to prepare the tissue homogenate, and centrifuged at 3000 ×g for 15 min. The concentrations of TNF-α, IL-1β, IL-2, and IL-10 in the prostate tissues was measured in an appropriate amount of supernatant by using ELISA method (American Sigma).
Statistical analysis
Descriptive and differential statistical analysis of the data were conducted. For normal distribution, the mean and standard deviation were used to describe the centralized and discrete trends, respectively. The variances were the same. A completely random design analysis of variance was used, and the SNK-q method was used to compare pairs. The test standard was α=0.05. The SAS9.1 software (North Carolina State University,United States)was used for all statistical analysis.