Electrical stimulation structurally affects the tissues of the rectum and anus of nulliparous rats

Abstract

Considering that the muscles of the anus perform a critical role in maintaining continence, losses in their structure can negatively affect the physiological control of the intestinal contents. Anorectal electro-stimulation (ARES) has been reported to have a positive effect on the functionality of treated patients, but how ARES affects the structural tissues of the anorectal segment remains unknown. Because the study of how ARES structurally affects human tissues is not possible, this study aimed to clarify these effects in a murine model, which has a similar anorectal segment (structure and physiology) to humans. For the descriptive and comparative study, randomly selected nulliparous adult Wistar rats (n = 5) were submitted to 30 anorectal sessions of ARES with a biphasic current (700 μs, 50 Hz from 2 to 4 mA). After treatment, the animals were euthanized, and the anorectal segments were dissected and processed for histopathological analysis. Our results showed that ARES increased the widths of the mucosal, submucosal and muscle layers of the rectum, as well as the number of leukocytes in the mucosa. ARES also caused hyperplasia of the smooth muscle of the internal anal sphincter and hypertrophy of the external anal sphincter muscle. In conclusion, our results showed that ARES had not only a positive effect on the structure (morphology) of all tissues associated with the rectum and anus but, more importantly, on the structural gain of the muscles (hyperplasia and hypertrophy), which could point to a functional gain of the anal sphincter, reinforcing the applicability of ARES as a non-invasive treatment for anal incontinence.

Keywords: anal sphincter; electrical stimulation; fecal incontinence; histology; rectum.

Figure 1

Photomicrographs of histological sections of the pelvic organs obtained from two nulliparous rats, a control (A) and one electrically stimulated (B), showing the colored rectum (R), vagina (V) and the urethra (U). Note greater width of layers in the rectum, mucosa (asterisk), submucosa (arrow) or muscle (star) in (B) compared with (A). Gomori trichrome staining. Scale bar: 1 mm.

Figure 2

Photomicrographs of histological sections of the rectum (A, B) and anus (C, D) from two nulliparous rats, representative of the control (A, C) or electro‐stimulated (B, D) group, showing a greater number of inflammatory cells in the mucosa (epithelium/asterisk; connective tissue/arrow) from the electro‐stimulated animal. Hematoxylin & Eosin staining. Scale bar: 50 μm.

Figure 3

Photomicrographs of the skeletal muscle fibers of the external anal sphincter muscle (EAS) which are representative of nulliparous rats of the control (a) and electro‐stimulated group (b). Observe the greater number of muscle fibers and their larger diameter in (B; area = 1.6 mm²) in comparison with (A). Hematoxylin & Eosin staining.