Effects of chronic treatment with botulinum toxin type A in salivary glands of rats: Histological and immunohistochemical analyses

Background: The intraglandular application of botulinum neurotoxin type A (BoNT-A) is used in patients with neuromotor disorders to control the escape of saliva. The aim of this study was to analyze the impact of repeated treatment with BoNT-A on the submandibular-sublingual complex of rats. Methods: A total of 35 Wistar rats were divided into three groups: control group (C), in which animals were not treated; group B, treated with 2.5 U intraglandular injections of BoNT-A (Prosigne (R)) and group G, that received bovine gelatine (Prosigne stabilizer). Three applications were performed in intervals of 35 days. Twelve and 35 days after ending the treatment, submandibular-sublingual complex was collected for histological analysis. Immunohistochemical reactions for calponin and specific muscle actin were also performed, besides detection of apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. Results: A decrease in mucosal and serous acini diameter was observed, with increased interstitial space after 12 days of treatment with BoNT-A, which was observed in a lesser degree on the 35th day. At 12 days, immunohistochemical analysis revealed a decrease in myoepithelial cells of serous acini in group B. TUNEL methods evidenced apoptosis in animals from group B. Conclusions: BoNT-A caused histological and cellular changes in submandibular-sublingual complex, followed by a tendency toward reversal after 35 days. The reversal characteristic of cellular changes in the submandibular-sublingual complex suggests that this BoNT-A formulation may be safely used for sialorrhea treatment.