Introduction: The baboon model of endometriosis is thought to mimic spontaneous human peritoneal disease relatively closely. Conventional histology of the lesions is similar. Angiogenesis and influx of immune cells occur in the developing lesions and their presence alters the gene expression profile in the eutopic endometrium1. Nerve fibres have been demonstrated in both ectopic and eutopic tissues of women with endometriosis2-3.
Aim: The aim of this study was to evaluate the density of nerve fibre formation during 3 and 15 month peritoneal lesion development compared with normal peritoneum in the baboon endometriosis model.
Methods: Peritoneal endometrioic tissue (n=12) female baboons (Papio anubis), collected 3 (early disease) and 15 (late disease) months after the initiation of experimental protocols4. Primary antibodies utilised were Protein Gene Product 9.5 (PGP9.5) (pan-neuronal), Neuropeptide Y (NPY) (sympathetic), Vasoactive Intestinal Polypeptide (VIP) (parasympathetic), Substance P (SP) (sensory), Nerve Growth Factor (NGF) and high-affinity receptor for NGF (TrK-A) following incubation the REALTM Detection system Alkaline Phosphatase/RED Rabbit/Mouse followed with liquid Fast Red Substrate Chromogen System.
Results: Positive staining of nerve fibres for PGP9.5, NPY, SP and VIP, significant increase in lesions of 15 months was observed compared to 3 months and control. The expression of NGF and Trk-A in both 3 and 15 month peritoneal endometriotic lesions was observed as (++) and in the control samples the expression was observed as (+).
Discussion: We confirmed that nerve fibres grow into these lesions within 3 months of lesion initiation (early stage of disease) but become much more dense in the more established stage of the disease 15 months. It is probable that the higher density of nerve fibres 15 months after the initiation of the experimental protocol may play an important role in the establishment of severity of the pathogenesis of pain and local tenderness.