Stressful events occurring early in life, including sexual abuse, may have a role in the development of BPS/IC in adult life. Here, we use the maternal deprivation model (MDM), which causes a stressful event very early in a mice life, to investigate the changes in the bladder pain pathways that may account for the late onset of bladder pain.
MDM was induced on female C57BL/6 WT mice by separating pups from mother and littermates for 1h from P2-P15. Experiments were performed at P156. Non separated pups were used as controls. Mechanical pain threshold was measured by Von Frey filaments. Then mice were anaesthetised and cystometry performed. Finally, bladders were harvested and used to measure norepinephrine (NE) levels or were fixed and stained with HE or Toluidine blue to check urothelium morphology or mast cell infiltration, respectively. MDM was repeated on MDM mice treated orally with the alpha1A-AR blocker silodosin from P157 to P172 and on TRPV1 knockout (KO) mice to investigate the role of alpha 1A-AR and TRPV1, respectively, on bladder pain. Additional WT animals were stimulated with subcutaneous phenylephrine (PHE 2.5 mg/kg) or saline and bladder voiding contractions (VC) determined in each group during capsaicin instillation.
NE levels were lower in WT than in MDM WT mice (0.09±0.01 pg/mg vs 0.17±0.07 pg/mg of bladder (P=0.02). MDM WT mice had lower abdomen mechanical pain threshold than WT controls (0.02±0.01g vs 0.08±0.03g, p=0.0003). MDM WT mice treated with silodosin had a pain threshold similar to controls (0.14±0.14g; P=0.3). TRPV1 KO and MDM TRPV1 KO mice had a similar abdominal pain threshold (0.13±0.18g and 0.28±0.14g, respectively; P=0.2). MDM WT mice had more reflex VC than controls (1.05±0.35 VC/min vs 0.48±0.15 VC/min, p=0.04). Silodosin treatment normalised the frequency of VC in MDM WT (0.33±0.15 VC/min; p=0.3). TRPV1-KO and MDM TRPV1-KO had similar VC (0.50±0.12 VC/min and 0.50±0.08 VC/min, P=1). Controls, TRPV1-KO, MDM TRPV1-KO and MDM+Silodosin had normal urothelium. MDM mice had evident areas of urothelial loss. Mastocytosis was not observed in MDM WT mice. PHE-stimulated animals showed a 3 times increase in bladder VC to capsaicin instillation, compared to controls (P=0.01).
MDM induces adrenergic overstimulation of the bladder leading to the activation of alpha 1A adrenoceptor, known to exist in nociceptors. As a consequence that induces an enhanced response of TRPV1 receptors leading to lower abdomen hyperalgesia and increase frequency of voiding contractions. MDM is adequate to study the mechanism that may lead early in life stressful events to cause bladder pain in adulthood. In addition our results suggest an involvement of alpha1A-AR and TRPV1 in this process.