© 2009 THE AUTHORS JOURNAL COMPILATION © 2 0 0 9 B J U I N T E R N A T I O N A L | 1 0 4 , 1 5 3 1 – 1 5 3 7 | doi:10.1111/j.1464-410X.2009.08617.x 1531 2009 THE AUTHORS. JOURNAL COMPILATION 2009 BJU INTERNATIONAL Investigative Urology LUMBOSACRAL SPINAL CORD MUSCARINIC RECEPTOR ACTIVATION AMELIORATES BLADDER IRRITATION MASUDA et al. Muscarinic receptor activation in the lumbosacral spinal cord ameliorates bladder irritation in rat cystitis models Hitoshi Masuda* ‡ , Nobutaka Ichiyanagi* ‡ , Minato Yokoyama*, Yasuyuki Sakai*, Kazunori Kihara*, Michel B. Chancellor † , William C. de Groat ‡ and Naoki Yoshimura †‡ *Department of Urology, Tokyo Medical and Dental University, Tokyo, Japan, and Departments of † Urology and ‡ Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA Accepted for publication 19 February 2009 pretreatment with intraperitoneal injection of CYP (150 mg/kg) 24 h before cystometry. In control rats during intravesical saline, the effects of above drugs on the bladder activity were also examined. RESULTS The intercontraction intervals (ICI) in AA- and CYP-treated rats were significantly shorter than those in control rats. Neostigmine (i.t.) significantly increased ICI dose-dependently without changing maximum voiding pressure in all groups. The mean (SEM) maximal percentage increases in ICI after i.t. neostigmine as compared with the pretreatment value in control, AA- and CYP-treated rats were 93.2 (18.5)%, 117.5 (20.2)% and 200.7 (19.6)%, respectively. The percentage increases of ICI in the CYP-treated group were significantly (P < 0.05) higher than those in the AA- treated or control groups. In all groups, pretreatment with atropine, but not MEC, almost completely antagonized the inhibitory effects of neostigmine. OXO-M produced almost the same effects as that of neostigmine in all groups. Conversely, i.t. epibatidine decreased the ICI in all groups and these excitatory effects were completely antagonized by pretreatment with MEC and significantly inhibited by pretreatment with MK-801(noncompetitive N-methyl-D- aspartate receptor antagonist). CONCLUSIONS These results indicate that accumulation of ACh by AChE inhibition in the spinal cord can ameliorate frequent urination in chemical cystitis via mAChRs, but not nAChRs. KEYWORDS cyclophosphamide, neostigmine, muscarinic receptors, spinal cord, C-fibre OBJECTIVE To investigate whether activation of spinal cholinergic pathways affects bladder activity in rats with chemical cystitis induced by acetic acid (AA) and cyclophosphamide (CYP). MATERIALS AND METHODS The effects of intrathecal (i.t.) application of neostigmine as an acetylcholine esterase (AChE) inhibitor, oxotremorine-M (OXO-M) as a muscarinic ACh receptor (mAChR) agonist or epibatidine as a nicotinic AChR (nACHR) agonist with or without atropine as a mAChR antagonist or mecamylamine (MEC) as a nAChR antagonist at the level of L6-S1 spinal cord on C-fibre mediated bladder irritation were examined by using continuous-infusion cystometry (0.1 mL/ min) in urethane-anaesthetized female Spraque-Dawley rats. Bladder irritation was induced by intravesical AA (0.25%) or INTRODUCTION Interstitial cystitis/painful bladder syndrome (PBlS) is a chronic bladder condition characterized by ‘the complaint of suprapubic pain related to bladder filling, accompanied by increased daytime and night-time frequency’ [1]. Accumulating evidence shows that enhanced afferent nerve activity from the lower urinary tract is closely associated with the pathogenesis of PBlS [2]. Therefore, an investigation of the regulatory mechanisms for afferent nerve activity may help to elucidate the pathogenesis of PBlS and establish a treatment strategy. Afferent nociceptive information that originates from the lower urinary tract is conveyed to second-order neurones in the dorsal horn of the spinal cord via axons of primary afferent neurones that are located in the lumbosacral dorsal root ganglion [3]. Afferent pathways innervating the urinary bladder consist of myelinated Aδ-fibres and unmyelinated C-fibres [4]. Both bladder afferents are mechanoceptive, whereas C- fibre afferents are responsible for bladder nociceptive responses [5]. Painful sensation induced by capsaicin, a pungent substance in hot peppers, is mediated by activation of the vanilloid receptor (transient receptor potential vanilloid subfamily 1, TRPV1), an ion channel protein, expressed in nociceptive primary afferent neurones [6]. The TRPV1 receptor has been reported to exist in urothelium, nerve fibres coursing in the suburothelial connective tissue and in the muscular layer in the urinary bladder [7]. Systemic injection with cyclophosphamide (CYP) induces a reproducible dose-dependent chemical cystitis in both mice and rats, and BJUI BJU INTERNATIONAL