Activation of Muscarinic Receptors in Rat Bladder Sensory Pathways Alters Reflex Bladder Activity

Abstract

Antimuscarinic drugs affect bladder sensory symptoms such as urgency and frequency, presumably by acting on muscarinic acetylcholine receptors (mAChRs) located in bladder sensory pathways including primary afferent nerves and urothelium. However, the expression and the function of these receptors are not well understood. This study investigated the role of mAChRs in bladder sensory pathways in vivo in urethane anesthetized rats. Intravesical administration of the mAChR agonist oxotremorine methiodide (OxoM) elicited concentration-dependent excitatory and inhibitory effects on the frequency of voiding. These effects were blocked by intravesical administration of the mAChR antagonist atropine methyl nitrate (5 M) and were absent in rats pretreated with capsaicin to desensitize C-fiber afferent nerves. Low concentrations of OxoM (5 M) decreased voiding frequency by ϳ30%, an effect blunted by inhibiting nitric oxide (NO) synthesis with L-NAME (N -nitro-L-arginine methyl ester hydrochloride; 5 mg/kg; i.v.). High concentrations of OxoM (40 M) increased voiding frequency by ϳ45%, an effect blunted by blocking purinergic receptors with PPADS (0.1-1 mM; intravesically). mAChR agonists stimulated release of ATP from cultured urothelial cells. Intravenous administration of OxoM (0.01-5 g/kg) did not mimic the intravesical effects on voiding frequency. These results suggest that activation of mAChRs located near the luminal surface of the bladder affects voiding functions via mechanisms involving ATP and NO release presumably from the urothelium, that in turn could act on bladder C-fiber afferent nerves to alter their firing properties. These findings suggest that the urothelial-afferent nerve interactions can influence reflex voiding function.

Comparison of the effect of anti-muscarinic agents on bladder activity, urinary ATP level, and autonomic nervous system in rats

“…Recently, it has been reported that the bladder urothelium secretes non-neurogenic acetylcholine, and that muscarinic receptors are expressed on bladder epithelial cells and on afferent nerve terminals in the bladder (3). The bladder urothelium also produces adenosine triphosphate (ATP) and the afferent nerve terminals in the bladder have purinergic receptors (14). In an animal experiment, ATP secreted by bladder epithelial cells influenced bladder activity, while a muscarinic receptor agonist evoked the release of ATP from cultured bladder epithelial cells (5).…”

199 Role of M2 and M3 Muscarinic Acetylcholine Receptor Subtypes in Activation of Bladder Afferent Pathways in Spinal Cord Injured Rats

“…23 It has been suggested that P2X receptors found on bladder sensory nerve terminals 24 may be activated by enhanced ATP release from the urothelium in pathologies such as SCI. 25 Kullmann et al 4 also reported that intravesical administration of Oxo-M induced bladder overactivity through the release of ATP from the urothelium in normal rats. Another possible mechanism is that Oxo-M directly activated mAChRs expressed on bladder afferent fibers since mAChRs are reportedly expressed on L6/S1 DRG cell bodies of bladder afferent neurons, suggesting that bladder afferent pathways might be under direct cholinergic control.…”

Neural Control of the Lower Urinary Tract

“…Figure 4 depicts possible interactions of urothelial cells with other bladder structures such as bladder nerves, interstitial cells, smooth muscle and blood vessels through autocrine (i.e., autoregulation) or paracrine mechanisms (release from nearby nerves or other cells). Examples of "sensor molecules" (i.e., receptors/ion channels) associated with neurons that have been identified in urothelium include receptors for bradykinin (110) neurotrophins (TrkA and p75) (453), purines (P2X and P2Y) (61, 86,111,379,628), norepinephrine (α and β) (53, 59, 357,383), acetylcholine (muscarinic and nicotinic) (43,46,108,355,356) protease activated receptors (PARs) (130,140), amiloride/mechanosensitive Na + channels (29,576,668), prostaglandin E 2 (PGE 2 ) receptors (EP1) (671), and a number of TRP channels (TRPV1, TRPV2, TRPV4, TRPM8, and TRPA1) (51,57,58,200,230,358,440,590,680) (Fig. 4).…”

“…Muscarinic receptors are expressed in the urothelium at high density (259) and there is a basal release of acetylcholine from the urothelium, which is increased by stretch and aging (694). Activation of the muscarinic receptors in the urothelium releases substances (e.g., ATP) that modulate afferent nerves and smooth muscle activity (50,148,259,355,356).…”