Central muscarinic mechanisms regulating voiding in rats

Area of Science:

• Neuroscience
• Urology
• Pharmacology

Background:

• The central nervous system (CNS) plays a crucial role in regulating micturition.
• Cholinergic pathways, particularly involving muscarinic receptors, are implicated in bladder control.

Purpose of the Study:

• To investigate the influence of muscarinic receptor stimulation and blockade on the central regulation of micturition in conscious female rats.
• To differentiate the roles of central versus peripheral muscarinic mechanisms in voiding control.

Main Methods:

• Conscious female rats underwent bladder infusions to induce contractions and voiding.
• Administration of increasing doses of muscarinic agonist oxotremorine-M (OXO-M) and antagonist atropine via intrathecal (i.t.), intracerebroventricular (i.c.v.), and intravenous (i.v.) routes.
• Evaluation of voiding parameters including bladder capacity (BC), maximal voiding pressure (MVP), pressure threshold (PT), and voiding efficiency (VE).

Main Results:

• Intrathecal and intracerebroventricular OXO-M increased bladder capacity and, at higher doses, maximal voiding pressure and pressure threshold, while reducing voiding efficiency.
• Intravenous OXO-M did not reproduce these effects, indicating central mechanisms.
• Atropine (1 microg) blocked OXO-M effects, while higher doses (10 microg) reduced maximal voiding pressure and voiding efficiency, and increased bladder capacity, suggesting tonically active excitatory muscarinic mechanisms.

Conclusions:

• Activation of central muscarinic receptors (brain and spinal cord) can suppress voluntary voiding and stimulate bladder activity during filling.
• Muscarinic inhibitory mechanisms regulating micturition are not tonically active.
• Muscarinic excitatory mechanisms in the CNS are tonically active, suggesting a complex interplay in voiding regulation.