An exploration of the control of micturition using a novel in situ arterially perfused rat preparation.

Prajni Sadananda,Anthony E Pickering,Julian F R Paton,Marcus J Drake

doi:10.3389/fnins.2011.00062

Abstract

Our goal was to develop and refine a decerebrate arterially perfused rat (DAPR) preparation that allows the complete bladder filling and voiding cycle to be investigated without some of the restrictions inherent with in vivo experimentation [e.g., ease and speed of set up (30 min), control over the extracellular milieu and free of anesthetic agents]. Both spontaneous (naturalistic bladder filling from ureters) and evoked (in response to intravesical infusion) voids were routinely and reproducibly observed which had similar pressure characteristics. The DAPR allows the simultaneous measurement of bladder intra-luminal pressure, external urinary sphincter–electromyogram (EUS–EMG), pelvic afferent nerve activity, pudendal motor activity, and permits excellent visualization of the entire lower urinary tract, during typical rat filling and voiding responses. The voiding responses were modulated or eliminated by interventions at a number of levels including at the afferent terminal fields (intravesical capsaicin sensitization–desensitization), autonomic (ganglion blockade with hexamethonium), and somatic motor (vecuronium block of the EUS) outflow and required intact brainstem/hindbrain-spinal coordination (as demonstrated by sequential hindbrain transections). Both innocuous (e.g., perineal stimulation) and nociceptive (tail/paw pinch) somatic stimuli elicited an increase in EUS–EMG indicating intact sensory feedback loops. Spontaneous non-micturition contractions were observed between fluid infusions at a frequency and amplitude of 1.4 ± 0.9 per minute and 1.4 ± 0.3 mmHg, respectively and their amplitude increased when autonomic control was compromised. In conclusion, the DAPR is a tractable and useful model for the study of neural bladder control showing intact afferent signaling, spinal and hindbrain co-ordination and efferent control over the lower urinary tract end organs and can be extended to study bladder pathologies and trial novel treatments.

Highlights

The urinary cycle consists of two-phases of bladder activity: filling and voiding, which are under both voluntary and autonomic neural control
We demonstrate that the preparation has intact bladder afferent–brainstem–bladder motor circuitry, which allows strong and consistent filling and voiding responses lasting for up to 4 h
As fluid entered the bladder, the wave appeared to be propagated into the bladder itself, which displayed a spontaneous non-micturition contraction (NMC)

Summary

Introduction

The urinary cycle consists of two-phases of bladder activity: filling and voiding, which are under both voluntary and autonomic neural control. The majority of the commonly utilized animal models for autonomic bladder studies involve urethane anaesthetized animals, as other known anaesthetics suppress the micturition reflex (Maggi et al, 1986). Acute studies of bladder function are technically challenging and often focus on the filling/storage mechanisms, since the voiding response is functionally inconsistent. In this respect, the alternative strategy of using conscious, telemetered animals has some advantages but the ability to study central neuronal control mechanisms is limited and recordings of peripheral afferents, possible are non-trivial (Zvara et al, 2010)

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