Hysteretic behavior of bladder afferent neurons in response to changes in bladder pressure.

Shani E Ross,Colin M Mahar,Tim M Bruns,Zachariah J Sperry

doi:10.1186/s12868-016-0292-5

Abstract

BackgroundMechanosensitive afferents innervating the bladder increase their firing rate as the bladder fills and pressure rises. However, the relationship between afferent firing rates and intravesical pressure is not a simple linear one. Firing rate responses to pressure can differ depending on prior activity, demonstrating hysteresis in the system. Though this hysteresis has been commented on in published literature, it has not been quantified.ResultsSixty-six bladder afferents recorded from sacral dorsal root ganglia in five alpha-chloralose anesthetized felines were identified based on their characteristic responses to pressure (correlation coefficient ≥ 0.2) during saline infusion (2 ml/min). For saline infusion trials, we calculated a maximum hysteresis ratio between the firing rate difference at each pressure and the overall firing rate range (or Hmax) of 0.86 ± 0.09 (mean ± standard deviation) and mean hysteresis ratio (or Hmean) of 0.52 ± 0.13 (n = 46 afferents). For isovolumetric trials in two experiments (n = 33 afferents) Hmax was 0.72 ± 0.14 and Hmean was 0.40 ± 0.14.ConclusionsA comprehensive state model that integrates these hysteresis parameters to determine the bladder state may improve upon existing neuroprostheses for bladder control.

Highlights

Mechanosensitive afferents innervating the bladder increase their firing rate as the bladder fills and pressure rises
Bladder units Seventy units from five experiments were identified as bladder units (ρ ≥ 0.2), with 57 units in sacral level 1 (S1) dorsal root ganglia (DRG) and 13 units in sacral level 2 (S2) DRG
There were 33 units with average ρ = 0.62 ± 0.19

Summary

Introduction

Mechanosensitive afferents innervating the bladder increase their firing rate as the bladder fills and pressure rises. The lower urinary tract (LUT) has two main functions: storage (continence) and voiding (micturition) of urine Normal operation of these two functions involves coordinated autonomic and voluntary neural control utilizing local, spinal, and supraspinal pathways [1] and can be affected in many conditions including spinal cord injury, Parkinson’s disease, and multiple sclerosis. Ross et al BMC Neurosci (2016) 17:57 threshold is reached and gradually increase their firing as the bladder fills and pressure rises [6, 10, 12, 16, 17] Pressure thresholds for these neurons are typically between 5 and 20 cmH20 [3, 10, 17, 18], with neurons of different pressure thresholds being successively recruited as the bladder fills [16]. Firing rate responses to pressure can differ depending on prior activity, demonstrating hysteresis in the system [8, 16]

Objectives

Results

Discussion

Conclusion