Transecting the hypogastric nerve to uncover the bladder-inhibitory pathways involved with saphenous nerve stimulation in anesthetized rats

Prolonged inhibition of bladder function is evoked by low-amplitude electrical stimulation of the saphenous nerve in urethane-anesthetized rats

To better understand the effects of saphenous nerve (SN) stimulation on bladder function, we investigated the duration of electrical stimulation as a key variable in eliciting urodynamic changes. SN stimulation is a novel approach to electrically modulating bladder function. In previous animal studies, bladder-inhibitory responses were evoked by low-amplitude (25 μA) stimulus pulses applied in short-duration (10 min) trials and at frequencies between 10 and 20 Hz. Experiments were performed in urethane-anesthetized rats that were separated into three groups: intravesical saline infusion + SN stimulation (group A), intravesical 0.1% acetic acid infusion + SN stimulation (group B), and intravesical saline infusion + no SN stimulation (group C). Changes in bladder function- basal bladder pressure (P base ), contraction amplitude (ΔP), and inter-contraction interval (T ICI )-were measured in response to stimulation trials applied for different durations (10, 20, and 40 min). Trials were also repeated at frequencies of 10 and 20 Hz. In group A, longer-duration (40 min) stimulation trials applied at 10 Hz evoked overflow incontinence (OI) episodes that were characterized by significant changes in P base (122.7 ± 9.1%, p = 0.026), ΔP (-60.8 ± 12.8%, p = 0.044), and T ICI (-43.2 ± 13.0%, p = 0.031). Stimulation-evoked OI was observed in 5 of 8 animals and lasted for 56.5 ± 10.7 min. In contrast, no significant changes in bladder function were observed in either group B or group C. Our findings show that longer-duration trials consisting of electrical pulses applied at 10 Hz are important stimulation parameters that elicit inhibitory bladder responses in anesthetized rodents.

Chronic bladder catheterization for precise urine collection in awake mice

Metabolic chambers are routinely used for urine collection in rodents. In mice, due to small urination volume, evaporation in the metabolic chambers (≈50%) distorts diuresis and urinalysis parameters. We have developed a new technique of bladder catheterization enabling long-term accurate and contamination-free urine collection in awake male and female mice for 30 days or longer. Daily diuresis in catheterized mice was twice higher as compared to metabolic cages. The twofold difference in urine recovery was preserved when the circadian variation of diuresis, the effects of furosemide, desmopressin and water load were estimated using the two techniques. Urine osmolarity, urinalysis, and microbiological parameters evidence higher quality of the catheter-collected urine. Using phenol red, we demonstrate utility of our technique for pharmacokinetic studies. 30 days after the surgery the catheters were patent and had minimal impact on the animals' heath. Bladder catheterization is a useful tool for physiological, pharmacological, and toxicological studies.

Mechanism of Action of Peripheral Nerve Stimulation

PURPOSE OF REVIEW

The number of applications for peripheral nerve stimulation (PNS) in the pain management field is ever-growing. With the increasing number of clinical applications for peripheral nerve stimulation, the purpose of this article is to review the mechanism of action surrounding PNS, the recent literature from January 2018 to January 2021, and pertinent clinical outcomes.

RECENT FINDINGS

The authors searched articles identified from PubMed (January 2018-January 2021), Cochrane Central Register of Controlled Trials databases (January 2018-January 2021), and Scopus (January 2018-January 2021) databases, and manually searched references of identified publications. Broad MeSH terms and Boolean operators were queried in each search, including the following terms and their respective synonyms: peripheral nerve stimulation, mechanism of action, biochemical pathway, and pain pathway. 15 consensus articles were selected for in-depth review and inclusion for qualitative analysis. PNS may activate and modulate higher central nervous system (CNS) centers, including the dorsal lateral prefrontal cortex, somatosensory cortex, anterior cingulate cortex, and parahippocampal areas. Neuromodulatory effects from PNS may also extend into the spinal columns. Also, PNS may lead to changes in endogenous neurotransmitters and affect the plasticity of NMDA pathways.