The different roles of opioid receptors in the inhibitory effects induced by sacral dorsal root ganglion stimulation on nociceptive and nonnociceptive conditions in cats

Pathways and parameters of sacral neuromodulation in rats

The stimulation paradigm for sacral neuromodulation has remained largely unchanged since its inception. We sought to determine, in rats, whether stimulation-induced increases in bladder capacity correlated with the proportion of sensory pudendal (PudS) neurons at each stimulated location (L6, S1). If supported, this finding could guide the choice of stimulation side (left/right) and level (S2, S3, S4) in humans. Unexpectedly, we observed that acute stimulation at clinically relevant (low) amplitudes [1-1.5 × motor threshold (Tm)], did not increase bladder capacity, regardless of stimulus location (L6 or S1). More importantly for the ability to test our hypothesis, there was little anatomic variation, and S1 infrequently contributed nerve fibers to the PudS nerve. During mapping studies we noticed that large increases in PudS nerve activation occurred at amplitudes exceeding 2Tm. Thus, additional cystometric studies were conducted, this time with stimulation of the L6-S1 trunk, to examine further the relationship between stimulation amplitude and cystometric parameters. Stimulation at 1Tm to 6Tm evoked increases in bladder capacity and decreases in voiding efficiency that mirrored those produced by PudS nerve stimulation. Many animal studies involving electrical stimulation of nerves of the lower urinary tract use stimulation amplitudes that exceed those used clinically (∼1Tm). Our results confirm that high amplitudes generate immediate changes in cystometric parameters; however, the relationship to low-amplitude chronic stimulation in humans remains unclear. Additional studies are needed to understand changes that occur with chronic stimulation, how these changes relate to therapeutic outcomes, and the contribution of specific nerve fibers to these changes.NEW & NOTEWORTHY Acute low-amplitude electrical stimulation of sacral nerve (sacral neuromodulation) did not increase bladder capacity in anesthetized CD, obese-prone, or obese-resistant rats. Increasing stimulation amplitude correlated with increases in bladder capacity and pudendal sensory nerve recruitment. It is unclear how the high-amplitude acute stimulation that is commonly used in animal experiments to generate immediate effects compares mechanistically to the chronic low-amplitude stimulation used clinically.

Efficacy of a novel wearable transcutaneous tibial nerve stimulation device on bladder reflex compared to implantable tibial nerve stimulation in cats

OBJECTIVE

To determine the efficacy of novel wearable transcutaneous tibial nerve stimulation (TTNS) device on bladder reflex in cats compared to implantable tibial nerve stimulation (ITNS).

MATERIALS AND METHODS

Two self-adhesive electrodes of the TTNS device were placed at the left leg, and ITNS was applied to stimulate the tibial nerve of the right leg, respectively. The intensity threshold (T) was defined as inducing observable toe movement. Multiple cystometrograms (CMGs) with normal saline (NS) infusion were performed to determine the inhibitory effects of TTNS and ITNS on the micturition reflex.

RESULTS

TTNS at 4 times T (4 T), 6 times T (6 T), and the maximum output current intensity 24 mA significantly increased the bladder capacity (BC) compared to the control level (8.70 ± 2.46 ml) (all p < 0.05); however, there was no statistical significance among the three intensities. At the same time, ITNS at 2 times T (2 T), 4 T, 6 T, and the current intension 24 mA could significantly increase the BC compared to the control level (all p < 0.05). Likewise, no significant difference was observed among the four intensities (p > 0.05). The T values of TTNS were higher than those of ITNS (p = 0.02). The inhibitory effects of TTNS and ITNS revealed no significant difference at their respective 2 T, 4 T, 6 T, and 24 mA. Neither TTNS nor ITNS changed the contraction duration and amplitude (all p > 0.05).

CONCLUSIONS

TTNS was effective in increasing BC. The non-invasive neuromodulation technique could achieve a similar effect as ITNS.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).