Changes in rat brainstem responsiveness to somatovisceral inputs following acute bladder irritation

Bladder-colon chronic cross-sensitization involves neuro-glial pathways in male mice

BACKGROUND

Irritable bowel syndrome and bladder pain syndrome often overlap and are both characterized by visceral hypersensitivity. Since pelvic organs share common sensory pathways, it is likely that those syndromes involve a cross-sensitization of the bladder and the colon. The precise pathophysiology remains poorly understood.

AIM

To develop a model of chronic bladder-colon cross-sensitization and to investigate the mech-anisms involved.

METHODS

Chronic cross-organ visceral sensitization was obtained in C57BL/6 mice using ultrasound-guided intravesical injections of acetic acid under brief isoflurane anesthesia. Colorectal sensitivity was assessed in conscious mice by measuring intracolonic pressure during isobaric colorectal distensions. Myeloperoxidase, used as a marker of colorectal inflammation, was measured in the colon, and colorectal permeability was measured using chambers. c-Fos protein expression, used as a marker of neuronal activation, was assessed in the spinal cord (L6-S1 level) using immunohistochemistry. Green fluorescent protein on the fractalkine receptor-positive mice were used to identify and count microglia cells in the L6-S1 dorsal horn of the spinal cord. The expression of NK1 receptors and MAPK-p38 were quantified in the spinal cord using western blot.

RESULTS

Visceral hypersensitivity to colorectal distension was observed after the intravesical injection of acetic acid vs saline (P < 0.0001). This effect started 1 h post-injection and lasted up to 7 d post-injection. No increased permeability or inflammation was shown in the bladder or colon 7 d post-injection. Visceral hypersensitivity was associated with the increased expression of c-Fos protein in the spinal cord (P < 0.0001). In green fluorescent protein on the fractalkine receptor-positive mice, intravesical acetic acid injection resulted in an increased number of microglia cells in the L6-S1 dorsal horn of the spinal cord (P < 0.0001). NK1 receptor and MAPK-p38 levels were increased in the spinal cord up to 7 d after injection (P = 0.007 and 0.023 respectively). Colorectal sensitization was prevented by intrathecal or intracerebroventricular injections of minocycline, a microglia inhibitor, by intracerebroventricular injection of CP-99994 dihydrochloride, a NK1 antagonist, and by intracerebroventricular injection of SB203580, a MAPK-p38 inhibitor.

CONCLUSION

We describe a new model of cross-organ visceral sensitization between the bladder and the colon in mice. Intravesical injections of acetic acid induced a long-lasting colorectal hypersensitivity to distension, mediated by neuroglial interactions, MAPK-p38 phosphorylation and the NK1 receptor.

Ultrastructural Changes in the Penumbra of the Local Cerebral Infarction in Rats

We studied changes in the ultrastructure of synapses and myelin nerve fibers that develop in the penumbra in 4 and 12 h and 2 and 4 days after modeling infarction in the frontoparietal cortex in rats. Ischemic stroke was induced by injection of a photosensitive dye into their bloodstream followed by illumination of the brain surface with a halogen lamp. Visible ultrastructural changes were observed in the penumbra zone, namely in the axodendritic and axospinous synapses; they consisted in polymorphism and disorganization of synaptic vesicles, mitochondrial swelling, swelling and vacuolization of the postsynaptic fragments of dendrites, and shortening and osmiophilia of the active zone. In the presynaptic terminals, clear-cut signs of transformation were observed only in 2 and 4 days after infarction modeling. These terminals were located at the ends of the degenerated myelinated axons of necrotic neurons. These findings demonstrate irreversible changes in the ultrastructure of synapses in the penumbra in 2-4 days after infarction and indicate the necessity of early treatment of strokes.

Acute sacral nerve stimulation reduces visceral mechanosensitivity in a cross-organ sensitization model

BACKGROUND

Sacral nerve stimulation (SNS) is a surgical treatment of fecal and urinary incontinence that consists of inserting a stimulating electrode into one of the s3 or s4 sacral holes. In addition to the benefit of SNS in the treatment of incontinence, recent studies showed that SNS is effective in the treatment of irritable bowel syndrome as well as bladder pain syndrome. The aim of this study was to evaluate the effect of SNS on visceral mechanosensitivity in a cross-organ sensitization rat model.

METHODS

Hypersensitive model was obtained by instillation of acetic acid into the bladder of rats during 5 minutes, 30 minutes before the start of the experiments. Visceral sensitivity was assessed by monitoring the change in mean arterial pressure in response to graded isobaric colorectal distension series. To decipher the mechanisms underlying SNS effect, rats were administered intravenously either a nonselective opioid receptor antagonist (naloxone) or a nitric oxide synthesis antagonist (L-NAME). Neuronal activation in the dorsal horn of the sacral spinal cord was measured by counting c-fos immunoreactive cells in response to colorectal distension and NMS.

KEY RESULTS

Intravesical acetic acid instillation increased mean arterial pressure variation in response to colorectal distension when compared to saline group. SNS reduced the variation in arterial pressure. Colorectal distension induced a rise in c-fos immunoreactive cells in the dorsal horn of the spinal cord. This effect was reduced by SNS.

CONCLUSIONS & INFERENCES

SNS reduces visceral mechanosensitivity in a cross-organ sensitization model.

MRI suggests increased tonicity of the levator ani in women with interstitial cystitis/bladder pain syndrome

INTRODUCTION AND HYPOTHESIS

In interstitial cystitis/bladder pain syndrome (IC/BPS), pelvic floor dysfunction may contribute significantly to pelvic pain. To determine if pelvic floor hypertonicity manifests alterations on magnetic resonance imaging (MRI) in patients with IC/BPS, we retrospectively compared pelvic measurements between patients and controls.

METHODS

Fifteen women with IC/BPS and 15 age-matched controls underwent pelvic MRI. Two blinded radiologists measured the pelvic musculature, including the H- and M lines, vaginal length, urethral length and cross-sectional area, levator width and length, and posterior puborectalis angle. MRI measures and clinical factors, such as age, parity, and duration of symptoms, were compared using a paired, two-tailed t test.

RESULTS

There were no significant differences in age, parity, or symptom duration between groups. Patients with IC/BPS exhibited shorter levator muscles (right: 5.0 ± 0.7 vs. 5.6 ± 0.8, left: 5.0 ± 0.8 vs. 5.7 ± 0.8 cm, P < 0.002) and a wider posterior puborectalis angle (35.0 ± 8.6 vs. 26.7 ± 7.9°, P < 0.01) compared with controls. The H line was shorter in patients with IC/BPS (7.8 ± 0.8 vs. 8.6 ± 0.9 cm, P < 0.02), while M line did not differ. Total urethral length was similar, but vaginal cuff and bladder neck distances to the H line were longer in patients with IC/BPS (5.7 ± 0.6 vs. 5.1 ± 0.9 cm, P < 0.02; 1.9 ± 0.4 vs. 1.4 ± 0.2 cm, P < 0.001, respectively).

CONCLUSIONS

Patients with IC/BPS have pelvic floor hypertonicity on MRI, which manifests as shortened levator, increased posterior puborectalis angles, and decreased puborectal distances. We identified evidence of pelvic floor hypertonicity in patients with IC/BPS, which may contribute to or amplify pelvic pain. Future studies are necessary to determine the MRI utility in understanding pelvic floor hypertonicity in patients with IC/BPS.

Effect of spinal manipulation thrust magnitude on trunk mechanical activation thresholds of lateral thalamic neurons

OBJECTIVES

High-velocity low-amplitude spinal manipulation (HVLA-SM), as performed by doctors who use manual therapy (eg, doctors of chiropractic and osteopathy), results in mechanical hypoalgesia in clinical settings. This hypoalgesic effect has previously been attributed to alterations in peripheral and/or central pain processing. The objective of this study was to determine whether thrust magnitude of a simulated HVLA-SM alters mechanical trunk response thresholds in wide dynamic range (WDR) and/or nociceptive specific (NS) lateral thalamic neurons.

METHODS

Extracellular recordings were carried out in the thalamus of 15 anesthetized Wistar rats. Lateral thalamic neurons having receptive fields, which included the lumbar dorsal-lateral trunk, were characterized as either WDR (n=22) or NS (n=25). Response thresholds to electronic von Frey (rigid tip) mechanical trunk stimuli were determined in 3 directions (dorsal-ventral, 45° caudalward, and 45° cranialward) before and immediately after the dorsal-ventral delivery of a 100-millisecond HVLA-SM at 3 thrust magnitudes (control, 55%, 85% body weight).

RESULTS

There was a significant difference in mechanical threshold between 85% body weight manipulation and control thrust magnitudes in the dorsal-ventral direction in NS neurons (P=.01). No changes were found in WDR neurons at either HVLA-SM thrust magnitude.

CONCLUSIONS

This study is the first to investigate the effect of HVLA-SM thrust magnitude on WDR and NS lateral thalamic mechanical response threshold. Our data suggest that, at the single lateral thalamic neuron level, there may be a minimal spinal manipulative thrust magnitude required to elicit an increase in trunk mechanical response thresholds.

Convergence and cross talk in urogenital neural circuitries

Despite common comorbidity of sexual and urinary dysfunctions, the interrelationships between the neural control of these functions are poorly understood. The medullary reticular formation (MRF) contributes to both mating/arousal functions and micturition, making it a good site to test circuitry interactions. Urethane-anesthetized adult Wistar rats were used to examine the impact of electrically stimulating different nerve targets [dorsal nerve of the penis (DNP) or clitoris (DNC); L6/S1 trunk] on responses of individual extracellularly recorded MRF neurons. The effect of bladder filling on MRF neurons was also examined, as was stimulation of DNP on bladder reflexes via cystometry. In total, 236 MRF neurons responded to neurostimulation: 102 to DNP stimulation (12 males), 64 to DNC stimulation (12 females), and 70 to L6/S1 trunk stimulation (12 males). Amplitude thresholds were significantly different at DNP (15.0 ± 0.6 μA), DNC (10.5 ± 0.7 μA), and L6/S1 trunk (54.2 ± 4.6 μA), whereas similar frequency responses were found (max responses near 30–40 Hz). In five males, filling/voiding cycles were lengthened with DNP stimulation (11.0 ± 0.9 μA), with a maximal effective frequency plateau beginning at 30 Hz. Bladder effects lasted ∼2 min after DNP stimulus offset. Many MRF neurons receiving DNP/DNC input responded to bladder filling (35.0% and 68.3%, respectively), either just before (43%) or simultaneously with (57%) the voiding reflex. Taken together, MRF-evoked responses with neurostimulation of multiple nerve targets along with different responses to bladder infusion have implications for the role of MRF in multiple aspects of urogenital functions.

Myofascial pain and pelvic floor dysfunction in patients with interstitial cystitis

INTRODUCTION AND HYPOTHESIS

The objectives of this study are to investigate myofascial pain in patients with interstitial cystitis (IC) and to correlate myofascial exam findings with validated questionnaires.

METHODS

A retrospective chart review was performed on 186 patients with a diagnosis of IC from April 2007 to December 2008. Demographics, history and physical examination, and validated pelvic floor dysfunction questionnaire scores were extracted. The data was evaluated with SPSS for Windows using Spearman's rho, Mann-Whitney, and Kruskal-Wallis statistical analyses.

RESULTS

Myofascial pain was demonstrated in 78.3% of IC patients with at least one myofascial trigger point, and 67.9% of patients had numerous areas of trigger points. Mild correlations were seen with trigger points and scores from the PUF, PFDI-20, and PFIQ-7 questionnaires.

CONCLUSIONS

Myofascial pain is prevalent among IC patients and positively correlated with pelvic floor dysfunction scores. These findings support evaluation of pelvic floor myofascial pain in IC patients and suggest a possible benefit from pelvic floor therapy.

Effects of 17beta-estradiol on responses of viscerosomatic convergent thalamic neurons in the ovariectomized female rat

Ovarian hormones have been shown to exert multiple effects on CNS function and viscerosomatic convergent activity. Ovariectomized (OVX) female rats were used in the present study to examine the long-term effects of proestrus levels of 17beta-estradiol (EB) delivered by a 60-day time-released subcutaneous pellet on the response properties of viscerosomatic convergent thalamic neurons. In addition, avoidance thresholds to mechanical stimulation for one of the convergent somatic territories, the trunk, was assessed using an electro-von Frey anesthesiometer before and at the end of the 6-wk post-OVX/implant period prior to the terminal electrophysiological experiments, which were done under urethane anesthesia. Rats implanted with an EB-containing pellet, relative to placebo controls, demonstrated 1) altered thalamic response frequencies and thresholds for cervix and vaginal but not colon stimulation; 2) some response variations for just the lateral group of thalamic subnuclei; and 3) altered thalamic response frequencies and thresholds for trunk stimulation. Thalamic response thresholds for trunk pressure in EB versus placebo rats were consistent with the avoidance thresholds obtained from the same groups. In addition, EB replacement affected visceral and somatic thresholds in opposite ways (i.e., reproductive-related structures were less sensitive to pressure, whereas somatic regions showed increased sensitivity). These results have obvious reproductive advantages (i.e., decreased reproductive organ sensitivity for copulation and increased trunk sensitivity for lordosis posturing), as well as possible clinical implications in women suffering from chronic pelvic pain syndromes and/or neuropathic pain.

The anterolateral abdominal wall muscles during vesical filling and evacuation: electromyographic study

OBJECTIVES

The role of the anterolateral abdominal wall muscles (AAWM) during vesical filling and evacuation has not been sufficiently addressed in the literature. We investigated the hypothesis that the AAWM exhibit increased electromyographic (EMG) activity on vesical distension and contraction that presumably assists in vesical evacuation.

METHODS

The effect of vesical balloon distension on vescial (VP) and vesical neck (VNP) pressures and on AAWM EMG activity was studied in 28 healthy volunteers of age 40.7 +/- 9.7 years (18 men and 10 women). This effect was tested after anesthetization on individual vesical and AAWM and after saline infiltration.

RESULTS

The VP and VNP showed gradual increase on incremental vesical balloon distension starting at a distending volume of 120 to 140 mL. At a mean volume of 364.6 +/- 23.8 mL, the VP increased to a mean of 36.6 +/- 3.2 cm H(2)O, the VNP decreased to 18.4 +/- 2.4 cm H(2)O, and AAWM EMG registered a significant increase. This effect disappeared with anesthetization on individual vesical or AAWM, but not with saline administration.

CONCLUSIONS

AAWM appear to contract simultaneously with vesical contraction; this action presumably increases the intra-abdominal pressure and assists vesical contraction. The AAWM contraction on vesical contraction seems to be mediated through a reflex that we call the "vesico-abdominal wall reflex." Further studies are required to investigate the role of this reflex in vesical disorders.

Urinary bladder irritation alters efficacy of vagal stimulation on rostral medullary neurons in chronic T8 spinalized rats

The presence of pelvic visceral inputs to neurons in the rostral medulla that are responsive to electrical stimulation of the abdominal branches of the vagus nerve (VAG-abd) was investigated in a complete chronic T8 spinal transection rat model. Using extracellular electrophysiological recordings from single medullary reticular formation (MRF) neurons, 371 neurons in 15 rats responsive to pinching the ear (search stimulus) were tested for somato-visceral and viscero-visceral convergent responses to stimulation of the following nerves/territories: VAG-abd, dorsal nerve of the penis, pelvic nerve, distention of urinary bladder and colon, penile stimulation, urethral infusion, and touch/pinch of the entire body surface. In addition to these mechanical and electrical stimuli, a chemical stimulus applied to the bladder was assessed as well. Of the total neurons examined, 205 were tested before and 166 tested beginning 20 min after application of a chemical irritant (2% acetic acid) to the urinary bladder (same rats used pre/post irritation). As with intact controls, many ear-responsive MRF neurons responded to the electrical stimulation of VAG-abd. Although MRF neuron responses failed to be evoked with direct (mechanical and electrical nerve) pelvic visceral stimuli, acute chemical irritation of the urinary bladder produced a significant increase in the number of MRF neurons responsive to stimulation of VAG-abd. The results of this study indicate a central effect that potentially relates to some of the generalized below level pelvic visceral sensations that have been documented in patients with complete spinal cord injury.