Dynamic bulbocavernosus reflex: dyssynergia evaluation following SCI

Balloon-tipped catheter for measuring urethral pressures

BACKGROUND

Better methods are needed for recording urethral function for complex urologic problems involving the bladder, urethra, and pelvic floor.

OBJECTIVE

To evaluate a balloon catheter for recording urethral pressure and function using bench-top testing and evaluation in an animal model.

METHODS

Balloon pressure-recording methods included slightly inflating the balloon with water and placing the pressure transducer on the distal end of the catheter. For bench-top testing, manual procedures and a silastic tube with a restriction were used. In 3 anesthetized dogs, pressure recorded from the skeletal urethral sphincter was induced with electrical stimulation of the sphincter. Anal sphincter pressure was also recorded.

RESULTS

Bench-top testing showed good pressure recordings, including a confined peak at the tube restriction. Animal tests showed urethral pressure records with rapid responses when electrical stimulation was applied. Peak pressure at the urethral skeletal sphincter was 55.7 +/- 15 cmH2O, which was significantly higher than the peak pressure recorded 2 cm distally in the proximal urethra (3.3 +/- 2.3 cmH2O). Peak anal pressures were smaller and unchanged for the 2 stimulations.

CONCLUSIONS

Balloon-pressure recordings showed rapid responses that were adequate for the tests conducted. In the animal model, high-pressure contractions specific to the skeletal urethral sphincter were shown. Balloon-tipped catheters warrant further investigation and may have applications for the evaluation of detrusor-sphincter dyssynergia after spinal cord injury or for stress urinary incontinence.

Activation and inhibition of the micturition reflex by penile afferents in the cat

Coordination of the urinary bladder and the external urethral sphincter is controlled by descending projections from the pons and is also subject to modulation by segmental afferents. We quantified the effects on the micturition reflex of sensory inputs from genital afferents traveling in the penile component of the somatic pudendal nerve by electrical stimulation of the dorsal nerve of the penis (DNP) in alpha-chloralose anesthetized male cats. Depending on the frequency of stimulation (range, 1-40 Hz), activation of penile afferents either inhibited contractions of the bladder and promoted urine storage or activated the bladder and produced micturition. Stimulation of the DNP at 5-10 Hz inhibited distension-evoked contractions and increased the maximum bladder capacity before incontinence. Conversely, stimulation at 33 and 40 Hz augmented distension-evoked contractions. When the bladder was filled above a threshold volume (70% of the volume necessary for distension-evoked contractions), stimulation at 20-40 Hz activated de novo the micturition reflex and elicited detrusor contractions that increased voiding efficiency compared with distension-evoked voiding. Electrical stimulation of the DNP with a cuff electrode or percutaneous wire electrode produced similar results. The ability to evoke detrusor contractions by activation of the DNP was preserved following acute spinal cord transection. These results demonstrate a clear role of genital afferents in modulating the micturition reflex and suggest the DNP as a potential target for functional restoration of bladder control using electrical stimulation.

Bulbocavernosus reflex during the micturition cycle in normal male subjects

BACKGROUND

To investigate normal changes in the bulbocavernosus reflex (BCR) during the micturition cycle, we examined the change in BCR during the micturition cycle using an evoked potential reaction of the BCR (BCR-EP).

METHODS

Fourteen normal subjects were examined in the study. The BCR-EP was recorded at empty bladder, filled bladder, during voiding and at empty bladder after voiding. To elicit the BCR-EP, the dorsal nerve of the penis was stimulated by two ring electrodes and an electromyogram of the external urethral sphincter was recorded. The maximum amplitude was measured to evaluate changes in the BCR.

RESULTS

The amplitude of the BCR was increased by bladder filling and the ratio of the amplitude at filled bladder/amplitude at empty bladder was 1.32 +/- 0.39. The stable BCR-EP elicited by stimulation at empty bladder disappeared during voluntary voiding in 13 of 14 subjects. However, as stimulation was increased in seven subjects, the BCR-EP was again seen clearly.

CONCLUSIONS

The BCR varies during the micturition cycle, although in normal subjects this variation occurs within a relatively narrow range. Changes in the BCR out of the normal range (e.g. large acceleration by bladder filling or insufficient inhibition during voiding) could suggest the existence of neurogenic disease.

Spinal cord neural organization controlling the urinary bladder and striated sphincter

The storage and elimination of urine requires the coordination of activity between the autonomic nervous system (thoracolumbar sympathetic and sacral parasympathetic divisions) controlling the urinary bladder and urethra and the lumbosacral somatic motoneurons innervating the striated sphincter and pelvic floor muscles. These three efferent systems involved in the control of lower urinary tract function receive segmental sensory information from various visceral organs and the perineum, as well as inputs from supraspinal regions. Ascending and descending connections between the various spinal segments levels and supraspinal regions provide the reflex substrates participating in normal bladder continence and micturition reflexes. Many of the actions of descending and segmental reflexes are mediated by excitatory and inhibitory sacral spinal interneurons located within the region of the parasympathetic preganglionic autonomic neurons and the sphincter ventral horn motoneurons. This review will: (1) discuss the basic organization and spinal elements of the reflex pathways subserving continence and micturition; (2) describe features of the identified sacral interneuronal circuitry contributing to the control of the bladder and sphincter function; and (3) discuss how changes in the control of these reflex pathways and neurons may contribute to abnormal patterns of bladder and sphincter function commonly observed following spinal cord injury.

Dimethyl sulfoxide binding to globular proteins: a nuclear magnetic relaxation dispersion study

The 2H magnetic relaxation dispersion (NMRD) technique was used to characterize interactions of dimethyl sulfoxide (DMSO) with globular proteins. A difference NMRD experiment involving the N-acetylglucosamine trisaccharide inhibitor, demonstrated that the DMSO 2H NMRD profile in lysozyme solution is due to a single DMSO molecule bound in the active cleft, with a molecular order parameter of 0.47 +/- 0.05 and a residence time in the range 10 ns to 5 ms. With the aid of transverse 2H relaxation data, the upper bound of the residence time was further reduced to 100 microns. A 1H shift titration experiment was also performed, yielding a binding constant of 2.3 +/- 0.3 M-1 at 27 degrees C. In contrast to lysozyme, no DMSO dispersion was observed for bovine pancreatic trypsin inhibitor (BPTI), indicating that a stable DMSO-protein complex requires a cleft of appropriate geometry in addition to hydrogen-bond and hydrophobic interactions.

Transport of proteins dissolved in organic solvents across biomimetic membranes

Using lipid-impregnated porous cellulose membranes as biomimetic barriers, we tested the hypothesis that to afford effective transmembrane transfer of proteins and nucleic acids, the vehicle solvent should be able to dissolve both the biopolymers and the lipids. While the majority of solvents dissolve one or the other, ethanol and methanol were found to dissolve both, especially if the protein had been lyophilized from an aqueous solution of a pH remote from the protein's isoelectric point. A number of proteins, as well as RNA and DNA, dissolved in these alcohols readily crossed the lipidized membranes, whereas the same biopolymers placed in nondissolving solvents (e.g., hexane and ethyl acetate) or in those unable to dissolve lipids (e.g., water and dimethyl sulfoxide) exhibited little transmembrane transport. The solubility of biopolymers in ethanol and methanol was further enhanced by complexation with detergents and poly(ethylene glycol); significant protein and nucleic acid transport through the lipidized membranes was observed from these solvents but not from water.