Feasibility of implant driven micturition in paraplegic dogs.

OBJECTIVE: This study evaluates the feasibility of using existing technology for implant driven micturition in paralyzed dogs (part I) and also examines a less invasive technique for implant driven micturition (part II). STUDY DESIGN: Part I. Sacral nerve root dimensions and bladder and urethral pressure responses to intradural and extradural sacral nerve root stimulation were measured to determine the optimal location and size for sacral nerve root electrodes. Part II. Sacral nerve roots were stimulated via wire electrodes introduced into the S2 foramina. ANIMALS OR SAMPLE POPULATION: Ten dogs (five dogs in part I and five dogs in part II). METHODS: Part I. Microtip pressure transducers were used to monitor bladder and urethral pressure responses to sacral nerve root stimulation with tripolar hook electrodes. After euthanasia, sacral nerve root, and spinal canal dimensions were measured. Part II. Bipolar electrical stimulation of the sacral nerve roots was performed by introducing wire electrodes into the S2 foramina. Bladder and urethral pressures were recorded as in part I. RESULTS: Part I. Stimulation of SI produced an increase in urethral, but not bladder, pressure. Stimulation of S2 or S3 produced increases in bladder pressure and decreases in urethral pressure. Intradural and extradural nerve roots were not significantly different with respect to nerve dimensions or effects on nerve stimulation. Part II. High bladder pressures were achieved, but effective voiding could not be produced, primarily because of urethral resistance. CONCLUSIONS: Part I. Extradural implantation was determined to be the most appropriate site based on ease of dissection, nerve root dimensions, and decreased risk of iatrogenic trauma. Enough space is available to implant two to four tripolar spiral nerve cuffs. Part II. Transforaminal sacral nerve root stimulation did not effectively empty the bladder. CLINICAL RELEVANCE: Clinical trials in paraplegic dogs are necessary to evaluate the number of sacral nerve cuff electrodes necessary to produce effective bladder emptying.

Further evidence to support the alpha 2-adrenergic nature of amitraz-induced decrease in intestinal motility.

The effect of amitraz, a formamidine insecticide, on in vitro intestinal contractions was studied in teh transmurally-stimulated guinea-pig ileum. An electrical stimulation (with 80 V/0.5 msec/0.1 Hz shown on the dial of the stimulator) caused the ileum to contract presumably via the release of acetylcholine. Amitraz (10(-7) to 10(-6) M) produced a dose-dependent inhibition of these transmurally-stimulated contractions. This effect of amitraz was blocked and reversed by idazoxan (10(-6) M), an alpha 2-adrenoceptor antagonist, but was not prevented by prazosin (10(-6) M), an alpha 1-adrenoceptor antagonist. These results suggest that alpha 2-adrenoceptors mediate the effects of amitraz on the transmurally-stimulated guinea-pig ileum. The results also suggest that amitraz decreases intestinal contraction by activating the alpha 2-adrenoceptors in the myenteric (Auerbach's) plexus, thus inhibiting parasympathetic tone.

Use of a pressure-sensitive radiotelemetering capsule to study the canine gastric interdigestive complex.

An inexpensive pressure-sensitive radiotelemetering capsule, transmitting at 100 MHz, was used to study gastric interdigestive complexes. The oscillator was frequency modulated; pressure changes on a rubber diaphragm caused displacements of a ferromagnetic core altering the frequency of oscillation by modifying the inductance in the circuit. The system was linear for applied pressures up to 40 mm of Hg; for 40 mm Hg the frequency decreased by 22 kHz. Three fasted dogs were used; an encapsulated radio pill picked up the presence fluctuations associated with gastric contractions and transmitted these signals as radio waves. An FM receiver intercepted, amplified, and relayed the signals to a chart recorder, which produced a permanent record. During the first part of each 24-hour recording period, cyclical interdigestive patterns consisting of a series of high-amplitude contractions followed by long-lasting quiescence were recorded. Regular outbursts showed mean durations ranging from 11.6 to 17.6 minutes, mean periods from 27 to 51 minutes, and mean amplitudes from 9.9 to 11.1 mm Hg. Noncyclical, irregular recordings were obtained during the last part of each recording period. These results are similar to ones obtained using force transducers.