Minimally-invasive electrical stimulation of the pudendal nerve: a pre-clinical study for neural control of the lower urinary tract.

Aims: Electrical stimulation of afferent pudendal nerve fibers can evoke sustained bladder contractions (SBC) in cats, yet evidence of therapeutic efficacy in human subjects is lacking. This pre-clinical study was undertaken to test the hypothesis that robust bladder contractions can be generated with a minimally-invasive needle electrode.

Materials And Methods: In seven adult cats, triggered electromyographic (EMG) signals from the external anal sphincter (EAS) were used to minimize the needle-to-nerve distance; while reflex bladder contractions were recorded as 20-sec trains of current pulses of varying amplitude (threshold to 10 mA) and frequency (1-100 Hz) were applied to the nerve.

Clinical response to varying the stimulus parameters in deep brain stimulation for essential tremor.

Deep brain stimulation (DBS) of the ventral intermediate nucleus of the thalamus for essential tremor is sometimes limited by side effects. The mechanisms by which DBS alleviates tremor or causes side effects are unclear; thus, it is difficult to select stimulus parameters that maximize the width of the therapeutic window. The goal of this study was to quantify the impact on side effect intensity (SE), tremor amplitude, and the therapeutic window of varying stimulus parameters.

Frequency-dependent selection of reflexes by pudendal afferents in the cat.

Activation of urethral or genital afferents of the pudendal nerve can elicit or inhibit micturition, and low frequency stimulation of the compound pudendal nerve (PN) is known to produce a continence response. The present study demonstrates that PN stimulation also can elicit a micturition-like response and that the response to PN stimulation is dependent on stimulation frequency. We measured the changes in bladder pressure and external urethral sphincter (EUS) electroneurogram (ENG) evoked by PN stimulation before and up to 16 h after spinal cord transection (SCT) in cats anaesthetized with alpha-chloralose.

Combined surface-focused acoustic microscopy in transmission and scanning ultrasonic holography.

Employment of ultrasound techniques in nondestructive testing may require identification of the acoustic modes contributing to imaging. Such identification can be achieved, with some restrictions, by time-of-flight analysis. Another approach is acoustic holography that reveals the propagation properties of any selected mode.

Combined phase-sensitive acoustic microscopy and confocal laser scanning microscopy.

Combined phase-sensitive acoustic microscopy (PSAM) at 1.2 GHz and confocal laser scanning microscopy (CLSM) in reflection and fluorescence has been implemented and applied to polymer blend films and fluorescently labeled fibroblasts and neuronal cells in order to explore the prospects and the various contrast mechanisms of this powerful technique. Topographic contrast is available for appropriate samples from CLSM in reflection and, with significantly higher precision, from the acoustic phase images.

Topography of spinal neurons active during hindlimb withdrawal reflexes in the decerebrate cat.

There exists a spatial organization of receptive fields and a modular organization of the flexion withdrawal reflex system. However, the three dimensional location and organization of interneurons interposed in flexion reflex pathways has not been systematically examined. We determined the anatomical locations of spinal neurons involved in the hindlimb flexion withdrawal reflex using expression of the immediate early gene c-fos and the corresponding FOS protein.

On interference effects in the elastodynamic Green's functions G33(x, omega) of Si and GaAs.

In this paper, we analyze interference effects present in the elastodynamic Green's functions G33(x,omega) of the cubic crystals Si and GaAs, which are associated with folded portions of the wave surface of the slow transverse (ST) acoustic mode. G33(x,omega) represents the three dimensional extension of the amplitude distribution imaged in the transmission acoustic microscopy of these crystals. The intensity contrast for oscillations of a particular wave vector k in the interference pattern is determined essentially by the 3D Fourier transform of G33(x,omega)G33*(x,omega).

Sites of neuronal excitation by epiretinal electrical stimulation.

Action potentials arising from retinal ganglion cells ultimately create visual percepts. In persons blind from retinitis pigmentosa and age-related macular degeneration, viable retinal ganglion cells remain, and the retina can be stimulated electrically to restore partial sight. However, it is unclear what neuronal elements in the retina are activated by epiretinal electrical stimulation.

Closed loop electrical control of urinary continence.

Purpose: Individuals with spinal cord injury or neurological disorders may have neurogenic detrusor contractions at low volumes (bladder hyperreflexia), which cause incontinence and can lead to significant health problems. Bladder contractions can be suppressed by electrical stimulation of inhibitory pathways but continuous activation may lead to habituation of the inhibitory reflex and loss of continence. We determined whether conditional stimulation with electrical stimulation of inhibitory pathways applied only at the onset of nascent bladder contractions allows the bladder to fill to a greater volume before continence is lost compared with continuous stimulation.

Bladder emptying by intermittent electrical stimulation of the pudendal nerve.

Persons with a suprasacral spinal cord injury cannot empty their bladder voluntarily. Bladder emptying can be restored by intermittent electrical stimulation of the sacral nerve roots (SR) to cause bladder contraction. However, this therapy requires sensory nerve transection to prevent dyssynergic contraction of the external urethral sphincter (EUS).

Current density distributions, field distributions and impedance analysis of segmented deep brain stimulation electrodes.

Deep brain stimulation (DBS) electrodes are designed to stimulate specific areas of the brain. The most widely used DBS electrode has a linear array of 4 cylindrical contacts that can be selectively turned on depending on the placement of the electrode and the specific area of the brain to be stimulated. The efficacy of DBS therapy can be improved by localizing the current delivery into specific populations of neurons and by increasing the power efficiency through a suitable choice of electrode geometrical characteristics.

Safety considerations for deep brain stimulation: review and analysis.

Deep brain stimulation has emerged rapidly as an effective therapy for movement disorders. Deep brain stimulation includes an implanted brain electrode and a pacemaker-like implanted pulse generator. The clinical application of deep brain stimulation proceeded in the absence of clear understandings of its mechanisms of action or extensive preclinical studies of safety and efficacy.

Detection of neurogenic detrusor contractions from the activity of the external anal sphincter in cat and human.

Aims: Individuals with spinal cord injury or neurological disorders may develop bladder contractions at low volumes (neurogenic detrusor overactivity), which can lead to significant health problems. Present devices can inhibit unwanted contractions through continuous electrical stimulation of sensory nerves, but do not enable conditional stimulation only at the onset of bladder contractions. The objectives of this study were to determine the relationship between the electrical activity of external anal sphincter (EAS) and bladder pressure during neurogenic detrusor contractions and to determine whether EAS activity could be used to detect the onset of bladder contractions.

Detecting the onset of hyper-reflexive bladder contractions from the electrical activity of the pudendal nerve.

Individuals with a spinal cord injury or neurological disorders may develop involuntary bladder contractions at low volumes (bladder hyper-reflexia), which can lead to significant health problems. Present devices can inhibit unwanted contractions through continuous stimulation, but do not enable conditional stimulation only at the onset of bladder contractions. The objectives of this study were to determine the relationship between the electrical activity of the pudendal nerve trunk (PNT) and bladder pressure during hyper-reflexive bladder contractions and to determine whether PNT activity could be used to detect the contractions.

Application of spatially and temporally apodized non-confocal acoustic transmission microscopy to imaging of directly bonded wafers.

Application of a line-shaped point spread function (PSF) to imaging of void defects in directly bonded wafers is considered. Two non-confocally adjusted spherical transducers are employed to implement an acoustic microscope operating in transmission with a time dependent point spread function, whose shape is optimized by both temporal apodization of the received signal and spatial apodization of the transducer aperture. Strong imaging artifacts resulting from the generation and detection of edge waves are eliminated in this way.

Temporal and spatial apodization in defocused acoustic transmission microscopy.

Two non-confocally adjusted spherical transducers are employed to implement an acoustic microscope operating in transmission with an approximately line-shaped point spread function (PSF). Such a PSF is of advantage in acoustic transmission line tomography and spatially resolved velocity measurements in solids. The foci of the transducers are viewed as diffraction-limited point transducers and appropriate time-selective signal acquisition is designed to restrict the ultrasound wave paths to the line connecting them.

Polarization of a spherical cell in a nonuniform extracellular electric field.

Polarization of cells by extracellular fields is relevant to neural stimulation, cardiac pacing, cardiac defibrillation, and electroporation. The electric field generated by an extracellular electrode may be nonuniform, and highly nonuniform fields are produced by microelectrodes and near the edges of larger electrodes. We solved analytically for the transmembrane voltage (phi(m)) generated in a spherical cell by a nonuniform extracellular field, as would arise from a point electrode.

Characterization of polymer thin films by phase-sensitive acoustic microscopy and atomic force microscopy: a comparative review.

The potential of phase-sensitive acoustic microscopy (PSAM) for characterizing polymer thin films is reviewed in comparison to atomic force microscopy (AFM). This comparison is based on results from three-dimensional vector contrast imaging and multimodal imaging using PSAM and AFM, respectively. The similarities and differences between the information that can be derived from the AFM topography and phase images, and the PSAM phase and amplitude micrographs are examined.

Functional magnetic resonance imaging of the human lumbar spinal cord.

Purpose: To determine whether consistent regions of activity could be observed in the lumbar spinal cord of single subjects with spin-echo functional MRI (fMRI) if several repeated experiments were performed within a single imaging session.

Materials And Methods: Repeated fMRI experiments of the human lumbar spinal cord were performed at 1.5 T with a single-shot spin-echo technique (half-Fourier single-shot turbo spin-echo (HASTE)) as used by previous investigators, and a modified method (fluid-attenuated inversion recovery (FLAIR)-HASTE) that nulled the otherwise highly variable signal from the cerebrospinal fluid (CSF).

Temporal excitation properties of paresthesias evoked by thalamic microstimulation.

Objective: The neuronal elements mediating the effects of deep brain stimulation (DBS) are unknown. The objective was to determine the strength-duration properties of the neuronal elements that mediate paresthesias evoked by thalamic microstimulation.

Methods: The strength-duration properties of the neuronal elements causing paresthesias were measured using intraoperative microstimulation of the human thalamus.

Structural mechanisms to produce differential dendritic gains.

The axons of sacral parasympathetic preganglionic neurons (PGNs) originate on a primary dendrite between 10 and 110 mum from the soma. Therefore, it was hypothesized that the location of the axon origin would impact the relative efficacy of ipsilateral and contralateral synaptic inputs. The morphology of two PGNs was reconstructed, and the transfer impedance was used to quantify the influence of synaptic inputs on the transmembrane potential at the axon initial segment.

Electrical localization of neural activity in the dorsal horn of the spinal cord: a modeling study.

Intraspinal microstimulation is a means of eliciting coordinated motor responses for restoration of function. However, detailed maps of the neuroanatomy of the human spinal cord are lacking, and it is not clear where electrodes should be implanted. We developed an electrical approach to localize active neurons in the spinal cord using potentials recorded from the surface of the spinal cord.

Spinal micturition reflex mediated by afferents in the deep perineal nerve.

Reflexes mediated by urethral sensory pathways are integral to urinary function. This study investigated the changes in bladder pressure and urethral sphincter activity resulting from electrical stimulation of afferents in the deep perineal nerve (DP), which innervates the urethra and surrounding muscles, before and after acute spinal cord transection (SCT) in cats anesthetized with alpha-chloralose monitored by blood pressure and heart rate. DP stimulation elicited bladder contractions before and after SCT but only if the bladder contained a sufficient volume of fluid (78% of the volume needed to cause distention-evoked reflex contractions).

Applied electric fields accelerate the diffusion rate and increase the diffusion distance of DiI in fixed tissue.

Lipophilic carbocyanine dyes are effective neuronal tracers in fixed tissue. However, their application has been limited by the slow diffusion, short tracing distances, and long durations of incubation in fixed tissue. We used applied dc electric fields, that exerted forces on the cationic dyes, to increase the diffusion velocity and maximal tracing distances of DiI and its analogs.