Nerve Electrode Research Articles

Model-based analysis and design of nerve cuff electrodes for restoring bladder function by selective stimulation of the pudendal nerve

Objective. Electrical stimulation of the pudendal nerve (PN) is being developed as a means to restore bladder function in persons with spinal cord injury. A single nerve cuff electrode placed on the proximal PN trunk may enable selective stimulation of distinct fascicles to maintain continence or evoke micturition. The objective of this study was to design a nerve cuff that enabled selective stimulation of the PN. Approach. We evaluated the performance of both flat interface nerve electrode (FINE) cuff and round cuff designs, with a range of FINE cuff heights and number of contacts, as well as multiple contact orientations. This analysis was performed using a computational model, in which the nerve and fascicle cross-sectional positions from five human PN trunks were systematically reshaped within the nerve cuff. These cross-sections were used to create finite element models, with electric potentials calculated and applied to a cable model of a myelinated axon to evaluate stimulation selectivity for different PN targets. Subsequently, the model was coupled to a genetic algorithm (GA) to identify solutions that used multiple contact activation to maximize selectivity and minimize total stimulation voltage. Main results. Simulations did not identify any significant differences in selectivity between FINE and round cuffs, although the latter required smaller stimulation voltages for target activation due to preserved localization of targeted fascicle groups. Further, it was found that a ten contact nerve cuff generated sufficient selectivity for all PN targets, with the degree of selectivity dependent on the relative position of the target within the nerve. The GA identified solutions that increased fitness by 0.7–45.5% over single contact activation by decreasing stimulation of non-targeted fascicles. Significance. This study suggests that using an optimal nerve cuff design and multiple contact activation could enable selective stimulation of the human PN trunk for restoration of bladder function.

Functional evidence for increased nitric oxide involvement in cardiovascular and autonomic modulation by the PVN in conscious HU rats

PVN is a pivotal hypothalamic integrative center for circulatory control and may play a role in autonomic regulation after cardiovascular deconditioning. Previous work demonstrates that neuronal nitric oxide (NO) synthase activity and protein expression is increased in the PVN of hindlimb unloaded (HU) rats, an animal model of cardiovascular deconditioning, compared to control. However, the functional role of increased nNOS is unknown. In this study we tested the hypothesis that tonic effects of NO in the PVN are augmented in HU rats. We studied the cardiovascular and autonomic responses to NOS inhibition in the PVN after return of HU rats to upright posture. Rats underwent 14 days HU or cage control (CC). Guide cannulas to the PVN were implanted on Day 9. Artery and vein catheters and renal nerve electrodes were implanted on Day 13 to record mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA). Baseline MAP was similar but resting HR was increased in conscious HU compared to control. Inhibition of NOS with L‐NMMA (2mM/100nL) into the PVN produced greater increases in MAP (CC: 13±1 vs. HU: 20±2 mmHg) and RSNA (CC: 155±34 vs. HU: 309±49% Baseline) in HU compared to control. Changes in HR to L‐NMMA were similar between groups. Data indicate that tonic NO function in the PVN is enhanced after HU in conscious rats and it may be part of the adjustments required for microgravity environment. HL55306

Optimization of selective stimulation parameters for multi-contact electrodes

BackgroundMulti-contact stimulating electrodes are gaining acceptance as a means for interfacing with the peripheral nervous system. These electrodes can potentially activate many independent populations of motor units within a single peripheral nerve, but quantifying their recruitment properties and the overlap in stimulation between contacts is difficult and time consuming. Further, current methods for quantifying overlap between contacts are ambiguous and can lead to suboptimal selective stimulation parameters. This study describes a novel method for optimizing stimulation parameters for multi-contact peripheral stimulating electrodes to produce strong, selective muscle contractions. The method is tested with four-contact spiral nerve-cuff electrodes implanted on bilateral femoral nerves of two individuals with spinal cord injury, but it is designed to be extendable to other electrode technologies with higher densities of contacts.MethodsTo optimize selective stimulation parameters for multi-contact electrodes, first, recruitment and overlap are characterized for all contacts within an electrode. Recruitment is measured with the twitch response to single stimulus pulses, and overlap between pairs of contacts is quantified by the deviation in their combined response from linear addition of individual responses. Simple mathematical models are fit to recruitment and overlap data, and a cost function is defined to maximize recruitment and minimize overlap between all contacts.ResultsResults are presented for four-contact nerve-cuff electrodes stimulating bilateral femoral nerves of two human subjects with spinal cord injury. Knee extension moments between 11.6 and 43.2 Nm were achieved with selective stimulation through multiple contacts of each nerve-cuff with less than 10% overlap between pairs of contacts. The overlap in stimulation measured in response to selective stimulation parameters was stable at multiple repeated time points after implantation.ConclusionsThese results suggest that the method described here can provide an automated means of determining stimulus parameters to achieve strong muscle contractions via selective stimulation through multi-contact peripheral nerve electrodes.

Antenna Coupling—A Novel Mechanism of Radiofrequency Electrosurgery Complication

(1) To determine if antenna coupling occurs in common operating room scenarios. (2) To define modifiable clinical variables that reduce the magnitude of antenna coupling. Mechanisms of electrosurgical burns where monitoring devices contact the surgical patient are unclear. Antenna coupling occurs when the "bovie" active electrode (electrically active transmitting antenna) emits energy, which is captured by a nonelectrically active wire (electrically inactive receiving antenna) in close proximity without direct contact. Monopolar radiofrequency energy was delivered to a laparoscopic instrument (electrically active transmitting antenna), whereas other nonelectrically active wires (electrically inactive receiving antenna) including electrocardiogram (EKG) lead, nonactive "bovie" pencil, and nerve electrode monitor were placed in proximity. Temperature changes of tissue placed adjacent to the electrically inactive receiving antennae were measured. Nonelectrically active wires (receiving antenna) increase tissue temperature when lying parallel to the active electrode cord: EKG pad 2.4°C ± 1.2°C (P = 0.002), "bovie" pencil tip 90°C ± 9°C (P < 0.001), and nerve electrode monitor 106°C ± 12°C (P < 0.001). Factors that reduced the heat generated by antenna coupling included the following: increasing angulation between transmitting and receiving antennae (parallel = 90°C ± 9°C; 45° angle = 53°C ± 10°C; perpendicular = 35°C ± 11°C; P < .001), increasing separation distance between parallel transmitting and receiving antenna (<1 cm = 90°C ± 9°C; 15 cm = 44°C ± 18°C; 30 cm = 39°C ± 2°C; P < .001); and decreasing generator power setting (15 W = 59°C ± 11°C; 30 W = 90°C ± 9°C; 45 W = 98°C ± 8°C; P < .001). Antenna coupling occurs in common operating room scenarios. Simple, practical measures by the surgeon, such as orienting the receiving antenna at a greater angle and with greater separation to the active electrode cord, or lowering the generator power setting reduce antenna coupling.

Implantation of a newly developed direct optic nerve electrode device for artificial vision in rabbits

The purpose of this study was to investigate the surgical procedures involved in the implantation of a newly developed direct optic nerve electrode device for inducing artificial vision. The electrode device comprised seven wire stimulation electrodes and a return electrode (diameter 50μm), one manipulation rod (diameter 100μm), and a cylindrical silicone board (diameter 2.0mm). The stimulation electrodes and the manipulation rod protruded through the board to allow implantation of the electrode tips into the optic disc of the rabbit eye. The surgical procedures required to insert the device into the vitreous cavity and implant the device into the optic disc were evaluated. When the electrodes were stimulated, electrically evoked potentials (EEPs) were recorded at the visual cortex. The electrode device was inserted into the vitreous cavity with no damage using a trocar through a scleral incision. The device was easily manipulated using vitreoretinal forceps in the vitreous cavity, and the electrode tips were implanted into the optic disc in a single insertion after vitrectomy. When electrical stimulation was applied, EEPs were recorded from all electrode pairs. The newly developed electrode device was inserted into the eye and implanted into the optic nerve disc smoothly and safely, suggesting that these surgical procedures are useful for our artificial vision system.

Renal sympathetic activation from long-term low-dose angiotensin II infusion in rabbits

Activation of renal sympathetic nerve activity (RSNA) has not been observed during long-term infusion of angiotensin II (AngII) which results in marked hypertension, despite activation of hypothalamic autonomic regions. We examined whether the function of central pathways influencing sympathetic activity is altered in conscious rabbits given a low dose of AngII that produces a modest hypertension and, therefore, limited secondary complications. Rabbits received AngII (20-30 ng/kg per min, subcutaneously) or sham treatment for 3 months at which time they were implanted with a renal sympathetic nerve electrode and the responses to airjet stress, baroreflexes and hypoxia were examined. AngII infusion for 3 months increased mean arterial pressure by 16% and RSNA by 43%. Increases in RSNA during airjet stress and hypoxia (10% O2) were 35 and 65% greater in AngII-treated rabbits than sham controls, respectively. Tachycardic responses were also enhanced. Baroreflexes were shifted to the right and upward in the AngII animals but baroreflex gain was similar in the two groups, indicating near complete resetting. Greater neuronal Fos-related antigen immunoreactivity was found in the vascular organ of the lamina terminalis, paraventricular and supraoptic hypothalamic nuclei in AngII-treated rabbits compared with sham. Our results suggest that low-dose AngII-treatment results in marked sympathetic activation at rest and during stress and hypoxia, due to activation of specific hypothalamic pathways. These mechanisms may contribute to sympathetic activation in conditions associated with chronic activation of the renin-angiotensin system such as obesity or renovascular disease.

What’s New in Shock, March 2012?

What’s New in Shock, March 2012?

Probabilistic modeling of selective stimulation of the human sciatic nerve with a flat interface nerve electrode

Ankle control is critical to both standing balance and efficient walking. The hypothesis presented in this paper is that a Flat Interface Nerve Electrode (FINE) placed around the sciatic nerve with a fixed number of contacts at predetermined locations and without a priori knowledge of the nerve's underlying neuroanatomy can selectively control each ankle motion. Models of the human sciatic nerve surrounded by a FINE of varying size were created and used to calculate the probability of selective activation of axons within any arbitrarily designated, contiguous group of fascicles. Simulations support the hypothesis and suggest that currently available implantable technology cannot selectively recruit each target plantar flexor individually but can restore plantar flexion or dorsiflexion from a site on the sciatic nerve without spillover to antagonists. Successful activation of individual ankle muscles in 90% of the population can be achieved by utilizing bipolar stimulation and/or by using a cuff with at least 20 contacts.

Comparison of Bipolar Lead Electrodes for High-Frequency Blocking of the Pudendal Nerve

Aims: High-frequency (HF) pudendal-nerve blocking that includes lead electrodes on the nerve are needed for spinal cord injury (SCI) patients to manage detrusor sphincter dyssynergia (DSD) that causes high urethral resistance. Several bipolar lead electrodes were compared using HF blocking stimulation parameters. Methods: Seven swine were anesthetized and urethral and anal sphincter pressures recorded. The left pudendal nerve adjacent to the sacral spine was exposed and proximal electrode used to induce intermittent contractions of urethral and anal sphincters. Blocking of sphincter contractions with electrodes at a distal location on the pudendal nerve with HF was evaluated. Initial HF tests used bipolar TECA electrodes at 1.2, 10 and 40 kHz; then, different electrodes and stimulating parameters were evaluated.Results: Initial results with HF demonstrated blocking of intermittent sphincter contractions induced by the proximal nerve electrode. Sphincter contraction blocking was greatest at 1.2 and 10 kHz at currents above 0.25 mA and was reduced at 40 kHz. Sphincter pressures, however, were elevated at the end of the 15 seconds of HF stimulation. These unwanted stimulatory effects on sphincter contraction were greatest at 1.2 kHz, reduced at 10 kHz, and least at 40 kHz. Further tests showed reduced nerve blocking effects using electrodes separated from the nerve or small helical Permaloc electrodes. Cutting the pudendal nerve centrally had no effect indicating that afferent fibers were not involved in the HF blocking effects. Conclusions: Bipolar TECA lead electrodes on the pudendal nerve stimulated at 10 kHz with1 to 5 mA of current were most effective in their nerve blocking effects with least unwanted stimulator effects. Nerve blocking without unwanted nerve stimulation was not observed with the variables tested. Therefore, unwanted stimulatory side effects should be anticipated in SCI patients when HF nerve blocking of the pudendal nerve with lead electrodes is implemented for urethral resistance. Thus, further testing is needed.

Development of a neurotechnological system for relieving phantom limb pain using transverse intrafascicular electrodes (TIME)

Phantom limb pain (PLP) is a chronic condition that develops in the majority of amputees. The underlying mechanisms are not completely understood, and thus, no treatment is fully effective. Based on recent studies, we hypothesize that electrical stimulation of afferent nerves might alleviate PLP by giving sensory input to the patient if nerve fibers can be activated selectively. The critical component in this scheme is the implantable electrode structure. We present a review of a novel electrode concept to distribute highly selective electrode contacts over the complete cross section of a peripheral nerve to create a distributed activation of small nerve fiber ensembles at the fascicular level, the transverse intrafascicular multichannel nerve electrode (TIME). The acute and chronic implantations in a small animal model exhibited a good surface and structural biocompatibility as well as excellent selectivity. Implantation studies on large animal models that are closer to human nerve size and anatomical complexity have also been conducted. They proved implant stability and the ability to selectively activate nerve fascicles in a limited proximity to the implant. These encouraging results have opened the way forward for human clinical trials in amputees to investigate the effect of selective electrical stimulation on PLP.

Non-invasive method for selection of electrodes and stimulus parameters for FES applications with intrafascicular arrays

High-channel-count intrafascicular electrode arrays provide comprehensive and selective access to the peripheral nervous system. One practical difficulty in using several electrode arrays to evoke coordinated movements in paralyzed limbs is the identification of the appropriate stimulation channels and stimulus parameters to evoke desired movements. Here we present the use of a six degree-of-freedom load cell placed under the foot of a feline to characterize the muscle activation produced by three 100-electrode Utah Slanted Electrode Arrays (USEAs) implanted into the femoral nerves, sciatic nerves, and muscular branches of the sciatic nerves of three cats. Intramuscular stimulation was used to identify the endpoint force directions produced by 15 muscles of the hind limb, and these directions were used to classify the forces produced by each intrafascicular USEA electrode as flexion or extension. For 451 USEA electrodes, stimulus intensities for threshold and saturation muscle forces were identified, and the 3D direction and linearity of the force recruitment curves were determined. Further, motor unit excitation independence for 198 electrode pairs was measured using the refractory technique. This study demonstrates the utility of 3D endpoint force monitoring as a simple and non-invasive metric for characterizing the muscle-activation properties of hundreds of implanted peripheral nerve electrodes, allowing for electrode and parameter selection for neuroprosthetic applications.

Microscale Electrode Implantation during Nerve Repair

The authors' goal is to develop a peripheral nerve electrode with long-term stability and fidelity for use in nerve/machine interfaces. Microelectromechanical systems use silicon probes that contain multichannel actuators, sensors, and electronics. The authors tested the null hypothesis that implantation of microelectromechanical systems probes does not have a detrimental effect on peripheral nerve function or regeneration. A rat hind-limb, peroneal nerve model was used in all experimental groups: intact nerve (control group, n=10); nerve division and repair (repair group, n=9); and nerve division, insertion of microelectromechanical systems probe, and repair (repair plus probe group, n=9). Nerve morphology, nerve to compound muscle action potential studies, walking tracks, and extensor digitorum longus muscle function tests were evaluated following an 80-day recovery. Repair and repair plus probe showed no differences in axon count, axon size, percentage nonneural area, compound muscle action potential amplitude, latency, muscle mass, muscle force, or walking track scores. Although there was some local fibrosis around each microelectromechanical systems probe, this did not lead to measurable detrimental effects in any anatomical or functional outcome measurements. The absence of a significant difference between the repair and the repair plus probe groups regarding histology, compound muscle action potential, walking tracks, and muscle force suggests that microelectromechanical systems electrodes are compatible with regenerating axons and show promise for establishing chemical and electrical interfaces with peripheral nerves.

Diamond-on-Polymer Microelectrode Arrays Fabricated Using a Chemical Release Transfer Process

This paper reports the design, fabrication, and characterization of diamond-on-polymer microelectrode arrays. A “diamond-first” chemical release transfer process was implemented to integrate diamond electrodes, grown at temperatures >; 700 °C, on a temperature-sensitive polynorbornene-based (PNB) substrate, allowing for the advantageous neural interfacing properties of diamond to be utilized in a flexible device. Intracortical probes with two electrodes and peripheral nerve electrode arrays with ten electrodes ranging in area from 800 to 41 000 μm2 were fabricated. Mechanical testing showed that the structures were flexible, with the composite structure having mechanical characteristics similar to bare PNB. Electrical testing confirmed that ohmic contacts were formed without a postanneal step and determined a diamond-on-polymer electrode impedance of ~ 1.5 MΩ at 1 kHz.

Hierarchical beamformer and cross-talk reduction in electroneurography

Electroneurography (ENG) is a method of recording neural activity within nerves. Using nerve electrodes with multiple contacts the activation patterns of individual neuronal fascicles can be estimated by measuring the surface voltages induced by the intraneural activity. The information about neuronal activation can be used for functional electric stimulation (FES) of patients suffering from spinal chord injury, or to control a robotic prosthetic limb of an amputee. However, the ENG signal estimation is a severely ill-posed inverse problem due to uncertainties in the model, low resolution due to limitations of the data, geometric constraints and the difficulty in separating the signal from biological and exogenous noise. In this paper, a reduced computational model for the forward problem is proposed, and the ENG problem is addressed by using beamformer techniques. Furthermore, we show that using a hierarchical statistical model, it is possible to develop an adaptive beamformer algorithm that estimates directly the source variances rather than the voltage source itself. The advantage of this new algorithm, e.g., over a traditional adaptive beamformer algorithm, is that it allows a very stable noise reduction by averaging over a time window. In addition, a new projection technique for separating sources and reducing cross-talk between different fascicle signals is proposed. The algorithms are tested on a computer model of realistic nerve geometry and time series signals.

Comparative analysis of transverse intrafascicular multichannel, longitudinal intrafascicular and multipolar cuff electrodes for the selective stimulation of nerve fascicles

The selection of a suitable nerve electrode for neuroprosthetic applications implies a trade-off between invasiveness and selectivity, wherein the ultimate goal is achieving the highest selectivity for a high number of nerve fascicles by the least invasiveness and potential damage to the nerve. The transverse intrafascicular multichannel electrode (TIME) is intended to be transversally inserted into the peripheral nerve and to be useful to selectively activate subsets of axons in different fascicles within the same nerve. We present a comparative study of TIME, LIFE and multipolar cuff electrodes for the selective stimulation of small nerves. The electrodes were implanted on the rat sciatic nerve, and the activation of gastrocnemius, plantar and tibialis anterior muscles was recorded by EMG signals. Thus, the study allowed us to ascertain the selectivity of stimulation at the interfascicular and also at the intrafascicular level. The results of this study indicate that (1) intrafascicular electrodes (LIFE and TIME) provide excitation circumscribed to the implanted fascicle, whereas extraneural electrodes (cuffs) predominantly excite nerve fascicles located superficially; (2) the minimum threshold for muscle activation with TIME and LIFE was significantly lower than with cuff electrodes; (3) TIME allowed us to selectively activate the three tested muscles when stimulating through different active sites of one device, both at inter- and intrafascicular levels, whereas selective activation using multipolar cuff (with a longitudinal tripolar stimulation configuration) was only possible for two muscles, at the interfascicular level, and LIFE did not activate selectively more than one muscle in the implanted nerve fascicle.

Effects of chronic sympatho-inhibition on renal excretory function in renovascular hypertension

Treatment of renovascular hypertension with drugs that directly target the renin-angiotensin system may compromise glomerular filtration and renal excretory function, leading to renal failure. Centrally acting sympathoinhibitory agents also inhibit the renin-angiotensin system, so we determined whether this treatment modality alters renal excretory function in rabbits with renovascular hypertension. Rabbits were equipped with bilateral renal artery flow probes and a renal nerve electrode. Hypertension was induced with a renal artery clip (2K1C) or rabbits were sham-clipped. After 2 weeks, a subcutaneous minipump was implanted to deliver rilmenidine (2.5 mg/kg per day) or vehicle for 3 weeks. Haemodynamic variables and renal function were studied under control conditions and during intravenous infusion of isotonic saline (154 mmol/l NaCl) at increasing rates of 4, 12 and 36 ml/kg per hour. Mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) were greater in 2K1C rabbits than sham-clipped rabbits, but total urine flow, sodium excretion and glomerular filtration rate were similar in the two groups. In 2K1C rabbits, rilmenidine reduced MAP to close to control levels and reduced RSNA (40%), but did not significantly alter basal renal blood flow, glomerular filtration rate, urine flow or sodium excretion. The natriuretic response to isotonic saline load in 2K1C rabbits was not significantly altered by rilmenidine. These observations show that chronic treatment of rabbits with renal artery stenosis with a centrally acting sympathoinhibitory agent, despite normalizing MAP, does not compromise renal excretory function. Thus, this treatment modality may be particularly useful in renovascular hypertension.

Separated interface nerve electrode prevents direct current induced nerve damage

Direct current, DC, can be used to quickly and reversibly block activity in excitable tissue, or to quickly and reversibly increase or decrease the natural excitability of a neuronal population. However, the practical use of DC to control neuronal activity has been extremely limited due to the rapid tissue damage caused by its use. We show that a separated interface nerve electrode, SINE, is a much safer method to deliver DC to excitable tissue and may be valuable as a laboratory research tool or potentially for clinical treatment of disease.

Design, fabrication and evaluation of a conforming circumpolar peripheral nerve cuff electrode for acute experimental use

Nerve cuff electrodes are a principle tool of basic and applied electro-neurophysiology studies and are championed for their ability to achieve good nerve recruitment with low thresholds. We describe the design and method of fabrication for a novel circumpolar peripheral nerve electrode for acute experimental use. This cylindrical cuff-style electrode provides approximately 270° of radial electrode contact with a nerve for each of an arbitrary number of contacts, has a profile that allows for simple placement and removal in an acute nerve preparation, and is designed for adjustment of the cylindrical diameter to ensure a close fit on the nerve. For each electrode, the electrical contacts were cut from 25 μm platinum foil as an array so as to maintain their positions relative to each other within the cuff. Lead wires were welded to each intended contact. The structure was then molded in silicone elastomer, after which the individual contacts were electrically isolated. The final electrode was curved into a cylindrical shape with an inner diameter corresponding to that of the intended target nerve. The positions of these contacts were well maintained during the molding and shaping process and failure rates during fabrication due to contact displacements were very low. Established electrochemical measurements were made on one electrode to confirm expected behavior for a platinum electrode and to measure the electrode impedance to applied voltages at different frequencies. These electrodes have been successfully used for nerve stimulation, recording, and conduction block in a number of different acute animal experiments by several investigators.

Use of an Experimentally Derived Leadfield in the Peripheral Nerve Pathway Discrimination Problem

The task of discriminating the neural pathways responsible for the activity recorded using a multi-contact nerve cuff electrode has recently been approached as an inverse problem of source localization, similar to EEG source localization. A major drawback of this method is that it requires a model of the nerve, and that the localization performance is highly dependent on the accuracy of this model. Using recordings from a 56-contact "matrix" cuff electrode placed on a rat sciatic nerve, we investigated a method that eliminates the need for a model, and uses instead an "experimental" leadfield constructed from a training set of experimental recordings. The resulting pathway-identification task is solved using an inverse problem framework. The experimental leadfield approach was able to identify the correct branch in cases in which a single fascicle was active with a success rate of 94.2%, but was not able to reliably identify combinations of fascicles. Nevertheless, the proposed methodology provides a framework for the study of multi-pathway discrimination, within which methods to improve performance can be investigated. Specifically, the influence of nerve anatomy and electrode design should be examined, and regularization approaches better suited to this novel inverse problem should be sought.

Neuronal nitric oxide synthase within paraventricular nucleus: blood pressure and baroreflex in two‐kidney, one‐clip hypertensive rats

The renin-angiotensin system is activated in the early phase of two-kidney, one-clip (2K-1C) hypertension. The paraventricular nucleus (PVN) integrates inputs regulating sympathetic outflow. The PVN receives inputs from plasma angiotensin II via projections from circumventricular organs and from renal afferent nerves transmitted via the nucleus tractus solitarii. Nitric oxide within the PVN may exert a sympathoinhibitory effect. These studies tested whether decreasing endogenous nitric oxide by introducing dominant negative (DN) constructs for neuronal nitric oxide synthase (nNOS) into PVN chronically augments hypertension and/or modulates baroreflex function. Male 6-week-old Sprague-Dawley rats underwent sham surgery or right renal artery clipping and placement of radiotelemetry transmitters. One week later, the PVN was injected bilaterally with 250 nl artificial cerebrospinal fluid containing 250 ng microl(-1) of RSV beta-galactosidase (beta-Gal), cytomegalovirus (CMV) wild-type (WT nNOS), or respiratory syncytial virus (RSV) haeme domain or RSV haemeRedF (DN nNOS). Haemodynamics were monitored for 5 weeks. Then left renal nerve electrodes were placed, and 2 days later the rats underwent baroreflex testing in the conscious state. The rise in mean arterial pressure (MAP) was significantly potentiated in the DN nNOS 2K-1C group beyond 15 days after PVN injection. By day 35, MAP in the 2K-1C groups was 152 +/- 6.3 (beta-Gal), 155.1 +/- 6.6 (WT nNOS) and 179 +/- 5.4 mmHg (DN nNOS; P < 0.01 versus all other groups). Sham-clipped rats remained normotensive. All groups displayed progressive bradycardia over time that was attenuated in the DN nNOS 2K-1C group. Baroreflex curves shifted to higher pressures, and baroreflex sensitivity of heart rate was diminished to a similar extent in all groups of 2K-1C rats. The baroreflex response of renal sympathetic nerve activity was preserved. The PVN tissue from DN nNOS rats had decreased dimerization of nNOS and generation of total nitric oxide. These findings indicate that chronic interference of nNOS dimerization required for generation of nitric oxide within the PVN potentiates the increase of blood pressure by modulating the sympathoexcitation that accompanies renovascular hypertension.