Inhibition of experimental seizures in canines by repetitive vagal stimulation.

Repetitive electrical stimulation of the canine cervical vagus nerve interrupts or abolishes motor seizures induced by strychnine and tremors induced by pentylenetetrazol (PTZ). Tremors were defined as rhythmic alternating contractions of opposing muscle groups, exerting much less force than seizure contractions. Seizures were induced by injection boluses of strychnine or PTZ at 1- to 4-min intervals until sustained muscle activity was observed electromyographically (EMG). Vagal stimulation terminated seizures in 0.5-5 s. There were prolonged periods with no spontaneous EMG activity after stimulation. The period of protection was approximately four times the stimulation period. The antiseizure actions of vagal stimulation were not altered by transection of the vagus distal to the stimulating electrode. Optimal stimulus parameters were estimated: strength, approximately 20 V (electrode resistance 1-5 omega); frequency 20-30 Hz; duration, approximately 0.2 ms. These data suggest that the antiseizure effects derive from stimulation of small-diameter afferent unmyelinated fibers in the vagus nerve. These results may form the basis of a new therapeutic approach to epilepsy.

The implantable neurocybernetic prosthesis system.

The neurocybernetic prosthesis system (NCP) is an implantable, multiprogrammable pulse generator that delivers constant current electrical signals to the vagus nerve for the purpose of reducing the frequency and severity of epileptic seizures. The signals are delivered on a predetermined schedule, or may be initiated by the patient with an external magnet. The device is implanted in a subcutaneous pocket in the chest just below the clavicle, similar to pacemaker placement. The stimulation signal is transmitted from the prosthesis to the vagus nerve through a lead connected to an electrode which is a multi-turn silicone helix, with a platinum band on the inner turn of one helix. The prosthesis can be programmed with any IBM- compatible personal computer using NCP software and a programming wand.

An implantable neurocybernetic prosthesis system.

The neurocybernetic prosthesis (Cyberonics, Inc.) is an implantable, multiprogrammable pulse generator that delivers constant current electrical signals to the vagus nerve for the purpose of reducing the frequency and/or severity of epileptic seizures. The device is implanted in a subcutaneous chest pocket just below the clavicle, similar to cardiac pacemaker placement. The stimulation signal is transmitted from the prosthesis to the vagus nerve through a stimulation lead. The prosthesis can be programmed using any IBM-compatible personal computer with programming software and a programming wand. The electrodes used in the first group of patients were found to break at an unacceptable rate. Design modifications appear to have resolved this problem.

Neuroinhibition of xylazine induced emesis.

Xylazine produces retching and vomiting presumably by activation of the chemoreceptor trigger zone (CTZ). The purpose of this project was to investigate whether neuroinhibition can prevent xylazine vomiting. Inhibitory neurons in the cervical vagus nerve of cats were stimulated with implanted cuff electrodes. Female cats, weighing from 3 to 4 kg, were anaesthetized with pentobarbital for surgical implantation of electrodes. After full recovery from surgery, animals were tested in weekly sessions. Stimulation was via a pulse generator connected to photon coupled linear isolator supplying constant current. Videotape was used to record observations. The range of effective stimulation was 1-10 ma, 4-100 Hz and 0.3-0.6 msec. Stimulation was initiated thirty sec. after subcutaneous injection of xylazine, 0.66 mg/kg. Stimulation of the inhibitory nerve group of the cervical vagus was effective in preventing vomiting in over 85% of the experimental trials. In addition to preventing emesis during stimulation, the latency of xylazine emesis was increased over control values. Repeated experimental trials of stimulation coupled with xylazine injection could result in the complete absence of emesis.