Abstract
The chronic effects of electrical stimulation in unrestrained awake rodents are best studied with a wireless neural stimulator that can operate unsupervised for several weeks or more. A robust, inexpensive, easily built, cranially implantable stimulator was developed to explore the restorative effects of brainstem stimulation after neurotrauma. Its connectorless electrodes directly protrude from a cuboid epoxy capsule containing all circuitry and power sources. This physical arrangement prevents fluid leaks or wire breakage and also simplifies and speeds implantation. Constant-current pulses of high compliance (34 volts) are delivered from a step-up voltage regulator under microprocessor control. A slowly pulsed magnetic field controls activation state and stimulation parameters. Program status is signaled to a remote reader by interval-modulated infrared pulses. Capsule size is limited by the two batteries. Silver oxide batteries rated at 8 mA-h were used routinely in 8 mm wide, 15 mm long and 4 mm high capsules. Devices of smaller contact area (5 by 12 mm) but taller (6 mm) were created for mice. Microstimulation of the rat's raphe nuclei with intermittent 5-min (50% duty cycle) trains of 30 μA, 1 ms pulses at 8 or 24 Hz frequency during 12 daylight hours lasted 21.1 days ±0.8 (mean ± standard error, Kaplan-Meir censored estimate, n = 128). Extended lifetimes (>6 weeks, no failures, n = 16) were achieved with larger batteries (44 mA-h) in longer (18 mm), taller (6 mm) capsules. The circuit and electrode design are versatile; simple modifications allowed durable constant-voltage stimulation of the rat's sciatic nerve through a cylindrical cathode from a subcutaneous pelvic capsule. Devices with these general features can address in small mammals many of the biological and technical questions arising neurosurgically with prolonged peripheral or deep brain stimulation.
Highlights
Deep brain stimulation (DBS) is used in man to block the ongoing symptoms of various chronic neurological disorders, most commonly the tremor of Parkinson’s disease and related forebrain disorders (Kringelbach et al, 2010; Oluigbo et al, 2012; Lozano and Lipsman, 2013)
In one series (n = 58), stimulation was applied for 7 days through platinum– iridium microelectrodes to the midbrain’s dorsal raphe or median raphe (Carballosa Gonzalez et al, 2013)
In the third series, 1 week (n = 20) or 3 weeks (n = 12) of stimulation was delivered through the tungsten microelectrodes to the midbrain periaqueductal gray matter, beginning 0, 2, or 21 days after implantation
Summary
Deep brain stimulation (DBS) is used in man to block the ongoing symptoms of various chronic neurological disorders, most commonly the tremor of Parkinson’s disease and related forebrain disorders (Kringelbach et al, 2010; Oluigbo et al, 2012; Lozano and Lipsman, 2013). Strong stimulation may produce harmful effects such as seizure foci (Albensi et al, 2007) or chemical, thermal and mechanical damage at the electrode-tissue interface (Cogan, 2008). Studying such effects over long periods in animal models is best done with implantable wireless stimulators. The main alternative is to tether the animal by electrically conducting cables to an external pulse generator, either continuously or for several hours daily, which risks breakage or entanglement of the intervening wires and distress to the subject
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