Brain ablation in the rat cerebral cortex using a tunable-free electron laser.

BACKGROUND AND OBJECTIVES: We used the MARK III free electron laser (FEL) tuned to molecular vibrational absorbance maxima in the infrared (IR) wavelength range of 3.0-6.45 microm to study the effect of these various wavelengths and a power level of 5 mJ/2 microseconds macropulse on photoablation of CNS tissue. STUDY DESIGN/MATERIALS AND METHODS: Laser lesions were produced in the parietal cortex of anesthetized rats using thermal confined mid-IR (infrared) laser pulses tuned to the -OH, -CH, amide 1, and amide 2 absorbance bands. Histological assessments following recovery periods of 4 hours, 4 days, and 3 weeks were performed to determine the size, shape, and character of the photoablative lesions. Cell density studies were done in adjacent edematous tissue. RESULTS: Significant differences in lesion size and shape were observed as a function of wavelength. Although maximum ablation and collateral damage seemed to coincide with spectral peaks in the mid-IR, area and depth/width ratios did not. CONCLUSIONS: It was found in these experiments that wavelengths in the mid-IR could be selected for optimal ablative properties. Using tunable, high-peak-power pulsed lasers, it will be possible to produce well-defined photoablative lesions that conform to small, irregularly shaped neurosurgical targets.

Exposure of the dorsal root ganglion in rats to pulsed radiofrequency currents activates dorsal horn lamina I and II neurons.

OBJECTIVE: Application of pulsed radiofrequency (RF) currents to the dorsal ganglion has been reported to produce long-term relief of spinal pain without causing thermal ablation. The present study was undertaken to identify spinal cord neurons activated by exposure of the dorsal ganglion to pulsed RF currents in rats. METHODS: Left-sided hemilaminectomy was performed in adult Sprague-Dawley rats to expose the C6 dorsal root ganglion. An RF electrode (0.5 mm diameter) with a thermocouple for temperature monitoring was positioned on the exposed ganglion, and rats were assigned to one of three treatment groups: pulsed RF treatment (20 ms of 500-kHz RF pulses delivered at a rate of 2 Hz for 120 s to produce tissue heated to 38 degrees C), continuous RF (continuous RF currents for 120 s to produce tissue heated to 38 degrees C), or sham treatment (no RF current; electrode maintained in contact with ganglion for 120 s). RESULTS: Treatment with pulsed RF but not continuous RF was associated with a significant increase in the number of cFOS-immunoreactive neurons in the superficial laminae of the dorsal horn as observed 3 hours after treatment. CONCLUSION: Exposure of the dorsal ganglion to pulsed RF currents activates pain-processing neurons in the dorsal horn. This effect is not mediated by tissue heating.

Self-mutilation following brachial plexus injury sustained at birth.

Self-mutilation after deafferentation injuries has been reported only rarely in adult humans. This behavior has been found to be similar to that observed in animals that have been subjected to experimental deafferentation. We present a child with a brachial plexus injury sustained at birth who began to bite her analgesic digits. Self-mutilation behavior in humans is reviewed and its relevance to current deafferentation pain animal models is examined. This behavior in humans further validates the current animal model of deafferentation pain.

The expression of a deafferentation syndrome in the Sprague-Dawley rat: effects of frontoparietal cortical lesions.

Forelimb sensorimotor (SMI) cortical lesions in the rat have been found to suppress a deafferentation syndrome which follows C5-T2 ganglionectomy/avulsion whether the cortical lesions were made prior to, or several days after, the dorsal root lesions. None of the 6 rats with only frontoparietal lesions developed a deafferentation syndrome. These results may be influenced by the presence of a sensorimotor amalgam in the parietal cortex of the rat.

Deafferentation hypersensitivity in the rat after dorsal rhizotomy: a possible animal model of chronic pain.

Unilateral dorsal rhizotomies were done at the cervicothoracic and lumbosacral spinal cord levels in rats. In preliminary experiments dermatome maps were determined for the roots to be sectioned. The behavior of 37 rats was observed for many months after the rhizotomies. The rats with the dorsal roots sectioned in the cervicothoracic spinal cord exhibited the following behavior: at the border of the skin adjacent to the zone of deafferentation, the rat scratched vigorously and progressively denuded the skin; self-mutilation of varying degrees occurred in the deafferented limb. In some animals scratching occurred in the contralateral skin dermatome opposite to the partially deafferented zone. The rats with the dorsal roots sectioned at the lumbosacral level exhibited hypersensitivity to cutaneous stimulation but there was no scratching or self-mutilation. These results are discussed in the light of previous similar research.