The Effect of Graded Spinal Cord Injury on the Extrapyramidal and Pyramidal Motor Evoked Potentials of the Rat

Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of long-term supraspinal control over spinal cord function. Primates and rats can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) the H-reflex when reward is based on H-reflex amplitude. An earlier study indicated that HRdown conditioning of the soleus H-reflex in rats is impaired following contusion injury to thoracic spinal cord. The extent of impairment was correlated with the percent of white matter lost at the injury site. The present study investigated the effects of spinal cord injury on HRup conditioning. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from 14 rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. At the lesion epicenter, 12-39% of the white matter remained. After control-mode data were collected, each rat was exposed to the HRup conditioning mode for 50 days. Final H-reflex amplitudes after HRup conditioning averaged 112% (+/-22% SD) of control. This value was significantly smaller than that for 13 normal rats exposed to HRup conditioning, in which final amplitude averaged 153% (+/-51%) SD of control. As previously reported for HRdown conditioning after spinal cord injury, success was inversely correlated with the severity of the injury as assessed by white matter preservation and by time to return of bladder function. HRup and HRdown conditioning are similarly sensitive to injury. These results further demonstrate that H-reflex conditioning is a sensitive measure of the long-term effects of injury on supraspinal control over spinal cord functions and could prove a valuable measure of therapeutic efficacy.

Section: Potential Usefulness Of H-reflex Conditioningmentioning

confidence: 99%

Operant Conditioning of H-Reflex Increase in Spinal Cord–Injured Rats

Chen

Wolpaw²,

Jakeman³

et al. 1999

“…MEPs and SEPs are measures of conduction in descending and ascending spinal cord pathways. They can be used to assess the integrity of spinal cord pathways after injury (Levy et al, 1986(Levy et al, ,1987 Simpson and Baskin, 1987; Fehlings et al, 1987Fehlings et al, , 1989Mutoh et al, 1991;Shiau et al, 1992). In contrast, Hreflex conditioning, although requiring appropriate activity in descending pathways, focuses on the segmental response to that activity.…”

Section: Potential Usefulness Of H-reflex Conditioningmentioning

confidence: 99%

Operant Conditioning of H-Reflex in Spinal Cord-Injured Rats

Chen

Wolpaw²,

Jakeman³

et al. 1996

Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of supraspinal control over spinal cord function. Both rats and primates can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) soleus H-reflex magnitude when exposed to an operant conditioning task. This study used H-reflex operant conditioning to assess and modify spinal cord function after injury. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. From 18 to 140 days after injury, background EMG, M response amplitude, and initial H-reflex amplitude were not significantly different from those of normal rats. HRdown conditioning was successful in some, but not all, spinal cord-injured rats. The H-reflex decrease achieved by conditioning was inversely correlated with the severity of the injury as assessed histologically or by time to return of bladder function. It was not correlated with the length of time between injury and the beginning of conditioning. The results confirm the importance of descending control from supraspinal structures in mediating operantly conditioned change in H-reflex amplitude. In conjunction with recent human studies, they suggest that H-reflex conditioning could provide a sensitive new means for assessing spinal cord function after injury, and might also provide a method for initiating and guiding functional rehabilitation.

Functional and Electrophysiological Characterization of Photochemical Graded Spinal Cord Injury in the Rat

García-Alías

Verdú²,

Forés³

et al. 2003

This study characterizes by functional and electrophysiological methods changes following photochemically induced injuries to the spinal cord in adult rats. The spinal cord was exposed by laminectomy and bathed with 1.5% rose bengal solution for 10 min (T12-L1 vertebrae). The excess dye was removed by saline rinse and the spinal cord was irradiated with "cold" light for 0, 1, 2.5, 5, and 10 min in different groups of rats. During the first 15 days postlesion, locomotion activity, pain sensibility, motor and somatosensory evoked potentials, and motor and nerve action potentials were evaluated. Graded locomotor and nociceptive recovery was observed in irradiated rats depending on the photoinduction time. At 15 days, the amplitude of motor and sensory evoked potentials was significantly lower in irradiated groups with respect to control rats. The amplitude of compound muscle action potentials and of reflex H wave after sciatic nerve stimulation decreased significantly in irradiated animals with respect to control rats, while the latency did not show significant differences. In irradiated groups, significant differences were seen between pre- and postoperative values for most functional and electrophysiological parameters analyzed. A significant negative relationship was found between the area of cystic cavity of the spinal cord and the functional and electrophysiological impairment.