Changes of somatosensory evoked potentials with increase of intracranial pressure in the rat's brain

Effects of hypodynamia-hypokinesia on somatosensory evoked potentials in the rat

The aim of this study was to determine if a prolonged period (7 or 14 days) of hypodynamia-hypokinesia (HH) affects the conduction of afferent input and the cortical and spinal responsiveness. Acute recordings of cortical and spinal somatosensory evoked potentials (SEPs) were performed after stimulation of the sciatic nerve in control rats and in rats submitted to 7 or 14 days of HH. HH was obtained by unloading the hindquarter. HH induced some subtle modifications in the SEP characteristics. Latency was increased for the spinal and cortical SEPs after 7 days of HH, and restored after 14 days of HH. A decrease in the amplitude was observed after 14 days of HH for the cortical SEP only. At the end of the experiment, the compound action potential of the sciatic nerve was recorded in vitro in order to evaluate the mean conduction velocity. Results indicate that the nerve velocity was reduced after 14 days of HH. The results also suggest that sensory conduction and/or cortical and spinal excitability are changed after HH.

Collagenase-induced intrastriatal hemorrhage in rats results in long-term locomotor deficits

BACKGROUND AND PURPOSE. Previous studies have shown that injection of the metalloproteinase collagenase directly into the caudate nucleus of rats causes an intracerebral hemorrhage. The purpose of the present study is to determine functional deficits associated with a collagenase-induced hemorrhagic lesion of the striatum.

METHODS

Twelve adult rats received a 2-microL infusion of bacterial collagenase (0.5 U in saline) into the right striatum. The rotational response to apomorphine (1 mg/kg SC) administration was then examined at 1, 4, 7, 21, 35, and 70 days after the surgery. In addition to the rotational asymmetry studies, the initiation of stepping movements in each forelimb was determined 8 weeks after the collagenase injections. In the assessment of rotational asymmetry and stepping ability, an additional six control animals received unilateral injections of saline alone. After behavioral testing, brains were processed for neuropathological evaluation.

RESULTS

A net ipsilateral rotation was noted at all posthemorrhage time periods. The average rotational asymmetries on these days were 14.57 +/- 2.9, 20.33 +/- 2.7, 19.99 +/- 4.4, 18.95 +/- 4.9, 17.03 +/- 4.9, and 14.4 +/- 4.7, respectively (data expressed as mean clockwise rotations per 5 minutes +/- SEM). The average number of steps initiated by the forelimb ipsilateral and contralateral to the lesion was 28.3 +/- 2.1 steps per minute and 13.6 +/- 1.5 steps per minute, respectively. This difference between left and right forelimb stepping was stable and reproducible for 3 consecutive days. Histological studies revealed a long-lasting hematoma cavity surrounded by dense reactive gliosis in the striatum.

CONCLUSIONS

We conclude that collagenase-induced intrastriatal hemorrhage results in long-term locomotor deficits and is therefore a useful model for developing and assessing therapeutic approaches for the restoration of neurological function after intracerebral hemorrhage.

Serial recording of sensory evoked potentials: a noninvasive prognostic indicator in fulminant liver failure

Sensory evoked potentials are markedly changed in patients with fulminant liver failure. It is unknown, however, whether serial recordings of sensory evoked potentials provide useful prognostic informations for patient management in fulminant liver failure. Ninety recordings of bilateral median nerve-stimulated short- and long-latency sensory evoked potentials were performed in 25 patients with fulminant liver failure (9 patients spontaneously recovered and survived, 8 patients were referred to emergency liver transplantation and 8 patients died). In all nine survivors the cortical long-latency sensory evoked potential N70 peak was constantly detectable between 74 and 162 ms. In all eight patients who subsequently underwent liver transplantation and in seven of eight patients who died, loss of the N70 peak developed during the course of fulminant liver failure. In 4 of 15 patients who were selected for liver transplantation according to the King's College criteria, the N70 peak was constantly detectable. All four transplantation candidates spontaneously recovered and survived without transplantation. In contrast, eight patients never did fulfill the criteria for liver transplantation. Five of them with constantly detectable N70 peak recovered spontaneously. However, in the remaining three patients loss of the N70 peak developed, and they ultimately died. The probability of correct outcome prediction by sensory evoked potentials is superior to that based on clinical criteria alone (0.96 vs. 0.72). Therefore serial recording of sensory evoked potentials may help identify (a) a subgroup among liver transplantation candidates who may spontaneously recover without transplantation and (b) a subgroup of patients with severe brain dysfunction who should undergo early liver transplantation even though they do not fulfill King's College criteria.

Somatosensory evoked potentials and intracranial pressure during chronic dilatation of an artificial extraparenchymal space-occupying lesion in cats

Somatosensory evoked potentials (SEP) and intracranial pressure (ICP) were studied in cats, suffering from a chronic space-occupying lesion produced by enlargement of an epidural balloon over the left sensomotory cortex. Our study shows that latency alterations of SEP are not dependent on the degree of ICP. Additionally, the results obtained demonstrate that chronic space-occupying lesions cause continuous prolongation of SEP latencies, probably produced by atrophy of the compressed tissue. Regarding the clinical importance of SEP measurements, we concluded that they are not suitable for estimating the degree of ICP. However, they are useful to evaluate tissue damage caused by mass effects in the acute and chronic phase of various space-occupying processes.

Sensory evoked potentials for selective monitoring of the rat spinal cord: a cerebellar evoked potential to assess ventral cord integrity

The purpose of this study was to evaluate two types of ascending sensory evoked potentials (SEPs) in the rat and their capacity for selective monitoring of dorsal versus ventral spinal cord integrity. SEPs were elicited by direct sciatic nerve stimulation. A cerebellar evoked response was recorded over the paramedian lobule of the cerebellar hemisphere (CEPpml) while somatosensory evoked potentials (SSEPs) were simultaneously recorded over the sensorimotor cortex. All components of the CEPpml and SSEP except the longest latency positive waves were present in each animal. At stimulus intensities of 3 to 10 mA, no significant changes in latency of the peaks were observed, but amplitudes of the longer latency responses tended to increase throughout this stimulation range. Unilateral sciatic stimulation resulted in bilateral cortical responses, larger ipsilaterally for the CEPpml, and contralaterally for the SSEP. Selective spinal cord lesions demonstrated N9 and P14 of the CEPpml to be mediated primarily through the ventral spinal cord, while P14 and N19 of the SSEP were conducted primarily through the dorsal columns. Sectioning of the cerebellar peduncles abolished N9 and P14 of the CEPpml despite persistence of the SSEP. This study demonstrates that selective assessment of the ventral and dorsal spinal cord is possible in the rat by monitoring SEPs.