SummaryElectrophysiological techniques provide an objective and non-invasive measure of neurological function. In order to undertake detailed evoked potential studies in rats on repeated occasions, it is necessary to find an appropriate anaesthetic agent which has minimal and reproducible effects on the parameters to be studied and also has a minimal effect on the general welfare of the animals. In this study we compared the effects of four common anaesthetic agents (ketamine-xylazine, medetomidine, isoflurane and fentanyljfluanisonemidazolam) on somatosensory evoked potentials (SEPs) in rats following electrical stimulation of the fore-and hind-paw. Fentanyljfluanisone-midazolam was found to be well tolerated by the animals and to have, in general, the least deleterious effect on SEPs. For example, the response recorded at the level of the somatosensory cortex (PIL following forelimb stimulation, appeared on average 1.80 ms earlier with fentanyljfluanisonemidazolam than with the other agents and the peak-to-peak amplitude (CI to CII) of the response recorded at the cervical (C31level was on average 5.86,..LV greater with fentanyljfluanisone-midazolam.Fentanyljfluanisone-midazolam is, therefore, recommended as the anaesthetic of choice for longitudinal studies of SEPs in the rat.
In mammals, severe and chronic deficiency of vitamin E (α-tocopherol) is associated with a characteristic neurological syndrome. Previously, we have shown that this syndrome is accompanied by electrophysiological abnormalities of neural and visual function. To investigate the molecular basis of the observed abnormalities, we used microarrays to monitor the expression of ∼14,000 genes in the cerebral cortex from rats which had received diets containing 0, 1.25 and 5.0 mg/kg diet of all-rac-α-tocopheryl acetate for 14 months. Compared to the groups receiving 1.25 and 5.0 mg/kg α-tocopheryl acetate, a total of 11 genes were statistically significantly upregulated (≧1.3-fold) and 34 downregulated (≤1.3-fold) in the vitamin E-deficient group. Increased expression was observed for the genes encoding the antioxidant enzyme catalase and the axon guidance molecule tenascin-R, while decreased expression was detected for genes encoding protein components of myelin and determinants of neuronal signal propagation. Thus our observations suggest that vitamin E deficiency results in transcriptional alterations in the cerebral cortex of the rat which are consistent with the observed neurological and electrophysiological alterations.
A rat model of vitamin E (alpha-tocopherol) deficiency with similar "clinical," electrophysiological, and neuropathological abnormalities to those seen in man was used to investigate the effects of various amounts and forms of alpha-tocopheryl acetate (alphaTA) on neural and visual function. Electrophysiological techniques provide an objective, non-invasive measure of neural and visual function. These techniques were used in the animal model to determine the minimum dietary requirement of vitamin E necessary to prevent neural and visual abnormalities. They were also used to compare the biological activities of the natural (RRR-) and synthetic (all-rac-) forms of alpha-tocopherol in neural tissues. The results were as follows: (1) Significant differences in neural and visual function were observed between deficient and control rats after approximately 8 months. (2) An intake of 1.0 mg/kg all-rac- or 0.75 mg/kg RRR-alphaTA was observed to marginally protect nerves from vitamin E deficiency. (3) The biological activity of all-rac-alpha-tocopherol in neural tissues was approximately 75% of RRR-alpha-tocopherol. (4) The concentration of free malondialdehyde (an indicator of lipid peroxidation) was significantly increased in tissues from the deficient compared to the control animals. These results are consistent with a deficiency of alpha-tocopherol causing increased lipid peroxidation leading to abnormal neural electrophysiology. They could also be explained by more specific but as yet undefined function(s) of alpha-tocopherol in neural tissues.
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