Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Expression of neuregulin and ErbB3 and ErbB4 after a traumatic lesion in the ventral funiculus of the spinal cord and in the intact primary olfactory system.
Neuron-derived neuregulins have been implicated in the regulation of glial cell function and survival. This factor family and its receptors may therefore be assumed to be of importance for the cellular response to traumatic injury. In this study we have examined the distribution of mRNA for neuregulin 1 (NRG1), ErbB3 and ErbB4-receptor tyrosine kinases after a ventral funiculus lesion in the lumbar spinal cord (VFL). ⋯ ErbB4 had strong expression in the embryonic spinal cord, but no evidence for lesion-induced regulation of ErbB4 receptors could be found after the VFL. Our data show that ErbB3 in the ventral roots was upregulated after a VFL and that NRG1 mRNA was initially downregulated in the motoneurons. The lesion-induced changes in the expression of NRG1 and ErbB3 in the injured spinal cord and denervated ventral root can be assumed to be of importance for axonal growth and the regulation of glial cell survival.
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Exposing rats to ether anaesthesia for 20 min induced a massive expression of c- fos like (FL) immunoreactivity in specific regions of the brain, including the basal ganglia. This expression of FL immunoreactivity in the basal ganglia was successfully blocked by local injections of muscimol (GABA(A) agonist) in the substantia nigra (SN). This model was used to investigate our recent finding that inhibition of caudal SN pars reticulata (SNpr) with muscimol is more potent in suppressing the motor component of tonic seizures than comparable inhibition of the rostral part. ⋯ In experiment II, rats were prepared with intracranial chronic cannulae through which the effects of muscimol (60 ng) injected unilaterally in either the rostral or caudal SNpr on c- fosexpression induced by ether were investigated. Injections in both sites caused remarkable suppression of the ether-induced c- fos throughout the ipsilateral SNpr; however, the rostral injection also inhibited the expression of c- fos in the STN, EPN and GP. The implications of these results for microinjection mapping studies of the SN are discussed.
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There is considerable evidence from studies on cats and monkeys that several cortical areas such as area 2v at the tip of the intraparietal sulcus, area 3av in the sulcus centralis, the parietoinsular vestibular cortex adjacent to the posterior insula (PIVC) and area 7 in the inferior parietal lobule are involved in the processing of vestibular information. Microelectrode recordings from these areas have shown that: (1) most of these cortical neurons are connected trisynaptically to the labyrinthine endorgans and (2) they receive converging vestibular, visual and somatosensory inputs. These data suggest that a multimodal cortical system is involved in postural and gaze control. ⋯ The latency period for the activation of five distinct cortical zones, including the prefrontal and/or the frontal lobe, the ipsilateral temporoparietal cortex, the anterior portion of the supplementary motor area (SMA) and the contralateral parietal cortex, was 6 ms. The short latency period recorded for each of these areas indicates that several trisynaptic pathways, passing through the vestibular nuclei and the thalamic neurons, link the primary vestibular afferents to the cortex. We suggest that all these areas, including the prefrontal area, process egomotion information and may be involved in planning motor synergies to counteract loss of equilibrium.
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Comparative Study
Differential response of synaptic zinc levels to sensory deprivation in the barrel cortex of young and adult mice.
The distribution of synaptic zinc after short-term (up to 48 h) tactile deprivation of vibrissae was investigated in the barrel cortex of mice using histochemical staining. In adult mice, 12 h after trimming selected rows of vibrissae, an increase in zinc staining in the deprived barrels was observed. This increase was still present 48 h after trimming. ⋯ In young (8-day-old) mice, the short-term deprivation did not alter zinc staining and only chronic sensory deprivation produced an increase in zinc staining. However, after long-term deprivation no changes were found in adult mice. These results suggest that different mechanisms might be involved in functional reorganization of zinc containing terminals in young and fully mature cerebral cortex.
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Mechanical changes underlying spastic hypertonia were explored using a parallel cascade system identification technique to evaluate the relative contributions of intrinsic and reflex mechanisms to dynamic ankle stiffness in healthy subjects (controls) and spastic, spinal cord injured (SCI) patients. We examined the modulation of the gain and dynamics of these components with ankle angle for both passive and active conditions. Four main findings emerged. ⋯ At full plantarflexion, there was no difference between SCI and control subjects; in the mid-range, reflex stiffness was abnormally high in SCI patients; at full dorsiflexion, both reflex and intrinsic stiffness were larger than normal. Fourth, differences between SCI and control subjects were smaller during the active than the passive condition, because intrinsic stiffness increased more in controls than SCI subjects; nevertheless, reflex gain remained abnormally high in SCI patients. These results elucidate the nature and origins of the mechanical abnormalities associated with hypertonia and provide a better understanding of its functional and clinical implications.