Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Reaching to grasp is of fundamental importance to primate motor behavior. One descending motor pathway that contributes to the control of this behavior is the rubrospinal tract. An important source of origin of the rubrospinal tract is the magnocellular red nucleus (RNm). ⋯ RNm neurons of our sample were activated strongly during reach-to-grasp, and discharge of a third of the neurons tested depended on the spatial location of the object grasped. Discharge of RNm neurons and EMG activity of many of the distal and proximal forelimb muscles we tested were larger for reaching to grasp in the upper and/or right than lower and left target locations. Based on comparisons of each individual neuron's discharge patterns during reaches with and without preshaping the hand, we conclude that target location-dependent modulations in discharge rate of the majority of RNm neurons whose discharge differed for reaching to grasp in the four target locations contributed to aspects of hand preshaping that covaried with reach direction.
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Triggering of balance corrections may depend on both leg and trunk proprioceptive inputs. To study this issue and to determine how a total proprioceptive loss in the legs (ToLPL) would affect postural reactions in different directions, we investigated the postural control of a patient with a long-standing dorsal root ganglionopathy. This patient had absent stretch reflexes at the ankle and knee joints, delayed reflexes at the hips, but normal muscle strength. ⋯ The lack of trunk flexibility and lateral instability this produced for roll tilts was offset by the ability to compensate by using a hitherto not described "deactivation response" strategy. The patient had a clinical picture usually described as "deafferented"; yet our roll tilt perturbations revealed delayed reflex responses in hip muscles. With vestibulospinal and neck-proprioceptive inputs, these responses may have helped with the development of compensation processes for the total leg proprioceptive deficit.
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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.