Retrograde cell degeneration in diencephalic and other structures after hemidecortication of rhesus monkeys

Ipsilesional and contralesional sensorimotor function after hemispherectomy: differences between distal and proximal function

Previous studies have reported mainly on contralesional somatosensory and motor function after hemispherectomy. So far, ipsilesional impairments have received little attention even though these have been reported in patients with less extensive lesions. In the current study we assessed ipsilesional and contralesional sensorimotor function in a group of 12 patients with hemispherectomy. In addition, we focused on differences between distal and proximal function and investigated several factors that may have contributed to individual differences between patients. The tests included tapping, force production, tactile double simultaneous stimulation, pressure sensitivity, passive joint movement sense and sensitivity to hot and cold. Ipsilesional impairments were found on all tests, except passive joint movement sense. Unexpectedly, no significant ipsilateral distal-proximal gradient was found for any of the measures. Both the removal of the diseased cerebral hemisphere and possible changes to the remaining brain structures may have affected ipsilesional sensorimotor function. Contralesional performance was impaired on all tests except for passive joint movement in the shoulder. The contralesional impairments were characterized by a distal-proximal gradient measured on all tests, except that of sensitivity to hot and cold. Distal function was always most impaired. The difference between distal and proximal motor function is in agreement with the established concepts of the motor pathways, with the motoneurons innervating proximal muscles receiving bilateral cortical and subcortical input. Age at onset of original brain damage correlated significantly with passive joint movement sense. Patients with known abnormalities to the remaining brain structures performed inferior on the tapping test only. No effect was found of the hemispheric side of removal.

Separate, parallel sensory and hedonic pathways in the mammalian somatosensory system

We propose that separate sensory and hedonic representations exist in each of the primary structures of the somatosensory system, including brainstem, thalamic and cortical components. In the dorsal horn of the spinal cord, the hedonic representation, which consists primarily of nociceptive-specific, wide dynamic range, and thermoreceptive neurons, is located in laminae I and II, while the sensory representation, composed primarily by low-threshold and wide dynamic range neurons, is found in laminae III through V. A similar arrangement is found in the caudal spinal trigeminal nucleus. Based on the available anatomical and electrophysiological data, we then determine the corresponding hedonic and sensory representations in the area of the dorsal column nuclei, ventrobasal and posterior thalamic complex, and cortex. In rodent primary somatosensory cortex, a hedonic representation can be found in laminae Vb and VI. In carnivore and primate primary and secondary somatosensory cortical areas no hedonic representation exists, and the activities of neurons in both areas represent the sensory aspect exclusively. However, there is a hedonic representation in the posterior part of insular cortex, bordering on retroinsular cortex, that receives projections from two thalamic areas in which hedonics are represented. The functions of the segregated components of the system are discussed, especially in relation to the subjective awareness of pain.

Visual pathways following cerebral hemispherectomy

The anatomical consequences of unilateral cerebral hemispherectomy in some animal models are reviewed. We have shown that the retinogenigulate pathway undergoes severe degenerative changes in hemispherectomized monkeys, greater than those shown in cats and we proposed that remaining retinal terminals to the dorsal lateral geniculate nucleus have little potential for conveying visual information any further. All subdivisions of the pulvinar undergo severe degeneration following hemispherectomy showing that the ascending tectofugal pathway is also shut off. On the other hand, the retina subserving the blind field is not depleted of ganglion cells which still send normal appearing terminals to the midbrain pretectum and superior colliculus. Visual information from the blind hemifield can thus gain access to the brain and could potentially reach the contralateral cerebral cortex through the midbrain commissure and possibly through thalamic commissural cells.

Grafts of fetal central nervous system tissue rescue axotomized Clarke's nucleus neurons in adult and neonatal operates

Many conditions are thought to contribute to neuron death after axotomy, including immaturity of the cell at the time of injury, inability to reestablish or maintain target contact, and dependence on trophic factors produced by targets. Exogenous application of neurotrophic factors and transplants of peripheral nerve and embryonic central nervous system (CNS) tissue temporarily rescue axotomized CNS neurons, but permanent rescue may require transplants that are normal targets of the injured neurons. We examined the requirements for survival of axotomized Clarke's nucleus (CN) neurons. Two months after hemisection of the spinal cord at the T8 segment, there was an ipsilateral 30% loss of neurons at the L1 segment in adult operates and a 40% loss in neonates. Transplants of embryonic spinal cord, cerebellum, and neocortex inserted into the T8 segment at the time of hemisection prevented virtually all of the cell death in both adults and neonates, but transplants of embryonic striatum were ineffective. None of the grafts prevented the somal atrophy of CN neurons caused by axotomy. Retrograde transport of fluoro-gold from the cerebellum demonstrated that 33% of all CN neurons at L1 project to the cerebellum, 50% of these died following a T8 hemisection, but all these projection neurons were rescued by a transplant of embryonic spinal cord. These results suggest that the rescue of axotomized CN neurons is relatively specific for the normal target areas of these neurons, but this specificity is not absolute and may depend on the distribution and synthesis of particular neurotrophic agents.

Ciliary neurotrophic factor prevents retrograde neuronal death in the adult central nervous system

The neurocytokine ciliary neurotrophic factor (CNTF) was described originally as an activity that supports the survival of neurons of the chicken ciliary ganglia in vitro. The widespread expression of CNTF and its principal binding protein, CNTF receptor alpha, in the central and peripheral nervous systems suggests a broader trophic role for this peptide. In the present study, we report that CNTF prevents axotomy-induced cell death of neurons in the anteroventral and anterodorsal thalamic nuclei of the adult rat. Using the polymerase chain reaction, we also demonstrate the presence of CNTF and CNTF receptor alpha mRNA in these same thalamic nuclei. The coincidence of CNTF and its receptor in a population of neurons responding to the factor suggests a paracrine function for CNTF. The present findings establish that CNTF has significant effects on neurons of the central nervous system in vivo and demonstrate that neurocytokines can prevent cell death in the adult central nervous system.

Serial changes in somatosensory evoked potentials following cerebral infarction

The relationship between somatosensory evoked potentials (SEPs) and recovery from stroke was investigated in 12 patients. All had suffered recent cerebral infarction. SEPs were performed within the first week, 6 weeks, 3 months and 6 months after stroke onset. Improvement of initially abnormal SEPs was maximal in the first 6 weeks and this correlated closely with the period of maximum clinical improvement. The results of this study suggest that the major effect of stroke on SEPs occurs acutely and is little affected by secondary degenerative processes.

Quantitative cytoarchitectural analysis of cellular degeneration in the dorsal lateral geniculate nuclei of cats and kittens with cerebral hemispherectomy

Quantitative morphometry was used to study the effects of maturationally dependent responses to brain trauma on the cytologic organization of the dorsal lateral geniculate nucleus (LGd). The left hemitelencephalon was removed in adult cats and in neonatal kittens and resultant changes in cell size and density were compared between these groups and with intact controls. Morphological changes were found bilaterally in all lesioned cats. Ipsilaterally, geniculate volume was reduced by 23% in kitten-lesioned cats and by 33% in adult-lesioned cats. The geniculate of both lesion groups contained fewer neurons in all laminae than did the nucleus of intact cats, but only the adult-lesioned cats showed a substantial increase in glial cell counts. Contralaterally, there was a tendency for a lower neuronal density in both lesion groups, but this was significant only for the A-laminae of adult-lesioned cats. Therefore, neonatal lesions spared more neurons bilaterally and produced minimal ipsilateral gliosis compared to the adult ablation. Results are discussed within the context of the "Gudden effect" which asserts that there is more retrograde degeneration in neonatal versus adult brain-lesioned animals.

Bilateral somatosensory evoked potentials in four patients with long-standing surgical hemispherectomy

Four patients were studied electrophysiologically 8 to 24 years after surgical removal of one cerebral hemisphere without damage to the striatum or diencephalon. Somatosensory evoked potentials (SEPs) to electrical stimulation of the median nerve on the left or right side were averaged and mapped out over the scalp. Stimulation on the side opposite to the missing hemisphere evoked brief P9 and P14 farfields and a slow N18 negative potential of 15- to 25-msec duration bilaterally. No additional focal response was detected over the remaining (ipsilateral) hemisphere for 60 msec after the stimulus. Because long-standing hemispherectomy entails massive retrograde degeneration of thalamocortical neurons, the preserved P14 and N18 responses must reflect neural activities generated below the thalamus that are volume conducted to the scalp bilaterally. The data clarify several current issues in the evaluation of SEP components.

There is less thalamic degeneration in neonatal-lesioned than in adult-lesioned cats after cerebral hemispherectomy

In order to study age-related processes of degeneration and recovery, the left hemitelencephalon was surgically removed in 5 adult cats and 5 neonatal kittens which were compared to 5 intact controls. After long survival, brains were sectioned in the coronal plane and thionine-stained. Drawings of gross and microscopic thalamic structures were made at 4 planes and computer-digitized to provide 7 measures: total thalamic area at planes A 7.5 and A 8.5; counts of neuroglia, small neurons (31-100 microns2) and large neurons (101-1000 microns2); area of neuroglia, small neurons and large neurons. All cellular measurements were in the ventrobasal complex at planes A 8.0 and A 10.0. Morphological changes were found bilaterally in all lesioned cats. Ipsilateral to the ablation in adult-lesioned cats, thalamic area, large neuron count and glia cells size were markedly and significantly decreased (P less than 0.01), while in neonatal-lesioned cats these changes were present but significantly reduced in magnitude compared to adult-lesioned animals. In addition, adult-lesioned cats showed a marked increase in glial cell numbers (P less than 0.01) and a decrease in small neuron size (P less than 0.01), while kitten-lesioned animals did not show changes in these measures. In the intact side of the brain, the thalamus of adult-lesioned cats was decreased in size (P less than 0.01), and glial cells were decreased in number and size (P less than 0.05), while in kitten-lesioned brains there were few changes. In both lesioned groups large neurons showed a significant increase in size (P less than 0.01). We conclude that neonatal hemispherectomy results in markedly less thalamic atrophy, retrograde neuronal degeneration and gliosis than the equivalent lesion in adults. The changes are discussed in the context of the increased neuroanatomical reorganization and functional recovery which were reported in neonatal- vs adult-lesioned animals.

Transneuronal degeneration of beta retinal ganglion cells in the cat

Transneuronal retrograde degeneration of retinal ganglion cells was investigated following neonatal visual cortex ablation in the cat. After a survival time of at least 18 months, retinal ganglion cells projecting to the thalamus were labelled by retrograde transport of horseradish peroxidase. Filled ganglion cells were classified into alpha, beta and gamma types on the basis of dendritic morphology. In normal cats, alpha cells made up 8-10% of the total population in the sample area, beta cells made up 64-67% and gamma cells made up 23-27%. In retinae of visual cortex-ablated cats, normal numbers of alpha and gamma cells were present, but the beta cell population was depleted by 90% of normal. Thalamic projections of surviving retinal ganglion cells were investigated by anterograde transport of tritiated proline injected into the eye. In these animals, ablation of visual cortex resulted in almost complete degeneration of laminae A and A1 of the dorsal lateral geniculate nucleus. In the radioautographic material, projections from the retina to the degenerated parts of laminae A and A1 were barely detectable. Survival of some ganglion cell populations and death of others after neonatal visual cortex ablation may be explained in terms of the pattern of projections of the different cell types. We conclude that the majority of beta cells degenerate following visual cortex ablation because of removal of cells in the dorsal lateral geniculate nucleus which form their sole or principal target. Alpha and gamma cells and 10% of beta-cells survive because of extensive collateral projections to targets other than cells of the laminae A and A1 of dorsal lateral geniculate nucleus.

Neuronal response of the hippocampal formation to injury: blood flow, glucose metabolism, and protein synthesis

The reaction of the hippocampal formation to entorhinal lesions was studied from the viewpoints of cerebral blood flow ([123I]isopropyl-iodoamphetamine[IMP])-glucose utilization ([14C]2-deoxyglucose), and protein synthesis ([14C]leucine), using single- and double-label autoradiography. Our study showed (i) decreased glucose utilization in the inner part, and increased glucose utilization in the outer part of the molecular layer of the dentate gyrus, starting 3 days after the lesion; (ii) increased uptake of [123I]IMP around the lesion from 1 to 3 days postlesion; and (iii) starting 3 days after the lesion, marked decrease in [14C]leucine incorporation into proteins and cell loss in the dorsal CA1 and dorsal subiculum in about one-half of the rats. These changes were present only in animals with lesions which invaded the ventral hippocampal formation in which axons of CA1 cells travel. By contrast, transsection of the 3rd and 4th cranial nerves resulted, 3 to 9 days after injury, in a striking increase in protein synthesis in the oculomotor and trochlear nuclei. These results raise the possibility that in some neurons the failure of central regeneration may result from the cell's inability to increase its rate of protein synthesis in response to axonal injury.

Transneuronal retrograde degeneration in the cat retina following neonatal ablation of visual cortex

Bilateral removal of the cortical visual area in newborn cats produces degeneration of retinal ganglion cells. Measurements of over 4,000 cells and calculation of neuron densities from sample areas of retina in the adult show that the medium sized cell population in peripheral retina is reduced by 68%, whereas the populations of small and large cells are not affected. The degeneration is greater in peripheral retina than in area centralis.

Quantitative data on cell loss and cellular atrophy of intralaminar nuclei following cortical and subcortical lesions

Morphological changes in the intralaminar nuclei centralis medialis, paracentralis and centralis lateralis of the thalamus of adult cats after cortical excisions have been determined by means of a quantitative method. The number and size of the remaining neurons on the operated side have been compared with those of the normal side. The differences between the normal and the operated side have been compared to those found between the two sides in the control animals. The most important result is the demonstration that after cortical ablations the intralaminar nuclei show not only chromatolytic or atrophic changes of their cells but also a true cell loss. These reactions are qualitatively similar to those observed in the specific nuclei of the thalamus, the only difference being a quantitative one. As a consequence it can be suggested that some intralaminar nuclei project to certain areas of the cerebral cortex which also receive projections from one or other specific thalamic nucleus. A large essential connection of the intralaminar nuclei, in particular the nucleus centralis medialis, with subcortical structures is confirmed.

The interpretation of the degenerative changes in the intralaminar nuclei of the thalamus

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