The structural effect of systemic NGF treatment on permanently axotomised dorsal root ganglion cells in adult rats.
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The effect of systemic NGF treatment on loss and shrinkage of dorsal root ganglion cells was studied in adult male rats after permanent axotomy. Nineteen 16 to 18-wk-old rats had their right 5th lumbar spinal nerve ligated and cut approximately 7 mm peripheral to the ganglion. Two days before the operation, treatment with subcutaneous injections of human recombinant NGF (1.0-0.5 mg/kg/day) was started in 9 test rats; 10 controls were given saline injections. After 1 mo the levels of substance P (SP) and calcitonin gene related peptide (CGRP) were significantly increased in intact sciatic nerve. The number and mean volume of perikarya were estimated using assumption-free stereological techniques including vertical sections, the Cavalieri principle, optical disectors, the planar rotator and systematic sampling techniques. Systemic NGF administration had no influence on survival of primary sensory neurons after axotomy. The number of perikarya was 14300 (S.D. = 1800) in axotomised ganglia in control rats versus 14700 (S.D. = 2100) in axotomised ganglia of NGF treated rats. The reduction of perikarya volume after axotomy was significantly less after NGF treatment (11600 microm3 in the control group versus 8000 microm3 in the NGF treated group). However, the apparent protection of NGF-treatment on perikaryal volume is explained by a hitherto unrecognised size effect on nonaxotomised dorsal root ganglion cells. The untreated rats had a mean volume of 24700 microm3 (S.D. = 2700 microm3) whereas rats treated with NGF had a volume of 20400 microm3 (S.D. = 1700 microm3) on the nonaxotomised side. In conclusion, systemic NGF treatment in adult rats has no effect on dorsal root ganglion cell loss in permanent axotomy whereas perikaryal size of intact nonaxotomised cells is reduced. (+info)
Fatal familial insomnia: clinical features and molecular genetics.
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Fatal familial insomnia (FFI) is an autosomal dominant prion disease clinically characterized by inattention, sleep loss, dysautonomia, and motor signs and pathologically characterized by a preferential thalamic degeneration. FFI is linked to a missense mutation at codon 178 of the prion protein gene, PRNP, coupled with the presence of the codon methionine at position 129, the locus of a methionine-valine polymorphism. Homozygotes at codon 129, expressing methionine also in the nonmutated allele, have a shorter disease course (often less than 1 year), prominent sleep and autonomic disturbances at disease onset, and pathology restricted to the thalamus. Heterozygotes at codon 129, expressing valine in the nonmutated allele, have a longer disease course (often longer than 1 year), ataxia and dysarthria at disease onset, and lesions widespread to cerebral cortex. Both in the thalamus and in the cortex, the limbic structures are those most consistently and severely involved: the anterior ventral and mediodorsal thalamic nuclei, the cingulate gyrus, and the orbitofrontal cortex. FFI is thus a prion disease selectively damaging the thalamocortical limbic structures. Loss of sleep, sympathetic hyperactivity, and flattening of vegetative and hormonal circadian oscillations characterize FFI and result from a homeostatic imbalance caused by the interruption of the thalamocortical limbic circuits, the phylogenetically most advanced structures involved in the control of the sleep-wake cycle and the body's homeostasis. The selective atrophy of the limbic thalamus that characterizes FFI might be due to the binding of FFI toxic PrP or PrPres to specific receptors on thalamolimbic neurons. (+info)
Leukocyte infiltration, neuronal degeneration, and neurite outgrowth after ablation of scar-forming, reactive astrocytes in adult transgenic mice.
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Reactive astrocytes adjacent to a forebrain stab injury were selectively ablated in adult mice expressing HSV-TK from the Gfap promoter by treatment with ganciclovir. Injured tissue that was depleted of GFAP-positive astrocytes exhibited (1) a prolonged 25-fold increase in infiltration of CD45-positive leukocytes, including ultrastructurally identified monocytes, macrophages, neutrophils, and lymphocytes, (2) failure of blood-brain barrier (BBB) repair, (3) substantial neuronal degeneration that could be attenuated by chronic glutamate receptor blockade, and (4) a pronounced increase in local neurite outgrowth. These findings show that genetic targeting can be used to ablate scar-forming astrocytes and demonstrate roles for astrocytes in regulating leukocyte trafficking, repairing the BBB, protecting neurons, and restricting nerve fiber growth after injury in the adult central nervous system. (+info)
Neural stem cells as engraftable packaging lines can mediate gene delivery to microglia: evidence from studying retroviral env-related neurodegeneration.
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The induction of spongiform myeloencephalopathy by murine leukemia viruses is mediated primarily by infection of central nervous system (CNS) microglia. In this regard, we have previously shown that CasBrE-induced disease requires late, rather than early, virus replication events in microglial cells (W. P. Lynch et al., J. Virol. 70:8896-8907, 1996). Furthermore, neurodegeneration requires the presence of unique sequences within the viral env gene. Thus, the neurodegeneration-inducing events could result from microglial expression of retroviral envelope protein alone or from the interaction of envelope protein with other viral structural proteins in the virus assembly and maturation process. To distinguish between these possible mechanisms of disease induction, we engineered the engraftable neural stem cell line C17-2 into packaging/producer cells in order to deliver the neurovirulent CasBrE env gene to endogenous CNS cells. This strategy resulted in significant CasBrE env expression within CNS microglia without the appearance of replication competent virus. CasBrE envelope expression within microglia was accompanied by increased expression of activation markers F4/80 and Mac-1 (CD11b) but failed to induce spongiform neurodegenerative changes. These results suggest that envelope expression alone within microglia is not sufficient to induce neurodegeneration. Rather, microglia-mediated disease appears to require neurovirulent Env protein interaction with other viral proteins during assembly or maturation. More broadly, the results presented here prove the efficacy of a novel method by which neural stem cell biology may be harnessed for genetically manipulating the CNS, not only for studying neurodegeneration but also as a paradigm for the disseminated distribution of retroviral vector-transduced genes. (+info)
A YAC mouse model for Huntington's disease with full-length mutant huntingtin, cytoplasmic toxicity, and selective striatal neurodegeneration.
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We have produced yeast artificial chromosome (YAC) transgenic mice expressing normal (YAC18) and mutant (YAC46 and YAC72) huntingtin (htt) in a developmental and tissue-specific manner identical to that observed in Huntington's disease (HD). YAC46 and YAC72 mice show early electrophysiological abnormalities, indicating cytoplasmic dysfunction prior to observed nuclear inclusions or neurodegeneration. By 12 months of age, YAC72 mice have a selective degeneration of medium spiny neurons in the lateral striatum associated with the translocation of N-terminal htt fragments to the nucleus. Neurodegeneration can be present in the absence of macro- or microaggregates, clearly showing that aggregates are not essential to initiation of neuronal death. These mice demonstrate that initial neuronal cytoplasmic toxicity is followed by cleavage of htt, nuclear translocation of htt N-terminal fragments, and selective neurodegeneration. (+info)
Robust regeneration of adult sensory axons in degenerating white matter of the adult rat spinal cord.
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We have recently reported that minimally disturbed adult CNS white matter can support regeneration of adult axons by using a novel microtransplantation technique to inject minute volumes of dissociated adult rat dorsal root ganglion neurons directly into adult rat CNS pathways (Davies et al., 1997). This atraumatic injection procedure minimized scarring and allowed considerable numbers of regenerating adult axons immediate access to the adult CNS glial terrain where they rapidly extended for long distances. A critical question remained as to whether degenerating white matter at acute and chronic stages (up to 3 months) after injury could still support regeneration. To investigate this, we have microtransplanted adult sensory neurons into degenerating white matter of the adult rat spinal cord several millimeters rostral to a severe lesion of the dorsal columns. Regeneration of donor sensory axons in both directions away from the site of transplantation was robust even within white matter undergoing fulminant Wallerian degeneration despite intimate contact with myelin. Along their route, the regrowing axons extended large numbers of collaterals into the adjacent dorsal horn. However, after entering the lesion, the rapidly extending growth cones stopped and became dystrophic within high concentrations of reactive glial matrix. Our results offer compelling evidence that the major environmental impediment to regeneration in the adult CNS is the molecular barrier that forms directly at the lesion site, and that degenerating white matter beyond the glial scar has a far greater intrinsic ability to support axon regeneration than previously thought possible. (+info)
Loss of distal axons and sensory Merkel cells and features indicative of muscle denervation in hindlimbs of P0-deficient mice.
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Mice lacking the major Schwann cell myelin component P0 show a severe dysmyelination with pathological features reminiscent of the Dejerine-Sottas syndrome in humans. Previous morphological and electrophysiological studies on these mice did not only demonstrate a compromised myelination and myelin maintenance, but were suggestive of an impairment of axons as well. Here, we studied the axonal pathology in P0-deficient mice by quantitative electron microscopy. In addition, we investigated epidermal receptor end organs by immunocytochemistry and muscle pathology by histochemistry. In proximal sections of facial and femoral nerves, axon calibers were significantly reduced, whereas the number of myelin-competent axons was not diminished in 5- and 17-month-old P0-deficient mice. However, in distal branches of the femoral and sciatic nerve (digital nerves innervating the skin of the first toe) the numbers of myelin-competent axons were reduced by 70% in 6-month-old P0-deficient mice. Immunolabeling of foot pads revealed a corresponding loss of Merkel cells by 75%, suggesting that survival of these cells is dependent on the presence or maintenance of their innervating myelinated axons. In addition, quadriceps and gastrocnemius muscles showed pathological features indicative of denervation and axonal sprouting. These findings demonstrate that loss of an important myelin component can initiate degenerative mechanisms not only in the Schwann cell but also in the distal portions of myelinated axons, leading to the degeneration of specialized receptor end organs and impairment of muscle innervation. (+info)
Ultrastructural changes in the chick thymus following unilateral vagotomy.
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The ultrastructure of the thymus in the chick (Gallus domesticus) was studied after unilateral vagotomy at survival times of 3, 7 and 10 days. Ultrastructural changes in the ipsilateral thymus were observed in axon boutons as well as in myoid and cystic cells in the medulla, especially those situated near the corticomedullary junction. Structural changes in axon boutons ranged from granular degeneration of the axonal cytoskeleton to vacuolation of the axoplasm. Myelin figures of different sizes and configurations and clumping of small agranular vesicles were commonly observed in the axon terminals. Degeneration of myoid cells appeared to peak at 7 days post-vagotomy. Changes ranged from oedematous appearance and intense vacuolation of the peripheral cytoplasm to disorganisation and clumping of myofibrils. In some myoid cells the sarcomeres showed granular degeneration at the I-bands and in others, the myofibrils were completely degenerated such that amorphous material and partially degenerated organelles filled the entire cell. The majority of cystic cells at 3 days post-vagotomy showed a uniform increase in electron density. Numerous electron dense bodies, some displaying concentric lamellation, were observed throughout the expanse of the cytoplasm. At 7 days post-vagotomy, the cytoplasm of some cells gave a "moth-eaten" appearance. Dying cystic cells were encountered at 10 days after vagotomy. Degeneration in the myoid and cystic cells suggests that these cellular components may be the putative targets of the vagal fibres in the chick thymus. The changes in these cells reflect a disturbance in the cell metabolism presumably brought about by the removal of vagal influence. (+info)