Transplants of fibroblasts genetically modified to express BDNF promote regeneration of adult rat rubrospinal axons and recovery of forelimb function.
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Adult mammalian CNS neurons do not normally regenerate their severed axons. This failure has been attributed to scar tissue and inhibitory molecules at the injury site that block the regenerating axons, a lack of trophic support for the axotomized neurons, and intrinsic neuronal changes that follow axotomy, including cell atrophy and death. We studied whether transplants of fibroblasts genetically engineered to produce brain-derived neurotrophic factor (BDNF) would promote rubrospinal tract (RST) regeneration in adult rats. Primary fibroblasts were modified by retroviral-mediated transfer of a DNA construct encoding the human BDNF gene, an internal ribosomal entry site, and a fusion gene of lacZ and neomycin resistance genes. The modified fibroblasts produce biologically active BDNF in vitro. These cells were grafted into a partial cervical hemisection cavity that completely interrupted one RST. One and two months after lesion and transplantation, RST regeneration was demonstrated with retrograde and anterograde tracing techniques. Retrograde tracing with fluorogold showed that approximately 7% of RST neurons regenerated axons at least three to four segments caudal to the transplants. Anterograde tracing with biotinylated dextran amine revealed that the RST axons regenerated through and around the transplants, grew for long distances within white matter caudal to the transplant, and terminated in spinal cord gray matter regions that are the normal targets of RST axons. Transplants of unmodified primary fibroblasts or Gelfoam alone did not elicit regeneration. Behavioral tests demonstrated that recipients of BDNF-producing fibroblasts showed significant recovery of forelimb usage, which was abolished by a second lesion that transected the regenerated axons. (+info)
Temporal sequence of changes in rat retina after UV-A and blue light exposure.
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Two spectral types of retinal light damage were induced in pigmented rats by irradiating small retinal patches at either 380 or 470 nm. The temporal sequence of changes in the retina was followed for up to 2 months by funduscopy and histology. For both damage types, fundus changes were best visible after 3 days. Histology showed that 380 nm specifically damaged photoreceptor cells, particularly the rods. All cell compartments of the rods, including the nucleus were affected already after 3 h. In the next days, damaged rods degenerated. At high doses (2.5 x the funduscopic threshold dose) all rods in the irradiated area were lost, resulting in a local photoreceptor lesion, which was still present at 2 months after the irradiation. At 470 nm, damage occurred both in the photoreceptor layer and in the pigment epithelium. Acute changes, at 1 h after irradiation, consisted mainly of damaged mitochondria in these layers. Next, the pigment epithelium showed swelling, an altered melanin distribution and, at high doses (2.5 x threshold), interruptions of the monolayer. Degeneration of photoreceptor cells was initially limited to a few scattered cells, but 3 days after high doses focal areas of massive degeneration were seen. At late stages, the cells of the pigment epithelium recovered and the photoreceptor layer showed a loss of cells. The results show that the spectral damage types are distinct in the early phases, indicating that different mechanisms are involved. Yet, the end effect of both damage types after exposure at doses up to 2.5 x the funduscopic threshold is remarkably similar and consists of local photoreceptor lesions. (+info)
Results following treatment of third cranial nerve palsy in children.
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PURPOSE: To investigate the etiology, sensory, motor, and cosmetic results of treatment for oculomotor (CNIII) palsy in children. METHODS: We conducted a retrospective review of the clinical records of children with a diagnosis of CNIII palsy who were followed up in our practice between 1981 and 1996. RESULTS: During the 15-year period, 49 children with 53 affected eyes were followed for a mean of 5.5 years. CNIII palsy was congenital in one third of cases and secondary to postnatal trauma in another third. Thirty-three of the eyes were affected before visual maturation (age 8 years) and 27 eyes developed amblyopia. None of the 6 eyes with amblyopia in which visual acuity could be quantitated had measurable improvement of Snellen acuity after treatment. Overall, visual acuity was between 6/5 and 6/12 at the last follow-up visit in 56% of affected eyes. Ocular alignment was greatly improved after recess-resect procedures on the horizontal rectus muscles, but binocular function was difficult to preserve or restore. Blepharoptosis improved after levator palpebrae muscle resection or eyelid suspension procedures. CONCLUSIONS: CNIII palsy may undergo partial resolution in children, but surgical treatment is frequently necessary. Although surgery can result in cosmetically acceptable alignment of the eyes, it rarely results in restoration or achievement of binocular function. Multiple procedures are often necessary to maintain good ocular alignment. Several surgical procedures may be needed to correct related blepharoptosis and maintain an acceptable eyelid position. Treatment of amblyopia is only effective in maintaining the level of visual acuity present at the onset of the CNIII palsy, and improvement in acuity is difficult to achieve. (+info)
Altered serotonin innervation patterns in the forebrain of monkeys treated with (+/-)3,4-methylenedioxymethamphetamine seven years previously: factors influencing abnormal recovery.
(28/2616)
The recreational drug (+/-)3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") is a potent and selective brain serotonin (5-HT) neurotoxin in animals and, possibly, in humans. The purpose of the present study was to determine whether brain 5-HT deficits persist in squirrel monkeys beyond the 18-month period studied previously and to identify factors that influence recovery of injured 5-HT axons. Seven years after treatment, abnormal brain 5-HT innervation patterns were still evident in MDMA-treated monkeys, although 5-HT deficits in some regions were less severe than those observed at 18 months. No loss of 5-HT nerve cell bodies in the rostral raphe nuclei was found, indicating that abnormal innervation patterns in MDMA-treated monkeys are not the result of loss of a particular 5-HT nerve cell group. Factors that influence recovery of 5-HT axons after MDMA injury are (1) the distance of the affected axon terminal field from the rostral raphe nuclei, (2) the degree of initial 5-HT axonal injury, and possibly (3) the proximity of damaged 5-HT axons to myelinated fiber tracts. Additional studies are needed to better understand these and other factors that influence the response of primate 5-HT neurons to MDMA injury and to determine whether the present findings generalize to humans who use MDMA for recreational purposes. (+info)
Neuroprotection by a novel compound, NS521.
(29/2616)
NS521 (1-(1-butyl)-4-(2-oxo-1-benzimidazolinyl)piperidine) belongs to a group of novel benzimidazolones, which exhibit neurotrophic-like activities. In vitro, NS521 rescued neuronal PC12 cells from death induced by serum and nerve growth factor deprivation. The survival effect of NS521 appeared to reflect a delay of the apoptotic process, because the extent of DNA fragmentation was attenuated transiently by NS521. NS521 did not preserve the neurites of the rescued cells, which, otherwise, appeared to be healthy and were able to regenerate when serum and nerve growth factor were added back to the culture. In vivo, NS521 provided significant protection against the delayed loss of hippocampal CA1 neurons in a gerbil model of transient global ischemia. A neuroprotective effect of NS521 in the peripheral nervous system also was observed in rats after transection of the sciatic nerve, where daily treatment with NS521 was found to inhibit retrograde degeneration of the transected nerve. The neuroprotective effect of NS521 is unlikely to be mediated through neurotrophin receptors, such as TrkA, because NS521 did not induce phosphorylation of the 44- and 42-kDa isoforms of mitogen-activated protein kinases (ERK1/2) in PC12 cells. (+info)
Recovery of functional response in the nucleus of the solitary tract after peripheral gustatory nerve crush and regeneration.
(30/2616)
Single-unit recording and transganglionic tracing techniques were used to assess the properties of, and inputs to, neurons within the rostral nucleus of the solitary tract (NST) after peripheral gustatory nerve injury and regeneration in adult hamsters (Mesocricetus auratus). Tastant-evoked responses were recorded from 43 neurons in animals in which the ipsilateral chorda tympani (CT) nerve was crushed 8 wk earlier (experimental animals) and from 46 neurons in unlesioned control animals. The 89 neurons were separated into three functional clusters named according to the best stimulus for neurons in the cluster: S, sucrose; N, sodium acetate; and H, HCl or KCl. Stimulus-evoked spike rates across all stimuli were 35.4 +/- 4.4% lower in the experimental hamsters. The largest difference in evoked spike rates occurred for neurons in the H cluster, in which the response to KCl also was delayed relative to normal responses. The response of S-cluster units to sucrose and saccharin was also lower in the experimental animals. The mean response rate and the time course of response of neurons in the N cluster did not differ between the two groups. For each cluster, the spontaneous rates and mean response profiles across eight stimuli were very similar in the experimental and control animals, and the breadth of tuning hardly differed. In both groups, Na+ responses in the N cluster were amiloride sensitive, and responses to the water rinse after stimulation with HCl were common in the S cluster. At 8-20 wk after nerve crush, biotinylated dextran tracing of the CT nerve revealed that the regenerated CT fibers did not sprout outside the normal terminal zone in the NST, but the density of the central terminal fibers was 36.9 +/- 6.35% lower than normal. After CT nerve crush and regeneration, the overall reduction in taste-evoked spike rates in NST neurons is likely a consequence of this change in terminal fibers; this in turn likely results from the known reduction in CT fibers regenerating past the crush site. In the face of this reduction, the normal taste-evoked spike rate in N-cluster neurons requires explanation. The observed recovery of normal specificity could be mediated by a restoration of specific connections by primary afferent fibers peripherally and centrally or by central compensatory mechanisms. (+info)
Regeneration of dorsal column fibers into and beyond the lesion site following adult spinal cord injury.
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Regeneration is abortive following adult mammalian CNS injury. We have investigated whether increasing the intrinsic growth state of primary sensory neurons by a conditioning peripheral nerve lesion increases regrowth of their central axons. After dorsal column lesions, all fibers stop at the injury site. Animals with a peripheral axotomy concomitant with the central lesion show axonal growth into the lesion but not into the spinal cord above the lesion. A preconditioning lesion 1 or 2 weeks prior to the dorsal column injury results in growth into the spinal cord above the lesion. In vitro, the growth capacity of DRG neurite is also increased following preconditioning lesions. The intrinsic growth state of injured neurons is, therefore, a key determinant for central regeneration. (+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)