Biomedical subjects

L Olson

Publications and source records attributed to L Olson.

At least 109 records · Page 6Linked to original sources

PubMed1997

Functional interactions between spinal cord grafts suggest asymmetries dictated by graft maturity.

Fetal spinal cord tissue grafts have been advocated as a possible repair strategy for spinal cord injury. In the present study, we used intraocular spinal cord grafts to model the interactions which may occur between fetal and adult spinal cord after making such a graft and to study to which extent functional connections can be expected to occur between the host and graft tissue. We first grafted fetal spinal cord to the anterior chamber of the eye where it was allowed to mature. A second piece of fetal spinal cord was then sequentially grafted in contact with the first graft. Electrophysiological recordings made from the older graft while electrically stimulating the younger graft provided evidence for an excitatory innervation from the younger spinal cord graft to the mature spinal cord which appeared to be glutamatergic. However, we only rarely found excitatory inputs from the first, mature spinal cord graft to the younger graft. Fiber connections between the two spinal cord grafts were verified by retrograde tracing and neurofilament immunohistochemistry. In no case was a trophic influence on graft volume observed between spinal cord grafts regardless of whether the transplantations were performed sequentially or at the same time. Even the introduction of a second graft to immature spinal cord tissue was ineffective. In contrast, we found a marked trophic, neuron-rescuing effect of spinal cord grafts upon cografts of fetal dorsal root ganglia. This latter observation is consistent with the hypothesis that spinal cord tissue can exert a trophic effect on developing sensory ganglia and demonstrates that many sensory neurons can survive in the presence of a central target and in the absence of the appropriate peripheral target. These intraocular experiments predict that fetal spinal cord grafted to the injured adult spinal cord may develop effective excitatory inputs with the host, while host-to-graft inputs may develop to a considerably smaller extent. Our results also suggest that the adult spinal cord does not exert marked trophic effects on growth of fetal spinal cord, while it does exert a trophic influence on central projections of dorsal root ganglia.

Animals↗

PubMed1997

The ability of human Schwann cell grafts to promote regeneration in the transected nude rat spinal cord.

Advances in the purification and expansion of Schwann cells (SCs) from adult human peripheral nerve, together with biomaterials development, have made the construction of unique grafts with defined properties possible. We have utilized PAN/PVC guidance channels to form solid human SC grafts which can be transplanted either with or without the channel. We studied the ability of grafts placed with and without channels to support regeneration and to influence functional recovery; characteristics of the graft and host/graft interface were also compared. The T9-T10 spinal cord of nude rats was resected and a graft was placed across the gap; methylprednisolone was delivered acutely to decrease secondary injury. Channels minimized the immigration of connective tissue into grafts but contributed to some necrotic tissue loss, especially in the distal spinal cord. Grafts without channels contained more myelinated axons (x = 2129 +/- 785) vs (x = 1442 +/- 514) and were larger in cross-sectional area ( x = 1.53 +/- 0.24 mm2) vs (x = 0.95 +/- 0.86 mm2). The interfaces formed between the host spinal cord and the grafts placed without channels were highly interdigitated and resembled CNS-PNS transition zones; chondroitin sulfate proteoglycans was deposited there. Whereas several neuronal populations including propriospinal, sensory, motoneuronal, and brainstem neurons regenerated into human SC grafts, only propriospinal and sensory neurons were observed to reenter the host spinal cord. Using combinations of anterograde and retrograde tracers, we observed regeneration of propriospinal neurons up to 2.6 mm beyond grafts. We estimate that 1% of the fibers that enter grafts reenter the host spinal cord by 45 days after grafting. Following retrograde tracing from the distal spinal cord, more labeled neurons were unexpectedly found in the region of the dextran amine anterograde tracer injection site where a marked inflammatory reaction had occurred. Animals with bridging grafts obtained modestly higher scores during open field [(x = 8.2 +/- 0.35) vs (x = 6.8 +/- 0.42), P = 0.02] and inclined plane testing (x = 38.6 +/- 0. 542) vs (x = 36.3 +/- 0.53), P = 0.006] than animals with similar grafts in distally capped channels. In summary, this study showed that in the nude rat given methylprednisolone in combination with human SC grafts, some regenerative growth occurred beyond the graft and a modest improvement in function was observed.

Adolescent↗

PubMed1997

Gait analysis of adult paraplegic rats after spinal cord repair.

This study presents a novel detailed method of analysis of rat gait and uses this method to demonstrate recovery of forward locomotion patterns in adult rats made paraplegic by surgical spinal cord transection and subjected to a novel strategy for spinal cord repair. Six normal rats were compared to five animals in which the cord was transected at T8-T9, and a 5-mm segment of the spinal cord removed, and to seven animals in which, following spinal cord transection and removal of a spinal cord segment, multiple intercostal peripheral nerve bridges were implanted, rerouting pathways from white to gray matter in both directions. The implanted area was filled with fibrin glue containing acidic fibroblast growth factor. Details of the repair strategy have been published (H. Cheng, Y. Cao, and L. Olson, 1996, Science 273: 510-513). Gait analysis was carried out 3 and 4 months after surgery and once in the normal animals. Animals were allowed to walk across a runway with a transparent floor. Each test consisted of five trials, and each trial was videorecorded from underneath. Using frame-by-frame playback, individual footprints were then recorded regarding location and order of limb use, as well as step quality (degree of weight bearing, etc.). These data allowed measuring runway transit time, five different measures of step numbers, all possible temporal patterns of limb use, stride length, and base of support. Transected controls remained paralyzed in the hindlimbs with only occasional reflex hindlimb movements without weight bearing. Animals subjected to the full repair procedure were significantly faster than the controls, used their hindlimbs for 25-30% of the movements, and regained several of the specific limb recruitment patterns used by normal rats. Taken together, the gait analysis data demonstrate remarkable recovery of coordinated gait in the repaired animals, which was significantly better than controls for all relevant parameters, while at the same time clearly inferior to normal rats for most of the examined parameters. We conclude that normal rats use a multitude of interchangeable step sequence patterns, and that our spinal cord repair strategy leads to recovery of some of these patterns following complete spinal cord transection. These data suggest functionally relevant neuronal communication across the lesion.

Animals↗

PubMed1997

Treatment strategies for neurodegenerative diseases based on trophic factors and cell transplantation techniques.

Treatment strategies based on transfer of genes, molecules, or cells to the central nervous system are summarized. When neurons are already degenerated, functional compensation can be effected by grafts of syngeneic or allogenic tissue to the target area. This technique is undergoing clinical trials in Parkinson's disease. Before degeneration has occurred, it may be possible to rescue "stressed" neurons, and stimulate terminal outgrowth using treatment with neurotrophic factors. Such approaches, with an emphasis on the NGF family of neurotrophins and their receptors, are reviewed. Finally, new molecular biology techniques may permit the transfer of genes directly into non-dividing cells of the central nervous system. These three approaches may have a more general applicability, and become important not only in neurodegenerative diseases, but also in other afflictions of the nervous system such as ischemia, stroke and injury.

Alzheimer Disease↗

PubMed1997

Downregulation of brain-derived neurotrophic factor mRNA in adult rat brain after acute administration of methylmercury.

Conventionally, assessment of the neurotoxicity of environmental pollutants relies on high-dosage treatment and nonspecific end points. In the present study, the early temporal and regional alterations in the mRNAs of neurotrophins were investigated following subtoxic doses of methylmercury (MeHg) in adult Sprague-Dawley rats using in situ hybridization histochemistry and phosphoimaging evaluation. Decreases in brain-derived neurotrophic (BDNF) mRNA labeling intensities were seen in the dentate gyrus (DG; 44% of controls), and in the CA1 (72% of controls) and CA3c (70% of controls) cell layers of hippocampus after 8 mg MeHg/kg (ip) at 4 h, and at 1 h only in the DG. The decrease in BDNF mRNA expression in the DG was dose-dependent. At 3 d, regional levels had recovered. No significant changes could be detected in mRNA levels of the BDNF high-affinity receptor trkB or neurotrophin-3 mRNA at either 1 h, 4 h, or 3 d. Cresyl violet staining and GFAP immunohistochemistry did not reveal any major neuropathology in hippocampus at 2 wk. Thus, MeHg causes specific downregulation of BDNF mRNA, unlike many other perturbations of central nervous system homeostasis that have been shown to lead to upregulation of this mRNA.

Animals↗

PubMed1997

Cellular and developmental patterns of expression of Ret and glial cell line-derived neurotrophic factor receptor alpha mRNAs.

Glial cell line-derived neurotrophic factor (GDNF) has recently been shown to signal by binding to GDNF receptor-alpha (GDNFR-alpha), after which the GDNF-GDNFR-alpha associates with and activates the tyrosine kinase receptor Ret. We have localized Ret messenger RNA (mRNA) in the developing and adult rodent and compared with to the expression of GDNF and GDNFR-alpha mRNA. Ret mRNA is strongly expressed in dopamine neurons and alpha-motor neurons as well as in thalamus, ruber and occluomotor nuclei, the habenular complex, septum, cerebellum, and brain stem nuclei. Ret mRNA was also found in several sensory systems, in ganglia, and in nonneuronal tissues such as teeth and vibrissae. Very strong Ret mRNA signals are present in kidney and the gastrointestinal tract, where Ret and GDNF mRNA expression patterns are precisely complementary. The presence of Ret protein was confirmed in adult dopamine neurons using immunohistochemistry. GDNFR-alpha mRNA was strongly expressed in the developing and adult dopamine neurons. It was also found in neurons in deep layers of cortex cerebri, in hippocampus, septum, the dentate gyrus, tectum, and the developing spinal cord. In the kidney and the gastrointestinal tract, GDNFR-alpha mRNA and Ret mRNA distribution overlapped. Dorsal root ganglia, cranial ganglia, and developing peripheral nerves were also positive. GDNFR-alpha was additionally found in sensory areas and in developing teeth. Sensory areas included inner ear, eye, olfactory epithelium, and the vomeronasal organ, as well as developing tongue papillae. The temporospatial pattern of expression of GDNFR-alpha mRNA did not always match that of Ret mRNA. For instance, GDNFR-alpha mRNA was also found in the developing ventral striatum, including the olfactory tubercle, and in hippocampus. These areas seemed devoid of Ret mRNA, suggesting that GDNFR-alpha might also have functions unrelated to Ret.

Animals↗

PubMed1997

Intraventricular injection of NGF, but not BDNF, induces rapid motor activation that is inhibited by nicotinic receptor antagonists.

The acute and subacute effects of intracerebroventricularly (ICV) administered nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) on locomotor activity were evaluated in awake adult rats. Immediately after ICV injection through an implanted cannula, locomotor activity was measured by a computerized system using infrared photocells, which allowed us to record locomotion, motility, and rearing simultaneously. A single dose of 5 microg mouse beta-NGF produced significant increases in horizontal ambulatory components of locomotor activity (locomotion and motility), but not vertical movement (rearing) 30-45 min after ICV administration. These increases lasted for at least 3-4 h. Systemic injection of 2.0 mg/kg mecamylamine, a central nicotinic receptor antagonist, inhibited the hyperactivity induced by NGF. Systemic injection of 0.5 mg/kg scopolamine, a muscarinic receptor antagonist, did not interfere with the NGF effects. Thus, while scopolamine induced marked increases in all three measures of behavior in both NGF and cytochrome-c-treated animals, locomotion and motility remained significantly higher in the NGF group. Immunohistochemistry demonstrated that NGF diffused readily from the ventricular space into brain parenchyma on the injected side and could be visualized 1 h after ICV injection. These results suggest that ICV administration of NGF increases locomotor activity by inducing acetylcholine release, and that nicotinic receptors are involved in the hyperactivity induced by NGF. ICV administration of 5 microg recombinant human BDNF had no significant effect on locomotor activity during the 0- to 4-h period after ICV injection. However, it produced significant decreases in locomotion, motility, and rearing 24-26 h later. Hence ICV administration of BDNF has entirely different effects on animal behavior from those evoked by NGF. While NGF elicits increases in ambulatory behavior within hours, BDNF causes delayed decreases in ambulatory behavior.

Animals↗

PubMed1997

Cellular expression of neurotrophin mRNAs during tooth development.

Target-derived neurotrophins support and sustain peripheral sensory neurons during development. In addition, it has been suggested that these growth factors could have developmental functions in non-neuronal tissues. To further elucidate the possible roles of neurotrophins in tooth morphogenesis and innervation, we have used in-situ hybridization to determine the specific sites of neurotrophin gene activity in pre- and postnatal rat jaws from E16 to P7. All four neurotrophins were expressed during tooth development with specific temporospatial patterns. Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNAs were mainly detected in the dental papilla/pulp in postnatal animals, and the pattern of expression correlated with the onset of dental innervation. In contrast, neurotrophin 3 (NT3) and neurotrophin 4 (NT4) mRNA expression patterns were predominantly epithelial and were strongest during early developmental stages when teeth are not yet innervated. Dental papilla NGF-mRNA expression was first seen in both epithelium and mesenchyme and later shifted to the odontoblast layer and the subodontoblast zone. BDNF-mRNA labeling was present in low levels in the early dental organ, but increased in the pulp and in the odontoblast cell layer of the developing teeth at later developmental stages. Both NT3 and NT4 mRNA were observed in the prenatal oral epithelium and the inner dental epithelium. NT3-mRNA labeling was seen mainly in the cervical loop region, fissure system depressions and cuspal tops, while NT4 mRNA was more evenly distributed in the dental epithelium. At P7, NT3-mRNA labeling was below detection level and NT4 mRNA expression was lower than at prior stages. Complementary to reports on the presence of low-affinity neurotrophin receptor (LANR), trkB and trkC mRNA in the developing teeth, our results suggest that neurotrophins may have multiple functions during tooth morphogenesis. Neurotrophins might participate in epithelial-mesenchymal interactions in early tooth morphogenetic events such as proliferation and differentiation of epithelial and mesenchymal cells. In addition, based on mRNA localization in postnatal animals, we also suggest that NGF and BDNF (beside glial cell line-derived neurotrophic factor) might participate in establishing and maintaining the innervation of the teeth, thus acting as classical neurotrophic factors.

Animals↗

PubMed1997

Farm-related injury mortality in New Mexico, 1980-91.

To compare the epidemiology of farm with non-farm occupational injury deaths, we reviewed state medical examiner data for all occupational injury deaths in New Mexico from 1980 to 1991. We identified 53 farm-related injury deaths for a rate of 21.3 per 100,000 worker-years. Farm workers were four times more likely than non-farm workers to die from occupational injury. American Indians had the highest farm injury death rate. Farm decedents were older than non-farm decedents (t498 = 6.29, p < 0.0001). Half of the farm decedents were 50 years of age or older; one-third were 60 years of age or older. Crush injuries accounted for half of all farm injury deaths including 18 of 23 motor vehicle deaths, half of these involving a tractor rollover. One in six farm injury deaths were from electrocution: one in five involved alcohol. Our study indicates that New Mexico has high farm-related injury mortality related to tractor use, alcohol intoxication, farm animals, and exposure to electricity. American Indians and older males are especially susceptible to these factors.

Accidents, Occupational↗

PubMed1997