Peter Batchelor

Reduced BDNF mRNA Expression in the Parkinson's Disease Substantia Nigra

Brain-derived neurotrophic factor (BDNF) has potent effects on survival and morphology of dopaminergic neurons and thus its loss could contribute to death of these cells in Parkinsons disease (PD). In situ hybridization revealed that BDNF mRNA is strongly expressed by dopaminergic neurons in control substantia nigra pars compacta (SNpc). In clinically and neuropathologically typical PD, SNpc BDNF mRNA expression is reduced by 70% (P = 0.001). This reduction is due, in part, to loss of dopaminergic neurons which express BDNF. However, surviving dopaminergic neurons in the PD SNpc also expressed less BDNF mRNA (20%, P = 0.02) than their normal counterparts. Moreover, while 15% of control neurons had BDNF mRNA expression >1 SD below the control mean, twice as many (28%) of the surviving PD SNpc dopaminergic neurons had BDNF mRNA expression below this value. This 13% difference in proportions (95% CI 8-17%, P < or = 0.000001) indicates the presence of a subset of neurons in PD with particularly low BDNF mRNA expression. Moreover, both control and PD neurons displayed a direct relationship between the density of BDNF mRNA expression per square micrometer of cell surface and neuronal size (r(2) = 0.93, P </= 0.00001) which was lost only in PD neurons expressing the lowest levels of BDNF mRNA. If BDNF is an autocrine/paracrine factor for SNpc dopaminergic neurons, loss of BDNF-expressing neurons may compromise the well-being of their surviving neighbors. Moreover, neurons expressing particularly low levels of BDNF mRNA may be those at greatest risk of injury in PD and possibly the trigger for the degeneration itself.

NGF receptor reexpression and NGF-mediated cholinergic neuronal hypertrophy in the damaged adult neostriatum

Adult cholinergic interneurons of the neostriatum are not immunoreactive for monoclonal antibody to NGF receptor, whereas the developing neostriatum is immunoreactive for this same antibody. Chronic NGF infusion into the adult neostriatum resulted in reexpression of the NGF receptor such that many cholinergic interneurons became immunoreactive for NGF receptor. NGF infusion dramatically increased the size and choline acetyltransferase immunoreactivity of these same cholinergic neurons. Additionally, in situ hybridization demonstrated an increase in the number of cells expressing NGF receptor mRNA in the NGF-infused striatum. These findings indicate that central cholinergic neurons which lose their NGF receptors during postnatal development will resume their NGF responsiveness when the tissue is damaged. Such a damage-induced mechanism may act to enhance the action of trophic factors, including NGF, released at the site of injury and enhance the responsiveness of damaged CNS neurons to exogenously administered trophic factors.

Macrophages and Microglia Produce Local Trophic Gradients That Stimulate Axonal Sprouting Toward but Not beyond the Wound Edge

Following injury to the mammalian CNS, axons sprout in the vicinity of the wound margin. Growth then ceases and axons fail to cross the lesion site. In this study, using dopaminergic sprouting in the injured striatum as a model system, we have examined the relationship of periwound sprouting fibers to reactive glia and macrophages. In the first week after injury we find that sprouting fibers form intimate relationships with activated microglia as they traverse toward the wound edge. Once at the wound edge, complicated plexuses of fibers form around individual macrophages. Axons, however, fail to grow further into the interior of the wound despite the presence of many macrophages in this location. We find that the expression of BDNF by activated microglia progressively increases as the wound edge is approached, while GDNF expression by macrophages is highest at the immediate wound margin. In contrast, the expression of both factors is substantially reduced within the macrophage-filled interior of the wound. Our data suggest that periwound sprouting fibers grow toward the wound margin along an increasing trophic gradient generated by progressively microglial and macrophage activation. Once at the wound edge, sprouting ceases over macrophages at the point of maximal neurotrophic factor expression and further axonal growth into the relatively poor trophic environment of the wound core fails to occur.

New dopaminergic neurons in Parkinson's disease striatum

A new population of dopaminergic neurons has been identified in Parkinsons disease striatum. These neurons are sufficiently numerous to have an important effect on dopaminergic function in the striatum.

Inhibiting BDNF expression by antisense oligonucleotide infusion causes loss of nigral dopaminergic neurons.

Brain derived neurotrophic factor (BDNF) expression is significantly reduced in the Parkinsons disease substantia nigra. This neurotrophin has potent affects on dopaminergic neuron survival protecting them from the neurotoxins MPTP and 6-hydroxydopamine (6-OHDA) commonly used to create animal models of Parkinsons disease and also promoting dopaminergic axonal sprouting. In this study, we demonstrate that an antisense oligonucleotide infusion (200 nM for 28 days) to prevent BDNF production in the substantia nigra of rats mimics many features of the classical animal models of Parkinsons disease. 62% of antisense treated rats rotate (P < or = 0.05) in response to dopaminergic receptor stimulation by apomorphine. 40% of substantia nigra pars compacta tyrosine hydroxylase immunoreactive neurons are lost (P < or = 0.00001) and dopamine uptake site density measured by (3)H-mazindol autoradiography is reduced by 34% (P < or = 0.005). Loss of haematoxylin and eosin stained nigral neurons is significant (P < or = 0.0001) but less extensive (34%). These observations indicate that loss of BDNF expression leads both to down regulation of the dopaminergic phenotype and to dopaminergic neuronal death. Therefore, reduced BDNF mRNA expression in Parkinsons disease substantia nigra may contribute directly to the death of nigral dopaminergic neurons and the development of Parkinsons disease.

Inhibition of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor expression reduces dopaminergic sprouting in the injured striatum

After striatal injury, sprouting dopaminergic fibres grow towards and intimately surround wound macrophages which, together with microglia, express the dopaminergic neurotrophic factors glial cell line‐derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF). To evaluate the importance of these endogenously secreted neurotrophic factors in generating striatal peri‐wound dopaminergic sprouting, the peri‐wound expression of BDNF or GDNF was inhibited by intrastriatal infusion of antisense oligonucleotides for 2 weeks in mice. Knock‐down of both BDNF and GDNF mRNA and protein levels in the wounded striatum were confirmed by in situ hybridization and enzyme‐linked immunosorbent assay, respectively. Dopamine transporter immunohisto‐chemistry revealed that inhibition of either BDNF or GDNF expression resulted in a marked decrease in the intensity of peri‐wound sprouting. Quantification of this effect using [H3]‐mazindol autoradiography confirmed that peri‐wound sprouting was significantly reduced in mice receiving BDNF or GDNF antisense infusions whilst control infusions of buffered saline or sense oligonucleotides resulted in the pronounced peri‐wound sprouting response normally associated with striatal injury. BDNF and GDNF thus appear to be important neurotrophic factors inducing dopaminergic sprouting after striatal injury.

Stem cell transplantation in traumatic spinal cord injury: a systematic review and meta-analysis of animal studies.

A systematic analysis of the literature shows that stem cell implantation can improve function in animal models of spinal cord injury, depending on the methods used.

Comparison of inflammation in the brain and spinal cord following mechanical injury.

Inflammation in the CNS predominantly involves microglia and macrophages, and is believed to be a significant cause of secondary injury following trauma. This study compares the microglial and macrophage response in the rat brain and spinal cord following discrete mechanical injury to better appreciate the degree to which these cells could contribute to secondary damage in these areas. We find that, 1 week after injury, the microglial and macrophage response is significantly greater in the spinal cord compared to the brain. This is the case for injuries to both gray and white matter. In addition, we observed a greater inflammatory response in white matter compared to gray matter within both the brain and spinal cord. Because activated microglia and macrophages appear to be effectors of secondary damage, a greater degree of inflammation in the spinal cord is likely to result in more extensive secondary damage. Tissue saving strategies utilizing anti-inflammatory treatments may therefore be more useful in traumatic spinal cord than brain injury.

Hypothermia Prior to Decompression: Buying Time for Treatment of Acute Spinal Cord Injury

Human spinal cord injury (SCI) is usually accompanied by persistent cord compression. Experimental data demonstrate that compression of the traumatized cord results in rapid neurological decline over hours. Undertaking decompression in humans within this time frame has proved impractical, with the time to surgery in studies of urgent decompression averaging between 10 and 24 h. There is, therefore, an important need for a therapy to prevent the neurological deterioration of patients prior to decompressive surgery. The aim of this study was to determine if hypothermia prevents compressive SCI, thereby limiting neurological decline. Rats were subjected to a moderate mid-thoracic SCI and spacers were inserted to compress the spinal cord by 45%. Decompression, by removal of the spacer, was performed immediately, and at 2 or 8 h post-injury. Hypothermia (33 degrees C) was commenced in half the animals at 30 mins post-injury and maintained for 7.5 h, with the other half remaining normothermic (37.3 degrees C). Motor recovery was assessed weekly, and the volume and area of tissue damage determined at the end of the 8-week study period. The results demonstrate that hypothermia significantly improves the behavioral and histological outcome of animals undergoing 8 h of compressive injury (the primary outcome measure). The hypothermia-treated group regained weight-supported locomotion (Basso-Beattie-Bresnahan [BBB] locomotor assessment score 9.5 +/- 0.9), while the normothermic group remained severely paraparetic (BBB score 5.3 +/- 0.6; p <or= 0.0005). Hypothermia significantly increased the volume and area of healthy tissue in the peri-injury region, as well as the volume of preserved white and grey matter. Overall, the data suggest that hypothermia may be a useful bridging therapy to prevent neurological decline prior to decompressive surgery.

Meta-Analysis of Pre-Clinical Studies of Early Decompression in Acute Spinal Cord Injury: A Battle of Time and Pressure

Background The use of early decompression in the management of acute spinal cord injury (SCI) remains contentious despite many pre-clinical studies demonstrating benefits and a small number of supportive clinical studies. Although the pre-clinical literature favours the concept of early decompression, translation is hindered by uncertainties regarding overall treatment efficacy and timing of decompression. Methods We performed meta-analysis to examine the pre-clinical literature on acute decompression of the injured spinal cord. Three databases were utilised; PubMed, ISI Web of Science and Embase. Our inclusion criteria consisted of (i) the reporting of efficacy of decompression at various time intervals (ii) number of animals and (iii) the mean outcome and variance in each group. Random effects meta-analysis was used and the impact of study design characteristics assessed with meta-regression. Results Overall, decompression improved behavioural outcome by 35.1% (95%CI 27.4-42.8; I2=94%, p<0.001). Measures to minimise bias were not routinely reported with blinding associated with a smaller but still significant benefit. Publication bias likely also contributed to an overestimation of efficacy. Meta-regression demonstrated a number of factors affecting outcome, notably compressive pressure and duration (adjusted r2=0.204, p<0.002), with increased pressure and longer durations of compression associated with smaller treatment effects. Plotting the compressive pressure against the duration of compression resulting in paraplegia in individual studies revealed a power law relationship; high compressive forces quickly resulted in paraplegia, while low compressive forces accompanying canal narrowing resulted in paresis over many hours. Conclusion These data suggest early decompression improves neurobehavioural deficits in animal models of SCI. Although much of the literature had limited internal validity, benefit was maintained across high quality studies. The close relationship of compressive pressure to the rate of development of severe neurological injury suggests that pressure local to the site of injury might be a useful parameter determining the urgency of decompression.