Impact of dendritic spine preservation in medium spiny neurons on dopamine graft efficacy and the expression of dyskinesias in parkinsonian rats.

Dopamine deficiency associated with Parkinson's disease (PD) results in numerous changes in striatal transmitter function and neuron morphology. Specifically, there is marked atrophy of dendrites and dendritic spines on striatal medium spiny neurons (MSN), primary targets of inputs from nigral dopamine and cortical glutamate neurons, in advanced PD and rodent models of severe dopamine depletion. Dendritic spine loss occurs via dysregulation of intraspine Cav1.3 L-type Ca(2+)channels and can be prevented, in animal models, by administration of the calcium channel antagonist, nimodipine. The impact of MSN dendritic spine loss in the parkinsonian striatum on dopamine neuron graft therapy remains unexamined. Using unilaterally parkinsonian Sprague-Dawley rats, we tested the hypothesis that MSN dendritic spine preservation through administration of nimodipine would result in improved therapeutic benefit and diminished graft-induced behavioral abnormalities in rats grafted with embryonic ventral midbrain cells. Analysis of rotational asymmetry and spontaneous forelimb use in the cylinder task found no significant effect of dendritic spine preservation in grafted rats. However, analyses of vibrissae-induced forelimb use, levodopa-induced dyskinesias and graft-induced dyskinesias showed significant improvement in rats with dopamine grafts associated with preserved striatal dendritic spine density. Nimodipine treatment in this model did not impact dopamine graft survival but allowed for increased graft reinnervation of striatum. Taken together, these results demonstrate that even with grafting suboptimal numbers of cells, maintaining normal spine density on target MSNs results in overall superior behavioral efficacy of dopamine grafts.

Increased cell suspension concentration augments the survival rate of grafted tyrosine hydroxylase immunoreactive neurons.

The poor survival rate (5-20%) of grafted embryonic dopamine (DA) neurons is one of the primary factors preventing cell replacement from becoming a viable treatment for Parkinson's disease. Previous studies have demonstrated that graft volume impacts grafted DA neuron survival, indicating that transplant parameters influence survival rates. However, the effects of mesencephalic cell concentration on grafted DA neuron survival have not been investigated. The current study compares the survival rates of DA neurons in grafts of varying concentrations. Mesencephalic cell suspensions derived from E14 Fisher 344 rat pups were concentrated to 25,000, 50,000, 100,000 and 200,000 cells/microl and transplanted into two 0.5 microl sites in the 6-OHDA-denervated rat striatum. Animals were sacrificed 10 days and 6 weeks post-transplantation for histochemical analysis of striatal grafts. The absolute number of DA neurons per graft increased proportionally to the total number of cells transplanted. However, our results show that the 200,000 cells/microl group exhibited significantly higher survival rates (5.48+/-0.83%) compared to the 25,000 cells/microl (2.81+/-0.39%) and 50,000 cells/microl (3.36+/-0.51%) groups (p=0.02 and 0.03, respectively). Soma size of grafted DA neurons in the 200,000 cells/microl group was significantly larger than that of the 25,000 cells/microl (p<0.0001) and 50,000 cells/microl groups (p=0.004). In conclusion, increasing the concentration of mesencephalic cells prior to transplantation, augments the survival and functionality of grafted DA neurons. These data have the potential to identify optimal transplantation parameters that can be applied to procedures utilizing stem cells, neural progenitors, and primary mesencephalic cells.

Advances in thin tissue Golgi-Cox impregnation: fast, reliable methods for multi-assay analyses in rodent and non-human primate brain.

In 1873 Camillo Golgi discovered a staining technique that allowed for the visualization of whole neurons within the brain, initially termed 'the black reaction' and is now known as Golgi impregnation. Despite the capricious nature of this method, Golgi impregnation remains a widely used method for whole neuron visualization and analysis of dendritic arborization and spine quantification. We describe a series of reliable, modified 'Golgi-Cox' impregnation methods that complement some existing methods and have several advantages over traditional whole brain 'Golgi' impregnation. First, these methods utilize 60-100µm thick brain sections, which allows for fast, reliable impregnation of neurons in rats (7-14 days) and non-human primates (NHP) (30 days) while avoiding the pitfalls of other 'rapid Golgi' techniques traditionally employed with thin sections. Second, these methods employ several common tissue fixatives, resulting in high quality neuron impregnation in brain sections from acrolein, glutaraldehyde, and paraformaldehyde perfused rats, and in glutaraldehyde perfused NHP brain tissue. Third, because thin sections are obtained on a vibratome prior to processing, alternate sections of brain tissue can be used for additional analyses such as immunohistochemistry or electron microscopy. This later advantage allows for comparison of, for example, dendrite morphology in sections adjacent to pertinent histochemical markers or ultrastructural components. Finally, we describe a method for simultaneous light microscopic visualization of both tyrosine hydroxylase immunohistochemistry and Golgi impregnation in the same tissue section. Thus, the methods described here allow for fast, high quality Golgi impregnation and conserve experimental subjects by allowing multiple analyses within an individual animal.

Subthalamic nucleus stimulation increases brain derived neurotrophic factor in the nigrostriatal system and primary motor cortex.

The mechanisms underlying the effects of long-term deep brain stimulation of the subthalamic nucleus (STN DBS) as a therapy for Parkinson's disease (PD) remain poorly understood. The present study examined whether functionally effective, long-term STN DBS modulates glial cell line-derived neurotrophic factor (GDNF) and/or brain-derived neurotrophic factor (BDNF) in both unlesioned and unilateral 6-hydroxydopamine lesioned rats. Lesioned rats that received two weeks of continuous unilateral STN DBS exhibited significant improvements in parkinsonian motor behaviors in tests of forelimb akinesia and rearing activity. Unilateral STN DBS did not increase GDNF in the nigrostriatal system, primary motor cortex (M1), or hippocampus of unlesioned rats. In contrast, unilateral STN DBS increased BDNF protein 2-3 fold bilaterally in the nigrostriatal system with the location (substantia nigra vs. striatum) dependent upon lesion status. Further, BDNF protein was bilaterally increased in M1 cortex by as much as 2 fold regardless of lesion status. STN DBS did not impact cortical regions that receive less input from the STN. STN DBS also was associated with bilateral increases in BDNF mRNA in the substantia nigra (SN) and internal globus pallidus (GPi). The increase observed in GPi was completely blocked by pretreatment with 5-Methyl-10,11-dihydro-5 H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), suggesting that the activation of N-methyl-D-aspartate (NMDA) receptors was involved in this phenomenon. The upregulation of BDNF associated with long term STN DBS suggest that this therapy may exert pronounced and underappreciated effects on plasticity in the basal ganglia circuitry that may play a role in the symptomatic effects of this therapy as well as support the neuroprotective effect of stimulation documented in this rat model.