Growing clinical, neuro-imaging and post-mortem data have implicated the cerebellum as playing an important role in the pathogenesis of essential tremor. Aside from a modest reduction of Purkinje cells in some post-mortem studies, Purkinje cell axonal swellings (torpedoes) are present to a greater degree in essential tremor cases than controls. Yet a detailed study of more subtle morphometric changes in the Purkinje cell axonal compartment has not been undertaken. We performed a detailed morphological analysis of the Purkinje cell axonal compartment in 49 essential tremor and 39 control brains, using calbindin D28k immunohistochemistry on 100-µm cerebellar cortical vibratome tissue sections. Changes in axonal shape [thickened axonal profiles (P = 0.006), torpedoes (P = 0.038)] and changes in axonal connectivity [axonal recurrent collaterals (P < 0.001), axonal branching (P < 0.001), terminal axonal sprouting (P < 0.001)] were all present to an increased degree in essential tremor cases versus controls. The changes in shape and connectivity were significantly correlated [e.g. correlation between thickened axonal profiles and recurrent collaterals (r = 0.405, P < 0.001)] and were correlated with tremor duration among essential tremor cases with age of onset >40 years. In essential tremor cases, thickened axonal profiles, axonal recurrent collaterals and branched axons were 3- to 5-fold more frequently seen on the axons of Purkinje cells with torpedoes versus Purkinje cells without torpedoes. We document a range of changes in the Purkinje cell axonal compartment in essential tremor. Several of these are likely to be compensatory changes in response to Purkinje cell injury, thus illustrating an important feature of Purkinje cells, which is that they are relatively resistant to damage and capable of mobilizing a broad range of axonal responses to injury. The extent to which this plasticity of the Purkinje cell axon is partially neuroprotective or ultimately ineffective at slowing further cellular changes and cell death deserves further study in essential tremor.

Based on accumulating post-mortem evidence of abnormalities in Purkinje cell biology in essential tremor, we hypothesized that regressive changes in dendritic morphology would be apparent in the Purkinje cell population in essential tremor cases versus age-matched controls. Cerebellar cortical tissue from 27 cases with essential tremor and 27 age-matched control subjects was processed by the Golgi-Kopsch method. Purkinje cell dendritic anatomy was quantified using a Neurolucida microscopic system interfaced with a motorized stage. In all measures, essential tremor cases demonstrated significant reductions in dendritic complexity compared with controls. Median values in essential tremor cases versus controls were: 5712.1 versus 10 403.2 µm (total dendrite length, P=0.01), 465.9 versus 592.5 µm (branch length, P=0.01), 22.5 versus 29.0 (maximum branch order, P=0.001), and 165.3 versus 311.7 (number of terminations, P=0.008). Furthermore, the dendritic spine density was reduced in essential tremor cases (medians=0.82 versus 1.02 µm(-1), P=0.03). Our demonstration of regressive changes in Purkinje cell dendritic architecture and spines in essential tremor relative to control brains provides additional evidence of a pervasive abnormality of Purkinje cell biology in this disease, which affects multiple neuronal cellular compartments including their axon, cell body, dendrites and spines.

Background Although essential tremor (ET) is among the most prevalent neurological diseases, its precise pathogenesis is not understood. Purkinje cell loss has been observed in some studies and is the focus of interest and debate. Expressing these data as Purkinje cells/layer length allows one to adjust for the inherent curved nature of the cerebellar folia. Capitalizing on the Essential Tremor Centralized Brain Repository, we quantified Purkinje cell linear density in cases vs. controls. Methods Free-floating, 100 μm, parasagittal cerebellar hemispheric sections were subjected to rabbit polyclonal anti-Calbindin D28k antibody, and 10 random fields/brain were selected for quantification of Purkinje cells/mm−1 Purkinje cell layer. Results Purkinje cell linear density was lower in 32 ET cases than 16 controls (1.14 ± 0.32 vs. 1.35 ± 0.31 per mm−1, p = 0.03). Purkinje cell linear density was inversely associated with torpedo count (r = −0.38, p = 0.028). Discussion The current sample of ET cases demonstrates a reduction in Purkinje cell number relative to that of controls. Greater Purkinje cell axonal remodeling (torpedoes) was found in individuals who had the most Purkinje cell drop out. The role of Purkinje cell loss in the pathogenesis of this disorder merits additional study.

Background Glioblastoma and primary CNS lymphoma (PCNSL) dictate different neurosurgical strategies; it is critical to distinguish between them preoperatively. However, current imaging modalities do not effectively differentiate them. We aim to examine the use of DWI and T1-weighted dynamic contrast-enhanced (DCE)-MRI as potential discriminative tools. Methods We retrospectively reviewed 18 PCNSL and 36 matched glioblastoma patients with pretreatment DWI- and DCE-MRI. VOIs were drawn around the tumor on contrast-enhanced T1WI and FLAIR images; these images were transferred onto coregistered ADC maps to obtain ADC, and onto DCE perfusion maps to obtain plasma volume (Vp) and permeability transfer constant (Ktrans). Histogram analysis was performed to determine mean (ADCmean) and relative ADCmean (rADCmean), and relative 90th percentile values for plasma volume (rVp90%tile) and permeability transfer constant (rKtrans90%tile). Non-parametric tests were used to assess differences and ROC analysis was performed for optimal threshold calculations. Results The enhancing component of PCNSL was found to have significantly lower ADCmean (1.1 × 103 vs 1.4 × 103; p<0.001) and rADCmean (1.5 vs 1.9; p<0.001) and rVp90%tile (3.7 vs 5.0; p<0.05) than the enhancing component of glioblastoma, but not significantly different rKtrans90%tile (5.4 vs 4.4; p=0.83). The non-enhancing portions of GBM and PCNSL did not differ in these parameters. Based on ROC analysis, mean ADC provided the best threshold (AUC 0.83) to distinguish primary CNS lymphoma from glioblastoma, which was not improved with normalized ADC or addition of perfusion parameters. Conclusion ADC was superior to DCE-MRI perfusion alone or in combination in differentiating PCNSL from glioblastoma.

Background In addition to tremor, patients with essential tremor (ET) may exhibit non-motor features, including a range of cognitive deficits. Several prospective, population-based epidemiological studies have reported an association between ET and incident dementia, especially Alzheimer's disease (AD). Moreover, in a brain repository-based study, a larger than expected proportion of ET patients also developed pathological changes characteristic of progressive supranuclear palsy, further suggesting a link between ET and tau pathology. Methods We selected a group of ET patients that were free of dementia clinically and without AD on postmortem examination. Our hypothesis was that neuronal tauopathic burden would be higher in the brains of these ET patients compared to controls. We compared Braak stage for neuronal tangles and Consortium to Establish a Registry for Alzheimer's Disease (CERAD) scores for neuritic plaques in the two groups. Results The two groups were similar in age (82.6±6.0 vs. 80.4±8.1, p=0.22). The 40 ET patients had a higher Braak neurofibrillary stage than 32 controls (means: 2.2 ± 1.2 vs. 1.2 ± 1.1; medians: 2.0 vs. 1.0, p <0.001). Meanwhile, CERAD scores for neuritic plaques were similar in patients and controls (means: 0.6 ± 0.9 vs. 0.5 ± 0.6; medians: 0.0 vs. 0.0, p = 0.83). Conclusion While ET itself is not a tauopathy (i.e., a neurodegenerative disorder among whose main features are accumulation of hyperphosphorylated tau protein), ET may predispose individuals to accumulate more widespread cellular tau aggregates, and thus tau could play a central role in the cognitive impairment that can accompany ET.

Genetic polymorphisms in Solute carrier family 1 (glial high affinity glutamate transporter), member 2 (SLC1A2) have been linked with essential tremor. SLC1A2 encodes excitatory amino acid transporter type 2 (EAAT2), which clears glutamate from the synaptic cleft. One postulated mechanism for essential tremor is the over-excitation of glutamatergic olivo-cerebellar climbing fibers, leading to excitotoxic death of Purkinje cells. Other glutamatergic excitatory signals are transmitted to Purkinje cells via parallel fibers of cerebellar granule neurons. Therefore, the expression level of glutamate transporters could be important in essential tremor pathogenesis. Using Western blotting, we compared the expression levels of the two main glutamate transporters in the cerebellar cortex, EAAT1 and EAAT2, in postmortem tissue from 16 essential tremor cases and 13 age-matched controls. We also studied the localization of EAAT1 and EAAT2 using immunohistochemistry in 10 essential tremor cases and 12 controls. EAAT1 protein levels were similar in cases and controls (1.12 ± 0.83 vs. 1.01 ± 0.69, p =0.71) whereas EAAT2 protein levels in essential tremor cases were only 1/3 of that in controls (0.35 ± 0.23 vs. 1.00 ± 0.62, p < 0.01). Interestingly, EAAT2, but not EAAT1, was expressed in astrocytic processes surrounding the Purkinje cell axon initial segment, a region of previously observed pathological changes in essential tremor. Our main finding, a significant reduction in cerebellar cortical EAAT2 protein levels in essential tremor, suggests that Purkinje cells in essential tremor might be more vulnerable to excitotoxic damage than those of controls.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-014-0157-z) contains supplementary material, which is available to authorized users.

Pretreatment Vp and K derived from dynamic contrast-enhanced MRI may be novel prognostic quantitative imaging biomarkers of progression-free survival in patients with PCNSL. These data should be prospectively validated in larger patient cohorts.

Background It would be useful to identify additional postmortem markers of Purkinje cell loss in essential tremor (ET). In hereditary cerebellar ataxia, Purkinje cell loss has been reported to result in a secondary increase in the density of the remaining cell populations in the cerebellar molecular layer. However, this phenomenon has not been studied in ET. We quantified cerebellar molecular layer cellular density in 15 ET cases, 15 controls, and 7 spinocerebellar ataxia (SCA) cases (2:2:1 ratio). Methods A standard neocerebellar tissue block was stained with Luxol fast blue Hematoxylin & Eosin. Within 5 selected fields, cell soma (e.g., stellate, basket, and glial cell bodies) were counted. Cellular density was the number of cells/cm2. Results The Purkinje cell count differed across the three groups (p<0.001), with the highest counts in controls, intermediate counts in ET cases and lowest counts in SCA cases. ET cases and controls had similar molecular layer cellular density (p=0.79) but SCA cases had higher values than both groups (p<0.01). A robust inverse correlation between Purkinje cell count and molecular layer cellular density (i.e., brains with more Purkinje cell loss had higher molecular layer cellular density), observed in SCA and controls (r= −0.55, p=0.008), was not observed in ET cases. Discussion Although Purkinje cell counts were reduced in ET cases compared to controls, an increase in molecular layer cellular density was not evident in ET. The increase in molecular layer cellular density, observed in SCA cases, may require a more marked loss of PCs than occurs in ET.