Heterotopic Transcallosal Projections Are Present throughout the Mouse Cortex

Transcallosal projection neurons are a population of pyramidal excitatory neurons located in layers II/III and to a lesser extent layer V of the cortex. Their axons form the corpus callosum thereby providing an inter-hemispheric connection in the brain. While transcallosal projection neurons have been described in some detail before, it is so far unclear whether they are uniformly organized throughout the cortex or whether different functional regions of the cortex contain distinct adaptations of their transcallosal connectivity. To address this question, we have therefore conducted a systematic analysis of transcallosal projection neurons and their axons across six distinct stereotactic coordinates in the mouse cortex that cover different areas of the motor and somatosensory cortices. Using anterograde and retrograde tracing techniques, we found that in agreement with previous studies, most of the transcallosal projections show a precise homotopic organization. The somata of these neurons are predominantly located in layer II/III and layer V but notably smaller numbers of these cells are also found in layer IV and layer VI. In addition, regional differences in the distribution of their somata and the precision of their projections exist indicating that while transcallosal neurons show a uniform organization throughout the mouse cortex, there is a sizeable fraction of these connections that are heterotopic. Our study thus provides a comprehensive characterization of transcallosal connectivity in different cortical areas that can serve as the basis for further investigations of the establishment of inter-hemispheric projections in development and their alterations in disease.

Physical exercise counteracts MPTP-induced changes in neural precursor cell proliferation in the hippocampus and restores spatial learning but not memory performance in the water maze

Parkinson's disease (PD) is characterized by a continuous loss of dopaminergic neurons in the substantia nigra, which not only leads to characteristic motor symptoms but also to cognitive impairments. Physical exercise has been shown to improve hippocampus-dependent cognitive functions in PD patients. Animal studies have demonstrated the involvement of adult hippocampal neurogenesis in exercise-induced improvements of visuo-spatial learning and memory. Here, we investigated the direct impact of voluntary wheel running on hippocampal neurogenesis and spatial learning and memory in the Morris water maze (MWM) using the1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We also analyzed striatal and hippocampal dopamine transmission and mRNA expression levels of dopamine receptors. We show that MPTP-induced spatial learning deficits were alleviated by short-term physical exercise but not MPTP-induced spatial memory impairments in either exercise intervention group. Neural precursor proliferation was transiently altered in MPTP-treated mice, while the cell survival was increased by exercise. Dopamine was progressively depleted by MPTP and its turnover altered by exercise. In addition, gene expression of dopamine receptor D1/D5 was transiently upregulated following MPTP treatment but not affected by physical exercise. Our findings suggest that physical exercise benefits spatial learning but not memory performance in the MWM after MPTP-induced dopamine depletion by restoring precursor cell proliferation in the hippocampus and influencing dopamine transmission. This adds to the understanding of cognitive decline and mechanisms for potential improvements by physical exercise in PD patients.

Circulating insulin-like growth factor binding protein-3 predicts one-year outcome after ischemic stroke

BACKGROUND

Insulin-like Growth Factor-1 (IGF-1) and Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) have been ascribed neuroprotective effects. We sought to determine whether levels of IGF-1 and IGFBP-3 predict functional outcome after ischemic stroke.

METHODS

IGF-1 and IGFBP-3 levels were measured in the first week after stroke in patients with first ischemic stroke who were enrolled in the Berlin Cream&Sugar Study. National Institutes of Health Stroke Scale (NIHSS) was collected at admission. Lesion volume was determined from acute MRI if available. Functional outcome according to the modified Rankin Scale (mRS) was assessed after one year. In multivariate analyses we identified parameters associated with unfavourable functional outcome (mRS>2).

RESULTS

We included 100 patients. 21 patients had an unfavourable functional outcome. IGF-1 levels were<- 2 standard deviation score (SDS) in 7 patients, and>2 SDS in 12 patients. IGFBP-3 levels were<the 5(th) percentile in 13 patients, and no patient had IGFBP-3 levels>the 95(th) percentile. Low levels of IGFBP-3 (p=0.002), NIHSS at admission (p=0.043) and age (p=0.001) were associated with unfavourable functional outcome in the univariate analyses. In multivariate analysis including IGFBP-3, IGF-1, age, thrombolysis and NIHSS only low IGFBP-3 levels (OR 7.2, 95%CI 1.8-29.0, p=0.006) were associated with unfavourable functional outcome. If lesion volume was incuded (n=71), only IGFBP-3 levels (OR 7.2, 95%CI 1.5-35.5, p=0.015) were associated with unfavourable functional outcome.

CONCLUSION

IGFBP-3 levels after ischemic stroke may independently predict functional outcome after one year.