Putative dendritic correlates of chronic traumatic encephalopathy: A preliminary quantitative Golgi exploration

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disorder that is associated with repetitive head impacts. Neuropathologically, it is defined by the presence of perivascular hyperphosphorylated tau aggregates in cortical tissue (McKee et al., 2016, Acta Neuropathologica, 131, 75-86). Although many pathological and assumed clinical correlates of CTE have been well characterized, its effects on cortical dendritic arbors are still unknown. Here, we quantified dendrites and dendritic spines of supragranular pyramidal neurons in tissue from human frontal and occipital lobes, in 11 cases with (M_age = 79 ± 7 years) and 5 cases without (M_age = 76 ± 11 years) CTE. Tissue was stained with a modified rapid Golgi technique. Dendritic systems of 20 neurons per region in each brain (N = 640 neurons) were quantified using computer-assisted morphometry. One key finding was that CTE neurons exhibited increased variability and distributional changes across six of the eight dendritic system measures, presumably due to ongoing degeneration and compensatory reorganization of dendritic systems. However, despite heightened variation among CTE neurons, CTE cases exhibited lower mean values than Control cases in seven of the eight dendritic system measures. These dendritic alterations may represent a new pathological marker of CTE, and further examination of dendritic changes could contribute to both mechanistic and functional understandings of the disease.

Dissecting Sholl Analysis into Its Functional Components

Sholl analysis has been an important technique in dendritic anatomy for more than 60 years. The Sholl intersection profile is obtained by counting the number of dendritic branches at a given distance from the soma and is a key measure of dendritic complexity; it has applications from evaluating the changes in structure induced by pathologies to estimating the expected number of anatomical synaptic contacts. We find that the Sholl intersection profiles of most neurons can be reproduced from three basic, functional measures: the domain spanned by the dendritic arbor, the total length of the dendrite, and the angular distribution of how far dendritic segments deviate from a direct path to the soma (i.e., the root angle distribution). The first two measures are determined by axon location and hence microcircuit structure; the third arises from optimal wiring and represents a branching statistic estimating the need for conduction speed in a neuron.

Comparative analysis of corrected tiger genome provides clues to its neuronal evolution

The availability of completed and draft genome assemblies of tiger, leopard, and other felids provides an opportunity to gain comparative insights on their unique evolutionary adaptations. However, genome-wide comparative analyses are susceptible to errors in genome sequences and thus require accurate genome assemblies for reliable evolutionary insights. In this study, while analyzing the tiger genome, we found almost one million erroneous substitutions in the coding and non-coding region of the genome affecting 4,472 genes, hence, biasing the current understanding of tiger evolution. Moreover, these errors produced several misleading observations in previous studies. Thus, to gain insights into the tiger evolution, we corrected the erroneous bases in the genome assembly and gene set of tiger using ‘SeqBug’ approach developed in this study. We sequenced the first Bengal tiger genome and transcriptome from India to validate these corrections. A comprehensive evolutionary analysis was performed using 10,920 orthologs from nine mammalian species including the corrected gene sets of tiger and leopard and using five different methods at three hierarchical levels, i.e. felids, Panthera, and tiger. The unique genetic changes in tiger revealed that the genes showing signatures of adaptation in tiger were enriched in development and neuronal functioning. Specifically, the genes belonging to the Notch signalling pathway, which is among the most conserved pathways involved in embryonic and neuronal development, were found to have significantly diverged in tiger in comparison to the other mammals. Our findings suggest the role of adaptive evolution in neuronal functions and development processes, which correlates well with the presence of exceptional traits such as sensory perception, strong neuro-muscular coordination, and hypercarnivorous behaviour in tiger.