Biology subjects

Vann, S.

Publications and source records attributed to Vann, S..

5 recordsLinked to original sources

bioRxiv2024

Reduced expression of calcium-binding proteins in the anteroventral thalamic nucleus of individuals with Down syndrome

The anterior thalamic nuclei are important for cognition, and memory in particular. However, little is known about how the anterior thalamic nuclei are affected in many neurological disorders partly due to difficulties in selective segmentation in in vivo scans, due to their size and location. Post-mortem studies, therefore, remain a valuable source of information about the status of the anterior thalamic nuclei. We used post-mortem tissue to assess the status of the anteroventral thalamic nucleus in Down syndrome using samples from males and females ranging from 22-65 years in age and comparing to tissue from age matched controls. As expected, there was increased beta-amyloid plaque expression in the Down syndrome group. While there was a significant increase in neuronal density in the Down syndrome group, the values showed more variation consistent with a heterogeneous population. The surface area of the anteroventral thalamic nucleus was smaller in the Down syndrome group suggesting the increased neuronal density was due to greater neuronal packing but likely fewer overall neurons. There was a marked reduction in the proportion of neurons immunoreactive for the calcium-binding proteins calbindin, calretinin, and parvalbumin in individuals with Down syndrome across all ages. These findings highlight the vulnerability of calcium-binding proteins in the anteroventral nucleus in Down syndrome, which could both be driven by, and exacerbate, Alzheimer-related pathology in this region.

neuroscience↗

bioRxiv2023

Reduced mammillary body volume in individuals with a schizophrenia diagnosis: an analysis of the COBRE data set

While the frontal cortices and medial temporal lobe are well-associated with schizophrenia, the involvement of wider limbic areas is less clear. The mammillary bodies are important for both complex memory formation and anxiety and are implicated in several neurological disorders that present with memory impairments. However, little is known about their role in schizophrenia. Post-mortem studies have reported both a loss of neurons in the mammillary bodies but also reports of increased mammillary body volume. The findings from in vivo MRI studies have also been mixed, but studies have typically only involved small sample sizes. To address this, we acquired mammillary body volumes from the open-source COBRE dataset, where we were able to manually measure the mammillary bodies in 72 individuals with a schizophrenia diagnosis and 74 controls. Participant age ranged from 18-65. We found the mammillary bodies to be smaller in the patient group, across both hemispheres, after accounting for the effects of total brain volume and gender. Hippocampal volumes, but not subiculum or total grey matter volumes, were also significantly lower in patients. Given the importance of the mammillary bodies for both memory and anxiety, this atrophy could contribute to the symptomology in schizophrenia.

neuroscience↗

bioRxiv2021

Apolipoprotein ε4 modifies obesity-related atrophy in the hippocampal formation of cognitively healthy adults.

Characterizing age- and risk-related hippocampal vulnerabilities may inform about the neural underpinnings of cognitive decline. We studied the impact of three risk-factors, Apolipoprotein (APOE)-{varepsilon}4, a family history of dementia, and central obesity, on CA1, CA2/3, dentate gyrus (DG) and subiculum in 158 cognitively healthy adults (38-71 years). Subfields were labelled with the Automatic Segmentation of Hippocampal Subfields (ASHS) and FreeSurfer (version 6) protocols. Volumetric and microstructural measurements from quantitative magnetization transfer and Neurite Orientation Density and Dispersion Imaging were extracted for each subfield and reduced to three principal components capturing apparent myelin/neurite packing, size/complexity, and metabolism. Aging was associated with an inverse U-shaped curve on myelin/neurite packing and affected all subfields. Obesity led to reductions in myelin/neurite packing and size/complexity regardless of APOE and FH status. However, amongst individuals with a healthy Waist-Hip-Ratio, APOE {varepsilon}4 carriers showed lower size/complexity than non-carriers. Protocol type did not affect this risk pattern. These findings provide novel evidence for interactive effects between APOE and central obesity on the hippocampal formation of cognitively healthy adults. HighlightsO_LIAge-related inverted U-shaped curve of hippocampal myelin/neurite packing C_LIO_LIObesity-related reductions of hippocampal myelin/neurite packing and size/complexity C_LIO_LIAPOE modifies the effects of obesity on hippocampal size/complexity C_LIO_LIAge-related slowing of spatial navigation C_LIO_LINo APOE, family history, or obesity effects on cognition C_LI

neuroscience↗

bioRxiv2019

Stable encoding of visual cues in the mouse retrosplenial cortex

The rodent retrosplenial cortex functions as an integrative hub for sensory and motor signals, serving roles in both navigation and memory. While retrosplenial cortex (RSC) is reciprocally connected with the sensory cortex, the form in which sensory information is represented in the retrosplenial cortex and how it interacts with behavioural state is unclear. Here, we used 2-photon cellular imaging of neural activity of putative excitatory (CaMKII expressing) and inhibitory (parvalbumin expressing) neurons to measure visual and running evoked activity in RSC and compare it to primary visual cortex (V1). We found that stimulus position and orientation information was preserved between V1 and RSC, and additionally that positional information was organised topographically. Stimulus directional preference was biased towards nasal-temporal flow. Locomotion modulation of activity of single neurons, both in darkness and light, was also more pronounced in RSC than V1, and strongest in parvalbumin-positive neurons. Longitudinal measurements of single neurons showed that these response features were stably maintained over many weeks. These data provide evidence for stable representations of visual cues in retrosplenial cortex which are highly spatially selective. These may provide sensory data to contribute to the formation of memories of spatial information.

neuroscience↗

bioRxiv2019

Mammillothalamic disconnection alters hippocampo-cortical oscillatory activity and microstructure: Implications for diencephalic amnesia

Diencephalic amnesia can be as disruptive as the more commonly known temporal lobe amnesia, yet the precise contribution of diencephalic structures to memory processes remains elusive. We used discrete lesions of the mammillothalamic tract to model aspects of diencephalic amnesia and assessed the impact of these lesions on multiple measures of activity and plasticity within the hippocampus and retrosplenial cortex. Lesions of the mammillothalamic tract had widespread indirect effects on hippocampo-cortical oscillatory activity within both theta and gamma bands. Both within-region oscillatory activity and cross-regional synchrony were altered. The network changes were state-dependent, displaying different profiles during locomotion and paradoxical sleep. Consistent with the associations between oscillatory activity and plasticity, complementary analyses using several convergent approaches revealed microstructural changes, which appeared to reflect a suppression of learning-induced plasticity in lesioned animals. Together, these combined findings suggest a mechanism by which damage to the medial diencephalon can impact upon learning and memory processes, highlighting important role for the mammillary bodies in the co-ordination of hippocampo-cortical activity.

neuroscience↗