Biology subjects

Thomsen, M. S.

Publications and source records attributed to Thomsen, M. S..

5 recordsLinked to original sources

bioRxiv2026

Freshwater input and tidal position regulate species turnover and interaction rewiring in intertidal ecological networks

The effect that environmental conditions have on community and network assembly processes remains unclear, in part because these processes operate at multiple scales. Because marine primary producers and microinvertebrates have limited mobility, are susceptible to multiple stressors, and can be observed interacting in situ, their habitat-based interactions provide an informative system for disentangling network organising processes. We sampled 646 habitat-use networks, quantifying interactions involving habitat-users and biogenic habitat-formers over 12 months at 9 sites within Te Ihutai/Avon-Heathcote estuary in Christchurch, Aotearoa New Zealand. Using generalised dissimilarity mixed-effect models, we examined whether changes to species interactions - deconstructed into species turnover and interaction rewiring - were modulated by environmental covariates, including freshwater discharge, elevation, temperature, spatial location and season. We found that with increasing dissimilarity in sites proximity to freshwater, interaction change was more driven by rewiring, whereas differences in elevation (i.e., between channels and non-channel habitats) were driven by species turnover, with more sessile species inhabiting tidal channels. The proximity of habitats also played a strong role, with nearby networks comprising more similar interactions, and species turnover becoming more prevalent with increasing distance. Our results highlight that the relative influence and magnitude of rewiring and species turnover in controlling estuarine interaction networks was affected by the individual species distributions across the estuary and their responses to separate, but co-occurring, environmental factors. Quantification of habitat-former/user interaction networks offers robust, albeit understudied, measures of processes that can underpin community assembly, highlighting their potential importance in research, management and conservation. Open research statementData are provided for peer review. The code for produced from the project analysis and used to draft this manuscript is shared via a public GitHub repository hosted by the Tonkin Research group (repo name: EstInteractTurn). The data used in the formal analysis is hosted on Zenodo, under the corresponding authors profile (doi: 10.5281/zenodo.20619091). The data and code was prepared following strict adherence to the FAIR principles, meaning all data was saved as comma-separated values (.csv) or native R data structures (.rds).

ecology↗

bioRxiv2024

Remodeling of the brain angioarchitecture in experimental chronic neurodegeneration

BackgroundChronic neurodegenerative diseases are characterized by substantial neuroinflammation with accumulation of macrophages, reactive microglia, and reactive astrocytes. Impairment of the brain vasculature is also commonly seen in chronic neurodegeneration with causal links warranting further investigation. MethodsTo address the effects of chronic neurodegeneration on regional vasculature, we performed a unilateral injection of a glutamate receptor agonist ibotenic acid into striatum of adult rats, which caused excitotoxicity in the substantia nigra pars reticulata (SNpr) due to imbalance between inhibitory inputs from the striatum and excitatory signals from the subthalamic nucleus. Brains were examined at 28 days (short-term neurodegeneration) and 91 days (long-term neurodegeneration). Dissected brain samples were analyzed for protein and gene expression using immunohistochemistry and qPCR. Brains were further analyzed for remodeling of vasculature labeled with wheat germ agglutinin (WGA) Alexa Fluor 647 conjugate using 3D deep confocal microscopy of optically cleared samples combined with machine learning-based image analysis. ResultsThe resulting neurodegeneration was accompanied by neuroinflammation, verified by the expression of inflammatory markers with gradual, regional loss of brain tissue. An in-depth analysis of the angioarchitecture of the degenerating SNpr revealed substantial changes of the vasculature with higher density, increased diameter, and number of tortuous vessels already after 28 days continuing at 91 days. Interestingly, the vascular remodeling changes occurred without changes in the expression of endothelial tight junction proteins, vascular basement membrane proteins, or markers of angiogenesis. ConclusionsThese results demonstrate how neurodegeneration causing prominent tissue loss in SNpr also leads to substantial remodeling of the angioarchitecture, while not altering the structural integrity of the vessel wall judged from the continuous expression of hallmarks of brain endothelial cells and the vascular basement membrane. We propose that this remodeling occurs as a consequence of the loss of brain tissue and with the resulting changes leaving the vasculature prone to additional vascular pathologies like vessel occlusion or formation of aneurysms.

neuroscience↗

bioRxiv2024

Endothelial and neuronal engagement by AAV-BR1 alleviates neurological symptoms and cholesterol deposition in a mouse model of Niemann-Pick type C2

BackgroundPatients with the genetic disorder Niemann-Pick type C2 disease (NP-C2) suffer from lysosomal accumulation of cholesterol causing both systemic and severe neurological symptoms. In a murine NP-C2 model, otherwise successful intravenous Niemann-Pick C2 protein (NPC2) replacement therapy fails to alleviate progressive neurodegeneration as infused NPC2 is unable to cross the blood-brain barrier (BBB). Genetic modification of brain endothelial cells (BECs) is thought to enable secretion of recombinant proteins thereby overcoming the restrictions of the BBB. We hypothesized that BBB-directed gene therapy using the AAV-BR1-NPC2 vector would transduce both BECs and neurons in a mouse model of NP-C2 (Npc2-/-). MethodsSix weeks old Npc2-/- mice were intravenously injected with the AAV-BR1-NPC2 vector. Post-mortem analyses included gene expression analyses, determination of NPC2 transduction in the CNS, and co-detection of cholesterol with NPC2 in neurons. ResultsThe vector exerted tropism for BECs and neurons resulting in a widespread NPC2 distribution in the brain with a concomitant reduction of cholesterol in adjacent neurons, presumably not transduced by the vector. ConclusionThe data suggests cross-correcting gene therapy to the brain via delivery of NPC2 from BECs and neurons.

neuroscience↗

bioRxiv2021

Systemic administration of Ivabradine, an HCN channel inhibitor, blocks spontaneous absence seizures

ObjectiveHyperpolarization-activated cyclic nucleotide-gated (HCN) channels are known to be involved in the generation of absence seizures (ASs), and there is evidence that cortical and thalamic HCN channel dysfunctions may have a pro-absence role. Many HCN channel blockers are available, but their role in ASs has been investigated only by localized brain injection or in in vitro model systems due to their limited brain availability. Here, we investigated the effect on ASs of orally administered ivabradine (an HCN channel blocker approved for the treatment of heart failure in humans) following injection of the P-glycoprotein inhibitor elacridar, that is known to increase penetration into the brain of drug substrates for this efflux transporter. The action of ivabradine was also tested following in vivo microinjection in the cortical initiation network (CIN) of the somatosensory cortex and in the thalamic ventrobasal nucleus (VB) as well as on cortical and thalamocortical neurons in brain slices. MethodsWe used EEG recordings in freely moving Genetic Absence Epilepsy from Strasbourg Rats (GAERS) to assess the action of oral administration of ivabradine, with and without elacridar, on ASs. Ivabradine was also microinjected in the CIN and VB of GAERS in vivo and applied to Wistar CIN and GAERS VB slices while recording patch-clamped cortical layer 5/6 and thalamocortical neurons, respectively. ResultsOral administration of ivabradine markedly and dose-dependently reduced ASs. Ivabradine injection in CIN abolished ASs and elicited small-amplitude 4-7 Hz waves (without spikes), whereas in the VB it was less potent. Moreover, ivabradine applied to GAERS VB and Wistar CIN slices selectively decreased HCN-channel-dependent properties of cortical layer 5/6 pyramidal and thalamocortical neurons, respectively. SignificanceThese results provide the first demonstration of the anti-absence action of a systemically administered HCN channel blocker, indicating the potential of this class of drugs as a novel therapeutic avenue for ASs.

neuroscience↗

bioRxiv2020

The blood-brain barrier studied in vitro across species

The blood-brain barrier (BBB) is formed by brain capillary endothelial cells (BECs) supported by pericytes and astrocytes. The BBB maintains homeostasis and protects the brain against toxic substances circulating in the blood, which consequently means that only a few drugs can pass the BBB. Thus for drug screening, understanding cell interactions, and pathology, in vitro BBB models have been developed using BECs from various animal sources. When comparing models of different species, differences exist especially in regards to the transendothelial electrical resistance (TEER). Thus, in the present study, we compared primary mice, rat, and porcine BECs (mBECs, rBECs, and pBECs) cultured in mono- and co-culture with astrocytes, to identify potential species-dependent differences that could explain the variations in TEER and aid to the selection of models for future in vitro BBB studies. The in vitro BBB models based on primary mBECs, rBECs, and pBECs were evaluated and compared in regards to major BBB characteristics. The barrier integrity was evaluated by the expression of tight junction proteins and measurements of TEER and apparent permeability (Papp). Furthermore, the cell size, the functionality of the P-glycoprotein (P-gp) efflux transporter, and the expression of the transferrin receptor were evaluated and compared. pBECs exhibit the highest TEER followed by rBECs and mBECs, but surprisingly the Papp was not that different, which might be explained by a significantly larger cell size of pBECs than rBECs and mBECs. The expression and organization of many tight junction proteins were in all three species influenced by co-culturing, which supports the findings that the TEER increases after co-culturing with astrocytes. Furthermore, all models had functional polarised P-gp efflux transporters and expressed the transferrin receptor. In conclusion, the choice of species for in vitro BBB modeling should be based on the purpose of the study.

neuroscience↗