Biology subjects

Chisholm, K. I.

Publications and source records attributed to Chisholm, K. I..

6 recordsLinked to original sources

bioRxiv2026

High-throughput light-sheet 3D microscopy of whole rodent brain microstructure for integration with MRI

Whole-brain cellular mapping is essential for understanding how differences in cellular architecture shape brain organisation and function. Magnetic Resonance Imaging (MRI) provides whole-brain coverage in humans and animal models but is only indirectly sensitive to cellular features. Integrating MRI with whole-brain microscopy is therefore critical for interpreting existing microstructural MRI metrics and developing new, more specific ones. Here, we present a scalable cross-resolution framework that integrates 3D light-sheet microscopy (LSM) of intact rodent brains with diffusion MRI (dMRI) to bridge cellular and macroscopic brain imaging. By combining active electrotransport-based tissue clearing and immunolabelling with accelerated LSM acquisitions, we achieve whole-brain multiplexed mapping of neuronal and glial populations in intact rodent brains on timescales comparable to conventional histology and 2D microscopy. This throughput enables LSM and MRI integration at scale, linking macroscopic MRI contrasts to microscopic cellular features within the same tissue. We apply this framework across eight genetically diverse mouse strains to develop predictive models of 3D microscopy-derived cellular features from multi-shell dMRI-derived contrasts. We demonstrate that data-driven combinations of state-of-the-art dMRI contrasts predict neuronal and astrocytic features better than individual contrasts, across all animals. Our novel approach enables 3D microscopy to guide the development and interpretation of microstructural MRI measures that are ultimately translatable to the living human brain.

neuroscience↗

bioRxiv2024

Characterising the stimulus-response function of mouse C-low threshold mechanoreceptors to mechanical stimuli in vivo

C-low threshold mechanoreceptors (C-LTMRs) in animals (termed C-tactile (CT) fibres in humans) are a subgroup of C-fibre primary afferents, which innervate hairy skin and respond to low threshold punctate indentations and brush stimuli. These afferents respond to gentle, touch stimuli and are implicated in mediating pleasant/affective touch. These afferents have traditionally been studied using low-throughput, technically challenging approaches, including microneurography in humans and teased fibre electrophysiology in other mammals. Here we suggest a new approach to studying genetically labelled C-LTMRs using in vivo calcium imaging. We used an automated rotating brush stimulus and Von Frey filaments, applied to the hairy skin of anaesthetised mice to mirror light and affective touch. Simultaneously we visualised changes in C-LTMR activity and confirmed that these neurons are sensitive to low-threshold punctate mechanical stimuli and brush stimuli with a strong preference for slow brushing speeds. We also reveal that C-LMTRs are directionally sensitive, showing more activity when brushed against the natural orientation of the hair. We present in vivo calcium imaging of genetically labelled C-LTMRs as a useful approach that can reveal new aspects of C-LTMR physiology.

neuroscience↗

bioRxiv2023

Assessing spontaneous sensory neuron activity using in vivo calcium imaging

Heightened spontaneous activity in sensory neurons is often reported in individuals living with chronic pain. It is possible to study this activity in rodents using electrophysiology, but these experiments require great skill and can be prone to bias. Here, we have examined whether in vivo calcium imaging with GCaMP6s can be used as an alternative approach. We show that spontaneously active calcium transients can be visualised in the fourth lumbar dorsal root ganglion (L4 DRG) via in vivo imaging in a mouse model of pain. Application of lidocaine to the nerve, between the inflamed site and the DRG, silenced spontaneous firing and revealed the true baseline level of calcium for spontaneously active neurons. We used this data to train a machine leaning algorithm to predict when a neuron is spontaneously active. We show that our algorithm is accurate in two different models of pain: intraplantar Complete Freunds Adjuvant and antigen-induced arthritis, with accuracies of 90.0% +/-1.2 and 85.9 % +/-2.1, respectively, assessed against visual inspection by an experienced observer. The algorithm can also detect neuronal activity in imaging experiments generated in a different lab using a different microscope configuration (Accuracy = 94.0 % +/2.2). We provide a Google Colaboratory Notebook to allow anyone easy access to this novel tool, for assessment of peripheral neuron activity in their own calcium imaging setups.

neuroscience↗

bioRxiv2022

In vivo calcium imaging shows that satellite glial cells have increased activity in painful states

Satellite glial cells (SGCs) are important for proper neuronal function of primary sensory neurons to whom they provide homeostatic support. Most research of SGC function has been performed with in vitro studies, but recent advances in calcium imaging and transgenic mouse models have enabled this first in vivo study of single cell SGC function in mouse models of inflammation and neuropathic pain. We found that in naive condition SGCs do not respond in a time-locked fashion to neuronal firing. In painful inflammatory and neuropathic states we detected time-locked signals in a subset of SGCs, but only with suprathreshold stimulation of the sciatic nerve. Surprisingly therefore, we conclude that most calcium signals in SGCs seem to develop at arbitrary intervals not directly linked to neuronal activity patterns. More in line with expectations, our experiments also revealed that the number of active SGCs was increased under conditions of inflammation or nerve injury. This could reflect the increased requirement for homeostatic support across dorsal root ganglion neuron populations, which are more active during such painful states.

neuroscience↗

bioRxiv2018

Novel mechanisms of bone cancer pain revealed with in vivo GCaMP6s imaging

Skeletal metastases are frequently accompanied by chronic pain that is mechanoceptive in nature and not easily managed by available therapies. The peripheral sensory profile of primary afferents responsible for transmitting the pain-related messages from cancerous bone to central sites is investigated here. We imaged thousands of primary sensory dorsal root ganglion neurons in vivo in healthy (sham-operated) and cancer-induced bone pain (CIBP) rats in order to analyse and compare their function. Utilising Markov Cluster Analysis we identified distinct clusters of primary afferent responses to limb compression and position. In CIBP rats, three times as many sensory afferents responded to knee compression in the leg ipsilateral to the tumour compared to sham-operated rats. We present evidence that the observed increase in sensory afferent response was not due to increased individual afferent activity but rather represents activation of silent nociceptors, whose origin we propose is largely from outside of the bone.

neuroscience↗

bioRxiv2017

Large scale in vivo recording of sensory neuron activity with GCaMP6

Greater emphasis on the study of intact cellular networks in their physiological environment has led to rapid advances in intravital imaging in the central nervous system, while the peripheral system remains largely unexplored. To assess large networks of sensory neurons we selectively label primary afferents with GCaMP6s and visualise their functional responses in vivo to peripheral stimulation. We show that we are able to monitor simultaneously the activity of hundreds of sensory neurons with sensitivity sufficient to detect, in most cases, single action potentials with a typical rise time of around 200 milliseconds, and an exponential decay with a time constant of approximately 700 milliseconds. Using this sensitive technique we are able to show that large scale recordings demonstrate the recently disputed polymodality of nociceptive primary afferents with between 40-80% of thermally sensitive DRG neurons responding also to noxious mechanical stimulation. We also specifically assess the small population of peripheral cold fibres and demonstrate significant sensitisation to cooling after a model of sterile and persistent inflammation, with significantly increased sensitivity already at decreases of 5{degrees}C when compared to uninflamed responses. This not only reveals interesting new insights into the (patho)physiology of the peripheral nervous system but also demonstrates the sensitivity of this imaging technique to physiological changes in primary afferents.\n\nSignificance StatementMost of our functional understanding of the peripheral nervous system has come from single unit recordings. However, the acquisition of such data is labour-intensive and usually low yield. Moreover, some questions are best addressed by studying populations of neurons. To this end we report on a system that monitors activity in hundreds of single sensory neurons simultaneously, with sufficient sensitivity to detect in most cases single action potentials. We use this technique to characterise nociceptor properties and demonstrate polymodality in the majority of neurons and their sensitization under inflammatory conditions. We therefore believe this approach will be very useful for the studies of the somatosensory system in general and pain in particular.

neuroscience↗