Biology subjects

Witton, J.

Publications and source records attributed to Witton, J..

9 recordsLinked to original sources

bioRxiv2026

Coordinated acetylcholine release and adaptation of neuronal representations in the retrosplenial cortex during contextual uncertainty

Accurate learning underpins optimal predictions and requires the brain to navigate uncertainty, identifying important information and distinguishing between expected and unexpected uncertainties. Theoretical models propose that the neuromodulator acetylcholine positively correlates with expected uncertainty, priming neuronal networks for learning. We tested this hypothesis by measuring acetylcholine release and neuronal representations in the retrosplenial cortex of mice whilst challenging them with expected and unexpected uncertainties of reward location. Acetylcholine release did not directly correlate with expected or unexpected uncertainty but instead increased with changes in expected uncertainty. In tandem, increased expected uncertainty shifted neuronal representations from a positional reference frame to focus on salient landmarks, such as reward location. Transitions in expected uncertainty also accelerated remapping of neuronal representations and behavioural adaptation when unexpected uncertainty was experienced. Thus, we demonstrate acetylcholine release in retrosplenial cortex discerns types of uncertainty and correlates with learning speed in uncertain environments.

neuroscience↗

bioRxiv2025

Anterior thalamic nucleus inputs to the retrosplenial cortex are unperturbed in the hAPP-J20 mouse model of Alzheimer's disease

Alzheimers disease (AD) is a neurodegenerative condition characterised by progressive loss of memory and general decline in cognitive function. Although research has traditionally focused on the hippocampus and entorhinal cortex, other regions important for memory and spatial navigation, such as the anterior thalamic nuclei (ATN) and retrosplenial cortex (RSC), are also affected. The RSC is an important brain region for both memory and spatial navigation, and displays dysfunction in humans during prodromal phases of AD. The ATN provide a major input to RSC, with loss of this input to RSC causing a dramatic reduction in the expression of the immediate early gene product c-Fos. The ATN to RSC connection may thus present a new target for therapeutic intervention in AD. Here, we set out to determine whether AD-like pathology perturbed projections from ATN to RSC using the hAPP-J20 amyloidopathy mouse model, using optogenetic activation of thalamic inputs combined with ex vivo patch clamp electrophysiology. We found that RSC displayed an age-dependent decline in basal c-Fos activity, with no additional effect of amyloid pathology on c-Fos expression. At all time points (3, 6 and 9 months) measured, we found no evidence of impairments in the synaptic strength or efficacy of the ATN projections to either granular or dysgranular subdivisions of RSC. We conclude that, in the hAPP-J20 mouse model, this pathway is unaffected by amyloid-{beta} overexpression.

neuroscience↗

bioRxiv2025

Gamma frequency neuronal oscillations modulate microglia morphology via colony stimulating factor 1 receptor and NFκB pathway signalling

Within the brain, neurons and glial cells engage in dynamic crosstalk to maintain homeostasis and regulate neuroimmune responses. Recent studies have implicated rhythmic neuronal network activity, most notably at gamma oscillation frequencies (approx. 25-100 Hz), in modulating the morphology and function of microglia, the brains primary immune cells. Little is known, however, about the cellular mechanisms underlying this form of neuroimmune communication. Using pharmacological and optogenetic models of gamma oscillations in mouse brain slices, we found that gamma oscillations stimulate microglia to adopt a reactive morphological phenotype via activation of colony stimulation factor 1 receptor (CSF1R) and nuclear factor {kappa}B-mediated signalling. Surprisingly, inhibition of two downstream mediators of CSF1R signalling - phosphoinositide-3-kinase or phospholipase C - did not prevent this effect, suggesting that neuron-microglia interactions in this context may occur via compensatory or alternative CSF1R-linked pathways. These findings provide important insights into how rhythmic brain activity regulates neuroimmune function, with potential implications for neurological health and disease.

neuroscience↗

bioRxiv2025

Dissection of retrosplenial cortex inputs: ubiquitous drive from anterior thalamus

The retrosplenial cortex (RSC) is a highly interconnected brain region involved in spatial navigation and associative learning. It forms extensive, reciprocal connections with sensory, hippocampal, parahippocampal, prefrontal, and thalamic areas. RSC comprises granular (gRSC) and dysgranular (dRSC) subdivisions with distinct connectivity and functions. Despite its emerging role in behaviour and its implication in memory-related disorders such as Alzheimers disease, the nature of its synaptic inputs remains poorly understood. Here, we combined viral anatomical tracing, optogenetic stimulation, and patch-clamp electrophysiology to investigate inputs from the anterior cingulate cortex (ACC), dorsal subiculum (dSub), and anterior thalamic nuclei (ATN) to gRSC and dRSC. Strikingly, all recorded RSC pyramidal neurons received ATN input, regardless of subdivision or cortical layer. Activation of ATN inputs evoked significantly larger post-synaptic responses than those from dSub or ACC, though both regions maintained substantial connectivity with RSC. While dSub projections appeared denser in gRSC, synaptic responses were larger in dRSC, albeit with lower input probability. Notably, NMDA receptor-mediated components of RSC excitatory inputs were weaker than expected, potentially explaining the reported inability to induce long-term potentiation in RSC in ex vivo neurophysiology experiments. This is the first study to characterise the synaptic properties of retrosplenial afferents. Our findings highlight the dominant influence of ATN inputs and raise important questions about how RSCs long-range connectivity supports its roles in memory and spatial navigation.

neuroscience↗

bioRxiv2023

Cryptococcus neoformans rapidly invades the murine brain by sequential breaching of airway and endothelial tissues barriers and engulfment by microglia

The fungus Cryptococcus neoformans causes lethal meningitis in humans with weakened immune systems and is estimated to account for 10-15% of AIDS-associated deaths worldwide. There are major gaps in our understanding of how this environmental fungus evades the immune system and invades the mammalian brain before the onset of overt symptoms. To investigate the dynamics of C. neoformans tissue invasion, we mapped early fungal localisation and host cell interactions at early times in infected brain, lung, and upper airways using mouse models of systemic and airway infection. To enable this, we developed an in situ imaging pipeline capable of measuring large volumes of tissue while preserving anatomical and cellular information by combining thick tissue sections, tissue clarification, and confocal imaging. Made possible by these techniques, we confirm high fungal burden in mouse upper airway turbinates after nasal inoculation. Surprisingly, most yeasts in turbinates were titan cells, indicating this microenvironment enables titan cell formation with faster kinetics than reported in mouse lungs. Importantly, we observed one instance of fungal cells enmeshed in lamina propria of upper airways, suggesting penetration of airway mucosa as a possible route of tissue invasion and dissemination to the bloodstream. We extend previous literature positing bloodstream dissemination of C. neoformans, via imaging C. neoformans within blood vessels of mouse lungs and finding viable fungi in the bloodstream of mice a few days after intranasal infection, suggesting that bloodstream access can occur via lung alveoli. In a model of systemic cryptococcosis, we show that as early as 24 h post infection, majority of C. neoformans cells traversed the blood-brain barrier, and are engulfed or in close proximity to microglia. Our work establishes that C. neoformans can breach multiple tissue barriers within the first days of infection. This work presents a new method for investigating cryptococcal invasion mechanisms and demonstrates microglia as the primary cells responding to C. neoformans invasion.

microbiology↗

bioRxiv2023

Synaptic alterations associated with disrupted sensory encoding in a mouse model of tauopathy

Synapse loss is currently the best biological correlate of cognitive decline in Alzheimers disease and other tauopathies. Synapses seem to be highly vulnerable to tau-mediated disruption in neurodegenerative tauopathies. However, it is unclear how and when this leads to alterations in function in relation to the progression of tauopathy and neurodegeneration. We used the well-characterised rTg4510 mouse model of tauopathy, at 5-6 months and 7-8 months of age, to study the functional impact of cortical synapse loss. The earlier age was used as a model of prodromal tauopathy, with the later age corresponding to more advanced tau pathology and presumed progression of neurodegeneration. Analysis of synaptic protein expression in the somatosensory cortex showed significant reductions in synaptic proteins and NMDA and AMPA receptor subunit expression in rTg4510 mice. Surprisingly, in vitro whole-cell patch clamp electrophysiology from putative pyramidal neurons in layer 2/3 of the somatosensory cortex suggested no functional alterations in layer 4 to layer 2/3 synaptic transmission at 5-6 months. From these same neurons, however, there were alterations in dendritic structure, with increased branching seen proximal to the soma in rTg4510 neurons. Therefore, in vivo whole-cell patch clamp recordings were utilised to investigate synaptic function and integration in putative pyramidal neurons in layer 2/3 of the somatosensory cortex. These recordings revealed a significant increase in the peak response to synaptically-driven sensory stimulation-evoked activity and a loss of temporal fidelity of the evoked signal to the input stimulus in rTg4510 neurons. Together, these data suggest that loss of synapses, changes in receptor expression, and dendritic restructuring may lead to alterations in synaptic integration at a network level. Understanding of these compensatory processes could identify targets to help delay symptomatic onset within dementia. Abbreviated summaryMeftah et al. report alterations to synaptic and dendrite properties in the rTg4510 mouse model of tauopathy associated with disrupted synaptic integration in vivo. Therefore, disrupted synaptic and network integration may be early markers of synapse loss in neurodegenerative tauopathies.

neuroscience↗

bioRxiv2022

Alterations to parvalbumin-expressing interneuron function and associated network oscillations in the hippocampal - medial prefrontal cortex circuit during natural sleep in APPNL-G-F mice

In the early stages of Alzheimers disease (AD), the accumulation of the peptide amyloid-{beta} (A{beta}) damages synapses and disrupts neuronal activity and leads to disruption of neuronal oscillations associated with cognition. This is thought to be largely due to impairments in CNS synaptic inhibition, particularly via parvalbumin (PV)-expressing interneurons that essential for generating several key oscillations. Research in this field has largely been conducted in mouse models that over-express humanised, mutated forms of AD-associated genes that produce exaggerated pathology. This has prompted the development and use of knock-in mouse lines that express these genes at an endogenous level, such as the AppNL-G-F/NL-G-F mouse model used in the present study. These mice appear to model the early stages of A{beta}-induced network impairments, yet an in-depth characterisation of these impairments in currently lacking. Therefore, using 16 month-old AppNL-G-F/NL-G-F mice, we analysed neuronal oscillations found in the hippocampal - medial prefrontal cortex (mPFC) during awake behaviour, rapid eye movement (REM) and non-REM (NREM) sleep to assess the extent of network dysfunction. No alterations to gamma oscillations were found to occur in the hippocampus or mPFC during either awake behaviour, REM or NREM sleep. However, during NREM sleep an increase in the amplitude of mPFC spindles and decrease in the power of hippocampal SWRs was identified. The former was associated with a decrease in the density of mPFC PV-expressing interneurons and the latter was accompanied by an increase in the synchronisation of PV-expressing interneuron activity, as measured using two-photon Ca2+ imaging. Furthermore, although changes were detected in local network function of mPFC and hippocampus, long-range communication between these regions appeared intact. Altogether, our results suggest that these NREM sleep-specific impairments represent the early stages of circuit breakdown in response to amyloidopathy.

neuroscience↗

bioRxiv2021

Beta bursting in the retrosplenial cortex is a neurophysiological correlate of environmental novelty which is disrupted in a mouse model of Alzheimer's disease.

The retrosplenial cortex (RSC) plays a significant role in spatial learning and memory, and is functionally disrupted in the early stages of Alzheimers disease. In order to investigate neurophysiological correlates of spatial learning and memory in this region we employed in vivo electrophysiology in awake, behaving mice, comparing neural activity between wild-type and J20 mice, a mouse model of Alzheimers disease-associated amyloidopathy. To determine the response of the RSC to environmental novelty local field potentials were recorded while mice explored novel and familiar recording arenas. In familiar environments we detected short, phasic bursts of beta (20-30 Hz) oscillations (beta bursts) which arose at a low but steady rate. Exposure to a novel environment rapidly initiated a dramatic increase in the rate, size and duration of beta bursts. Additionally, theta-beta cross-frequency coupling was significantly higher during novelty, and spiking of neurons in the RSC was significantly enhanced during beta bursts. Finally, aberrant beta bursting was seen in J20 mice, including increased beta bursting during novelty and familiarity, yet a loss of coupling between beta bursts and spiking activity. These findings, support the concept that beta bursting may be responsible for the activation and reactivation of neuronal ensembles underpinning the formation and maintenance of cortical representations, and that disruptions to this activity in J20 mice may underlie cognitive impairments seen in these animals.

neuroscience↗

bioRxiv2019

Impaired speed encoding is associated with reduced grid cell periodicity in a mouse model of tauopathy

Dementia is associated with severe spatial memory deficits which arise from dysfunction in hippocampal and parahippocampal circuits. For spatially-sensitive neurons, such as grid cells, to faithfully represent the environment these circuits require precise encoding of direction and velocity information. Here we have probed the firing rate coding properties of neurons in medial entorhinal cortex (MEC) in a mouse model of tauopathy. We find that grid cell firing patterns are largely absent in rTg4510 mice, while head direction tuning remains largely intact. Conversely, neural representation of running speed information was significantly disturbed, with smaller proportions of MEC cells having firing rates correlated with locomotion in rTg4510 mice. Additionally, the power of local field potential oscillations in the theta and gamma frequency bands, which in wildtype mice are tightly linked to running speed, was invariant in rTg4510 mice. These deficits in locomotor speed encoding likely severely impact path integration systems in dementia.

neuroscience↗