Biology subjects

Marshall, J. J.

Publications and source records attributed to Marshall, J. J..

6 recordsLinked to original sources

bioRxiv2026

Movement refinement and cholinergic regulation of outcome-dependent updating during skilled reaching.

Motor skill learning transforms initially variable actions into precise and reproducible movements, yet conventional measures of task success can obscure the distinct processes through which this refinement occurs. We combined detailed outcome scoring and kinematic analysis of single-pellet reaching in mice to resolve how individual components of the action change with practice. Decomposing reaching into successive stages revealed improvements in targeting and retrieval, while grasp success after pellet contact did not change detectably. Paw trajectories became more consistent across both successful and unsuccessful reaches, whereas changes in the mean speed profile were detected in successful reaches. To examine how striatal cholinergic signaling contributes to movement refinement and the influence of recent outcomes on subsequent actions, we monitored acetylcholine (ACh) in vivo and inhibited cholinergic interneurons (CINs) during training. ACh was elevated before reach onset and declined during execution across all reach outcomes, with no detectable change between early and late training. CIN inhibition had little effect on movement refinement across days, but altered how recent outcomes influenced the next reach, most clearly following attempts in which the pellet was grasped and then lost. These findings distinguish refinement of the practiced movement from outcome-dependent adjustments to its execution. Together, they raise the possibility that the pre-reach ACh elevation plays a role in enabling the evaluation of recent outcomes to update the execution of the next reach.

neuroscience↗

bioRxiv2026

PKNs are required for cardiac hypertrophy induced by angiotensin II in mice

Of the three PKN isoforms, only homozygous Pkn2 knockout in mice is embryonic lethal; mice with Pkn2 haploinsufficiency or Pkn1/3 double knockout (Pkn1/3DKO) have no overt abnormalities. In adult mice, Pkn1/2 are implicated in development of cardiac disease, but studies of Pkn3 in the heart are lacking. Our hypothesis was that a role for Pkn1/3 in adult hearts would be revealed by pathophysiological stress. Here, we report expression profiles of PKNs in cardiac cells, identifying PKN2 as the dominant isoform with expression of PKN3 largely restricted to endothelial/immune cells. To test the hypothesis, Pkn1/3DKO, heterozygous Pkn2 knockout (Pkn2Het) and wild-type mice were treated with 0.8 mg/kg/d AngII, and cardiac function/dimensions assessed using speckle-tracking echocardiography. Baseline assessment identified minor differences in the left ventricle (LV) basal region in Pkn2Het (not Pkn1/3DKO) vs wild-type mice. AngII induced similar increases in LV end diastolic mass (LVEDM) in wild-type and Pkn1/3DKO mice at 3 d. LVEDM increased further in wild-type mice by 7d, but the initial response in Pkn1/3DKO mice was lost whilst stroke volume and cardiac output declined. Thus, hypertrophy was initiated in Pkn1/3DKO mouse hearts but not sustained. AngII increased cardiac fibrosis in wild-type mice together with mRNAs for cardiomyocyte hypertrophy and matrix proteins; this was suppressed in Pkn1/3DKO mice. Changes in expression of mRNA markers for cardiac non-myocytes suggested this was associated with vascular and immune cell dysfunction. In conclusion, Pkn2 does not substitute for Pkn1/3 in developing cardiac hypertrophy, and Pkn1/3 have an independent role in AngII-induced cardiac hypertrophy.

biochemistry↗

bioRxiv2026

A pathogenic AMPA receptor gating mutation disrupts synapse-mitochondrion axis and stalls synapse maturation

AMPA receptors (AMPARs) are central regulators of excitatory synaptic transmission and play critical roles in activity-dependent synapse maturation and circuit development. De novo missense mutations in AMPAR subunits have been widely linked to neurodevelopmental disorders (NDDs). Despite this, how these variants lead to neuronal dysfunction remain poorly understood. Here, we investigate the consequences of a recurrent pathogenic mutation in the GluA1 subunit (GRIA1 p.A636T), which alters AMPAR gating properties and is associated with autism spectrum disorder and intellectual disability. We developed a GluA1A636T knock-in mouse model, we show that GluA1A636T mice exhibit impairments in hippocampal-dependent learning and working memory accompanied by reduced baseline activity of CA1 neurons in vivo. Mass spectrometry-based quantitative proteomic analyses of juvenile and adult hippocampal samples revealed that the A636T mutation significantly alters synaptic protein expression at both ages. Notably, the mutation drives a robust upregulation of mitochondrial proteins specifically in adult mice. Consistent with this, dendritic mitochondria in adult GluA1A636T mice exhibited altered morphology and increased oxidative stress. Electrophysiological analyses further revealed abnormalities in synaptic function, including reduced basal excitatory transmission, persistence of functionally silent synapses in adulthood, and altered synaptic plasticity consistent with impaired synapse maturation. Together, these findings demonstrate that a pathogenic AMPAR gating mutation disrupts the coordinated development of synaptic and metabolic programs in the hippocampus, linking altered excitatory signaling to delayed mitochondrial stress and enduring circuit dysfunction. Our study provides a developmental framework for understanding how disease-associated AMPAR variants impair brain function and highlights synapse-mitochondria coupling as a critical axis in glutamate receptor ionotropic (GRI) disorders.

neuroscience↗

bioRxiv2023

Modulation of the spatiotemporal dynamics of striatal direct pathway neurons and motor output by mGluR5

Striatal spiny-projection neurons (SPNs) integrate glutamatergic inputs from the motor cortex and thalamus with neuromodulatory signals to regulate motor output. In vivo Ca2+ imaging has demonstrated that spatially overlapping ensembles of direct and indirect pathway SPNs (dSPNs, iSPNs) are co-active during spontaneous movement. This co-activity is statistically greater among nearby neurons, correlates with behavioral state, and changes in an SPN-type-specific manner under pathological conditions. How this co-activity arises and whether is important for movement are not well understood. Co-activity likely arises from shared excitatory inputs, the strength of which are scaled by well-characterized mechanisms of synaptic plasticity. Here, we show that the Group I metabotropic glutamate receptor 5 (mGluR5), which regulates the strength of corticostriatal synapses, is a key mediator of behaviorally relevant SPN co-activity. Pharmacological modulation of mGluR5 signaling bidirectionally altered movement and co-activity, but not the absolute level of activity in dSPNs. Targeted deletion of mGluR5 in dSPNs recapitulated the effects on spatiotemporal neural dynamics and movement, consistent with a striatum-specific effect of mGluR5 modulation. Targeted deletion of mGluR5 also produced changes in the synaptic properties of dSPNs. Separate from any effects on overall activity, our results show that excitatory synaptic modulation influences motor function by coordinating the spatial co-activation of dSPNs in vivo.

neuroscience↗

bioRxiv2022

PKN2 deficiency leads both to prenatal congenital cardiomyopathy and defective angiotensin II stress responses.

BackgroundThe protein kinase PKN2 is required for embryonic development, and PKN2 knockout mice die as a result of failure in expansion of mesoderm tissues, cardiac development and neural tube closure. In the adult, cardiomyocyte PKN2 and PKN1 (in combination) are required for cardiac adaptation to pressure-overload. The role of PKN2 in contractile cardiomyocytes during development and its role in the adult heart remain to be fully established. MethodsWe used mice with cardiomyocyte-directed knockout of PKN2 or global PKN2 haploinsufficiency. Cardiac function and dimensions were assessed with high resolution episcopic microscopy, MRI, micro-CT and echocardiography. Biochemical and histological changes were assessed. ResultsCardiomyocyte-directed PKN2 knockout embryos displayed striking abnormalities in the compact myocardium, with frequent myocardial clefts and diverticula, ventricular septal defects and abnormal heart shape. The sub-Mendelian homozygous knockout survivors developed cardiac failure. RNASeq data showed upregulation of PKN2 in patients with dilated cardiomyopathy, suggesting an involvement in adult heart disease. Given the rarity of homozygous survivors with cardiomyocyte-specific deletion of PKN2, this was explored using mice with constitutive heterozygous PKN2 knockout. Cardiac hypertrophy resulting from hypertension induced by angiotensin II was reduced in haploinsufficient PKN2 mice relative to wild-type littermates, with suppression of cardiomyocyte hypertrophy and cardiac fibrosis. ConclusionsCardiomyocyte PKN2 is essential for heart development and formation of compact myocardium, and is also required for cardiac hypertrophy in hypertension. Thus, PKN signalling may offer therapeutic options for managing congenital and adult heart diseases.

developmental biology↗

bioRxiv2018

Development of photoactivatable drugs enables nicotinic optopharmacology

Photoactivatable ( caged) pharmacological agents have revolutionized neuroscience but the palette of available ligands is limited. We describe a general method for caging tertiary amines using an unconventional quaternary ammonium linkage that is chemically stable and elicits a desirable red-shift in activation wavelength. A photoactivatable nicotine (PA-Nic) prepared using this strategy could be uncaged via 1- or 2-photon excitation, making it useful for optopharmacology experiments to study nicotinic acetylcholine receptors (nAChRs) in different experimental preparations and spatiotemporal scales.

neuroscience↗