Biology subjects

Cowell, R. M.

Publications and source records attributed to Cowell, R. M..

4 recordsLinked to original sources

bioRxiv2024

Cortico-amygdala synaptic structural abnormalities produced by templated aggregation of α-synuclein

Parkinsons disease (PD) and Dementia with Lewy bodies (DLB) are characterized by neuronal -synuclein (-syn) inclusions termed Lewy Pathology, which are abundant in the amygdala. The basolateral amygdala (BLA), in particular, receives projections from the thalamus and cortex. These projections play a role in cognition and emotional processing, behaviors which are impaired in -synucleinopathies. To understand if and how pathologic -syn impacts the BLA requires animal models of -syn aggregation. Injection of -synuclein pre-formed fibrils (PFFs) into the striatum induces robust -synuclein aggregation in excitatory neurons in the BLA that corresponds with reduced contextual fear conditioning. At early time points after aggregate formation, cortico-amygdala excitatory transmission is abolished. The goal of this project was to determine if -syn inclusions in the BLA induce synaptic degeneration and/or morphological changes. In this study, we used C57BL/6J mice injected bilaterally with PFFs in the dorsal striatum to induce -syn aggregate formation in the BLA. A method was developed using immunofluorescence and three-dimensional reconstruction to analyze excitatory cortico-amygdala and thalamo-amygdala presynaptic terminals closely juxtaposed to postsynaptic densities. The abundance and morphology of synapses were analyzed at 6- or 12-weeks post-injection of PFFs. -Syn aggregate formation in the BLA did not cause a significant loss of synapses, but cortico-amygdala and thalamo-amygdala presynaptic terminals and postsynaptic densities with aggregates of -synuclein show increased volumes, similar to previous findings in human DLB cortex, and in non-human primate models of PD. Transmission electron microscopy showed that PFF-injected mice showed reduced intervesicular distances similar to a recent study showing phospho-serine-129 -synuclein increases synaptic vesicle clustering. Thus, pathologic -synuclein causes major alterations to synaptic architecture in the BLA, potentially contributing to behavioral impairment and amygdala dysfunction observed in synucleinopathies.

neuroscience↗

bioRxiv2023

Differential activation states of direct pathway striatal output neurons associated with thedevelopment of L-DOPA-induced dyskinesia.

L-DOPA-induced dyskinesia (LID) is a debilitating motor side effect arising from chronic dopamine replacement therapy with L-DOPA for the treatment of Parkinson disease (PD). The emergence of LID is linked to heightened sensitivity of striatal dopaminergic signaling and driven by abnormal fluctuations in synaptic dopamine levels following each administration of L- DOPA. This maladaptive plasticity narrows the therapeutic window for L-DOPA treatment, even as the progressive worsening of PD symptoms demands escalating doses. The heterogeneous composition of the striatum, including diverse subpopulations of medium spiny output neurons (MSNs), interneurons, and supporting cells, has complicated the precise identification of the cell(s) underlying LID development and persistence. To elucidate the cellular and molecular mechanisms of LID, we used single nucleus RNA-sequencing (snRNA-seq) to establish a comprehensive striatal transcriptional profile during the development and maintenance of LID in an animal model. Hemiparkinsonian mice were treated with vehicle or L-DOPA for progressive durations (1, 5, or 10 d) and nuclei from the striata were processed for snRNA-seq. Our analysis found that a limited population of dopamine D1 receptor-expressing MSNs (D1-MSNs), arising from both the patch and matrix compartments, formed three subclusters in response to L-DOPA treatment that expressed cellular markers of activation. These activated D1-MSN subpopulations display many of the transcriptional changes previously associated with LID; however, the prevalence and transcriptional behavior of activated D1-MSNs was differentially influenced by the extent of L-DOPA experience. The differentially expressed genes found in these D1-MSNs indicated that acute L-DOPA induced upregulation of multiple plasticity-related transcription factors and regulators of MAPK signaling, while repeated L-DOPA exposure induced numerous genes associated with synaptic remodeling, learning and memory, and transforming growth factor-{beta} (TGF{beta}) signaling. Notably, repeated L-DOPA led to a sensitization in the expression of Inhba, a member of the activin/TGF{beta} superfamily, in activated D1-MSNs. We tested pharmacological inhibition of its receptor, ALK4, and found that it impaired LID development. Collectively, these data suggest that distinct subsets of D1-MSNs become differentially responsive to L-DOPA due to the aberrant induction of the molecular mechanisms necessary for neuronal entrainment, similar to those processes underlying hippocampal learning and memory formation. Our data further suggests that activin/TGF{beta} signaling may play an essential role in LID development in this subpopulation of D1-MSNs.

neuroscience↗

bioRxiv2021

PV-specific loss of the transcriptional coactivator PGC-1α slows down the evolution of epileptic activity in an acute ictogenic model.

The transcriptional coactivator, PGC-1 (peroxisome proliferator activated receptor gamma coactivator 1), plays a key role coordinating energy requirement within cells. Its importance is reflected in the growing number of psychiatric and neurological conditions that have been associated with reduced PGC-1 levels. In cortical networks, PGC-1 is required for the induction of parvalbumin (PV) expression in interneurons, and PGC-1 deficiency affects synchronous GABAergic release. It is unknown, however, how this affects cortical excitability. We show here that knocking down PGC-1 specifically in the PV-expressing cells (PGC-1PV-/-), blocks the activity-dependent regulation of the synaptic proteins, SYT2 and CPLX1. More surprisingly, this cell-class specific knock-out of PGC-1 appears to have a novel anti-epileptic effect, as assayed in brain slices bathed in 0 Mg2+ media. The rate of pre-ictal discharges developed approximately equivalently in wild-type and PGC-1PV-/- brain slices, but the intensity of these discharges was lower in PGC-1PV-/- slices, as evident from the reduced power in the gamma range and reduced firing rates in both PV interneurons and pyramidal cells during these discharges. Reflecting this reduced intensity in the pre-ictal discharges, the PGC-1PV-/- brain slices experienced many more discharges before transitioning into a seizure-like event. Consequently, there was a large increase in the latency to the first seizure-like event in brain slices lacking PGC-1 in PV interneurons. We conclude that knocking down PGC-1 limits the range of PV interneuron firing, and this slows the pathophysiological escalation during ictogenesis.

neuroscience↗

bioRxiv2021

Impaired clock gene expression and abnormal diurnal regulation of hippocampal inhibitory transmission and spatial memory in a mouse model of Alzheimers disease

Patients with Alzheimers disease (AD) often have fragmentation of sleep/wake cycles and disrupted 24-h (circadian) activity. Despite this, little work has investigated the potential underlying day/night disruptions in cognition and neuronal physiology in the hippocampus. The molecular clock, an intrinsic transcription-translation feedback loop that regulates circadian behavior, may also regulate hippocampal neurophysiological activity. We hypothesized that disrupted diurnal variation in clock gene expression in the hippocampus corresponds with loss of normal day/night differences in membrane excitability, synaptic physiology, and cognition. We previously reported that the Tg-SwDI mouse model of AD has disrupted circadian locomotor rhythms and neurophysiological output of the suprachiasmatic nucleus (the primary circadian clock). Here, we report that Tg-SwDI mice failed to show day-night differences in a spatial working memory task, unlike wild-type controls that exhibited enhanced spatial working memory at night. Moreover, Tg-SwDI mice had lower levels of Per2, one of the core components of the molecular clock, at both mRNA and protein levels when compared to age-matched controls. Interestingly, we discovered neurophysiological impairments in area CA1 of the Tg-SwDI hippocampus. In controls, spontaneous inhibitory post-synaptic currents (sIPSCs) in pyramidal cells showed greater amplitude and lower inter-event interval during the day than the night. However, the normal day/night differences in sIPSCs were absent (amplitude) or reversed (inter-event interval) in pyramidal cells from Tg-SwDI mice. In control mice, current injection into CA1 pyramidal cells produced more firing during the night than during the day, but no day/night difference in excitability was observed in Tg-SwDI mice. The normal day/night difference in excitability in controls was blocked by GABA receptor inhibition. Together, these results demonstrate that the normal diurnal regulation of inhibitory transmission in the hippocampus is diminished in a mouse model of AD, leading to decreased daytime inhibition onto hippocampal CA1 pyramidal cells. Uncovering disrupted day/night differences in circadian gene regulation, hippocampal physiology, and memory in AD mouse models may provide insight into possible chronotherapeutic strategies to ameliorate Alzheimers disease symptoms or delay pathological onset.

neuroscience↗