Biology subjects

McCann, K. E.

Publications and source records attributed to McCann, K. E..

9 recordsLinked to original sources

bioRxiv2025

Impact of early locus coeruleus lesions in the TgF344 Alzheimer's disease rat model

INTRODUCTIONIn murine models of Alzheimers disease (AD), lesioning the locus coeruleus-norepinephrine (LC-NE) system with DSP-4 exacerbates AD-like neuropathology and cognitive impairment. However, the impact of LC lesions during prodromal stages is poorly characterized. METHODSTgF344-AD and wild-type rats received monthly injections of DSP-4 or saline from 1-5 months of age, a time point preceding forebrain plaque or tangle deposition in TgF344-AD rats, after which behavior and pathology were assessed. RESULTSDSP-4 compromised LC cell bodies, fibers, and NE content. LC lesion and the AD transgene each affected several affective behaviors and/or cognition individually, but few interactions were found and DSP-4 failed to exacerbate behavioral phenotypes or neuropathology in TgF344-AD rats. DISCUSSIONCombined with previous literature, our data suggest that LC lesions exacerbate pre-existing AD-like pathology and behavioral impairments, rather than accelerate their onset. Further characterization of LC lesions in TgF344-AD rats at different ages is warranted. Research-in-ContextO_LISystemic review: The authors reviewed existing literature using traditional sources, including PubMed. Previous studies investigated the impact of locus coeruleus (LC) lesions on Alzheimers disease (AD)-like neuropathology and behavior in murine models of AD. However, the impact of LC degeneration in an animal model that expresses both amyloid and endogenous tau pathology at a time point before the emergence of significant forebrain pathology is underexplored. C_LIO_LIInterpretation: We expanded the behavioral and molecular characterization of TgF344-AD rats in response to N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4)-induced LC lesions during the pre-pathology stages of disease. Unexpectedly, we found that TgF344-AD genotype and DSP-4 rarely interacted to exacerbate AD-related symptoms or pathology. C_LIO_LIFuture Directions: Our results indicate LC lesions do not accelerate onset of AD-like neuropathology or behavioral impairment in this model. Future studies in older TgF344-AD animals and using different DSP-4 treatment regimens would help clarify the relationship between LC integrity and AD progression. C_LI HighlightsO_LILocus coeruleus damage causes apathy-like behavior and changes in arousal C_LIO_LITgF344-AD genotype induces social recognition deficits and anxiety-like behavior C_LIO_LILocus coeruleus damage and TgF344-AD genotype rarely interact to worsen deficits C_LIO_LIInteractions that exacerbate Alzheimers disease neuropathology were also scarce C_LI

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bioRxiv2023

Entorhinal cortex vulnerability to human APP expression promotes hyperexcitability and tau pathology

Preventative treatment for Alzheimers Disease is of dire importance, and yet, cellular mechanisms underlying early regional vulnerability in Alzheimers Disease remain unknown. In human patients with Alzheimers Disease, one of the earliest observed pathophysiological correlates to cognitive decline is hyperexcitability. In mouse models, early hyperexcitability has been shown in the entorhinal cortex, the first cortical region impacted by Alzheimers Disease. The origin of hyperexcitability in early-stage disease and why it preferentially emerges in specific regions is unclear. Using cortical-region and cell-type-specific proteomics coupled with ex vivo and in vivo electrophysiology, we uncovered differential susceptibility to human-specific amyloid precursor protein (hAPP) in a model of sporadic Alzheimers. Unexpectedly, our findings reveal that early entorhinal hyperexcitability may result from intrinsic vulnerability of parvalbumin (PV) interneurons, rather than the suspected layer II excitatory neurons. This vulnerability of entorhinal PV interneurons is specific to hAPP, as it could not be recapitulated with increased murine APP expression. However, partial replication of the findings could be seen after introduction of a murine APP chimera containing a humanized amyloid-beta sequence. Surprisingly, neurons in the Somatosensory Cortex showed no such vulnerability to adult-onset hAPP expression. hAPP-induced hyperexcitability in entorhinal cortex could be ameliorated by enhancing PV interneuron excitability in vivo. Co-expression of human Tau with hAPP decreased circuit hyperexcitability, but at the expense of increased pathological tau species. This study suggests early disease interventions targeting non-excitatory cell types may protect regions with early vulnerability to pathological symptoms of Alzheimers Disease and downstream cognitive decline.

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bioRxiv2023

Genetic disruption of dopamine β-hydroxylase dysregulates innate responses to predator odor in mice

In rodents, exposure to predator odors such as cat urine acts as a severe stressor that engages innate defensive behaviors critical for survival in the wild. The neurotransmitters norepinephrine (NE) and dopamine (DA) modulate anxiety and predator odor responses, and we have shown previously that dopamine {beta}-hydroxylase knockout (Dbh -/-), which reduces NE and increases DA in mouse noradrenergic neurons, disrupts innate behaviors in response to mild stressors such as novelty. We examined the consequences of Dbh knockout (Dbh -/-) on responses to predator odor (bobcat urine) and compared them to Dbh-competent littermate controls. Over the first 10 min of predator odor exposure, controls exhibited robust defensive burying behavior, whereas Dbh -/- mice showed high levels of grooming. Defensive burying was potently suppressed in controls by drugs that reduce NE transmission, while excessive grooming in Dbh -/- mice was blocked by DA receptor antagonism. In response to a cotton square scented with a novel "neutral" odor (lavender), most control mice shredded the material, built a nest, and fell asleep within 90 min. Dbh -/- mice failed to shred the lavender-scented nestlet, but still fell asleep. In contrast, controls sustained high levels of arousal throughout the predator odor test and did not build nests, while Dbh -/- mice were asleep by the 90-min time point, often in shredded bobcat urine-soaked nesting material. Compared with controls exposed to predator odor, Dbh -/- mice demonstrated decreased c-fos induction in the anterior cingulate cortex, lateral septum, periaqueductal gray, and bed nucleus of the stria terminalis, but increased c-fos in the locus coeruleus and medial amygdala. These data indicate that relative ratios of central NE and DA signaling coordinate the type and valence of responses to predator odor.

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bioRxiv2023

Tyrosinase-induced neuromelanin accumulation triggers rapid dysregulation and degeneration of the mouse locus coeruleus

The locus coeruleus (LC), the major source of norepinephrine (NE) in the brain, is among the first sites of pathology in both Alzheimers disease (AD) and Parkinsons disease (PD), and it undergoes catastrophic degeneration later in both disorders. Dysregulation of the LC is thought to contribute to early behavioral symptoms of AD and PD such as anxiety and sleep disturbances, while frank LC loss promotes cognitive decline. However, the mechanisms responsible for this selective vulnerability are unknown. It has been suggested that neuromelanin (NM) pigment contributes to LC susceptibility, but a causal relationship has been difficult to test because rodents do not naturally produce NM. Here, we report that viral-mediated expression of human tyrosinase-induced pigmentation in male and female mouse LC neurons recapitulated key macroscopic and ultrastructural features of natural primate NM. One week of NM accumulation resulted in LC neuron hyperactivity, reduced tissue NE levels, transcriptional changes, and anxiety-like behavior. By 6 weeks, NM accumulation was associated with severe cell-autonomous LC neuron degeneration, neuroinflammation, and microglial engulfment of the pigment granules, while the anxiety-like behavior abated. These phenotypes are reminiscent of LC dysfunction and cell death in AD and PD, validating this model for studying the consequences of NM accumulation in the LC as it relates to neurodegenerative diseases. Significance StatementAlzheimers disease (AD) and Parkinsons disease (PD) are the most common neurodegenerative diseases worldwide. Because therapies that cure or prevent their progression are lacking, research is focused on the identifying the earliest signs of disease as targets for diagnosis and treatment. The locus coeruleus (LC), the main source of norepinephrine (NE) in the brain, is one of the first brain regions affected in both AD and PD. Early on, LC dysregulation promotes behavioral symptoms of AD and PD, while its subsequent degeneration accelerates disease progression. Here we identify neuromelanin (NM) pigment as an LC vulnerability factor that induces neuronal hyperactivity followed by cell death. Approaches that mitigate NM accumulation and toxicity may target the earliest phases of neurodegenerative disease.

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bioRxiv2022

Age-dependent dysregulation of locus coeruleus firing in a transgenic rat model of Alzheimers disease

Accumulation of hyperphosphorylated tau in the locus coeruleus (LC) is a ubiquitous feature of prodromal Alzheimers disease (AD), and LC neurons degenerate as AD progresses. Tau-mediated LC dysfunction may contribute to early neuropsychiatric symptoms, while loss of LC integrity is associated with conversion to cognitive impairment. Hyperphosphorylated tau alters firing rates in other brain regions, but its effects on LC neurons have not been described. The purpose of this study was to characterize changes in firing properties of LC neurons when they are the only cells containing hyperphosphorylated tau, as well as later in disease when {beta}-amyloid (A{beta}) and tau pathology is abundant in the forebrain. Single unit LC activity was recorded from anesthetized wild-type (WT) and TgF344-AD rats, which carry the APP/PS1 transgene. Similar to human AD, these rats develop hyperphosphorylated tau in the LC (at 6 months) prior to A{beta} or tau pathology in forebrain regions (at 12-15 months). At baseline, LC neurons from TgF344-AD rats were hypoactive at both ages compared to WT littermates, but showed elevated spontaneous bursting properties, particularly in younger animals. Differences in footshock-evoked LC firing depended on age, with 6-month TgF344-AD rats demonstrating aspects of hyperactivity, and aged transgenic rats showing hypoactivity relative to WT. Tau-induced alterations in LC firing rates may contribute to the pathophysiology of AD, with early hyperactivity associated with prodromal symptoms, followed by hypoactivity contributing to cognitive impairment. These results support further investigation into disease stage-dependent noradrenergic interventions for AD. HighlightsO_LIRecorded locus coeruleus (LC) neurons in a rat model of Alzheimers disease (AD) C_LIO_LITgF344-AD rats develop early endogenous LC tau pathology akin to human AD C_LIO_LI6- and 15-month TgF344-AD rats had reduced tonic LC firing C_LIO_LILC neurons from 6-month TgF344-AD rats were hyperactive in response to footshock C_LIO_LILC neuron dysfunction may contribute to AD symptoms C_LI

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bioRxiv2022

The Neurotoxin DSP-4 Dysregulates the Locus Coeruleus-Norepinephrine System and Recapitulates Molecular and Behavioral Aspects of Prodromal Neurodegenerative Disease

The noradrenergic locus coeruleus (LC) is among the earliest sites of tau and alpha-synuclein pathology in Alzheimers disease (AD) and Parkinsons disease (PD), respectively. The onset of these pathologies coincides with loss of noradrenergic fibers in LC target regions and the emergence of prodromal symptoms including sleep disturbances and anxiety. Paradoxically, these prodromal symptoms are indicative of a noradrenergic hyperactivity phenotype, rather than the predicted loss of norepinephrine (NE) transmission following LC damage, suggesting the engagement of complex compensatory mechanisms. Because current therapeutic efforts are targeting early disease, interest in the LC has grown, and it is critical to identify the links between pathology and dysfunction. We employed the LC-specific neurotoxin DSP-4, which preferentially damages LC axons, to model early changes in the LC-NE system pertinent to AD and PD in male and female mice. DSP-4 (2 doses of 50 mg/kg, 1 week apart) induced LC axon degeneration, triggered neuroinflammation and oxidative stress, and reduced tissue NE levels. There was no LC cell death or changes to LC firing, but transcriptomics revealed reduced expression of genes that define noradrenergic identity and other changes relevant to neurodegenerative disease. Despite the dramatic loss of LC fibers, NE turnover and signaling were elevated in terminal regions and were associated with anxiogenic phenotypes in multiple behavioral tests. These results represent a comprehensive analysis of how the LC-NE system responds to axon/terminal damage reminiscent of early AD and PD at the molecular, cellular, systems, and behavioral levels, and provides potential mechanisms underlying prodromal neuropsychiatric symptoms.

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bioRxiv2022

Norepinephrine and dopamine contribute to distinct repetitive behaviors induced by novel odorant stress in male and female mice

Exposure to unfamiliar odorants induces an array of repetitive defensive and non-defensive behaviors in rodents which likely reflect adaptive stress responses to the uncertain valence of novel stimuli. Mice genetically deficient for dopamine {beta}-hydroxylase (Dbh-/-) lack the enzyme required to convert dopamine (DA) into norepinephrine (NE), resulting in globally undetectable NE and supranormal DA levels. Because catecholamines modulate novelty detection and reactivity, we investigated the effects of novel plant-derived odorants on repetitive behaviors in Dbh-/- mice and Dbh+/- littermate controls, which have catecholamine levels comparable to wild-type mice. Unlike Dbh+/- controls, which exhibited vigorous digging in response to novel odorants, Dbh-/- mice displayed excessive grooming. Drugs that block NE synthesis or neurotransmission suppressed odorant-induced digging in Dbh+/- mice, while a DA receptor antagonist attenuated grooming in Dbh-/- mice. The testing paradigm elicited high circulating levels of corticosterone regardless of Dbh genotype, indicating that NE is dispensable for this systemic stress response. Odorant exposure increased NE and DA abundance in the prefrontal cortex (PFC) of Dbh+/- mice, while Dbh-/- animals lacked NE and had elevated PFC DA levels that were unaffected by novel smells. Together, these findings suggest that novel odorant-induced increases in central NE tone contribute to repetitive digging and reflect psychological stress, while central DA signaling contributes to repetitive grooming. Further, we have established a simple method for repeated assessment of stress-induced repetitive behaviors in mice, which may be relevant for modeling neuropsychiatric disorders like Tourette syndrome or obsessive-compulsive disorder that are characterized by stress-induced exacerbation of compulsive symptoms.

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bioRxiv2021

Consequences of endogenous and virally-induced hyperphosphorylated tau on behavior and cognition in a rat model of Alzheimer's disease

BackgroundThe locus coeruleus (LC) is one of the earliest brain regions to accumulate hyperphosphorylated tau, but a lack of animal models that recapitulate this pathology has hampered our ability to understand its contributions to the pathophysiology of Alzheimers disease (AD). ObjectiveWe previously reported that TgF344-AD rats, which overexpress mutant human amyloid precursor protein and presenilin-1, accumulate early endogenous hyperphosphorylated tau in the LC. Here, we used TgF344-AD rats and a wild-type (WT) human tau virus to interrogate the effects of endogenous hyperphosphorylated rat tau and human tau in the LC on AD-related neuropathology and behavior. MethodsTwo-month old TgF344-AD and WT rats received bilateral LC infusions of WT human tau or mCherry control virus driven by the noradrenergic-specific PRSx8 promoter. Rats were subsequently assessed at 6 and 12 months for arousal (sleep latency), anxiety-like behavior (open field, elevated plus maze, novelty-suppressed feeding), passive coping (forced swim task), and learning and memory (Morris water maze and fear conditioning). Hippocampal microglia, astrocyte, and AD pathology were evaluated using immunohistochemistry. ResultsIn general, the effects of age were more pronounced than genotype or treatment; older rats displayed greater hippocampal pathology, took longer to fall asleep, had reduced locomotor activity, floated more, and had impaired cognition compared to younger animals. TgF344-AD rats showed increased anxiety-like behavior and impaired learning and memory. The tau virus had negligible influence on most measures. ConclusionEffects of hyperphosphorylated tau on AD-like neuropathology and behavioral symptoms were subtle. Further investigation of different forms of tau is warranted.

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bioRxiv2020

Binding affinities of oxytocin, vasopressin, and Manning Compound at oxytocin and V1a receptors in Syrian hamster brains

Oxytocin (OT) and arginine vasopressin (AVP), as well as synthetic ligands targeting their receptors (OTR, V1aR), are used in a wide variety of research contexts, but typically their pharmacological properties are determined in only a few species. Syrian hamsters (Mesocricetus auratus) have a long history of use as a behavioral and biomedical model for the study of oxytocin and vasopressin, and more recently, hamsters have been used to investigate behavioral consequences of OT-mediated activation of V1aRs. We sought to determine the binding affinities of OT, AVP, and the selective V1aR antagonist, Manning compound, in OTRs and V1aRs found in hamster brains. We performed saturation binding asays to determine the Kd values for the selective OTR and V1aR radioligands, [125I]OVTA and [125I]LVA in hamster brains. We then performed competition binding assays to determine Ki values for OT, AVP, and Manning compond at both the OTR and V1aR. We found that OT and AVP each had the highest affinity for their canonical receptors (OT-OTR Ki=4.28 nM; AVP-V1ar Ki=4.70 nM), and had the lowest affinity for their non-canonical ligands (OT-V1aR=495.2nM; AVP-OTR Ki=36.1 nM). Manning compound had the highest affinity for the V1aR (MC-V1aR Ki=6.87 nM; MC-OTR Ki=213.8 nM), but Manning compound was not as selective for the V1aR as has been reported in rat receptor. When comparing these data to previously published work, we found that the promiscuity of the V1aR in hamsters with respect to oxytocin and vasopressin binding is more similar to the promiscuity of the human V1aR than the rat V1aR receptor. Moreover, the selectivity of oxytocin at hamster receptors is more similar to the selectivity of oxytocin at human receptors than the selectivity of oxytocin at rat receptors. These data highlight the importance of determining the pharmacological properties of behaviorally relevant compounds in diverse models species.

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