Biology subjects

Bedard, M. L.

Publications and source records attributed to Bedard, M. L..

9 recordsLinked to original sources

bioRxiv2026

Xylazine's k-opioid agonist activity is not shared with other FDA-approved alpha2-adrenergic agonists

Xylazine is a 2-adrenergic agonist typically used in as a sedative and analgesic in veterinary medicine. For some years, xylazine has been reported as an additive to fentanyl on the illicit drug market and has been associated with severe side-effects including severe ulcerations and potential amputations at the sites of injection along with an increased risk of respiratory depression and death. We recently reported that xylazine has modest {kappa} opioid agonist activity in vitro and in vivo and asked if other 2-adrenergic agonists had similar off-target activities. To test this hypothesis, we profiled US FDA-approved 2-adrenergic agonists at 320 G protein coupled receptors (GPCRs) to identify potentially deleterious and/or beneficial off-targets. Although all other tested 2-adrenergic agonists were devoid of {kappa} opioid agonist activity, each had a distinct pattern of activity at various GPCRs and differential patterns of signaling bias at 2-receptor subtypes. These findings suggest potential molecular targets for both side-effects and therapeutic activities among known 2-adrenergic agonists.

neuroscience↗

bioRxiv2025

Characterization of hippocampal subfields using histology-based annotated postmortem MRI: Lessons for in vivo segmentation II

High-resolution in vivo magnetic resonance imaging (MRI) of hippocampal subfields is a rapidly advancing field due to their implication in cognition, disorder, and disease. Hippocampal subfield segmentation on in vivo MRI is generally guided by postmortem reference material, which has been limited by small sample sizes that preclude comprehensive characterization of subfield border locations and their variability. Addressing this, we characterized hippocampal subfield border variability in two ultra-high-resolution postmortem MRI datasets with combined annotated histological sections, including cases with and without dementia. We examined: 1) the order of appearance and disappearance of subfields along the long axis of the hippocampus; 2) the order of appearance and disappearance of subicular subregions; 3) the medial-lateral position of subicular subregional boundaries along the hippocampal body; 4) the location of the CA3 relative to hippocampal head digitations; 5) the subfield borders in the hippocampal body relative to a volume proportion of the dark band; and 6) the association of hippocampal length and subiculum-CA1 border location with diagnosis, demographic factors, and factors related to postmortem imaging. Our findings reaffirmed that there is a consistent order of appearance and disappearance of subfields in the hippocampal head and tail, respectively. The subicular subregions exhibited a first in, last out order of appearance and disappearance, and pre/parasubiculum consistently occupied half of the subicular complex in coronal slices throughout the hippocampal body. Hippocampal head digitations were not a reliable landmark for CA3 appearance, but SRLM proportionality did offer a potentially consistent approach for estimating CA2 and CA3 subfield borders in relation to the hippocampal border. No clear relationship was found between the anatomical features and diagnosis, demographic factors, and factors related to postmortem imaging. These findings have implications for the development and harmonization of hippocampal subfield segmentation protocols and interpretation of high-resolution functional MRI studies of the human hippocampus.

neuroscience↗

bioRxiv2025

Xylazine and fentanyl co-administration delays wound healing in mice

Xylazine, a veterinary sedative increasingly found in the unregulated drug supply, is associated with severe skin wounds in humans, particularly when co-used with fentanyl. Despite growing concern, the mechanisms underlying these wounds remain unclear. To investigate how xylazine and fentanyl affect wound healing, we administered subcutaneous injections of saline, xylazine (3.2 mg/kg), fentanyl (1.0 mg/kg), or their combination to female C57BL/6J mice for 28 days. After a standardized punch biopsy, wound closure was tracked for 14 days, with continued drug exposure. Mice receiving the xylazine-fentanyl combination exhibited significantly delayed wound healing compared to all other groups, as shown by slower closure rates and increased area under the healing curve. A follow-up study without chronic pretreatment showed that acute xylazine-fentanyl exposure still altered healing dynamics, although it did not significantly delay time to closure. Neither drug alone impaired healing at the tested doses. These findings suggest that prior exposure to xylazine and fentanyl contributes to impaired wound healing and support the hypothesis that xylazine-associated wounds may arise from delayed healing of pre-existing skin injuries rather than spontaneous formation. This is the first preclinical model of xylazine-related wound impairment and provides a foundation for future research into biological mechanisms and potential interventions for these emerging soft tissue injuries.

pharmacology and toxicology↗

bioRxiv2025

Glutamate delta-1 receptors regulate a novel tonic excitatory conductance in the mouse bed nucleus of the stria terminalis and influence neuronal function

The plasticity of ionotropic receptors (mainly AMPARs and NMDARs) within the glutamatergic system has long been investigated as a mechanism for physiological and pathological adaptive learning. The tetrameric delta glutamate receptors ({delta}GluRs, GluD1 and GluD2) are homologs of the AMPARs and NMDARs, however they are insensitive to glutamate. These proteins, especially GluD1, have been implicated in multiple psychiatric conditions and play a functional role in synapses assembly and stability, but recent evidence suggests they also may supply a tonic excitatory conductance, are sensitive to poly-amine blockade, and regulate synaptic plasticity. Here we use whole-cell patch clamp electrophysiology to functionally characterize these receptors in the dorsolateral bed nucleus of the stria terminalis (dlBNST) and investigate their modulation of both synaptic transmission and cell excitability. Our results suggest that {delta}GluRs, and in particular GluD1, carry a tonic conductance, modulate excitatory synapses, and regulate cell excitability in the dlBNST. These results imply that GluD1 functions to regulate the flow of information through the BNST and may play a role in affect, stress, and substance use disorders.

neuroscience↗

bioRxiv2025

Developing an anatomically valid segmentation protocol for anterior regions of the medial temporal lobe for neurodegenerative diseases

BackgroundThe anterior portion of the medial temporal lobe (MTL) is one of the first regions targeted by pathology in sporadic Alzheimers disease (AD) and Limbic-predominant Age-related TDP-43 Encephalopathy (LATE) indicating a potential for metrics from this region to serve as imaging biomarkers. Leveraging a unique post-mortem dataset of histology and magnetic resonance imaging (MRI) scans we aimed to 1) develop an anatomically valid segmentation protocol for anterior entorhinal cortex (ERC), Brodmann Area (BA) 35, and BA36 for in vivo 3 tesla (T) MRI and 2) incorporate this protocol in an automated approach. MethodsWe included 20 cases (61-97 years old, 50% females) with and without neurodegenerative diseases (11 vs. 9 cases) to ensure generalizability of the developed protocol. Digitized MTL Nissl-stained coronal histology sections from these cases were annotated and registered to same-subject post-mortem MRI. The protocol was developed by determining the location of histological borders of the MTL cortices in relation to anatomical landmarks. Subsequently the protocol was applied to 15 cases twice, with a 2-week interval, to assess intra-rater reliability with the Dice Similarity Index (DSI). Thereafter it was implemented in our in- house Automatic Segmentation of Hippocampal Subfields (ASHS)-T1 approach and evaluated with DSIs. ResultsThe anterior histological border distances of ERC, BA35 and BA36 were evaluated with respect to various anatomical landmarks and the distance relative to the beginning of the hippocampus was chosen. To formulate segmentation rules, we examined the histological sections for the location of borders in relationship to anatomical landmarks in the coronal sections. The DSI for the anterior MTL cortices for the intra-rater reliability was 0.85-0.88 and for the ASHS-T1 against the manual segmentation was 0.62-0.65. DiscussionWe developed a reliable segmentation protocol and incorporated it in an automated approach. Given the vulnerability of the anterior MTL cortices to tau deposition in AD and LATE, the updated approach is expected to improve imaging biomarkers for these diseases.

neuroscience↗

bioRxiv2025

Xylazine potentiates the interoceptive effects of fentanyl in male and female rats

RationaleXylazine, a sedative typically used in veterinary medicine, has been increasingly detected as an adulterant in the unregulated opioid supply and present in opioid overdose deaths. Therefore, xylazine-adulterated fentanyl is a growing public health concern. People who use drugs have reported that xylazine changes and prolongs the effects of fentanyl ObjectivesWe used standard operant drug discrimination procedures to better understand how xylazine impacts the discriminative stimulus/interoceptive effects of fentanyl. MethodsMale and female Long-Evans rats (n=23) were trained to discriminate fentanyl (0.032 mg/kg intraperitoneal) such that one lever was reinforced with sucrose on days when fentanyl was administered, and the other lever was reinforced when vehicle was administered. Once rats met testing criteria, we tested a dose range of fentanyl to confirm discriminative stimulus control, then we tested if xylazine alone produced fentanyl-like effects and if the addition of xylazine to fentanyl impacted fentanyl interoceptive effects. ResultsStimulus control was confirmed, as rats showed increased percent responses on the fentanyl-appropriate lever as well as decreased response rates for increasing doses of fentanyl. Xylazine alone did not substitute for the stimulus effects of fentanyl but produced similar response rate reductions as fentanyl alone. Xylazine co-administered with fentanyl potentiated the stimulus effects of lower doses of fentanyl in both males and females and potentiated response rate reductions. ConclusionsThese results indicate that xylazine enhances the interoceptive effects of fentanyl, which may inform clinical research about xylazine-adulterated fentanyl.

neuroscience↗

bioRxiv2023

Xylazine is an agonist at kappa opioid receptors and exhibits sex-specific responses to naloxone administration

Xylazine has been found in the unregulated drug supply at increasing rates, usually in combination with fentanyl. It has become critical to understand its basic pharmacology, how it impacts behavior, and how it interacts with fentanyl in rodent models of opioid administration. Despite commentary from scientists, politicians, and public health officials, it is not known if xylazine impacts the efficacy of naloxone, the opioid receptor antagonist used to reverse opioid induced respiratory depression. Furthermore, few studies have examined the effects of xylazine alone, without co-administration of ketamine. Here, we examine the impact of xylazine alone and in combination with fentanyl on several key behaviors in male and female mice. We demonstrate differential locomotor responses by dose and sex to xylazine. Surprisingly, our results further indicate that naloxone precipitates withdrawal from xylazine and a fentanyl/xylazine combination, in both sexes, with enhanced sensitivity in females. Further, we show that xylazine is a full agonist at the kappa opioid receptor, a potential mechanism for its naloxone sensitivity. One-Sentence SummaryWe present surprising new insights into xylazine and fentanyl pharmacology with immediate implications for clinical practice and frontline public health.

neuroscience↗

bioRxiv2022

Probing different paradigms of morphine withdrawal on sleep behavior in male and female C57BL/6J mice

Opioid misuse has dramatically increased over the last few decades resulting in many people suffering from opioid use disorder (OUD). The prevalence of opioid overdose has been driven by the development of new synthetic opioids, increased availability of prescription opioids, and more recently, the COVID-19 pandemic. Coinciding with increases in exposure to opioids, the United States has also observed increases in multiple Narcan (naloxone) administrations as life-saving measures for respiratory depression, and, thus, consequently, naloxone-precipitated withdrawal. Sleep dysregulation is a main symptom of OUD and opioid withdrawal syndrome, and therefore, should be a key facet of animal models of OUD. Here we examine the effect of precipitated and spontaneous morphine withdrawal on sleep behaviors in C57BL/6J mice. We find that morphine administration and withdrawal dysregulate sleep, but not equally across morphine exposure paradigms. Furthermore, many environmental triggers promote relapse to drug-seeking/taking behavior, and the stress of disrupted sleep may fall into that category. We find that sleep deprivation dysregulates sleep in mice that had previous opioid withdrawal experience. Our data suggest that the 3-day precipitated withdrawal paradigm has the most profound effects on opioid-induced sleep dysregulation and further validates the construct of this model for opioid dependence and OUD. HighlightsO_LIMorphine withdrawal differentially dysregulates the sleep of male and female mice C_LIO_LI3-day precipitated withdrawal results in larger changes than spontaneous withdrawal C_LIO_LIOpioid withdrawal affects responses to future sleep deprivation differently between sexes C_LI

neuroscience↗

bioRxiv2021

3D Mapping of Neurofibrillary Tangle Burden in the Human Medial Temporal Lobe

Tau protein neurofibrillary tangles (NFT) are closely linked to neuronal/synaptic loss and cognitive decline in Alzheimers disease (AD) and related dementias. Our knowledge of the pattern of NFT progression in the human brain, critical to the development of imaging biomarkers and interpretation of in vivo imaging studies in AD, is based on conventional 2D histology studies that only sample the brain sparsely. To address this limitation, ex vivo MRI and dense serial histological imaging in 18 human medial temporal lobe (MTL) specimens were used to construct 3D quantitative maps of NFT burden in the MTL at individual and group levels. These maps reveal significant variation in NFT burden along the anterior-posterior axis. While early NFT pathology is thought to be confined to the transentorhinal region, we find similar levels of NFT burden in this region and other MTL subregions, including amygdala, temporopolar cortex, and subiculum/CA1.

neuroscience↗