Integrated multimodal cell atlas of Alzheimer's disease.

Alzheimer's disease (AD) is the most common cause of dementia in older adults. Neuropathological and imaging studies have demonstrated a progressive and stereotyped accumulation of protein aggregates, but the underlying molecular and cellular mechanisms driving AD progression and vulnerable cell populations affected by disease remain coarsely understood. The current study harnesses single cell and spatial genomics tools and knowledge from the BRAIN Initiative Cell Census Network to understand the impact of disease progression on middle temporal gyrus cell types. We used image-based quantitative neuropathology to place 84 donors spanning the spectrum of AD pathology along a continuous disease pseudoprogression score and multiomic technologies to profile single nuclei from each donor, mapping their transcriptomes, epigenomes, and spatial coordinates to a common cell type reference with unprecedented resolution. Temporal analysis of cell-type proportions indicated an early reduction of Somatostatin-expressing neuronal subtypes and a late decrease of supragranular intratelencephalic-projecting excitatory and Parvalbumin-expressing neurons, with increases in disease-associated microglial and astrocytic states. We found complex gene expression differences, ranging from global to cell type-specific effects. These effects showed different temporal patterns indicating diverse cellular perturbations as a function of disease progression. A subset of donors showed a particularly severe cellular and molecular phenotype, which correlated with steeper cognitive decline. We have created a freely available public resource to explore these data and to accelerate progress in AD research at SEA-AD.org.

Cell-type specific molecular signatures of aging revealed in a brain-wide transcriptomic cell-type atlas.

Biological aging can be defined as a gradual loss of homeostasis across various aspects of molecular and cellular function. Aging is a complex and dynamic process which influences distinct cell types in a myriad of ways. The cellular architecture of the mammalian brain is heterogeneous and diverse, making it challenging to identify precise areas and cell types of the brain that are more susceptible to aging than others. Here, we present a high-resolution single-cell RNA sequencing dataset containing ~1.2 million high-quality single-cell transcriptomic profiles of brain cells from young adult and aged mice across both sexes, including areas spanning the forebrain, midbrain, and hindbrain. We find age-associated gene expression signatures across nearly all 130+ neuronal and non-neuronal cell subclasses we identified. We detect the greatest gene expression changes in non-neuronal cell types, suggesting that different cell types in the brain vary in their susceptibility to aging. We identify specific, age-enriched clusters within specific glial, vascular, and immune cell types from both cortical and subcortical regions of the brain, and specific gene expression changes associated with cell senescence, inflammation, decrease in new myelination, and decreased vasculature integrity. We also identify genes with expression changes across multiple cell subclasses, pointing to certain mechanisms of aging that may occur across wide regions or broad cell types of the brain. Finally, we discover the greatest gene expression changes in cell types localized to the third ventricle of the hypothalamus, including tanycytes, ependymal cells, and Tbx3+ neurons found in the arcuate nucleus that are part of the neuronal circuits regulating food intake and energy homeostasis. These findings suggest that the area surrounding the third ventricle in the hypothalamus may be a hub for aging in the mouse brain. Overall, we reveal a dynamic landscape of cell-type-specific transcriptomic changes in the brain associated with normal aging that will serve as a foundation for the investigation of functional changes in the aging process and the interaction of aging and diseases.

Recurrent giant cell myocarditis after heart transplant: a case report.

Background: Giant cell myocarditis (GCM) is a rare but well-known cause of fulminant myocarditis. Despite optimal medical therapy, many patients progress to orthotopic heart transplant (OHT). We present a case of recurrent GCM following OHT, including complex considerations in patient management and infectious sequelae. Case summary: A 33-year-old previously healthy male presented with 2 months of worsening shortness of breath. Transthoracic echocardiogram (TTE) demonstrated a left ventricular ejection fraction of 30-35%. After ruling out an ischaemic aetiology, he was discharged on guideline-directed medical therapy and later presented with productive cough, worsening dyspnoea on exertion, and diarrhoea. He was found to have elevated troponins and N-terminal pro-brain natriuretic peptide, lactic acidosis, progression of severe bi-ventricular dysfunction on TTE and right heart catheterization, and low cardiac index (1.0 L/min/m2) requiring inotropes. He then required left ventricular assist device as a bridge to OHT. Pathology of the apical core diagnosed GCM as the cause of his fulminant heart failure. He eventually underwent heart transplantation, which was complicated by recurrent GCM. Treatment required intensification of his immunosuppressive regimen, which led to multiple infectious sequelae including norovirus, Shiga-like toxin producing Escherichia coli, and disseminated nocardia of the lung and brain. As of the most recent follow-up, the patient is currently clinically stable. Discussion: Although recurrent GCM after OHT has been reported in the literature, the prognosis is not well understood and there are no clear guidelines regarding management. This case summarizes clinical considerations, treatment strategies, and adverse effects of recurrent GCM treatment.

Initial Experience in Monitoring QT Intervals Using a Six-lead Contactless Mobile Electrocardiogram in an Inpatient Setting.

Mobile electrocardiograms (ECGs) (mECGs) using smartphone applications are an emerging technology. In the coronavirus disease 2019 (COVID-19) era, minimizing patient contact has gained increasing importance. Additionally, increased QT/corrected QT (QTc) monitoring has concurrently been required. The KardiaMobile 6L ECG device, cleared by the United States Food and Drug Administration (FDA) for recording ECGs, along with the KardiaStation tablet application is a platform (AliveCor, Mountain View, CA, USA) that addresses these two issues. A team of residents, fellows, hospitalists, and cardiologists identified inpatients in need of QT/QTc interval monitoring to pilot the adoption of a system composed of a KardiaMobile 6L ECG device with the accompanying KardiaStation tablet application. Concurrent standard ECGs provided validation. Adoption and performance issues were recorded. Four patients agreed to participate in QT/QTc interval monitoring, three of whom were positive for severe acute respiratory syndrome coronavirus 2 viral infection. After basic instructions were given to the patients and their clinical nurses, all patients recorded mECGs successfully. Patients were able to record their own mECG tracings at least once without any assistance. The 12-lead ECGs and mECGs each showed the correct rhythm, and the measured QTc intervals on each modality were consistently acceptable (< 500 ms). Contactless ECGs were successfully uploaded to KardiaStation for QT/QTc interval measurement and archiving. In this study, we showed that an FDA-cleared product, KardiaMobile 6L, has the ability to provide high-quality contactless ECGs for reliable QT/QTc interval measurements. Hospitalized patients were able to perform recordings when requested after receiving simple instructions at the time of first use. This technology has applications during the COVID-19 pandemic and beyond.

Retrospective Chart Review on Real-World Use of Latanoprostene Bunod 0.024% in Treatment-Naïve Patients with Open-Angle Glaucoma.

INTRODUCTION: The objective of this study was to evaluate real-world effectiveness of latanoprostene bunod (LBN) ophthalmic solution 0.024% in treatment-naïve patients newly diagnosed with open-angle glaucoma (OAG) or ocular hypertension. METHODS: This multicenter retrospective chart review included patients aged ≥ 18 years, with no history of medical, laser, or surgical intraocular pressure (IOP)-lowering intervention and at least two follow-up visits (spanning ≥ 2 months) following initiation of LBN treatment. Extracted data included age, sex, race, cup-to-disk ratio, central corneal thickness, IOP, visual acuity (VA), concomitant medications, and adverse events. In patients treated bilaterally, the eye with the higher baseline IOP was the study eye. RESULTS: Medical charts for 65 patients (mean [SD] age, 59 [14] years; 53.8% female) encompassing 125 eyes treated with LBN were reviewed across nine clinical sites. Mean (SD) IOP at baseline was 21.7 (5.9) mmHg. Mean days to first and second follow-up visit were 43 and 141, respectively. LBN use resulted in a mean (SD) reduction from baseline of 7.1 (4.7) and 7.3 (5.1) mmHg at the first and second follow-up visits, respectively (P < 0.0001 for both). Reductions among patients with IOP > 21 mmHg (n = 30) at baseline were 10.0 (4.5) and 11.1 (4.6) mmHg at the first and second follow-up visits (P < 0.0001 for both). There were no meaningful changes in VA. Adverse events appeared infrequent, with only one report of ocular redness. CONCLUSION: In this real-world, retrospective chart review, LBN 0.024% use resulted in robust IOP lowering in newly diagnosed OAG patients new to treatment, and appeared well tolerated.

De novo TBR1 variants cause a neurocognitive phenotype with ID and autistic traits: report of 25 new individuals and review of the literature.

TBR1, a T-box transcription factor expressed in the cerebral cortex, regulates the expression of several candidate genes for autism spectrum disorders (ASD). Although TBR1 has been reported as a high-confidence risk gene for ASD and intellectual disability (ID) in functional and clinical reports since 2011, TBR1 has only recently been recorded as a human disease gene in the OMIM database. Currently, the neurodevelopmental disorders and structural brain anomalies associated with TBR1 variants are not well characterized. Through international data sharing, we collected data from 25 unreported individuals and compared them with data from the literature. We evaluated structural brain anomalies in seven individuals by analysis of MRI images, and compared these with anomalies observed in TBR1 mutant mice. The phenotype included ID in all individuals, associated to autistic traits in 76% of them. No recognizable facial phenotype could be identified. MRI analysis revealed a reduction of the anterior commissure and suggested new features including dysplastic hippocampus and subtle neocortical dysgenesis. This report supports the role of TBR1 in ID associated with autistic traits and suggests new structural brain malformations in humans. We hope this work will help geneticists to interpret TBR1 variants and diagnose ASD probands.

Distinct Laminar Requirements for NMDA Receptors in Experience-Dependent Visual Cortical Plasticity.

Primary visual cortex (V1) is the locus of numerous forms of experience-dependent plasticity. Restricting visual stimulation to one eye at a time has revealed that many such forms of plasticity are eye-specific, indicating that synaptic modification occurs prior to binocular integration of thalamocortical inputs. A common feature of these forms of plasticity is the requirement for NMDA receptor (NMDAR) activation in V1. We therefore hypothesized that NMDARs in cortical layer 4 (L4), which receives the densest thalamocortical input, would be necessary for all forms of NMDAR-dependent and input-specific V1 plasticity. We tested this hypothesis in awake mice using a genetic approach to selectively delete NMDARs from L4 principal cells. We found, unexpectedly, that both stimulus-selective response potentiation and potentiation of open-eye responses following monocular deprivation (MD) persist in the absence of L4 NMDARs. In contrast, MD-driven depression of deprived-eye responses was impaired in mice lacking L4 NMDARs, as was L4 long-term depression in V1 slices. Our findings reveal a crucial requirement for L4 NMDARs in visual cortical synaptic depression, and a surprisingly negligible role for them in cortical response potentiation. These results demonstrate that NMDARs within distinct cellular subpopulations support different forms of experience-dependent plasticity.

Decompression Retinopathy After Goniotomy in a Child: A Case Report.

PURPOSE: To report a case of ocular decompression retinopathy that developed in a child after undergoing goniotomy for uncontrolled pediatric uveitic glaucoma. PATIENT AND METHODS: We describe an 11-year-old Hispanic boy with a history of idiopathic uveitis and elevated intraocular pressure (IOP) in both eyes. He developed marked elevation of the IOP in the right eye (44 mm Hg) despite glaucoma medical therapy. RESULTS: The patient's right eye was treated with goniotomy, with reduction of vision to 20/70 and IOP to between 4 and 7 mm Hg during the first week postoperatively. The retina developed diffuse hemorrhages, both deep and superficial. Many of these hemorrhages had white centers. The findings were consistent with decompression retinopathy. The retinal hemorrhages began to improve 2 weeks and had cleared by 6 weeks after surgery. The IOP measurements ranged between 14 and 16 mm Hg from 2 to 6 weeks after goniotomy and the vision returned to preoperative baseline of 20/20-2 in the right eye. Six weeks after the initial surgery, the left eye was treated with goniotomy with no complications. CONCLUSIONS: Ocular decompression retinopathy, an uncommon complication of glaucoma surgery, can occur after goniotomy.

Contrasting roles for parvalbumin-expressing inhibitory neurons in two forms of adult visual cortical plasticity.

The roles played by cortical inhibitory neurons in experience-dependent plasticity are not well understood. Here we evaluate the participation of parvalbumin-expressing (PV+) GABAergic neurons in two forms of experience-dependent modification of primary visual cortex (V1) in adult mice: ocular dominance (OD) plasticity resulting from monocular deprivation and stimulus-selective response potentiation (SRP) resulting from enriched visual experience. These two forms of plasticity are triggered by different events but lead to a similar increase in visual cortical response. Both also require the NMDA class of glutamate receptor (NMDAR). However, we find that PV+ inhibitory neurons in V1 play a critical role in the expression of SRP and its behavioral correlate of familiarity recognition, but not in the expression of OD plasticity. Furthermore, NMDARs expressed within PV+ cells, reversibly inhibited by the psychotomimetic drug ketamine, play a critical role in SRP, but not in the induction or expression of adult OD plasticity.

Social environment alters opioid-induced hyperalgesia and antinociceptive tolerance in adolescent mice.

BACKGROUND: Chronic opioid treatment is complicated by the development of tolerance and hyperalgesia. Social environment alters both opioid-induced behaviours and nociceptive mechanisms. Our previous studies demonstrated that, in adolescent rodents, the susceptibility to acquire opioid dependence and reward is dependent on the nature of social housing conditions. Specifically, our previous studies demonstrate that housing morphine-treated mice with drug-naïve animals mitigates the abuse liability of opioids. Thus, this study tested the effect of social housing conditions on the development of adaptive processes to morphine antinociception. METHOD: Adolescent males were group-housed in different conditions. In the mixed treatment condition, mice treated with 20 mg/kg morphine (i.e. 'morphine cage-mates') and saline (i.e. 'saline cage-mates') were housed together. In the separated treatment conditions, all mice in the cage received morphine (i.e. 'morphine only') or saline (i.e. 'saline only'). All animals were tested for baseline pain sensitivity and for the response to morphine in the tail withdrawal, hot plate, acetone and von Frey filament tests, during and after discontinuation of opioid treatment. RESULTS: Both morphine cage-mate and morphine only animals developed antinociceptive tolerance. However, this effect was more robust and persistent in the morphine only group. Notably, morphine only animals, but not morphine cage-mates, developed opioid-induced hyperalgesia. CONCLUSION: This study demonstrates that housing morphine-treated mice with drug-naïve animals mitigates the development of opioid-induced hyperalgesia and antinociceptive tolerance. Thus, this study indicates that social environment influences the effectiveness of opioid pain management.

Metabotropic glutamate receptor signaling is required for NMDA receptor-dependent ocular dominance plasticity and LTD in visual cortex.

A feature of early postnatal neocortical development is a transient peak in signaling via metabotropic glutamate receptor 5 (mGluR5). In visual cortex, this change coincides with increased sensitivity of excitatory synapses to monocular deprivation (MD). However, loss of visual responsiveness after MD occurs via mechanisms revealed by the study of long-term depression (LTD) of synaptic transmission, which in layer 4 is induced by acute activation of NMDA receptors (NMDARs) rather than mGluR5. Here we report that chronic postnatal down-regulation of mGluR5 signaling produces coordinated impairments in both NMDAR-dependent LTD in vitro and ocular dominance plasticity in vivo. The data suggest that ongoing mGluR5 signaling during a critical period of postnatal development establishes the biochemical conditions that are permissive for activity-dependent sculpting of excitatory synapses via the mechanism of NMDAR-dependent LTD.

Race, Pain, and Beliefs Associated with Interest in Complementary and Alternative Medicine among Inner City Veterans.

OBJECTIVE: To investigate the prevalence and determinants of complementary and alternative medicine (CAM) interest level among a racially diverse cohort of inner city veterans who receive primary care at the VA Medical Center. DESIGN: Cross-sectional survey study SETTING: Philadelphia VA Medical Center SUBJECTS: Primary care patients (n = 258) METHODS: Interest in CAM was measured using a single item question. Patient treatment beliefs were assessed using validated instruments. We evaluated factors associated with patient interest in CAM using a multivariate logistic regression model. RESULTS: In this sample of 258 inner city primary care VA patients, interest in CAM was high 80% (n = 206). Interest in CAM was strongly associated with African American race [adjusted odds ratio (AOR) 2.19, 95% Confidence Interval (CI) 1.05-4.60, P = 0.037], higher levels of education (AOR 4.33, 95% CI 1.80-10.40, P = 0.001), presence of moderate to severe pain (AOR 2.02, 95% CI 1.02-4.78, P = 0.043), and expectations of benefit from CAM use (AOR 1.21, 95% CI 1.06-1.36, P = 0.004). CONCLUSIONS: CAM approaches have broad appeal within this inner city cohort of veterans, particularly among African Americans, those that experience pain and those that expect greater benefit from CAM. These findings may inform the development of patient-centered integrative pain management for veterans.

Visual recognition memory, manifested as long-term habituation, requires synaptic plasticity in V1.

Familiarity with stimuli that bring neither reward nor punishment, manifested through behavioral habituation, enables organisms to detect novelty and devote cognition to important elements of the environment. Here we describe in mice a form of long-term behavioral habituation to visual grating stimuli that is selective for stimulus orientation. Orientation-selective habituation (OSH) can be observed both in exploratory behavior in an open arena and in a stereotyped motor response to visual stimuli in head-restrained mice. We found that the latter behavioral response, termed a 'vidget', requires V1. Parallel electrophysiological recordings in V1 revealed that plasticity, in the form of stimulus-selective response potentiation (SRP), occurred in layer 4 of V1 as OSH developed. Local manipulations of V1 that prevented and reversed electrophysiological modifications likewise prevented and reversed memory demonstrated behaviorally. These findings suggest that a form of long-term visual recognition memory is stored via synaptic plasticity in primary sensory cortex.

Generational differences in complementary and alternative medicine (CAM) use in the context of chronic diseases and pain: baby boomers versus the silent generation.

BACKGROUND: More people are supplementing conventional medicine with complementary and alternative medicine (CAM), but studies have not compared CAM use between baby boomers (adults born from 1946 to 1964) and the so-called silent generation (born from 1925 to 1945). METHODS: This study compares CAM usage between baby boomers (n = 7734) and the silent generation (n = 4682) through secondary analyses of the 2007 National Health Interview Survey data. The analysis also compares chronic disease and pain status. Multivariate logistic regression models were developed to identify generational differences. RESULTS: Although the silent generation reported twice as many chronic disease (51.3% vs 26.1%; P < .001) and more painful conditions (56.1% vs 52.2%; P < .001), baby boomers were more likely to use CAM within the past year (43.1% vs 35.4%; P < .001). Adjusting for covariates, baby boomers with heart disease, cancer, and diabetes were more likely to use CAM than adults from the silent generation. Chronic pain status was independently associated with greater CAM use (adjusted odds ratio, 2.26; 95% confidence interval, 2.03-2.52). CONCLUSIONS: Baby boomers reported significantly higher rates of CAM use than the silent generation for both chronic diseases and painful conditions. Family physicians caring for the aging population must use patient-centered communication about the risks/benefits of CAM, which is necessary to promote effective coping with chronic illnesses and pain.

Shared decision-making and patient control in radiation oncology: implications for patient satisfaction.

BACKGROUND: Shared decision-making (SDM) has been linked to important health care quality outcomes. However, to the authors' knowledge, the value of SDM has not been thoroughly evaluated in the field of radiation oncology. The objective of the current study was to determine the association between SDM and patient satisfaction during radiotherapy (RT). The authors also explored patient desire for and perception of control during RT, and how these factors relate to patient satisfaction, anxiety, depression, and fatigue. METHODS: A cross-sectional survey of 305 patients undergoing definitive RT was conducted. Patients self-reported measured variables during the last week of RT. Relationships between variables were evaluated using chi-square analyses. RESULTS: Among study participants, 31.3% of patients experienced SDM, 32.3% perceived control in treatment decisions, and 76.2% reported feeling very satisfied with their care. Patient satisfaction was associated with perceived SDM (84.4% vs 71.4%; P < .02) and patient-perceived control (89.7% vs 69.2%; P < .001). Furthermore, the perception of having control in treatment decisions was associated with increased satisfaction regardless of whether the patient desired control. Increased anxiety (44.0% vs 20.0%; P < .02), depression (44.0% vs 15.0%; P < .01), and fatigue (68.0% vs 32.9%; P < .01) were reported in patients who desired but did not perceive control over their treatments, compared with those who both desired and perceived control. CONCLUSIONS: The findings of the current study emphasize the value of SDM and patient-perceived control during RT, particularly as it relates to patient satisfaction and psychological distress. Regardless of a patient's desire for control, it is important to engage patients in the decision-making process.

Integrative Reiki for cancer patients: a program evaluation.

OBJECTIVE: This mixed methods study sought to evaluate the outcomes of an integrative Reiki volunteer program in an academic medical oncology center setting. METHOD: We used de-identified program evaluation data to perform both quantitative and qualitative analyses of participants' experiences of Reiki sessions. The quantitative data were collected pre- and postsession using a modified version of the distress thermometer. The pre- and postsession data from the distress assessment were analyzed using a paired Student's : test. The qualitative data were derived from written responses to open-ended questions asked after each Reiki session and were analyzed for key words and recurring themes. RESULTS: Of the 213 pre-post surveys of first-time sessions in the evaluation period, we observed a more than 50% decrease in self-reported distress (from 3.80 to 1.55), anxiety (from 4.05 to 1.44), depression (from 2.54 to 1.10), pain (from 2.58 to 1.21), and fatigue (from 4.80 to 2.30) with P < .001 for all. Using conservative estimates that treat missing data as not endorsing Reiki, we found 176 (82.6%) of participants liked the Reiki session, 176 (82.6%) found the Reiki session helpful, 157 (73.7%) plan to continue using Reiki, and 175 (82.2%) would recommend Reiki to others. Qualitative analyses found that individuals reported that Reiki induced relaxation and enhanced spiritual well-being. CONCLUSIONS: An integrative Reiki volunteer program shows promise as a component of supportive care for cancer patients. More research is needed to evaluate and understand the impact that Reiki may have for patients, caregivers, and staff whose lives have been affected by cancer.

Traumatic ruptured globe eye injuries in a large urban center.

BACKGROUND: The purpose of this study was to examine patient characteristics and outcomes in a group of consecutive patients with ruptured globe eye injuries at Kings County Hospital Center, a large, urban, level 1 trauma center. METHODS: A retrospective chart review was performed to identify all patients with ruptured globe eye injuries seen between January 2009 and October 2011. Thirty-eight patients who sustained ruptured globe eye injuries from all causes were investigated for etiology and final visual outcomes. RESULTS: Eight eyes in which vision could be assessed were evaluated as having no light perception at presentation and three of these eyes required primary enucleation. Of the 38 eyes, orbit fractures were found in 15 eyes and an intraocular foreign body was found in six eyes. DISCUSSION: Our cohort revealed a 37.5% rate of primary enucleation in eyes with no light perception, which we believe to be a reflection of the severity of injury. All three cases were secondary to a gunshot wound. Further, our sample, although small in size, revealed a very high percentage of eyes that were ruptured secondary to violent causes compared with other studies.

Early mitochondrial abnormalities in hippocampal neurons cultured from Fmr1 pre-mutation mouse model.

Pre-mutation CGG repeat expansions (55-200 CGG repeats; pre-CGG) within the fragile-X mental retardation 1 (FMR1) gene cause fragile-X-associated tremor/ataxia syndrome in humans. Defects in neuronal morphology, early migration, and electrophysiological activity have been described despite appreciable expression of fragile-X mental retardation protein (FMRP) in a pre-CGG knock-in (KI) mouse model. The triggers that initiate and promote pre-CGG neuronal dysfunction are not understood. The absence of FMRP in a Drosophila model of fragile-X syndrome was shown to increase axonal transport of mitochondria. In this study, we show that dissociated hippocampal neuronal culture from pre-CGG KI mice (average 170 CGG repeats) express 42.6% of the FMRP levels and 3.8-fold higher Fmr1 mRNA than that measured in wild-type neurons at 4 days in vitro. Pre-CGG hippocampal neurons show abnormalities in the number, mobility, and metabolic function of mitochondria at this early stage of differentiation. Pre-CGG hippocampal neurites contained significantly fewer mitochondria and greatly reduced mitochondria mobility. In addition, pre-CGG neurons had higher rates of basal oxygen consumption and proton leak. We conclude that deficits in mitochondrial trafficking and metabolic function occur despite the presence of appreciable FMRP expression and may contribute to the early pathophysiology in pre-CGG carriers and to the risk of developing clinical fragile-X-associated tremor/ataxia syndrome.

Morphine-induced stereotyped thigmotaxis could appear as enhanced fear and anxiety in some behavioural tests.

This study questions whether the classical interpretation for unconditional fear/anxiety tests is valid when animals are under the influence of some drugs of abuse. We used a modified version of the trimethylthiazoline (TMT)-avoidance task, a measure of unconditional fear. Halfway into a corridor maze we placed a 3-cm-high barrier. This provided a wall in the middle of the corridor, one that the mice can easily climb over. Saline- and morphine-treated mice were randomly placed in the 'safe' or 'unsafe' (TMT) side and observed for 10 min. As expected, saline-injected mice spent only about 25% of the time in the TMT side, regardless of the side they were initially placed into. In contrast, morphine-treated mice did not cross the barrier even once, regardless of their initial placement. Specifically, morphine-treated mice initially placed in the TMT side appeared to exhibit the expected reduction in unconditional fear, that is, spending the entire time in the TMT side, a significant increase over the controls. Yet, morphine-treated mice placed in the safe side never even entered the TMT side; thus, these mice appeared to exhibit a behavioural response that is classically interpreted as increased fear, that is, spending significantly less time in the TMT side versus the controls. In summary, this study demonstrates that the classical interpretation of some unconditioned fear or anxiety tests could be misleading when animals are under the influence of drugs that might induce other competing behaviours.