Lasting dynamic effects of the psychedelic 2,5-dimethoxy-4-iodoamphetamine ((±)-DOI) on cognitive flexibility

Psychedelic drugs can aid fast and lasting remission from various neuropsychiatric disorders, though the underlying mechanisms remain unclear. Preclinical studies suggest serotonergic psychedelics enhance neuronal plasticity, but whether neuroplastic changes can also be seen at cognitive and behavioural levels is unexplored. Here we show that a single dose of the psychedelic 2,5-dimethoxy-4-iodoamphetamine ((±)-DOI) affects structural brain plasticity and cognitive flexibility in young adult mice beyond the acute drug experience. Using ex vivo magnetic resonance imaging, we show increased volumes of several sensory and association areas one day after systemic administration of 2 mgkg-1 (±)-DOI. We then demonstrate lasting effects of (±)-DOI on cognitive flexibility in a two-step probabilistic reversal learning task where 2 mgkg-1 (±)-DOI improved the rate of adaptation to a novel reversal in task structure occurring one-week post-treatment. Strikingly, (±)-DOI-treated mice started learning from reward omissions, a unique strategy not typically seen in mice in this task, suggesting heightened sensitivity to previously overlooked cues. Crucially, further experiments revealed that (±)-DOI's effects on cognitive flexibility were contingent on the timing between drug treatment and the novel reversal, as well as on the nature of the intervening experience. (±)-DOI's facilitation of both cognitive adaptation and novel thinking strategies may contribute to the clinical benefits of psychedelic-assisted therapy, particularly in cases of perseverative behaviours and a resistance to change seen in depression, anxiety, or addiction. Furthermore, our findings highlight the crucial role of time-dependent neuroplasticity and the influence of experiential factors in shaping the therapeutic potential of psychedelic interventions for impaired cognitive flexibility.

Protocol for tissue processing and paraffin embedding of mouse brains following ex vivo MRI

Combining histology and ex vivo MRI from the same mouse brain is a powerful way to study brain microstructure. Mouse brains prepared for ex vivo MRI are often kept in storage solution for months, potentially becoming brittle and showing reduced antigenicity. Here, we describe a protocol for mouse brain dissection, tissue processing, paraffin embedding, sectioning, and staining. We then detail registration of histology to ex vivo MRI data from the same sample and extraction of quantitative histological measurements.

Factors predicting the transition from acute to persistent pain in people with 'sciatica': the FORECAST longitudinal prognostic factor cohort study protocol

INTRODUCTION

Sciatica is a common condition and is associated with higher levels of pain, disability, poorer quality of life, and increased use of health resources compared with low back pain alone. Although many patients recover, a third develop persistent sciatica symptoms. It remains unclear, why some patients develop persistent sciatica as none of the traditionally considered clinical parameters (eg, symptom severity, routine MRI) are consistent prognostic factors.The FORECAST study (factors predicting the transition from acute to persistent pain in people with 'sciatica') will take a different approach by exploring mechanism-based subgroups in patients with sciatica and investigate whether a mechanism-based approach can identify factors that predict pain persistence in patients with sciatica.

METHODS AND ANALYSIS

We will perform a prospective longitudinal cohort study including 180 people with acute/subacute sciatica. N=168 healthy participants will provide normative data. A detailed set of variables will be assessed within 3 months after sciatica onset. This will include self-reported sensory and psychosocial profiles, quantitative sensory testing, blood inflammatory markers and advanced neuroimaging. We will determine outcome with the Sciatica Bothersomeness Index and a Numerical Pain Rating Scale for leg pain severity at 3 and 12 months.We will use principal component analysis followed by clustering methods to identify subgroups. Univariate associations and machine learning methods optimised for high dimensional small data sets will be used to identify the most powerful predictors and model selection/accuracy.The results will provide crucial information about the pathophysiological drivers of sciatica symptoms and may identify prognostic factors of pain persistence.

ETHICS AND DISSEMINATION

The FORECAST study has received ethical approval (South Central Oxford C, 18/SC/0263). The dissemination strategy will be guided by our patient and public engagement activities and will include peer-reviewed publications, conference presentations, social media and podcasts.

TRIAL REGISTRATION NUMBER

ISRCTN18170726; Pre-results.

7,8-dihydroxyflavone enhances long-term spatial memory and alters brain volume in wildtype mice

Introduction: 7,8-dihydroxyflavone (7,8-DHF) is a low molecular weight compound that can cross the blood brain barrier and has been implicated in numerous functions and behaviours. It is thought to have neuroprotective capability and has been shown to alleviate symptoms in a wide range of diseases.

Methods: 7,8-DHF was administered systemically to wildtype mice during Morris water maze training. Long-term spatial memory was assessed 28 days later. Ex-vivo T2-weighted (T2w) imaging was undertaken on a subset of these mice to assess brain-wide changes in volume.

Results: We found that systemic 7,8-DHF administration during the training period enhanced spatial memory 28 days later. Volumetric changes were observed in numerous brain regions associated with a broad range of functions including cognition, sensory, and motor processing.

Discussion: Our findings give the first whole brain overview of long-term anatomical changes following 7,8-DHF administration providing valuable information for assessing and understanding the widespread effects this drug has been shown to have in behaviour and disease.

MRI and pathology correlations in the medulla in sudden unexpected death in epilepsy (SUDEP): a postmortem study

AIMS

Sudden unexpected death in epilepsy (SUDEP) likely arises as a result of autonomic dysfunction around the time of a seizure. In vivo MRI studies report volume reduction in the medulla and other brainstem autonomic regions. Our aim, in a pathology series, is to correlate regional quantitative features on 9.4T MRI with pathology measures in medullary regions.

METHODS

Forty-seven medullae from 18 SUDEP, 18 nonepilepsy controls and 11 epilepsy controls were studied. In 16 cases, representing all three groups, ex vivo 9.4T MRI of the brainstem was carried out. Five regions of interest (ROI) were delineated, including the reticular formation zone (RtZ), and actual and relative volumes (RV), as well as T1, T2, T2* and magnetization transfer ratio (MTR) measurements were evaluated on MRI. On serial sections, actual and RV estimates using Cavalieri stereological method and immunolabelling indices for myelin basic protein, synaptophysin and Microtubule associated protein 2 (MAP2) were carried out in similar ROI.

RESULTS

Lower relative RtZ volumes in the rostral medulla but higher actual volumes in the caudal medulla were observed in SUDEP (P < 0.05). No differences between groups for T1, T2, T2* and MTR values in any region was seen but a positive correlation between T1 values and MAP2 labelling index in RtZ (P < 0.05). Significantly lower MAP2 LI were noted in the rostral medulla RtZ in epilepsy cases (P < 0.05).

CONCLUSIONS

Rostro-caudal alterations of medullary volume in SUDEP localize with regions containing respiratory regulatory nuclei. They may represent seizure-related alterations, relevant to the pathophysiology of SUDEP.

Nimodipine Reduces Dysfunction and Demyelination in Models of Multiple Sclerosis

Objective

Treatment of relapses in multiple sclerosis (MS) has not advanced beyond steroid use, which reduces acute loss of function, but has little effect on residual disability. Acute loss of function in an MS model (experimental autoimmune encephalomyelitis [EAE]) is partly due to central nervous system (CNS) hypoxia, and function can promptly improve upon breathing oxygen. Here, we investigate the cause of the hypoxia and whether it is due to a deficit in oxygen supply arising from impaired vascular perfusion. We also explore whether the CNS‐selective vasodilating agent, nimodipine, may provide a therapy to restore function, and protect from demyelination in 2 MS models.

Methods

A variety of methods have been used to measure basic cardiovascular physiology, spinal oxygenation, mitochondrial function, and tissue perfusion in EAE.

Results

We report that the tissue hypoxia in EAE is associated with a profound hypoperfusion of the inflamed spinal cord. Treatment with nimodipine restores spinal oxygenation and can rapidly improve function. Nimodipine therapy also reduces demyelination in both EAE and a model of the early MS lesion.

Interpretation

Loss of function in EAE, and demyelination in EAE, and the model of the early MS lesion, seem to be due, at least in part, to tissue hypoxia due to local spinal hypoperfusion. Therapy to improve blood flow not only protects neurological function but also reduces demyelination. We conclude that nimodipine could be repurposed to offer substantial clinical benefit in MS. ANN NEUROL 2020 ANN NEUROL 2020;88:123–136

Whole brain 31 P MRSI at 7T with a dual-tuned receive array

PURPOSE

The design and performance of a novel head coil setup for 31 P spectroscopy at ultra-high field strengths (7T) is presented. The described system supports measurements at both the 1 H and 31 P resonance frequencies.

METHODS

The novel coil consists of 2, actively detunable, coaxial birdcage coils to give homogeneous transmit, combined with a double resonant 30 channel receive array. This allows for anatomical imaging combined with 31 P acquisitions over the whole head, without changing coils or disturbing the subject. A phosphate buffer phantom and 3 healthy volunteers were scanned with a pulse acquire CSI sequence using both the novel array coil and a conventional transceiver birdcage. Four different methods of combining the array channels were compared at 3 different levels of SNR.

RESULTS

The novel coil setup delivers significantly increased 31 P SNR in the peripheral regions of the brain, reaching up to factor 8, while maintaining comparable performance relative to the birdcage in the center.

CONCLUSIONS

The new system offers the potential to acquire whole brain 31 P MRSI with superior signal relative to the standard options.

Effect of Fluorinert on the Histological Properties of Formalin-Fixed Human Brain Tissue

Fluorinert (perfluorocarbon) represents an inexpensive option for minimizing susceptibility artifacts in ex vivo brain MRI scanning, and provides an alternative to Fomblin. However, its impact on fixed tissue and histological analysis has not been rigorously and quantitatively validated. In this study, we excised tissue blocks from 2 brain regions (frontal pole and cerebellum) of 5 formalin-fixed specimens (2 progressive supranuclear palsy cases, 3 controls). We excised 2 blocks per region per case (20 blocks in total), one of which was subsequently immersed in Fluorinert for a week and then returned to a container with formalin. The other block from each region was kept in formalin for use as control. The tissue blocks were then sectioned and histological analysis was performed on each, including routine stains and immunohistochemistry. Visual inspection of the stained histological sections by an experienced neuropathologist through the microscope did not reveal any discernible differences between any of the samples. Moreover, quantitative analysis based on automated image patch classification showed that the samples were almost indistinguishable for a state-of-the-art classifier based on a deep convolutional neural network. The results showed that Fluorinert has no effect on subsequent histological analysis of the tissue even after a long (1 week) period of immersion, which is sufficient for even the lengthiest scanning protocols.

Melatonin as an adjunct to therapeutic hypothermia in a piglet model of neonatal encephalopathy: A translational study

Therapeutic hypothermia is only partially protective for neonatal encephalopathy; there is an urgent need to develop treatments that augment cooling. Our objective was to assess safety, efficacy and pharmacokinetics of 5 and 15 mg/kg/24 h melatonin (proprietary formulation) administered at 2 h and 26 h after hypoxia-ischemia (HI) with cooling in a piglet model. Following moderate cerebral HI, 30 piglets were eligible and randomized to: i) Hypothermia (33.5 °C, 2-26 h) and vehicle (HT + V;n = 13); b) HT and 5 mg/kg melatonin over 6 h at 2 h and 26 h after HI (HT + Mel-5;n = 4); c) HT and 15 mg/kg melatonin over 6 h at 2 h and 26 h after HI (HT + Mel-15;n = 13). Intensive care was maintained for 48 h; brain MRS was acquired and cell death (TUNEL) evaluated at 48 h. Comparing HT + V with HT + Mel-5 and HT + Mel-15, there was no difference in blood pressure or inotropic support needed, brain Lactate/N Acetylaspartate at 24 h and 48 h was similar, ATP/phosphate pool was higher for HT + Mel-15 versus HT + V at 24 h (p = 0.038) but not 48 h. A localized reduction in TUNEL positive cell death was observed in the sensorimotor cortex in the 15 mg/kg melatonin group (HT + Mel-15 versus HT + V; p < 0.003) but not in the 5 mg/kg melatonin group (HT + Mel-5 versus HT + V; p = 0.808). Putative therapeutic melatonin levels were reached 8 h after HI (10⁴ increase from baseline; ~15-30 mg/l). Mean ± SD peak plasma melatonin levels after the first infusion were 0.0014 ± 0.0012 mg/l in the HT + V group, 3.97 ± 1.53 mg/l in the HT + Mel-5 group and 16.8 ± 8.3 mg/l in the HT + Mel-15 group. Protection was dose dependent; 15 mg/kg melatonin started 2 h after HI, given over 6 h, was well tolerated and augmented hypothermic protection in sensorimotor cortex. Earlier attainment of therapeutic plasma melatonin levels may optimize protection by targeting initial events of reperfusion injury. The time window for intervention with melatonin, as adjunct therapy with cooling, is likely to be narrow and should be considered in designing future clinical studies.

PRO-QUEST: a rapid assessment method based on progressive saturation for quantifying exchange rates using saturation times in CEST

PURPOSE

To develop a new MRI technique to rapidly measure exchange rates in CEST MRI.

METHODS

A novel pulse sequence for measuring chemical exchange rates through a progressive saturation recovery process, called PRO-QUEST (progressive saturation for quantifying exchange rates using saturation times), has been developed. Using this method, the water magnetization is sampled under non-steady-state conditions, and off-resonance saturation is interleaved with the acquisition of images obtained through a Look-Locker type of acquisition. A complete theoretical framework has been set up, and simple equations to obtain the exchange rates have been derived.

RESULTS

A reduction of scan time from 58 to 16 minutes has been obtained using PRO-QUEST versus the standard QUEST. Maps of both T₁ of water and B₁ can simply be obtained by repetition of the sequence without off-resonance saturation pulses. Simulations and calculated exchange rates from experimental data using amino acids such as glutamate, glutamine, taurine, and alanine were compared and found to be in good agreement. The PRO-QUEST sequence was also applied on healthy and infarcted rats after 24 hours, and revealed that imaging specificity to ischemic acidification during stroke was substantially increased relative to standard amide proton transfer-weighted imaging.

CONCLUSION

Because of the reduced scan time and insensitivity to nonchemical exchange factors such as direct water saturation, PRO-QUEST can serve as an excellent alternative for researchers and clinicians interested to map pH changes in vivo.

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

Objective

Conventional magnetic resonance imaging (MRI) of the multiple sclerosis spinal cord is limited by low specificity regarding the underlying pathological processes, and new MRI metrics assessing microscopic damage are required. We aim to show for the first time that neurite orientation dispersion (i.e., variability in axon/dendrite orientations) is a new biomarker that uncovers previously undetected layers of complexity of multiple sclerosis spinal cord pathology. Also, we validate against histology a clinically viable MRI technique for dispersion measurement (neurite orientation dispersion and density imaging,NODDI), to demonstrate the strong potential of the new marker.

Methods

We related quantitative metrics from histology and MRI in four post mortem spinal cord specimens (two controls; two progressive multiple sclerosis cases). The samples were scanned at high field, obtaining maps of neurite density and orientation dispersion from NODDI and routine diffusion tensor imaging (DTI) indices. Histological procedures provided markers of astrocyte, microglia, myelin and neurofilament density, as well as neurite dispersion.

Results

We report from both NODDI and histology a trend toward lower neurite dispersion in demyelinated lesions, indicative of reduced neurite architecture complexity. Also, we provide unequivocal evidence that NODDI‐derived dispersion matches its histological counterpart (P < 0.001), while DTI metrics are less specific and influenced by several biophysical substrates.

Interpretation

Neurite orientation dispersion detects a previously undescribed and potentially relevant layer of microstructural complexity of multiple sclerosis spinal cord pathology. Clinically feasible techniques such as NODDI may play a key role in clinical trial and practice settings, as they provide histologically meaningful dispersion indices.

Combined Ex Vivo 9.4T MRI and Quantitative Histopathological Study in Normal and Pathological Neocortical Resections in Focal Epilepsy

High-resolution magnetic resonance imaging (MRI) may improve the preoperative diagnosis of focal cortical dysplasia (FCD) in epilepsy. Quantitative 9.4T MRI was carried out (T1, T2, T2* and magnetization transfer ratio) on 13 cortical resections, representing pathologically confirmed FCD (five cases) and normal cortex. Quantitative immunohistochemistry for myelination (myelin basic protein/SMI94), neuronal populations [microtubule-associated protein 2 (MAP2), neurofilament (SMI31, SMI32), synaptophysin, NeuN, calbindin], reactive glia (GFAP), microglia (CD68) and blood-brain barrier permeability (albumin) was carried out in 43 regions of interest (ROI) from normal and abnormal white matter and cortex. MRI was spatially aligned and quantitative analysis carried out on corresponding ROI. Line profile analysis (LPA) of intensity gradients through the cortex was carried out on MRI and immunostained sections. An inverse correlation was noted between myelin/SMI94 and T1, T2 (P < 0.005) and T2* (P < 0.05; Spearman's correlation) and a positive correlation between neuronal MAP2 and T1 (P < 0.005) and T2* (P < 0.05) over all ROI. Similar pathology-MRI correlations were observed for histologically unremarkable white matter ROI only. LPA showed altered gradient contours in regions of FCD, reflecting abnormal cortical lamination and myelo-architecture, including a preoperatively undetected FCD case. This study demonstrates the ability of quantitative 9.4T MRI to detect subtle differences in neuronal numbers and myelination in histologically normal appearing white matter and LPA in the evaluation of cortical dyslamination. These methods may be translatable to the in vivo detection of mild cortical malformations.

Cause and prevention of demyelination in a model multiple sclerosis lesion

Objective

Demyelination is a cardinal feature of multiple sclerosis, but it remains unclear why new lesions form, and whether they can be prevented. Neuropathological evidence suggests that demyelination can occur in the relative absence of lymphocytes, and with distinctive characteristics suggestive of a tissue energy deficit. The objective was to examine an experimental model of the early multiple sclerosis lesion and identify pathogenic mechanisms and opportunities for therapy.

Methods

Demyelinating lesions were induced in the rat spinal dorsal column by microinjection of lipopolysaccharide, and examined immunohistochemically at different stages of development. The efficacy of treatment with inspired oxygen for 2 days following lesion induction was evaluated.

Results

Demyelinating lesions were not centered on the injection site, but rather formed 1 week later at the white–gray matter border, preferentially including the ventral dorsal column watershed. Lesion formation was preceded by a transient early period of hypoxia and increased production of superoxide and nitric oxide. Oligodendrocyte numbers decreased at the site shortly afterward, prior to demyelination. Lesions formed at a site of inherent susceptibility to hypoxia, as revealed by exposure of naive animals to a hypoxic environment. Notably, raising the inspired oxygen (80%, normobaric) during the hypoxic period significantly reduced or prevented the demyelination.

Interpretation

Demyelination characteristic of at least some early multiple sclerosis lesions can arise at a vascular watershed following activation of innate immune mechanisms that provoke hypoxia, and superoxide and nitric oxide formation, all of which can compromise cellular energy sufficiency. Demyelination can be reduced or eliminated by increasing inspired oxygen to alleviate the transient hypoxia. Ann Neurol 2016;79:591–604

Vessel size index measurements in a rat model of glioma: comparison of the dynamic (Gd) and steady-state (iron-oxide) susceptibility contrast MRI approaches

Vessel size index (VSI), a parameter related to the distribution of vessel diameters, may be estimated using two MRI approaches: (i) dynamic susceptibility contrast (DSC) MRI following the injection of a bolus of Gd-chelate. This technique is routinely applied in the clinic to assess intracranial tissue perfusion in patients; (ii) steady-state susceptibility contrast with USPIO contrast agents, which is considered here as the standard method. Such agents are not available for human yet and the steady-state approach is currently limited to animal studies. The aim is to compare VSI estimates obtained with these two approaches on rats bearing C6 glioma (n = 7). In a first session, VSI was estimated from two consecutive injections of Gd-Chelate (Gd(1) and Gd(2)). In a second session (4 hours later), VSI was estimated using USPIO. Our findings indicate that both approaches yield comparable VSI estimates both in contralateral (VSI{USPIO} = 7.5 ± 2.0 µm, VSI{Gd(1)} = 6.5 ± 0.7 µm) and in brain tumour tissues (VSI{USPIO} = 19.4 ± 7.1 µm, VSI{Gd(1)} = 16.6 ± 4.5 µm). We also observed that, in the presence of BBB leakage (as it occurs typically in brain tumours), applying a preload of Gd-chelate improves the VSI estimate with the DSC approach both in contralateral (VSI{Gd(2)} = 7.1 ± 0.4 µm) and in brain tumour tissues (VSI{Gd(2)} = 18.5 ± 4.3 µm) but is not mandatory. VSI estimates do not appear to be sensitive to T(1) changes related to Gd extravasation. These results suggest that robust VSI estimates may be obtained in patients at 3 T or higher magnetic fields with the DSC approach.