IntroductionConcussion triggers rapid and transient surges in extracellular amino acids, largely driven by pathological activation of N-methyl-D-aspartate (NMDA) receptors. Targeting this ultra-acute excitotoxic window remains challenging, in part because many NMDA receptor antagonists exhibit slow delivery kinetics or limited brain penetrance when administered systemically. Intranasal drug delivery may help overcome these limitations by enabling faster central nervous system access. Here, we compared the capacity of intranasally administered MK-801, a high-affinity non-competitive NMDA receptor antagonist, and intranasal ketamine, a clinically used antagonist with distinct pharmacokinetic and receptor-binding properties, to modulate early neurochemical responses following experimental concussion.Materials and methodsAdult rats underwent a validated weight-drop concussion model followed by continuous hippocampal microdialysis. Extracellular glutamate, taurine, glycine, gamma-aminobutyric acid, glutamine, and serine were quantified every 10 min for 60 min before and after injury using high-performance liquid chromatography. Animals received intranasal MK-801 (10 mg/kg), ketamine (10 mg/kg), or vehicle immediately after concussion or sham procedures. Righting time was recorded as an early post-treatment behavioral outcome. MK-801 concentrations in plasma and brain were quantified by liquid chromatography-tandem mass spectrometry to assess central exposure. A composite excitotoxic index was calculated to summarize excitatory-inhibitory neurochemical imbalance.ResultsVehicle-treated concussed animals exhibited marked elevations in glutamate, taurine, and glycine within the first 10 min post-injury, accompanied by prolonged righting times. Intranasal MK-801 attenuated these ultra-acute neurochemical surges, reduced the composite excitotoxic index, and was associated with shorter righting times comparable to those observed in sham animals. In contrast, intranasal ketamine did not significantly alter amino acid dynamics or righting time under the conditions tested. MK-801 achieved measurable brain exposure following intranasal administration, with comparable brain-to-plasma ratios in sham and concussed animals.DiscussionIntranasal delivery of MK-801 modulates ultra-acute excitotoxic neurochemical disturbances following concussion in a rodent model. The lack of comparable effects with ketamine under the tested conditions highlights the importance of pharmacokinetic properties and receptor-binding kinetics when targeting the brief post-injury excitotoxic window. These findings provide proof-of-concept evidence supporting further investigation of rapid intranasal NMDA receptor antagonism as a strategy to influence early glutamatergic dysregulation after concussion.

Altered extracellular amino acid concentrations following concussion or mild traumatic brain injury can result in delayed neuronal damage through overactivation of NMDA glutamatergic receptors. However, the consequences of repeated concussions prior to complete recovery are not well understood. In this study, we utilized in vivo cerebral microdialysis and a weight-drop model to investigate the acute neurochemical response to single and repeated concussions in adult rats that were fully conscious. A microdialysis probe was inserted into the hippocampus and remained in place during impact. Primary outcomes included concentrations of glutamate, GABA, taurine, glycine, glutamine, and serine, while secondary outcomes were righting times and excitotoxic indices. Compared to sham injury, the first concussion resulted in significant increases in glutamate, GABA, taurine, and glycine levels, longer righting times, and higher excitotoxic indices. Following the second concussion, righting times were significantly longer, suggesting cumulative effects of repeated concussion while only partial increases were observed in glutamate and taurine levels. GABA and glycine levels, and excitotoxic indices were comparable to sham injury. These findings suggest that single and repeated concussions may induce acute increases in several amino acids, while repeated concussions could exacerbate neurological symptoms despite less pronounced neurochemical changes.

Children who experienced moderate perinatal asphyxia (MPA) are at risk of developing long lasting subtle cognitive and behavioral deficits, including learning disabilities and emotional problems. The prefrontal cortex (PFC) regulates cognitive flexibility and emotional behavior. Neurons that release serotonin (5-HT) project to the PFC, and compounds modulating 5-HT activity influence emotion and cognition. Whether 5-HT dysregulations contribute to MPA-induced cognitive problems is unknown. We established a MPA mouse model, which displays recognition and spatial memory impairments and dysfunctional cognitive flexibility. We found that 5-HT expression levels, quantified by immunohistochemistry, and 5-HT release, quantified by in vivo microdialysis in awake mice, are reduced in PFC of adult MPA mice. MPA mice also show impaired body temperature regulation following injection of the 5-HT1A receptor agonist 8-OH-DPAT, suggesting the presence of deficits in 5-HT auto-receptor function on raphe neurons. Finally, chronic treatment of adult MPA mice with fluoxetine, an inhibitor of 5-HT reuptake transporter, or the 5-HT1A receptor agonist tandospirone rescues cognitive flexibility and memory impairments. All together, these data demonstrate that the development of 5-HT system function is vulnerable to moderate perinatal asphyxia. 5-HT hypofunction might in turn contribute to long-term cognitive impairment in adulthood, indicating a potential target for pharmacological therapies.

Positron Emission Tomography (PET) ligands have advanced Alzheimer's disease (AD) diagnosis and treatment. Using autoradiography and cryo-EM, we identified AD brain tissue with elevated tau burden, purified filaments, and determined the structure of second-generation high avidity PET ligand MK-6240 at 2.31 Å resolution, which bound at a 1:1 ratio within the cleft of tau paired-helical filament (PHF), engaging with glutamine 351, lysine K353, and isoleucine 360. This information elucidates the basis of MK-6240 PET in quantifying PHF deposits in AD and may facilitate the structure-based design of superior ligands against tau amyloids.

The excitatory neurotransmitter glutamate plays a critical role inexperience-dependent neuroplasticity, including addiction-related processes. Todate, however, it is not possible to measure glutamate release in the livinghuman brain. Positron emission tomography (PET) with [11C]ABP688, aselective allosteric antagonist of metabotropic type 5 glutamate (mGlu5)receptors, could offer an effective strategy. To test this proposition, weconducted a series of studies in rats using microdialysis and[11C]ABP688 microPET imaging, and in humans using PET and magneticresonance spectroscopy (MRS). Significant calcium-dependent glutamate releasewas identified in the ventral striatum of awake rats (190.5 ± 34.7%,p< 0.05;n= 7) followingadministration of a low dose of ethanol (EtOH; 20%, 0.5 g/kg), a pharmacologicalchallenge readily translatable to human research. Simultaneous microdialysis andmicroPET studies in anesthetized rats yielded concurrent increases in glutamaterelease (126.9 ± 5.3%,p < 0.001;n= 11) and decreases in striatal[11C]ABP688 binding (6.8 ± 9.6%,p <0.05). These latter two effects, however, were not significantlycorrelated (r= 0.25,p= 0.46).In humans, a laboratory stressor yielded significant changes in self-reportedmood (ps < 0.041), sympathetic system activations(ps < 0.042), and the MRS index of striatalglutamate reuptake following excitatory neurotransmission, Glx/Cr levels(p= 0.048). These effects, however, were notaccompanied by significant changes in [11C]ABP688 BPND(ps > 0.21,n= 9) orcorrelated with each other (ps > 0.074). Together, thesestudies document EtOH-induced glutamate release from neurons, EtOH-induceddecreases in [11C]ABP688 binding, and stress-induced changes inglutamate turnover, yet fail to provide evidence that the PET[11C]ABP688 method can be exploited to quantify moderate changes inglutamate release. The results underscore the need for highly controlled testingconditions during PET measures of mGlu5 receptors.

Abstract The excitatory neurotransmitter glutamate plays a critical role in experience-dependent neuroplasticity, including addiction-related processes. To date, however, it is not possible to measure glutamate release in the living human brain. Positron emission tomography (PET) with [11C]ABP688, a selective allosteric antagonist of metabotropic type 5 glutamate (mGlu5) receptors, could offer an effective strategy. To test this proposition, we conducted a series of studies in rats using microdialysis and [11C]ABP688 microPET imaging, and in humans using PET and magnetic resonance spectroscopy (MRS). Significant calcium-dependent glutamate release was identified in the ventral striatum of awake rats (190.5 ± 34.7%, p < 0.05; n = 7) following administration of a low dose of ethanol (EtOH; 20%, 0.5 g/kg), a pharmacological challenge readily translatable to human research. Simultaneous microdialysis and microPET studies in anesthetized rats yielded concurrent increases in glutamate release (126.9 ± 5.3%, p < 0.001; n = 11) and decreases in striatal [11C]ABP688 binding (6.8 ± 9.6%, p < 0.05). These latter two effects, however, were not significantly correlated (r = 0.25, p = 0.46). In humans, a laboratory stressor yielded significant changes in self-reported mood (ps < 0.041), sympathetic system activations (ps < 0.042), and the MRS index of striatal glutamate reuptake following excitatory neurotransmission, Glx/Cr levels (p = 0.048). These effects, however, were not accompanied by significant changes in [11C]ABP688 BPND (ps > 0.21, n = 9) or correlated with each other (ps > 0.074). Together, these studies document EtOH-induced glutamate release from neurons, EtOH-induced decreases in [11C]ABP688 binding, and stress-induced changes in glutamate turnover, yet fail to provide evidence that the PET [11C]ABP688 method can be exploited to quantify moderate changes in glutamate release. The results underscore the need for highly controlled testing conditions during PET measures of mGlu5 receptors.

Binding in alpha-synuclein containing brain regions have been described for both Flortaucipir ([18F]AV-1451) and [18F]MK-6240. Here we assessed whether alpha-Synuclein constitutes a target for these tau imaging agents. We used autoradiographic dot blot to validate specific and evaluate off-target interactions of [18F]MK-6240 and [18F]AV-1451 using sarkosyl-insoluble extracts from PSP, CBD, PiD, and AD cortical tissue which contain fibrillar forms of tau. Tissue concentrations of alpha-Synuclein are orders of magnitude lower than NFTs leading us to use recombinant alpha-Synuclein PFFs to evaluate potential off-target interactions. Briefly, 1:100 dilutions of each preparation were incubated with 82 fmol of mass in a 30uL total volume. Samples were incubated for 90 minutes at 37°C. Reactions were terminated by pipetting the solution in triplicate onto a glass fiber filter held within a 96-well dot-blot aspiration device and the samples were immobilized. Unbound ligand was washed three times with ice cold PBS. The glass fiber filters were transferred to a cassette for exposure to autoradiographic film for 90 minutes and the activity in photostimulated luminescence units per mm 2 was calculated using ImageJ software v.1.8.0. Disintegrations were corrected for decay and normalized to cerebellar extracts for both ligands. [18F]MK-6240 demonstrated high specificity, binding in AD extracts and AD extracts subject to trypsin treatment. [18F]AV-1451 demonstrated similar binding in both native and trypsinized AD extracts, while also showing overlapping binding profiles in human alpha-synuclein PFFs but not in mouse alpha-synuclein PFFs. [18F]AV-1451 binds to recombinant human alpha-Synuclein PFFs as it does to native AD-tau PHFs. Future experiments should assess patient derived alpha-Synuclein aggregates as a potential off target binding to [18F]AV-1451.

Prenatal exposure to maternal immune activation (MIA) and chronic adolescent cannabis use have both been identified as environmental risk factors for neuropsychiatric disorders. However, most individuals exposed to a single risk factor do not typically develop major mental illness, which suggests that multiple exposures may be required for illness onset. Here, we examine whether combined exposure to prenatal MIA and adolescent delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, lead to enduring neuroanatomical and behavioural changes in adult offspring, potentially reflecting changes in humans indicative of mental illness. Mice were prenatally exposed to a viral mimetic, poly I:C (5mg/kg), or vehicle at gestational day (GD)9, and then postnatally exposed to chronic THC (5mg/kg) or vehicle by intraperitoneal injections during adolescent development (postnatal day [PND]28-45). Longitudinal in vivo whole-brain magnetic resonance imaging (MRI) was performed pre-treatment, PND25, post-treatment, PND50, and in adulthood, PND85, followed by a series of behavioural tests aimed at assessing anxiety-like and locomotor, social, and sensorimotor gating behaviour. Post-mortem assessment of cannabinoid (CB)1 and 2 receptor expressing cells was performed in developmentally altered regions identified by MRI (anterior cingulate and somatosensory cortices, striatum, and hippocampus). We hypothesized that there would be differential, but synergistic effects of each exposure. Briefly, we found subtle deviations in neurodevelopmental trajectory and subthreshold anxiety-like behaviours were observed in mice exposed to both risk factors. Sex-dependent effects were observed in patterns of shared brain-behaviour covariation, suggesting that exposure to MIA and THC may affect males and females in different ways. Density of CB1 and CB2 receptor positive cells was significantly decreased in all regions assessed for all mice exposed to either one or both risk factors, relative to controls. These findings suggest that there may be a cumulative effect of risk factor exposure on gross neuroanatomical and behavioural development, and that the endocannabinoid system may be sensitive to both prenatal MIA, adolescent THC, or the combination. For full details, see our publication: . In this dataset, you will find a total of 243 preprocessed structural MRIs (in MINC format) acquired at postnatal day ~25, ~50, and ~85 in mice exposed to poly I:C or vehicle control (0.9% sterile saline) at GD9, and then postnatally treated with vehicle or THC from PND 28-45. These are T1-weighted structural images at 100 micron isotropic resolution acquired on a 7 Tesla Bruker Biospec 70/30; matrix size of 180 x 160 x 90; 14.5 minutes, 20 degrees and TE/TR of 4.5/20 ms (2 averages, ~14 minutes). Anesthesia was induced with 3% isoflurane in oxygen and a (0.075 mg/kg bolus) dexmedetomidine injection. Anesthesia was maintained during the scan between 1.5-0.5% isoflurane, and a constant infusion of dexmedetomidine (0.05mg/kg/h continuous mg/kg during scan). T1-weighted scans were preprocessed by stripping native coordinates, flipping left-right to maintain fidelity, denoising, correcting inhomogeneities in the bias field using the N4 algorithm, and registering in LSQ6 alignment (i.e. 6 degrees of freedom are allowed for imagine alignment: translations and rotations along x, y, and z dimensions). The demographics information for each animal is included in the demographics.csv file. Behavioural tests were performed following the postnatal day 85 scans in all animals with a 2 day rest period. These include: open field test, three chambered social approach, and prepulse inhibition. The data for all of these tests is presented in its own individual .csv spreadsheet. Included in this data set are the structural MRIs in MINC format, the behavioural .csv data, and a readme.txt file providing further detail on the data structure and content, and on how to interpret the data column titles. DICOMS are also available for the structural MRI data, as are the raw (not-preprocessed) MINC files, available upon request to the authors. Finally, the authors would like to acknowledge the funding bodies that supported the completion of this work including the Canadian Institute for Health Research, the Fonds de Recherche du Québec en Santé, and the Healthy Brains for Healthy Lives at McGill University.

In Parkinson’s disease (PD), motor dysfunctions only become apparent after extensive loss of DA innervation. This resilience has been hypothesized to be due to the ability of many motor behaviors to be sustained through a diffuse basal tone of DA; but experimental evidence for this is limited. Here we show that conditional deletion of the calcium sensor synaptotagmin-1 (Syt1) in DA neurons (Syt1 cKO DA mice) abrogates most activity-dependent axonal DA release in the striatum and mesencephalon, leaving somatodendritic (STD) DA release intact. Strikingly, Syt1 cKO DA mice showed intact performance in multiple unconditioned DA-dependent motor tasks and even in a task evaluating conditioned motivation for food. Considering that basal extracellular DA levels in the striatum were unchanged, our findings suggest that activity-dependent DA release is dispensable for such tasks and that they can be sustained by a basal tone of extracellular DA. Taken together, our findings reveal the striking resilience of DA-dependent motor functions in the context of a near-abolition of phasic DA release, shedding new light on why extensive loss of DA innervation is required to reveal motor dysfunctions in PD.

RationaleThe Netrin-1/DCC guidance cue pathway is critically involved in the adolescent organization of the mesocorticolimbic dopamine circuitry. Adult mice heterozygous for Dcc show reduced dopamine release in the nucleus accumbens in response to amphetamine and, in turn, blunted sensitivity to the rewarding effects of this drug. ObjectiveHere, we tested whether the protective effects of Dcc haploinsufficiency are specific to stimulant drugs of abuse or instead extrapolate to opioids and ethanol. MethodsWe used the place preference paradigm to measure the rewarding effects of cocaine (20 mg/kg), morphine (5 or 10 mg/Kg), or ethanol (20%) in adult (PND 75) male Dcc haploinsufficient mice or their wild-type litter mates. In a second experiment, we compared in these two genotypes, in vivo dopamine release in the nucleus accumbens after a single i.p. injection of morphine (10 mg/kg). ResultsWe found reduced morphine-induced dopamine release in the nucleus accumbens of Dcc haploinsufficient male mice, but, contrary to the effects of stimulant drugs, there is no effect of genotype on morphine-induced conditioned preference. ConclusionThese findings show that reduced drug-induced mesolimbic dopamine in Dcc haploinsufficient male mice protects specifically against the rewarding effects of stimulant drugs, but not against the rewarding properties of morphine and ethanol. These results suggest that these drugs exert their rewarding effect via different brain circuits.

Mutations in HPRT1, a gene encoding a rate-limiting enzyme for purine salvage, cause Lesch-Nyhan disease which is characterized by self injury and motor impairments. We leveraged stem cell and genetic engineering technologies to model the disease in isogenic and patient derived forebrain and midbrain cell types. Dopaminergic progenitor cells deficient in HPRT showed decreased intensity of all developmental cell-fate markers measured. Metabolic analyses revealed significant loss of all purine derivatives, except hypoxanthine, and impaired glycolysis and oxidative phosphorylation. real-time glucose tracing demonstrated increased shunting to the pentose phosphate pathway for de novo purine synthesis at the expense of ATP production. Purine depletion in dopaminergic progenitor cells resulted in loss of RHEB, impairing mTORC1 activation. These data demonstrate dopaminergic-specific effects of purine salvage deficiency and unexpectedly reveal that dopaminergic progenitor cells are programmed to a high-energy state prior to higher energy demands of terminally differentiated cells.

OBJECTIVE Alterations in amino acid concentrations are a major contributor to the persistent neurological and behavioral effects induced by concussions and mild traumatic brain injuries (TBIs). Glutamate, the most abundant excitatory amino acid in the CNS, has a major role in the pathophysiological process of concussion. The indiscriminate liberation of glutamate immediately after a concussion triggers an excitotoxic response that leads to cell death, neuronal damage, and the dysfunction of surviving neurons, largely by overactivation of N-methyl-d-aspartate (NMDA) glutamatergic receptors. The aim of the present study was to investigate the efficacy of prophylactic versus therapeutic administration of MK-801, a promising NMDA receptor antagonist, on the acute changes in amino acid extracellular concentrations involved in excitotoxicity resulting from a concussive trauma. METHODS The immediate neurochemical response to a concussion cannot be characterized in humans. Therefore, the authors used their previously validated combination of a weight-drop concussion rat model and in vivo cerebral microdialysis. The microdialysis probe was inserted inside the hippocampus and left inserted at impact to allow uninterrupted sampling of amino acids of interest immediately after concussion. The primary outcome included amino acid concentrations and the secondary outcome included righting time. Samples were taken in 10-minute increments for 60 minutes before, during, and 60 minutes after impact, and analyzed for glutamate, gamma-aminobutyric acid, taurine, glycine, glutamine, and serine using high-performance liquid chromatography. Righting time was acquired as a neurological restoration indicator. Physiological saline or 10 mg/kg MK-801 was administrated intraperitoneally 60 minutes before or immediately following induction of sham injury or concussion. RESULTS Following induction of concussion, glutamate, taurine, and glycine levels as well as righting times in cases from the MK-801 treatment group were comparable to those of vehicle-treated animals. In contrast, righting times and amino acid concentrations observed within the first 10 minutes after induction of concussion in cases assigned to the MK-801 prophylaxis group were comparable to those of sham-injured animals. CONCLUSIONS These results suggest that presynaptic actions and peak availability of MK-801 following prophylactic administration significantly inhibit the immediate and indiscriminate release of glutamate, taurine, and glycine in extracellular fluid after a concussion.

Dysregulation of habit formation has been recently proposed as pivotal to eating disorders. Here, we report that a subset of patients suffering from restrictive anorexia nervosa have enhanced habit formation compared with healthy controls. Habit formation is modulated by striatal cholinergic interneurons. These interneurons express vesicular transporters for acetylcholine (VAChT) and glutamate (VGLUT3) and use acetylcholine/glutamate cotransmission to regulate striatal functions. Using mice with genetically silenced VAChT (VAChT conditional KO, VAChTcKO) or VGLUT3 (VGLUT3cKO), we investigated the roles that acetylcholine and glutamate released by cholinergic interneurons play in habit formation and maladaptive eating. Silencing glutamate favored goal-directed behaviors and had no impact on eating behavior. In contrast, VAChTcKO mice were more prone to habits and maladaptive eating. Specific deletion of VAChT in the dorsomedial striatum of adult mice was sufficient to phenocopy maladaptive eating behaviors of VAChTcKO mice. Interestingly, VAChTcKO mice had reduced dopamine release in the dorsomedial striatum but not in the dorsolateral striatum. The dysfunctional eating behavior of VAChTcKO mice was alleviated by donepezil and by l-DOPA, confirming an acetylcholine/dopamine deficit. Our study reveals that loss of acetylcholine leads to a dopamine imbalance in striatal compartments, thereby promoting habits and vulnerability to maladaptive eating in mice.

Reduced expression of a schizophrenia-associated gene Dystrobrevin Binding Protein 1 (DTNBP1) and its protein product dysbindin-1, has been reported in the brains of schizophrenia patients. DTNBP1-null mutant Sdy (Sandy) mice exhibit several behavioral features relevant to schizophrenia. Changes in dopaminergic as well as gluta-matergic and GABAergic neurotransmission in cortico-limbic regions have been reported in Sdy mice. Since dysbindin-1 is expressed in multiple brain regions, it is not known whether dopamine (DA) changes observed in Sdy null mutants are due to dysbindin-1 deficiency in DAergic neurons specifically. Here, using a mouse line with conditional knockout (cKO) of DTNBP1 in DA neurons, we studied the effects of dysbindin-1 deficiency on DA release and DA-dependent behaviors. Spontaneous locomotor activity of cKO mice in novel environment was significantly reduced initially but was comparable at later time points with littermate controls. However, the locomotion-enhancing effect of a low dose of D-amphetamine (d-AMPH; 2.5 mg/kg, ip) was significantly attenuated in the cKO mice suggesting a dampened mesolimbic DA transmission. Similarly, the prepulse inhibition disrupting effect of d-AMPH was found to be significantly reduced in the mutant mice. No significant differences between the cKO and control mice were observed in tests of anxiety, spatial learning and memory and social interaction. In- vivo microdialysis in the nucleus accumbens (NAc) showed a decrease in d-AMPH-induced extracellular DA release in the cKO mice. No significant alterations in protein levels of DA transporter, phosphorylated CaM kinase-II or Akt308 in the NAc were observed in the cKO mice. Taken together, our data suggest an important role of dysbindin-1 in maintaining mesolimbic DA tone and call for further investigations identifying mechanisms linking dysbindin-1, DA and schizophrenia.

Making high-quality dopamine (DA)-producing cells for basic biological or small molecule screening studies is critical for the development of novel therapeutics for disorders of the ventral midbrain. Currently, many ventral midbrain assays have low signal-to-noise ratio due to low levels of cellular DA and the rate-limiting enzyme of DA synthesis, tyrosine hydroxylase (TH), hampering discovery efforts. Using intensively characterized ventral midbrain cells derived from human skin, which demonstrate calcium pacemaking activity and classical electrophysiological properties, we show that an L-type calcium agonist can significantly increase TH protein levels and DA content and release. Live calcium imaging suggests that it is the immediate influx of calcium occurring simultaneously in all cells that drives this effect. Genome-wide expression profiling suggests that L-type calcium channel stimulation has a significant effect on specific genes related to DA synthesis and affects expression of L-type calcium receptor subunits from the CACNA1 and CACNA2D families. Together, our findings provide an advance in the ability to increase DA and TH levels to improve the accuracy of disease modeling and small molecule screening for disorders of the ventral midbrain, including Parkinson's disease.

Persistent cognitive and motor symptoms are known consequences of concussions/mild traumatic brain injury (mTBIs) that can be partly attributable to altered neurotransmission. Indeed, cerebral microdialysis studies in rodents have demonstrated an excessive extracellular glutamate release in the hippocampus within the first 10 min following trauma. Microdialysis offers the clear advantage of in vivo neurotransmitter continuous sampling while not having to sacrifice the animal. In addition to the aforementioned technique, a closed head injury model that exerts rapid acceleration and deceleration of the head and torso is needed, as such a factor is not available in many other animal models. The Wayne State weight-drop model mimics this essential component of human craniocerebral trauma, allowing the induction of an impact on the head of an unrestrained rodent with a falling weight. Our novel and translational rat model combines cerebral microdialysis with the Wayne State weight-drop model to study, in lightly anesthetized and unrestrained adult rats, the acute changes in extracellular neurotransmitter levels following concussion. In this protocol, the microdialysis probe was inserted inside the hippocampus as region of interest, and was left inserted in the brain at impact. There is a high density of terminals and receptors in the hippocampus, making it a relevant region to document altered neurotransmission following concussion. When applied to adult Sprague-Dawley rats, our combined model induced increases in hippocampal extracellular glutamate concentrations within the first 10 min, consistent with the previously reported post-concussion symptomology. This combined weight-drop model provides a reliable tool for researchers to study early therapeutic responses to concussions in addition to repetitive brain injury, since this protocol induces a closed-head mild trauma.

Concussions/mild traumatic brain injury (mTBI) represent a major public health concern due to persistent behavioral and neurological effects. The mechanisms by which concussions lead to such effects are partly attributable to an hyperacute indiscriminate glutamate release. Cerebral microdialysis studies in rodents reported a peak of extracellular glutamate 10 minutes after injury. Microdialysis has the advantage of being one of the few techniques allowing the quantification of neurotransmitters in vivo and at different time points following injury. In addition to the clear advantages afforded by microdialysis, the Wayne State weight-drop model induces an impact on the skull of a subject unrestrained by the fall of a weight. The latter model allows rapid acceleration and deceleration of the head and torso, an essential feature in human craniocerebral trauma and a factor that is missing from many existing animal concussion models. In the present study, we applied the Wayne State procedure and microdialysis to document, in awake rats, the acute changes in extracellular hippocampal glutamate and GABA levels resulting from concussive trauma. We studied the dorsal CA1 hippocampal region as it contains a high density of glutamatergic terminal and receptors, thus making it vulnerable to excitotoxic insult. Using HPLC, dialysate levels of hippocampal glutamate and GABA were measured in adult male Sprague-Dawley rats in 10 min increments for 60 min prior to, during and for 90 min following concussive trauma induced by the Wayne State weight-drop procedure. Sham control animals were treated in the same manner but without receiving the concussive trauma procedure. Our results show that concussive trauma is followed, within 10 min, by a robust, transient 3-fold increase in hippocampal glutamate levels; such changes were not seen in controls. In contrast, GABA levels were unaffected by the concussive trauma procedure. The findings derived from the approach used here are generally consistent with those of previous other studies. They also provide a crucial in vivo validation of the Wayne State procedure as a model with promising translational potential for pre-clinical studies on early therapeutic responses to concussion.Abbreviations: TBI: traumatic brain injurymTBI: mild traumatic brain injuryECF: extracellular fluidCCI: controlled cortical impactFPI: fluid percussion injury

BACKGOUND: Alcohol use disorder (AUD) is devastating and poorly treated, and innovative targets are actively sought for prevention and treatment. The orphan G protein-coupled receptor GPR88 is enriched in mesocorticolimbic pathways, and Gpr88 knockout mice show hyperactivity and risk-taking behavior, but a potential role for this receptor in drug abuse has not been examined. METHODS: We tested Gpr88 knockout mice for alcohol-drinking and -seeking behaviors. To gain system-level understanding of their alcohol endophenotype, we also analyzed whole-brain functional connectivity in naive mice using resting-state functional magnetic resonance imaging. RESULTS: Gpr88 knockout mice showed increased voluntary alcohol drinking at both moderate and excessive levels, with intact alcohol sedation and metabolism. Mutant mice also showed increased operant responding and motivation for alcohol, while food and chocolate operant self-administration were unchanged. Alcohol place conditioning and alcohol-induced dopamine release in the nucleus accumbens were decreased, suggesting reduced alcohol reward in mutant mice that may partly explain enhanced alcohol drinking. Seed-based voxelwise functional connectivity analysis revealed significant remodeling of mesocorticolimbic centers, whose hallmark was predominant weakening of prefrontal cortex, ventral tegmental area, and amygdala connectional patterns. Also, effective connectivity from the ventral tegmental area to the nucleus accumbens and amygdala was reduced. CONCLUSIONS: Gpr88 deletion disrupts executive, reward, and emotional networks in a configuration that reduces alcohol reward and promotes alcohol seeking and drinking. The functional connectivity signature is reminiscent of alterations observed in individuals at risk for AUD. The Gpr88 gene, therefore, may represent a vulnerability/ resilience factor for AUD, and a potential drug target for AUD treatment.