Neurochemical Responses Research Articles

Behavioral and neurochemical responses derived from dopaminergic intrastriatal grafts in hemiparkinsonian rats engaged in a novel motor task

BackgroundPutative treatments derived from in vivo stem cell transplant-derived dopamine (DA) in hemiparkinsonian rats have been assessed via DA-agonist-induced rotations involving imbalanced intra-hemispheric striatal DA receptor stimulation. However, such tests obscure the natural responses of grafts to sensory stimuli, and drug-induced plasticity can modify the circuit being tested. Thus, we propose an alternative testing strategy using a novel water tank swimming apparatus. New methodMicrodialysis was used to compare striatal DA levels when rats were: (1) in a rest-phase within a bowl-shaped apparatus, or (2) in an active forced-swim phase within a specially-equipped water tank. Resting-phase DA release levels were compared with active-phase levels obtained while rats were required to swim in the water-tank task. Behavioral variables such as asymmetric circling while swimming (rotations), front-limb strokes, and front-limb reaches were captured by a camera for analysis. Results and comparison with existing methodsTransplanted cells had a very modest effect on percentage of contralateral front-limb strokes, but did not reduce lesion-induced rotational asymmetry in the swim task. Neither striatal DA levels, nor their breakdown products, were significantly different between transplanted and sham-transplanted groups. Our new behavioral test eliminates the need for pharmacological stimulation, enabling simultaneous assessment of DA released in resting and active phases to explore graft control. ConclusionsOur new method allows for accurate assessments of stem cell therapy for PD as an alternative to “rotation” tests. Use of natural motivations to engage in sensory-driven motor tasks provides more accurate insights into ongoing graft-derived behavioral support.

Sex‐selective effects of prior binge‐like drinking followed by intermittent stress and ethanol drinking on alterations in several brain protein levels and neurosteroids

Alcohol misuse and abuse are serious problems in our society and stress may increase the risk for escalation of drinking from recreational to problematic. We are continuing to explore the effect of prior binge drinking on subsequent drinking behaviors and the response to intermittent predator odor stress exposure, which is a model of traumatic stress. Adult male and female C57BL/6 mice had either 7 binge ethanol sessions (binge) or drank water (control). Following a 30‐day abstinence period, all mice were provided free access to 10% ethanol (10E) and water via lickometers for 4 weeks, with 30 min exposure to predator odor during the middle 2 weeks (2X/week). At 24 hrs after the final drinking session, mice were euthanized, and brains were harvested and frozen for Western Blot analyses vs separate naïve age‐matched mice. Dissected prefrontal cortex (PFC) and hippocampus (HIPP) were assayed for levels of the GABAA receptor a2 and a4 subunits, P450scc (an enzyme involved in steroidogenesis), and synaptophysin and ARC (activity‐regulated cytoskeletal protein), two proteins involved in synaptic plasticity. Western blot analyses found divergent responses across proteins and by sex. For the GABAA receptor a2 and a4 subunits, treatments (binge and control) decreased levels by 20–25% in male PFC but not HIPP versus naïve mice. Binge and control females displayed a similar decrease in PFC levels of the a4 subunit, whereas PFC levels of the a2 GABAA receptor subunit were increased by 25% compared to naïve mice. Additional sex differences were observed for the effect of the binge and control treatment groups versus naïve mice on P450scc levels: a 20% decrease in relative protein levels in male PFC versus a 15–30% increase in levels for both the female PFC and HIPP. Treatments also increased levels of synaptophysin in male and female HIPP by 20–30%, compared to naïve mice, with only the female PFC having a 30% increase in ARC levels. Alterations in relative protein levels were similar for the control and binge animals versus naïve mice, suggesting that the repeated predator odor stress and ethanol drinking had the greatest influence on assayed neuroaptations in the PFC and HIPP. Simultaneous analysis of ten plasma neurosteroid levels by gas chromatography‐mass spectrometry showed that treatment significantly increased levels of several GABAA receptor active neurosteroids in these male and female mice versus naïve animals. Taken together, these data reinforce the importance of assessing sex differences, as there were divergent neurochemical responses between males and females. These data also implicate the influence of neurosteroids on responses to the impact of prior binge‐like drinking on subsequent ethanol drinking and effects of stress.Support or Funding InformationSupported by BX001070 and BX002966 (DF) from the Department of Veteran AffairsThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Acupuncture therapy in treating migraine: results of a magnetic resonance spectroscopy imaging study.

BackgroundAcupuncture has been proven to be effective as an alternative therapy in treating migraine, but the pathophysiological mechanisms of the treatment remain unclear. This study investigated possible neurochemical responses to acupuncture treatment.Patients and methodsProton magnetic resonance spectroscopy imaging was used to investigate biochemical levels pre- and post-acupuncture treatment. Participants (N=45) included subjects diagnosed with: 1) migraine without aura; 2) cervicogenic headache; and 3) healthy controls. Participants in the two patient groups received verum acupuncture using acupoints that target migraine without aura but not cervicogenic headache, while the healthy controls received a sham treatment. All participants had magnetic resonance spectroscopy scans before and after the acupuncture therapy. Levels of brain metabolites were examined in relation to clinical headache assessment scores.ResultsA significant increase in N-acetylaspartate/creatine was observed in bilateral thalamus in migraine without aura after the acupuncture treatment, which was significantly correlated with the headache intensity score.ConclusionThe data demonstrate brain biochemical changes underlying the effect of acupuncture treatment of migraine.

A multifaceted investigation into the effects of acute exercise on indices of brain function.

Participation in regular exercise is important for the maintenance and improvement of brain health across the lifespan. These beneficial effects are realized almost immediately, as a single bout of exercise transiently improves cognitive function after cessation from exercise. This postexercise time period represents an opportunity to strategically prescribe cognitively stimulating activities for enhancing brain plasticity and function. Mechanistically, acute exercise is proposed to upregulate brain-derived neurotrophic factor (BDNF) expression and increase regional activation and arousal of brain areas involved in cognitive control; however, the specific mechanisms underlying this facilitation are poorly understood. The purpose of this study was to (i) investigate BDNF responses to small muscle mass exercise to probe a potential mechanism of BDNF release during exercise; (ii) create and validate an equipment-free exercise protocol for use in a magnetic resonance imaging (MRI) scanner, with the eventual goal of investigating brain responses during exercise that may underlie improved cognition; and (iii) determine the effect of a very brief bout of high-intensity interval exercise (HIIE) on neuroelectric indices of reinforcement learning in young adults. Serum BDNF, platelet, and the amount of BDNF per platelet responses were measured following short-duration, maximal effort and long-duration, submaximal effort forearm handgrip exercise. We assessed the magnitude and reliability of metabolic responses to a novel whole-body isometric contraction (WBI) exercise protocol. We also characterized the amount of head movement created by WBI. The event-related potential component associated with reward-based learning was assessed before and after a bout of HIIE. Forearm handgrip exercise significantly increased serum BDNF, platelets, and BDNF per platelet, suggesting the possibility of splenic and cellular contribution of BDNF in response to handgrip exercise. WBI reliably evokes metabolic responses that are similar in magnitude to previous in-MRI studies, and creates head movement suitable for MRI scanning. HIIE abolishes neuroelectric indices of reward learning, likely owing to incomplete recovery from exercise. These findings advance our understanding of neurochemical and neuroelectric responses to acute exercise and introduce a novel tool that stands to further elucidate the regional brain responses to exercise that may underlie enhanced cognition after exercise.

Sex differences in the synergistic effect of prior binge drinking and traumatic stress on subsequent ethanol intake and neurochemical responses in adult C57BL/6J mice.

Alcohol-use disorders (AUDs) are characterized by repeated episodes of binge drinking. Based on reports that exposure to predator odor stress (PS) consistently increases ethanol intake, the present studies examined whether prior binge drinking differentially altered responsivity to PS and subsequent ethanol intake in male and female mice, when compared to mice without prior binge exposure. Initial studies in naïve male and female C57BL/6J mice confirmed that 30-min exposure to dirty rat bedding significantly increased plasma corticosterone (CORT) levels and anxiety-related behavior, justifying the use of dirty rat bedding as PS in the subsequent drinking studies. Next, separate groups of male and female C57BL/6J mice received seven binge ethanol sessions (binge) or drank water (controls), followed by a 1-month period of abstinence. Then, 2-bottle choice ethanol intake (10% or 10E vs. water, 23h/day) was measured in lickometer chambers for 4 weeks. After baseline intake stabilized, exposure to intermittent PS (2×/week×2 weeks) significantly enhanced ethanol intake after the 2nd PS in male, but not female, binge mice vs. baseline and vs. the increase in controls. However, in a subgroup of females (with low baselines), PS produced a similar increase in 10E intake in control and binge mice vs. baseline. Analysis of lick behavior determined that the enhanced 10E intake in binge male mice and in the female low baseline subgroup was associated with a significant increase in 10E bout frequency and 10E licks throughout the circadian dark phase. Thus, PS significantly increased 10E intake and had a synergistic interaction with prior binge drinking in males, whereas PS produced a similar significant increase in 10E intake in the low baseline subgroup of binge and control females. Plasma CORT levels were increased significantly in both binge and control animals after PS. CORT levels at 24-h withdrawal from daily 10E intake were highest in the groups with elevated 10E licks (i.e., binge males and control females). At 24-h withdrawal, protein levels of GABAA receptor α1 subunit, corticotropin releasing factor receptor 1, and glucocorticoid receptor in prefrontal cortex (PFC) and hippocampus (HC) were differentially altered in the male and female mice vs. levels in separate groups of age-matched naïve mice, with more changes in HC than in PFC and in females than in males. Importantly, the sexually divergent changes in protein levels in PFC and HC add to evidence for sex differences in the neurochemical systems influenced by stress and binge drinking, and argue for sex-specific pharmacological strategies to treat AUD.

MicroRNA-34 Contributes to the Stress-related Behavior and Affects 5-HT Prefrontal/GABA Amygdalar System through Regulation of Corticotropin-releasing Factor Receptor 1.

Recent studies show that microRNA-34 (miR-34) family is critical in the regulation of stress response also suggesting that it may contribute to the individual responsiveness to stress. We have recently demonstrated that mice carrying a genetic deletion of all miR-34 isoforms (triple knockout, TKO) lack the stress-induced serotonin (5-HT) and GABA release in the medial prefrontal cortex (mpFC) and basolateral amygdala (BLA), respectively. Here, we evaluated if the absence of miR-34 was also able to modify the stress-coping strategy in the forced swimming test. We found that the blunted neurochemical response to stress was associated with lower levels of immobility (index of active coping behavior) in TKO compared to WT mice. Interestingly, among the brain regions mostly involved in the stress-related behaviors, the miR-34 displayed the strongest expression in the dorsal raphe nuclei (DRN) of wild-type (WT) mice. In the DRN, the corticotropin-releasing factor receptors (CRFR) 1 and 2, contribute to determine the stress-coping style and the CRFR1 is a target of miR-34. Thus, we hypothesized that the miR-34-dependent modulation of CRFR1 expression may be involved in the DRN regulation of stress-coping strategies. In line with this hypothesis, we found increased CRFR1 levels in the DNR of TKO compared to WT mice. Moreover, infusion of CRFR1 antagonist in the DRN of TKO mice reverted their behavioral and neurochemical phenotype. We propose that miR-34 modulate the mpFC 5-HT/BLA GABA response to stress acting on CRFR1 in the DRN and that this mechanism could contribute to determine individual stress-coping strategy.

Food Addiction, High-Glycemic-Index Carbohydrates, and Obesity.

Treatment success in obesity remains low, and recently food addiction has been delineated as an underlying etiologic factor with therapeutic relevance. Specifically, current treatment focuses on reduced food intake and increase of physical activity, whereas interventions for addiction encompass behavioral therapy, abstinence, and environmental interventions such as taxation, restrictions on advertising, and regulation of school menus. Here, we reviewed the pertinent literature on food addiction with a specific focus on the role of high-glycemic-index carbohydrates in triggering addictive symptoms. Three lines of evidence support the concept of food addiction: (a) behavioral responses to certain foods are similar to substances of abuse; (b) food intake regulation and addiction rely on similar neurobiological circuits; (c) individuals suffering from obesity or addiction show similar neurochemical- and brain activation patterns.High-glycemic-index carbohydrates elicit a rapid shift in blood glucose and insulin levels, akin to the pharmacokinetics of addictive substances. Similar to drugs of abuse, glucose and insulin signal to the mesolimbic system to modify dopamine concentration. Sugar elicits addiction-like craving, and self-reported problem foods are rich in high-glycemic-index carbohydrates. These properties make high-glycemic-index carbohydrates plausible triggers for food addiction. We argue that food addiction is a plausible etiological factor contributing to the heterogeneous condition and phenotype of obesity. In at least a subset of vulnerable individuals, high-glycemic-index carbohydrates trigger addiction-like neurochemical and behavioral responses.

Mercury associated neurochemical response in Arctic barnacle goslings (Branta leucopsis)

There remains great concern over mercury pollution in the Arctic, though relatively little is known about impacts on biota that inhabit Arctic terrestrial systems. To help address this, the current study was performed with barnacle goslings (Branta leucopsis) from a coal mine-impacted site and a control site near Ny-Ålesund, Spitsbergen (Svalbard). The works focused mainly on mercury, as coal contains trace levels of this element. Total mercury concentrations were quantified in soil and vegetation from the two sites, as well as feces and liver from the goslings. Next, the mercury exposures were related to dopamine 2 (D2)- and NMDA-receptors in the brain, given that mercury is a proven neurotoxicant. Soil and vegetation in the mining area contained mercury levels that were approximately 3- and 2.2-times higher than in the control site. Despite a significant difference between the sites, the soil and vegetation mercury levels where were within ranges found at other Arctic locations. Goslings grazing in the mine-impacted area contained significantly higher hepatic mercury levels than those sampled from the control site. Compared to other species, the hepatic concentrations were relatively low possibly due to dilution of the mercury in growing goslings (growth dilution) and deposition of mercury in the growing feathers. Hepatic mercury concentrations were positively related to D2-neuroreceptor levels but not to NMDA-receptor levels thus suggesting a possible subtle neurological effect. To our knowledge, this is among the first studies on mercury exposure in Arctic terrestrial organisms, and one of the first to document potential subtle neurological responses associated with exposure to low, environmentally relevant mercury levels, which also can be found at other locations in the Arctic. However, as a pilot effort, the results here need to be examined in additional studies that include, for example, lager study designs, different geographic sites and other terrestrial species.

Dissociation of place preference and tolerance responses to sucrose using a dopamine antagonist in the planarian

In rodents, sucrose has been found to elicit addictive-like behaviours like the development of tolerance and the association with cues present at the time of consumption. Furthermore, the neurochemical response to sucrose binges is equivalent to the one observed in response to the abuse of addictive substances like cocaine. The experiments reported here address the effects of sucrose on an invertebrate model, the Platyhelminth brown planarian. The animals exposed to a 10% sucrose solution in one context developed a conditioned place preference (CPP) which was subsequently extinguished in the absence of the rewarding agent. However, one exposure to sucrose per se sufficed to reinstate the CPP response, suggesting sucrose-induced CPP can be characterised as a standard Pavlovian response. The same training procedure led to the development of context-specific tolerance to the effects of sucrose. However, comparing animals treated with dopamine D1 antagonist (SCH-23390) with control animals showed that the establishment of CPP, but not the development of tolerance, is mediated by the dopamine reward system.

N-Methyl-d-aspartate receptor co-agonist availability affects behavioral and neurochemical responses to cocaine: insights into comorbid schizophrenia and substance abuse.

Both schizophrenia (SZ) and substance abuse (SA) exhibit significant heritability. Moreover, N-methyl-d-aspartate receptors (NMDARs) have been implicated in the pathophysiology of both SZ and SA. We hypothesize that the high prevalence of comorbid SA in SZ is due to dysfunction of NMDARs caused by shared risk genes. We used transgenic mice with a null mutation of the gene encoding serine racemase (SR), the enzyme that synthesizes the NMDAR co-agonist d-serine and an established risk gene for SZ, to recreate the pathology of SZ. We determined the effect of NMDAR hypofunction resulting from the absence of d-serine on motivated behavior by using intracranial self-stimulation and neurotransmitter release in the nucleus accumbens by using in vivo microdialysis. Compared with wild-type mice, SR-/- mice exhibited similar baseline intracranial self-stimulation thresholds but were less sensitive to the threshold-lowering (rewarding) and the performance-elevating (stimulant) effects of cocaine. While basal dopamine (DA) and glutamate release were elevated in the nucleus accumbens of SR-/- mice, cocaine-induced increases in DA and glutamate release were blunted. γ-Amino-butyric acid efflux was unaffected in the SR-/- mice. Together, these findings suggest that the impaired NMDAR function and a consequent decrease in sensitivity to cocaine effects on behavior are mediated by blunted DA and glutamate responses normally triggered by the drug. Projected to humans, NMDAR hypofunction due to mutations in SR or other genes impacting glutamatergic function in SZ may render abused substances less potent and effective, thus requiring higher doses to achieve a hedonic response, resulting in elevated drug exposure and increased dependence/addiction.

The association of stress with non-motor symptoms and quality of life in Parkinson’s disease

Background: Non-motor symptoms(NMS) are a prominent feature in Parkinson's Disease(PD), often manifesting prior to motor symptoms. Studies have indicated the diversity of NMS and its adverse effect on Quality of Life(QoL). Stress is when strain is placed on a system, and most people will experience it in their lifetime as acute stress, however it may develop into chronic stress. Stress triggers a cascade of neurochemical and hormonal responses influenced by the hypothalamo-pituitary axis which are also associated with NMS such as anxiety and depression, features known to adversely affect QoL in PD.

Fatigue and stress reactivity are differently related to cigarette craving and hormone responses to neurotransmitter related drugs in nicotine deprived smokers

Lack of drive in depression has been reported to derive from deficiency of dopamine, whereas high responsiveness of the noradrenergic and serotonergic system have been found to be associated with anxiety related components of depression. Since, furthermore, the three neurotransmitters and depression are relevant in smoking motivation, the present experiment investigates if fatigability (FA) and stress reactivity (SR), the two corresponding components of depressiveness measured as personality dimensions in the normal range, can be separated by drug induced hormone responses and cigarette craving and their combined effects. Method36 Healthy male smokers assessed for FA and SR by questionnaires were tested under noradrenergic (NA), serotonergic (5-HT) and dopaminergic (DA) pharmacological stimulation in a placebo controlled balanced crossover design with respect to time and size of drug induced hormone responses and measures of cigarette craving during nicotine deprivation. ResultsRevealed that both FA and SR were related to early 5-HT responses but only FA showed late and low DA responses confirming the DA deficiency hypothesis. Smoking urge was increased by the noradrenergic drug merely in stress sensitive individuals, and larger prolactin responses to DA were associated with increased smoking urge. ConclusionsFacets of depressiveness can be discriminated by neurotransmitter related hormone responses. Personality related differences in motivation may be revealed by psychotropic drugs, and their underlying mechanisms may become evident by neurochemical responses to psychotropic drugs.

Sensitivity to cocaine in adult mice is due to interplay between genetic makeup, early environment and later experience

Although early aversive postnatal events are known to increase the risk to develop psychiatric disorders later in life, rarely they determine alone the nature and outcome of the psychopathology, indicating that interaction with genetic factors is crucial for expression of psychopathologies in adulthood. Moreover, it has been suggested that early life experiences could have negative consequences or confer adaptive value in different individuals. Here we suggest that resilience or vulnerability to adult cocaine sensitivity depends on a “triple interaction” between genetic makeup x early environment x later experience. We have recently showed that Repeated Cross Fostering (RCF; RCF pups were fostered by four adoptive mothers from postnatal day 1 to postnatal day 4. Pups were left with the last adoptive mother until weaning) experienced by pups affected the response to a negative experience in adulthood in opposite direction in two genotypes leading DBA2/J, but not C57BL/6J mice, toward an “anhedonia-like” phenotype.Here we investigate whether exposure to a rewarding stimulus, instead of a negative one, in adulthood induces an opposite behavioral outcome. To test this hypothesis, we investigated the long-lasting effects of RCF on cocaine sensitivity in C57 and DBA female mice by evaluating conditioned place preference induced by different cocaine doses and catecholamine prefrontal-accumbal response to cocaine using a “dual probe” in vivo microdialysis procedure. Moreover, cocaine-induced c-Fos activity was assessed in different brain regions involved in processing of rewarding stimuli. Finally, cocaine-induced spine changes were evaluated in the prefrontal-accumbal system. RCF experience strongly affected the behavioral, neurochemical and morphological responses to cocaine in adulthood in opposite direction in the two genotypes increasing and reducing, respectively, the sensitivity to cocaine in C57 and DBA mice.

Acute effects of amitriptyline on adult zebrafish: Potential relevance to antidepressant drug screening and modeling human toxidromes

The need to develop novel antidepressants is an emerging problem in biomedicine. An aquatic vertebrate species, the zebrafish (Danio rerio) may serve as a useful in-vivo screen for CNS drugs, and displays high sensitivity to a wide range of antidepressants. Amitriptyline is a commonly used tricyclic antidepressant which acts primarily as a serotonin and noradrenaline reuptake inhibitor. Here, we characterize drug-induced behavioral and neurochemical responses in adult zebrafish following their acute exposure to amitriptyline. Overall, the drug at 1 and 5mg/L significantly increased time spent in top and shortened the latency to enter it, thereby paralleling recent reports on zebrafish ‘serotonin toxicity-like behavior’ caused by various serotonergic agents. The 10mg/L dose of the drug also significantly decreased top entries and maximal velocity and evoked overt ataxia, likely due to emerging non-specific toxic effects. Amitriptyline at 5 and 10mg/L also dose-dependently increased serotonin turnover, but not noradrenaline levels, in zebrafish whole-brain samples. Overall, zebrafish high sensitivity to acute effects of amitriptyline can help improve our understanding of psychopharmacological profiles of this compound and the related CNS drugs, and contributes further to the development of aquatic experimental models of human toxidromes.

Cutaneous TRPM8-expressing sensory afferents are a small population of neurons with unique firing properties.

It has been well documented that the transient receptor potential melastatin 8 (TRPM8) receptor is involved in environmental cold detection. The role that this receptor plays in nociception however, has been somewhat controversial since conflicting reports have shown different neurochemical identities and responsiveness of TRPM8 neurons. In order to functionally characterize cutaneous TRMP8 fibers, we used two ex vivo somatosensory recording preparations to functionally characterize TRPM8 neurons that innervate the hairy skin in mice genetically engineered to express GFP from the TRPM8 locus. We found several types of cold‐sensitive neurons that innervate the hairy skin of the mouse but the TRPM8‐expressing neurons were found to be of two specific populations that responded with rapid firing to cool temperatures. The first group was mechanically insensitive but the other did respond to high threshold mechanical deformation of the skin. None of these fibers were found to contain calcitonin gene‐related peptide, transient receptor potential vanilloid type 1 or bind isolectin B4. These results taken together with other reports suggest that TRPM8 containing sensory neurons are environmental cooling detectors that may be nociceptive or non‐nociceptive depending on the sensitivity of individual fibers to different combinations of stimulus modalities.

Human COMT over-expression confers a heightened susceptibility to dyskinesia in mice

Catechol-O-methyltransferase (COMT) degrades dopamine and its precursor l-DOPA and plays a critical role in regulating synaptic dopamine actions. We investigated the effects of heightened levels of COMT on dopamine-regulated motor behaviors and molecular alterations in a mouse model of dyskinesia. Transgenic mice overexpressing human COMT (TG) and their wildtype (WT) littermates received unilateral 6-OHDA lesions in the dorsal striatum and were treated chronically with l-DOPA for two weeks. l-DOPA-induced dyskinesia was exacerbated in TG mice without altering l-DOPA motor efficacy as determined by contralateral rotations or motor coordination. Inductions of FosB and phospho-acetylated histone 3 (molecular correlates of dyskinesia) were potentiated in the lesioned striatum of TG mice compared with their WT littermates. The TG mice had lower basal levels of dopamine in the striatum. In mice with lesions, l-DOPA induces a greater increase in the dopamine metabolite 3-methoxytyramine in the lesioned striatum of dyskinetic TG mice than in WT mice. The levels of serotonin and its metabolite were similar in TG and WT mice. Our results demonstrate that human COMT overexpression confers a heightened susceptibility to l-DOPA-induced dyskinesia and alters molecular and neurochemical responses in the lesioned striatum of mice.

Age-dependent dopamine transporter dysfunction and Serine129 phospho-\u03b1-synuclein overload in G2019S LRRK2 mice

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic cause of Parkinson’s disease. Here, we investigated whether the G2019S LRRK2 mutation causes morphological and/or functional changes at nigro-striatal dopamine neurons. Density of striatal dopaminergic terminals, nigral cell counts, tyrosine hydroxylase protein levels as well as exocytotic dopamine release measured in striatal synaptosomes, or striatal extracellular dopamine levels monitored by in vivo microdialysis were similar between ≥12-month-old G2019S knock-in mice and wild-type controls. In vivo striatal dopamine release was insensitive to the LRRK2 inhibitor Nov-LRRK2-11, and was elevated by the membrane dopamine transporter blocker GBR-12783. However, G2019S knock-in mice showed a blunted neurochemical and motor activation response to GBR-12783 compared to wild-type controls. Western blot and dopamine uptake analysis revealed an increase in dopamine transporter levels and activity in the striatum of 12-month-old G2019S KI mice. This phenotype correlated with a reduction in vesicular monoamine transporter 2 levels and an enhancement of vesicular dopamine uptake, which was consistent with greater resistance to reserpine-induced hypolocomotion. These changes were not observed in 3-month-old mice. Finally, Western blot analysis revealed no genotype difference in striatal levels of endogenous α-synuclein or α-synuclein bound to DOPAL (a toxic metabolite of dopamine). However, Serine129-phosphorylated α-synuclein levels were higher in 12-month-old G2019S knock-in mice. Immunohistochemistry confirmed this finding, also showing no genotype difference in 3-month-old mice. We conclude that the G2019S mutation causes progressive dysfunctions of dopamine transporters, along with Serine129-phosphorylated α-synuclein overload, at striatal dopaminergic terminals, which are not associated with dopamine homeostasis dysregulation or neuron loss but might contribute to intrinsic dopaminergic terminal vulnerability. We propose G2019S knock-in mice as a presymptomatic Parkinson’s disease model, useful to investigate the pathogenic interaction among genetics, aging, and internal or environmental factors leading to the disease.

Synaptic vesicle glycoprotein 2C (SV2C) modulates dopamine release and is disrupted in Parkinson disease.

Members of the synaptic vesicle glycoprotein 2 (SV2) family of proteins are involved in synaptic function throughout the brain. The ubiquitously expressed SV2A has been widely implicated in epilepsy, although SV2C with its restricted basal ganglia distribution is poorly characterized. SV2C is emerging as a potentially relevant protein in Parkinson disease (PD), because it is a genetic modifier of sensitivity to l-DOPA and of nicotine neuroprotection in PD. Here we identify SV2C as a mediator of dopamine homeostasis and report that disrupted expression of SV2C within the basal ganglia is a pathological feature of PD. Genetic deletion of SV2C leads to reduced dopamine release in the dorsal striatum as measured by fast-scan cyclic voltammetry, reduced striatal dopamine content, disrupted α-synuclein expression, deficits in motor function, and alterations in neurochemical effects of nicotine. Furthermore, SV2C expression is dramatically altered in postmortem brain tissue from PD cases but not in Alzheimer disease, progressive supranuclear palsy, or multiple system atrophy. This disruption was paralleled in mice overexpressing mutated α-synuclein. These data establish SV2C as a mediator of dopamine neuron function and suggest that SV2C disruption is a unique feature of PD that likely contributes to dopaminergic dysfunction.

Neurochemical responses to chromatic and achromatic stimuli in the human visual cortex

In the present study, we aimed at determining the metabolic responses of the human visual cortex during the presentation of chromatic and achromatic stimuli, known to preferentially activate two separate clusters of neuronal populations (called “blobs” and “interblobs”) with distinct sensitivity to color or luminance features. Since blobs and interblobs have different cytochrome-oxidase (COX) content and micro-vascularization level (i.e., different capacities for glucose oxidation), different functional metabolic responses during chromatic vs. achromatic stimuli may be expected. The stimuli were optimized to evoke a similar load of neuronal activation as measured by the bold oxygenation level dependent (BOLD) contrast. Metabolic responses were assessed using functional 1H MRS at 7 T in 12 subjects. During both chromatic and achromatic stimuli, we observed the typical increases in glutamate and lactate concentration, and decreases in aspartate and glucose concentration, that are indicative of increased glucose oxidation. However, within the detection sensitivity limits, we did not observe any difference between metabolic responses elicited by chromatic and achromatic stimuli. We conclude that the higher energy demands of activated blobs and interblobs are supported by similar increases in oxidative metabolism despite the different capacities of these neuronal populations.

Glutamate and Opioid Antagonists Modulate Dopamine Levels Evoked by Innately Attractive Male Chemosignals in the Nucleus Accumbens of Female Rats.

Sexual chemosignals detected by vomeronasal and olfactory systems mediate intersexual attraction in rodents, and act as a natural reinforcer to them. The mesolimbic pathway processes natural rewards, and the nucleus accumbens receives olfactory information via glutamatergic projections from the amygdala. Thus, the aim of this study was to investigate the involvement of the mesolimbic pathway in the attraction toward sexual chemosignals. Our data show that female rats with no previous experience with males or their chemosignals display an innate preference for male-soiled bedding. Focal administration of the opioid antagonist β-funaltrexamine into the posterior ventral tegmental area does not affect preference for male chemosignals. Nevertheless, exposure to male-soiled bedding elicits an increase in dopamine efflux in the nucleus accumbens shell and core, measured by microdialysis. Infusion of the opioid antagonist naltrexone in the accumbens core does not significantly affect dopamine efflux during exposure to male chemosignals, although it enhances dopamine levels 40 min after withdrawal of the stimuli. By contrast, infusion of the glutamate antagonist kynurenic acid in the accumbens shell inhibits the release of dopamine and reduces the time that females spend investigating male-soiled bedding. These data are in agreement with previous reports in male rats showing that exposure to opposite-sex odors elicits dopamine release in the accumbens, and with data in female mice showing that the behavioral preference for male chemosignals is not affected by opioidergic antagonists. We hypothesize that glutamatergic projections from the amygdala into the accumbens might be important to modulate the neurochemical and behavioral responses elicited by sexual chemosignals in rats.