The Vertebrate Brain, Evidence of Its Modular Organization and Operating System: Insights into the Brain's Basic Units of Structure, Function, and Operation and How They Influence Neuronal Signaling and Behavior

Inhibition of glutamate-carboxypeptidase-II in dorsolateral prefrontal cortex: potential therapeutic target for neuroinflammatory cognitive disorders

Glutamate carboxypeptidase-II (GCPII) expression in brain is increased by inflammation, e.g. by COVID19 infection, where it reduces NAAG stimulation of metabotropic glutamate receptor type 3 (mGluR3). GCPII-mGluR3 signaling is increasingly linked to higher cognition, as genetic alterations that weaken mGluR3 or increase GCPII signaling are associated with impaired cognition in humans. Recent evidence from macaque dorsolateral prefrontal cortex (dlPFC) shows that mGluR3 are expressed on dendritic spines, where they regulate cAMP-PKA opening of potassium (K⁺) channels to enhance neuronal firing during working memory. However, little is known about GCPII expression and function in the primate dlPFC, despite its relevance to inflammatory disorders. The present study used multiple label immunofluorescence and immunoelectron microscopy to localize GCPII in aging macaque dlPFC, and examined the effects of GCPII inhibition on dlPFC neuronal physiology and working memory function. GCPII was observed in astrocytes as expected, but also on neurons, including extensive expression in dendritic spines. Recordings in dlPFC from aged monkeys performing a working memory task found that iontophoresis of the GCPII inhibitors 2-MPPA or 2-PMPA markedly increased working memory-related neuronal firing and spatial tuning, enhancing neural representations. These beneficial effects were reversed by an mGluR2/3 antagonist, or by a cAMP-PKA activator, consistent with mGluR3 inhibition of cAMP-PKA-K⁺ channel signaling. Systemic administration of the brain penetrant inhibitor, 2-MPPA, significantly improved working memory performance without apparent side effects, with largest effects in the oldest monkeys. Taken together, these data endorse GCPII inhibition as a potential strategy for treating cognitive disorders associated with aging and/or neuroinflammation.

Caloric Restriction Alters Postprandial Responses of Essential Brain Metabolites in Young Adult Mice

Caloric restriction (CR) has been shown to extend longevity and protect brain function in aging. However, the effects of CR in young adult mice remain largely unexplored. In addition to the fundamental, long-term changes, recent studies demonstrate that CR has a significant impact on transient, postprandial metabolic flexibility and turnover compared to control groups. The goal of this study was to identify the brain metabolic changes at a transient (2 h) and steady (6 h) postprandial state in young mice (5–6 months of age) fed with CR or ad libitum (AL; free eating). Using metabolomics profiling, we show that CR mice had significantly higher levels of neurotransmitters (e.g., glutamate, N-acetylglutamate), neuronal integrity markers (e.g., NAA and NAAG), essential fatty acids (e.g., DHA and DPA), and biochemicals associated carnitine metabolism (related to reduced oxidative stress and inflammation) in the cerebral cortex and hippocampus at 2-h. These biochemicals remained at high levels at the 6-h postprandial time-point. The AL mice did not show the similar increases in essential fatty acid and carnitine metabolism until the 6-h time-point, and failed to show increases in neurotransmitters and neuronal integrity markers at any time-point. On the other hand, metabolites related to glucose utilization—glycolysis and pentose phosphate pathway (PPP)—were low in the CR mice throughout the 6-h period and significantly increased at the 6-h time-point in the AL mice. Our findings suggest that CR induces distinct postprandial responses in metabolites that are essential to maintain brain functions. CR mice produced higher levels of essential brain metabolites in a shorter period after a meal and sustained the levels for an extended period, while maintaining a lower level of glucose utilization. These early brain metabolism changes in the CR mice might play a critical role for neuroprotection in aging. Understanding the interplay between dietary intervention and postprandial metabolic responses from an early age may have profound implications for impeding brain aging and reducing risk for neurodegenerative disorders.

Proton magnetic resonance spectroscopy revealed differences in the glutamate + glutamine/creatine ratio of the anterior cingulate cortex between healthy and pediatric post-traumatic stress disorder patients diagnosed after 2008 Wenchuan earthquake

AIMS

Earthquakes always leave many surviving teenagers suffering from various mental problems, such as post-traumatic stress disorder (PTSD). We studied the metabolites in current and remitted pediatric PTSD patients and healthy controls after an earthquake, aiming to find the neurochemistry differences in these teenagers.

METHODS

Proton magnetic resonance spectroscopy ((1) H-MRS) was performed in the anterior cingulate cortex (ACC) of 21 healthy, 10 PTSD and 23 remitted subjects.

RESULTS

Significantly lower glutamate + glutamine/creatine (Glx/Cr) levels in the ACC (1.15 ± 0.14 vs 1.37 ± 0.08, P = 0.047) were found in PTSD subjects relative to remitted subjects; and significantly lower Glx/Cr levels in the ACC (1.37 ± 0.08 vs 1.59 ± 0.10, P = 0.045) were found in remitted subjects relative to healthy controls.

CONCLUSIONS

Our findings imply that the Glx/Cr ratio in the ACC can be used to differentiate not only between healthy and pediatric PTSD patients, but also between the current and remitted phases of pediatric PTSD. The changes in the Glx/Cr ratio may be caused by brain dysfunction in the current phase and recovery in the remitted phase.

Oxytocin's neurochemical effects in the medial prefrontal cortex underlie recovery of task-specific brain activity in autism: a randomized controlled trial

The neuropeptide oxytocin may be an effective therapeutic strategy for the currently untreatable social and communication deficits associated with autism. Our recent paper reported that oxytocin mitigated autistic behavioral deficits through the restoration of activity in the ventromedial prefrontal cortex (vmPFC), as demonstrated with functional magnetic resonance imaging (fMRI) during a socio-communication task. However, it is unknown whether oxytocin exhibited effects at the neuronal level, which was outside of the specific task examined. In the same randomized, double-blind, placebo-controlled, within-subject cross-over clinical trial in which a single dose of intranasal oxytocin (24 IU) was administered to 40 men with high-functioning autism spectrum disorder (UMIN000002241/000004393), we measured N-acetylaspartate (NAA) levels, a marker for neuronal energy demand, in the vmPFC using (1)H-magnetic resonance spectroscopy ((1)H-MRS). The differences in the NAA levels between the oxytocin and placebo sessions were associated with oxytocin-induced fMRI signal changes in the vmPFC. The oxytocin-induced increases in the fMRI signal could be predicted by the NAA differences between the oxytocin and placebo sessions (P=0.002), an effect that remained after controlling for variability in the time between the fMRI and (1)H-MRS scans (P=0.006) and the order of administration of oxytocin and placebo (P=0.001). Furthermore, path analysis showed that the NAA differences in the vmPFC triggered increases in the task-dependent fMRI signals in the vmPFC, which consequently led to improvements in the socio-communication difficulties associated with autism. The present study suggests that the beneficial effects of oxytocin are not limited to the autistic behavior elicited by our psychological task, but may generalize to other autistic behavioral problems associated with the vmPFC.

Mitochondrial Aspartate/Glutamate Carrier SLC25A12 and Autism Spectrum Disorder: a Meta-Analysis

Mitochondrial dysfunction has been reported to be involved in the pathophysiology of autism spectrum disorder (ASD). Studies investigating the possible association between ASD and polymorphism in SLC25A12, which encodes the mitochondrial aspartate/glutamate carrier, have yielded inconsistent results. We conducted a systematic review and meta-analysis of such studies to elucidate if and which SLC25A12 single nucleotide polymorphisms (SNPs) are associated with ASD. We searched PubMed, Ovid, Web of Science, and ERIC databases through September 20th, 2014. Odds ratios (ORs) were aggregated using random effect models. Sensitivity analyses were conducted based on study design (family-based or case-control). Fifteen out of 79 non-duplicate records were retained for qualitative synthesis. We pooled 10 datasets from 9 studies with 2001 families, 735 individuals with ASD and 632 typically developing (TD) individuals for the meta-analysis of rs2292813, as well as 11 datasets from 10 studies with 2016 families, 852 individuals with ASD and 1058 TD individuals for the meta-analysis of rs2056202. We found a statistically significant association between ASD and variant in rs2292813 (OR = 1.190, 95% CI 1.052-1.346, P = 0.006) as well as in rs2056202 (OR = 1.206, 95% CI 1.035-1.405, P = 0.016). Sensitivity analyses including only studies with family-based design demonstrated significant association between ASD and polymorphism in rs2292813 (OR = 1.216, 95% CI 1.075-1.376, P = 0.002) and rs2056202 (OR = 1.267, 95% CI 1.041-1.542, P = 0.018). In contrast, sensitivity analyses including case-control design studies only failed to find a significant association. Further research on the role of SLC25A12 and ASD may pave the way for potential innovative therapeutic interventions.

Changes in metabolites after treatment with memantine in fibromyalgia. A double-blind randomized controlled trial with magnetic resonance spectroscopy with a 6-month follow-up

AIM

To evaluate the efficacy of memantine on metabolite levels in different areas of the brain and to determine whether changes in metabolite levels correlate with clinical variables in Fibromyalgia (FM) patients.

METHODS

Doubled-blind parallel randomized controlled trial. Twenty-five patients diagnosed with FM were enrolled in the study. Patients were administered questionnaires on pain, anxiety, depression, quality of life, and cognitive impairment, and single-voxel MRS of the brain was performed. All assessments were performed at baseline and after 6 months of treatment with memantine or placebo.

RESULTS

Patients treated with memantine exhibited a significant increase in the glutamate (P = 0.010), glutamate/creatine ratio (P = 0.013), combined glutamate + glutamine (P = 0.016) and total N-acetyl-aspartate (NAA+NAAG) (P = 0.034) in the posterior cingulate cortex compared with those on placebo. Furthermore, the memantine group exhibited increases in creatine (P = 0.013) and choline (Cho) (P = 0.025) in the right posterior insula and also a correlation between choline and the Fibromyalgia Impact Questionnaire (FIQ) in the posterior insula (P = 0.050) was observed.

CONCLUSION

Memantine treatment resulted in an increase in cerebral metabolism in FM patients, suggesting its utility for the treatment of the illness.

Higher glutamate+glutamine and reduction of N-acetylaspartate in posterior cingulate according to age range in patients with cognitive impairment and/or pain

RATIONALE AND OBJECTIVES

The aim of the study was to analyze 1) whether the metabolite levels in the posterior cingulate cortex (PCC) are different in healthy individuals compared to a group of patients with cognitive impairment and/or pain and 2) whether there exists a correlation between brain metabolites and the age of a patient.

MATERIALS AND METHODS

Two hundred seven patients with cognitive impairment and/or pain (66 mild cognitive impairment, 54 fibromyalgia, 36 Alzheimer disease, 33 interictal migraine, 10 somatization disorder, and 8 after trigeminal neuralgia, and 193 healthy participants adjusted for gender and age. Proton magnetic resonance spectroscopy (MRS) of the brain was performed with the voxel placed in the ventral PCC and postprocessed with LCModel (Stephen Provencher, Oakville, Ontario, Canada).

RESULTS

Using linear regression and adjusting for gender and age, mean brain metabolite values for the pathological group, when compared to healthy controls, were significantly lower in N-acetylaspartate (P=.003) and N-acetylaspartate/creatine (P=.015) and significantly greater in glutamate+glutamine (P<.001) and glutamate+glutamine/creatine (P<.000). All metabolites were significantly correlated with age: glutamate, glutamate+glutamine, N-acetylaspartate, and their creatine ratios exhibited a negative correlation, whereas myoinositol and choline exhibited a positive correlation.

CONCLUSIONS

Although the number of patients is relatively small with heterogeneous state of disease, MRS in PCC may serve as a useful noninvasive tool for diagnostic of patients with cognitive impairment and pain.

The Directive 2010/63/EU on animal experimentation may skew the conclusions of pharmacological and behavioural studies

All laboratory animals shall be provided some form of environmental enrichment (EE) in the nearest future (Directive 2010/63/EU). Displacing standard housing with EE entails the possibility that data obtained under traditional housing may be reconsidered. Specifically, while EE often contrasts the abnormalities of consolidated disease models, it also indirectly demonstrates that their validity depends on housing conditions. We mimicked a situation in which the consequences of a novel pharmacological compound were addressed before and after the adoption of the Directive. We sub-chronically exposed standard- or EE-reared adolescent CD1 mice (postnatal days 23-33) to the synthetic compound JWH-018, and evaluated its short- and long-term potential cannabinoid properties on: weight gain, locomotion, analgesia, motor coordination, body temperature, brain metabolism (¹H MRI/MRS), anxiety- and depressive-related behaviours. While several parameters are modulated by JWH-018 independently of housing, other effects are environmentally mediated. The transition from standard housing to EE shall be carefully monitored.

Reduced N-acetylaspartate in the hippocampus in patients with fibromyalgia: a meta-analysis

Fibromyalgia (FM) is a stress-associated syndrome with chronic, widespread pain. Patients with FM also present disturbances of cognition and memory. As the hippocampus is vulnerable to stress exposure and involved in cognition, memory and pain perception, we hypothesize that the abnormal function of the hippocampus is implicated in the pathophysiology of FM. N-acetylaspartate (NAA), a metabolite that can be measured using proton magnetic resonance spectroscopy (1H MRS), is recognized as a marker of neuronal structure and function. We performed a systematic review and meta-analysis of 1H MRS studies investigating NAA levels in patients with FM. A comprehensive literature search through MEDLINE, Embase and Web of Science yielded nine studies; among these nine, four studies met our criteria for inclusion. A random effect model with 51 patients with FM and 38 controls revealed a significant NAA reduction in the hippocampus. The current meta-analysis suggested a neuronal abnormality in the hippocampus in patients with FM.

Age-related change of neurochemical abnormality in attention-deficit hyperactivity disorder: a meta-analysis

Prevalence and symptoms of attention-deficit hyperactivity disorder (ADHD) change with advancing age. However, neurochemical background of such age-related change is yet to be elucidated. We therefore conducted a meta-analysis of 16 proton magnetic resonance spectroscopy studies comprising 270 individuals with ADHD and 235 controls. Standardized mean differences were calculated and used as an effect size. Sensitivity analyses and meta-regression to explore the effect of age on neurochemical abnormality were performed. A random effects model identified a significantly higher-than-normal N-acetylaspartate (NAA) in the medial prefrontal cortex (mPFC), but no significant differences of other metabolites in that area. No significant difference in metabolite levels was demonstrated in any other region. Sensitivity analysis of children with ADHD revealed significantly higher-than-normal NAA, whereas no significant difference was found in adults with ADHD. Meta-regression revealed significant correlation between advanced age and normal levels of NAA in the mPFC, suggesting that age-dependent abnormality of NAA level in the mPFC is a potential neural basis of age-related change of symptoms of ADHD.