Blockade of astrocytic glutamate uptake in the prefrontal cortex induces anhedonia

Major depression is associated with both dysregulated glutamatergic neurotransmission and fewer astrocytes in limbic areas including the prefrontal cortex (PFC). These deficits may be functionally related. Notably, astrocytes regulate glutamate levels by removing glutamate from the synapse via the glutamate transporter (GLT-1). Previously, we demonstrated that central blockade of GLT-1 induces anhedonia and c-Fos expression in the PFC. Given the role of the PFC in regulating mood, we hypothesized that GLT-1 blockade in the PFC alone would be sufficient to induce anhedonia in rats. We microinjected the GLT-1 inhibitor, dihydrokainic acid (DHK), into the PFC and examined the effects on mood using intracranial self-stimulation (ICSS). At lower doses, intra-PFC DHK produced modest increases in ICSS thresholds, reflecting a depressive-like effect. At higher doses, intra-PFC DHK resulted in cessation of responding. We conducted further tests to clarify whether this total cessation of responding was related to an anhedonic state (tested by sucrose intake), a nonspecific result of motor impairment (measured by the tape test), or seizure activity (measured with electroencephalogram (EEG)). The highest dose of DHK increased latency to begin drinking without altering total sucrose intake. Furthermore, neither motor impairment nor evidence of seizure activity was observed in the tape test or EEG recordings. A decrease in reward value followed by complete cessation of ICSS responding suggests an anhedonic-like effect of intra-PFC DHK; a conclusion that was substantiated by an increased latency to begin sucrose drinking. Overall, these results suggest that blockade of astrocytic glutamate uptake in the PFC is sufficient to produce anhedonia, a core symptom of depression.     

Comprehensive gene expression profiling in the prefrontal cortex links immune activation and neutrophil infiltration to antinociception

Functional neuroimaging studies have implicated the prefrontal cortex (PFCTX) in descending modulation of pain and the placebo effect. This study was performed to elucidate comprehensive PFCTX gene expression in an animal model of persistent trigeminal pain. Adult male C57BL/6J mice received facial carrageenan injection and showed sustained increase in nociceptive responses. Microarray analyses of differentially expressed genes in the PFCTX at 3 d after injection showed "immune system process" as the dominant ontology term and increased mRNA expression of S100a8, S100a9, Lcn2, Il2rg, Fcgr1, Fcgr2b, C1qb, Ptprc, Ccl12, and Cd52 were verified by RT-PCR. Upregulation of S100A8, S100A9, and lipocalin 2 (LCN2) were confirmed by Western blots, and cells in the PFCTX were double immunolabeled with MPO, indicating they were neutrophils. Analyses of blood of facial carrageenan-injected mice also showed increased mRNA expression of these markers, suggesting transmigration of activated neutrophils into the brain. Other immune-related genes, Il2rg, Fcgr2b, C1qb, Ptprc, and Ccl12 were upregulated in the PFCTX but not blood. Approximately 70% of S100A9-positive cells in the PFCTX of carrageenan-injected mice were located in capillaries adherent to endothelial cells, whereas 30% were within the brain parenchyma. Carrageenan-injected mice showed significantly reduced nociceptive responses after injection of C terminus of murine S100A9 protein in the lateral ventricles and PFCTX but not somatosensory barrel cortex. Together, these findings demonstrate activation of immune-related genes in the PFCTX during inflammatory pain and highlight an exciting role of neutrophils in linking peripheral inflammation with immune activation of the PFCTX and antinociception.     

Response channel activation and the lateral prefrontal cortex

The role of lateral prefrontal cortex in transducing perception into action was studied in 10 patients with chronic, unilateral lesions. They identified colors in the center of a visual display, while a flanking, distractor color was presented simultaneously in either the ipsilesional or contralesional field. The flanker could be either the same color as the target, or incompatible with the correct response. The effects of compatible and incompatible flankers on reaction time (RT) served as a measure of response channel activation by the flanker. Flankers in the contralesional field influenced RT less than did those in the ipsilesional field. These results suggest that the lateral prefrontal cortex is involved in maintaining stimulus-response channels.     

Microglial expression of GAT-1 in the cerebral cortex

Microglial cells are the immune cells of the brain that, by sensing the microenvironment, permit a correct brain development and function. They communicate with other glial cells and with neurons, releasing and responding to a number of molecules that exert effects on surrounding cells. Among these, neurotransmitters and, in particular, gamma-aminobutyric acid (GABA) has recently gained interest in this context. We demonstrated the expression of GABA transporter 1 (GAT-1) in microglial cells both in soma and cell processes. We show that microglial cell treatment with 1,2,5,6-tetrahydro-1-[2-[[(diphenylmethylene)amino]oxy]ethyl]-3-pyridinecarboxylic acid hydrochloride (NNC-711), a potent and selective GAT-1 inhibitor, significantly reduced Na⁺-dependent GABA uptake. On the other hand, GABA uptake was significantly increased by cell treatment with (S)-1-[2-[tris(4-methoxyphenyl)methoxy]ethyl]-3-piperidinecarboxylic acid (SNAP-5114), a GAT-2/3 inhibitor, and this effect was completely blocked by the botulinum toxin BoNT/C1, that specifically cleaves and inactives syntaxin 1A (STX1A). Overall, these findings show that microglial cells express GAT-1 and indicate that STX1A plays an important role in the regulation of GAT-1-dependent GABA uptake in microglia.     

Sustained activation and executive control in the avian prefrontal cortex

We review our studies examining neural correlates of directed forgetting and executive control in the avian prefrontal cortex. One of the fundamental forms of executive control is the ability to selectively filter information, retaining that which is critical for the current purposes and discarding that which is not. In our first experiment, we trained birds on a directed-forgetting version of a delayed matching-to-sample task. Following a sample stimulus, a bird heard either a remember tone indicating that a memory test would follow, or a forget tone indicating that no memory test would be given. We found that neural activity in the avian prefrontal cortex increased when the bird was told to remember, and decreased when the bird was told to forget. Behavioral probe tests confirmed that the animals were forgetting on forget trials.Although the sustained activation observed on remember trials and the absence of such activation on forget trials could be a code of remembering and forgetting the sample stimulus, it could also be a code of the possibility of obtaining a reward. To address this issue we conducted a second study in which we used three cues: remember, forget, and forget–reward. The forget–reward cue instructed the subject to forget the sample yet at the same time provided a free reward. Neural activity on forget–reward trials matched that on remember trials tentatively indicating that the sustained activation on remember trials might be a reward code rather than a sample stimulus code. Behavioral probe tests, however, failed to indicate that the animals were forgetting on forget–reward trials, and hence it still is possible that the sustained activation could be a code for memory of the sample stimulus.     

Decreased VEGFR2 expression and increased phosphorylated Akt1 in the prefrontal cortex of individuals with schizophrenia

The Akt signaling pathway involves various cellular processes and depends on extracellular stimuli. Since Akt signaling participates in cytoprotection, synapse plasticity, axon extension, and neurotransmission in the nervous system, alteration in Akt signaling might be a potential cause of schizophrenia. In this study, we performed multiplex fluorescent bead based immunoassays for members of the Akt signaling pathway in postmortem brains of controls and patients with schizophrenia. Vascular endothelial growth factor receptor 2 (VEGFR2/KDR) was significantly decreased in the prefrontal cortex (PFC) of patients with schizophrenia, and the expression level of VEGFR2 was inversely correlated with the positive symptom subscale of the Diagnostic Instrument for Brain Studies (DIBS) in patients with schizophrenia. There was also an increase in phosphorylated Akt1 in the PFC in the patients, though the ratio of phospho/total Akt1 is not significantly different. In the nucleus accumbens (NAcc) there was no significant difference in expression and phosphorylation levels of Akt signaling proteins. Genetic analysis revealed a significant correlation of a SNP of KDR (rs7692791) with ERK1/2 and Akt1 phospho/total rates. Since VEGFR2 participates in angiogenesis and neurotrophic activation, either or both functions might be responsible for onset of schizophrenia.     

Regional haemodynamic responses to activation of the medial prefrontal cortex depressor region

Electrical or chemical stimulation of the medial prefrontal cortex (MPFC) produces depressor and sympathoinhibitory responses. To characterise the MPFC depressor response more fully, we determined the regional haemodynamic changes which occurred in response to stimulation of the MPFC. In halothane-anaesthetised rats, we recorded arterial blood pressure and renal, superior mesenteric, and iliac arterial vascular conductance using miniaturised Doppler flow probes. Electrical stimulation of the MPFC (50-100 microA) was used to map the location of the depressor region. Increases in vascular conductance (or increases in blood flow) were recorded from the renal (+2.3+/-0.5 kHz/mmHgx10(3)), mesenteric (+4.4+/-0.4 kHz/mmHgx10(3)), and iliac (+8.3+/-1.0 kHz/mmHgx10(3)) vascular beds in response to stimulation of the MPFC depressor region coinciding with the ventral infralimbic (IL) and dorsal peduncular (DP) cortical areas. Similar responses were obtained after microinjection of the chemical excitant L-glutamate (n=3, 100 nl, 100 mM), indicating that the responses were due to excitation of cell bodies and not due to axons traversing the area. Administration of the nitric oxide synthesis inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 25 micromol/kg, i.v., n=5) significantly reduced the MPFC depressor response (51%, 12.5+/-1.2 to 6.1+/-2.5 mmHg). The increases in conductance in the hindquarter and mesenteric vascular beds were significantly reduced after L-NAME treatment (mesenteric by 77%, iliac by 70%), but there was no significant reduction of renal flow (35%). These observations indicate that the depressor region of the MPFC is localised to ventral regions (IL and DP) and that the depressor response is mediated by increased conductance in the hindquarters and mesenteric vascular beds. Furthermore, the depressor response may be mediated, in part, by release of nitric oxide in these vascular beds.     

Decreased expression of mGluR5 within the dorsolateral prefrontal cortex in autism and increased microglial number in mGluR5 knockout mice: Pathophysiological and neurobehavioral implications

Metabotropic glutamate receptor 5 (mGluR5) and microglial abnormalities have been implicated in autism spectrum disorder (ASD). However, controversy exists as to whether the receptor is down or upregulated in functioning in ASD. In addition, whilst activation of mGluR5 has been shown to attenuate microglial activation, its role in maintaining microglial homeostasis during development has not been investigated. We utilised published microarray data from the dorsolateral prefrontal cortex (DLPFC) of control (n = 30) and ASD (n = 27) individuals to carry out regression analysis to assess gene expression of mGluR5 downstream signalling elements. We then conducted a post-mortem brain stereological investigation of the DLPFC, to estimate the proportion of mGluR5-positive neurons and glia. Finally, we carried out stereological investigation into numbers of microglia in mGluR5 knockout mice, relative to wildtype littermates, together with assessment of changes in microglial somal size, as an indicator of activation status. We found that gene expression of mGluR5 was significantly decreased in ASD versus controls (p = 0.018) as well as downstream elements SHANK3 (p = 0.005) and PLCB1 (p = 0.009) but that the pro-inflammatory marker NOS2 was increased (p = 0.047). Intensity of staining of mGluR5-positive neurons was also significantly decreased in ASD versus controls (p = 0.016). Microglial density was significantly increased in mGluR5 knockout animals versus wildtype controls (p = 0.011). Our findings provide evidence for decreased expression of mGluR5 and its signalling components representing a key pathophysiological hallmark in ASD with implications for the regulation of microglial number and activation during development. This is important in the context of microglia being considered to play key roles in synaptic pruning during development, with preservation of appropriate connectivity relevant for normal brain functioning.     

Sex differences in brain activation to anticipated and experienced pain in the medial prefrontal cortex

Previous studies on sex differences in neural responses to noxious stimuli yielded mixed results. Both increased and decreased brain activation in several brain areas in women as compared to men has been reported. The current event-related functional magnetic resonance imaging study used a parametric design with different levels of the intensity of electrical stimulation in order to investigate sex differences in brain activation during pain processing. Four intensity levels, which were determined individually according to subjective ratings, ranging from stimulation below the stimulus detection threshold to moderately painful stimuli, were applied. Females experienced mild and moderate pain at lower stimulus intensity than males. Pronounced sex differences in brain activation were found in response to stimulation below the detection threshold and for the most intense pain stimuli in the medial prefrontal cortex (MPFC). Under both the conditions, women showed stronger activation in a region of the pregenual MPFC, which has been implicated in introspective, self-focused information processing. The results suggest that women, as compared to men, show increased self-related attention during anticipation of pain and in response to intense pain.     

Cyclooxygenase-2 expression in the hippocampus of genetically epilepsy susceptible El mice was increased after seizure

It has been suggested that cyclooxygenase (COX)-2 and prostaglandin play a role in epilepsy. We studied the expression of COX-2 in the hippocampus and the effect of oral administration of indomethacin, a COX inhibitor, on seizure activity in genetically seizure-susceptible El mice. COX-2 protein significantly increased in the hippocampi of El mice after epileptic seizure. Indomethacin did shorten the duration from seizure onset to full recovery in El mice although the threshold and the duration of seizure were not changed.     

Dopaminergic D2 receptor activation modulates FGF-2 gene expression in rat prefrontal cortex and hippocampus

We have investigated the role of dopaminergic receptors in modulation of basic fibroblast growth factor (FGF-2) expression in rat prefrontal cortex and hippocampus, two brain regions important for cognition. We found that FGF-2 expression is upregulated by quinpirole, a D2 agonist, in prefrontal cortex and to a lesser extent in hippocampus. This modulation was specific for dopamine D2 receptors because no effect was observed when the dopamine D1 and D3 agonists, SKF38393 and 7-OH-DPAT, respectively, were administered. Our findings show that activation of dopaminergic D2 receptors modulates FGF-2 expression in rat prefrontal cortex and hippocampus. Our data highlight the complex modulation of FGF-2 expression in limbic areas pointing to this trophic molecule as a putative target of drugs used against acute and chronic neurodegenerative diseases such as Parkinson's disease.     

Microglial activation contributes to depressive-like behavior in dopamine D3 receptor knockout mice

We previously demonstrated that the dopamine D3 receptor (D3R) inhibitor, NGB2904, increases susceptibility to depressive-like symptoms, elevates pro-inflammatory cytokine expression, and alters brain-derived neurotrophic factor (BDNF) levels in mesolimbic dopaminergic regions, including the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), and ventral tegmental area (VTA) in mice. The mechanisms by which D3R inhibition affects neuroinflammation and onset of depression remain unclear. Here, using D3R-knockout (D3RKO) and congenic wild-type C56BL/6 (WT) mice, we demonstrated that D3RKO mice displayed depressive-like behaviors, increased tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 levels, and altered BDNF expression in selected mesolimbic dopaminergic regions. D3R expression was localized to astrocytes or microglia in the mPFC, NAc, and VTA in WT mice. D3RKO mice exhibited a large number of Iba1-labelled microglia in the absence of glial fibrillary acidic protein (GFAP)-labelled astrocytes in mesolimbic dopaminergic brain areas. Inhibition or ablation of microglia by minocycline (25 mg/kg and 50 mg/kg) or PLX3397 (40 mg/kg) treatment ameliorated depressive-like symptoms, alterations in pro-inflammatory cytokine levels, and BDNF expression in the indicated brain regions in D3RKO mice. Minocycline therapy alleviated the increase in synaptic density in the NAc in D3RKO mice. These findings suggest that microglial activation in selected mesolimbic reward regions affects depressive-like behaviors induced by D3R deficiency.     

Detecting emotion in others: increased insula and decreased medial prefrontal cortex activation during emotion processing in elite adventure racers

Understanding the neural processes that characterize elite performers is a first step to develop a neuroscience model that can be used to improve performance in stressful circumstances. Adventure racers are elite athletes that operate in small teams in the context of environmental and physical extremes. In particular, awareness of team member’s emotional status is critical to the team’s ability to navigate high-magnitude stressors. Thus, this functional magnetic resonance imaging (fMRI) study examined the hypothesis that adventure racers would show altered emotion processing in brain areas that are important for resilience and social awareness. Elite adventure racers (n = 10) were compared with healthy volunteers (n = 12) while performing a simple emotion face-processing (modified Hariri) task during fMRI. Across three types of emotional faces, adventure racers showed greater activation in right insula, left amygdala and dorsal anterior cingulate. Additionally, compared with healthy controls adventure racers showed attenuated right medial prefrontal cortex activation. These results are consistent with previous studies showing elite performers differentially activate neural substrates underlying interoception. Thus, adventure racers differentially deploy brain resources in an effort to recognize and process the internal sensations associated with emotions in others, which could be advantageous for team-based performance under stress.     

吗啡成瘾和正常大鼠前额叶皮质表达的蛋白质组学变化

The prefrontal cortex is involved in the regulation and control of substance addiction-related cognitive,behavioral,and emotional changes.The present study identified prefrontal cortex protein profiles in morphine-addicted rats;these were subsequently compared with normal rats.Results showed 87 protein spots with differentially expressed levels in the morphine addiction group,with the majority located in meta acid zones at pH 4.2-6.8 and having a molecular weight of 30-110 kDa.In addition,2 protein spots were identified as being associated with neurotoxicity(Snap25 isoform β-Snap25 of synaptosomal-associated protein 25 and β-actin).     

Multi-channel near-infrared spectroscopy shows reduced activation in the prefrontal cortex during facial expression processing in pervasive developmental disorder

Aim: The purpose of the present study was to investigate whether individuals with pervasive developmental disorders (PDD) show differential activation during an emotional activation task compared with age‐ and sex‐matched controls, by measuring changes in the concentration of oxygenated (oxyHb) and deoxygenated (deoxyHb) hemoglobin, using near‐infrared spectroscopy (NIRS). Methods: Fourteen patients with PDD and 14 age‐ and sex‐matched healthy controls participated in the study. The relative changes of concentrations of oxyHb and deoxyHb were measured on NIRS during an implicit processing task of fearful expression using Japanese standard faces. Results: PDD patients had significantly reduced oxyHb changes in the prefrontal cortex (PFC) compared to healthy controls. Conclusion: PFC dysfunction may exist in PDD.     

Fos expression in the orbital prefrontal cortex after exposure to the fixed-interval peak procedure

It has been proposed that cortico-striato-thalamo-cortical circuits that incorporate the prefrontal cortex and dorsal striatum regulate interval timing behaviour. The present experiment examined whether performance on the fixed-interval peak procedure (FIPP), an immediate timing schedule, would induce neuronal activity in cortical and striatal areas, as revealed by enhanced expression of the Fos protein, a marker for neuronal activation. Regional Fos expression was compared between rats trained on the FIPP and rats trained on a variable-interval (VI) schedule matched to the FIPP for overall response rate and reinforcer delivery. Response rate in the peak trials of the FIPP conformed to a temporally differentiated pattern, which was well described by a modified Gaussian function; in agreement with previous findings, the peak time occurred close to the time at which the reinforcer was delivered in the fixed-interval trials, and the Weber fraction was within the range of values reported previously. The density of Fos-positive neurones (counts mm(-2)) in the orbital prefrontal cortex (OPFC) was greater in rats exposed to the FIPP than in rats exposed to the VI schedule, suggesting a greater activation of this area during the performance of the former task. This is consistent with the results of previous studies that have implicated the OPFC in interval timing behaviour. However, there was no significant difference between the levels of Fos expression in the dorsal or ventral striatum of the rats trained under the two schedules.