Effects of acute ovarian hormone suppression on the human brain: an in vivo 1H MRS study

A previous proton magnetic resonance spectroscopy ((1)H MRS) study carried out by our group indicated that post-menopausal women who started taking oestrogen therapy (ET) at or around the menopause had a significantly lower choline (Cho) concentration in the hippocampus and parietal lobe than those who were ET naïve, suggesting that long-term ET positively modulates neuronal/glial membrane turnover in older females. The objective of the current study was to determine whether neuronal membrane turnover is modulated by sex hormones in younger women following a pharmacologic challenge that induced acute ovarian hormone suppression. We carried out an in vivo(1)H MRS study in a group of 10 premenopausal women pre- and post-8 weeks of acute ovarian suppression with a Gonadotrophin Releasing Hormone analogue (GnRHa) (two Zoladex 3.6 mg implants). We report that young women, post-ovarian suppression, had a significant increase in Cho concentration (and Cho/Cr ratio) in the dorsolateral prefrontal cortex (DLPFC). They also showed a trend to a significant increase in Cho concentration in the hippocampus. This supports our previous findings and adds to the evidence that neuronal/glial membrane metabolism is affected by sex hormones in women.

Alpha 2A-adrenoceptor-specific stimulation of [35S]GTP gamma S binding to membrane preparations of rat frontal cortex

Functional activation of alpha 2A adrenergic receptors in the crude membranes from rat frontal cortex was studied by a [35S]-guanosine 5'-O-(gamma-thiotriphosphate) ([35S]GTP gamma S) binding assay. alpha 2A agonists UK14304 and guanfacine decreased the ability of GDP to compete with [35S]GTP gamma S binding to the membranes and 0.1 mM GDP was found to be optimal for the following functional experiments. However, even after careful optimization of experimental conditions the specificity of ligands for rat alpha 2 adrenoceptors were not sufficient, as agonists as well as antagonists became activators of other signal transduction systems before achieving their maximal effect in the alpha 2A-adrenergic system. Only using compromising concentration of agonist (up to 1 microM UK14304) and antagonist (up to 1 microM RS79948) to inhibit agonist's effect, allowed us to filtrate out alpha 2A specific effect for characterization of signal transduction in rat frontal cortex membranes for the comparison efficacies of this system for different animals from behavioral experiments.

Glutamate uptake is reduced in prefrontal cortex in Huntington's disease

Huntington's disease (HD) is caused by a CAG repeat expansion in the HD gene, but how this mutation causes neuronal dysfunction and degeneration is unclear. Inhibition of glutamate uptake, which could cause excessive stimulation of glutamate receptors, has been found in animals carrying very long CAG repeats in the HD gene. In seven HD patients with moderate CAG expansions (40-52), repeat expansion and HD grade at autopsy were strongly correlated (r=0.88, p=0.0002). Uptake of [(3)H]glutamate was reduced by 43% in prefrontal cortex, but the level of synaptic (synaptophysin, AMPA receptors) and astrocytic markers (GFAP, glutamate transporter EAAT1) were unchanged. Glutamate uptake correlated inversely with CAG repeat expansion (r= -0.82, p=0.015). The reducing agent dithiothreitol improved glutamate uptake in controls, but not in HD brains, suggesting irreversible oxidation of glutamate transporters in HD. We conclude that impairment of glutamate uptake may contribute to neuronal dysfunction and degeneration in HD.

GAD1 mRNA expression and DNA methylation in prefrontal cortex of subjects with schizophrenia

Dysfunction of prefrontal cortex in schizophrenia includes changes in GABAergic mRNAs, including decreased expression of GAD1, encoding the 67 kDa glutamate decarboxylase (GAD67) GABA synthesis enzyme. The underlying molecular mechanisms remain unclear. Alterations in DNA methylation as an epigenetic regulator of gene expression are thought to play a role but this hypothesis is difficult to test because no techniques are available to extract DNA from GAD1 expressing neurons efficiently from human postmortem brain. Here, we present an alternative approach that is based on immunoprecipitation of mononucleosomes with anti-methyl-histone antibodies differentiating between sites of potential gene expression as opposed to repressive or silenced chromatin. Methylation patterns of CpG dinucleotides at the GAD1 proximal promoter and intron 2 were determined for each of the two chromatin fractions separately, using a case-control design for 14 schizophrenia subjects affected by a decrease in prefrontal GAD1 mRNA levels. In controls, the methylation frequencies at CpG dinucleotides, while overall higher in repressive as compared to open chromatin, did not exceed 5% at the proximal GAD1 promoter and 30% within intron 2. Subjects with schizophrenia showed a significant, on average 8-fold deficit in repressive chromatin-associated DNA methylation at the promoter. These results suggest that chromatin remodeling mechanisms are involved in dysregulated GABAergic gene expression in schizophrenia.

Motor cortex stimulation for pain control induces changes in the endogenous opioid system

BACKGROUND

Motor cortex stimulation (MCS) for neuropathic pain control induces focal cerebral blood flow changes involving regions with high density of opioid receptors. We studied the possible contribution of the endogenous opioid system to MCS-related pain relief.

METHODS

Changes in opioid receptor availability induced by MCS were studied with PET scan and [(11)C]diprenorphine in eight patients with refractory neuropathic pain. Each patient underwent two preoperative (test-retest) PET scans and one postoperative PET scan acquired after 7 months of chronic MCS.

RESULTS

The two preoperative scans, performed at 2 weeks interval, did not show significant differences. Conversely, postoperative compared with preoperative PET scans revealed significant decreases of [(11)C]diprenorphine binding in the anterior middle cingulate cortex (aMCC), periaqueductal gray (PAG), prefrontal cortex, and cerebellum. Binding changes in aMCC and PAG were significantly correlated with pain relief.

CONCLUSION

The decrease in binding of the exogenous ligand was most likely explained by receptor occupancy due to enhanced secretion of endogenous opioids. Motor cortex stimulation (MCS) may thus induce release of endogenous opioids in brain structures involved in the processing of acute and chronic pain. Correlation of this effect with pain relief in at least two of these structures supports the role of the endogenous opioid system in pain control induced by MCS.

Administration of oral methylphenidate during adolescence prevents suppressive development of dopamine projections into prefrontal cortex and amygdala after an early pharmacological challenge in gerbils

The enduring effects of postweaning subchronic methylphenidate (MP) treatment and/or previous early preweaning methamphetamine (MA) application on dopamine (DA) fiber density were investigated in multiple cortical and subcortical areas of the gerbil brain. The study aimed to explore three questions: (1) is the development of DA fiber innervation in control animals sensitive to a clinically relevant subchronic treatment with MP? (2) Is the development of DA fiber innervation in the forebrain altered by a single early MA challenge? (3) If so, might the subsequent institution of a therapeutically relevant MP application scheme interfere with such early induced alternative developmental trajectories for DA fiber innervation? For this purpose, gerbils pretreated both with saline and MA (50 mg/kg, i.p.) on day 14 received either H(2)O or MP (5 mg/kg) orally on days 30 to 60. On day 90, DA fibers were immunohistochemically detected and quantified. As a result, MP on its own did not have any significant influence on the postnatal development of the DA fiber systems, whereas it prevented a previously MA triggered suppressive development of DA fiber innervation in the prefrontal cortex and amygdala complex (30% less fiber innervation in both areas). Thus, MP prevented previously initiated miswiring of DA fibers from actually being implemented in the gerbil forebrain. During earlier studies, rather complex miswiring has been documented in response to an early preweaning MA challenge. This miswiring was associated with functional deficits resembling some of the symptoms of patients with ADHD. Therefore, morphogenetic properties of MP need further attention.

Chronic treatment with a dopamine uptake blocker changes dopamine and acetylcholine but not glutamate and GABA concentrations in prefrontal cortex, striatum and nucleus accumbens of the awake rat

The present study was aimed to investigate the effects of a chronic treatment with the dopamine uptake blocker nomifensine on the in vivo extracellular concentrations of dopamine, acetylcholine, glutamate and GABA in the prefrontal cortex, striatum and nucleus accumbens. Male Wistar rats received intraperitoneal (i.p.) daily injections of nomifensine (10 mg/kg) or saline for 22 days. Microdialysis experiments were performed on days 1, 8, 15 and 22 of treatment to evaluate the effects of the injection of nomifensine or saline. Motor activity of the animals was monitored during microdialysis experiments. Injections of nomifensine increased extracellular concentration of dopamine in striatum and nucleus accumbens, but not in prefrontal cortex. Acetylcholine concentrations in striatum but not in nucleus accumbens were increased by nomifensine on days 15 and 22 of treatment. In prefrontal cortex, nomifensine increased acetylcholine levels without differences among days. No changes were found on glutamate and GABA concentrations in the three areas studied. Injections of nomifensine also increased spontaneous motor activity and stereotyped behaviour without differences among days. These results show that systemic chronic treatment with a dopamine uptake blocker produces differential effects on extracellular concentrations of dopamine and acetylcholine, but not glutamate and GABA, in different areas of the brain.

Melatonin prevents formaldehyde-induced neurotoxicity in prefrontal cortex of rats: an immunohistochemical and biochemical study

This study was undertaken to investigate the protective effects of melatonin against formaldehyde-induced neurotoxicity in prefrontal cortex of rats. For this purpose, 21 male Wistar rats were divided into three groups. The rats in Group I were used as a control, while the rats in Group II were injected every other day with formaldehyde. The rats in Group III received melatonin daily while exposed to formaldehyde. At the end of 14-day experimental period, all rats were killed by decapitation. The brains of the rats were removed and the prefrontal cortex tissues were obtained from all brain specimens. Some of the prefrontal cortex tissue specimens were used for determination of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) levels. The remaining prefrontal cortex tissue specimens were used for immunohistochemical evaluation. The levels of SOD and GSH-Px were significantly decreased, and MDA levels, were significantly increased in rats treated with formaldehyde compared with those of the controls. In the immunohistochemical evaluation of this group, apoptotic cells were observed. However, increased SOD and GSH-Px enzyme activities, and decreased MDA levels, were detected in the rats administered melatonin while exposed to formaldehyde. Furthermore, apoptotic changes caused by formaldehyde were decreased in these rats. The results of our study suggest that melatonin treatment prevents formaldehyde-induced neuronal damage in prefrontal cortex.

Immunohistochemical and immunoblot analysis of Dopamine and cyclic AMP-regulated phosphoprotein, relative molecular mass 32,000 (DARPP-32) in the prefrontal cortex of subjects with schizophrenia and bipolar disorder

Dopamine and cyclic adenosine 3':5'-monophosphate (AMP)-regulated phosphoprotein, relative molecular mass 32,000 (DARPP-32), plays an important role in modulating the functions of various neurotransmitter systems. To explore the alterations in DARPP-32 in subjects with schizophrenia and bipolar disorder, we employed immunohistochemical and Western blotting techniques and examined the distribution and expression of DARPP-32 in the postmortem dorsolateral prefrontal cortex (DLPFC) from 12 subjects with schizophrenia, 10 subjects with bipolar disorder, and 11 control subjects. Immunohistochemical study demonstrated that DARPP-32 immunolabeling in the neuronal soma from subjects with schizophrenia and bipolar disorder was lower than in that from the controls. The results of the immunoblot analysis were consistent with those of the immunohistochemistry, and the amount of DARPP-32 in subjects with schizophrenia and bipolar disorder was found to be lower than that in the control subjects. The present study suggests that DARPP-32 decreases in the DLPFC of patients with schizophrenia and bipolar disorder, and further suggests that this decrease is associated with dysfunction of dopaminoceptive neurons in the DLPFC of patients affected by these two mental disorders.

HPA axis dysfunction in unmedicated major depressive disorder and its normalization by pharmacotherapy correlates with alteration of neural activity in prefrontal cortex and limbic/paralimbic regions

Dysregulation of the hypothalamic-pituitary-adrenocortical (HPA) axis is one of the most prominent neurobiological findings in major depressive disorder (MDD). The relationship of regional brain metabolism to HPA axis dysfunction in depressed patients, however, is still unclear. In this study, to examine the clinical pharmacotherapeutic effects on HPA axis function and brain metabolism in MDD patients, we performed the combined dexamethasone (DEX)/corticotropin-releasing hormone (CRH) test on 24 antidepressant-free patients with MDD a few days after positron emission tomography (PET) with a radiotracer, [(18)F]-fluorodeoxyglucose (FDG). Moreover, 10 patients who responded to pharmacotherapy were re-tested. 75% of unmedicated MDD patients exhibited a heightened cortisol response to the DEX/CRH test, and thus were defined as non-suppressors. Non-suppressors showed a marked hypometabolism in the medial prefrontal cortex as compared with suppressors. After successful pharmacotherapy, enhanced cortisol responsiveness normalized. Prior to treatment of the unmedicated MDD, a significant hypometabolism in various frontal regions and a significant hypermetabolism in the right hippocampus and parahippocampal gyrus were observed compared with controls. Metabolic activity in treatment responders showed a normalizing pattern in almost all the areas that had been characterized by metabolic abnormality at baseline except for the medial prefrontal cortex. These results indicate that depressed patients remitted with antidepressant treatment were accompanied by resolution of HPA dysregulation and alteration of regional glucose metabolism in the prefrontal cortical, limbic and paralimbic regions.

Molecular components and functions of the endocannabinoid system in mouse prefrontal cortex

Background

Cannabinoids have deleterious effects on prefrontal cortex (PFC)-mediated functions and multiple evidences link the endogenous cannabinoid (endocannabinoid) system, cannabis use and schizophrenia, a disease in which PFC functions are altered. Nonetheless, the molecular composition and the physiological functions of the endocannabinoid system in the PFC are unknown.

Methodology/Principal Findings

Here, using electron microscopy we found that key proteins involved in endocannabinoid signaling are expressed in layers V/VI of the mouse prelimbic area of the PFC: presynaptic cannabinoid CB1 receptors (CB1R) faced postsynaptic mGluR5 while diacylglycerol lipase α (DGL-α), the enzyme generating the endocannabinoid 2-arachidonoyl-glycerol (2-AG) was expressed in the same dendritic processes as mGluR5. Activation of presynaptic CB1R strongly inhibited evoked excitatory post-synaptic currents. Prolonged synaptic stimulation at 10Hz induced a profound long-term depression (LTD) of layers V/VI excitatory inputs. The endocannabinoid -LTD was presynaptically expressed and depended on the activation of postsynaptic mGluR5, phospholipase C and a rise in postsynaptic Ca²⁺ as predicted from the localization of the different components of the endocannabinoid system. Blocking the degradation of 2-AG (with URB 602) but not of anandamide (with URB 597) converted subthreshold tetanus to LTD-inducing ones. Moreover, inhibiting the synthesis of 2-AG with Tetrahydrolipstatin, blocked endocannabinoid-mediated LTD. All together, our data show that 2-AG mediates LTD at these synapses.

Conclusions/Significance

Our data show that the endocannabinoid -retrograde signaling plays a prominent role in long-term synaptic plasticity at the excitatory synapses of the PFC. Alterations of endocannabinoid -mediated synaptic plasticity may participate to the etiology of PFC-related pathologies.

Prenatal stress alters the negative correlation between neuronal activation in limbic regions and behavioral responses in rats exposed to high and low anxiogenic environments

Behavioral adaptation to an anxiogenic environment involves the activity of various interconnected limbic regions, such as the amygdala, hippocampus and prefrontal cortex. Prenatal stress (PS) in rats affects the ability to cope with environmental challenges and alters brain plasticity, leading to long-lasting behavioral and neurobiological alterations. We examined in PS and control animals whether behavioral reactivity was correlated to neuronal activation by assessing Fos protein expression in limbic regions of rats exposed to a low or high anxiogenic environment (the closed and open arms of an elevated plus maze, respectively). A negative correlation was found between behavioral and neuronal activation, with a lower behavioral reactivity and a higher neuronal response observed in rats exposed to the more anxiogenic environment (the open arm) with respect to the less anxiogenic environment (the closed arm). Interestingly, the variation in the neurobehavioral response between the two arms of the maze was less pronounced in rats that had been subjected to PS. This study provides a remarkable example of how long-lasting changes in brain plasticity induced by PS affect the ability of limbic neurons to cope with anxiogenic stimuli of different strength.

Lack of RIC-3 congruence with β2 subunit-containing nicotinic acetylcholine receptors in bipolar disorder

Nicotinic acetylcholine receptor (nAChR) dysfunction occurs in individuals with schizophrenia (SZ) and may also affect individuals with bipolar disorder (BP). The molecular mechanisms for these disease-associated cholinergic deficits are not known. In vitro, the protein RIC-3 (resistance to inhibitors of cholinesterase-3) aids the assembly and trafficking of alpha7-nAChRs but has unclear action on the biogenesis of alpha4/beta2-nAChRs. To evaluate RIC-3/nAChR dynamics in diseased and normal human brain tissue, we measured RIC-3, alpha7-, alpha4- and beta2-nAChRs transcript levels in postmortem prefrontal cortex of individuals with SZ (n=31), BP (n=28) and unaffected controls (NC, n=33). Of the 28 individuals with BP, 20 had a history of psychotic symptoms. We compared relative message abundances between diagnostic groups and tested correlations of RIC-3 with each nAChR message subtype. RIC-3 and alpha4 messages were significantly increased in BP compared with NC (RIC-3, P< or =0.002; alpha4, P< or =0.04). RIC-3 message was also upregulated in SZ (P< or =0.04). In BP with psychoses, RIC-3 and alpha4 levels were increased compared with BP without psychoses (both P< or =0.02) and compared with NC (RIC-3, P< or =0.0003; alpha4, P< or =0.004). In correlation regression analyses, RIC-3 expression was very highly correlated to alpha7, alpha4 and beta2 in NC (alpha7, P< or =2.5e-05; alpha4, P< or =2.5e-09; beta2, P< or =0.003) and in SZ (alpha7, P< or =1e-07; alpha4, P< or =7e-07; beta2, P< or =3e-09). RIC-3 also strongly correlated with alpha7 and alpha4 in BP (alpha7, P< or =0.003; alpha4, P< or =3.5e-07). RIC-3 was modestly correlated with beta2 in BP overall (P< or =0.04), but showed no significant correlation in BP with psychoses (P< or =0.31) compared with a significant correlation in BP without psychoses (P< or =0.007). In conclusion, coordinated RIC-3/alpha4 upregulation and discordant RIC-3/beta2 levels suggest that alpha4/beta2 nAChR deficits in BP may occur from dysregulated RIC-3 chaperoning of the beta2 nAChR subunit in a subset of patients affected by psychotic features.

Orbitofrontal dysfunction in a monozygotic twin discordant for postpartum affective psychosis: a functional magnetic resonance imaging study

BACKGROUND

Incomplete concordance for psychosis in monozygotic (MZ) twins has been interpreted as indicative of non-genetic cofactors in transmission of the illness. In this case study, we consider childbirth a landmark in the onset of psychotic symptoms, leading to the diagnosis of puerperal psychosis and then to bipolar/schizoaffective disorder. At the end of the third trimester, there is a sudden drop in estrogen, which exerts prominent effects on the serotonergic system in the orbitofrontal cortex (OFC).

OBJECTIVES

The purpose of the present study was to investigate OFC activation during emotional processing in MZ twins discordant for affective psychosis.

METHODS

Blood-oxygen-level-dependent activation using functional magnetic resonance imaging was measured during the passive viewing of emotional film excerpts.

RESULTS

Consistent with our hypothesis, a significant locus of activation was found in the left OFC in the normal MZ twin, but not in the psychosis MZ twin.

CONCLUSIONS

The personality changes noted in the psychosis MZ twin (postpartum psychosis) may be related to dysfunctional OFC. Ms J's childbirth may have triggered the onset of psychotic symptoms, leading to the diagnosis of bipolar or schizoaffective disorder.

Adult mice with reduced Nurr1 expression: an animal model for schizophrenia

The transcription factor Nurr1 (NR4A2) has been found to play a critical role in the development of midbrain dopaminergic neurons. Nurr1 heterozygous (+/-) male and female mice expressing 35-40% of normal levels of Nurr1 were generated and examined in animal models related to symptoms of schizophrenia. The Nurr1 (+/-) mice displayed hyperactivity in a novel environment, which persisted after administration of the dopamine-mimetic amphetamine and the N-methyl-D-aspartate receptor antagonist phencyclidine. The Nurr1 (+/-) mice were deficient in the retention of emotional memory and showed an enhanced response to swim stress. In addition, Nurr1 (+/-) male mice displayed a reduced dopamine turnover in the striatum and an enhanced dopamine turnover in the prefrontal cortex, while female mice showed an opposite pattern. These results show that Nurr1 (+/-) mice display a pattern of behaviors indicative of potential relevance for symptoms of schizophrenia combined with a gender-specific abnormal dopamine transmission in the striatum and prefrontal cortex, respectively. This suggests that the Nurr1 mutant mouse may be a potential animal model for studies on some of the behavioral and molecular mechanisms underlying schizophrenia.

Reduced CREB phosphorylation after chronic lithium treatment is associated with down-regulation of CaM kinase IV in rat hippocampus

Lithium is widely used in the treatment of bipolar disorder, although its mechanism of action is not fully clear. This study was undertaken to assess the effects of prolonged lithium administration on cAMP responsive element-binding protein (CREB) phosphorylation and CaM kinase IV (CaMKIV), one of the main kinases phosphorylating CREB in neurons following synaptic activation. CREB total protein expression and phosphorylation (Ser133), as well as CaMKIV enzymatic activity, phosphorylation of Thr196 (the activator residue) and kinase expression level were assessed in total homogenates and nuclei from the hippocampus and prefrontal/frontal cortex following 5 wk lithium treatment. Whereas no significant effects were found in prefrontal/frontal cortex, lithium administration reduced CREB phosphorylation and at the same time down-regulated CaMKIV (enzymatic activity, phospho-Thr196 and protein expression level) in cell nuclei from the hippocampus. These data suggest for the first time the involvement of CaMKIV in the mechanism of action of lithium.

Further evidence for altered myelin biosynthesis and glutamatergic dysfunction in schizophrenia

Recent studies have provided evidence for neuronal and oligodendrocyte-related abnormalities being associated with schizophrenia. However, the functional interplay and causal relationship between these two abnormalities is poorly understood. In this report, we provide data that identify myelin and fatty-acid biosynthesis dysfunction in schizophrenia based on post-mortem brain studies (prefrontal cortex) utilizing parallel metabolic and transcriptomics investigations. We detected a significant up-regulation of N-acetylaspartate (NAA) by HPLC analysis. Microarray and Q-PCR investigations revealed mRNA abnormalities for several enzymes involved in NAA metabolism. Additionally, glutamatergic neurotransmission components were also found to be affected. Our results suggest that, apart from the previously reported alterations in myelin-related protein synthesis, myelin synthesis itself may be directly affected in schizophrenia as indicated by changes in key enzymes involved in NAA metabolism. A decrease in NAA catabolism in oligodendrocytes would severely reduce acetate levels required to produce myelin lipids and may subsequently affect glutamatergic neurotransmission.

Reduction of synapsin III in the prefrontal cortex of individuals with schizophrenia

We analyzed the expression of a presynaptic protein, synapsin III, in individuals with schizophrenia. Since levels of synapsin III were previously found to be significantly reduced in the hippocampus of individuals with schizophrenia, we examined another brain region believed to be a major locus of dysfunction in schizophrenia, the dorsolateral prefrontal cortex (DLPFC). Western blot analyses using tissue obtained from the Stanley Foundation Neuropathology Consortium revealed that synapsin III levels were significantly decreased in the DLPFC of individuals with schizophrenia compared to controls. These findings are consistent with growing evidence of presynaptic abnormalities and prefrontal cortical dysfunction in schizophrenia.

Social isolation and expression of serotonergic neurotransmission-related genes in several brain areas of male mice

Early-life events influence brain development and evoke long-lasting behavioral consequences. Postweaning social isolation in rodents induces emotional and neurochemical alterations similar to those observed among some human psychopathologies. Central serotonergic neurotransmission is intimately involved in the observed adjustments, but the impact of social deprivation on serotonergic gene expression is unknown. We investigated the effects of prolonged early social isolation on emotion-related behaviors and 5-hydroxytryptamine (5-HT)-related gene transcription in mice. After weaning, male C57BL/6J mice were reared singly or in groups of four for 6 weeks. Gene expression of 5-HT(1A), 5-HT(1B), 5-HT(2A), 5-HT(2C), 5-HT(3A), 5-HT(6) and 5-HT(7) receptors and of 5-HT transporter and tryptophan hydroxylase-2 was determined by quantitative real-time polymerase chain reaction in distinct brain areas. Single-housed mice were hyperactive in a novel environment and showed signs of aggressive behavior. Housing condition did not alter weight gain or body temperature. Isolation markedly reduced transcription of all postsynaptic 5-HT receptors in the prefrontal cortex and reduced 5-HT(1B), 5-HT(2A) and 5-HT(2C) in both hypothalamus and midbrain. In contrast, the only alteration in the hippocampus was 5-HT(6) overexpression. Neither 5-HT transporter nor synthetic enzyme gene transcription differed between housing conditions. In conclusion, early social isolation in mice induces robust changes in postsynaptic 5-HT receptors gene transcription, motor hyperactivity and behavioral disinhibition. The overall pattern of decreased gene expression in the prefrontal cortex highlights its high vulnerability to environment. Furthermore, this is the first study to present a general representation of 5-HT-related gene expression in specific brain areas after social isolation and identifies novel candidates that may be critical for underlying molecular mechanisms.

Mapping the apetitive and aversive systems with emotional pictures using a block-design fMRI procedure

Negative emotional pictures from the International Affective Pictures System (IAPS) have been successful in mapping brain areas related to the aversive system. However, the capacity of positive emotional pictures to study the brain areas related to the appetitive system (i.e., nucleus accumbens, prefrontal cortex) is less established. In this study, we used a block fMRI design to investigate this issue, including emotional pictures as background while participants performed a vowel-consonant discrimination task. Importantly, participants were heterosexual males and all positive pictures were related to erotic couples, opposite-sex erotica, or romantic scenes. Negative pictures were similar to those used in previous studies. Results were consistent with previous studies using event-related designs, showing activation of amygdala, lateral prefrontal cortex, and occipito-temporal areas, but positive pictures showed a significant activation in the left nucleus accumbens. These findings provide evidence of the utility of block designs in emotional research (positive emotional pictures).

Strain differences in basal and post-citalopram extracellular 5-HT in the mouse medial prefrontal cortex and dorsal hippocampus: relation with tryptophan hydroxylase-2 activity

We used the microdialysis technique to compare basal extracellular serotonin (5-HT) and the response to citalopram in different strains of mice with functionally different allelic forms of tryptophan hydroxylase-2 (TPH-2), the rate-limiting enzyme in brain 5-HT synthesis. DBA/2J, DBA/2N and BALB/c mice carrying the 1473G allele of TPH-2 had less dialysate 5-HT in the medial prefrontal cortex and dorsal hippocampus (DH) (20-40% reduction) than C57BL/6J and C57BL/6N mice carrying the 1473C allele. Extracellular 5-HT estimated by the zero-net flux method confirmed the result of conventional microdialysis. Citalopram, 1.25, 5 and 20 mg/kg, dose-dependently raised extracellular 5-HT in the medial prefrontal cortex of C57BL/6J mice, with maximum effect at 5 mg/kg, but had significantly less effect in DBA/2J and BALB/c mice and in the DH of DBA/2J mice. A tryptophan (TRP) load enhanced basal extracellular 5-HT in the medial prefrontal cortex of DBA/2J mice but did not affect citalopram's ability to raise cortical and hippocampal extracellular 5-HT. The impairment of 5-HT synthesis quite likely accounts for the reduction of basal 5-HT and the citalopram-induced rise in mice carrying the mutated enzyme. These findings might explain why DBA/2 and BALB/c mice do not respond to citalopram in the forced swimming test. Although TRP could be a useful strategy to improve the antidepressant effect of citalopram (Cervo et al. 2005), particularly in subjects with low 5-HT synthesis, the contribution of serotonergic and non-serotonergic mechanisms to TRP's effect remains to be elucidated.

Neurochemical and neurobehavioral effects of ganstigmine (CHF2819), a novel acetylcholinesterase inhibitor, in rat prefrontal cortex: an in vivo study

Ganstigmine (CHF2819) is a novel, orally active acetylcholinesterase inhibitor that induces a stimulation of brain cholinergic transmission. In vivo studies show that, in rat prefrontal cortex, extracellular acetylcholine (ACh) concentrations are significantly increased either after local (1 and 10 microM) or oral (1.5 and 3 mg/kg) administration. Moreover, repeated oral treatment (six consecutive days; 3 mg/kg) with ganstigmine significantly increases basal extracellular concentrations of ACh in rat prefrontal cortex. Then, acute ganstigmine administration induces a significant increase in extracellular ACh concentrations (actual values) with respect to the last sample in ganstigmine-treated rats. Concentrations of serotonin (5-HT) and noradrenaline (NA) are not affected by any oral dose of ganstigmine (1.5 and 3 mg/kg) used. Moreover, levels of dopamine (DA) and metabolites are not modified either. Basal extracellular concentrations of 5-HT, NA, DA and metabolites are not affected by repeated (six consecutive days) ganstigmine treatment (3 mg/kg). Furthermore, there is no effect of the challenge dose of ganstigmine (3 mg/kg) on 5-HT, NA, DA and metabolites levels. Finally, ganstigmine reverses the scopolamine-induced deficits of habituation and non-spatial working memory in rats. Taken together, these findings suggest that ganstigmine appears to be a suitable candidate for the treatment of the cholinergic deficit in patients with Alzheimer's disease.

Caffeine and accumbens shell dopamine

It has been reported that caffeine (1.5-30 mg/kg i.p.) as well as specific A1 (DPCPX, 8-cyclopentyl-1,3-dipropylxanthine) receptor antagonists fail to increase extracellular dopamine (DA) in the shell of the nucleus accumbens (NAc). However, it has also been reported that caffeine (10 and 30 mg/kg i.p.) and the A1 antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT) increases NAc shell DA. To clarify this issue rats were implanted with microdialysis probes at different sites in the NAc shell, in the medial prefrontal cortex (PFCX, infralimbic cortex), and at the border between those areas. Irrespective of probe placement within the NAc shell and of the use of different surgical anesthetics (chloral hydrate and ketamine), we failed to observe changes in dialysate DA after 10 and 30 mg/kg i.p. of caffeine. Similarly negative results were obtained with DPCPX and CPFPX, two potent and selective A1 receptor antagonists. A significant increase of DA was obtained after caffeine when probes were located at the border between the NAc shell and the PFCX (10 and 30 mg/kg) or in the PFCX (10 mg/kg). In view of this and of our previous report that caffeine increases dialysate DA in the medial PFCX, we conclude that the increase in dialysate DA by caffeine observed by others arises from the medial PFCX rather than from the NAc shell as a result of placement of microdialysis probes at the border between the NAc shell and the PFCX.

Individual differences in response to novelty predict prefrontal cortex dopamine transporter function and cell surface expression

Previous research has shown that individual differences in response to novelty predict self-administration and the locomotor response to psychostimulant drugs of abuse. The aim of the present study was to determine if individual differences in response to novelty based on inescapable or free-choice novelty tests predict dopamine transporter (DAT) function and trafficking as well as nicotine-induced modulation of DAT. Results show that the maximal velocity (Vmax) of [3H]dopamine uptake into prefrontal cortex (PFC) synaptosomes correlated negatively with the locomotor response to inescapable novelty. In contrast, Vmax correlated positively with novelty place preference in the free-choice novelty test. The divergent correlations between DAT and the two behavioral phenotypes suggest a differential contribution of DAT in these phenotypes, which are known not to be isomorphic. Furthermore, rats categorized as high responders to inescapable novelty had lower Vmax values, which were accompanied by less DAT expression at the cell surface in PFC compared with low responders, suggesting that inherent individual differences in DAT cellular localization may underlie the differential response to novelty. Compared with the saline control, nicotine increased Vmax and cell surface DAT immunoreactivity in PFC from high responders but not from low responders. Similarly, nicotine increased Vmax and cell surface DAT in PFC in rats classified as low in novelty place preference but not in rats classified as high in novelty place preference. Thus, despite the different behavioral phenotypes, the pharmacological effect of nicotine to increase DAT function and cell surface expression was apparent, such that rats with inherently lower DAT function show a greater sensitivity to the neurochemical effect of nicotine.

A BDNF infusion into the medial prefrontal cortex suppresses cocaine seeking in rats

The medial prefrontal cortex (mPFC) is critical for reinstatement of cocaine seeking and is the main source of brain-derived neurotrophic factor (BDNF) to striatal regions of the brain relapse circuitry. To test the hypothesis that BDNF in the mPFC regulates cocaine-seeking behavior, rats were trained to press a lever for cocaine infusions (0.2 mg/inf, 2 h/day) paired with light+tone conditioned stimulus (CS) presentations on 10 consecutive days. After the last self-administration session, rats received a single infusion of BDNF (0.75 microg/0.5 microL/side) into the mPFC; this manipulation produced protracted effects on cocaine-seeking behavior (non-reinforced lever pressing). BDNF pretreatment administered after the last session attenuated cocaine seeking 22 h later and, remarkably, it also blocked cocaine-induced suppression of phospho-extracellular-regulated kinase and elevated BDNF immunoreactivity in the nucleus accumbens. The same pretreatment also suppressed cocaine-seeking behavior elicited by response-contingent CS presentations after 6 days of forced abstinence or extinction training, as well as a cocaine challenge injection (10 mg/kg, i.p.) after extinction training. However, BDNF infused into the mPFC had no effect on food-seeking behavior. Furthermore, BDNF infused on the sixth day of abstinence failed to alter responding, suggesting that the regulatory influence of BDNF is time limited. The suppressive effects of BDNF infused into the mPFC on cocaine seeking indicate that BDNF regulates cortical pathways implicated in relapse to drug seeking and that corticostriatal BDNF adaptations during early abstinence diminish compulsive drug seeking.