Functional interactions between somatodendritic dopamine release, glutamate receptors and brain-derived neurotrophic factor expression in mesencephalic structures of the brain

Antidepressants Promote and Prevent Cancers

The review states that antidepressants (ADs) increase brain-derived neurotrophic factor (BDNF) transmission concomitantly in the brain and the blood: ADs increasing BDNF synthesis in specific areas of the central nervous system (CNS) could presumably affect megakaryocyte's production of platelets. ADs increase BDNF levels in the CNS and improve mood. In the blood, ADs increase BDNF release from platelets. The hypothesis presented here is that the release of BDNF from platelets contributes to the ADs effects on neurogenesis and on tumor growth in the cancer disease. Oncological studies indicate that chemicals ADs exert an aggravating effect on the cancer disease, possibly by promoting proplatelets formation and enhancing BDNF release from platelets in the tumor.

Lineage- and Sex-Dependent Behavioral and Biochemical Transgenerational Consequences of Developmental Exposure to Lead, Prenatal Stress, and Combined Lead and Prenatal Stress in Mice

BACKGROUND

Lead (Pb) exposure and prenatal stress (PS) during development are co-occurring risk factors with shared biological substrates. PS has been associated with transgenerational passage of altered behavioral phenotypes, whereas the transgenerational behavioral or biochemical consequences of Pb exposure, and modification of any such effects by PS, is unknown.

OBJECTIVES

The present study sought to determine whether Pb, PS, or combined Pb and PS exposures produced adverse transgenerational consequences on brain and behavior.

METHODS

Maternal Pb and PS exposures were carried out in F0 mice. Outside breeders were used at each subsequent breeding, producing four F1-F2 lineages: [F1 female-F2 female (FF), FM (male), MF, and MM]. F3 offspring were generated from each of these lineages and examined for outcomes previously found to be altered by Pb, PS, or combined Pb and PS in F1 offspring: behavioral performance [fixed-interval (FI) schedule of food reward, locomotor activity, and anxiety-like behavior], dopamine function [striatal expression of tyrosine hydroxylase (Th)], glucocorticoid receptor (GR) and plasma corticosterone, as well as brain-derived neurotrophic factor (BDNF) and total percent DNA methylation of Th and Bdnf genes in the frontal cortex and hippocampus.

RESULTS

Maternal F0 Pb exposure produced runting in F3 offspring. Considered across lineages, F3 females exhibited Pb-related alterations in behavior, striatal BDNF levels, frontal cortical Th total percentage DNA methylation levels and serum corticosterone levels, whereas F3 males showed Pb- and PS-related alterations in behavior and total percent DNA methylation of hippocampal Bdnf. However, numerous lineage-specific effects were observed, most of greater magnitude than those observed across lineages, with outcomes differing by F3 sex.

DISCUSSION

These findings support the possibility that exposures of previous generations to Pb or PS may influence the brain and behavior of future generations. Observed changes were sex-dependent, with F3 females showing multiple changes through Pb-exposed lineages. Lineage effects may occur through maternal responses to pregnancy, altered maternal behavior, epigenetic modifications, or a combination of mechanisms, but they have significant public health ramifications regardless of mechanism. https://doi.org/10.1289/EHP4977.

Dopamine D3 receptor: A neglected participant in Parkinson Disease pathogenesis and treatment?

Parkinson disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms which relentlessly and progressively lead to substantial disability and economic burden. Pathologically, these symptoms follow the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) associated with abnormal α-synuclein (α-Syn) deposition as cytoplasmic inclusions called Lewy bodies in pigmented brainstem nuclei, and in dystrophic neurons in striatal and cortical regions (Lewy neurites). Pharmacotherapy for PD focuses on improving quality of life and primarily targets dopaminergic pathways. Dopamine acts through two families of receptors, dopamine D1-like and dopamine D2-like; dopamine D3 receptors (D3R) belong to dopamine D2 receptor (D2R) family. Although D3R's precise role in the pathophysiology and treatment of PD has not been determined, we present evidence suggesting an important role for D3R in the early development and occurrence of PD. Agonist activation of D3R increases dopamine concentration, decreases α-Syn accumulation, enhances secretion of brain derived neurotrophic factors (BDNF), ameliorates neuroinflammation, alleviates oxidative stress, promotes neurogenesis in the nigrostriatal pathway, interacts with D1R to reduce PD associated motor symptoms and ameliorates side effects of levodopa (L-DOPA) treatment. Furthermore, D3R mutations can predict PD age of onset and prognosis of PD treatment. The role of D3R in PD merits further research. This review elucidates the potential role of D3R in PD pathogenesis and therapy.

BDNF provides many routes toward STN DBS-mediated disease modification

The concept that subthalamic nucleus deep brain stimulation (STN DBS) may be disease modifying in Parkinson's disease (PD) is controversial. Several clinical trials that enrolled subjects with late‐stage PD have come to disparate conclusions on this matter. In contrast, some clinical studies in early‐ to midstage subjects have suggested a disease‐modifying effect. Dopaminergic innervation of the putamen is essentially absent in PD subjects within 4 years after diagnosis, indicating that any neuroprotective therapy, including STN DBS, will require intervention within the immediate postdiagnosis interval. Preclinical prevention and early intervention paradigms support a neuroprotective effect of STN DBS on the nigrostriatal system via increased brain‐derived neurotrophic factor (BDNF). STN DBS‐induced increases in BDNF provide a multitude of mechanisms capable of ameliorating dysfunction and degeneration in the parkinsonian brain. A biomarker for measuring brain‐derived neurotrophic factor‐trkB signaling, though, is not available for clinical research. If a prospective clinical trial were to examine whether STN DBS is disease modifying, we contend the strongest rationale is not dependent on a preclinical neuroprotective effect per se, but on the myriad potential mechanisms whereby STN DBS‐elicited brain‐derived neurotrophic factor‐trkB signaling could provide disease modification. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Action potential and calcium dependence of tonic somatodendritic dopamine release in the Substantia Nigra pars compacta

Despite the importance of somatodendritic dopamine (DA) release in the Substantia Nigra pars compacta (SNc), its mechanism remains poorly understood. Using a novel approach combining fast-scan controlled-adsorption voltammetry (FSCAV) and single-unit electrophysiology, we have investigated the mechanism of somatodendritic release by directly correlating basal (non-stimulated) extracellular DA concentration ([DA]_out ), with pharmacologically-induced changes of firing of nigral dopaminergic neurons in rat brain slices. FSCAV measurements indicated that basal [DA]_out in the SNc was 40.7 ± 2.0 nM (at 34 ± 0.5°C), which was enhanced by amphetamine, cocaine, and L-DOPA, and reduced by VMAT2 inhibitor, Ro4-1284. Complete inhibition of firing by TTX decreased basal [DA]_out , but this reduction was smaller than the effect of D₂ receptor agonist, quinpirole. Despite similar effects on neuronal firing, the larger decrease in [DA]_out evoked by quinpirole was attributed to cell membrane hyperpolarization and greater reduction in cytosolic free Ca²⁺ ([Ca²⁺ ]_in ). Decreasing extracellular Ca²⁺ also reduced basal [DA]_out , despite increasing firing frequency. Furthermore, inhibiting L-type Ca²⁺ channels decreased basal [DA]_out , although specific Ca_v 1.3 channel inhibition did not affect firing rate. Inhibition of sarcoplasmic/endoplasmic reticulum Ca²⁺ -ATPase (SERCA) also decreased [DA]_out , demonstrating the importance of intracellular Ca²⁺ stores for somatodendritic release. Finally, in vivo FSCAV measurements showed that basal [DA]_out in the SNc was 79.8 ± 10.9 nM in urethane-anesthetized rats, which was enhanced by amphetamine. Overall, our findings indicate that although tonic somatodendritic DA release is largely independent of action potentials, basal [DA]_out is strongly regulated by voltage-dependent Ca²⁺ influx and release of intracellular Ca²⁺ . OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Role of Brain NUCB2/nesfatin-1 in the Stress-induced Modulation of Gastrointestinal Functions

Background

Nucleobindin2 (NUCB2)/nesfatin-1 plays a well-established role in homeostatic functions associated with food intake and stress integration.

Aim

This review focusses on NUCB2/nesfatin-1’s central effects on gastrointestinal functions and will summarize the effects on food intake, motility and secretion with focus on the upper gastrointestinal tract.

Results

We will highlight the stressors that influence brain NUCB2/nesfatin-1 expression and discuss functional implications. In addition to traditional acute psychological and physical stressors such as restraint stress and abdominal surgery we will look at immunological, visceral and metabolic stressors as well as a chronic combination stress model that have been shown to affect NUCB2/nesfatin-1 signaling and describe associated functional consequences.

Peripheral injection of bombesin induces c-Fos in NUCB2/nesfatin-1 neurons

As anorexigenic hormones bombesin and nucleobindin2 (NUCB2)/nesfatin-1 decrease food intake in rodents. Both hormones have been described in brain nuclei that play a role in the modulation of hunger and satiety, like the paraventricular nucleus of the hypothalamus (PVN) and the nucleus of the solitary tract (NTS). However, the direct interaction of the two hormones is unknown so far. The aim of study was to elucidate whether bombesin directly interacts with NUCB2/nesfatin-1 neurons in the PVN and NTS. Therefore, we injected bombesin intraperitoneally (ip) at two doses (26 and 32nmol/kg body weight) and assessed c-Fos activation in the PVN, arcuate nucleus (ARC) and NTS compared to vehicle treated rats (0.15M NaCl). We also performed co-localization studies with oxytocin or tyrosine hydroxylase. Bombesin at both doses increased the number of c-Fos positive neurons in the PVN (p<0.05) and NTS (p<0.05) compared to vehicle, while in the ARC no modulation was observed (p>0.05). In the PVN and NTS the number of c-Fos positive neurons colocalized with NUCB2/nesfatin-1 increased after bombesin injection compared to vehicle treatment (p<0.05). Moreover, an increase of activated NUCB2/nesfatin-1 immunoreactive neurons that co-expressed oxytocin in the PVN (p<0.05) or tyrosine hydroxylase in the NTS (p<0.05) was observed compared to vehicle. Our results show that peripherally injected bombesin activates NUCB2/nesfatin-1 neurons in the PVN and NTS giving rise to a possible interaction between bombesin and NUCB2/nesfatin-1 in the modulation of food intake.

Beneficial effects of sodium butyrate in 6-OHDA induced neurotoxicity and behavioral abnormalities: Modulation of histone deacetylase activity

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Recent studies have investigated the involvement of epigenetic modifications in PD. Histone deacetylase (HDAC) inhibitors have been reported to be beneficial in cognitive and motor deficit states. The present study was designed to investigate the effect of sodium butyrate, a HDAC inhibitor in 6-hydroxydopamine (6-OHDA) - induced experimental PD like symptoms in rats. To produce motor deficit, 6-OHDA was administered unilaterally in the right medial forebrain bundle. Three weeks after 6-OHDA administration, the rats were challenged with apomorphine. Following this, the animals were treated with sodium butyrate (150 and 300 mg/kg i.p.) once daily for 14 days. Movement abnormalities were assessed by battery of behavioral tests. Biochemically, oxidative stress markers, neuroinflammation and dopamine were measured in striatal brain homogenate. Further, to explore the molecular mechanism(s), we measured the level of global H3 histone acetylation and brain derived neurotrophic factor (BDNF). 6-OHDA administration results in significant motor deficit along with reduction in striatal dopamine level. 6-OHDA treated rats showed elevated oxidative stress and neuroinflammatory markers. Treatment with sodium butyrate results in significant attenuation of motor deficits and increased striatal dopamine level. Moreover, sodium butyrate treatment attenuated the oxidative stress and neuroinflammatory markers. These effects occur concurrently with increased global H3 histone acetylation and BDNF levels. Thus, the observed results of the present study are indicative for the therapeutic potential of HDAC inhibitors in PD.

Sex-dependent impacts of low-level lead exposure and prenatal stress on impulsive choice behavior and associated biochemical and neurochemical manifestations

A prior study demonstrated increased overall response rates on a fixed interval (FI) schedule of reward in female offspring that had been subjected to maternal lead (Pb) exposure, prenatal stress (PS) and offspring stress challenge relative to control, prenatal stress alone, lead alone and lead+prenatal stress alone (Virgolini et al., 2008). Response rates on FI schedules have been shown to directly relate to measures of self-control (impulsivity) in children and in infants (Darcheville et al., 1992, 1993). The current study sought to determine whether enhanced effects of Pb±PS would therefore be seen in a more direct measure of impulsive choice behavior, i.e., a delay discounting paradigm. Offspring of dams exposed to 0 or 50ppm Pb acetate from 2 to 3 months prior to breeding through lactation, with or without immobilization restraint stress (PS) on gestational days 16 and 17, were trained on a delay discounting paradigm that offered a choice between a large reward (three 45mg food pellets) after a long delay or a small reward (one 45mg food pellet) after a short delay, with the long delay value increased from 0s to 30s across sessions. Alterations in extinction of this performance, and its subsequent re-acquisition after reinforcement delivery was reinstated were also examined. Brains of littermates of behaviorally-trained offspring were utilized to examine corresponding changes in monoamines and in levels of brain derived neurotrophic factor (BDNF), the serotonin transporter (SERT) and the N-methyl-d-aspartate receptor (NMDAR) 2A in brain regions associated with impulsive choice behavior. Results showed that Pb±PS-induced changes in delay discounting occurred almost exclusively in males. In addition to increasing percent long delay responding at the indifference point (i.e., reduced impulsive choice behavior), Pb±PS slowed acquisition of delayed discounting performance, and increased numbers of both failures to and latencies to initiate trials. Overall, the profile of these alterations were more consistent with impaired learning/behavioral flexibility and/or with enhanced sensitivity to the downshift in reward opportunities imposed by the transition from delay discounting training conditions to delay discounting choice response contingencies. Consistent with these behavioral changes, Pb±PS treated males also showed reductions in brain serotonin function in all mesocorticolimbic regions, broad monoamine changes in nucleus accumbens, and reductions in both BDNF and NMDAR 2A levels and increases in SERT in frontal cortex, i.e., in regions and neurotransmitter systems known to mediate learning/behavioral flexibility, and which were of greater impact in males. The current findings do not fully support a generality of the enhancement of Pb effects by PS, as previously seen with FI performance in females (Virgolini et al., 2008), and suggest a dissociation of the behaviors controlled by FI and delay discounting paradigms, at least in response to Pb±PS in rats. Collectively, however, the findings remain consistent with sex-dependent differences in the impacts of both Pb and PS and with the need to understand both the role of contingencies of reinforcement and underlying neurobiological effects in these sex differences.

Neuropathological changes in the substantia nigra in schizophrenia but not depression

Schizophrenia is a chronic, disabling neuropsychiatric disorder characterised by positive, negative and cognitive symptoms. The aetiology is not known, although genetic, imaging and pathological studies have implicated both neurodevelopmental and neurodegenerative processes. The substantia nigra is a basal ganglia nucleus responsible for the production of dopamine and projection of dopaminergic neurons to the striatum. The substantia nigra is implicated in schizophrenia as dopamine has been heavily implicated in the dopamine hypothesis of schizophrenia and the prevalent psychotic symptoms and the monoamine theory of depression, and is a target for the development of new therapies. Studies into the major dopamine delivery pathways in the brain will therefore provide a strong base in improving knowledge of these psychiatric disorders. This post-mortem study examines the cytoarchitecture of dopaminergic neurons of the substantia nigra in schizophrenia (n = 12) and depression (n = 13) compared to matched controls (n = 13). Measures of nucleolar volume, nuclear length and nuclear area were taken in patients with chronic schizophrenia and major depressive disorder against matched controls. Astrocyte density was decreased in schizophrenia compared to controls (p = 0.030), with no change in oligodendrocyte density observed. Significantly increased nuclear cross-sectional area (p = 0.017) and length (p = 0.021), and increased nucleolar volume (p = 0.037) in dopaminergic neurons were observed in schizophrenia patients compared with controls, suggesting nuclear pleomorphic changes. No changes were observed in depression cases compared to control group. These changes may reflect pathological alterations in gene expression, neuronal structure and function in schizophrenia.

Serotonin receptors expressed in Drosophila mushroom bodies differentially modulate larval locomotion

Drosophila melanogaster has been successfully used as a simple model to study the cellular and molecular mechanisms underlying behaviors, including the generation of motor programs. Thus, it has been shown that, as in vertebrates, CNS biogenic amines (BA) including serotonin (5HT) participate in motor control in Drosophila. Several evidence show that BA systems innervate an important association area in the insect brain previously associated to the planning and/or execution of motor programs, the Mushroom Bodies (MB). The main objective of this work is to evaluate the contribution of 5HT and its receptors expressed in MB to motor behavior in fly larva. Locomotion was evaluated using an automated tracking system, in Drosophila larvae (3^rd-instar) exposed to drugs that affect the serotonergic neuronal transmission: alpha-methyl-L-dopa, MDMA and fluoxetine. In addition, animals expressing mutations in the 5HT biosynthetic enzymes or in any of the previously identified receptors for this amine (5HT_1AR, 5HT_1BR, 5HT₂R and 5HT₇R) were evaluated in their locomotion. Finally, RNAi directed to the Drosophila 5HT receptor transcripts were expressed in MB and the effect of this manipulation on motor behavior was assessed. Data obtained in the mutants and in animals exposed to the serotonergic drugs, suggest that 5HT systems are important regulators of motor programs in fly larvae. Studies carried out in animals pan-neuronally expressing the RNAi for each of the serotonergic receptors, support this idea and further suggest that CNS 5HT pathways play a role in motor control. Moreover, animals expressing an RNAi for 5HT_1BR, 5HT₂R and 5HT₇R in MB show increased motor behavior, while no effect is observed when the RNAi for 5HT_1AR is expressed in this region. Thus, our data suggest that CNS 5HT systems are involved in motor control, and that 5HT receptors expressed in MB differentially modulate motor programs in fly larvae.

Role of NUCB2/Nesfatin-1 in the hypothalamic control of energy homeostasis

Hunger and satiety are regulated in a complex fashion by a few food intake stimulatory (orexigenic) and a multitude of inhibitory (anorexigenic) factors produced in the periphery (mainly in the gastrointestinal tract) or directly in the brain. Within the brain, the hypothalamus plays a pivotal role as a production site of food intake regulatory factors. Importantly, this site integrates peripheral and central signaling factors to orchestrate food intake and in the long term body weight. Our knowledge on these regulatory pathways is not static but rather rapidly changing as new factors as well as up- and downstream signaling pathways of already known transmitters are uncovered. Hypothalamic nucleobindin2 (NUCB2), the precursor of nesfatin-1, was first described in 2006 and nesfatin-1 found to be a novel anorexigenic modulator of food intake and body weight. The initial report stimulated several groups to investigate the biological actions of nesfatin-1 and subsequent studies delineated the underlying brain mechanisms involved in its food reducing effect. Of interest was the demonstration that NUCB2 also exerts its anorexigenic action in the paraventricular nucleus of the hypothalamus and is regulated at this site by changes in metabolic status with a diurnal rhythm inversely related to that of feeding in rats. The present review describes the current state-of-knowledge on central nesfatin-1's effects on food intake and body weight and highlights important missing links regarding cellular signaling mechanisms involved in nesfatin-1's action.

Anatomical and electrophysiological changes in striatal TH interneurons after loss of the nigrostriatal dopaminergic pathway

Using transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of the tyrosine hydroxylase (TH) promoter, we have previously shown that there are approximately 3,000 striatal EGFP-TH interneurons per hemisphere in mice. Here, we report that striatal TH-EGFP interneurons exhibit a small, transient but significant increase in number after unilateral destruction of the nigrostriatal dopaminergic pathway. The increase in cell number is accompanied by electrophysiological and morphological changes. The intrinsic electrophysiological properties of EGFP-TH interneurons ipsilateral to 6-OHDA lesion were similar to those originally reported in intact mice except for a significant reduction in the duration of a characteristic depolarization induced plateau potential. There was a significant change in the distribution of the four previously described electrophysiologically distinct subtypes of striatal TH interneurons. There was a concomitant increase in the frequency of both spontaneous excitatory and inhibitory post-synaptic currents, while their amplitudes did not change. Nigrostriatal lesions did not affect somatic size or dendritic length or branching, but resulted in an increase in the density of proximal dendritic spines and spine-like appendages in EGFP-TH interneurons. The changes indicate that electrophysiology properties and morphology of striatal EGFP-TH interneurons depend on endogenous levels of dopamine arising from the nigrostriatal pathway. Furthermore, these changes may serve to help compensate for the changes in activity of spiny projection neurons that occur following loss of the nigrostriatal innervation in experimental or in early idiopathic Parkinson's disease by increasing feedforward GABAergic inhibition exerted by these interneurons.

Phenotypic characterization of retinoic acid differentiated SH-SY5Y cells by transcriptional profiling

Multiple genetic and environmental factors play a role in the development and progression of Parkinson's disease (PD). The main neuropathological hallmark of PD is the degeneration of dopaminergic (DAergic) neurons in the substantia nigra pars compacta. To study genetic and molecular contributors to the disease process, there is a great need for readily accessible cells with prominent DAergic features that can be used for reproducible in vitro cellular screening. Here, we investigated the molecular phenotype of retinoic acid (RA) differentiated SH-SY5Y cells using genome wide transcriptional profiling combined with gene ontology, transcription factor and molecular pathway analysis. We demonstrated that RA induces a general neuronal differentiation program in SH-SY5Y cells and that these cells develop a predominantly mature DAergic-like neurotransmitter phenotype. This phenotype is characterized by increased dopamine levels together with a substantial suppression of other neurotransmitter phenotypes, such as those for noradrenaline, acetylcholine, glutamate, serotonin and histamine. In addition, we show that RA differentiated SH-SY5Y cells express the dopamine and noradrenalin neurotransmitter transporters that are responsible for uptake of MPP(+), a well known DAergic cell toxicant. MPP(+) treatment alters mitochondrial activity according to its proposed cytotoxic effect in DAergic neurons. Taken together, RA differentiated SH-SY5Y cells have a DAergic-like phenotype, and provide a good cellular screening tool to find novel genes or compounds that affect cytotoxic processes that are associated with PD.

BDNF Val66Met and DRD2 Taq1A polymorphisms interact to influence PTSD symptom severity: a preliminary investigation in a South African population

BACKGROUND

We evaluated the role that selected variants in serotonin transporter (5-HTT), dopamine receptor 2 (DRD2) and brain-derived neurotrophic factor (BDNF) genes play in PTSD symptom severity in an at-risk population. We also investigated the interaction between the genetic variants to determine whether these variables and the interactions between the variables influenced the severity of PTSD symptoms.

METHODS

PTSD symptoms were quantitatively assessed using the Davidson Trauma Scale (DTS) in 150 participants from an at-risk South African population. All participants were genotyped for the 5-HTTLPR, DRD2 Taq1A and BDNF Val66Met polymorphisms. Gene-gene interactions were investigated using various linear models. All analyses were adjusted for age, gender, major depressive disorder diagnosis, level of resilience, level of social support and alcohol dependence.

RESULTS

A significant interaction effect between DRD2 Taq1A and BDNF Val66Met variants on DTS score was observed. On the background of the BDNF Val66Val genotype, DTS score increased significantly with the addition of a DRD2 Taq1A A1 allele. However, on the BDNF Met66 allele background, the addition of an A1 allele was found to reduce total DTS score.

CONCLUSIONS

This study provides preliminary evidence for an epistatic interaction between BDNF Val66Met and DRD2 Taq1A polymorphisms on the severity of PTSD symptoms, where both too little and too much dopamine can result in increased PTSD symptom severity.

An NR2B-Dependent Decrease in the Expression of trkB Receptors Precedes the Disappearance of Dopaminergic Cells in Substantia Nigra in a Rat Model of Presymptomatic Parkinson's Disease

Compensatory changes occurring during presymptomatic stages of Parkinson's disease (PD) would explain that the clinical symptoms of the disease appear late, when the degenerative process is quite advanced. Several data support the proposition that brain-derived neurotrophic factor (BDNF) could play a role in these plastic changes. In the present study, we evaluated the expression of the specific BDNF receptor, trkB, in a rat model of presymptomatic PD generated by intrastriatal injection of the neurotoxin 6-OHDA. Immunohistochemical studies revealed a decrease in trkB expression in SN pars compacta (SNc) seven days after 6-OHDA injection. At this time point, no change in the number of tyrosine hydroxylase (TH) immunoreactive (TH-IR) cells is detected, although a decrease is evident 14 days after neurotoxin injection. The decrease in TH-positive cells and trkB expression in SNc was significantly prevented by systemic administration of Ifenprodil, a specific antagonist of NR2B-containing NMDA receptors. Therefore, an NR2B-NMDA receptor-dependent decrease in trkB expression precedes the disappearance of TH-IR cells in SNc in response to 6-OHDA injection. These results support the idea that a functional coupling between NMDA receptors and BDNF/trkB signalling may be important for the maintenance of the dopaminergic phenotype in SNc during presymptomatic stages of PD.

Somatodendritic dopamine release requires synaptotagmin 4 and 7 and the participation of voltage-gated calcium channels

Somatodendritic (STD) dopamine (DA) release is a key mechanism for the autoregulatory control of DA release in the brain. However, its molecular mechanism remains undetermined. We tested the hypothesis that differential expression of synaptotagmin (Syt) isoforms explains some of the differential properties of terminal and STD DA release. Down-regulation of the dendritically expressed Syt4 and Syt7 severely reduced STD DA release, whereas terminal release required Syt1. Moreover, we found that although mobilization of intracellular Ca(2+) stores is inefficient, Ca(2+) influx through N- and P/Q-type voltage-gated channels is critical to trigger STD DA release. Our findings provide an explanation for the differential Ca(2+) requirement of terminal and STD DA release. In addition, we propose that not all sources of intracellular Ca(2+) are equally efficient to trigger this release mechanism. Our findings have implications for a better understanding of a fundamental cell biological process mediating transcellular signaling in a system critical for diseases such as Parkinson disease.

Nesfatin-1: a novel inhibitory regulator of food intake and body weight

The protein nucleobindin 2 (NUCB2) or NEFA (DNA binding/EF-hand/acidic amino acid rich region) was identified over a decade ago and implicated in intracellular processes. New developments came with the report that post-translational processing of hypothalamic NUCB2 may result in nesfatin-1, nesfatin-2 and nesfatin-3 and convergent studies showing that nesfatin-1 and full length NUCB2 injected in the brain potently inhibit the dark phase food intake in rodents including leptin receptor deficient Zucker rats. Nesfatin-1 also reduces body weight gain, suggesting a role as a new anorexigenic factor and modulator of energy balance. In light of the obesity epidemic and its associated diseases, underlying new mechanisms regulating food intake may be promising targets in the drug treatment of obese patients particularly as the vast majority of them display reduced leptin sensitivity or leptin resistance while nesfatin-1's mechanism of action is leptin independent. Although much progress on the localization of NUCB2/nesfatin-1 in the brain and periphery as well as on the understanding of nesfatin-1's anorexic effect have been achieved during the past three years, several important mechanisms have yet to be unraveled such as the identification of the nesfatin-1 receptor and the regulation of NUCB2 processing and nesfatin-1 release.

Nesfatin-1--role as possible new potent regulator of food intake

Nesfatin-1 is an 82 amino acid peptide recently discovered in the brain which is derived from nucleobindin2 (NUCB2), a protein that is highly conserved across mammalian species. Nesfatin-1 has received much attention over the past two years due to its reproducible food intake-reducing effect that is linked with recruitment of other hypothalamic peptides regulating feeding behavior. A growing amount of evidence also supports that various stressors activate fore- and hindbrain NUCB2/nesfatin-1 circuitries. In this review, we outline the central nervous system distribution of NUCB2/nesfatin-1, and recent developments on the peripheral expression of NUCB2/nesfatin-1, in particular its co-localization with ghrelin in gastric X/A-like cells and insulin in ss-cells of the endocrine pancreas. Functional studies related to the characteristics of nesfatin-1's inhibitory effects on dark phase food intake are detailed as well as the central activation of NUCB2/nesfatin-1 immunopositive neurons in the response to psychological, immune and visceral stressors. Lastly, potential clinical implications of targeting NUCB2/nesfatin-1 signaling and existing gaps in knowledge to ascertain the role and mechanisms of action of nesfatin-1 are presented.

Motor activity-induced dopamine release in the substantia nigra is regulated by muscarinic receptors

Nigro-striatal neurons release dopamine not only from their axon terminals in the striatum, but also from somata and dendrites in the substantia nigra. Somatodendritic dopamine release in the substantia nigra can facilitate motor function by mechanisms that may act independently of axon terminal dopamine release in the striatum. The dopamine neurons in the substantia nigra receive a cholinergic input from the pedunculopontine nucleus. Despite recent efforts to introduce this nucleus as a potential target for deep brain stimulation to treat motor symptoms in Parkinson's disease; and the well-known antiparkinsonian effects of anticholinergic drugs; the cholinergic influence on somatodendritic dopamine release is not well understood. The aim of this study was to investigate the possible regulation of locomotor-induced dopamine release in the substantia nigra by endogenous acetylcholine release. In intact and 6-OHDA hemi-lesioned animals alike, the muscarinic antagonist scopolamine, when perfused in the substantia nigra, amplified the locomotor-induced somatodendritic dopamine release to approximately 200% of baseline, compared to 120-130% of baseline in vehicle-treated animals. A functional importance of nigral muscarinic receptor activation was demonstrated in hemi-lesioned animals, where motor performance was significantly improved by scopolamine to 82% of pre-lesion performance, as compared to 56% in vehicle-treated controls. The results indicate that muscarinic activity in the substantia nigra is of functional importance in an animal Parkinson's disease model, and strengthen the notion that nigral dopaminergic regulation of motor activity/performance is independent of striatal dopamine release.

Mu opioid receptor modulation of somatodendritic dopamine overflow: GABAergic and glutamatergic mechanisms

Mu opioid receptor (MOR) regulation of somatodendritic dopamine neurotransmission in the ventral tegmental area (VTA) was investigated using conventional microdialysis in freely moving rats and mice. Reverse dialysis of the MOR agonist DAMGO (50 and 100 microm) into the VTA of rats produced a concentration-dependent increase in dialysate dopamine concentrations. Basal dopamine overflow in the VTA was unaltered in mice lacking the MOR gene. However, basal gamma-aminobutyric acid (GABA) overflow in these animals was significantly increased, whereas glutamate overflow was decreased. Intra-VTA perfusion of DAMGO into wild-type (WT) mice increased dopamine overflow. GABA concentrations were decreased, whereas glutamate concentrations in the VTA were unaltered. Consistent with the loss of MOR, no effect of DAMGO was observed in MOR knockout (KO) mice. These data provide the first direct demonstration of tonically active MOR systems in the VTA that regulate basal glutamatergic and GABAergic neurotransmission in this region. We hypothesize that increased GABAergic neurotransmission following constitutive deletion of MOR is due to the elimination of a tonic inhibitory influence of MOR on GABAergic neurons in the VTA, whereas decreased glutamatergic neurotransmission in MOR KO mice is a consequence of intensified GABA tone on glutamatergic neurons and/or terminals. As a consequence, somatodendritic dopamine release is unaltered. Furthermore, MOR KO mice do not exhibit the positive correlation between basal dopamine levels and the glutamate/GABA ratio observed in WT mice. Together, our findings indicate a critical role of VTA MOR in maintaining an intricate balance between excitatory and inhibitory inputs to dopaminergic neurons.

Dopamine D1-like receptor activation induces brain-derived neurotrophic factor protein expression

Recent studies showed that dopamine or D1 receptor-selective agonists increased brain-derived neurotrophic factor (BDNF) mRNA and protein expression in neuronal cultures, and this action was blocked by SCH23390. Moreover, SKF38393 activated Trk receptors and downstream signaling in striatal neurons. This study examined whether dopamine agonists induce the expression of BDNF protein in rat brain tissue. Acute slice preparations were incubated with dopamine agonists in Hibernate A medium and BDNF protein was measured by a sensitive enzyme-linked immunosorbent assay. Results showed that dopamine increased BDNF in tissue slices after 24 h of incubation. Furthermore, SKF38393 produced a significant increase in BDNF protein in striatal and hippocampal tissue slices. These findings suggest that the induction of BDNF expression may constitute a downstream response to D1-like dopamine receptor activation.

Enhancing aromatic L-amino acid decarboxylase activity: implications for L-DOPA treatment in Parkinson's disease

Aromatic L-amino acid decarboxylase (AAAD) is an essential enzyme for the formation of catecholamines, indolamines, and trace amines. Moreover, it is a required enzyme for converting L-DOPA to dopamine when treating patients with Parkinson's disease (PD). There is now substantial evidence that the activity of AAAD in striatum is regulated by activation and induction, and second messengers play a role. Enzyme activity can be modulated by drugs acting on a number of neurotransmitter receptors including dopamine (D1-4), glutamate (NMDA), serotonin (5-HT(1A), 5-HT(2A)) and nicotinic acetylcholine receptors. Generally, antagonists enhance AAAD activity; while, agonists may diminish it. Enhancement of AAAD activity is functional, as the formation of dopamine from exogenous L-DOPA mirrors activity. Following a lesion of nigrostriatal dopaminergic neurons, AAAD in striatum responds more robustly to pharmacological manipulations, and this is true for the decarboxylation of exogenous L-DOPA as well. We review the evidence for parallel modulation of AAAD activity and L-DOPA decarboxylation and propose that this knowledge can be exploited to optimize the formation of dopamine from exogenous L-DOPA. This information can be used as a blue print for the design of novel L-DOPA treatment adjuvants to benefit patients with PD.

Dopamine D3 receptor-preferring agonists increase dendrite arborization of mesencephalic dopaminergic neurons via extracellular signal-regulated kinase phosphorylation

Clinical improvements in Parkinson's disease produced by dopamine D3 receptor-preferring agonists have been related to their neuroprotective actions and, more recently, to their neuroregenerative properties. However, it is unclear whether dopamine agonists produce their neurotrophic effects by acting directly on receptors expressed by the mesencephalic dopaminergic neurons or indirectly on receptors expressed by astrocytes, via release of neurotrophic factors. In this study, we investigated the effects of the dopamine D3 receptor-preferring agonists quinpirole and 7-hydroxy-N,N-di-propyl-2-aminotetralin (7-OH-DPAT), as well as of the indirect agonist amphetamine, on dopaminergic neurons identified by tyrosine hydroxylase immunoreactivity (TH-IR). Experiments were performed on neuronal-enriched primary cultures containing less than 0.5% of astrocytes prepared from the mouse embryo mesencephalon. After 3 days of incubation, both quinpirole (1-10 microm) and 7-OH-DPAT (5-500 nm) dose-dependently increased the maximal dendrite length (P < 0.001), number of primary dendrites (P < 0.01) and [3H]dopamine uptake (P < 0.01) of TH-IR-positive mesencephalic neurons. Similar effects were observed with 10 microm amphetamine. All neurotrophic effects were blocked by the unselective D2/D3 receptor antagonist sulpiride (5 microm) and by the selective D3 receptor antagonist SB-277011-A at a low dose (50 nm). Quinpirole and 7-OH-DPAT also increased the phosphorylation of extracellular signal-regulated kinase (ERK) within minutes, an effect blocked by pretreatment with SB-277011-A. Inhibition of the D2/D3 receptor signalling pathway to ERK was obtained with PD98059, GF109203 or LY294002, resulting in blockade of neurotrophic effects. These data suggest that dopamine agonists increase dendritic arborizations of mesencephalic dopaminergic neurons via a direct effect on D2/D3 receptors, preferentially involving D3 receptor-dependent neurotransmission.

Nesfatin-1 immunoreactivity in rat brain and spinal cord autonomic nuclei

Nesfatin-1 is one of the peptide products of posttranslational processing of the nucleobindin-2 (NUCB2) gene, suggested to have physiological relevance to suppress food intake and body weight gain in rats. Nesfatin-1-immunoreactive cells have been found in distinct nuclei in the rat brain related to circuitries regulating food intake. Here, we report novel yet undescribed localization of NUCB2/nesfatin-1 at the mRNA and protein level in the rat central nervous system. Immunohistochemical staining revealed the localization of NUCB2/nesfatin-1 in the piriform and insular cortex, endopiriform nucleus, nucleus accumbens, lateral septum, bed nucleus of stria terminalis, central amygdaloid nucleus, medial preoptic area, dorsal raphe nucleus, ambiguus nucleus, ventrolateral medulla and gigantocellular reticular nucleus, as well as Purkinje-cells of the cerebellum. In the spinal cord, nesfatin-1 immunoreactivity (IR) was found in both sympathetic and parasympathetic preganglionic neuronal groups and in the dorsal area X from lower thoracic to sacral segments. The immunohistochemical results were confirmed by RT-PCR in the central amygdaloid nucleus, nucleus accumbens, cerebellum and lumbar spinal cord microdissected by punch technique. The features and distributions of nesfatin-1 IR and mRNA expression in the brain and spinal cord suggest that NUCB2/nesfatin-1 could play a wider role in autonomic regulation of visceral-endocrine functions besides food intake.

Nesfatin-1 immunoreactivity in rat brain and spinal cord autonomic nuclei

Nesfatin-1 is one of the peptide products of posttranslational processing of the nucleobindin-2 (NUCB2) gene, suggested to have physiological relevance to suppress food intake and body weight gain in rats. Nesfatin-1-immunoreactive cells have been found in distinct nuclei in the rat brain related to circuitries regulating food intake. Here, we report novel yet undescribed localization of NUCB2/nesfatin-1 at the mRNA and protein level in the rat central nervous system. Immunohistochemical staining revealed the localization of NUCB2/nesfatin-1 in the piriform and insular cortex, endopiriform nucleus, nucleus accumbens, lateral septum, bed nucleus of stria terminalis, central amygdaloid nucleus, medial preoptic area, dorsal raphe nucleus, ambiguus nucleus, ventrolateral medulla and gigantocellular reticular nucleus, as well as Purkinje-cells of the cerebellum. In the spinal cord, nesfatin-1 immunoreactivity (IR) was found in both sympathetic and parasympathetic preganglionic neuronal groups and in the dorsal area X from lower thoracic to sacral segments. The immunohistochemical results were confirmed by RT-PCR in the central amygdaloid nucleus, nucleus accumbens, cerebellum and lumbar spinal cord microdissected by punch technique. The features and distributions of nesfatin-1 IR and mRNA expression in the brain and spinal cord suggest that NUCB2/nesfatin-1 could play a wider role in autonomic regulation of visceral-endocrine functions besides food intake.

Transgenic reporter mice as tools for studies of transplantability and connectivity of dopamine neuron precursors in fetal tissue grafts

Cell therapy for Parkinson's disease (PD) is based on the idea that new midbrain dopamine (mDA) neurons, implanted directly into the brain of the patient, can structurally and functionally replace those lost to the disease. Clinical trials have provided proof-of-principle that the grafted mDA neurons can survive and function after implantation in order to provide sustained improvement in motor function for some patients. Nonetheless, there are a number of issues limiting the application of this approach as mainstream therapy, including: the use of human fetal tissue as the only safe and reliable source of transplantable mDA neurons, and variability in the therapeutic outcome. Here we review recent progress in this area from investigations using rodent models of PD, paying particular attention to the use of transgenic reporter mice as tools for neural transplantation studies. Cell type-specific expression of reporter genes, such as green fluorescent protein, affords valuable technical advantages in transplantation experiments, such as the ability to selectively isolate specific cell fractions from mixed populations prior to grafting, and the unambiguous visualization of graft-derived dopamine neuron fiber patterns after transplantation. The results from these investigations have given new insights into the transplantability of mDA precursors as well as their connectivity after grafting and have interesting implications for the development of stem cell based approaches for the treatment of PD.

Nociceptin/orphanin FQ modulates motor behavior and primary motor cortex output through receptors located in substantia nigra reticulata

This study was set to investigate whether motor effects of nociceptin/orphanin FQ (N/OFQ) can be related to changes in primary motor cortex output. N/OFQ injected i.c.v. biphasically modulated motor performance, low doses being facilitating and higher ones inhibitory. These effects were counteracted by the N/OFQ receptor antagonist [Nphe(1) Arg(14),Lys(15)]N/OFQ-NH(2) (UFP-101) confirming the specificity of N/OFQ action. However, UFP-101 alone facilitated motor performance, suggesting that endogenous N/OFQ inhibits motor function. N/OFQ and UFP-101 injected into the substantia nigra reticulata but not motor cortex replicated these effects, suggesting motor responses were mediated by subcortical circuits involving the basal ganglia. Intracortical microstimulation technique showed that i.c.v. N/OFQ also biphasically modulated motor cortex excitability and movement representation. Low N/OFQ doses caused a leftward shift of threshold distribution curve in the forelimb area without affecting the number of effective sites. Conversely, high N/OFQ doses increased unresponsive and reduced excitable (movement) sites in vibrissa but not forelimb area. However, increased threshold currents and rightward shift of threshold distribution curve were observed in both areas, suggesting an overall inhibitory effect on cortical motor output. UFP-101 alone evoked effects similar to low N/OFQ doses, suggesting tonic inhibitory control over forelimb movement by endogenous N/OFQ. As shown in behavioral experiments, these effects were replicated by intranigral, but not intracortical, N/OFQ or UFP-101 injections. We conclude that N/OFQ receptors located in the substantia nigra reticulata mediate N/OFQ biphasic control over motor behavior, possibly through changes of primary motor cortex output.

Dendritic transmitter release: a comparison of two model systems

Information flow through neurones was historically considered to be linear, with dendrites receiving information from incoming synaptic terminals, the soma processing the information and the axon carrying it to the terminal that synapses upon another cell or end organ. However, recent studies have shown that dendrites can release transmitters themselves, and thereby communicate with neighbouring structures, whether these are adjacent neurones or incoming synapses. Due to their anatomical features, the magnocellular vasopressin and oxytocin containing neurones of the hypothalamic supraoptic and paraventricular nuclei and the dopamine neurones of the substantia nigra have revealed important aspects of dendritic function including mechanisms of dendritic transmitter release.

Dopamine D1 receptor-induced signaling through TrkB receptors in striatal neurons

In addition to its role as a neurotransmitter, dopamine can stimulate neurite outgrowth and morphological effects upon primary neurons. To investigate the signal transduction mechanisms used by dopamine in developing striatal neurons, we focused upon the effects of activating the dopamine D1 receptor. Using the D1 receptor agonist SKF38393, we found that Trk neurotrophin receptors were activated in embryonic day 18 striatal neurons. K-252a, a Trk tyrosine kinase inhibitor, and a dopamine D1 receptor antagonist could block the effects of SKF38393. The increase in TrkB phosphorylation was not the result of increased neurotrophin production. Induction of TrkB activity by SKF38393 was accompanied by the phosphorylation of several Trk signaling proteins, including phospholipase Cgamma, Akt, and MAPK. Biotinylation experiments followed by immunostaining by phospho-TrkB-specific antibodies indicated that the mechanism involved increased TrkB surface expression by dopamine D1 receptor activation. This increase in cell surface TrkB expression was dependent upon an increase in intracellular Ca(2+). These results indicate that stimulation of dopamine D1 receptors can be coupled to the neurotrophin receptor signaling to mediate the effects of dopamine upon striatal neurons.

The cannabinoid CB1 receptor is expressed on serotonergic and dopaminergic neurons

The endocannabinoid system is involved in memory, cognition, and pain perception by the presynaptic cannabinoid CB(1) receptor, which is expressed at high levels in many brain regions. Functional studies have shown that activation of cannabinoid CB(1) receptors inhibits the synaptic release of many neurotransmitters such as gamma-aminobutyric acid, glutamate, acetylcholine and monoamines. Monoamines, however, are known not only to be released from and taken back up at nerve terminals but also at extrasynaptic axonal and somatodendritic sites. Here we present immunocytochemical data documenting cannabinoid CB(1) receptor expression on neurite extensions and over cell bodies of serotonergic and dopaminergic neurons.

Subtoxic N-methyl-D-aspartate delayed neuronal death in ischemic brain injury through TrkB receptor- and calmodulin-mediated PI-3K/Akt pathway activation

Previous studies have shown that subtoxic NMDA moderated the neuronal survival in vitro and vivo. We performed this experiment to clarify the precise mechanism underlie subtoxic NMDA delayed neuronal death in ischemic brain injury. We found that pretreatment of NMDA (100 mg/kg) increased the number of the surviving CA1 pyramidal cells of hippocampus at 5 days of reperfusion. This dose of NMDA could also enhance Akt activation after ischemia/reperfusion (I/R). Here, we examined the possible mechanism that NMDA induced Akt activation. On the one hand, we found NMDA receptor-mediated Akt activation was associated with increased expression of BDNF (brain-derived neurotrophic factor) and activation of its high-affinity receptor TrkB after I/R in the hippocampus CA1 region, which could be held down by TrkB receptor antagonist K252a. On the other hand, we found that NMDA enhanced the binding of Ca2+-dependent calmodulin (CaM) to p85 (the regulation subunit of PI-3K), which led to the activation of Akt. W-13, an active CaM inhibitor, prevented the combination of CaM and p85 and subsequent Akt activation. Furthermore, NMDA receptor-mediated Akt activation was reversed by combined treatment with LY294002, the specific blockade of PI-3K. Taken together, our results suggested that subtoxic NMDA exerts the neuroprotective effect via activation of prosurvival PI-3K/Akt pathway against ischemic brain injury, and BDNF-TrkB signaling and Ca2+-dependent CaM cascade might contribute to NMDA induced activation of PI-3K/Akt pathway.

Correlation between serum brain-derived neurotrophic factor level and an in vivo marker of cortical integrity

BACKGROUND

Brain-derived neurotrophic factor (BDNF) signaling at synapses improves synaptic strengthening associated with learning and memory. In the present study we hypothesized that serum BDNF concentration is associated with in vivo level of cerebral N-acetylaspartate (NAA), a well established marker of neuronal integrity.

METHODS

In 36 healthy subjects BDNF serum concentration and absolute concentration of NAA together with other metabolites were measured by proton magnetic resonance spectroscopy (1H-MRS) in regions with high BDNF levels (anterior cingulate cortex [ACC], left hippocampus). Relationship between BDNF concentration and brain metabolites was studied in linear regression analysis with BDNF concentration as dependent variable and metabolite concentrations, age, and gender as predictor variables.

RESULTS

The BDNF serum concentrations were positively associated with the concentrations of NAA (T = 2.193, p = .037) and total choline (T = 1.997, p = .055; trend) but not total creatine or glutamate in the ACC. No significant association was observed between BDNF serum concentration and absolute metabolite concentrations in the hippocampus.

CONCLUSIONS

The preliminary data might indicate that BDNF serum concentration reflects some aspects of neuronal plasticity as indicated by its association with NAA level in the cerebral cortex. The results would be in line with the notion that BDNF plays a central role in the regulation of neuronal survival and differentiation in the human brain.

Robust syntaxin-4 immunoreactivity in mammalian horizontal cell processes

Horizontal cells mediate inhibitory feed-forward and feedback communication in the outer retina; however, mechanisms that underlie transmitter release from mammalian horizontal cells are poorly understood. Toward determining whether the molecular machinery for exocytosis is present in horizontal cells, we investigated the localization of syntaxin-4, a SNARE protein involved in targeting vesicles to the plasma membrane, in mouse, rat, and rabbit retinae using immunocytochemistry. We report robust expression of syntaxin-4 in the outer plexiform layer of all three species. Syntaxin-4 occurred in processes and tips of horizontal cells, with regularly spaced, thicker sandwich-like structures along the processes. Double labeling with syntaxin-4 and calbindin antibodies, a horizontal cell marker, demonstrated syntaxin-4 localization to horizontal cell processes; whereas, double labeling with PKC antibodies, a rod bipolar cell (RBC) marker, showed a lack of co-localization, with syntaxin-4 immunolabeling occurring just distal to RBC dendritic tips. Syntaxin-4 immunolabeling occurred within VGLUT-1-immunoreactive photoreceptor terminals and underneath synaptic ribbons, labeled by CtBP2/RIBEYE antibodies, consistent with localization in invaginating horizontal cell tips at photoreceptor triad synapses. Vertical sections of retina immunostained for syntaxin-4 and peanut agglutinin (PNA) established that the prominent patches of syntaxin-4 immunoreactivity were adjacent to the base of cone pedicles. Horizontal sections through the OPL indicate a one-to-one co-localization of syntaxin-4 densities at likely all cone pedicles, with syntaxin-4 immunoreactivity interdigitating with PNA labeling. Pre-embedding immuno-electron microscopy confirmed the subcellular localization of syntaxin-4 labeling to lateral elements at both rod and cone triad synapses. Finally, co-localization with SNAP-25, a possible binding partner of syntaxin-4, indicated co-expression of these SNARE proteins in the same subcellular compartment of the horizontal cell. Taken together, the strong expression of these two SNARE proteins in the processes and endings of horizontal cells at rod and cone terminals suggests that horizontal cell axons and dendrites are likely sites of exocytotic activity.

Effects of NGF and BDNF on baseline glutamate and dopamine release in the hippocampal formation of the adult rat

It has been shown using in vitro techniques that BDNF and NGF evoke neurotransmitter release in the hippocampus but this phenomenon has not been demonstrated in vivo to date. We therefore performed in vivo microdialysis in urethane-anesthetized Fischer 344 rats. The microdialysis probe was implanted stereotaxically into the CA1 area of the hippocampus. Three hours after the implantation of the probe, glutamate (Glu) and dopamine (DA) levels had reached a stable baseline. Four baseline samples were collected every 15 min at a flow rate of 1 microL/min. The growth factors were delivered (1 microL/10 min) using a microinjector attached to the microdialysis probe. We found that BDNF and NGF, when administered into the hippocampus, evoked dopamine and glutamate release in a dose-dependent fashion. NGF produced a biphasic response in the release of Glu, and a uniphasic response in the release of DA, both of which were calcium dependent. The neurotransmitter release induced by NGF was blocked by tetrodotoxin, indicating neuronal origin of this response. The BDNF induced release of DA and Glu was decreased in low calcium conditions, indicating that it is at least partially calcium dependent. Furthermore, BDNF-induced neurotransmitter release was partially blocked by pre-treatment with K252a, an antagonist for tyrosine kinase receptors, indicating that BDNF is acting through Trk receptors to induce neurotransmitter release. These results demonstrate a close relationship between the growth factors BDNF and NGF and the neurotransmitters DA and Glu in the hippocampus of intact animals.

Mice with conditional inactivation of fibroblast growth factor receptor-2 signaling in oligodendrocytes have normal myelin but display dramatic hyperactivity when combined with Cnp1 inactivation

Fibroblast growth factor receptors (Fgfr) comprise a widely expressed family of developmental regulators implicated in oligodendrocyte (OL) maturation of the CNS. Fgfr2 is expressed by OLs in myelinated fiber tracks. In vitro, Fgfr2 is highly upregulated during OL terminal differentiation, and its activation leads to enhanced growth of OL processes and the formation of myelin-like membranes. To investigate the in vivo function of Fgfr2 signaling by myelinating glial cells, we inactivated the floxed Fgfr2 gene in mice that coexpress Cre recombinase (cre) as a knock-in gene into the OL-specific 2',3'-cyclic nucleotide phosphodiesterase (Cnp1) locus. Surprisingly, no obvious defects were detected in brain development of these conditional mutants, including the number of OLs, the onset and extent of myelination, the ultrastructure of myelin, and the expression level of myelin proteins. However, unexpectedly, a subset of these conditional Fgfr2 knock-out mice that are homozygous for cre and therefore are also Cnp1 null, displayed a dramatic hyperactive behavior starting at approximately 2 weeks of age. This hyperactivity was abolished by treatment with dopamine receptor antagonists or catecholamine biosynthesis inhibitors, suggesting that the symptoms involve a dysregulation of the dopaminergic system. Although the molecular mechanisms are presently unknown, this novel mouse model of hyperactivity demonstrates the potential involvement of OLs in neuropsychiatric disorders, as well as the nonpredictable role of genetic interactions in the behavioral phenotype of mice.

Partial depletion of dopamine in substantia nigra impairs motor performance without altering striatal dopamine neurotransmission

Previous data indicate that the release of somatodendritic dopamine in substantia nigra influences motor activity and coordination, but the relative importance of somatodendritic dopamine release vs. terminal striatal dopamine release remains to be determined. We utilized simultaneous measurement of dopamine neurotransmission by microdialysis and motor performance assessment by rotarod test to investigate the effects of local dopamine depletion in rats. The vesicular monoamine transporter inhibitor tetrabenazine (100 microm) was administered locally in substantia nigra as well as in striatum. Nigral tetrabenazine administration decreased nigral dopamine dialysate concentrations to 7% of baseline and whole-tissue dopamine content by 60%. Nigral dopamine depletion was associated with a reduction in motor performance to 73 +/- 6% of pretreatment value, but did not alter dialysate dopamine concentrations in the ipsilateral striatum. Striatal tetrabenazine administration decreased striatal dopamine dialysate concentrations to 5% of baseline and doubled the somatodendritic dopamine response to motor activity, but it was not associated with changes in motor performance or dopamine content in striatal tissue. Simultaneous treatment of substantia nigra and striatum reduced motor performance to 58 +/- 5% of the pretreatment value. The results of this study indicate that partial depletion of nigral dopamine stores can significantly impair motor functions, and that increased nigral dopamine release can counteract minor impairments of striatal dopamine transmission.

Differential distributions of the Ca2+ -dependent activator protein for secretion family proteins (CAPS2 and CAPS1) in the mouse brain

The Ca(2+)-dependent activator protein for secretion (CAPS/Cadps) family consists of two members, CAPS1 and CAPS2, and plays an important role in secretory granule exocytosis. It has been shown that CAPS1 regulates catecholamine release from neuroendocrine cells, whereas CAPS2 is involved in the release of two neurotrophins, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), from parallel fibers of cerebellar granule cells. Although both CAPS proteins are expressed predominantly in the brain, their cellular and regional distributions in the brain are largely unknown. In this study we analyzed the immunohistochemical distributions of the CAPS family proteins in the mouse brain. In most areas of the embryonic nervous system CAPS1 and CAPS2 proteins were complementarily expressed. In the postnatal brain, CAPS1 was widespread at different levels. On the other hand, CAPS2 was localized to distinct cell types and fibers of various brain regions, including the olfactory bulb, cerebrum, hippocampal formation, thalamus, mesencephalic tegmentum, cerebellum, medulla, and spinal cord, except for some regions that overlapped with CAPS1. These CAPS2 cellular distribution patterns had the marked feature of coinciding with those of BDNF in various brain regions. Immunolabels for CAPS2 were also colocalized with those for some proteins related to exocytosis (VAMP and SNAP-25) and endocytosis (Dynamin I) in the cell soma and processes of the mesencephalic tegmentum and cerebellum, suggesting that these proteins might be involved in the dynamics of CAPS2-associated vesicles, although their colocalization on vesicles remains elusive. These results demonstrate that the CAPS family proteins are involved in the secretion of different secretory substances in developing and postnatal brains, and that CAPS2 is probably involved in BDNF secretion in many brain areas.

12-O-tetradecanoyl-phorbol-13-acetate-dependent up-regulation of dopaminergic gene expression requires Ras and neurofibromin in human IMR-32 neuroblastoma

The dopaminergic transcriptional programme is highly regulated during development and in the adult, in response to activation of membrane receptor signalling cascades. Gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis, is known to be regulated by receptors that act through protein kinase C (PKC) or Ras signalling. To investigate possible interactions between these two pathways before they converge on Raf activation, we evaluated whether phorbol ester (12-O-tetradecanoyl-phorbol-13-acetate, TPA)-dependent PKC activation required Ras for regulation of TH expression in IMR-32 cells. We found that long-term treatment with TPA, which induces down-regulation of PKC-alpha, led to induction of both protein and message levels of TH by autocrine factors. This was dependent on endogenous Ras, but independent of the transcription factor Nurr1. Moreover, this mechanism of action mimicked the effects of overexpression of the Ras-GAP domain of neurofibromin, GAP-related domain (GRD) I, which is part of the upstream mechanism for regulation of Ras activation and a PKC-alpha substrate. Overexpression of Ras also led to transcriptional and translational up-regulation of TH, independent of Nurr1 induction, as well as distinct phenotypic changes consistent with cell hypertrophy and increased secretory activity shown by induction of expression of vesicular monoamine transporter 2 and synaptosomal-associated protein-25. Most interestingly, overexpression of GRDI and down-regulation of the endogenous GRDII neurofibromin led to significant increases in Nurr1 message, possibly reflecting a transcriptional hierarchy during development. Taken together, these studies suggest that PKC-alpha, neurofibromin and Ras are essential in regulation of TH gene expression in IMR-32 cells.