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ABSTRACT: The A10 region contains different neurons: dopamine (expressing tyrosine hydroxylase; TH), GABA, glutamate-only (expressing the vesicular glutamate transporter 2; VGluT2), and TH-VGluT2 (coexpressing TH and VGluT2). We used three methods to investigate proteins necessary for the synthesis (aromatic L: -amino acid decarboxylase, AADC) or transport (vesicular monoamine transporter; VMAT2 or dopamine transporter; DAT) of dopamine within TH neurons in the A10 region. By in situ hybridization-immunohistochemistry, we found that all TH neurons in the A10 region had AADC, but not all had VMAT2, DAT or D2 receptors (D(2)R). To determine whether TH-VGluT2 neurons account for TH neurons lacking these dopamine markers, we implemented an anatomical "mirror technique", and found that not all TH-VGluT2 neurons lacked VMAT2, DAT or D(2)R. Next, by quantitative RT-PCR of individual micro-dissected TH neurons, we discovered two classes of TH-VGluT2 and three classes of TH-only neurons with different latero-medial distribution. Some of the TH-VGluT2 neurons had both VMAT2 and DAT (TH-VGluT2 Class 1); others lacked detectable levels of both transporters (TH-VGluT2 Class 2). Most of the TH-only neurons contained VMAT2 and DAT (TH-only Class 1), a few had DAT without detectable VMAT2 (TH-only Class 2), and others lacked detectable levels of both transporters (TH-only Class 3). We concluded that (a) the majority of TH neurons lacking DAT are TH-VGluT2 neurons, (b) very few TH-only neurons express DAT without VMAT2, and (c) TH-VGluT2 neurons lacking DAT also lack VMAT2. Thus, the A10 region contains dopamine neurons with differential compartmentalization and unique signaling properties.
Brain Structure and Function 08/2012; · 5.63 Impact Factor
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ABSTRACT: Human immunodeficiency virus (HIV) primarily infects glial cells in the central nervous system (CNS). Recent evidence suggests that HIV-infected individuals who abuse drugs such as methamphetamine (METH) have higher viral loads and experience more severe neurological complications than HIV-infected individuals who do not abuse drugs. The aim of this study was to determine the effect of METH on HIV expression from the HIV long terminal repeat (LTR) promoter and on an HIV integrated provirus in microglial cells, the primary host cells for HIV in the CNS. Primary human microglial cells immortalized with SV40 T antigen (CHME-5 cells) were cotransfected with an HIV LTR reporter and the HIV Tat gene, a key regulator of viral replication and gene expression, and exposed to METH. Our results demonstrate that METH treatment induced LTR activation, an effect potentiated in the presence of Tat. We also found that METH increased the nuclear translocation of the nuclear factor kappa B (NF-κB), a key cellular transcriptional regulator of the LTR promoter, and the activity of an NF-κB-specific reporter plasmid in CHME-5 cells. The presence of a dominant-negative regulator of NF-κB blocked METH-related activation of the HIV LTR. Furthermore, treatment of HIV-latently infected CHME-5 (CHME-5/HIV) cells with METH induced HIV expression and nuclear translocation of the p65 subunit of NF-κB. These results suggest that METH can stimulate HIV gene expression in microglia cells through activation of the NF-κB signaling pathway. This mechanism may outline the initial biochemical events leading to the observed increased neurodegeneration in HIV-positive individuals who use METH.
Journal of NeuroVirology 05/2012; 18(5):400-10. · 2.31 Impact Factor
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ABSTRACT: In humans, exposure to contexts previously associated with heroin use can provoke relapse. In rats, exposure to heroin-paired contexts after extinction of drug-reinforced responding in different contexts reinstates heroin seeking. This effect is attenuated by inhibition of glutamate or dopamine transmission in nucleus accumbens shell, or inactivation of ventral medial prefrontal cortex (mPFC). Here, we used an anatomical asymmetrical disconnection procedure to demonstrate that an interaction between glutamatergic projections from ventral mPFC to accumbens shell and local dopamine D(1) postsynaptic receptors contributes to context-induced reinstatement of heroin seeking. We also combined the marker of neuronal activity, Fos, with the retrograde tracer Fluoro-Gold to assess activation in this pathway during context-induced reinstatement. Rats were trained to self-administer heroin for 12 d; drug infusions were paired with a discrete tone-light cue. Lever pressing was subsequently extinguished in a nondrug-associated context in the presence of the discrete cue. Rats were then tested in the heroin- or extinction-associated contexts under extinction conditions. Injections of muscimol + baclofen into ventral mPFC in one hemisphere and D(1)-family receptor antagonist SCH 23390 into the contralateral or ipsilateral accumbens shell decreased context-induced reinstatement. Unilateral injections of muscimol + baclofen into ventral mPFC or SCH 23390 into the accumbens shell had no effect. Context-induced reinstatement was associated with increased Fos expression in ventral mPFC neurons, including those projecting to accumbens shell, with higher double-labeling in the ipsilateral projection than in the contralateral projection. Our results demonstrate that activation of glutamatergic projections from ventral mPFC to accumbens shell, previously implicated in inhibition of cocaine relapse, promotes heroin relapse.
Journal of Neuroscience 04/2012; 32(14):4982-91. · 7.11 Impact Factor
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ABSTRACT: The canonical two neuron model of opioid reward posits that mu opioid receptor (MOR) activation produces reward by disinhibiting midbrain ventral tegmental area (VTA) dopamine neurons through inhibition of local GABAergic interneurons. Although indirect evidence supports the neural circuit postulated by this model, its validity has been called into question by growing evidence for VTA neuronal heterogeneity and the recent demonstration that MOR agonists inhibit GABAergic terminals in the VTA arising from extrinsic neurons. In addition, VTA MOR reward can be dopamine-independent. To directly test the assumption that MOR activation directly inhibits local GABAergic neurons, we investigated the properties of rat VTA GABA neurons directly identified with either immunocytochemistry for GABA or GAD65/67, or in situ hybridization for GAD65/67 mRNA. Utilizing co-labeling with an antibody for the neural marker NeuN and in situ hybridization against GAD65/67, we found that 23±3% of VTA neurons are GAD65/67(+). In contrast to the assumptions of the two neuron model, VTA GABAergic neurons are heterogeneous, both physiologically and pharmacologically. Importantly, only 7/13 confirmed VTA GABA neurons were inhibited by the MOR selective agonist DAMGO. Interestingly, all confirmed VTA GABA neurons were insensitive to the GABA(B) receptor agonist baclofen (0/6 inhibited), while all confirmed dopamine neurons were inhibited (19/19). The heterogeneity of opioid responses we found in VTA GABAergic neurons, and the fact that GABA terminals arising from neurons outside the VTA are inhibited by MOR agonists, make further studies essential to determine the local circuit mechanisms underlying VTA MOR reward.
PLoS ONE 01/2012; 7(7):e42365. · 4.09 Impact Factor
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ABSTRACT: The mesocorticolimbic dopamine (DA) system plays important roles in reward, motivation, learning, memory, and movement. This system arises from the A10 region, comprising the ventral tegmental area and three adjacent midline nuclei (caudal linear nucleus, interfascicular nucleus, and rostral linear nucleus of the raphe). DAergic and GABAergic neurons are intermingled in this region with recently discovered glutamatergic neurons expressing the vesicular glutamate transporter 2 (VGluT2). Here, we show by in situ hybridization and immunohistochemistry that there are two subpopulations of neurons expressing VGluT2 mRNA in the A10 region: (1) a major subpopulation that expresses VGluT2 but lacks tyrosine hydroxylase (TH; VGluT2-only neurons), present in each nucleus of the A10 region, and (2) a smaller subpopulation that coexpresses VGluT2 and TH (VGluT2-TH neurons). By quantitative real-time PCR, we determined the mRNA copy numbers encoding VGluT2 or TH in samples of individual microdissected TH immunoreactive (IR) neurons. Data from both in situ hybridization and from mRNA quantification showed that VGluT2 mRNA is not present in every TH-IR neuron, but restricted to a subset of TH-IR neurons located in the medial portion of the A10 region. By integration of tract tracing, in situ hybridization, and immunohistochemistry, we found that VGluT2-only neurons and VGluT2-TH neurons each innervate both the prefrontal cortex and the nucleus accumbens. These findings establish that in addition to the well-recognized mesocorticolimbic DA-only and GABA-only pathways, there exist parallel mesocorticolimbic glutamate-only and glutamate-DA pathways.
Journal of Neuroscience 06/2011; 31(23):8476-90. · 7.11 Impact Factor
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ABSTRACT: It is widely accepted that midbrain dopamine (DA) neurons encode actual and expected reward values by phasic alterations in firing rate. However, how DA neurons encode negative events in the environment is still unclear because some DA neurons appear to be depressed and others excited by aversive stimuli. Here, we show that exposing fear-conditioned rats to stimuli predicting electrical shock elicited three types of biphasic responses, each of which contained an inhibitory pause, in neurochemically identified ventral tegmental area (VTA) DA neurons. The duration of the inhibitory pause in these responses of VTA DA neurons was in direct proportion to the increase in respiratory rate reflecting the level of conditioned fear. Our results suggest that the duration of inhibition of VTA DA neurons encodes negative emotional values of signals predicting aversive events in the environment.
Journal of Neuroscience 05/2011; 31(20):7471-6. · 7.11 Impact Factor
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ABSTRACT: The ventral tegmental area (VTA) contributes to reward and motivation signaling. In addition to the well established populations of dopamine (DA) or GABA VTA neurons, glutamatergic neurons were recently discovered in the VTA. These glutamatergic neurons express the vesicular glutamate transporter 2, VGluT2. To investigate whether VTA glutamatergic neurons establish local synapses, we tagged axon terminals from resident VTA neurons by intra-VTA injection of Phaseolus vulgaris leucoagglutinin (PHA-L) or an adeno-associated virus encoding wheat germ agglutinin (WGA) and by immunoelectron microscopy determined the presence of VGluT2 in PHA-L- or WGA-positive terminals. We found that PHA-L- or WGA-positive terminals from tagged VTA cells made asymmetric or symmetric synapses within the VTA. VGluT2 immunoreactivity was detected in the vast majority of PHA-L- or WGA-positive terminals forming asymmetric synapses. These results indicate that both VTA glutamatergic and nonglutamatergic (likely GABAergic) neurons establish local synapses. To examine the possible DAergic nature of postsynaptic targets of VTA glutamatergic neurons, we did triple immunolabeling with antibodies against VGluT2, tyrosine hydroxylase (TH), and PHA-L. From triple-labeled tissue, we found that double-labeled PHA-L (+)/VGluT2 (+) axon terminals formed synaptic contacts on dendrites of both TH-positive and TH-negative cells. Consistent with these anatomical observations, in whole-cell slice recordings of VTA neurons we observed that blocking action potential activity significantly decreased the frequency of synaptic glutamatergic events in DAergic and non-DAergic neurons. These observations indicate that resident VTA glutamatergic neurons are likely to affect both DAergic and non-DAergic neurotransmission arising from the VTA.
Journal of Neuroscience 01/2010; 30(1):218-29. · 7.11 Impact Factor
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ABSTRACT: Stress-induced reinstatement of cocaine-seeking is blocked by antagonists for the stress-related neurohormone corticotropin-releasing factor (CRF). One site of this action is the ventral tegmental area (VTA), where mild footshock stress causes CRF release, glutamate release, and dopaminergic activation in cocaine-experienced but not cocaine-naive animals. Infusion of CRF into VTA has similar effects to footshock in cocaine-experienced animals but fails to cause significant VTA glutamate release or dopaminergic activation in cocaine-naive animals. The reinstatement, glutamate release, and dopamine release are prevented by VTA infusions of CRF-receptor 2 (CRF-R2) but not CRF-R1 antagonists. Reinstatement is triggered by some but not all CRF-R2 agonists and some but not all CRF-R1 agonists; the common denominator of the effective agonists is that they bind to the CRF-binding protein (CRF-BP), which appears to be essential for the behavioral and VTA effects of stress and CRF in cocaine-experienced animals. In situ hybridization reveals mRNA for CRF-R1 and CRF-BP but not CRF-R2 in a subset of VTA dopamine neurons. Electron microscopy reveals primarily asymmetric synapses between a subset of VTA terminals containing glutamate and CRF and a subset of VTA dopaminergic neurons and primarily symmetric synapses between a subset of CRF terminals that do not contain glutamate and a subset of GABAergic neurons in VTA. Thus, a complex and not yet fully understood interaction of CRF, glutamate, and the mesocorticolimbic dopamine system is established by experience with cocaine, and this alteration appears to contribute importantly to the transition from casual to compulsive cocaine-seeking.
Brain research 09/2009; 1314:38-43. · 2.46 Impact Factor
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ABSTRACT: Ventral tegmental area (VTA) brain-derived neurotrophic factor (BDNF) contributes to time-dependent increases in cue-induced cocaine seeking after withdrawal (incubation of cocaine craving). Here, we studied the role of glial cell line-derived neurotrophic factor (GDNF) in incubation of cocaine craving because, like BDNF, GDNF provides trophic support to midbrain dopamine neurons.
We first trained rats to self-administer intravenous cocaine for 10 days (6 hours/d, cocaine injections were paired with a tone-light cue). We then manipulated VTA GDNF function and assessed cue-induced cocaine seeking in extinction tests after withdrawal from cocaine.
VTA injections of an adeno-associated virus (AAV) vector containing rat GDNF cDNA (5 x 10(8) viral genomes) on withdrawal Day 1 increased cue-induced cocaine seeking on withdrawal days 11 and 31; this effect was not observed after VTA injections of an AAV viral vector containing red fluorescent protein (RFP). Additionally, VTA, but not substantial nigra (SN), GDNF injections (1.25 microg or 12.5 microg/side) immediately after the last cocaine self-administration session increased cue-induced drug seeking on withdrawal days 3 and 10; this effect was reversed by VTA injections of U0126, which inhibits the activity of extracellular signal-regulated kinases (ERK). Finally, interfering with VTA GDNF function by chronic delivery of anti-GDNF monoclonal neutralizing antibodies via minipumps (600 ng/side/d) during withdrawal Days 1-14 prevented the time-dependent increases in cue-induced cocaine seeking on withdrawal days 11 and 31.
Our results indicate that during the first weeks of withdrawal from cocaine self-administration, GDNF-dependent neuroadaptations in midbrain VTA neurons play an important role in the development of incubation of cocaine craving.
Biological psychiatry 05/2009; 66(2):137-45. · 8.93 Impact Factor
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ABSTRACT: The pedunculopontine tegmental nucleus (PPTg) and laterodorsal tegmental nucleus (LDTg) provide cholinergic afferents to several brain areas. This cholinergic complex has been suggested to play a role in sleep, waking, motor function, learning and reward. To have a better understanding of the neurochemical organization of the PPTg/LDTg we characterized the phenotype of PPTg/LDTg neurons by determining in these cells the expression of transcripts encoding choline acetyltransferase (ChAT), glutamic acid decarboxylase (GAD) or the vesicular glutamate transporters (vGluT1, vGluT2 and vGluT3). Within the PPTg/LDTg complex we found neurons expressing ChAT, vGluT2 or GAD transcripts, these neuronal phenotypes were intermingled, but not homogeneously distributed within the PPTg or LDTg. Previous studies suggested the presence of either glutamate or gamma-aminobutyric acid (GABA) immunolabeling in a large number of PPTg/LDTg cholinergic neurons, leading to the widespread notion that PPTg/LDTg cholinergic neurons co-release acetylcholine together with either glutamate or GABA. To assess the glutamatergic or GABAergic nature of the PPTg/LDTg cholinergic neurons, we combined in situ hybridization (to detect vGluT2 or GAD transcripts) and immunohistochemistry (to detect ChAT), and found that over 95% of all PPTg/LDTg cholinergic neurons lack transcripts encoding either vGluT2 mRNA or GAD mRNA. As the vast majority of PPTg/LDTg cholinergic neurons lack transcripts encoding essential proteins for the vesicular transport of glutamate or for the synthesis of GABA, co-release of acetylcholine with either glutamate or GABA is unlikely to be a major factor in the interactions between acetylcholine, glutamate and GABA at the postsynaptic site.
European Journal of Neuroscience 02/2009; 29(2):340-58. · 3.63 Impact Factor
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ABSTRACT: Corticotropin-releasing factor (CRF) and related peptides play a role in mediating neuronal effects of stress. These peptides mediate stress responses by their interactions with the CRF receptors and the CRF-binding protein (CRF-BP). Because the CRF-BP is implicated in neurotransmission within the ventral tegmental area (VTA), we investigated whether the CRF-BP is expressed in VTA neurons. By in situ hybridization, we detected cellular expression of CRF-BP mRNA in the VTA; no such expression was seen in neighboring substantia nigra pars compacta (SNC) or substantia nigra pars reticulata. By double in situ hybridization, we determined that VTA neurons with CRF-BP mRNA coexpressed transcripts encoding either tyrosine hydroxylase [TH; a marker for dopamine (DA) neurons] or glutamic acid decarboxylase [GAD; synthesizing enzyme of gamma-aminobutyric acid (GABA)]. Neurons with CRF-BP mRNA represented 25% of the total population of TH-expressing neurons and 28% of the total population of GAD-expressing neurons, indicating that discrete subpopulations of dopaminergic and GABAergic neurons are present in the VTA. Within the total population of neurons containing CRF-BP mRNA, 70% coexpressed TH mRNA and only 27% coexpressed GAD mRNA. As far as we are aware, we provide the first anatomical evidence that a molecule, CRF-BP, is encoded by DAergic neurons of the VTA but not by those of the SNC. We propose, based on the observation that the majority of VTA neurons expressing CRF-BP mRNA are DAergic, that in the VTA interactions of CRF-BP with CRF, or with CRF-related peptides, are likely to be mediated predominantly by DAergic neurons.
The Journal of Comparative Neurology 08/2008; 509(3):302-18. · 3.81 Impact Factor
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ABSTRACT: In earlier studies, the volatile anesthetics and the endogenous cannabinoid anandamide have been shown to inhibit the function of alpha(7)-nicotinic acetylcholine receptors. In the present study, interactions between the effects of volatile anesthetics and anandamide on the function of alpha(7)-nicotinic acetylcholine receptors expressed in Xenopus oocytes were investigated using the two-electrode voltage-clamp technique. Anandamide and volatile anesthetics isoflurane and halothane inhibited currents evoked with acetylcholine (100 microM) in a reversible and concentration-dependent manner. Coapplication of anandamide and volatile anesthetics caused a significantly greater inhibition of alpha(7)-nicotinic acetylcholine receptor function than anandamide or volatile anesthetics alone. Analyses of oocytes by matrix-assisted laser desorption/ionization mass spectroscopy indicated that volatile anesthetics did not alter the lipid profile of oocytes. Results of studies with chimeric alpha(7)-nicotinic acetylcholine-5-HT(3) receptors comprised of the N-terminal domain of the alpha(7)-nicotinic acetylcholine receptor and the transmembrane and carboxyl-terminal domains of 5-HT(3) receptors suggest that while isoflurane inhibition of the alpha(7)-nicotinic acetylcholine receptor is likely to involve the N-terminal region of the receptor, the site of action for anandamide involves transmembrane and carboxyl-terminal domains of the receptors. These data indicate that endocannabinoids and isoflurane have additive inhibitory effects on alpha(7)-nicotinic acetylcholine receptor function through allosteric binding sites located on the distinct regions of the receptor.
European Journal of Pharmacology 04/2008; 582(1-3):42-51. · 2.52 Impact Factor
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ABSTRACT: Interactions between stress and the mesocorticolimbic dopamine (DA) system have been suggested from behavioral and electrophysiological studies. Because corticotropin-releasing factor (CRF) plays a role in stress responses, we investigated possible interactions between neurons containing CRF and those producing DA in the ventral tegmental area (VTA). We first investigated the cellular distribution of CRF in the VTA by immunolabeling VTA sections with anti-CRF antibodies and analyzing these sections by electron microscopy. We found CRF immunoreactivity present mostly in axon terminals establishing either symmetric or asymmetric synapses with VTA dendrites. We established that nearly all CRF asymmetric synapses are glutamatergic, insofar as the CRF-immunolabeled axon terminals in these synapses coexpressed the vesicular glutamate transporter 2, and that the majority of CRF symmetric synapses are GABAergic, insofar as the CRF-immunolabeled axon terminals in these synapses coexpressed glutamic acid decarboxylase, findings that are of functional importance. We then looked for synaptic interactions between CRF- and DA-containing neurons, by using antibodies against CRF and tyrosine hydroxylase (TH; a marker for DA neurons). We found that most synapses between CRF-immunoreactive axon terminals and TH neurons are asymmetric (in the majority likely to be glutamatergic) and suggest that glutamatergic neurons containing CRF may be part of the neuronal circuitry that mediates stress responses involving the mesocorticolimbic DA system. The presence of CRF synapses in the VTA offers a mechanism for interactions between the stress-associated neuropeptide CRF and the mesocorticolimbic DA system.
The Journal of Comparative Neurology 03/2008; 506(4):616-26. · 3.81 Impact Factor
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ABSTRACT: Induction of the immediate early gene protein product Fos has been used extensively to assess neural activation in the striatum after repeated amphetamine administration to rats in their home cages. However, this technique has not been used to examine striatal activation after repeated administration outside the home cage, an environment where repeated drug administration produces more robust psychomotor sensitization. We determined the dose-response relationship for amphetamine-induced psychomotor activity and Fos expression in nucleus accumbens and caudate-putamen 1 week after repeated administration of amphetamine or saline in locomotor activity chambers. Repeated administration of amphetamine enhanced amphetamine-induced locomotor activity and stereotypy and Fos expression in nucleus accumbens, but not in caudate-putamen. In comparison, levels of Fos expression induced by 1mg/kg amphetamine were not altered in nucleus accumbens or caudate-putamen by repeated amphetamine administration in the home cage. Double-labeling of Fos protein and enkephalin mRNA indicates that Fos is expressed in approximately equal numbers of enkephalin-negative and enkephalin-positive neurons in nucleus accumbens and caudate-putamen following injections outside the home cage. Furthermore, repeated amphetamine administration increased drug-induced Fos expression in enkephalin-positive, but not enkephalin-negative, neurons in nucleus accumbens. We conclude that repeated amphetamine administration outside the home cage recruits the activation of enkephalin-containing nucleus accumbens neurons during sensitized amphetamine-induced psychomotor activity.
Behavioural Brain Research 01/2008; 185(2):88-98. · 3.42 Impact Factor
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ABSTRACT: The effects of the antipsychotic clozapine on the function of the cloned alpha(7) subunit of the nicotinic acetylcholine (nACh) receptor expressed in Xenopus oocytes was investigated by using the two-electrode voltage-clamp technique. Clozapine reversibly inhibited nicotine (10 microM)-induced currents in a concentration-dependent manner (300 nM to 90 microM), with an IC(50) value of 3.2+/-0.4 microM. The effect of clozapine was not dependent on the membrane potential. Clozapine did not affect the activity of endogenous Ca(2+)-dependent Cl(-) channels since the inhibition by clozapine was unaltered by the intracellularly injected Ca(2+) chelator BAPTA and perfusion with Ca(2+)-free bathing solution containing 2mM Ba(2+). Clozapine decreased the maximal nicotine-induced responses without significantly affecting its potency, indicating that it acts as a noncompetitive antagonist on alpha(7)-nACh receptors. In hippocampal slices, the whole-cell recordings from CA1 pyramidal neurons indicated that the increases in the frequency and amplitudes of the GABA-mediated spontaneous inhibitory postsynaptic currents induced by bath application of 2 mM choline, a specific agonist for alpha(7)-nACh receptors, were abolished after 10 min application of 5 microM clozapine. In conclusion, these results demonstrate that clozapine inhibits the function of alpha(7)-nACh receptors expressed in Xenopus oocytes and in hippocampal neurons.
Neuropharmacology 03/2007; 52(2):387-94. · 4.81 Impact Factor
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ABSTRACT: The ventral tegmental area (VTA) is thought to play an important role in reward function. Two populations of neurons, containing either dopamine (DA) or gamma-amino butyric acid (GABA), have been extensively characterized in this area. However, recent electrophysiological studies are consistent with the notion that neurons that utilize neurotransmitters other than DA or GABA are likely to be present in the VTA. Given the pronounced phenotypic diversity of neurons in this region, we have proposed that additional cell types, such as those that express the neurotransmitter glutamate may also be present in this area. Thus, by using in situ hybridization histochemistry we investigated whether transcripts encoded by genes for the two vesicular glutamate transporters, VGluT1 or VGluT2, were expressed in the VTA. We found that VGluT2 mRNA but not VGluT1 mRNA is expressed in the VTA. Neurons expressing VGluT2 mRNA were differentially distributed throughout the rostro-caudal and medio-lateral aspects of the VTA, with the highest concentration detected in rostro-medial areas. Phenotypic characterization with double in situ hybridization of these neurons indicated that they rarely co-expressed mRNAs for tyrosine hydroxylase (TH, marker for DAergic neurons) or glutamic acid decarboxylase (GAD, marker for GABAergic neurons). Based on the results described here, we concluded that the VTA contains glutamatergic neurons that in their vast majority are clearly non-DAergic and non-GABAergic.
European Journal of Neuroscience 02/2007; 25(1):106-18. · 3.63 Impact Factor
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ABSTRACT: In the striatum, adenosine A2A and dopamine D2 receptors exert reciprocal antagonistic interactions that modulate the function of GABAergic enkephalinergic neurons. We have previously shown that stimulation of adenosine A1 receptors allows the stimulation of A2A receptors to overcome a tonic inhibitory effect of D2 receptors and induce striatal expression of c-fos. In the present work, by studying co-localization of c-Fos immunoreactivity and preproenkephalin and preprodynorphin transcripts, we show that co-administration of the A1 receptor agonist CPA and the A2A receptor agonist CGS 21680 increases the striatal expression of c-fos in GABAergic enkephalinergic but not in GABAergic dynorphinergic neurons. Co-administration of CPA and CGS 21680 also induced a significant increase in the striatal expression of preproenkephalin. The results underscore the role of adenosine in the activation of gene expression in the GABAergic enkephalinergic neuron.
Neuropsychopharmacology 11/2006; 31(10):2173-9. · 7.99 Impact Factor
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ABSTRACT: Many studies have examined the effect of experimenter-delivered methamphetamine on the mesolimbic and nigrostriatal dopamine pathways. In contrast, little is known about the effect of methamphetamine self-administration on these neuronal pathways. We studied the effect of methamphetamine self-administration on two key regulators of dopamine transmission, tyrosine hydroxylase (TH), and dopamine transporter (DAT), in components of the mesolimbic and nigrostriatal dopamine pathways.
Rats self-administered methamphetamine (0.1 mg/kg per infusion, fixed-ratio-1 reinforcement schedule) or saline (control condition) for 9 h/day over 10 days. The brains of these rats were collected after 1 or 30 days of forced abstinence and the expression levels of TH and DAT were assayed by in situ, hybridization and western blot.
TH mRNA and protein levels were increased in the ventral tegmental area (VTA, the cell body region of the mesolimbic dopamine system) and the substantia nigra pars compacta (SNC, the cell body region of the nigrostriatal dopamine system) after 1 day, but not 30 days, of forced abstinence from methamphetamine. In contrast, methamphetamine self-administration had no effect on TH protein levels in dopaminergic terminals located in the nucleus accumbens and caudate-putamen. In addition, methamphetamine self-administration had no effect on DAT mRNA levels in the VTA.
Results suggest that extended daily access to self-administered methamphetamine results in a transient, short-lasting effect on mesolimbic and nigrostriatal dopamine neurons of the rat brain.
Psychopharmacologia 06/2006; 185(4):505-13. · 4.08 Impact Factor
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ABSTRACT: Previous reports have indicated that the expression of bone morphogenetic protein-7 (BMP7) is enhanced after ischemic injury in brain. This upregulation may induce endogenous neurorepair in the ischemic brain. The purpose of this study was to examine neuroregenerative effects of BMP7 after ischemia-reperfusion injury. Adult Sprague-Dawley rats were anesthetized with chloral hydrate. Right middle cerebral artery (MCA) was transiently ligated with 10-O suture for 1 h. One day after MCA occlusion, vehicle or BMP7 was infused to the contralateral cerebral ventricle. To identify possible neurogenesis, bromodeoxyurindine (BrdU) was systemically injected on the fourth and fifth days after MCA occlusion. Animals treated with BMP7 showed a rapid correction of body asymmetry and neurological deficits, suggesting BMP7 facilitates recovery after stroke. Animals were sacrificed at 1 month after stroke and brains were analyzed using immunohistological techniques. BMP7 treatment enhanced immunoreactivity of BrdU in the subventricular zone, lesioned cortex, and corpus callosum. These BrdU-positive cells co-labeled with nestin and NeuN. Our behavioral and anatomical data suggest that BMP7 promotes neuroregeneration in stroke animals, possibly through the proliferation of new neuronal precursors after ischemia.
Journal of the Neurological Sciences 02/2006; 240(1-2):21-9. · 2.35 Impact Factor
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ABSTRACT: Long-lasting, activity-dependent changes in synaptic efficacy at excitatory synapses are critical for experience-dependent synaptic plasticity. Synaptic plasticity at excitatory synapses is determined both presynaptically by changes in the probability of neurotransmitter release, and postsynaptically by changes in the availability of functional postsynaptic glutamate receptors. Two kinds of synaptic plasticity have been described. In homosynaptic or Hebbian plasticity, the events responsible for synaptic strengthening occur at the same synapse as is being strengthened. Homosynaptic plasticity is activity-dependent and associative, because it associates the firing of a postsynaptic neuron with that of the presynaptic neuron. Heterosynaptic plasticity, on the other hand, is activity-independent and the synaptic strength is modified as a result of the firing of a third, modulatory neuron. It has been suggested that long-term changes in synaptic strength, which are associated with gene transcription, can only be induced with the involvement of heterosynaptic plasticity. The neuromodulator adenosine plays an elaborated pre- and postsynaptic control of glutamatergic neurotransmission. This paper reviews the evidence suggesting that in some striatal excitatory synapses, adenosine can provide the heterosynaptic-like modulation essential for stabilizing homosynaptic plasticity without the need of a "third, modulatory neuron".
Journal of Integrative Neuroscience 01/2006; 4(4):445-64. · 0.76 Impact Factor
