Hippocampal dopamine receptors modulate the motor activation and the increase in dopamine levels in the rat nucleus accumbens evoked by chemical stimulation of the ventral hippocampus

Profiling transcriptomic responses of human stem cell-derived medium spiny neuron-like cells to exogenous phasic and tonic neurotransmitters

Transcriptomic responses to neurotransmitters contribute to the complex processes driving memory and addiction. Advances in both measurement methods and experimental models continue to improve our understanding of this regulatory layer. Here we focus on the experimental potential of stem cell derived neurons, currently the only ethical model that can be used in reductionist and experimentally perturbable studies of human cells. Prior work has focused on generating distinct cell types from human stem cells, and has also shown their utility in modeling development and cellular phenotypes related to neurodegeneration. Here we seek an understanding of how stem cell derived neural cultures respond to perturbations experienced during development and disease progression. This work profiles transcriptomic responses of human medium spiny neuron-like cells with three specific goals. We first characterize transcriptomic responses to dopamine and dopamine receptor agonists and antagonists presented in dosing patterns mimicking acute, chronic, and withdrawal regimens. We also assess transcriptomic responses to low and persistent tonic levels of dopamine, acetylcholine, and glutamate to better mimic the in vivo environment. Finally, we identify similar and distinct responses between hMSN-like cells derived from H9 and H1 stem cell lines, providing some context for the extent of variability these types of systems will likely pose for experimentalists. The results here suggest future optimizations of human stem cell derived neurons to increase their in vivo relevance and the biological insights that can be garnered from these models.

Activation of the ventral subiculum reinvigorates behavior after failure to achieve a goal: Implications for dopaminergic modulation of motivational processes

Previous studies confirm that brief electrical stimulation of glutamatergic afferents from the ventral subiculum (vSub) can significantly enhance dopamine release in the ventral striatum for an extended duration (>20 min). However, the functional significance of this effect on motivated behavior remains to be specified. Here we tested the hypothesis that brief electrical stimulation of the ventral subiculum (20 Hz for 10 s) might increase effort expenditure for food rewards. Motivation was assessed by a progressive ratio lever pressing task, which requires continuous escalation of the numbers of lever presses to receive each subsequent sucrose pellet, eventually resulting in the failure to achieve the required ratio for a food reward. vSub stimulation at the start of a session did not affect the rate or total number of lever presses prior to reaching the "break point". In contrast, stimulation of the vSub with identical parameters on a post break point trial resulted in a significant increase in total responses. These findings demonstrate that activation of the vSub with parameters that modulate dopamine efflux in the nucleus accumbens can re-activate goal-directed behavior after failure to achieve a goal. Our data highlight a possible role for the vSub in the pathophysiology and potential treatment of motivational processes linked to psychiatric disease.

Adult Neurogenesis and Psychiatric Disorders

Psychiatric disorders continue to be among the most challenging disorders to diagnose and treat because there is no single genetic or anatomical locus that is causative for the disease. Current treatments are often blunt tools used to ameliorate the most severe symptoms, at the risk of disrupting functional neural systems. There is a critical need to develop new therapeutic strategies that can target circumscribed functional or anatomical domains of pathology. Adult hippocampal neurogenesis may be one such domain. Here, we review the evidence suggesting that adult hippocampal neurogenesis plays a role in emotional regulation and forms of learning and memory that include temporal and spatial memory encoding and context discrimination, and that its dysregulation is associated with psychiatric disorders, such as affective disorders, schizophrenia, and drug addiction. Further, adult neurogenesis has proven to be an effective model to investigate basic processes of neuronal development and converging evidence suggests that aberrant neural development may be an etiological factor, even in late-onset diseases. Constitutive neurogenesis in the hippocampus of the mature brain reflects large-scale plasticity unique to this region and could be a potential hub for modulation of a subset of cognitive and affective behaviors that are affected by multiple psychiatric disorders.

Brain structure and function correlates of cognitive subtypes in schizophrenia

Stable neuropsychological deficits may provide a reliable basis for identifying etiological subtypes of schizophrenia. The aim of this study was to identify clusters of individuals with schizophrenia based on dimensions of neuropsychological performance, and to characterize their neural correlates. We acquired neuropsychological data as well as structural and functional magnetic resonance imaging from 129 patients with schizophrenia and 165 healthy controls. We derived eight cognitive dimensions and subsequently applied a cluster analysis to identify possible schizophrenia subtypes. Analyses suggested the following four cognitive clusters of schizophrenia: (1) Diminished Verbal Fluency, (2) Diminished Verbal Memory and Poor Motor Control, (3) Diminished Face Memory and Slowed Processing, and (4) Diminished Intellectual Function. The clusters were characterized by a specific pattern of structural brain changes in areas such as Wernicke's area, lingual gyrus and occipital face area, and hippocampus as well as differences in working memory-elicited neural activity in several fronto-parietal brain regions. Separable measures of cognitive function appear to provide a method for deriving cognitive subtypes meaningfully related to brain structure and function. Because the present study identified brain-based neural correlates of the cognitive clusters, the proposed groups of individuals with schizophrenia have some external validity.

Dopamine D1/D5 receptor signaling regulates synaptic cooperation and competition in hippocampal CA1 pyramidal neurons via sustained ERK1/2 activation

Synaptic cooperation and competition are important components of synaptic plasticity that tune synapses for the formation of associative long‐term plasticity, a cellular correlate of associative long‐term memory. We have recently reported that coincidental activation of weak synapses within the vicinity of potentiated synapses will alter the cooperative state of synapses to a competitive state thus leading to the slow decay of long‐term plasticity, but the molecular mechanism underlying this is still unknown. Here, using acute hippocampal slices of rats, we have examined how increasing extracellular dopamine concentrations interact and/or affect electrically induced long‐term potentiation (LTP) in the neighboring synapses. We demonstrate that D1/D5‐receptor‐mediated potentiation at the CA1 Schaffer collateral synapses differentially regulates synaptic co‐operation and competition. Further investigating the molecular players involved, we reveal an important role for extracellular signal‐regulated kinases‐1 and 2 (ERK1/2) as signal integrators and dose‐sensors. Interestingly, a sustained activation of ERK1/2 pathway seems to be involved in the differential regulation of synaptic associativity. The concentration‐dependent effects of the modulatory transmitter, as demonstrated for dopaminergic signaling in the present study, might offer additional computational power by fine tuning synaptic associativity processes for establishing long‐term associative memory in neural networks. © 2015 The Authors Hippocampus Published by Wiley Periodicals, Inc.

Inhibitory Effect of Berberis vulgaris Aqueous Extract on Acquisition and Reinstatement Effects of Morphine in Conditioned Place Preferences (CPP) in Mice

Background:

It has been elucidated that Berberis vulgaris (barberry) can alleviate morphine withdrawal syndrome. Also it has been reported that aqueous extract of barberry possibly have inhibitory effect on NMDA receptors.

Objectives:

In this study, we decided to evaluate the effects of aqueous extract of B. vulgaris fruit on morphine tendency in mice using conditioned place preference (CPP) method.

Materials and Methods:

In experiment 1 (acquisition phase), mice underwent morphine-induced conditioned place preference (CPP) training with injections of morphine (40 mg/kg). In experiment 2 (extinction and reinstatement phases), mice underwent the same CPP training as in experiment 1 and subsequent extinction training on day 16th a reinstatement by CPP was done by injection of reminding 10 mg/kg morphine.

Results:

The administration of morphine (40 mg/kg for four days) produced place preference. In the first method, the aqueous extract of barberry (200 mg/kg) prevented morphine tendency to white cell in CPP method. In the second method, after inter-peritoneal injection of aqueous extracts of barberry at 100 and 200 mg/kg, the animals tendency toward the white cells of CPP chamber on the sixteenth day (after a reminder injection of morphine 10 mg/kg) was significantly reduced.

Conclusions:

These results show that aqueous extract of barberry can reduce the acquisition and reinstatement of morphine-induced conditioned place preference.

Functional correlation between GABAergic and dopaminergic systems of dorsal hippocampus and ventral tegmental area in passive avoidance learning in rats

The aim of the present study was to investigate the existence of possible functional correlation between GABA-A and dopamine (DA) receptors of the dorsal hippocampus and the ventral tegmental area (VTA) in passive avoidance learning. Two guide cannulas were stereotaxically implanted in the CA1 region of the dorsal hippocampus and the VTA of male Wistar rats. In order to measure memory retrieval, the animals were trained in a step-through type passive avoidance task and tested 24 h after training. Post-training intra-CA1 administration of a GABA-A receptor agonist, muscimol (0.01-0.02 μg/rat) dose-dependently impaired memory retrieval. Post-training intra-VTA administration of SCH23390 (a dopamine D1 receptor antagonist; 0.1-0.8 μg/rat) or sulpiride (a D2 receptor antagonist; 0.5-1.5 μg/rat) decreased the inhibitory effect of muscimol (0.02 μg/rat, intra-CA1) on memory retrieval. Intra-VTA administration of the same doses of SCH23390, but not sulpiride, decreased the step-through latencies. On the other hand, post-training administration of muscimol (0.02 μg/rat) into the VTA inhibited memory retrieval. The administration of SCH23390 (0.01-0.2 μg/rat) or sulpiride (0.1-1 μg/rat) into the CA1 region, immediately after training, had no effect on memory retrieval. Furthermore, the amnesic effect of intra-VTA administration of muscimol was significantly decreased by intra-CA1 administration of sulpiride (0.5 and 1 μg/rat, intra-CA1), but not SCH23390. The practical conclusion is that the relationship between the hippocampus and the VTA may regulate memory formation in passive avoidance learning. Also, the correlation between the hippocampus and VTA by a dopaminergic system may be involved in mediating muscimol-induced amnesia.

Local hippocampal methamphetamine-induced reinforcement

Drug abuse and addiction are major problems in the United States. In particular methamphetamine (METH) use has increased dramatically. A greater understanding of how METH acts on the brain to induce addiction may lead to better therapeutic targets for this problem. The hippocampus is recognized as an important structure in learning and memory, but is not typically associated with drug reinforcement or reward processes. Here, the focus is on the hippocampus which has been largely ignored in the addiction literature as compared to the nucleus accumbens (NAc), ventral tegmental area (VTA), and prefrontal cortex (PFC). The results show that METH administered unilaterally via a microdialysis probe to rats’ right dorsal hippocampus will induce drug-seeking (place preference) and drug-taking (lever-pressing) behavior. Furthermore, both of these responses are dependent on local dopamine (DA) receptor activation, as they are impaired by a selective D₁/D₅ receptor antagonist. The results suggest that the hippocampus is part of the brain's reward circuit that underlies addiction.

Neurobehavioral abnormalities in the dysbindin-1 mutant, sandy, on a C57BL/6J genetic background

Sandy mice have a deletion mutation in the gene encoding dysbindin-1, Dtnbp1, with consequent reduction of the protein in heterozygotes and its loss in homozygotes. The sandy mouse thus serves as an animal model of dysbindin-1 function. As this protein is concentrated in synaptic tissue and affects transmitter release, it may affect neuronal processes that mediate behavior. To investigate the neurobehavioral effects of the Dtnbp1 mutation, we studied littermate sandy and wild-type controls on a C57BL/6J genetic background. The three animal groups were indistinguishable in their external physical characteristics, sensorimotor skills and indices of anxiety-like behaviors. In the open field, however, homozygous animals were hyperactive and appeared to show less habituation to the initially novel environment. In the Morris water maze, homozygous animals displayed clear deficits in spatial learning and memory with marginal deficits in visual association learning. Apart from the last mentioned deficits, these abnormalities are consistent with hippocampal dysfunction and in some cases with elevated dopaminergic transmission via D2 dopamine receptors. As similar deficits in spatial learning and memory have been found in schizophrenia, where decreased dysbindin-1 has been found in the hippocampus, the sandy mouse may also model certain aspects of cognition and behavior relevant to schizophrenia.

Presynaptic type III neuregulin 1 is required for sustained enhancement of hippocampal transmission by nicotine and for axonal targeting of alpha7 nicotinic acetylcholine receptors

Both the neuregulin 1 (Nrg1) and alpha7 nicotinic acetylcholine receptor (alpha7*nAChRs) genes have been linked to schizophrenia and associated sensory-motor gating deficits. The prominence of nicotine addiction in schizophrenic patients is reflected in the normalization of gating deficits by nicotine self-administration. To assess the role of presynaptic type III Nrg1 at hippocampal-accumbens synapses, an important relay in sensory-motor gating, we developed a specialized preparation of chimeric circuits in vitro. Synaptic relays from Nrg1(tm1Lwr) heterozygote ventral hippocampal slices to wild-type (WT) nucleus accumbens neurons (1) lack a sustained, alpha7*nAChRs-mediated phase of synaptic potentiation seen in comparable WT/WT circuits and (2) are deficient in targeting alpha7*nAChRs to presynaptic sites. Thus, selective alteration of the level of presynaptic type III Nrg1 dramatically affects the modulation of glutamatergic transmission at ventral hippocampal to nucleus accumbens synapses.

Neural circuits engaged in ventral hippocampal modulation of dopamine function in medial prefrontal cortex and ventral striatum

Dopamine (DA) transmission in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) is crucial for various cognitive processes. However, our understanding of the regulation of DA efflux by glutamatergic afferents to these areas is incomplete. Using microdialysis in freely moving rats, we provide evidence in the present study that brief stimulation (20 Hz, 10 s) of the ventral hippocampus potently increases DA efflux in the mPFC, NAc, and ventral tegmental area for 30-40 min. Subsequent experiments show that the stimulation-evoked increase in DA efflux in the mPFC depends on local activation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate, but not N-methyl-D-aspartate, receptors in the mPFC. Additionally, neural activity and ionotropic glutamate receptor activation in the ventral tegmental area are necessary for ventral hippocampal stimulation to increase mPFC DA efflux. Blocking neural activity or ionotropic glutamate receptors in the ventral tegmental area also attenuated the stimulation-evoked increase in DA efflux in the NAc. Evidence in support of a role for the mPFC in the stimulation-evoked increase in NAc DA was not obtained. Taken together, these observations highlight the important role of the ventral hippocampus in modulating forebrain DA efflux via separate neural circuits.

Voxel-based morphometry in unmedicated patients with restless legs syndrome

BACKGROUND

The pathophysiology of restless legs syndrome (RLS) is not yet understood. A prior voxel-based morphometry (VBM) study reported gray matter increase in the pulvinar of the thalamus in a group of patients, most of whom were on medical treatment. Since there is evidence that medication can change the volume of cerebral structures, the question arises as to whether the reported morphometric alterations are caused by the RLS itself or, alternatively, are a consequence of drug treatment. To address this issue, we performed VBM in unmedicated RLS patients.

METHODS

Fourteen patients with idiopathic RLS with no (n=11) or only minimal (n=3) treatment exposure in the past and 14 age- and sex-matched healthy subjects were investigated. All subjects were free of psychotropic drugs for at least 4 months. Morphological data were analyzed by using optimized VBM.

RESULTS

We did not detect any structural changes except for slightly increased gray matter density in the ventral hippocampus (p=0.046 on the left and p=0.055 on the right side) and in the middle orbitofrontal gyrus (p=0.046 on the right and p=0.097 on the left side).

CONCLUSION

Our study could not confirm the findings of a prior study. A possible explanation for the divergent findings is the difference between the populations examined. Since, in our study, essentially treatment-naïve patients were investigated, it is possible that the prior findings reflect treatment-induced effects on cerebral morphology in RLS.

Glutamate-dopamine-GABA interactions in the aging basal ganglia

The study of neurotransmitter interactions gives a better understanding of the physiology of specific circuits in the brain. In this review we focus mostly on our own results on the interaction of the neurotransmitters glutamate, dopamine and GABA in the basal ganglia during the normal process of aging. We review first the studies on the action of endogenous glutamate on the extracellular concentrations of dopamine and GABA in the neostriatum and nucleus accumbens during aging. It was found that there exists an age-related change in the interaction of glutamate, dopamine and GABA and that these effects of aging exhibit a dorsal-to-ventral pattern of effects with no changes in the dorsal parts (dorsal striatum) and changes in the most ventral parts (nucleus accumbens). Second we reviewed the data on the effects of different ionotropic and metabotropic glutamate receptor agonists on the extracellular concentrations of dopamine and GABA in the nucleus accumbens. The results obtained clearly show the different contribution of each glutamate receptor subtype in the age-related changes produced on the interaction of glutamate, dopamine and GABA in this area of the brain. Third the effects of an enriched environment on the action of AMPA and NMDA-receptor agonists in the nucleus accumbens of rats during aging are also evaluated. Finally, and since the nucleus accumbens has been suggested to play a role in emotion and motivation and also motor behaviour, we speculated on the possibility of a specific contribution for the different glutamatergic pathways terminating in the nucleus accumbens and their interaction with a decreased dopamine playing a relevant role in motor behaviour during aging.

Serotonin and Dopamine Interactions in Rodents and Primates: Implications for Psychosis and Antipsychotic Drug Development

Since the late 1950s, appreciation of dopamine receptor blockade has played a primary role in understanding the mechanism underlying the therapeutic effects of antipsychotic drugs in schizophrenic patients in treating the positive symptoms of schizophrenia (e.g., delusions and hallucinations). Development of the second generation of antipsychotic drugs, otherwise known as atypical antipsychotic drugs, has resulted in treatments with improved subjective tolerability but relatively modest improvements in the negative symptoms of schizophrenia such as avolition, flat affect, and anhedonia. The major current challenge is to develop medications which can further improve negative symptoms treatment and also tackle the intractable clinical problems of cognitive impairment associated with schizophrenia. Further advances along these lines with respect to the dopaminergic and serotonergic neurostransmitter systems will be aided by an appreciation of the interaction between dopamine and serotonin receptor subtypes in a range of key brain structures, such as the prefrontal cortex, thalamus, striatum, amygdala, hippocampus, and the brain stem nuclei, from which the cell bodies of monoaminergic-containing neurons originate. Increasing emphasis on the use of animal models which are homologous to critical aspects of the pathophysiology in the brains of schizophrenic patients will also be required, especially as negative symptoms and cognitive impairment become an important focus for generating novel therapeutics.

Memory and frontal lobe functions; possible relations with dopamine D2 receptors in the hippocampus

Cerebral cortical regions are thought to be important for cognitive functions such as memory and executive function. Although the functional associations between dopamine D2 receptors and motor and cognitive functions have been extensively examined in the striatum using positron emission tomography (PET), the role of dopamine D2 receptors in extrastriatal regions has been unexplored. We aimed to investigate the relationship between dopamine D2 receptors in extrastriatal regions and the performance of a broad spectrum of cognitive functions including memory, language, attention, and executive function in healthy subjects. Extrastriatal dopamine D2 receptors were measured in 25 male subjects using PET with [(11)C]FLB457. After the PET scans, a battery of neuropsychological tests was administered to all subjects. We found that the binding potential (BP) of [(11)C]FLB457 in the hippocampus was positively correlated with memory function. Furthermore, BP of [(11)C]FLB457 in the hippocampus, but not in the prefrontal cortex, was associated with frontal lobe functions such as executive function and verbal fluency. Our findings suggest that dopamine D2 receptors in the hippocampus might affect the local hippocampal function, but also brain functions outside the hippocampus such as the prefrontal cortex.

Effect of drug-induced ascorbic acid release in the striatum and the nucleus accumbens in hippocampus-lesioned rats

The mechanism of ethanol, morphine, methamphetamine (MAP), and nicotine-induced ascorbic acid (AA) release in striatum, and nucleus accumbens (NAc) is not well understood. Our previous study showed that the glutamatergic system was involved in the addictive drug-induced AA release in NAc and striatum. Furthermore, frontal decortication eliminates drug-induced ascorbic acid release in the striatum but not in the NAc. In the present study, the roles of the hippocampus in drug-induced AA release in the striatum and NAc were studied by using microdialysis coupled to high performance liquid chromatography with electrochemical detection (HPLC-ECD). Ethanol (3.0 g/kg, i.p.), methamphetamine (3.0 mg/kg, i.p.), and nicotine (1.5 mg/kg, i.p.) significantly stimulated AA release in the striatum and NAc, respectively. Morphine (20 mg/kg, i.p.) significantly stimulated AA release in the striatum, but not in the NAc. After hippocampal lesion by kainic acid, AA release induced by ethanol, methamphetamine, and nicotine could be eliminated in NAc, but not in the striatum. These results suggest that the hippocampus might be a common and necessary area in addictive drug-induced AA release in the NAc, which also imply that different pathways might be involved in drug-induced AA release in the striatum and the NAc of the rats.

Effects of dorsal and ventral hippocampal NMDA stimulation on nucleus accumbens core and shell dopamine release

This study has analysed the effects of infusing N-methyl-D-aspartate (NMDA) into either the ventral or dorsal hippocampus on dopamine (DA) transmission in the nucleus accumbens (NAC) core or shell for the first time. Dopamine was measured using in vivo microdialysis with high performance liquid chromatography with electrochemical detection (HPLC-EC). Unilateral NMDA infusion (0.5 microg) into the ventral hippocampus (VH) increased extracellular DA levels in NAC shell during the first 30 min following infusion compared to saline (SAL) infused animals. In contrast, NAC core DA levels were unaffected. NMDA infusion into the dorsal hippocampus (DH) led to a decrease in NAC core DA levels; this effect was not observed in the SAL-infused group. DA levels in NAC shell remained unaltered. At the end of the experiments, we examined the response to a systemic amphetamine (AMPH) injection of 1mg/kg on extracellular DA levels of the NAC core and shell. Interestingly, on2ly animals previously infused with NMDA into the VH exhibited a sensitized DA response in the NAC shell in response to the AMPH injection. We can conclude that VH activation has an acute stimulatory effect on DA release in the shell and that DH activation has a suppressive effect on extracellular DA levels in the core.

Dissociating ventral and dorsal subicular dopamine D1 receptor involvement in instrumental learning, spontaneous motor behavior, and motivation

A series of experiments investigating the role of dopamine D1 receptors in the ventral subiculum (vSUB) and dorsal subiculum (dSUB), 2 subregions of the hippocampal formation, found that D1 receptor antagonism (3.0 nmol/0.5 microl SCH-23390 bilaterally) in the vSUB impaired instrumental learning and performance, reduced break point in progressive ratio (PR) tests, and produced an intrasession decline in responding during test sessions, but had no effect on spontaneous motor or food-directed behavior. In contrast, D1 receptor blockade in the dSUB had no effect on instrumental learning, performance, PR break point, or food-directed behavior, but reduced spontaneous motor behavior. These results suggest a dissociation between the vSUB and dSUB with respect to the role of dopamine in various aspects of motivated and motor behavior. Further, D1 activation in the vSUB may be a critical component of motivational arousal associated with learned contextual cues.

NMDA and dopamine interactions in the nucleus accumbens modulate cortical acetylcholine release

The nucleus accumbens (NAC) plays a key role in directing appropriate motor output following the presentation of behaviorally relevant stimuli. As such, we postulate that accumbens efferents also participate in the modulation of neuronal circuits regulating attentional processes directed toward the identification and selection of these stimuli. In this study, N-methyl-d-aspartate (NMDA) and D1 ligands were perfused into the shell region of the NAC of awake rats. Cortical cholinergic transmission, a mediator of attentional processes, was measured via microdialysis probes inserted into the prefrontal cortex (PFC). NMDA perfusions (150 or 250 microm) into NAC resulted in significant increases in acetylcholine (ACh) efflux in PFC (150-200% above baseline levels). Co-administration of the D1 antagonist SCH-23390 (150 microm) markedly attenuated (by approx. 70%) ACh efflux following perfusions of 150 microm NMDA but not following 250 microm NMDA, suggesting that D1 receptor activity contributes to the ability of the lower but not the higher concentration of NMDA to increase cortical ACh release. Collectively, these data reveal a positive modulation of NMDA receptors by D1 receptors in NAC that is expressed trans-synaptically at the level of cortical transmission. This modulation may underlie the coordinated linking of attentional processes and motor output following exposure to salient and behaviorally relevant stimuli.

Opiates, psychostimulants, and adult hippocampal neurogenesis: Insights for addiction and stem cell biology

Once thought to produce global, nonspecific brain injury, drugs of abuse are now known to produce selective neuro-adaptations in particular brain regions. These neuro-adaptations are being closely examined for clues to the development, maintenance, and treatment of addiction. The hippocampus is an area of particular interest, as it is central to many aspects of the addictive process, including relapse to drug taking. A recently appreciated hippocampal neuro-adaptation produced by drugs as diverse as opiates and psychostimulants is decreased neurogenesis in the sub-granular zone (SGZ). While the role of adult-generated neurons is not clear, their functional integration into hippocampal circuitry raises the possibility that decreased adult SGZ neurogenesis may alter hippocampal function in such a way as to maintain addictive behavior or contribute to relapse. Here, we review the impact of opiates and psychostimulants on the different stages of cell development in the adult brain, as well as the different stages of the addictive process. We discuss how examination of drug-induced alterations of adult neurogenesis advances our understanding of the complex mechanisms by which opiates and psychostimulants affect brain function while also opening avenues for novel ways of assessing the functional role of adult-generated neurons. In addition, we highlight key discrepancies in the field and underscore the necessity to move "beyond BrdU"--beyond merely counting new hippocampal cells labeled with the S phase marker bromodeoxyuridine--so as to probe mechanistic questions about how drug-induced alterations in adult hippocampal neurogenesis occur and what the functional ramifications of alterations in neurogenesis are for addiction.

Hippocampal dopamine receptors modulate cFos expression in the rat nucleus accumbens evoked by chemical stimulation of the ventral hippocampus

Recently, we have shown that D1 and D2 receptors in the ventral hippocampus (VH) modulate both the locomotor activation and the increase in dopamine (DA) levels in the rat nucleus accumbens (NAc) induced by NMDA stimulation of the VH. In the present study we analyze the possible role of VH D1 and D2 receptors in the modulation of the cFos expression in NAc (core and shell subregions) and in dorsal striatum. This was assessed by immunohistochemical analysis of cFos expression in the rat brains after retro-dialysis application of NMDA (50mM, 10 min) into VH, in absence and in presence of either the D1/D5 receptor antagonist SCH 23390 (100 and 250 microM, 60 min) or the D2 receptor antagonist raclopride (100 and 250 microM, 60 min). NMDA induced a robust increase in the cFos expression in the NAc shell, both in the ipsilateral and contralateral side. No statistically significant increases were observed in the NAc core and in the dorsal striatum. Simultaneous application of SCH 23390 and NMDA into the VH attenuated the NMDA-evoked cFos expression in NAc shell. In contrast, raclopride had no significant effect. Our present results show that the NMDA receptor mediated effects in the VH require D1 receptors and suggest that DA in VH strongly modulates the excitatory outputs from this brain area.