NO-synthase dependent increase in citrulline extracellular level in the nucleus accumbens during acquisition and expression of conditioned emotional response

In Sprague-Dawley rats, by means of in vivo microdialysis combined with HPLC analysis, it was shown that acquisition and expression of conditioned emotional response resulted in increase in extracellular level of citrulline: a nitric oxide co-product, in the nucleus accumbens. The rise extracellular citrulline caused by the acquisition of the response was significantly reduced by intraaccumbens infusion of 7-nitroindasole (0.5 mM), a selective inhibitor of neuronal NO-synthase, and completely prevented by intraaccumbens infusion of N-nitroarginine (0.5 mM): a nonselective NO-synthase inhibitor. The increase in citrulline extracellular level cased by expression of the conditioned emotional response is completely prevented by infusion of both NO-synthase inhibitors. The data obtained suggest that the acquisition and the expression of the conditioned emotional response increase the production of nitric oxide in the n. accumbens, predominantly due to activation of the neuronal NO-synthase.     

D1 dopamine receptors regulate citrulline extracellular level in the nucleus accumbens during expression of conditioned fear response

In rats, expression of conditioned fear response increased extracellular level of citrulline in the nucleus accumbens. Infusion of SCH-23390 into the nucleus accumbens exerted no long-term effect on the baseline citrulline level but attenuated the increase in the extracellar citrulline produced by the expression of the response. The data obtained suggest that, during the expression of the conditioned fear response, the dopaminergic input to the n. accumbens might act via D1 receptors to stimulate NO production within this brain area.     

Citrulline extracellular level in the nucleus accumbens during acquisition and extinction of classical conditioned fear response with pain reinforcement

By means of in vivo microdialysis combined with HPLC analysis, we have shown that extracellular levels of citrulline (NO co-product) and arginine (NO precursor) increase in the rat n. accumbens during acquisition and expression of a classical fear response. The conditioned rise of citrulline and arginine levels gradually decreased in the course of extinction. The renewal of the response produced an increase in extracellular citrulline and arginine levels. These data suggest that the acquisition of conditioned fear response causes an increase in NO production in the n. accumbens that weakens during the extinction and is restored during the reinstatement of the response.     

Citrulline extracellular level in the nucleus accumbens during feeding behaviour

In Sprague-Dawley rats, by means of in vivo microdialysis combined with HPLC analysis it was shown that a consumption of a novel food did not produce any changes in extracellular levels ofcitrulline (an NO-co-product) in the medial n. accumbens. In contrast, the rejection of the novel food caused a rise of the extracellular citrulline level in this brain area which can be completely prevented by intra-accumbal infusion of 0.5 mM 7-nitroindazple, a neuronal NO-synthase inhibitor. The data obtained reveal for the first time that new food rejection (but not its consumption) is characterized by neuronal NO-synthase activation and, very likely, NO production in the medial nucleus accumbens.     

The enhancement of glutamate release in the nucleus accumbens of rats with a destroyed hippocampal formation during an emotional conditioned response]

It was shown by means of in vivo microdialysis combined with HPLC/EC analysis that the exocytotoxic lesions of the hippocampal formation impaired the emotional conditioning and led to additional glutamate release in the n. accumbens during acquisition and performance of the conditioned response. Thus, it was shown that the disruption of glutamatergic synaptic transmission in the n. accumbens results in a compensatory increase in the volume glutamatergic transmission in this structure.     

Effects of motivational and emotional factors on glutamate release in the nucleus accumbens of rats during feeding

Food intake was shown to decrease the glutamate extracellular level in the nucleus accumbens in both deprived and non-deprived Spraque-Dawly rats. Feeding combined with presentation of a tone previously paired with foot shock caused an increase in the glutamate extracellular level in deprived rats only, whereas the tone alone had no effect. The data suggest that emotional and motivational variations exert co-operative effect on the glutamate release in the nucleus accumbens during feeding.     

Alimentary conditioned reflex behavior in the rat following injection of 6-hydroxydopamine into the caudate nucleus and nucleus accumbens

In Wistar rats with degenerated dopaminergic terminals of the caudate and accumbens nuclei (administration of 6-hydroxydopamine, 30 mcg, bilaterally), an alimentary conditioned reflex was elaborated in a T-maze. Degeneration of the caudate nucleus terminals disturbed the elaboration, while degeneration of N. accumbens terminals did not affect the learning.     

Sources contributing to the average extracellular concentration of dopamine in the nucleus accumbens

Mesolimbic dopamine neurons fire in both tonic and phasic modes resulting in detectable extracellular levels of dopamine in the nucleus accumbens (NAc). In the past, different techniques have targeted dopamine levels in the NAc to establish a basal concentration. In this study, we used in vivo fast scan cyclic voltammetry (FSCV) in the NAc of awake, freely moving rats. The experiments were primarily designed to capture changes in dopamine caused by phasic firing - that is, the measurement of dopamine 'transients'. These FSCV measurements revealed for the first time that spontaneous dopamine transients constitute a major component of extracellular dopamine levels in the NAc. A series of experiments were designed to probe regulation of extracellular dopamine. Lidocaine was infused into the ventral tegmental area, the site of dopamine cell bodies, to arrest neuronal firing. While there was virtually no instantaneous change in dopamine concentration, longer sampling revealed a decrease in dopamine transients and a time-averaged decrease in the extracellular level. Dopamine transporter inhibition using intravenous GBR12909 injections increased extracellular dopamine levels changing both frequency and size of dopamine transients in the NAc. To further unmask the mechanics governing extracellular dopamine levels we used intravenous injection of the vesicular monoamine transporter (VMAT2) inhibitor, tetrabenazine, to deplete dopamine storage and increase cytoplasmic dopamine in the nerve terminals. Tetrabenazine almost abolished phasic dopamine release but increased extracellular dopamine to ～500?nM, presumably by inducing reverse transport by dopamine transporter (DAT). Taken together, data presented here show that average extracellular dopamine in the NAc is low (20-30?nM) and largely arises from phasic dopamine transients.     

Serotonin-mediated increases in the extracellular levels of beta-endorphin in the arcuate nucleus and nucleus accumbens: a microdialysis study

Although the involvement of both endogenous opioid and serotonergic systems in modulation of pain and emotion was suggested, the neurochemical interaction between these systems in the brain has not previously been studied directly. Herein, the effects of the local application of serotonin (5-HT) and fluoxetine (a 5-HT reuptake inhibitor) on extracellular levels of beta-endorphin in the arcuate nucleus and nucleus accumbens were assessed in freely moving rats using in vivo microdialysis. The mean basal concentrations of beta-endorphin in dialysates obtained from the arcuate nucleus and nucleus accumbens were 259.9 and 143.3 pM, respectively. Specific lesion of the serotonergic system by 5,7-dihydroxytryptamine (5,7-DHT) caused a significant decrease in these dialysate beta-endorphin levels. When 5-HT (0.25-5 microM) was added to the perfusion solution, the levels of beta-endorphin in the dialysate from the arcuate nucleus increased (186-296% of baseline), in a concentration-dependent manner. In the nucleus accumbens, 0.5 and 2 microM 5-HT in the perfusion fluid did not affect the levels of beta-endorphin in the dialysate, whereas 5 and 10 microM 5-HT caused an increase of approximately 190% of baseline. When fluoxetine (250 microM) was present in the perfusing solution, the levels of beta-endorphin in the dialysates from the arcuate nucleus and nucleus accumbens increased two- to threefold. This effect was not obtained in the 5,7-DHT-lesioned rats. Thus, 5-HT, either endogenously or exogenously delivered, appears to facilitate the release of beta-endorphin in the arcuate nucleus and nucleus accumbens. This indication of an interaction between serotonergic and endorphinic systems may be relevant for assessing pain and mood disorder circuits and the mode of action of antidepressant drugs.     

Effect of experimenter-delivered and self-administered cocaine on extracellular beta-endorphin levels in the nucleus accumbens

Beta-endorphin is an endogenous opioid peptide that has been hypothesized to be involved in the behavioral effects of drugs of abuse including psychostimulants. Using microdialysis, we studied the effect of cocaine on extracellular levels of beta-endorphin in the nucleus accumbens, a brain region involved in the reinforcing effects of psychostimulant drugs. Experimenter-delivered cocaine (2 mg/kg, i.v.) increased extracellular beta-endorphin immunoreactive levels in the nucleus accumbens, an effect attenuated by 6-hydroxy-dopamine lesions or systemic administration of the D1-like receptor antagonist, SCH-23390 (0.25 mg/kg, i.p.). The effect of cocaine on beta-endorphin release in the nucleus accumbens was mimicked by a local perfusion of dopamine (5 microm) and was blocked by coadministration of SCH-23390 (10 microm). Self-administered cocaine (1 mg/kg/infusion, i.v.) also increased extracellular beta-endorphin levels in the nucleus accumbens. In addition, using functional magnetic resonance imaging, we found that cocaine (1 mg/kg, i.v.) increases regional brain activity in the nucleus accumbens and arcuate nucleus. We demonstrate an increase in beta-endorphin release in the nucleus accumbens following experimenter-delivered and self-administered cocaine mediated by the local dopaminergic system. These findings suggest that activation of the beta-endorphin neurons within the arcuate nucleus-nucleus accumbens pathway may be important in the neurobiological mechanisms underlying the behavioral effects of cocaine.     

Fluctuations in nucleus accumbens extracellular glutamate and glucose during motivated glucose‐drinking behavior: dissecting the neurochemistry of reward

While motivated behavior involves multiple neurochemical systems, few studies have focused on the role of glutamate, the brain's excitatory neurotransmitter, and glucose, the energetic substrate of neural activity in reward‐related neural processes. Here, we used high‐speed amperometry with enzyme‐based substrate‐sensitive and control, enzyme‐free biosensors to examine second‐scale fluctuations in the extracellular levels of these substances in the nucleus accumbens shell during glucose‐drinking behavior in trained rats. Glutamate rose rapidly after the presentation of a glucose‐containing cup and before the initiation of drinking (reward seeking), decreased more slowly to levels below baseline during consumption (sensory reward), and returned to baseline when the ingested glucose reached the brain (metabolic reward). When water was substituted for glucose, glutamate rapidly increased with cup presentation and in contrast to glucose drinking, increased above baseline after rats tasted the water and refused to drink further. Therefore, extracellular glutamate show distinct changes associated with key events of motivated drinking behavior and opposite dynamics during sensory and metabolic components of reward. In contrast to glutamate, glucose increased at each stimulus and behavioral event, showing a sustained elevation during the entire behavior and a robust post‐ingestion rise that correlated with the gradual return of glutamate levels to their baseline. By comparing active drinking with passive intra‐gastric glucose delivery, we revealed that fluctuations in extracellular glucose are highly dynamic, reflecting a balance between rapid delivery because of neural activity, intense metabolism, and the influence of ingested glucose reaching the brain.

     

Food reward and cocaine increase extracellular dopamine in the nucleus accumbens as measured by microdialysis

Dopamine was measured by microdialysis in the nucleus accumbens of freely moving rats while they experienced rewarding food, brain stimulation and drugs. Extracellular dopamine increased 37% when the animals pressed a lever for food reward. Electrical stimulation of a lateral hypothalamic feeding-reward (self-stimulation) site caused a similar increase in dopamine, with or without food. At the site in the nucleus accumbens where rats will administer amphetamine to themselves, injections of amphetamine or cocaine increased extracellular dopamine five-fold. Thus amphetamine and cocaine increase dopamine in a behavior reinforcement system which is normally activated by eating. Conversely, the release of dopamine by eating could be a factor in addiction to food.     

D(3) receptor ligands modulate extracellular dopamine clearance in the nucleus accumbens

An involvement of the D(3) dopamine receptor in the regulation of extracellular dopamine has been suggested. However, the mechanisms mediating this effect are unclear. We have used the technique of no net flux microdialysis under transient conditions to examine the influence of the D(3) -preferring agonist (+)-PD128907 upon extracellular dopamine levels in the nucleus accumbens of the mouse. (+)-PD 128907 (0.1 mg/kg intraperitoneally) significantly decreased extracellular dopamine. This decrease was associated with a marked increase in the extraction fraction, which suggests an increase in dopamine clearance. The ability of D(3) -preferring compounds to modulate dopamine uptake was investigated in vitro using rotating disk electrode voltammetry. (+)-PD 128907 (10 nm) significantly increased the initial clearance rate of 3 microm dopamine in rat nucleus accumbens tissue suspensions. Kinetic analysis revealed no change in the apparent K (m) of uptake but it showed a 33% increase in V (max). In contrast, the D(3) antagonist GR 103691 (10 nm) significantly decreased dopamine uptake. Consistent with the low levels of D(3) receptors in the dorsal striatum, neither compound affected uptake in tissue suspensions from this brain region. These data indicate that D(3) receptor activation increases dopamine uptake in the nucleus accumbens and suggest that this receptor subtype can regulate extracellular dopamine by modulating the DA transporter activity.     

Dynamics of the level of extracellular dopamine in the rat brain during formation of conditioned fear and acoustic startle habituation

The content of extracellular dopamine (DA) was estimated in dorsal striatum (DS), nucleus accumbens (Nac), and prefrontal cortex (Pfc) of rat brain during two sessions of acoustic startle habituation consisting of 10 trials each with 24-hour intersession and 20-s intertrial intervals. Startle amplitude and freezing behavior were recorded. A decrease in the content of extracellular DA in the DS and an increase in the DA content in Nac were observed during both sessions of habituation with return to a baseline level immediately after termination of the sessions. During the second session, the startle amplitude and change in the DA content in both structures were much lower than during the first session. During the first session, the DA level in DS remained unchanged but dropped in Nac. In the Pfc the DA level increased during both habituation sessions and in the period between the session. Time of freezing prior to acoustic stimulation in the second sessions (that is known to be an indication of conditioned fear) correlated with the DA level in DS on the day of training and with the DA level in Nac just before the beginning of the second session. The role of the dopaminergic system in formation and retrieval of different components of defensive behavior is discussed.     

Effect of blocking of glutamatergic inputs to the striatum on regulation of extracellular dopamine level in the striatum by theN. accumbens

Investigation on awake rats of the Sprague-Dawley line, involving intrabrain dialysis in combination with radioenzymatic analysis of dopamine level, demonstrated that intrastriatal applications by the dialysis perfusion of diethyl glutamate (0.1 mM), a wide spectrum-action blocker of excitatory amino acid receptors, prevents, whereas applications of D,L-2-amino-5-phosphonovaleric acid or kinurenate, blockers of N-methyl-D-aspartate (NMDA) receptors (in the same concentrations), do not prevent an increase in the dopamine level in the extracellular space of the dorsal striatum, caused by application of haloperidol (1.0 mM) to then. accumbens.The findings lead to the assumption that participation of the glutamatergic inputs to the straitum in the transmission of tonic inhibitory effects of then. accumbens to the striatal dopaminergic system is mediated by non-NMDA type receptors.Neirofiziologiya/Neurophysiology, Vol. 25, No. 4, pp. 302–306, July–August, 1993.     

Changes in microRNA expression profile in hippocampus during the acquisition and extinction of cocaine-induced conditioned place preference in rats

Background

MicroRNA (miRNA) emerges as important player in drug abuse. Yet, their expression profile in neurological disorder of cocaine abuse has not been well characterized. Here, we explored the changes of miRNA expression in rat hippocampus following repeated cocaine exposure and subsequent abstinence from cocaine treatment.

Results

Conditioned place preference (CPP) procedure was used to assess the acquisition and extinction of cocaine-seeking behavior in rats. MiRNA microarray was performed to examine miRNAs levels in rat hippocampus. Quantitative RT-PCR was conducted to further confirm results in microarray study. Finally, bioinformatic predictions were made to suggest potential target genes of cocaine-responsive miRNA in this study. MiRNA array found that 34 miRNA levels were changed in rat hippocampus while acquiring cocaine CPP and 42 miRNAs levels were altered after the cocaine-induced CPP were extinguished, as compared to normal controls. The findings from qRT-PCR study support results from microarray analysis.

Conclusions

The current study demonstrated dynamic changes in miRNA expression in rat hippocampus during the acquisition and extinction of cocaine-induced CPP. Some miRNAs which have been previously reported to be involved in brain disorders and drug abuse, including miR-133b, miR-134, miR-181c, miR-191, miR-22, miR-26b, miR-382, miR-409-3p and miR-504, were found to be changed in their expression following repeated cocaine exposure and subsequent abstinence from cocaine treatment. These findings may extend our understanding of the regulatory network underlying cocaine abuse and may provide new targets for the future treatment of drug abuse.     

β-Lactam antibiotic produces a sustained reduction in extracellular glutamate in the nucleus accumbens of rats

We investigated the short- and long-term effects of ceftriaxone on glutamate transporter subtype 1 (GLT-1) transporter activity and extracellular glutamate in the rat nucleus accumbens. Repeated ceftriaxone administration (50, 100 or 200 mg/kg, i.p.) produced a dose-dependent reduction in glutamate levels that persisted for 20 days following discontinuation of drug exposure. The ceftriaxone effect was prevented by the GLT-1 transporter inhibitor dihydrokainate (1 μM, intra-accumbal). These results suggest that β-lactam antibiotics produce an enduring reduction in glutamatergic transmission in the brain reward center.     

Changes in gene expression within the nucleus accumbens and striatum following sexual experience

Sexual experience, like repeated drug use, produces long-term changes including sensitization in the nucleus accumbens and dorsal striatum. To better understand the molecular mechanisms underlying the neuroadaptations following sexual experience, we employed a DNA microarray approach to identify genes differentially expressed between sexually experienced and sexually naive female hamsters within the nucleus accumbens and dorsal striatum. For 6 weeks, a stimulus male was placed in the home cage of one-half of the hormonally primed, ovariectomized female hamsters. On the seventh week, the two experimental groups were subdivided, with one half paired with a stimulus male. In comparison with sexually naive animals, sexually experienced hamsters receiving a stimulus male on week 7 exhibited an increase in a large number of genes. Conversely, sexually experienced female hamsters not receiving a stimulus male on week 7 exhibited a reduction in the expression of many genes. For directional changes and the categories of genes regulated by the experimental conditions, data were consistent across the nucleus accumbens and dorsal striatum. However, the specific genes exhibiting changes in expression were disparate. These experiments, among the first to profile genes regulated by female sexual behavior, will provide insight into the mechanisms by which both motivated behaviors and drugs of abuse induce long-term changes in the mesolimbic and nigrostriatal dopamine pathways.     

Dopamine-dependent inhibition of glycine release in the rat nucleus accumbens during feeding

Food intake decreased the glycine extracellular level in the rat n.accumbens. Tetrodotoxin prevented the decrease, whereas D,L-threo-beta-hydroxyaspartic acid exerted no effect. Raclopride (D2 dopamine receptor antagonist) increased the glycine extracellular level in food intake. The data obtained suggest that during feeding the glycine release in the n.accumbens is controlled by the D2 dopamine receptors.     

Intermittent administration of morphine alters protein expression in rat nucleus accumbens

Repeated exposure to drugs of abuse causes time-dependent neuroadaptive changes in the mesocorticolimbic system of the brain that are considered to underlie the expression of major behavioral characteristics of drug addiction. We used a 2-D gel-based proteomics approach to examine morphine-induced temporal changes in protein expression and/or PTM in the nucleus accumbens (NAc) of morphine-sensitized rats. Rats were pretreated with saline [1 mL/kg subcutaneously (s.c.)] or morphine (10 mg/kg, s.c.) once daily for 14 days and the animals were decapitated 1 day later. The NAc was extracted and proteins resolved by 2-DE. Several protein functional groups were found to be regulated in the morphine-treated group, representing cytoskeletal proteins, proteins involved in neurotransmission, enzymes involved in energy metabolism and protein degradation, and a protein that regulates translation.