A study of the effects of buspirone, BMY 13805, and 1-PP on dopaminergic metabolism in the nucleus accumbens using in vivo voltammetry in freely moving rats

The effects of buspirone, a buspirone analogue (BMY 13805) and a buspirone metabolite (1-PP) on dopaminergic metabolism in the nucleus accumbens were investigated using in vivo voltammetry. Differential pulse voltammetry coupled with electrochemically pretreated carbon fiber electrodes was used to provide a continuous and selective measure of the 3,4-dihydroxyphenylacetic acid (DOPAC). An implanted micromanipulator enabled the use of freely moving animals. Buspirone injections induced a marked and rapid increase of the DOPAC peak in the nucleus accumbens. Buspirone was 10 times more potent when injected subcutaneously than intraperitoneally. BMY 13805 and 1-PP were without effect on dopaminergic metabolism in the nucleus accumbens. In conclusion, the anxiolytic properties of these drugs and their effects on dopaminergic metabolism do not appear related.     

Regionally and functionally distinct serotonin3 receptors control in vivo dopamine outflow in the rat nucleus accumbens

Central serotonin(3) (5-HT(3)) receptors control the mesoaccumbens dopamine (DA) pathway. This control is thought to be conditional and might involve regionally distinct subpopulations of 5-HT(3) receptors. Here, using in vivo microdialysis in rats, we assessed the relative contribution of nucleus accumbens (Nacc) 5-HT(3) receptors to the overall influence exerted by 5-HT(3) receptors on accumbal DA release induced by different drugs or treatments. In freely moving rats, pre-treatment with 5-HT(3) antagonists (0.1 mg/kg ondansetron and/or 0.03 mg/kg MDL 72222, s.c.) reduced DA efflux enhanced by morphine (1-10 mg/kg, s.c.) and haloperidol (0.01 mg/kg, s.c.), but not amphetamine (1-2.5 mg/kg, i.p.) or cocaine (10-20 mg/kg, i.p.), the latter two drugs do not trigger depolarization-stimulated DA exocytosis. Intra-Nacc administration of ondansetron (1 microm) in freely moving rats reduced the DA effects elicited by 10 mg/kg morphine, but not 1 mg/kg morphine or haloperidol. The 5-HT(1A) agonist 8-OH-DPAT (0.1 mg/kg, s.c.), known to decrease central 5-HT tone, reduced 10 but not 1 mg/kg morphine-stimulated DA outflow in freely moving rats. In halothane-anaesthetized rats, intra-Nacc ondansetron (1 microm) application reduced dorsal raphe nucleus electrical stimulation (20Hz)-induced DA outflow. Our results show that regionally distinct populations of 5-HT(3) receptors control the depolarization-dependent exocytosis of DA and suggest that the involvement of Nacc 5-HT(3) receptors occurs only when central DA and 5-HT tones are concomitantly increased.     

Effect of stress and ACTH on dopamine metabolism in the nucleus accumbens and frontal cortex

The effect of ACTH and electric foot shock stress on DOPAC content were determined in the frontal cortex and nucleus accumbens. Twenty min of stress enhanced DOPAC levels in the frontal cortex and in the nucleus accumbens by about 80% and 35%, respectively. On the other hand, a single dose of ACTH failed to change DOPAC concentration in the above brain areas. The present results show that the activation of mesolimbic and mesocortical dopaminergic systems is not mediated by ACTH secretion.     

The role of dopamine in the nucleus accumbens in analgesia

Opioid and psychostimulant drugs have long been used for the relief of chronic pain in the clinical situation. Animal studies confirm that these drugs alleviate persistent or tonic pain. Little is known, however, about the neural systems underlying the suppression of tonic pain except that they are different from those mediating the suppression of phasic (i.e., sharp and short-lasting) pain. Although spinal and brainstem-descending pain suppression mechanisms play a role in mediating the inhibition of tonic pain, it appears that this response is additionally mediated by the activation of mechanisms lying rostral to the brainstem. Recent studies suggest that the activation of mesolimbic dopamine (DA) neurons, arising from the cell bodies of the ventral tegmental area (VTA) and projecting to the nucleus accumbens (NAcc), plays an important role in mediating the suppression of tonic pain. Other studies suggest that this pain-suppression system involving the activation of mesolimbic DA neurons is naturally triggered by exposure to stress, through the endogenous release of opioids and substance P (SP) in the midbrain.     

Regulation of nucleus accumbens dopamine release by the dorsal raphe nucleus in the rat

The effects of microinfusingl-glutamate, serotonin (5-HT), (±)-8-hydroxy-2-(di-N-propylamino) tetralin (8-OH DPAT; a 5-HT_1A agonist), and muscimol (a GABA_A agonist) into the dorsal raphe nucleus on the extracellular levels of 5-HT, dopamine (DA) and their metabolites in the nucleus accumbens were studied in unanesthetized, freely moving, adult male Wistar rats, using the technique of microdialysis coupled with small-bore HPLC. Administration of 0.75 gl-glutamate produced a 25–50% increase (P<0.05) in the extracellular levels of both 5-HT and DA. On the other hand, infusion of 8-OH DPAT and, to a lesser extent, 5-HT produced a significant (P<0.05) decrease in the extracellular levels of both 5-HT and DA. Muscimol (0.25 or 0.50 g) had little effect on the extracellular concentrations of 5-HT or DA following its administration. In general, the extracellular levels of the major metabolites of 5-HT and DA in the nucleus accumbens were not altered by microinfusion of any of the agents. The data indicate that (a) the 5-HT neurons projecting to the nucleus accumbens from the dorsal raphe nucleus can be activated by excitatory amino acid receptors and inhibited by stimulation of 5-HT_1A autoreceptors, and (b) the dorsal raphe nucleus 5-HT neuronal system may regulate the ventral tegmental area DA projection to the nucleus accumbens.Special issue dedicated to Dr. Morris H. Aprison     

In vivo regulation of dopamine and noradrenaline release by alpha2A-adrenoceptors in the mouse nucleus accumbens

The present study investigated the role of alpha2A-adrenoceptor (alpha2A-AR) subtype in the regulation of noradrenaline (NA) and dopamine (DA) release in the nucleus accumbens (NAc). The effect of locally infused and systemically injected alpha2-AR agonist, dexmedetomidine (DMT), and alpha2-AR antagonist, atipamezole, on NA and DA release was investigated in alpha2A-AR knockout and control mice by using in vivo microdialysis. In addition, we compared the drug effects on DA and NA release in the NAc to their effect on locomotor activity. Baseline NA and DA concentrations did not differ between genotypes. Local infusion of DMT decreased, in a concentration-dependent manner, NA, but not DA, levels in the control mice. However, systemic injection of DMT decreased both NA and DA levels in the control mice. In both cases DMT had no effects on transmitter release in alpha2A-AR knockout mice. Our results suggest that alpha2-ARs regulate the release of NA, but not DA, at the terminal level in the NAc. However, alpha2-ARs regulate DA release in the NAc indirectly by their effect on DA neurones in the ventral tegmental area via an unknown mechanism. In both cases the regulation is mediated by alpha2A-adrenoceptor subtype. Also the modulation of locomotor activity by alpha2-AR agonist and antagonist seems to be mediated via alpha2A-adrenoceptors.     

Lack of effect of chronic desipramine treatment on dopaminergic activity in the nucleus accumbens of the rat

The binding of [³H]SCH 23390 to dopamine (DA) D₁-receptors was measured in the nucleus accumbens of rats treated chronically with desipramine for 14 days. DA D₁ — and D₂-receptor binding using [³H]SCH 23390 and [³H]spiperone, respectively as ligands, was determined in rats treated for 28 days. NeitherB _max norK _d values were influenced by chronic desipramine treatment. In addition, chronic desipramine treatment (28 days) did not influence the dose dependent, quinpirole (10–1000 nM)-mediated inhibition of the electrically stimulated release of [³H]DA and [¹⁴C]ACh from nucleus accumbens slices or the dose dependent increase in [³H]DA release and decrease in [¹⁴C]ACh release in the presence of 1 and 10 M nomifensine. Therefore, our results suggest that the effect of chronic antidepressant treatment cannot be attributed to changes in either DA D₁₁-or D₂-receptor binding or DA D₂-receptor function in the nucleus accumbens.     

In vivo evidence that genetic background controls impulse-dependent dopamine release induced by amphetamine in the nucleus accumbens

Amphetamine is known to increase dopamine (DA) release by acting directly on dopamine transporters (DAT), primarily through a mechanism that is independent of impulse flow. We present evidence to show that impulse-dependent increase in DA outflow in the nucleus accumbens (NAc) is produced by amphetamine depending on genetic background. Systemic amphetamine produced higher accumbal DA release in the widely exploited C57BL/6J background than in the DBA/2J. By contrast, intra-accumbens perfusion using increasing doses of amphetamine dramatically increased DA outflow in the DBA/2J background, whereas very low DA outflow was evident in C57BL/6J mice. The fast sodium channel blocker tetrodotoxin infused through the microdialysis probe abolished accumbal DA release induced by systemic amphetamine only in the C57BL/6J background. Finally, medial prefrontal excitotoxic lesion abolished amphetamine-induced mesoaccumbens DA release in C57BL/6J mice, without significantly affecting it in the DBA/2J background. These results represent the first functional evidence in an in vivo study that amphetamine can increase DA release in the NAc mainly through an impulse-dependent mechanism regulated by prefronto-cortical glutamatergic transmission. Moreover, they point to a genetic control of impulse-dependent DA release in the accumbens, providing an exploitable tool to investigate aetiological factors involved in psychopathology and drug addiction.     

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.     

Role of the presynaptic receptors in the control of dopamine synthesis in the striate complex and nucleus accumbens

The role of presynaptic receptors on dopamine synthesis, at both nigrostriatal and mesolimbic systems, has been studied after dopamine uptake drastically increases the dopamine and DOPAC levels at n. accumbens but not at striatum. The present data suggest that presynaptic receptors are a decisive factor regulating dopamine synthesis at nigrostriatal system. However, the end-product inhibition could be the most important autoregulatory mechanism at the mesolimbic system.     

The effects of haloperidol and amphetamine on ascorbic acid and uric acid in caudate and nucleus accumbens of rats as measured by voltammetry in vivo

The ability of haloperidol (0.1 mg/kg) to reduce the amphetamine-induced (2 and 5 mg/kg) increase in ascorbic and uric acid in anterior caudate and in nucleus accumbens was tested using voltammetry in vivo. In both areas, haloperidol reduced the amphetamine-induced increase in uric acid. In both areas, haloperidol only marginally affected the amphetamine-induced increase in ascorbic acid. Amphetamine-induced increases in uric acid were more nearly dose-related than changes in ascorbic acid. Of the two compounds, uric acid seems more likely to be associated with dopamine.     

Cumulative effect of norepinephrine and dopamine carrier blockade on extracellular dopamine increase in the nucleus accumbens shell, bed nucleus of stria terminalis and prefrontal cortex

We investigated, by microdialysis in various brain areas, the possibility that dopamine could be captured by the norepinephrine transporter when the dopamine transporter is pharmacologically blocked. Administration of reboxetine, a selective blocker of the norepinephrine transporter, 20 min after the administration of GBR 12909, a selective blocker of the dopamine transporter, produced an increase of dopamine output in the nucleus accumbes shell (+408% above basal) greater than that obtained by GBR 12909 alone (+308% above basal). On the contrary, reboxetine did not increase further the dopamine output produced by GBR 12909 in the nucleus accumbens core or in the dorsal caudate, areas lacking a consistent noradrenergic innervations. A cumulative effect of dopamine and norepinephrine transporter blockade on the output of dopamine in dialysates was also observed in the bed nucleus of stria terminalis and in the prefrontal cortex. This study shows that dopamine extracellular concentration can be elevated by norepinephrine transporter blockade, even in areas where the dopamine transporter is predominant, when the latter is pharmacologically blocked. This phenomenon may have relevance in psychostimulant dependence as well as in antidepressant pharmacology.     

Nociceptin differentially affects morphine-induced dopamine release from the nucleus accumbens and nucleus caudate in rats

The effects induced by nociceptin on morphine-induced release of dopamine (DA), 3,4-dihydroxyphenilacetic acid (DOPAC) and homovanillic acid (HVA) in the nucleus accumbens and nucleus caudate were studied in rats by microdialysis with electrochemical detection. Nociceptin administered intracerebroventricularly (i.c.v.) at doses of 2, 5 and 10 nmol/rat changed neither DA nor metabolites release in the shell of the nucleus accumbens or in the nucleus caudate. Morphine administered intraperitoneally (i.p.) (2, 5, and 10 mg/kg) increased DA and metabolites release more in the shell of the nucleus accumbens than in the nucleus caudate. When nociceptin (5 or 10 nmol) was administered 15 min before morphine (5 or 10 mg/kg), it significantly reduced morphine-induced DA and metabolites release in the shell of the nucleus accumbens, whereas only a slight, nonsignificant reduction was observed in the nucleus caudate. Our data indicate that nociceptin may regulate the stimulating action associated with morphine-induced DA release more in the nucleus accumbens than in the nucleus caudate, and are consistent with recent observations that nociceptin reversed ethanol- and morphine-induced conditioned place preference. Therefore, the nociceptin-induced reduction of DA release stimulated by morphine in the nucleus accumbens, and the results obtained with nociceptin in the conditioned place preference procedure suggest a role for nociceptin in the modulation of the behavioral and neurochemical effects of abuse drugs.     

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.     

Influence of cholecystokinin on the synaptosomal dopamine uptake in the nucleus accumbens of rats

The influence of the sulfated cholecystokinin octapeptide (CCK-8S) on the synaptosomal high-affinity [³H]dopamine (DA) uptake was investigated in the medial and lateral part of nucleus accumbens in rats. CCK-8S induced a concentration-dependent biphasic inhibition of [³H]-DA uptake in both subregions. After preincubation of CCK-8S with the synaptosomes the inhibitory effect was completely abolished. Kinetic analysis of the uptake influence suggests an uncompetitive inhibition by CCK-8S; this means that CCK-8S attacks only the DA-uptake carrier complex by inhibitory manner. The possible regulatory relevance of this mechanism is discussed.     

Cholecystokinin/dopamine/GABA interactions in the nucleus accumbens: biochemical and functional correlates.

The present article reviews our recent biochemical and microdialysis studies showing the evidence for an antagonistic CCK(B)/D(2) receptor interaction in the regulation of dopaminergic transmission in the nucleus accumbens and GABAergic transmission in the ipsilateral ventral pallidum. Since the nucleus accumbens plays a crucial role in regulating the output from the limbic system and consequently motivation, it may be speculated that a dysregulation of this receptor interaction may have consequences in a wide range of central nervous system disorders.     

Effects of cholecystokinin peptides and neurotensin on dopamine release and metabolism in the rostral and caudal part of the nucleus accumbens using intracerebral dialysis in the anaesthetized rat

By means of intracerebral microdialysis effects of cholecystokinin peptides and neurotensin administered via the microdialysis probe have been studied on dopamine release and metabolism in the nucleus accumbens and neostriatum of the halothane anaesthetized male rat. Levels of extra cellular dopamine (DA) and its metabolites 3,4 dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were assessed in nuc. accumbens (rostral and caudal part) using high performance liquid chromatography in combination with electrochemical detection.

(1) In the rostral part of the nuc. accumbens CCK-8 (10 and 100 μM), CCK-33 (100 μM) but not CCK-4 (10 and 100 μM) increased the levels of DA in the perfusate without increasing the extracellular levels of DOPAC and HVA. (2) In the caudal nuc. accumbens CCK-8 and CCK-4 in concentrations of 10 μM and 100 μ M of CCK-33 had no effect on DA release and metabolism, since the extracellular levels of DA, DOPAC and HVA were not changed. (3) In the rostral nuc. accumbens perfusion with 10 μM of neurotensin but not with any other concentration of neurotensin (0.01, 0.1, 1 and 100 μM) increased the levels of DA in the extracellular fluid. (4) In the caudal nuc. accumbens a 40 min perfusion with neutrotensin produced a concentration dependent increase of the levels of DA in the perfusate (peak action at 10 μ M) which in this case was associated with increases in the extracellular levels of DOPAC and HVA. (5) By means of receptor autoradiography using (3-[¹²⁵I]iodotyrosyl³) neurotensin it was found that a 40 min perfusion with this radioligand in the rostral nuc. accumbens reached a total volume of 0.051 mm³. The diffusion of the radioligand was limited to the rostral or caudal part of the nuc. accumbens depending upon the site of placement of the dialysis probe.

The results indicate the existence of cholecystokinin (CCK) receptors in the rostral nuc. accumbens, which are sensitive to CCK-8 and CCK-33 but not to CCK-4, and which facilitate DA release without producing any detectable increase in DA metabolites. In contrast, such receptors do not appear to play a similar role in the regulation of DA release in the caudal nuc. accumbens, where DA terminals contain CCK-like immunoreactivity. Furthermore, the results indicate that neurotensin receptors exist both in the rostral and caudal nuc. accumbens, where they inter alia enhance the release of DA. In the caudal nuc. accumbens these effects of neurotensin are also associated with an increase of DA metabolites, possibly suggesting that in this region neurotensin receptors may also control DA synthesis.     

Orexin-A up-regulates dopamine D2 receptor and mRNA in the nucleus accumbens Shell

Molecular Biology Reports - Orexins-A (OrxA) and -B (OrxB) neuropeptides are synthesized by a group of neurons located in the lateral hypothalamus and adjacent perifornical area, which send their...     

Phencyclidine (PCP) injected in the nucleus accumbens increases extracellular dopamine and serotonin as measured by microdialysis

Phencyclidine (PCP; 20 micrograms in 0.5 microliter) was tested by local brain injection for neurochemical effects in the nucleus accumbens and striatum of rats. Changes in dopamine turnover could not be detected in postmortem tissue assays. In contrast, extracellular levels of dopamine significantly increased as measured by microdialysis in freely moving animals. PCP also increased extracellular levels of serotonin and decreased 3,4-dihydroxyphenylacetic acid (DOPAC), but did not change homovanillic acid (HVA) or 5-hydroxyindoleacetic acid (5HIAA). Microdialysis suggests that PCP acts in some dopamine terminal regions to increase extracellular dopamine and serotonin.     

Asymmetry in the dopamine content in the nucleus accumbens and the motor preference in rats

A number of published studies reported a correlation between the paw preference in mice and asymmetry of tissue concentrations of dopamine (DA) and DA metabolites measured in the nucleus accumbens (NAcb) the DA concentration being higher in the nucleus ipsylateral to a preferred paw. This study aimed to investigate whether such asymmetry existed in rats. The paw preference was defined by reaching into a small horizontal tube for a food pellet. Tissue concentration of DA was measured by high-performance liquid chromatography with electrochemical detection. It was shown that the DA concentration in the left NAcb was significantly higher in "left-handed" rats than in "right-handed" animals. Within the group of "right-handers", the DA concentration was significantly higher in the right NAcb than in the left NAcb. The results confirm in part the experimental data obtained in mice and support the hypothesis that the paw preference is paralleled by elevated tissue DA in the ipsylateral NAcb of rodents.