Activation Of Mesolimbic Dopamine Neurons Research Articles

Stress and dopamine: implications for the pathophysiology of chronic widespread pain

Fibromyalgia has been called a “stress-related disorder” due to the onset and exacerbation of symptoms in the context of stressful events. Evidence suggests that inhibition of tonic pain is mediated by activation of mesolimbic dopamine neurons, arising from the cell bodies of the ventral tegmental area and projecting to the nucleus accumbens. This pain-suppression system is activated by acute stress, via the release of endogenous opioids and substance P within the ventral tegmental area. However, prolonged exposure to unavoidable stress produces both reduction of dopamine output in the nucleus accumbens and development of persistent hyperalgesia. It is proposed that a stress-related reduction of dopaminergic tone within the nucleus accumbens contributes to the development of hyperalgesia in the context of chronic stress and thus plays a role in the pathogenesis of fibromyalgia. A stress-related dysfunction of mesolimbic dopaminergic activity might serve as the basis for other fibromyalgia-associated phenomena as well.

Abused Inhalants and Central Reward Pathways

Inhalant abuse remains a significant health problem among the younger segment of society. In fact, the use of inhalants in this population trails only that of nicotine, alcohol, and marijuana. Toluene is a common ingredient in many of the substances sought out for inhalation abuse, apparently for its euphorigenic and hallucinogenic effects. Because drugs of abuse share the common property of altering the activity of mesolimbic dopamine neurons, it is reasonable to suspect that toluene-induced changes in this CNS pathway may underlie its abuse potential. Here we will provide in vivo and in vitro electrophysiological data and behavioral evidence linking toluene exposure in rats to activation of mesolimbic dopamine neurons. Exposure of rats to 11,000 ppm of inhaled toluene produced time-dependent activation of dopamine neurons within the midbrain ventral tegmental area (VTA). In the rat brain slice preparation, perfusion with toluene (23-822 microM) also evoked an increase in activity of both dopamine and nondopamine neurons within the VTA. These excitatory effects could not be found in adjacent non-VTA nuclei, nor were they sensitive to the glutamate antagonists CGS19755 or CNQX. In behavioral studies, systemic administration of toluene produced a dose-dependent locomotor hyperactivity that was attenuated by either pretreatment with the D2 dopamine receptor antagonist remoxipride or by 6-hydroxydopamine lesions of the nucleus accumbens. These findings show that toluene can activate dopamine neurons within the mesolimbic reward pathway, an effect that may underlie the abuse potential of inhaled substances containing toluene.

Cigarette smoke inhalation stimulates dopaminergic neurons in rats.

In humans, nicotine is self administered by inhalation of tobacco smoke as opposed to animal models, where nicotine is administered via systemic injection. The aim of the present study was to clarify whether tobacco smoke inhalation would affect dopaminergic projections differently from the reported activation after the systemic administration of nicotine. For this purpose, tobacco smoke from cigarettes containing 1.0 or 0.1 mg nicotine was delivered by inhalation to rats, while recording from antidromically identified nigrostriatal and mesolimbic dopamine neurons. Smoke inhalation from 1.0 mg nicotine cigarettes caused a peculiar abrupt increase of discharge activity of mesolimbic dopamine neurons, while nigrostriatal cells were less responsive. This activation was promptly antagonized by mecamylamine (2.0 mg/kg, i.v.). In contrast, smoke delivered from 0.1 mg nicotine cigarettes was ineffective. These findings suggest that the boosting activation of mesolimbic dopamine neurons by inhaled nicotine might be relevant for the rewarding properties of tobacco smoking and also for the effectiveness of new treatments to stop smoking.

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.

SB 242 084, a selective serotonin 2C receptor antagonist, increases dopaminergic transmission in the mesolimbic system

Electrophysiological techniques and in vivo microdialysis were used to investigate the effect of SB 242 084, a potent and selective 5-HT 2C receptor antagonist in the control of nigro-striatal and mesolimbic dopaminergic function. Thus, extracellular single unit recordings were performed from neurochemically-identified dopamine (DA) neurons in the substantia nigra, pars compacta (SNc) and the ventral tegmental area (VTA), as well as monitoring of striatal and accumbal basal DA release in anesthetized rats following the administration of SB 242 084 and RO 60-0175. Administration of SB 242 084 (160–640 μg/kg, i.v.) caused a dose-dependent increase in the basal firing rate of VTA DA neurons, reaching its maximum (27.8±6%, above baseline) after 640 μg/kg. Moreover, bursting activity was significantly enhanced by SB 242 084 in the VTA. On the other hand, SB 242 084 (160–640 μg/kg, i.v.) did not cause any significant change in the basal firing rate and bursting activity of DA neurons in the SNc. Injection of the 5-HT 2C receptor agonist RO 60-0175 (80–320% μg/kg, i.v.) dose-dependently decreased the basal firing of DA neurons in the VTA but not in the SNc. RO 60-0175 exerted its maximal inhibitory effect (53.9±15.1%, below baseline) in the VTA at the dose of 320 μg/kg. Basal DA release (34.8±9%, above baseline) and dihydroxyphenylacetic acid (DOPAC) efflux (19.7±7%, above baseline) were significantly enhanced in the nucleus accumbens following the intraperitoneal administration of 10 mg/kg SB 242 084. Intraperitoneal injection of 5 mg/kg SB 242 084 significantly increased DA release (16.4±6%, above baseline) in the nucleus accumbens, but did not affect DOPAC efflux. In the striatum, SB 242 084 (5 and 10 mg/kg, i.p.) only slightly increased DA release above baseline (3.5±4 and 11.2±6%, respectively), without affecting DOPAC efflux in this area. However, the effect of SB 242 084 in the striatum was rendered more evident by the fact that injection of the vehicle used to dissolve the drug in a group of control rats, significantly reduced basal DA output by 19.6±7%. Stimulation of 5-HT 2C receptors by RO 60-0175 (1 mg/kg, i.p.) significantly decreased DA release in the nucleus accumbens by 26.1±4% (below baseline) 60 min after injection. On the other hand, RO 60-0175 (1 mg/kg, i.p.) did not cause any significant change of DA release in the striatum. However, DOPAC efflux was reduced by RO 60-0175 (1 mg/kg, i.p.) both in the striatum and the nucleus accumbens. Taken together, these data indicate that the central 5-HT system exerts a tonic and phasic inhibitory control on mesolimbic DA neuron activity and that 5-HT 2C receptor subtypes are involved in this effect. Moreover, these findings might open new possibilities for the employment of 5-HT 2C receptor antagonists in the treatment of neuropsychiatric disorders related to a hypofunction of central DA neurons.

Orphanin FQ and Behavioral Sensitization to Cocaine

The recently identified endogenous ligand for the ORL-1 (opioid receptor-like) receptor, orphanin FQ, has been shown to induce hypolocomotion and to decrease extracellular dopamine levels in the nucleus accumbens (N.Acc) after intraventricular (ICV) administration. This study investigated the effect of intraventral tegmental area (VTA) administration of orphanin FQ on the hyperlocomotor effects of peripheral cocaine administration and on the development of behavioral sensitization to cocaine. The administration of cocaine (40 mg/kg IP) once daily for 3 days to male Sprague–Dawley rats resulted in an enhanced locomotor response to a subsequent challenge of cocaine (10 mg/kg IP) 5 days later. The bilateral administration of orphanin FQ (10 μg/side or 30 μg/side) into the VTA 5–10 min prior to the administration of cocaine (40 mg/kg IP) produced a transient (15–30 min) decrease in the hyperlocomotor response to cocaine on day 1 but not on days 2 and 3 of the sensitization paradigm. Such orphanin FQ pretreatment on days 1–3 had no effect on the development of a sensitized response to cocaine (10 mg/kg IP) 5–7 days after the last orphanin FQ injection. However, repeated intra-VTA administration of orphanin FQ (30 μg/side) alone for 3 days resulted in a sensitized response to a single dose of cocaine (10 mg/kg IP) given 5–7 days later. These results indicate that orphanin FQ decreases the activity of mesolimbic dopamine neurons via an action in the VTA, an effect that is both transient and demonstrates rapid tolerance, and consequently, is insufficient to prevent the development of cocaine sensitization. The ability of the peptide to induce cocaine sensitization when administered alone despite its acute inhibitory effects is unique and requires further study to elucidate the mechanisms responsible.

Lasting reduction in mesolimbic dopamine neuronal activity after morphine withdrawal.

The activity of mesolimbic dopaminergic neurons was investigated in rats at various times after a chronic regimen of morphine, which produced, upon suspension, a marked somatic withdrawal syndrome. Single-cell extracellular recording techniques, coupled with antidromic identification from the nucleus accumbens, were used to monitor neuronal activity while behavioural observations allowed quantification of the somatic signs of morphine withdrawal. Temporal correlation of electrophysiological indices, such as firing rate and burst firing, with scores obtained through behavioural assessments proved negative, in that somatic signs were pronounced at 24 h after suspension of treatment and then subsided to control values at 72 h after the last morphine injection. In contrast, the firing rate and burst firing of mesolimbic dopaminergic neurons were found to be reduced at 1, 3 and 7 days after morphine withdrawal. After 14 drug-free days, electrophysiological analysis revealed an apparent normalization of various parameters. However, at this time, intravenous administration of morphine produced an increment of electrical activity which was significantly higher than that obtained in control (saline treated) rats. Further, administration of the opiate antagonist naltrexone, administered without prior morphine, at 3, 7 and 14 days after the last morphine administration, failed to alter dopaminergic neuronal activity. The results indicate: (i) that the activity of mesolimbic dopaminergic neurons remains reduced well after somatic signs of withdrawal have disappeared; (ii) after 14 days of withdrawal, the augmented magnitude of the electrophysiological response to exogenous morphine suggests an increased sensitivity of opiate receptors; and (iii) the lack of relationship between dopaminergic activity and somatic signs of withdrawal corroborates the notion that dopaminergic activity in the mesolimbic system does not participate in the neurobiological mechanisms responsible for somatic withdrawal. The present results may be relevant to the phenomenon of drug addiction in humans and consequent relapse after drug-free periods.

Nicotine activates and desensitizes midbrain dopamine neurons.

Tobacco use in developed countries is estimated to be the single largest cause of premature death. Nicotine is the primary component of tobacco that drives use, and like other addictive drugs, nicotine reinforces self-administration and place preference in animal studies. Midbrain dopamine neurons normally help to shape behaviour by reinforcing biologically rewarding events, but addictive drugs such as cocaine can inappropriately exert a reinforcing influence by acting upon the mesolimbic dopamine system. Here we show that the same concentration of nicotine achieved by smokers activates and desensitizes multiple nicotinic receptors thereby regulating the activity of mesolimbic dopamine neurons. Initial application of nicotine can increase the activity of the dopamine neurons, which could mediate the rewarding aspects of tobacco use. Prolonged exposure to even these low concentrations of nicotine, however, can cause desensitization of the nicotinic receptors, which helps to explain acute tolerance to nicotine's effects. The effects suggest a cellular basis for reports that the first cigarette of the day is the most pleasurable, whereas the effect of subsequent cigarettes may depend on the interplay between activation and desensitization of multiple nicotinic receptors.

N-methyl- d-aspartate receptor antagonism in the ventral tegmental area diminishes the systemic nicotine-induced dopamine release in the nucleus accumbens

Systemic nicotine enhances burst firing of dopamine neurons in the ventral tegmental area and dopamine release in the nucleus accumbens, mainly via stimulation of nicotinic acetylcholine receptors in the ventral tegmental area. Given that both the neuronal activity of mesolimbic dopamine neurons and terminal dopamine release are regulated by excitatory amino acid inputs to the ventral tegmental area and that nicotine facilitates glutamatergic transmission in brain, we investigated the putative role of ionotropic glutamate receptors within the ventral tegmental area for the effects of nicotine on dopamine release in the nucleus accumbens using microdialysis, with one probe implanted in the ventral tegmental area for drug application and another in the ipsilateral nucleus accumbens for measuring dopamine, in awake rats. Systemic nicotine (0.5 mg/kg, s.c.) and infusion of nicotine (1.0 mM) into the ventral tegmental area increased dopamine output in the nucleus accumbens. Intrategmental infusion of α-amino-3-hydroxy-5-methylisoxazole-4-propionate (0.1 mM) or N-methyl- d-aspartate (0.3 mM) increased accumbal dopamine release; these effects were antagonized by concomitant infusion of a selective antagonist at N-methyl- d-aspartate receptors, 2-amino-5-phosphonopentanoic acid (0.3 mM), and non- N-methyl- d-aspartate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (0.3 mM), respectively. Infusion of either antagonist (0.3 or 1.0 mM) into the ventral tegmental area did not affect basal dopamine levels, whereas infusion of 2-amino-5-phosphonopentanoic acid, but not 6-cyano-7-nitroquinoxaline-2,3-dione, starting 40 min before nicotine injection dose-dependently attenuated the nicotine-induced increase in accumbal dopamine release. Concurrent intrategmental infusion of 2-amino-5-phosphonopentanoic acid and nicotine decreased nicotine-induced dopamine release in the nucleus accumbens. These results indicate that the stimulatory action of nicotine on the mesolimbic dopamine system is to a considerable extent mediated via stimulation of N-methyl- d-aspartate receptors within the ventral tegmental area.

Effects of selective activation of dopamine D 2 and D 3 receptors on prolactin secretion and the activity of tuberoinfundibular dopamine neurons

Dopamine agonists with activity at both dopamine D 2 and D 3 receptor subtypes stimulate tuberoinfundibular dopamine neurons and inhibit prolactin secretion from the anterior pituitary. The purpose of the present study was to identify the dopamine receptor subtypes mediating these effects using recently developed selective agonists for dopamine D 2 (PNU-95,666) and D 3 (PD128907) receptors. The activity of tuberoinfundibular dopamine neurons was estimated by measuring either the synthesis (accumulation of 3,4-dihydroxyphenylalanine [DOPA] following inhibition of decarboxylase activity) or metabolism (3,4-dihydroxyphenylacetic acid [DOPAC] concentrations) of dopamine in the median eminence, the region of the hypothalamus containing axon terminals of these neurons. In one experiment, the activity of mesolimbic dopamine neurons was also determined by measuring DOPA accumulation in terminals of these neurons in the nucleus accumbens. Activation of dopamine D 2 receptors with PNU-95,666 caused dose- and time-related increases in DOPAC concentrations in median eminence which were temporally correlated with decreases in plasma prolactin concentrations. Activation of dopamine D 3 receptors with PD128907 decreased DOPA concentrations in the nucleus accumbens, but had no effect on concentrations of DOPAC or DOPA in the median eminence or prolactin in plasma. These results reveal that tuberoinfundibular dopamine neurons are regulated by dopamine D 2 rather than D 3 receptors, and suggest that the ability of mixed dopamine D 2/D 3 receptor agonists to increase the activity of these neurons is mediated by an action at dopamine D 2 receptors. Furthermore, these results confirm that tuberoinfundibular dopamine neurons are not regulated by inhibitory dopamine D 2 or D 3 autoreceptors.

Local muscimol disinhibits mesolimbic dopaminergic activity as examined by brain microdialysis and Fos immunohistochemistry

Infusion of muscimol (5×10 −5 M, 60 min) into the nucleus accumbens (NAC) through a dialysis membrane caused a significant increase in extracellular dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC). Fos-like immunoreactivity induced by intra-NAC infusion of muscimol was seen ipsilaterally in many accumbofugal target areas, but no Fos-positive neurons were seen in the vicinity of the dialysis membrane in the NAC. Sequential staining of Fos and tyrosine hydroxylase (TH) immunoreactivities revealed that a portion of A10 dopaminergic neurons were double-labelled. These results suggest that muscimol in the NAC disinhibits mesolimbic DA neuronal activity possibly through activity of the accumbofugal GABA neuron system.

Δ9-Tetrahydrocannabinol excites rat VTA dopamine neurons through activation of cannabinoid CB1 but not opioid receptors

Behavioral, biochemical and recent electrophysiological data have increasingly implicated the involvement of dopamine in the central actions of cannabinoid compounds. However, the site and mechanism by which cannabinoids stimulate dopamine systems has been somewhat controversial. Central opioid systems have also been suggested to play a role in some cannabinoid-induced behaviors as evidenced by their attenuation in the presence of the opioid antagonist naloxone. However, recent studies using the cannabinoid receptor-selective antagonist SR141716A suggest that the central actions of psychoactive cannabinoids are mediated principally through activation of CB1 receptors. Using single cell electrophysiological recordings in the rat we assessed the effects of both SR141716A and naloxone on Δ 9-tetrahydrocannabinol (THC)-induced activation of ventral tegmental dopamine neurons. While dopamine cell firing was dose-dependently increased following cumulative dosing with Δ 9-THC it was partially or completely inhibited following pretreatment with 0.5 and 2 mg/kg SR14171 6A, respectively. However, 1 and 10 mg/kg naloxone failed to alter the response to Δ 9-THC. These data provide the first evidence that Δ 9-THC-induced changes in mesolimbic dopamine neuronal activity are mediated by the CB1 cannabinoid receptor, but a causal link for the involvement of opioid systems could not be established.

Significant differences in the activity of midbrain dop amine neurons between male fischer 344 (f344) and lewis rats: an in vivo electrophysiological study

There is a significant difference between the Lewis and Fischer 344 rats regarding their propensity to self-administer drugs of abuse. This study compares the number and the firing pattern of spontaneously active dopamine (DA) neurons in the substantia nigra pars compacta (SNC) and ventral tegmental area (VTA) in these two strains of rats. This was accomplished using the technique of in vivo extracellular recording. The number of spontaneously active DA neurons in the SNC and VTA of the Lewis rat were significantly lower compared to that of the F344 rats. Furthermore, a greater percentage of SNC and VTA DA neurons in the Lewis rats exhibited a burst firing pattern compared to F344 rats. These findings indicate that F344 and Lewis rats possess differences in mesolimbic DA neuronal activity and this may be a factor in explaining the different propensities between the two strains to self-administer drugs.

Facilitatory modulation of mesolimbic dopamine neuronal activity by a μ-opioid agonist and nicotine as examined with in vivo microdialysis

Administration of either Tyr- d-Ala-Gly-MePhe-Gly(ol) (DAGO), a μ-opioid agonist, or nicotine into the VTA (A10) caused an increase in both dopamine (DA) and its metabolite levels in both the A10 region and DA nerve terminals in the nucleus accumbens of rats when assessed with dual probe brain dialysis. These findings show that DAGO and nicotine increase both axonal- and somatodendritic-DA release, as well as metabolic activity in mesolimbic DA neurons, possibly by inducing an increase in neuronal impulse flow.

Prefrontal cortex regulates burst firing and transmitter release in rat mesolimbic dopamine neurons studied in vivo

The influence of the medial prefrontal cortex (PFC) on mesolimbic dopamine activity was studied with electrophysiological techniques and in vivo voltammetry in the chloral hydrate-anesthetized male rat. Glutamate injected into the PFC selectively increased burst firing of single dopamine cells in the ventral tegmental area and enhanced the release of dopamine from nerve terminals in the nucleus accumbens. PFC injection of the local anesthetic lidocaine produced the opposite effects on burst firing and terminal release. This selective modulation of the dynamic activity of mesolimbic dopamine neurons by the prefrontal cortex might be important in motivation, learning and schizophrenia.

Increased extracellular dopamine in the nucleus accumbens of the rat elicited by a conditional stimulus for food: an electrochemical study.

Stearate-modified graphite paste electrodes were implanted chronically into dopamine terminal regions in the nucleus accumbens or caudate nucleus of the rat. Reverse dialysis was used to demonstrate a selective response of these electrodes to dopamine, but not 3,4-dihydroxyphenylacetic acid or ascorbic acid. In a separate behavioural experiment, a significant increase in the chronoamperometric response was observed during presentation of a conditional stimulus predictive of food, and the electrochemical response remained elevated during and following consumption of the meal. Similar trends were observed from electrodes in the caudate nucleus. These data confirm the activation of mesolimbic dopamine neurons by incentive stimuli predictive of food and possibly by consumption of food. Together with other recent data on sex- and thirst-related increases in dopamine levels in the nucleus accumbens, these findings are consistent with a role for the nucleus accumbens as an interface between motivation and activation of the motor system.

Effects of competitive [formula omitted] antagonists on midbrain dopamine neurons: An electrophysiological and behavioral comparison to phencyclidine

Electrophysiological and behavioral methods were used to evaluate and compare the effects of the competitive N- methyl- d- aspartate (NMDA) receptor Mocker, NPC 12626, with the non-competitive NMDA antagonist, phencyclidine (PCP), on the activity of mesolimbic dopamine neurons. NPC 12626 (50 mg/kg, i.p.) produced a degree of locomotor hyperactivity comparable to that seen with PCP (5 mg/kg). However, 6-hydroxydopamine lesions of the nucleus accumbens blocked the PCP-induced hyperactivity but not the behavioral activation evoked by NPC 12626. Single-unit extracellular recordings from ventral tegmental A 10 dopamine neurons also found marked differences between the competitive and non-competitive NMDA antagonists. Intravenous injections of NPC 12626 and CGS 19755 in doses up to 60 mg/kg failed to change A 10 activity. This was in contrast to the striking bimodal dose-dependent increase-decrease in firing rate elicited by PCP. The absence of an effect of NPC 12626 on a 10 neurons was not evidently related to a lack of access to central sites since NPC pretreatment (40 mg/kg, i.v.) completely antagonized the neurotoxicity caused by intrastriatal injection of quinolinic acid, an NMDA agonist, but not that caused by the non-NMDA compound, kainic acid. Thus, competitive NMDA antagonists do not share PCP's properties of activating mesolimbic dopaminergic systems, and as such they may be devoid of the potent psychotomimetic effects or the abuse liability associated with non-competitive NMDA receptor Mockers such as PCP.

A comparison of the effects of intra-accumbens injections of amphetamine and morphine on reinstatement of heroin intravenous self-administration behavior

In rats previously trained to self-administer heroin intravenously, the application of morphine directly to the ventral tegmental area (VTA) has been shown to reinstate responding after a period of extinction, suggesting that the activation of mesolimbic dopamine neurons might underlie the priming effects of i.v. injections of opiates and stimulants found previously. In the present experiments rats were trained to self-administer heroin intravenously. Following extinction training, and after a period of at least 30 min of no responding, bilateral microinjections of either 0.5 μl saline or 10 μ/0.5 μl (+)-amphetamine sulfate were made into the N. accumbens. Amphetamine, but not saline reinstated self-administration behavior for about 1 h. In contrast, bilateral intra-accumbens injections of either 5 or 10 μg/ increased locomotor activity measured in independent tests. Because the locomotor activity produced by intra-accumbens morphine occurs independent of the mesolimbic dopamine system, unlike that produced by VTA morphine and intra-accumbens amphetamine, and because it does not show sensitization, it is argued that the reinstatement effects of opiates and stimulants on self-administration behavior are mediated by the mesolimbic dopamine system, and may be related to the ability of opiates and stimulant drugs to cause sensitization within that system.

Role of mesencephalic glycine in locomotor activity

Microinjection of glycine (20 μg) into the ventral mesencephalon of rats caused a stimulation of locomotor activity. Microinjection of haloperidol (5 μg) into the nucleus accumbens immediately before the glycine injection did not reduce this locomotor stimulation. In rats with 6-hydroxydopamine-induced destruction of mesolimbic dopamine (DA) terminals the ability of apomorphine (0.1 mg/kg, s.c.) to stimulate locomotor activity was reduced by microinjection of the glycine antagonist strychnine into the ventral mesencephalon. Increased glycinergic activity in the ventral mesencephalon therefore appears to stimulate locomotor activity by a mechanism other than the activation of mesolimbic DA neurons.

Effect of DN-1417, a thyrotropin releasing hormone analog, on dopaminergic neurons in rat brain

Acute and chronic effects of γ-butyrolactone-γ-carbonyl-histidyl-prolinamide (DN-1417) were investigated on motor activity, dopamine (DA) metabolites and DA receptors in various brain regions of rats. The motor activity, as measured with Automex recorder, was enhanced after a single injection with DN-1417 (20 mg/kg, IP), and the motor stimulating action persisted during 21 daily injections. Acute DN-1417 elevated both homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in 7 brain regions, prefrontal cortex polar, medial and lateral fields, nucleus accumbens, olfactory tubercles, amygdala and striatum. After chronic treatment for 7 days, the acute effect of DN-1417 on DA metabolites disappeared in all regions except for the striatum in which DN-1417 still increased HVA and DOPAC. The response of striatal DA metabolites was also observed after chronic treatment for 21 days. Chronic DN-1417 produced no significant change in 3H-spiperone binding in the prefrontal cortex, nucleus accumbens, olfactory tubercles and striatum, while striatal 3H-DA binding displaced by 30 nM spiperone was enhanced after chronic treatment. These results indicate that DN-1417 interacts with mesocortical, mesolimbic and nigrostriatal DA systems in the different modes of action. The lack of tolerance to motor hyperactivity, however, raises the question as to whether DN-1417-induced hyperactivity may be mediated by the activation of mesolimbic DA neurons. The involvement of nigrostriatal neurons in DN-1417-induced motor hyperactivity is suggested.