Contralateral turning elicited by unilateral stimulation of dopamine D2 and D1 receptors in the nucleus accumbens of rats is due to stimulation of these receptors in the shell, but not the core, of this nucleus

Emotion in action: When emotions meet motor circuits

The brain is a remarkably complex organ responsible for a wide range of functions, including the modulation of emotional states and movement. Neuronal circuits are believed to play a crucial role in integrating sensory, cognitive, and emotional information to ultimately guide motor behavior. Over the years, numerous studies employing diverse techniques such as electrophysiology, imaging, and optogenetics have revealed a complex network of neural circuits involved in the regulation of emotional or motor processes. Emotions can exert a substantial influence on motor performance, encompassing both everyday activities and pathological conditions. The aim of this review is to explore how emotional states can shape movements by connecting the neural circuits for emotional processing to motor neural circuits. We first provide a comprehensive overview of the impact of different emotional states on motor control in humans and rodents. In line with behavioral studies, we set out to identify emotion-related structures capable of modulating motor output, behaviorally and anatomically. Neuronal circuits involved in emotional processing are extensively connected to the motor system. These circuits can drive emotional behavior, essential for survival, but can also continuously shape ongoing movement. In summary, the investigation of the intricate relationship between emotion and movement offers valuable insights into human behavior, including opportunities to enhance performance, and holds promise for improving mental and physical health. This review integrates findings from multiple scientific approaches, including anatomical tracing, circuit-based dissection, and behavioral studies, conducted in both animal and human subjects. By incorporating these different methodologies, we aim to present a comprehensive overview of the current understanding of the emotional modulation of movement in both physiological and pathological conditions.

Lateral preoptic and ventral pallidal roles in locomotion and other movements

The lateral preoptic area (LPO) and ventral pallidum (VP) are structurally and functionally distinct territories in the subcommissural basal forebrain. It was recently shown that unilateral infusion of the GABAA receptor antagonist, bicuculline, into the LPO strongly invigorates exploratory locomotion, whereas bicuculline infused unilaterally into the VP has a negligible locomotor effect, but when infused bilaterally, produces vigorous, abnormal pivoting and gnawing movements and compulsive ingestion. This study was done to further characterize these responses. We observed that bilateral LPO infusions of bicuculline activate exploratory locomotion only slightly more potently than unilateral infusions and that unilateral and bilateral LPO injections of the GABAA receptor agonist muscimol potently suppress basal locomotion, but only modestly inhibit locomotion invigorated by amphetamine. In contrast, unilateral infusions of muscimol into the VP affect basal and amphetamine-elicited locomotion negligibly, but bilateral VP muscimol infusions profoundly suppress both. Locomotor activation elicited from the LPO by bicuculline was inhibited modestly and profoundly by blockade of dopamine D2 and D1 receptors, respectively, but was not entirely abolished even under combined blockade of dopamine D1 and D2 receptors. That is, infusing the LPO with bic caused instances of near normal, even if sporadic, invigoration of locomotion in the presence of saturating dopamine receptor blockade, indicating that LPO can stimulate locomotion in the absence of dopamine signaling. Pivoting following bilateral VP bicuculline infusions was unaffected by dopamine D2 receptor blockade, but was completely suppressed by D1 receptor blockade. The present results are discussed in a context of neuroanatomical and functional organization underlying exploratory locomotion and adaptive movements.

Investigating complex basal ganglia circuitry in the regulation of motor behaviour, with particular focus on orofacial movement

Current concepts of basal ganglia function have evolved from the essentially motoric, to include a range of extramotoric functions that involve not only dopaminergic but also cholinergic, γ-aminobutyric acid (GABA)ergic and glutamatergic mechanisms. We consider these mechanisms and their efferent systems, including spiralling, feed-forward striato-nigro-striatal circuitry, involving the dorsal and ventral striatum and the nucleus accumbens (NAc) core and shell. These processes are illustrated using three behavioural models: turning-pivoting, orofacial movements in rats and orofacial movements in genetically modified mice. Turning-pivoting indicates that dopamine-dependent behaviour elicited from the NAc shell is funnelled through the NAc-nigro-striato-nigro-pedunculopontine pathway, whereas acetylcholine-dependent behaviour elicited from the NAc shell is funnelled through the NAc-ventral pallidum-mediodorsal thalamus pathway. Cooperative/synergistic interactions between striatal D1-like and D2-like dopamine receptors regulate individual topographies of orofacial movements that are funnelled through striatal projection pathways and involve interactions with GABAergic and glutamatergic receptor subtypes. This application of concerted behavioural, neurochemical and neurophysiological techniques implicates a network that is yet broader and interacts with other neurotransmitters and neuropeptides within subcortical, cortical and brainstem regions to 'sculpt' aspects of behaviour into its topographical collective.

Accumbal core: essential link in feed-forward spiraling striato-nigro-striatal in series connected loop

The goal of the present study was to establish the behavioral role of the nucleus accumbens (Nacc) core in the feed-forward spiraling striato-nigro-striatal circuitry that transmits information from the Nacc shell toward the dorsal subregion of the neostriatum (DS) in freely moving rats. Unilateral injection of μ-opioid receptor agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO; 1 and 2 μg), but not the δ 1-opioid receptor agonist [D-Pen(2,5)]-enkephalin (4 μg) or the δ2-opioid receptor agonist [D-Ala(2),Glu(4)]-deltorphin (2 μg), into the ventral tegmental area (VTA) produced contraversive circling in a dose-dependent manner. The effect of DAMGO was μ-opioid receptor-specific, because the μ-opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 (0.1 and 1 μg), which alone did not elicit any turning behavior, dose-dependently inhibited the effect of DAMGO. Injection of the dopamine D1/D2 receptor antagonist cis-(Z)-flupentixol (1 and 10 μg) into the Nacc shell ipsilaterally to the VTA significantly inhibited DAMGO (2 μg)-induced circling. Similar injections of cis-(Z)-flupentixol into the Nacc core inhibited DAMGO-induced circling, but, in addition, replaced circling by pivoting, namely turning behavior during which the rat rotates around its disfunctioning hindlimb. The present findings show that unilateral stimulation of μ-, but not δ-, opioid receptors in the VTA elicits contraversive circling that requires a relatively hyperdopaminergic activity in both the shell and the core of the Nacc at the opioid-stimulated side of the brain. The Nacc core plays an essential role in the transmission of information directing the display of pivoting that is elicited by an increased dopaminergic activity in the Nacc shell. It is concluded that the Nacc core is an essential link in the feed-forward spiraling striato-nigro-striatal circuitry that transmits information from the Nacc shell toward the DS in freely moving rats.

Role of orexin receptors in the nucleus accumbens in dopamine-dependent turning behaviour of rats

The role of orexin receptors in the nucleus accumbens shell in rat turning behaviour of rats was studied. Unilateral injection of neither the orexin 1 and 2 receptor agonist orexin A (2 microg) nor the orexin 1 receptor antagonist SB 334867 (20 ng) into the nucleus accumbens shell elicited turning behaviour. Unilateral injection of a mixture of dopamine D(1) (SKF 38393) and D2 (quinpirole) receptor agonists into the nucleus accumbens shell has been found to elicit contraversive pivoting. Orexin A (1 and 2 microg) dose-dependently potentiated the contraversive pivoting induced by a mixture of SKF 38393 (1 microg) and quinpirole (10 microg) injected into the nucleus accumbens shell whereas SB 334867 (10 and 20 ng) did not significantly affect the pivoting. The potentiating effect of orexin A (2 microg) on the dopaminergic pivoting was not significantly inhibited by SB 334867 (10 and 20 ng) injected into the nucleus accumbens shell. The contraversive pivoting induced by a mixture of SKF 38393 (1 microg) and quinpirole (10 microg) injected into the nucleus accumbens shell was also potentiated by the orexin 2 receptor agonist orexin B (0.5, 1 and 2 microg), which alone did not elicit turning behaviour. These results suggest that orexin 2 receptors in the nucleus accumbens shell play a modulatory role in rat turning behaviour.

A vehicle injection into the right core of the nucleus accumbens both reverses the region-specificity and alters the type of contralateral turning elicited by unilateral stimulation of dopamine D2/D3 and D1 receptors in the left core of the nucleus accumbens

The goal of the present study was to analyse to what extent variables such as (1) injected volume, (2) nature of the solvent of drugs (saline versus distilled water) and (3) placement of an additional cannula to inject the solvent of the drugs at the opposite side of the brain, influenced the behavioural effects of the combined administration of the dopamine D(1) receptor agonist (+/-)-1-phenyl-2,3,4,5-tetrahydro-[1H]-3-benzazepine-7,8-diol (SKF 38393, 5.0 microg) and the dopamine D(2)/D(3) receptor agonist quinpirole (10.0 microg) into the shell or core of the nucleus accumbens of freely moving rats. First, we found that increasing the injected volume from 0.2 microl to 0.5 microl significantly increased the amount of contralateral turning after injection of the drugs into the shell and, especially, the core of rats equipped with one cannula. More importantly, the type of turning behaviour changed: instead of a predominance of pivoting, both pivoting and circling appeared. Second, replacing the solvent saline by distilled water resulted in a minor, but significant, decrease of the amount of contralateral turning elicited from either the shell or the core of the nucleus accumbens of rats equipped with one cannula. The type of turning was not changed by this new solvent. Third, and most importantly, this study showed that the vehicle injection into the right core exerted a potentiating effect on the number of contralateral rotations elicited by injections of SKF 38393+quinpirole into the left core, whereas such a vehicle injection into the right shell did not affect the number of contralateral rotations elicited by injections of SKF 38393+quinpirole into the left shell. The type of turning in these rats was not changed when compared to rats equipped with one cannula. It is hypothesized that the fluid injected into the core, directly or indirectly, enhanced the dopaminergic asymmetry between the left and the right brain, implying that this manipulation anyhow reduced the dopaminergic activity in the region under discussion. In conclusion, subtle changes in the methodology used to study both the behaviour-specificity and the region-specificity of drug injections into the brain significantly directs the outcome of such studies.

Adrenergic receptors in the nucleus accumbens shell differentially modulate dopamine and acetylcholine receptor-mediated turning behaviour

The role of alpha- and beta-adrenoceptors in the nucleus accumbens shell in turning behaviour of rats was investigated. Unilateral injections of the alpha-adrenoceptor agonist (phenylephrine; 10 microg) and antagonist (phentolamine; 10 microg) as well as the beta-adrenoceptor agonist (isoprenaline; 1 microg) and antagonist (propranolol; 5 microg) into the nucleus accumbens shell did not produce turning behaviour more than that of control vehicle injection. Unilateral injection of a mixture of dopamine D(1) ((+/-)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol, SKF 38393; 5 microg) and D(2) (quinpirole; 10 microg) receptor agonists into the nucleus accumbens shell has been found to elicit contraversive pivoting. Such pivoting was dose-dependently inhibited by phenylephrine (5, 10 microg), injected into the nucleus accumbens shell, and the inhibitory effect of phenylephrine (10 microg) was antagonised by phentolamine (10 microg) that per se had no effect on this pivoting. Isoprenaline (0.5, 1 microg) dose-dependently increased the contraversive pivoting induced by the mixture of SKF 38393 (1 microg) and quinpirole (10 microg) injected into the nucleus accumbens shell. The effect of isoprenaline (1 microg) was antagonised by propranolol (5 microg) that per se had no effect on this pivoting. It is concluded that stimulation of accumbal alpha-adrenoceptors inhibits the dopamine-dependent pivoting in contrast to stimulation of accumbal beta-adrenoceptors that facilitates this dopamine-dependent pivoting. Unilateral injection of the acetylcholine receptor agonist carbachol (5 microg) into the nucleus accumbens shell has been found to elicit contraversive circling. Such circling was significantly reduced by accumbal administration of either phenylephrine (10, 20 microg) or phentolamine (5, 10 microg) in a dose-independent manner; moreover, both drugs potentiated, but did not counteract, each other's effects. Carbachol-induced circling was also reduced by propranolol (2.5, 5 microg), but again in an aspecific manner. It is concluded that alpha- and beta-adrenergic agents have an effect on accumbal acetylcholine receptor-mediated circling through a non-adrenergic mechanism. The impact of the present study for putative new treatments of various neuropsychiatric and neurological disorders is discussed.

Cooperative activation of D1-like and D2-like dopamine receptors in the nucleus accumbens shell is required for the reinstatement of cocaine-seeking behavior in the rat

Activation of D1-like (D1, D5) or D2-like (D1, D3, D4) dopamine receptors in the nucleus accumbens shell is sufficient to reinstate cocaine-seeking behavior in rats. The goal of these experiments was to assess whether cooperative activation of D1-like and D2-like dopamine receptors in the accumbens shell is required to promote cocaine reinstatement. Rats were initially trained to self-administer cocaine (0.25 mg, i.v.) using a fixed-ratio schedule of reinforcement for approximately 21 days. Animals subsequently underwent an extinction phase during which saline was substituted for cocaine. Once cocaine self-administration behavior was extinguished (defined as <15% of the total responses maintained during self-administration), dopamine receptor agonist-induced reinstatement of cocaine seeking was assessed. Administration of the selective D1/5 agonist R-(+)-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF-81297) (1.0 microg) or the D2/3 receptor agonist trans-(-)-(4aR)-4,4a,5,6,7,8,8a,9-octahydro-5-propyl-1H-pyrazolo[3,4-g]quinoline hydrochloride (quinpirole) (3.0 microg) directly into the nucleus accumbens shell promoted reinstatement of cocaine seeking. In order to determine if endogenous dopamine tone in the accumbens shell is required for dopamine receptor agonist-induced reinstatement of cocaine seeking, D1/5 or D2/3 dopamine receptor antagonists were administered into the nucleus accumbens shell prior to a selective dopamine receptor agonist. Microinfusion of the D2/3 dopamine receptor antagonist sulpiride ((S)-5-aminosulfonyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-methoxybenzamide) (1.0 microg) into the nucleus accumbens shell 10 minutes prior to SKF-81297 (1.0 microg) blocked the ability of this D1-like dopamine receptor agonist to reinstate cocaine seeking. Similarly, administration of the selective D1/5 dopamine receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH-23390) (1.0 microg) into the nucleus accumbens shell prior to quinpirole (3.0 microg) blocked reinstatement of drug-seeking behavior elicited by this D2/3 dopamine receptor agonist. Moreover, intra-accumbal shell co-administration of subthreshold doses of quinpirole (1.5 microg) and SKF-81297 (0.1 microg) promoted cocaine-seeking behavior. Collectively, these results indicate that cooperative activation of D1-like and D2-like dopamine receptors in the nucleus accumbens shell is necessary to reinstate cocaine seeking in rats.

Effects of intra-nucleus accumbens shell administration of dopamine agonists and antagonists on cocaine-taking and cocaine-seeking behaviors in the rat

RATIONALE

Dopamine signaling in the nucleus accumbens (NAc) plays an important role in regulating drug-taking and drug-seeking behaviors, but the role of D(1)- and D(2)-like receptors in this regulation remains unclear.

OBJECTIVES

Our objective was to study the role of NAc D(1)- and D(2)-like receptors in the reinstatement of cocaine-seeking behavior and the regulation of stabilized cocaine intake in rats.

METHODS

Using a within-session reinstatement procedure, whereby animals self-administer cocaine (90 min) and extinguish responding (150 min) in a single session, we assessed the ability of NAc microinfusions of the D(1) agonist SKF 81297 and the D(2) agonist 7-OH-DPAT to reinstate extinguished cocaine seeking. The effects of the D(1) antagonist SCH 23390 and the D(2) antagonist eticlopride pretreatment on agonist- and cocaine-primed reinstatement were also measured. Similar agonist and antagonist treatments were tested for their ability to modulate stabilized cocaine and sucrose self-administration.

RESULTS

Intra-NAc infusions of either SKF 81297 (0.3-3.0 microg) or 7-OH-DPAT (1.0-10.0 microg) dose-dependently reinstated cocaine seeking with greater efficacy in the medial core than in the shell subregion and at doses that also stimulated locomotor behavior. Intra-NAc shell infusions of SCH 23390 (1.0 microg) and eticlopride (3.0-10.0 microg) blocked cocaine-primed reinstatement (2.0 mg/kg, i.v.) and indiscriminately blocked reinstatement induced by either intra-NAc D(1) or D(2) agonists. Doses of agonists that triggered reinstatement failed to alter stabilized cocaine intake, whereas doses of antagonists that blocked reinstatement increased cocaine intake in the shell.

CONCLUSIONS

Both D(1) and D(2) receptors in the NAc play a prominent, and perhaps cooperative, role in regulating cocaine-taking and cocaine-seeking behaviors.

Acetylcholine receptor effects on accumbal shell dopamine-mediated turning behaviour in rats

The nature of acetylcholine receptor effects on dopaminergic functions within the nucleus accumbens shell was studied in rats, using turning behaviour as read-out parameter. Unilateral injections of the acetylcholine receptor agonist, carbachol (1.0-5.0 microg), into the nucleus accumbens shell dose-dependently elicited contraversive circling. Unilateral injections of the combination of a fixed dose of the dopamine D(2) receptor agonist, quinpirole (10.0 microg), with increasing doses of the dopamine D(1) receptor agonist, SKF 38393 (1.0-5.0 microg), into the nucleus accumbens shell dose-dependently elicited contraversive pivoting. The same held for the combination of a fixed dose of SKF 38393 (5.0 microg) with increasing doses of quinpirole (5.0 and 10.0 microg), which was injected into the nucleus accumbens shell. The nicotinic acetylcholine receptor antagonist, mecamylamine (5.0 and 10.0 microg), injected into the nucleus accumbens shell, which alone did not elicit any turning behaviour, significantly suppressed both the contraversive circling induced by carbachol (5.0 microg) and the contraversive pivoting induced by the mixture of SKF 38393 (5.0 microg) and quinpirole (10.0 microg). The muscarinic acetylcholine receptor antagonist, methylscopolamine (1.0 and 2.5 microg), injected into the nucleus accumbens shell, which alone did not elicit any turning behaviour, significantly suppressed the contraversive circling induced by carbachol (5.0 microg), whereas it significantly increased the contraversive pivoting induced by both the mixture of SKF 38393 (1.0 microg) and quinpirole (10.0 microg) and the mixture of SKF 38393 (5.0 microg) and quinpirole (5.0 microg). Neither SKF 38393 (5.0 microg) nor quinpirole (10.0 microg) injected into the nucleus accumbens shell affected the contraversive circling induced by carbachol (5.0 microg). Carbachol (1.0 microg) injected into the nucleus accumbens shell caused a slight initial potentiation followed by an inhibition of the contraversive pivoting induced by the mixture of SKF 38393 (5.0 microg) and quinpirole (10.0 microg). These results confirm that stimulation of both nicotinic and muscarinic acetylcholine receptors in the nucleus accumbens shell is required for the accumbens-dependent, acetylcholine-mediated circling. The study provides the original evidence that stimulation of nicotinic acetylcholine receptors in the nucleus accumbens shell is required for the accumbens-dependent, dopamine-mediated pivoting. Finally, the present study shows that muscarinic acetylcholine receptors in the nucleus accumbens shell play an inhibitory role in the production of the accumbens-dependent, dopamine-mediated pivoting.

Simultaneous AMPA/kainate receptor blockade and dopamine D2/3 receptor stimulation in the nucleus accumbens decreases brain stimulation reward in rats

Interactions between dopamine (DA) and glutamate (GLU) in the mesocorticolimbic pathway of the brain may influence motivation and reward. Previous work from this laboratory has demonstrated that alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptor blockade may potentiate decreases in exploratory motor activity induced by the DA D(2/3) receptor agonist 7-OH-DPAT in the nucleus accumbens septi (NAS). This study investigated the interaction of AMPA/kainate receptor antagonists CNQX or NBQX with 7-OH-DPAT on ventral tegmental area (VTA) brain stimulation reward (BSR). Effects of these compounds, alone and combined, were measured in male Sprague-Dawley rats stereotaxically implanted with a unilateral VTA electrode and bilateral guide cannulae in the NAS core or shell subregions. Rate-frequency analysis was used to assess BSR frequency thresholds and maximum response rates of rats trained to lever-press for reinforcing electrical stimulation. When given alone, CNQX (0.5 microg), NBQX (0.5 microg), or 7-OH-DPAT (5.0 microg) did not affect BSR frequency thresholds. Co-administration of CNQX or NBQX with 7-OH-DPAT synergistically increased BSR frequency thresholds, indicative of decreased reward. These data indicate that simultaneous AMPA/kainate receptor blockade and DA D(2/3) receptor stimulation in the NAS may act synergistically to inhibit motivated behaviours such as electrical brain self-stimulation.

Locomotion induced by non-contingent intracranial stimulation: comparison to psychomotor stimulant

Non-contingent experimenter-applied stimulation (nEAS) to the ventral mesencephalon, unlike contingent intracranial self-stimulation (ICSS), elicits high rates of general locomotion. This locomotion may be due to the nature of the presentation of stimulation, in that nEAS is non-contingent, while ICSS depends on a specific and focused response (e.g., bar pressing). Psychomotor stimulants also elicit high amounts of general locomotion, with the locomotion attributed to increased dopamine release. Interestingly, dopamine release decreases or is absent with repeated ICSS, but not nEAS. This suggests that the locomotion elicited by nEAS may be the result of DA release similar to that observed with psychomotor stimulants. To determine the relationship between locomotion induced by nEAS and psychomotor stimulants, locomotion elicited by nEAS was directly compared to that produced by cocaine, a psychomotor stimulant and indirect DA agonist. Six groups of rats were examined: (1) DA+ group: rats were implanted with a stimulating electrode in the ventral mesencephalon and activation of DA neurons was verified during surgery by monitoring DA release in the striatum; (2) DA- group: rats were also implanted with stimulating electrodes, but the location in the ventral mesencephalon did not elicit DA release; (3) 10-mg/kg cocaine group: rats were exposed to a low dose (10 mg/kg) of cocaine; (4) 40-mg/kg cocaine group: rats were exposed to a high dose (40 mg/kg) of cocaine; (5) saline group: rats were injected with saline; and (6) naive group: rats received no treatment. The topography of behavior was assessed in all rats during four periods: a pre-treatment baseline, treatment, early post-treatment, and a late post-treatment end point. The results suggest that locomotion elicited by nEAS was stereotypic, dependent upon DA release and similar, but not identical, to psychomotor stimulant-induced locomotion.

GABAA and GABAB receptors in the nucleus accumbens shell differentially modulate dopamine and acetylcholine receptor-mediated turning behaviour

The ability of GABAA and GABAB receptors in the shell of the nucleus accumbens to modulate distinct types of turning behaviour was investigated in freely moving rats, using the unilateral injection technique. The GABAA receptor agonist muscimol and the GABAA receptor antagonist bicuculline did not produce turning behaviour; the same holds for the GABAB agonist baclofen and the GABAB antagonist 2-hydroxysaclofen. A mixture of the dopamine D1 receptor agonist SKF 38393 and the dopamine D(2/3) receptor agonist quinpirole has been found to elicit contraversive pivoting, when injected into the shell. This pivoting was dose-dependently inhibited by muscimol, and the inhibitory effect of muscimol was antagonised by bicuculline. Pivoting was also dose-dependently inhibited by baclofen; however, 2-hydroxysaclofen did not antagonise the inhibitory effect. The acetylcholine receptor agonist carbachol has been found to elicit contraversive circling, when injected into the shell. This carbachol-induced circling was inhibited by baclofen, and 2-hydroxysaclofen antagonised the inhibitory effect. Carbachol-induced circling was also partially inhibited by muscimol; however, the inhibitory effect of muscimol was not antagonised by bicuculline. It is concluded that mesolimbic GABAA receptors exert an inhibitory control on dopamine-dependent pivoting that can be elicited from the shell of the nucleus accumbens, and that GABAB receptors exert an inhibitory control on acetylcholine-dependent circling that can be elicited from the shell of the nucleus accumbens. This data extends the earlier reported findings that the neurochemical substrate in the shell of the nucleus accumbens that mediates dopamine-dependent pivoting is fundamentally different from the shell substrate that mediates acetylcholine-dependent circling.

Role of mu- and delta-opioid receptors in the nucleus accumbens in turning behaviour of rats

The role of mu-, delta1- and delta2-opioid receptors in the nucleus accumbens in pivoting was investigated in freely moving rats. Unilateral injections of the mu-opioid receptor agonist, [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO, 1 and 2 microg) and the delta2-opioid receptor agonist, deltorphin II (1 and 2 microg), but not the delta1-opioid receptor agonist, [D-Pen(2,5)]-enkephalin (DPDPE, 1-4 microg), into the shell or the core of the nucleus accumbens significantly induced contraversive pivoting. The pivoting induced by DAMGO (2 microg) and deltorphin II (2 microg) was inhibited significantly by the mu-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 (CTOP, 0.1 and 1 microg), and the delta2-opioid receptor antagonist, naltriben (NTB, 0.1 and 1 mg/kg, i.p.), respectively. The DAMGO (2 microg)- or deltorphin II (2 microg)-induced pivoting was also inhibited significantly by co-administration of the dopamine D1/D2 receptor antagonist, cis(Z)-flupentixol (1 and 10 microg). The pivoting induced by unilateral injections of a mixture of dopamine D1 (SKF 38393, 5 microg) and D2 (quinpirole, 10 microg) receptor agonists into the shell was significantly inhibited by cis(Z)-flupentixol (1 and 10 microg) or NTB (1 and 3 mg/kg, i.p.), but not CTOP (1 microg) or delta1-opioid receptor antagonist, (E)-7-benzylidenenaltrexone (1 mg/kg, i.p.). The contraversive pivoting elicited by the cholinergic agonist, carbachol (5 microg), into the core was inhibited by co-administration of the muscarinic M1 antagonist, pirenzepine (1 microg), but not cis(Z)-flupentixol (1 microg). The results suggest that unilateral activation of mu- or delta2-opioid, but not delta1-opioid, receptors in the core and/or shell of the nucleus accumbens elicits contraversive pivoting that requires intact dopamine D1/D2 receptors in the shell, but not intact muscarinic M1 mechanism in the core. The study also shows that delta2-opioid, but not mu- and delta1-opioid, receptors in the core and/or shell modulate the shell-specific, dopamine D1/D2 receptor mechanisms involved in the production of pivoting.

Subthalamic high frequency stimulation induced rotations are differentially mediated by D1 and D2 receptors

High frequency stimulation (HFS) of the subthalamic nucleus (STN) has clinically emerged as a promising approach in the treatment of Parkinson's disease, epilepsy, dystonia as well as compulsive and possibly other mood disorders. The underlying mechanisms are incompletely understood, but are definitely related to high frequency and likely to involve the dopamine (DA)-system. To further test this hypothesis the present study investigated the modulation of STN-HFS-induced circling by systemic and intracerebral injection of drugs acting on DA receptors in naive freely moving rats. Within this experimental setup, unilateral STN-HFS alone induced intensity-dependent circling. Systemic injections of selective D1- (SCH-23390) and D2-((-)-sulpiride) antagonists as well as the mixed D1 and D2 agonist apomorphine dose-dependently reduced STN-HFS-induced rotational behavior. Intracerebral microinjections of (-)-sulpiride but not SCH-23390 decreased circling when injected intrastriatally and increased the number of rotations when injected intranigrally (pars reticulata (SNr)). These data reveal that STN-HFS-induced contralateral circling is differentially modulated by D1 and D2 receptors. While D2 receptor-mediated effects involve the dorso-/ventrolateral striatum and the SNr, D1 receptors probably exert their actions via brain areas outside the striatum and SNr. These findings suggest the nigrostriatal DA-system to be specifically involved in the mediation of STN-HFS-induced motor effects.

Role of AMPA and NMDA receptors in the nucleus accumbens shell in turning behaviour of rats: interaction with dopamine receptors

The role of AMPA and NMDA receptors in the shell of the nucleus accumbens in turning behaviour of rats was investigated. Unilateral injection of the AMPA receptor agonist, AMPA (0.25, 0.4, 0.5 and 1 microg), into the shell of the nucleus accumbens dose-dependently produced contraversive pivoting, namely tight head-to-tail turning marked by abnormal hindlimb backward stepping, while injection of AMPA (0.5 microg) into the core produced only a marginal effect. This shell-specific AMPA effect was dose-dependently inhibited by the AMPA receptor antagonist, NBQX (1 and 10 ng), which alone did not produce turning behaviour. The AMPA-induced pivoting was also dose-dependently inhibited by the non-competitive NMDA receptor antagonist, MK-801 (0.1 and 0.5 microg). Neither MK-801 (0.1, 0.5 and 5 microg) nor the NMDA receptor agonist, NMDA (0.5 and 1 microg), injected unilaterally into the shell, produced turning behaviour. Unilateral injection of a mixture of dopamine D(1) (SKF 38393, 5 microg) and D(2) (quinpirole, 10 microg) receptor agonists into the shell has been found to elicit contraversive pivoting. The dopamine D(1)/D(2) receptor antagonist, cis-(Z)-flupentixol (1 and 10 microg), injected into the shell, in doses known to block dopamine D(1)/D(2) receptor-mediated pivoting, also significantly inhibited AMPA (0.5 microg)-induced pivoting. Moreover, both NBQX (1 and 10 ng) and MK-801 (0.1 and 0.5 microg), injected into the shell, significantly inhibited dopamine D(1)/D(2) receptor-mediated pivoting. It is therefore concluded that unilateral stimulation of AMPA receptors in the shell of the nucleus accumbens can elicit contraversive pivoting, and that both AMPA and dopamine D(1)/D(2) receptors play a critical role in shell-specific pivoting in contrast to NMDA receptors that at best play only a modulatory role.

Disruption of dopaminergic neurotransmission in nucleus accumbens core inhibits the locomotor stimulant effects of nicotine and D-amphetamine in rats

The locomotor stimulant effects of nicotine and amphetamine appear to be dependent on dopamine transmission in the nucleus accumbens. The present aim was to elucidate the contributions of the accumbens core and medial shell to these effects. In the first experiment, rats received bilateral intra-accumbens infusion of the dopaminergic antagonist eticlopride (or saline) prior to saline or nicotine (0.2 mg/kg s.c.) challenge. Eticlopride inhibited basal and nicotine-induced locomotor activity more effectively when infused into the core (0.0625--0.5 microg/side) than into the medial shell (0.5--1 microg/side). In a second experiment, rats received 6-hydroxydopamine infused into the core or medial shell, and were subsequently tested with saline, nicotine (0.2 mg/kg s.c.) and D-amphetamine (0.75 mg/kg s.c.). Residual dopaminergic innervation was assessed by autoradiographic [(125)I]RTI-55 labelling of the dopamine transporter. [(125)I]RTI-55 labelling in the accumbens core was positively correlated with the locomotor stimulant effects of both nicotine and D-amphetamine. In contrast, [(125)I]RTI-55 labelling in the medial shell was associated negatively with amphetamine-induced activity. Recent evidence suggests that dopamine release in the medial shell may mediate the reinforcing effect of nicotine and D-amphetamine. In contrast, the present findings suggest that dopamine release in the core subregion contributes preferentially to the locomotor stimulant effects of nicotine and D-amphetamine.

GABA(A) agents injected into the ventral pallidum differentially affect dopaminergic pivoting and cholinergic circling elicited from the shell of the nucleus accumbens

The ability of GABA(A) receptors in the ventral pallidum to modulate shell-specific behavior was studied. Injections of the non-selective acetylcholine receptor agonist, carbachol (5 microg), into the shell of the nucleus accumbens elicited contraversive circling, namely turning marked by normal stepping; in contrast, injections of a mixture of dopamine D(1) (SKF 38393, 5 microg) and D(2) (quinpirole, 10 microg) receptor agonists into this brain structure elicited contraversive pivoting, namely turning marked by abnormal hindlimb stepping. Unilateral injections of the GABA(A) receptor agonist muscimol (10, 25 and 50 ng) into the ventral pallidum dose-dependently mimicked shell-specific circling, especially when given at a level +8.6mm anterior to the interaural line; this effect was GABA(A) receptor specific, because it was prevented by the GABA(A) receptor antagonist bicuculline (150 ng). Unilateral pallidal injections of a dose of muscimol that was ineffective per se (10 ng) abolished contraversive pivoting elicited by shell injections of dopamine receptor agonists; instead, it elicited moderate ipsiversive pivoting. Pallidal injections of bicuculline (150 ng) replaced the contraversive pivoting elicited by dopamine receptor agonist with ipsiversive circling. In contrast, unilateral pallidal injections of 10 ng muscimol (anterior +8.6mm level) suppressed the contraversive circling elicited by shell injections of carbachol; instead, it elicited moderate ipsiversive pivoting. Pallidal injections of bicuculline (150 ng) produced short-lasting ipsiversive circling that was followed by contraversive pivoting. We conclude that the ventromedial portion of the ventral pallidum contains GABA(A) receptors that are crucial for the transmission of information from the shell of the nucleus accumbens via the ventral pallidum towards other brain structures; this holds especially for information about shell-specific circling elicited by carbachol. The same portion of the ventral pallidum also contains GABA(A) receptors that control the transfer of information from the nucleus accumbens towards structures outside the ventral pallidum; this holds especially for information about shell-specific pivoting elicited by dopaminergic agonists.

Analysis of dopamine receptor antagonism upon feeding elicited by mu and delta opioid agonists in the shell region of the nucleus accumbens

The nucleus accumbens (NAcc) has been implicated as an important reward site for the mediation of unconditioned reinforcers such as food. Although both mu-selective and delta-selective opioid agonists in the NAcc induce spontaneous and palatable feeding, these effects are mediated by multiple opioid receptor subtypes within the nucleus. A role for dopaminergic mediation of feeding in the NAcc is based upon selective antagonist-induced suppression of feeding induced by systemic amphetamine. The present study investigated whether feeding elicited by infusion of either mu ([D-Ala(2), NMe-Phe(4), Gly-ol(5)]-enkephalin) or delta(2) ([D-Ala(2), Glu(4)]-deltorphin) opioid receptor subtype agonists in the shell region of the NAcc would be modified by intra-accumbens pretreatment with equimolar (12-100 nmol) doses of either D(1)-selective (SCH23390) or D(2)-selective (raclopride) antagonists. Both opioid agonists displayed comparable magnitudes and durations of feeding responses in the NAcc. SCH23390 significantly and dose-dependently reduced mu agonist-induced feeding in the NAcc with significant reductions noted following the two higher, but not two lower doses. In contrast, raclopride pretreatment produced inconsistent effects upon mu agonist-induced feeding with limited actions across doses and test times. Further, neither SCH23390 nor raclopride pretreatment in the NAcc affected feeding elicited by the delta(2) opioid agonist. These data indicate that the role of dopamine receptors in mediating opioid-induced feeding within the shell region of the NAcc is both dependent upon the dopamine receptor subtype that was blocked (D(1) vs. D(2)) as well as the opioid receptor subtype which was being stimulated mu vs. delta(2)).

Modification of dopamine D(1) receptor knockout phenotype in mice lacking both dopamine D(1) and D(3) receptors

Experimental evidence suggests that dopamine D(1) and D(3) receptors may interact in an opposing or synergistic fashion. To investigate interactions between both receptors in behaviour, we have used dopamine D(1) and D(3) receptor knockout mice to generate mice lacking both receptors. D(1)(-/-)D(3)(-/-) mice were viable, fertile and showed no gross morphological abnormalities. In an open field, they exhibited lower activity than wild-type, D(1)(-/-) and D(3)(-/-) mice. D(1)(-/-)D(3)(-/-) mice performed equally poorly in the rotarod and Morris water maze tasks as their D(1)(-/-) littermates. Basal locomotor activity and anxiety-like behaviour were normal in D(1)(-/-)D(3)(-/-) mice. Combined deletion of both receptors abolished the exploratory hyperactivity and anxiolytic-like behaviour of dopamine D(3) receptor mutant phenotype and further attenuated the low exploratory phenotype of D(1)(-/-) mice. These results imply an interaction of both receptors in the expression of exploratory behaviour in a novel environment, and the need for the presence of intact dopamine D(1) receptor for the expression of certain behaviours manifested in dopamine D(3) receptor mutant phenotype. In addition, dopamine D(1) receptor, but not dopamine D(3) receptor, is involved in the ability to perform on the rotarod and spatial learning.

Turning in rats following intraaccumbens shell injections of amphetamine or eticlopride

In recent years there has been interest in possible differential behavioral functions of the core and shell subregions of the nucleus accumbens. The present study compared the effects of accumbens core and shell injections of (+)-amphetamine on turning behavior in rats; the turning effects of the selective D2 antagonist (-)-eticlopride injected into the shell were also tested. Rats (n = 28) were implanted unilaterally with guide cannulae and subsequently tested for turning in seven 20-min sessions. Amphetamine (10.0 and 20.0 microg but not 5.0 microg/ 0.5 microl) elicited contralateral turning following injection into the shell, while the same doses into the core had no effect. In animals given systemic amphetamine (2.0 mg/kg), eticlopride (10.0 but not 1.0 or 0.1 microg/0.5 microl) injected into the shell region of the accumbens produced ipsilateral turning. These results suggest that the accumbens shell, but not the core, is a critical site for turning behavior.

An integrative neuroanatomical perspective on some subcortical substrates of adaptive responding with emphasis on the nucleus accumbens

Neuroanatomical substrates associated in the literature with adaptive responding are discussed, with a focus on the nucleus accumbens. While it is emphasized that the accumbens exhibits multiple levels of complex organization, a fairly complete list of brief descriptions of recent studies devoted specifically to the accumbens shell and core subterritories is presented in tabular format. The distinct patterns of connectivity of the accumbens core and shell and structures related to them by connections are described. Multiple inputs, outputs and abundant reciprocity of connections within the ventral parts of the basal ganglia are emphasized and the implications for "through-put" of impulses is considered. It is noted, at least on neuroanatomical grounds, that there is ample reason to expect feed forward processing from shell and structures with which it is associated to core and structures with which it is associated. Furthermore, the potential for additional feed forward processing involving several forebrain functional anatomical systems, inlcuding the ventral striatopallidum, extended amygdala and magnocellular basal forebrain complex is considered. It is intended that from the considerations recorded here a conceptual framework will begin to emerge that is amenable to further experimental substantiation as regards how multiple basal forebrain systems and the cortices to which they are related by connections work together to fashion a unitary object--the adaptive response.

Behavioural and neurochemical effects of cholinergic and dopaminergic agonists administered into the accumbal core and shell in rats

The first goal of this study was to investigate whether turning behaviour elicited by unilateral injections of the cholinergic agonist carbachol into the shell of the nucleus accumbens differs from that elicited by similar injections into the core of this nucleus, and to compare the behavioural effects with the known effects of such injections of the mixture of the dopamine D1 and D2 receptor agonists SKF 38393 (5 microg) and quinpirole (10 microg). The second goal was to investigate whether these injections of carbachol produce neurochemical alterations in the ventrolateral striatum that differ from similar injections of the mixture of the dopamine D1 and D2 receptor agonists into these brain regions. Injections of carbachol into the shell produced predominantly (a) contralateral circling marked by normal stepping and running in wide circles during the initial 50 min and (b) postural asymmetry during the following 75 min; similar injections into the core produced (a) contralateral pivoting, namely pathological head-to-tail turning marked by abnormal hindlimb stepping during the initial 50 min and (b) postural asymmetry during the next 75 min. The postural asymmetry seen after the carbachol injections was closely associated with the drug-induced increase in the dopamine release measured by microdialysis in the ipsilateral striatum. Injections of the mixture of dopamine agonists into the shell, but not core, also produced pivoting. These shell injections increased the dopamine release in the ipsilateral striatum, and decreased it in the contralateral striatum. The relative increase in the ipsilateral striatum was closely associated with the drug-induced pivoting. The data show that stimulation of cholinergic and dopaminergic receptors in the shell and core elicit effects that vary according to the subregion of the nucleus accumbens. It is concluded that the accumbens-specific, cholinergic effects are mediated via substrates that differ from those involved in the shell-specific, dopaminergic effects.

Associative processes in addiction and reward. The role of amygdala-ventral striatal subsystems

Only recently have the functional implications of the organization of the ventral striatum, amygdala, and related limbic-cortical structures, and their neuroanatomical interactions begun to be clarified. Processes of activation and reward have long been associated with the NAcc and its dopamine innervation, but the precise relationships between these constructs have remained elusive. We have sought to enrich our understanding of the special role of the ventral striatum in coordinating the contribution of different functional subsystems to confer flexibility, as well as coherence and vigor, to goal-directed behavior, through different forms of associative learning. Such appetitive behavior comprises many subcomponents, some of which we have isolated in these experiments to reveal that, not surprisingly, the mechanisms by which an animal sequences responding to reach a goal are complex. The data reveal how the different components, pavlovian approach (or sign-tracking), conditioned reinforcement (whereby pavlovian stimuli control goal-directed action), and also more general response-invigorating processes (often called "activation," "stress," or "drive") may be integrated within the ventral striatum through convergent interactions of the amygdala, other limbic cortical structures, and the mesolimbic dopamine system to produce coherent behavior. The position is probably not far different when considering aversively motivated behavior. Although it may be necessary to employ simplified, even abstract, paradigms for isolating these mechanisms, their concerted action can readily be appreciated in an adaptive, functional setting, such as the responding by rats for intravenous cocaine under a second-order schedule of reinforcement. Here, the interactions of primary reinforcement, psychomotor activation, pavlovian conditioning, and the control that drug cues exert over the integrated drug-seeking response can be seen to operate both serially and concurrently. The power of our analytic techniques for understanding complex motivated behavior has been evident for some time. However, the crucial point is that we are now able to map these components with increasing certainty onto discrete amygdaloid, and other limbic cortical-ventral striatal subsystems. The neural dissection of these mechanisms also serves an important theoretical purpose in helping to validate the various hypothetical constructs and further developing theory. Major challenges remain, not the least of which is an understanding of the operation of the ventral striatum together with its dopaminergic innervation and its interactions with the basolateral amygdala, hippocampal formation, and prefrontal cortex at a more mechanistic, neuronal level.

Functional-anatomical implications of the nucleus accumbens core and shell subterritories

The nucleus accumbens, a major part of the ventral striatum, comprises numerous subterritories and compartments, of which the core and shell appear to be dominant. Shell exhibits greater chemical neuroanatomical diversity than core and is rather directly connected to it by a robust, feed-forward, striatopallido-thalamocortico-striatal pathway. Shell and extended amygdala share afferents, but the two are distinguished by their outputs, strongly toward cortex for shell and descendent toward brain stem effector sites for extended amygdala. Shell responds independently to stimulation by excitatory amino acids and dopamine, which are more mutually permissive in the core. Accordingly, the shell responds to a broad variety of physiological and pharmacological stimuli, including psychomotor and opioid drugs. Whereas locomotion and oro-facial movements are elicitable from the shell, lesions and blockade of EAA transmission in the core reduce locomotion. It is hypothesized that core-shell has a feed-forward functional organization.

Dissociation in effects of lesions of the nucleus accumbens core and shell on appetitive pavlovian approach behavior and the potentiation of conditioned reinforcement and locomotor activity by D-amphetamine

Dopamine release within the nucleus accumbens (NAcc) has been associated with both the rewarding and locomotor-stimulant effects of abused drugs. The functions of the NAcc core and shell were investigated in mediating amphetamine-potentiated conditioned reinforcement and locomotion. Rats were initially trained to associate a neutral stimulus (Pavlovian CS) with food reinforcement (US). After excitotoxic lesions that selectively destroyed either the NAcc core or shell, animals underwent additional CS-US training sessions and then were tested for the acquisition of a new instrumental response that produced the CS acting as a conditioned reinforcer (CR). Animals were infused intra-NAcc with D-amphetamine (0, 1, 3, 10, or 20 microg) before each session. Shell lesions affected neither Pavlovian nor instrumental conditioning but completely abolished the potentiative effect of intra-NAcc amphetamine on responding with CR. Core-lesioned animals were impaired during the Pavlovian retraining sessions but showed no deficit in the acquisition of responding with CR. However, the selectivity in stimulant-induced potentiation of the CR lever was reduced, as intra-NAcc amphetamine infusions dose-dependently increased responding on both the CR lever and a nonreinforced (control) lever. Shell lesions produced hypoactivity and attenuated amphetamine-induced activity. In contrast, core lesions resulted in hyperactivity and enhanced the locomotor-stimulating effect of amphetamine. These results indicate a functional dissociation of subregions of the NAcc; the shell is a critical site for stimulant effects underlying the enhancement of responding with CR and locomotion after intra-NAcc injections of amphetamine, whereas the core is implicated in mechanisms underlying the expression of CS-US associations.

Intraaccumbens injections of substance P, morphine and amphetamine: effects on conditioned place preference and behavioral activity

The nucleus accumbens of the rat plays a critical role in behavioral activation and appetitive motivation. Within the nucleus accumbens, the shell subarea may be especially relevant, since this site is anatomically related to other brain areas that are considered to play a critical role in the processing of motivation. We investigated the behavioral effects of local drug treatments aimed at the shell of the nucleus accumbens and tested the indirect dopamine agonist d-amphetamine, the opiate agonist morphine, and the neurokinin substance P. These substances are known to exert positive reinforcing effects, and can affect behavioral activity; effects that are physiologically closely related to the nucleus accumbens and its inputs and outputs. Our results show that unilateral microinjections of amphetamine (1.0 microg, 10.0 microg) into the shell of the nucleus accumbens dose-dependently stimulated behavioral activity (locomotion, rears, sniffing), and led to conditioned place preference. Furthermore, the effect of amphetamine on place preference was negatively related to the psychomotor stimulant action on rears. Morphine injections (5.0 microg) also stimulated behavioral activity and elicited contraversive turning, but were ineffective with respect to place preference. Finally, the neuropeptide substance P, injected in a dose range of 0.1-10.0 ng, had no significant behavioral effects. These findings are discussed with respect to the role of dopaminergic, peptidergic and cholinergic mechanisms in the nucleus accumbens. It is suggested that dopamine, opiates, and neurokinins in the shell of the nucleus accumbens are differentially involved in mediating behavioral activity and appetitive motivation.

Role of dopamine D1 and D2 receptors in the nucleus accumbens in mediating reward

The objectives of this study were to examine the involvement of D1 and D2 receptors within the nucleus accumbens (ACB) in mediating reinforcement. The intracranial self-administration (ICSA) of D1 and D2 agonists was used to determine whether activating D1 and/or D2 receptors within the ACB of Wistar rats is reinforcing. At concentrations of 0.25, 0.50, and 1.0 mM (25, 50, and 100 pmol/100 nl of infusion), neither the D1 agonist R(+)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol [SKF 38393 (SKF)] hydrochloride nor the D2 agonist (-)-quinpirole (Quin) hydrochloride was self-administered into the shell region of the ACB. On the other hand, equimolar mixtures of SKF and Quin (SKF+Quin), at concentrations of 0.25, 0.50, and 1.0 mM each, were significantly self-infused into the ACB shell. The core region of the ACB did not support the ICSA of SKF+Quin at any of these concentrations. Rats increased lever pressing when the response requirement was increased from a fixed ratio 1 (FR1) to FR3, and they responded significantly more on the infusion lever than they did on the control lever. Coadministration of either 0.50 mM R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine (SCH 23390) hydrochloride, a D1 antagonist, or 0.50 mM S(-)-sulpiride, a D2 antagonist, completely abolished the ICSA of the mixture of SKF+Quin (each at 0.50 mM) into the ACB shell. The present results suggest that concurrent activation of D1- and D2-type receptors in the shell of the ACB had a cooperative effect on DA-mediated reward processes.

Behavioural effects of 7-OH-DPAT are solely due to stimulation of dopamine D2 receptors in the shell of the nucleus accumbens; jaw movements

The goal of this study was to determine whether the dopamine D3 receptor in limbic structures plays a role in the shell-specific and dopamine-dependent display of jaw movements in rats. When combined with the dopamine D1 receptor agonist (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1- phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine (SKF 82958, 5 micrograms), the putative dopamine D3 receptor agonist (+/-)-7-hydroxy-N, N-di-n-propyl-2-aminotetralin (7-OH-DPAT, 10 micrograms) produced repetitive jaw movements following injection into the shell, but not the core, of the nucleus accumbens. This behaviour was only partially inhibited by local blockade of dopamine D1 receptors (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine, SCH 23390, 500 ng), dopamine D2 receptors (domperidone, 50 and 100 ng) or dopamine D2/3 receptors (l-sulpiride, 25 ng). Combined blockade of both dopamine D1 and D2 receptors in the shell completely antagonized the jaw movements elicited by the cocktail of SKF 82958 and 7-OH-DPAT. Replacing 7-OH-DPAT by another putative dopamine D3 receptor agonist, S(+)-(4aR, 10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[I]benzopyrano[4, 3-b]-1, 4-oxazin-9-ol (PD 128,907, 10 micrograms), in the cocktail did not produce jaw movements, when administered into the shell. Injection of the cocktail of SKF 82958 and 7-OH-DPAT into the ventrolateral striatum, which contains nearly no dopamine D3 receptors, also elicited jaw movements. It is concluded that mesolimbic dopamine D3 receptors play no role in the dopamine-dependent and shell-specific jaw movements: the contribution of 7-OH-DPAT in the cocktail of SKF 82958 and 7-OH-DPAT to the display of jaw movements is solely due to its ability to activate dopamine D2 receptors.

Behavioural effects of 7-OH-DPAT are solely due to stimulation of dopamine D2 receptors in the shell of the nucleus accumbens; turning behaviour

The goal of this study was to determine whether the dopamine D3 receptor in limbic structures plays a role in the shell-specific and dopamine-dependent display of turning behaviour in rats. When combined with the dopamine D1 receptor agonist (+/-)-1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine-7,8-diol (SKF-38393, 5 micrograms), the putative dopamine D3 receptor agonist (+/-)-7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT, 1, 5 and 10 micrograms) elicited contralateral turning in a dose-dependent manner following unilateral injection into the shell, but not the core, of the nucleus accumbens. The turning pattern displayed was identical to that reported previously after intra-accumbens administration of the cocktail of SKF-38393 and the dopamine D2 receptor agonist quinpirole. The behaviour under study was dose-dependently attenuated by local administration of the dopamine D1 receptor antagonist R(+)-7-chloro-8-hydroxy-3- methyl-I-phroyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390: 10 and 100 ng), the dopamine D2 receptor antagonist domperidone (25 and 50 ng) or the dopamine D2/3 receptor antagonist l-sulpiride (5 and 25 ng). Combined blockade of both dopamine D1 and D2 receptors in the shell with a dose of either antagonist alone that produced just a moderate reduction (10 ng SCH 23390 and 50 ng domperidone) completely antagonized the turning behaviour elicited by the cocktail of SKF-38393 and 7-OH-DPAT. Replacing 7-OH-DPAT by another putative dopamine D3 receptor agonist,S(+)-(4aR, 10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4, 3-b]-1, 4-oxazin-9-ol (PD 128,907, 10 micrograms), in the cocktail did produce no turning behaviour at all. It is concluded that mesolimbic dopamine D3 receptors play no role in the dopamine-dependent and shell-specific turning behaviour: the contribution of 7-OH-DPAT in the cocktail of SKF-38393 and 7-OH-DPAT to the display of turning behaviour is solely due to its ability to activate dopamine D2 receptors.