Dissimilarities between cholinergic and dopaminergic turning elicited by nucleus accumbens stimulation in freely moving rats

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.

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.

Requirement for the endocannabinoid system in social interaction impairment induced by coactivation of dopamine D1 and D2 receptors in the piriform cortex

The dopamine receptor family consists of D1-D5 receptors (D1R-D5R), and we explored the contributions of each dopamine receptor subtype in the piriform cortex (PirC) to social interaction impairment (SII). Rats received behavioral tests or electrophysiological recording of PirC neuronal activity after injection of the D1R/D5R agonist SKF38393, the D2R/D3R/D4R agonist quinpirole, or both, with or without pretreatment with dopamine receptor antagonists, D1R or D5R antisense oligonucleotides, the cannabinoid CB1 receptor antagonist AM281, or the endocannabinoid transporter inhibitor VDM11. Systemic injection of SKF38393 and quinpirole together, but not each one alone, induced SII and increased PirC firing rate, which were blocked by D1R or D2R antagonist. Intra-PirC microinfusion of SKF38393 and quinpirole together, but not each one alone, also induced SII, which was blocked by D1R antisense oligonucleotides or D2R antagonist but not by D3R or D4R antagonist or D5R antisense oligonucleotides. SII induced by intra-PirC SKF38393/quinpirole was blocked by AM281 and enhanced by VDM11, whereas neither AM281 nor VDM11 alone affected social interaction behavior. Coadministration of SKF38393 and quinpirole produced anxiolytic effects without significant effects on locomotor activity, olfaction, and acquisition of olfactory short-term memory. These findings suggest that SII induced by coactivation of PirC D1R and D2R requires the endocannabinoid system.

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.

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.

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.

Gabaa receptors in the pedunculopontine tegmental nucleus play a crucial role in rat shell-specific dopamine-mediated, but not shell-specific acetylcholine-mediated, turning behaviour

The role of GABA(A) receptors in the pedunculopontine tegmental nucleus in turning behaviour of rats was studied. Unilateral injection of the GABA(A) receptor agonist, muscimol (25-100 ng), into the pedunculopontine tegmental nucleus dose-dependently produced contraversive pivoting, namely tight head-to-tail turning marked by abnormal hindlimb backward stepping. This effect was GABA(A) receptor specific, since it was prevented by the GABA(A) receptor antagonist, bicuculline (50 ng), which alone did not elicit turning behaviour. 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, whilst unilateral injection of the acetylcholine receptor agonist (carbachol, 5 microg) into the same site is known to elicit contraversive circling, namely turning marked by normal stepping. The pivoting induced by a mixture of SKF 38393 (5 microg) and quinpirole (10 microg) injected into the nucleus accumbens shell was significantly inhibited by bicuculline (50 ng) injected into the pedunculopontine tegmental nucleus, whereas muscimol (25 ng) had no effect. Neither muscimol (25 ng) nor bicuculline (50 ng) modulated the contraversive circling induced by carbachol (5 microg) injected into the nucleus accumbens shell. It is therefore concluded that unilateral stimulation of GABA(A) receptors in the pedunculopontine tegmental nucleus can elicit contraversive pivoting and that the pedunculopontine tegmental nucleus is one of the output stations of the accumbens region that mediates shell-specific, dopaminergic pivoting, but not of the accumbens region that mediates shell-specific, cholinergic circling.

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.

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.

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.

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.

Rats self-administer carbachol directly into the nucleus accumbens

The potential reinforcing effect of the muscarinic cholinergic agonist carbachol within the nucleus accumbens (ACB) was examined in female Wistar rats by using the technique of intracranial self-administration. Rats dose dependently self-administered solutions of 0.0-6.6 mM (in a volume of 100 nL per injection) directly into the ACB. Rats self-administered the 3.3 and 6.6 mM doses significantly more than the group given only vehicle. The caudate putamen did not support reliable self-administration of the 6.6-mM dose. Rats exhibited preference for the lever that produced infusions of 3.3 and 6.6 mM carbachol into the ACB over the lever that had no consequence. The self-infusion of the 6.6-mM dose into the ACB was inhibited by the coadministration of the muscarinic antagonist scopolamine (0.25 mM), but not by the nicotinic antagonist mecamylamine (6.6 mM). The present results suggest that direct activation of muscarinic receptors within the ACB supports self-administration and could result from reinforcement or from elicitation of a novel stimulus.

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

The goal of this study was to determine whether dopamine D2 and/or D1 receptors in the shell and the core of the nucleus accumbens of rats have a differential role in turning behaviour. Unilateral injection of a mixture of the dopamine D2 receptor agonist quinpirole (10 micrograms) and the dopamine D1 receptor agonist 1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7, 8-diol (SKF 38393, 5 micrograms) into the shell of the nucleus accumbens produced contralateral turning, when doses which per se were ineffective were injected. This effect was far greater than that found after similar injections into the core of the nucleus accumbens. The effect elicited from the shell was significantly attenuated by prior administration of either the dopamine D2 receptor antagonist l-sulpiride (25 mg/0.5 microliters) or the dopamine D1 receptor antagonist (8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol (SCH 23390, 0.5 micrograms/0.5 microliters) into the same region. These data together with the fact that l-sulpiride is known to be a valid tool to differentiate the involvement of distinct regions within the shell underlie the conclusion that dopamine D2 and D1 receptors in the shell, but not the core, of the nucleus accumbens play a critical role in the contralateral turning induced by unilateral injection of dopamine receptor agonists into this nucleus. The results are discussed in view of the known output pathways of the shell.

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.

Stimulation of acetylcholine or dopamine receptors in the nucleus accumbens differentially alters dopamine release in the striatum of freely moving rats

The present study examined whether unilateral stimulation of acetylcholine or dopamine receptors in the nucleus accumbens induces an asymmetry in dopamine transmission in the ventrolateral striatum. For this purpose, a microdialysis technique was used to measure dopamine release in both sides of the ventrolateral striatum following unilateral injections of carbachol (5 micrograms/0.5 microliter) or a mixture of dopamine D1 and dopamine D2 receptor agonists (1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine-7,8-diol 5 micrograms + quinpirole 10 micrograms/0.5 microliter) into the nucleus accumbens. The results show that carbachol injection increased dopamine release in the ipsilateral striatum without changing dopamine release in the contralateral striatum, whereas the dopamine D1/D2 receptor agonist mixture injected unilaterally into the nucleus accumbens produced an increase followed by a decrease in dopamine release in the ipsilateral striatum, but only a decrease in dopamine release in the contralateral striatum. The biochemical effects of the cholinergic treatment greatly outlasted the drug-induced contralateral turning, whereas the biochemical effects of the dopaminergic treatment showed a good correlation with the drug-induced contralateral turning. The present study provides biochemical evidence that unilateral stimulation of acetylcholine or dopamine receptors in the nucleus accumbens elicits an asymmetry in dopaminergic activity in the ventrolateral striatum. The present study also provides biochemical evidence that two distinct neural substrates are involved in the effects of cholinergic and dopaminergic manipulation of the nucleus accumbens.