Noriaki Koshikawa

Phenotypic studies on dopamine receptor subtype and associated signal transduction mutants: insights and challenges from 10 years at the psychopharmacology–molecular biology interface

BackgroundMutants with targeted gene deletion (‘knockout’) or insertion (transgenic) of D1, D2, D3, D4 and D5 dopamine (DA) receptor subtypes are complemented by an increasing variety of double knockout and transgenic-‘knockout’ models, together with knockout of critical components of DA receptor signalling cascades such as Gαolf[Gγ7], adenylyl cyclase type 5, PKA [RIIβ] and DARPP-32. However, it is increasingly recognised that these molecular techniques have a number of inherent limitations. Furthermore, there are poorly understood methodological factors that contribute to inconsistent phenotypic findings between laboratories.ObjectiveThis review seeks to document the impact of DA receptor subtype and related transduction mutants on our understanding of the behavioural roles of these entities, primarily at the level of unconditioned psychomotor behaviour.MethodsIt includes ethologically based and orofacial movement studies in our own laboratories, since these are the only studies to systematically compare each of the D1, D2, D3, D4 and D5 receptor and DARPP-32 signal transduction ‘knockouts’.DiscussionThere is a particular emphasis on identifying methodological factors that might influence phenotypic effects and account for inconsistencies. The findings are offered empirically to (1) specify the extent of phenotypic diversity among individual DA receptor subtypes and transduction components and (2) indicate relationships between D1, D2, D3, D4 and D5 receptor subtype proteins, associated Gαi/Gαs/Gαolf[Gγ7]–adenylyl cyclase type 5–PKA [RIIβ]–DARPP-32 signalling cascades and behaviour. The findings are also offered heuristically as a base for such phenotypic comparisons at additional levels of behaviour so that a yet more complete phenotypic profile might emerge.

Effects of intrastriatal injections of selective dopamine D-1 and D-2 agonists and antagonists on jaw movements of rats

The effects of bilateral intrastriatal injections of the selective D-1 and D-2 antagonists, SCH23390 and sulpiride on apomorphine-induced jaw movements were studied in ketamine-anaesthetized rats after C1 spinal transection. A photo-transducer attached to the lower mandible automatically detected jaw movements. Apomorphine (0.2, 0.5 and 1.0 mg/kg i.v.) dose dependently increased jaw movements, an effect prevented by prior administration into the ventral striatum of either SCH23390 (0.1, 0.5 and 1 microgram) or sulpiride (125 ng). To be effective, SCH23390 had to be given less than 30 min before apomorphine whereas sulpiride had to be given earlier. Sulpiride injected into the dorsal striatum potentiated the effects of apomorphine, an action prevented by administering the sulpiride with SCH23390. Local application of the selective D-1 and D-2 agonists, SKF38393 (5 micrograms) and quinpirole (10 micrograms) into sites within the ventral striatum from which repeated jaw movements could be obtained by electrical stimulation, also evoked jaw movements; the effects of combining the two drugs were much greater than the effects of either drug alone.

Interactions among mu- and delta-opioid receptors, especially putative delta1- and delta2-opioid receptors, promote dopamine release in the nucleus accumbens.

The effect of interactions among mu- and delta-opioid receptors, especially the putative delta(1)- and delta(2)-opioid receptors, in the nucleus accumbens on accumbal dopamine release was investigated in awake rats by in vivo brain microdialysis. In agreement with previous studies, perfusion of the nucleus accumbens with the mu-, delta(1)- and delta(2)-opioid receptor agonists [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO), [D-Pen(2,5)]-enkephalin (DPDPE) and [D-Ser(2)]Leu-enkephalin-Thr(6), respectively, significantly enhanced the extracellular amount of accumbal dopamine in a dose-related manner (5.0 nmol and 50.0 nmol). However, the highest concentration tested (50.0 nmol) of DAMGO induced a biphasic effect, i.e. a rapid onset increase lasting for 75 min followed by a slower onset gradual and prolonged increase. The mu-opioid receptor antagonist D-Phe-Cys-Tyr-d-Trp-Orn-Thr-Phe-Thr-NH(2) (0.15 nmol) primarily reduced the DAMGO-induced second component. The delta(1)-opioid receptor antagonist (E)-7-benzylidenenaltrexone (0.15 nmol) significantly reduced the first component and abolished the second component induced by DAMGO, while the delta(2)-opioid receptor antagonist naltriben (1.5 nmol) significantly reduced only the first component. The DPDPE (50.0 nmol)-induced dopamine increase was almost completely abolished by (E)-7-benzylidenenaltrexone, but only partially reduced by D-Phe-Cys-Tyr-d-Trp-Orn-Thr-Phe-Thr-NH(2) and naltriben. The [D-Ser(2)]Leu-enkephalin-Thr(6) (50.0 nmol)-induced dopamine increase was almost completely abolished by naltriben, but not at all by D-Phe-Cys-Tyr-d-Trp-Orn-Thr-Phe-Thr-NH(2) and (E)-7-benzylidenenaltrexone. The non-selective opioid receptor antagonist naloxone (0.75 and 1.5 nmol) dose-dependently reduced the effects of DAMGO, DPDPE and [D-Ser(2)]Leu-enkephalin-Thr(6) but only to about 10-25% of the control values. Moreover, perfusion with the sodium channel blocker tetrodotoxin (0.1 nmol) reduced the DAMGO-induced dopamine increase by 75%, while it almost completely abolished the increase induced by DPDPE or [D-Ser(2)]Leu-enkephalin-Thr(6). The results show that stimulation of mu-opioid receptors or, to a lesser degree, delta(1)-opioid receptors results in a large naloxone-sensitive increase and a small naloxone-insensitive increase of extracellular dopamine. It is suggested that the naloxone-insensitive component is also tetrodotoxin-insensitive. Furthermore, it is hypothesized that stimulation of mu-opioid receptors activates delta(1)-receptors, which in turn activate delta(2)-opioid receptors, thereby giving rise to a rapid onset increase of extracellular dopamine. In addition, it is hypothesized that stimulation of another group of mu-opioid receptors activates a second group of delta(1)-opioid receptors that is not coupled to delta(2)-opioid receptors and mediates a slow onset increase of extracellular dopamine. Finally, it is suggested that stimulation of delta(1)- or delta(2)-opioid receptors inhibits mu-opioid receptors involved in the slow onset increase in extracellular dopamine, whereas stimulation of delta(1)-, but not delta(2)-, opioid receptors is suggested to activate mu-opioid receptors involved in the rapid increase in extracellular dopamine.

Fentanyl increases dopamine release in rat nucleus accumbens: involvement of mesolimbic mu- and delta-2-opioid receptors

The effects of the mu-receptor agonist fentanyl on extracellular levels of dopamine in rat nucleus accumbens were studied in awake animals by in vivo brain microdialysis. Fentanyl dose-dependently increased the levels of dopamine when given intravenously (microg/kg) or via a microdialysis probe placed into the ventral tegmental area or the nucleus accumbens (nmol). The effect of fentanyl given into the nucleus accumbens was blocked by systemic administration of the non-selective opioid receptor antagonist naloxone and by accumbens administration of D-Phe-Cys-Tyr-D-Trp-Om-Thr-Phe-Thr-NH2 (nmol), a mu-opioid receptor antagonist, and naltrindole (nmol), a non-selective delta-opioid receptor antagonist, in a dose-dependent manner. The delta2-opioid receptor antagonist, naltriben (nmol), also blocked the effects of fentanyl, whereas the delta1-opioid receptor antagonist, (E)-7-benzylidenenaltrexone (nmol), was ineffective. When marginally effective doses of D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 and naltriben were given simultaneously, the effect of fentanyl was nearly fully blocked; the pretreatment itself had no effect. Administration of the mu-opioid receptor agonist [D-Ala2, N-Me-Phe4,Gly5-ol]-enkephalin (nmol), the delta1-opioid receptor agonist [D-Pen2,5]-enkephalin (nmol) or the delta2-opioid receptor agonist [D-Ala2,Glu4]-deltorphin (nmol) into the nucleus accumbens enhanced the amount of accumbal dopamine. This study provides evidence that not only activation of delta1- and delta2-opioid receptors, but also activation of mu-opioid receptors in the nucleus accumbens increases the release of accumbal dopamine in freely moving rats. We suggest that the effect of intra-accumbens administration of fentanyl upon accumbal release of dopamine is either due to the simultaneous activation of mu-opioid receptors and delta2-opioid receptors or due to activation of mu-opioid receptors that interact with delta2-opioid receptors in a complex manner.

Opposite effects of midazolam and β-carboline-3-carboxylate ethyl ester on the release of dopamine from rat nucleus accumbens measured by in vivo mudialysis

This report describes the effects of midazolam and beta-carboline-3-carboxylate ethyl ester (beta-CCE) on extracellular concentrations of dopamine in the nucleus accumbens of freely moving rats measured by in vivo microdialysis. The two compounds had opposite effects, midazolam (0.075 and 0.15 mg/kg i.v.) dose dependently decreasing, and beta-CCE (3 and 10 mg/kg i.p.) dose dependently increasing, dialysate concentrations of dopamine. Flumazenil (6 micrograms/kg i.v.) did not affect the efflux of dopamine but it prevented the effects of both midazolam and beta-CCE on dopamine efflux. N6-Cyclohexyladenosine (0.1, and 1 mg/kg i.p.), a selective adenosine A1 agonist, dose dependently increased the efflux of dopamine. This effect was blocked by 8-cyclopentyl-1,3-dipropylxanthine (25 mg/kg i.p.), a selective adenosine A1 receptor antagonist, a dose which given alone did not affect dopamine efflux; responses to midazolam were not affected. 3,7-Dimethyl-1-propargylxanthine (1 and 3 mg/kg i.p.), a selective adenosine A2 receptor antagonist, did not mimic the effects of beta-CCE. The results suggest that midazolam and beta-CCE modulate dopamine release in the nucleus accumbens by an action at the benzodiazepine binding site associated with the GABAA receptor complex.

Role of the Nucleus Accumbens and the Striatum in the Production of Turning Behaviour in Intact Rats

Recent knowledge of the mechanisms underlying turning or circling behaviour in intact rats is reviewed. Most interest has been directed towards the striatum because of the classical hypothesis that turning behaviour results from lateral differences in the activity of the bilateral nigrostriatal pathway. However, the assumption that asymmetrical activation of the striatum is a necessary condition for dopamine-dependent turning behaviour has been questioned by several studies showing that unilateral injection of amphetamine or dopamine receptor agonists into the nucleus accumbens, a target of the mesolimbic dopaminergic system, also produces reliable circling away from the side of injection. Apart from discussing differences in stepping patterns of turning and discussing the role of the dopamine D1/D2 receptor interaction, the present survey focuses attention upon the two-component hypothesis, especially in relation to our recent studies in which activities of dopamine D1 and D2 receptors in the striatum and the nucleus accumbens have been manipulated separately in intact rats. It is hypothesized that turning behaviour is produced by asymmetry within nucleus accumbens circuits which involve neuronal connections from the nucleus accumbens to the A9 cell area, which in turn projects to the ventrolateral striatum that determines the direction of turning.

Effects of dopamine D1 and D2 agonists and antagonists injected into the nucleus accumbens and globus pallidus on jaw movements of rats

The effects of bilateral injections of selective D1 and D2 agonists and antagonists into the anteromedial part of the nucleus accumbens and the globus pallidus on apomorphine-induced jaw movements were studied in ketamine-anaesthetized rats after C1 spinal transection. Both SCH 23390 (0.1 and 1 micrograms) and 1-sulpiride (5 and 25 ng) injected into the nucleus accumbens suppressed the display of jaw movements after apomorphine (0.5 mg/kg i.v.). Injection of 1-sulpiride (5 and 25 ng) into the globus pallidus also blocked the effect of apomorphine, whereas SCH 23390 (1 microgram) injected into the same site was ineffective in this respect. Simultaneous application of the selective D1 and D2 agonists, SKF (1 or 5 micrograms) + quinpirole (10 micrograms), into the nucleus accumbens strongly potentiated the effect induced by local administration of each drug alone; a comparable, but smaller, effect was seen after simultaneous injections of these agents into the globus pallidus. These results show that dopaminergic mechanisms within the nucleus accumbens are involved in apomorphine-induced jaw movements, and that the expression of these movements requires concurrent activation of D1 and D2 receptors.

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 µg) and the dopamine D1 receptor agonist 1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7, 8-diol (SKF 38393, 5 µg) 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 antagonistl-sulpiride (25 ng/0.5 µl) 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 µg/0.5 µl) into the same region. These data together with the fact thatl-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.

Topographical assessment and pharmacological characterization of orofacial movements in mice: dopamine D1-like vs. D2-like receptor regulation

A novel procedure for the assessment of orofacial movement topographies in mice was used to study, for the first time, the individual and interactive involvement of dopamine D(1)-like vs. D(2)-like receptors in their regulation. The dopamine D(1)-like receptor agonists A 68930 ([1R,3S]-1-aminomethyl-5,6-dihydroxy-3-phenyl-isochroman) and SK&F 83959 (3-methyl-6-chloro-7,8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine) each induced vertical jaw movements with tongue protrusions and incisor chattering. The dopamine D(1)-like receptor antagonists SCH 23390 ([R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) and BW 737C ([S]-6-chloro-1-[2,5-dimethoxy-4-propylbenzyl]-7-hydroxy-2-methyl-1,2,3,4-tetrahydroisoquinoline) antagonised these responses, while the dopamine D(2)-like receptor antagonist YM 09151-2 (cis-N-[1-benzyl-2-methyl-pyrrolidin-3-yl]-5-chloro-2-methoxy-4-methylaminobenzamide) attenuated those to SK&F 83959 and released horizontal jaw movements. These findings suggest some role for a dopamine D(1)-like receptor that is coupled to a transduction system other than/additional to adenylyl cyclase, and for dopamine D(1)-like:D(2)-like receptor interactions, in the regulation of individual orofacial movement topographies in the mouse. This methodology will allow the use of knockout mice to clarify the roles of individual dopamine receptor subtypes in their regulation.

Role of dopamine D1 and D2 receptors in the nucleus accumbens in jaw movements of rats : a critical role of the shell

Given the differences in the dopamine neurotransmission between the shell and the core of the nucleus accumbens, as well as the differential involvement of these two domains in oral behaviour of rats, it was decided to determine whether or not dopamine D1 and/or dopamine D2 receptors differentially direct oral behaviour in these two domains in rats. Intra-accumbens injections of the dopamine D1 receptor agonist (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine (SKF 82958: 5 micrograms/0.2 microliters), the dopamine D2 receptor agonist quinpirole (10 micrograms/0.2 microliters) and their combination were used to assess the role of these accumbens domains in jaw movements of rats. The present study shows that the combined administration of SKF 82958 and quinpirole into the shell, but not the core, of the nucleus accumbens produced a highly significant increase in jaw movements, when doses which per se were nearly ineffective, were injected. This effect was fully inhibited by prior administration of either the dopamine D1 receptor antagonist R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390: 0.5 microgram/0.2 micrograms) or the dopamine D2 receptor antagonist (-)-sulpiride (25 ng/0.5 microliter) into the same region. It is concluded that dopamine D1 and D2 receptors in the shell, but not the core, of the nucleus accumbens are involved in jaw movements of the rat, providing the first piece of evidence that dopamine D1 and D2 receptors in the shell of the nucleus accumbens mediate a particular behaviour.