Katsunori Tomiyama

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.

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.

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.

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.

Dopamine D-1 but not D-2 receptor stimulation of the dorsal striatum potentiates apomorphine-induced jaw movements in rats

The effects of bilateral injections of selective D-1 and D-2 agonists and antagonists into the dorsal striata on apomorphine-induced jaw movements were studied in ketamine-anaesthetized rats after C1 spinal transection. A phototransducer attached to the lower mandible automatically detected jaw movements. YM-09151-2 (0.2 and 0.5 micrograms) and cis(Z)-flupentixol (0.5 and 1 microgram) injected into the dorsal striatum increased the frequency of jaw movements after apomorphine (0.2 mg/kg i.v.). The effects were prevented by administration of SCH23390 (1 microgram) with YM-09151-2 (0.5 microgram) or cis(Z)-flupentixol (1 microgram). Injection of SCH23390 (1 microgram) alone into the dorsal striatum failed to alter the apomorphine (0.5 mg/kg i.v.)-induced jaw movements. Local application of the selective D-1 agonists, SKF38393 (5 micrograms) and SKF75670 (10 micrograms), into the dorsal striatum potentiated the apomorphine (0.2 mg/kg i.v.)-induced jaw movements, while a D-2 agonist, quinpirole (10 micrograms), injected into the same site attenuated these movements. These data are suggestive of an oppositional D-1: D-2 receptor interaction in the dorsal striatum.

Sulpiride injection into the dorsal striatum increases methamphetamine-induced gnawing in rats

Sulpiride injected into the dorsal striatum enhanced both methamphetamine- and apomorphine-induced gnawing but blocked both when injected into the ventral striatum. The hyperlocomotion produced by methamphetamine was reduced by sulpiride injected into the dorsal striatum. The DA, DOPAC and HVA concentrations in the ventral striatum were increased 60 min after the injection of sulpiride into the dorsal striatum. Possible reasons for the enhancement of methamphetamine-induced gnawing by sulpiride injected into the dorsal striatum are discussed.

Ketamine anaesthesia has no effect on striatal dopamine metabolism in rats.

Striatal levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid and homovanillic acid in rats were not altered for at least 6 h after a ketamine injection (100 mg/kg). Striatal DA turnover which was measured by giving alpha-methyl-p-tyrosine after ketamine was unchanged. Even the dose regimen of ketamine which anaesthetized animals for approximately 3.5 h (100 mg/kg + 5 maintenance injections of 50 mg/kg at 30 min intervals) produced no alteration in DA turnover for at least 9 h. These results suggest that ketamine anaesthesia will not adversely affect studies investigating central DAergic mechanisms in rats.

In Vivo Microdialysis Evidence for Transient Dopamine Release by Benzazepines in Rat Striatum

Abstract: The effects of benzazepine derivatives on extracellular levels of dopamine (DA) and l‐3,4‐dihydroxyphenylacetic acid (DOPAC) in the dorsal striatum of freely moving rats were studied using in vivo microdialysis. Direct injection of SKF‐38393 (0.5 or 1.5 µg/0.5 µl), a selective D1 receptor agonist, into the striatum through a cannula secured alongside a microdialysis probe produced a rapid dose‐dependent transient increase in striatal DA efflux and a more gradual reduction in efflux of DOPAC. The rapid increase in DA efflux was not affected by infusion of tetrodotoxin (TTX; 2 µM) or Ca2+‐free Ringers solution and occurred after either enantiomer of SKF‐38393. A TTX‐insensitive increase in DA level similar to that induced by SKF‐38393 was also seen after other benzazepines acting as agonists (SKF‐75670 and SKF‐82958, each 1.5 µg in 0.5 µl) and antagonists (SCH‐23390, 1.5 µg in 0.5 µl) at the D1 receptor and after (+)‐amphetamine. These effects were inhibited by infusion of nomifensine (100 µM). It is concluded that the transient increases in striatal DA efflux seen after intrastriatal injection of SKF‐38393 and other benzazepines are not mediated by presynaptic D1 receptors but by an amphetamine‐like action on the dopamine transporter.