Comparative phenotypic resolution of spontaneous, D2-like and D1-like agonist-induced orofacial movement topographies in congenic mutants with dopamine D2 vs. D3 receptor ?knockout?

Orofacial movements in phospholipase C-related catalytically inactive protein-1/2 double knockout mice: Effect of the GABAergic agent diazepam and the D(1) dopamine receptor agonist SKF 83959

Orofacial movements are regulated by D(1)-like dopamine receptors interacting with additional mechanisms. Phospholipase C-related catalytically inactive protein (PRIP) regulates cell surface expression of GABA(A) receptors containing a gamma2 subunit. Mutant mice with double knockout of PRIP-1 and PRIP-2 were used to investigate aspects of GABAergic regulation of orofacial movements and interactions with D(1) mechanisms. Vertical jaw movements, tongue protrusions and movements of the head and vibrissae were reduced in PRIP-1/2 double knockouts. The GABA(A)ergic agent diazepam reduced movements of the head and vibrissae; these effects were unaltered in PRIP-1/2 double knockouts. The D(1)-like agonist SKF 83959 induced vertical jaw movements, incisor chattering, and movements of the head and vibrissae that were unaltered in PRIP-1/2 double knockouts. However, SKF 83959-induced tongue protrusions were reduced in PRIP-1/2 double knockouts. PRIP-mediated regulation of GABA(A)ergic receptor mechanisms influences topographically distinct aspects of orofacial movement and interacts with D(1) receptor systems.

Assessment of jaw movements by magnetic sensor in relation to topographies of orofacial behaviour in freely moving rats: Studies with the dopamine D(1)-like receptor agonists SKF 83822 vs SKF 83959

This study applies new magnetic sensor-electromyographic technology for recording jaw movements in freely moving rats to analyse topographies of orofacial movement that occur in association with individual elements of behaviour under challenge with two dopamine D(1)-like receptor agonists, SKF 83822 ([R/S]-6-chloro-7, 8-dihydroxy-3-allyl-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine) and SKF 83959([R/S]-3-methyl-6-chloro-7, 8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine). Grooming of the snout/face involved primarily dominant-mouth opening jaw movements with small activation of digastric muscles; subsequent grooming of the flank/trunk was characterised by repetitive, uniform jaw movements with small activation of digastric and masseter muscles. In contrast, grooming of the fingers and tail typically involved high-frequency jaw movements with variable vertical jaw movements and/or strong activation of masseter muscles. Vacuous chewing involved two distinct patterns of jaw movements: a dominant-closing pattern, with strong activation of masseter muscles, and a dominant-opening pattern, with slight activation of masseter muscles. SKF 83822 stimulates dopamine D(1)-like receptors and activates adenylate cyclase but not phosphoinositide hydrolysis, while SKF 83959 stimulates dopamine D(1)-like receptors and activates phosphoinositide hydrolysis but not adenylate cyclase. These agonists exerted differential effects on jaw movements, as SKF 83959 induced more jaw movements per episode of syntactic grooming than SKF 83822, while SKF 83822 induced more jaw movements during non-syntactic grooming than SKF 83959. Magnetic sensor technology in freely moving animals resolved distinct topographies of orofacial movement and informs on their relationship to other behaviours in the rodent repertoire and to dopamine D(1)-like receptor function.

Phenotype of spontaneous orofacial dyskinesia in neuregulin-1 'knockout' mice

Studies in antipsychotic-naïve patients with schizophrenia indicate a baseline level of spontaneous involuntary movements, particularly orofacial dyskinesia. Neuregulin-1 is associated with risk for schizophrenia and its functional role can be studied in 'knockout' mice. We have shown previously that neuregulin-1 'knockouts' evidence disruption in social behaviour. Neuregulin-1 'knockouts' were assessed for four topographies of orofacial movement, both spontaneously and under challenge with the D(1)-like dopamine receptor agonist SKF 83959. Neuregulin-1 'knockouts' evidenced an increase in spontaneous incisor chattering, particularly among males. SKF 83959 induced incisor chattering, vertical jaw movements and tongue protrusions; the level of horizontal jaw movements was increased and that of tongue protrusions decreased in neuregulin-1 'knockouts'. These findings indicate that the schizophrenia risk gene neuregulin-1 is involved in the regulation of not only social behaviour but also orofacial dyskinesia. Orofacial dyskinesia in neuregulin-1 mutants may indicate some modest genetic relationship between risk for schizophrenia and vulnerability to spontaneous movement disorder.

Differential involvement of cyclase- versus non-cyclase-coupled D1-like dopamine receptors in orofacial movement topography in mice: studies with SKF 83822

Though orofacial movements are fundamental motor patterns that are known to be regulated critically by D1-like dopamine receptors, these processes remain poorly understood. This uncertainty is heightened by evidence for putative D1-like receptors that are linked not only to adenylyl cyclase (AC) but also to phospholipase C (PLC). Using a new method, we have characterised four topographies of orofacial movement in the mouse using the novel D1-like agonist SKF 83822, which stimulates AC but not PLC. These were compared with responses to SKF 83959, which stimulates PLC but not AC. Also, effects were characterised using the D1-like antagonist SCH 23390 and the D2-like antagonist YM 09151-2. SKF 83822 induced vertical jaw movements with incisor chattering but inhibited horizontal jaw movements; there was little effect on tongue protrusions. Vertical jaw movements induced by SKF 83822 were inhibited by SCH 23390 but uninfluenced by YM 09151-2, while YM 09151-2 released horizontal jaw movements; thus, D1-like agonist-induced, AC-mediated vertical jaw movements constitute a 'pure' D1-like-dependent process that does not involve D1-like:D2-like interactions, while horizontal jaw movements involve oppositional interactions. Orofacial movements in mice appear to consist of at least four phenomenologically dissociable topographies that are mechanistically distinct. They are regulated differentially by AC- and/or PLC-dependent processes and these processes involve distinct D1-like:D2-like interactions.

C57BL/6J and DBA/2J mice vary in lick rate and ingestive microstructure

Fluid licking in mice is an example of a rhythmic behavior thought to be under the control of a central pattern generator. Inbred strains of mice have been shown to differ in mean or modal interlick interval (ILI) duration, suggesting a genetic-based variation. We investigated water licking in the commonly used inbred strains C57BL/6J (B6) and DBA/2J (D2), using a commercially available contact lickometer. Results from 20-min test sessions indicated that D2 mice lick at a faster rate than B6 mice (10.6 licks/s vs. 8.5 licks/s), based on analysis of the distribution of short-duration ILIs (50-160 ms). This strain difference was independent of sex, extent of water deprivation or total number of licks. D2 mice also displayed a faster lick rate when the strains were tested with a series of brief (5 s) trials. However, when ingestion over the entire 20-min session was analyzed, it was evident that D2 mice had an overall slower rate of ingestion than B6 mice. This was because of the tendency for D2 mice to have more very long pauses (>30 s) between sequences of licking bursts. Overall, it appeared that D2 mice licked more efficiently, ingesting more rapidly during excursions to the spout that were fewer and farther between.

Disruption of orofacial movement topographies in congenic mutants with dopamine D5 but not D4 receptor or DARPP-32 transduction 'knockout'

The role of D(1)-like [D(1), D(5)] and D(2)-like [D(2), D(3), D(4)] dopamine receptors and dopamine transduction via DARPP-32 in topographies of orofacial movement was assessed in restrained mice with congenic D(4) vs. D(5) receptor vs. DARPP-32 'knockout'. D(4) and DARPP-32 mutants evidenced no material phenotype; also, there were no alterations in topographical responsivity to either the selective D(2)-like agonist RU 24213 or the selective D(1)-like agonist SK and F 83959. In contrast, D(5) mutants evidenced an increase in spontaneous vertical jaw movements, which habituated more slowly than in wildtypes, and a decrease in horizontal jaw movements; topographical responsivity to SK and F 83959 and RU 24213 was unaltered. D(5) receptors regulate distinct topographies of vertical and horizontal jaw movement in an opposite manner. In assuming that the well-recognised role of the D(1)-like family in regulating orofacial movements involves primarily D(1) receptors, a role for their D(5) counterparts may have been overlooked.

Topographical resolution of jaw movements mediated by cyclase- vs. non-cyclase-coupled dopamine D1-like receptors: Studies with SK&F 83822

This study examined the effects on orofacial movement topography of SK&F 83822 ([R/S]-6-chloro-7,8-dihydroxy-3-allyl-1-[3-methylphenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine), which stimulates dopamine D(1)-like receptors coupled to stimulation of adenylyl cyclase (AC) but not phosphoinositide (PI) hydrolysis, in comparison with SK&F 83959 ([R/S]-3-methyl-6-chloro-7,8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine), which stimulates PI hydrolysis but not AC. SK&F 83822 alone induced chattering, while SK&F 83959 alone exerted little effect. SK&F 83822 and SK&F 83959 each in combination with the dopamine D(2)-like agonist quinpirole resulted in synergistic induction of non-chattering movements with tongue protrusions. These effects were blocked by the dopamine D(1)-like receptor antagonist SCH 23390 ([R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine). However, 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) exerted a biphasic effect on synergism with SK&F 83822: chattering was initially released but antagonised thereafter. Only antagonism was seen for synergism with SK&F 83959. While both AC- and PI-coupled dopamine D(1)-like receptors participate in synergistic dopamine D(1)-like:D(2)-like receptor interactions, topographically specific synergistic and oppositional dopamine D(1)-like:D(2)-like interactions evident with SK&F 83822 reflect the involvement primarily of D(1)-like receptors coupled to AC rather than PI.

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

BACKGROUND

Mutants 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 G alpha(olf)[G gamma7], adenylyl cyclase type 5, PKA [RIIbeta] 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.

OBJECTIVE

This 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.

METHODS

It 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'.

DISCUSSION

There 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 G alpha(i)/G alpha(s)/G alpha(olf)[G gamma7]-adenylyl cyclase type 5-PKA [RIIbeta]-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.

Ethological resolution of behavioural topography and D1-like versus D2-like agonist responses in congenic D5 dopamine receptor mutants: identification of D5:D2-like interactions

The phenotypic ethogram of congenic dopamine D(5) receptor "knockout" mice was evaluated. Each individual topography of behaviour within the natural repertoire was assessed over the extended course of initial exploration of and subsequent habituation to the environment, and following challenge with a series of D(1)-like agonists. Over initial exploration, D(5)-null mice evidenced a modest reduction in locomotion and a modest increase in sifting. Subsequent habituation revealed additional phenotypic effects, primarily overall reduction in grooming and delayed habituation of rearing. Among D(1)-like agonists, A 68930 stimulates both adenylyl cyclase and a putative D(1)-like receptor coupled to stimulation of phospholipase C-mediated phosphoinositide hydrolysis; conversely, SK&F 83959 stimulates phosphoinositide hydrolysis but not adenylyl cyclase while SK&F 83822 stimulates adenylyl cyclase but not phosphoinositide hydrolysis. Though programmed grooming syntax and episodic seizure activity induced by A 68930 and SK&F 83822 were unaltered, grooming induced by SK&F 83959 was reduced in D(5) mutants. Stereotyped, ponderous locomotion induced by the D(2)-like agonist RU 24213 was enhanced in D(5) mutants. Phenotypic and pharmacological characterisation of congenic D(5)-null mice at an ethological level identifies novel functional roles for the D(5) receptor in mediating discrete topographies of behaviour relating to exploration, sequential motor coordination, and how these processes change over the course of interaction with and habituation to the environment. Additionally, they indicate the involvement of phosphoinositide hydrolysis and D(5):D(2)-like interactions in regulating these processes.

Phenotypic analysis of dopamine receptor knockout mice; recent insights into the functional specificity of dopamine receptor subtypes

The functional specificity of dopamine receptor subtypes remains incompletely understood, in part due to the absence of highly selective agonists and antagonists. Phenotypic analysis of dopamine receptor knockout mice has been instrumental in identifying the role of dopamine receptor subtypes in mediating dopamine's effects on motor function, cognition, reward, and emotional behaviors. In this article, we provide an update of recent studies in dopamine receptor knockout mice and discuss the limitations and future promise of this approach.

Ethologically Based Resolution of D2-Like Dopamine Receptor Agonist-versus Antagonist-Induced Behavioral Topography in Dopamine- and Adenosine 3′,5′-Monophosphate-Regulated Phosphoprotein of 32 kDa “Knockout” Mutants Congenic on the C57BL/6 Genetic Background

Given the critical role of dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein of 32 kDa (DARPP-32) in the regulation of dopaminergic function, DARPP-32-null mutant mice congenic on the inbred C57BL/6 strain for 10 generations were examined phenotypically for their ethogram of responsivity to the selective D2-like receptor agonist RU 24213 (N-n-propyl-N-phenylethyl-p-3-hydroxyphenylethylamine) and the selective D2-like receptor antagonist YM 09151-2 (cis-N-[1-benzyl-2-methyl-pyrrolidin-3-yl]-5-chloro-2-methoxy-4-methylaminobenzamide), using procedures that resolve all topographies of behavior in the natural repertoire. After vehicle challenge, levels of sniffing and rearing seated were reduced in DARPP-32 mutants; the injection procedure seems to constitute a "stressor" that reveals phenotypic effects of DARPP-32 deletion not apparent under natural conditions. Topographical effects of 0.3 to 10.0 mg/kg RU 24213, primarily induction of sniffing and ponderous locomotion with accompanying reductions in rearing, grooming, sifting and chewing, were not altered to any material extent in DARPP-32-null mice. However, topographical effects of 0.005 to 0.625 mg/kg YM 09151-2, namely, reduction in sniffing, locomotion, rearing, grooming, and chewing but not sifting, were essentially absent in DARPP-32 mutants. Thus, the D2-like receptor agonist-mediated ethogram was essentially conserved, whereas major elements of the corresponding D2-like receptor antagonist-mediated ethogram were essentially absent in DARPP-32-null mice. This suggests some relationship between 1) extent of tonic dopaminergic activation of DARPP-32 mechanisms and 2) compensatory mechanisms consequent to the developmental absence of DARPP-32, which may emerge to act differentially on individual elements of the DARPP-32 system. Critically, the present data indicate that phenotypic effects of a given gene deletion using an agonist acting on the system disrupted cannot be generalized to a corresponding antagonist, and vice versa.