Topographical assessment and pharmacological characterization of orofacial movements in mice: dopamine D(1)-like vs. D(2)-like receptor regulation

Antipsychotic Behavioral Phenotypes in the Mouse Collaborative Cross Recombinant Inbred Inter-Crosses (RIX)

Schizophrenia is an idiopathic disorder that affects approximately 1% of the human population, and presents with persistent delusions, hallucinations, and disorganized behaviors. Antipsychotics are the standard pharmacological treatment for schizophrenia, but are frequently discontinued by patients due to inefficacy and/or side effects. Chronic treatment with the typical antipsychotic haloperidol causes tardive dyskinesia (TD), which manifests as involuntary and often irreversible orofacial movements in around 30% of patients. Mice treated with haloperidol develop many of the features of TD, including jaw tremors, tongue protrusions, and vacuous chewing movements (VCMs). In this study, we used genetically diverse Collaborative Cross (CC) recombinant inbred inter-cross (RIX) mice to elucidate the genetic basis of antipsychotic-induced adverse drug reactions (ADRs). We performed a battery of behavioral tests in 840 mice from 73 RIX lines (derived from 62 CC strains) treated with haloperidol or placebo in order to monitor the development of ADRs. We used linear mixed models to test for strain and treatment effects. We observed highly significant strain effects for almost all behavioral measurements investigated (P < 0.001). Further, we observed strong strain-by-treatment interactions for most phenotypes, particularly for changes in distance traveled, vertical activity, and extrapyramidal symptoms (EPS). Estimates of overall heritability ranged from 0.21 (change in body weight) to 0.4 (VCMs and change in distance traveled) while the portion attributable to the interactions of treatment and strain ranged from 0.01 (for change in body weight) to 0.15 (for change in EPS). Interestingly, close to 30% of RIX mice exhibited VCMs, a sensitivity to haloperidol exposure, approximately similar to the rate of TD in humans chronically exposed to haloperidol. Understanding the genetic basis for the susceptibility to antipsychotic ADRs may be possible in mouse, and extrapolation to humans could lead to safer therapeutic approaches for schizophrenia.

Modelling the neuromotor abnormalities of psychotic illness: Putative mechanisms and systems dysfunction

Limitations in access to antipsychotic-naïve patients and in the incisiveness of studies that can be conducted on them, together with the inevitability of subsequent antipsychotic treatment, indicate an enduring role for animal models that can inform on the pathobiology of neuromotor abnormalities in schizophrenia and related psychotic illness. This review focusses particularly on genetically modified mouse models that involve genes associated with risk for schizophrenia and with mechanisms implicated in the neuromotor abnormalities evident in psychotic patients, as well as developmental models that seek to mirror the trajectory, phenomenology and putative pathophysiology of psychotic illness. Such abnormalities are inconsistent and subtle in mice mutant for some schizophrenia risk genes but more evident for others. The phenotype of dopaminergic and glutamatergic mutants indicates the involvement of these mechanisms, informs on the roles of specific receptor subtypes, and implicates the interplay of cortical and subcortical processes. Developmental models suggest a criticality in the timing of early adversity for diversity in the relative emergence of psychological symptoms vis-à-vis neuromotor abnormalities in the overall psychosis phenotype. These findings elaborate current concepts of dysfunction in a neuronal network linking the cerebral cortex, basal ganglia, thalamus and cerebellum. Both findings in model systems and clinical evidence converge in indicating that any distinction between 'psychomotor' and 'neuromotor' abnormality is artificial and arbitrary due to a unitary origin in developmentally determined systems/network dysfunction that underlies the lifetime trajectory of psychotic illness.

Genetics of adverse reactions to haloperidol in a mouse diallel: a drug-placebo experiment and Bayesian causal analysis

Haloperidol is an efficacious antipsychotic drug that has serious, unpredictable motor side effects that limit its utility and cause noncompliance in many patients. Using a drug-placebo diallel of the eight founder strains of the Collaborative Cross and their F1 hybrids, we characterized aggregate effects of genetics, sex, parent of origin, and their combinations on haloperidol response. Treating matched pairs of both sexes with drug or placebo, we measured changes in the following: open field activity, inclined screen rigidity, orofacial movements, prepulse inhibition of the acoustic startle response, plasma and brain drug level measurements, and body weight. To understand the genetic architecture of haloperidol response we introduce new statistical methodology linking heritable variation with causal effect of drug treatment. Our new estimators, "difference of models" and "multiple-impute matched pairs", are motivated by the Neyman-Rubin potential outcomes framework and extend our existing Bayesian hierarchical model for the diallel (Lenarcic et al. 2012). Drug-induced rigidity after chronic treatment was affected by mainly additive genetics and parent-of-origin effects (accounting for 28% and 14.8% of the variance), with NZO/HILtJ and 129S1/SvlmJ contributions tending to increase this side effect. Locomotor activity after acute treatment, by contrast, was more affected by strain-specific inbreeding (12.8%). In addition to drug response phenotypes, we examined diallel effects on behavior before treatment and found not only effects of additive genetics (10.2-53.2%) but also strong effects of epistasis (10.64-25.2%). In particular: prepulse inhibition showed additivity and epistasis in about equal proportions (26.1% and 23.7%); there was evidence of nonreciprocal epistasis in pretreatment activity and rigidity; and we estimated a range of effects on body weight that replicate those found in our previous work. Our results provide the first quantitative description of the genetic architecture of haloperidol response in mice and indicate that additive, dominance-like inbreeding and parent-of-origin effects contribute strongly to treatment effect heterogeneity for this drug.

Dopamine is involved in food-anticipatory activity in mice

When food is available during a restricted and predictable time of the day, mammals exhibit food-anticipatory activity (FAA), an increase in locomotor activity preceding the presentation of food. Although many studies have attempted to locate the food-entrainable circadian oscillator in the central nervous system, the pathways that mediate food entrainment are a matter of controversy. The present study was designed to determine the role of dopaminergic and histaminergic systems on FAA. Mice were given access to food for 2 h (ZT12-ZT14), and FAA was defined as the locomotor activity that occurred 2 h before the availability of food. Dopamine D(1) receptor (R), D(2)R, and histamine H(1)R-specific antagonists were used to clarify the role of dopamine and histamine receptors in FAA induced by food restriction (FR). FAA was monitored by infrared locomotor activity sensors. Mice were sacrificed at ZT12 on the 14th day of FR, and monoamine concentrations were determined by high-performance liquid chromatography coupled to electrochemical detection (HPLC-ECD). The results showed that pretreatment with the D(1)R antagonist SCH23390 at 1, 3, or 10 µg/kg significantly reduced FAA by 19% (p < 0.05), 26% (p < 0.05), or 19% (p < 0.01), respectively, and the D(2)R antagonist raclopride at 22, 67, or 200 µg/kg significantly reduced FAA by 16% (p < 0.05), 36% (p < 0.01), or 41% (p < 0.01), respectively, as compared with vehicle control. Moreover, coadministration of SCH23390 (10 µg/kg) and raclopride (200 µg/kg) synergistically inhibited FAA by 57% (p < 0.01) as compared with vehicle control. Consistently, the levels of dopamine and its metabolites in the striatum and midbrain were significantly increased during FAA, even with the pretreatment of D(1)R and D(2)R antagonists. However, pretreatment with pyrilamine at 2.5, 5, or 10 mg/kg did not significantly reduce FAA, although it reduced the locomotor activity during the dark period in ad libitum mice. These results strongly indicate that the dopaminergic system plays an essential role in the FAA in mice.

Genome-wide association mapping of loci for antipsychotic-induced extrapyramidal symptoms in mice

Tardive dyskinesia (TD) is a debilitating, unpredictable, and often irreversible side effect resulting from chronic treatment with typical antipsychotic agents such as haloperidol. TD is characterized by repetitive, involuntary, purposeless movements primarily of the orofacial region. In order to investigate genetic susceptibility to TD, we used a validated mouse model for a systems genetics analysis geared toward detecting genetic predictors of TD in human patients. Phenotypic data from 27 inbred strains chronically treated with haloperidol and phenotyped for vacuous chewing movements were subject to a comprehensive genomic analysis involving 426,493 SNPs, 4,047 CNVs, brain gene expression, along with gene network and bioinformatic analysis. Our results identified ~50 genes that we expect to have high prior probabilities for association with haloperidol-induced TD, most of which have never been tested for association with human TD. Among our top candidates were genes regulating the development of brain motor control regions (Zic4 and Nkx6-1), glutamate receptors (Grin1 and Grin2a), and an indirect target of haloperidol (Drd1a) that has not been studied as well as the direct target, Drd2.

Phenotypic disruption to orofacial movement topography in conditional mutants with generalized CamKIIa/Cre D1Tox versus striatal-specific DARPP-32/Cre D1Tox ablation of D1 dopamine receptor-expressing cells

Orofacial movements were quantified in (a) DARPP-32/Cre D1Tox mutants, having progressive loss of D1 dopamine receptor expressing striatal medium spiny neurons and (b) CamKIIa/Cre D1Tox mutants, having progressive, generalized loss of forebrain D1 receptor expressing cells. Horizontal jaw movements and tongue protrusions were reduced in DARPP-32/Cre but not in CamKIIa/Cre mutants; head and vibrissae movements were increased in DARPP-32/Cre but decreased in CamKIIa/Cre mutants. In drug challenge studies, tongue protrusions were increased in CamKIIa/Cre mutants following vehicle, suggesting a stress-related phenotype. These findings indicate that mice with progressive loss of striatal-specific D1 receptor expressing cells have an orofacial phenotype that may be modulated by the loss of extrastriatal D1 receptor expressing cells. As progressive loss of D1 dopamine receptor-expressing cells is a hallmark feature of Huntington's disease (HD), these findings may inform the functional role of loss of this cell population in the overall pathobiology of HD.

Antipsychotic-induced vacuous chewing movements and extrapyramidal side effects are highly heritable in mice

Pharmacogenomics is yet to fulfill its promise of manifestly altering clinical medicine. As one example, a predictive test for tardive dyskinesia (TD) (an adverse drug reaction consequent to antipsychotic exposure) could greatly improve the clinical treatment of schizophrenia but human studies are equivocal. A complementary approach is the mouse-then-human design in which a valid mouse model is used to identify susceptibility loci, which are subsequently tested in human samples. We used inbred mouse strains from the Mouse Phenome Project to estimate the heritability of haloperidol-induced activity and orofacial phenotypes. In all, 159 mice from 27 inbred strains were chronically treated with haloperidol (3 mg kg(-1) per day via subdermal slow-release pellets) and monitored for the development of vacuous chewing movements (VCMs; the mouse analog of TD) and other movement phenotypes derived from open-field activity and the inclined screen test. The test battery was assessed at 0, 30, 60, 90 and 120 days in relation to haloperidol exposure. As expected, haloperidol caused marked changes in VCMs, activity in the open field and extrapyramidal symptoms (EPS). Unexpectedly, factor analysis demonstrated that these measures were imprecise assessments of a latent construct rather than discrete constructs. The heritability of a composite phenotype was ∼0.9 after incorporation of the longitudinal nature of the design. Murine VCMs are a face valid animal model of antipsychotic-induced TD, and heritability estimates from this study support the feasibility of mapping of susceptibility loci for VCMs.

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.

Rotation and immediate-early gene expression in rats treated with the atypical D1 dopamine agonist SKF 83822

Classical agonists of the dopamine D1 receptor activate both adenylyl cyclase and phospholipase C (PLC) signaling pathways. As a result, the extent to which these two pathways are essentially involved in various effects produced by D1 receptor agonists is currently uncertain. In the present report we examined the effects of SKF 83822, a dopamine D1 agonist which has been reported to activate adenylyl cyclase, but not PLC, on behavior and immediate early gene (IEG) expression in rats with unilateral 6-hydroxydopamine lesions. SKF 83822 (25-100 microg/kg) induced dose dependent contralateral rotation in these subjects, and, additionally, stimulated strong expression of the IEG products c-Fos, Fra2, Zif/268 and Arc in the deinnervated striatum. All of these effects could be antagonized by pretreatment with the selective D1 dopamine antagonist SCH 23390 (0.5 mg/kg). Although PLC may be involved in many effects mediated through dopamine D1 receptors, these results suggest that direct activation of PLC is not necessary for the induction of either rotation or IEG expression in dopamine depleted rats.

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.

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.

The atypical dopamine D1 receptor agonist SKF 83959 induces striatal Fos expression in rats

The effects of dopamine D1 receptor agonists are often presumed to result from an activation of adenylyl cyclase, but dopamine D1 receptors may also be linked to other signal transduction cascades and the relative importance of these various pathways is currently unclear. SKF 83959 is an agonist at dopamine D1 receptors linked to phospholipase C, but has been reported to be an antagonist at receptors linked to adenylyl cyclase. The current report demonstrates that SKF 83959 induces pronounced, nonpatchy, expression of the immediate-early gene product Fos in the striatum of intact rats which can be converted to a patchy pattern by pretreatment with the dopamine D2-like receptor agonist quinpirole. In rats with unilateral 6-hydroxydopamine lesions SKF 83959 induces strong behavioral rotation and a greatly potentiated Fos response. All of the responses to SKF 83959, in both intact and dopamine-depleted animals, can be blocked by pretreatment with the dopamine D1 receptor antagonist SCH-23390. In intact subjects, SKF 83959 induced Fos expression less potently than the standard dopamine D1 receptor agonist SKF 82958, but the two drugs were approximately equipotent in deinnervated animals. These results demonstrate for the first time that possession of full efficacy at dopamine D1 receptors linked to adenylyl cyclase is not a necessary requirement for the induction of striatal Fos expression in intact animals and suggest that alternative signal transduction pathways may play a role in dopamine agonist induced Fos expression, especially in dopamine-depleted subjects.

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.

A comparison of the locomotor stimulant effects of D1-like receptor agonists in mice

Efficacy in stimulating adenylyl cyclase (AC) has traditionally been used to distinguish dopamine D1-like receptor agonists from dopamine D2-like receptor agonists. However, there is a limited association between the effects of D1-like agonists in behavioral assays and their effectiveness at stimulating AC. Other second messenger actions might contribute to the behavioral effects of D1-like agonists, as there is evidence for a link to the hydrolysis of phosphoinositide (PI). The present study compared the locomotor stimulant effects of five D1-like receptor agonists having different efficacies in assays of AC and PI activity. All D1-like agonists produced long-lasting biphasic effects on locomotor activity. SKF 38393, the prototypical partial agonist (based on AC activity), produced limited changes in locomotor activity, whereas the partial agonists SKF 75670 and SKF 77434 produced locomotor stimulant effects that were similar to or greater than those of the full efficacy agonists SKF 82958 and SKF 81297. However, there did not appear to be a relationship between maximal behavioral effects and AC stimulation or PI hydrolysis. The results suggest a complex relationship between the behavioral effects of D1-like agonists and their intrinsic efficacies as measured by AC and /or PI stimulation. Although a limited number of compounds were examined, neither second messenger system alone appears to account fully for these behavioral effects. The current classification of D1-like agonists according to their intrinsic efficacies as defined by AC stimulation needs further scrutiny.

Prenatal ethanol preferentially enhances reactivity of the dopamine D1 but not D2 or D3 receptors in offspring

Reports of prenatal ethanol (ETOH) effects on the dopamine system are inconsistent. In an attempt to clarify this issue, dams were given 35% ethanol-derived calories as the sole nutrient source in a liquid diet from the 10th through the 20th day of gestation (ETOH). Controls were pair-fed (PF) an isocaloric liquid diet or given ad libitum access to laboratory chow (LC). Prenatal exposure to both liquid diets reduced body weight of offspring relative to LC controls, more so for ETOH than for PF exposure. Prenatal ETOH also decreased litter size and viability, relative to both LC and PF control groups. On postnatal days 21-23, male and female offspring were given an injection of saline vehicle or one of eight specific dopamine receptor agonists or antagonists. Immediately after injection subjects were placed in individual observation cages, and over the following 30 min, eight behaviors (square entries, grooming, rearing, circling, sniffing, yawning, head and oral movements) were observed and quantified. No prenatal treatment effects on drug-induced behaviors were observed for dopamine D2 (Apomorphine, DPAT or Quinpirole) or D3 (PD 152255, Nafadotride, Apo or Quin effects on yawning) receptor agonists or antagonists, or for the vehicle control. In contrast, prenatal treatment effects were seen with drugs affecting the dopamine D1 receptor. Both D1 agonists (SKF 38393) and antagonists (SCH 23390 and high doses of spiperone) altered behaviors, especially oral and sniffing behaviors, in a manner which suggested enhanced dopamine D1 drug sensitivity in both ETOH and PF offspring relative to LC controls. These results suggest that at this age, both sexes experience a prenatal undernutrition-linked increase in the behavioral response to dopamine D1 agonists and antagonists, which can be intensified by gestational exposure to alcohol.

D1-like dopamine receptor-mediated function in congenic mutants with D1 vs. D5 receptor "knockout"

Current understanding of the functional roles of individual dopamine D1-like [D1, D5] and D2-like [D2L/s, D3, D4] receptor subtypes remains incomplete. In particular, the lack of pharmacological agonists and antagonists able to distinguish between D1 and D5 receptors means that any differential roles in the regulation of behavior are poorly understood. Mutant mice with targeted gene deletion ("knockout") of individual dopamine receptor subtypes offer an important alternative approach to resolving these functional roles. In congenic D1 mutants examined ethologically, progressive increases in specific topographies of behavior over wildtypes were considerably greater than those in D1 mutants on a mixed genetic background; D1 knockout appears to influence the neuronal substrate(s) of habituation to disrupt sculpture of the changing topography of behavior from initial exploration through to quiescence. Similarly, the D1 receptor appears to regulate specific topographies of orofacial movement in the mouse as these are "sculpted" in a time-dependent manner. Although the well-recognized role of the D1-like family in regulating several aspects of behavioral topography has been assumed to involve primarily D1 receptors, this presumption may require modification to accommodate a subtle but not negligible role for their D5 counterparts as evidenced in the phenotype of congenic D5 mutants.

Dopamine D1 receptors involved in locomotor activity and accumbens neural responses to prediction of reward associated with place

Predicting reward is essential in learning approach behaviors. Dopaminergic activity has been implicated in reward, movement, and cognitive processes, all essential elements in learning. The nucleus accumbens (NAc) receives converging inputs from corticolimbic information-processing areas and from mesolimbic dopamine neurons originating in the ventral tegmental area. Previously, we reported that in mice, a dopamine D2 receptor knockout (D2R-KO) eliminated the prereward inhibitory response, increased place-field size of NAc neurons, and reduced locomotor activity without marked change in intracranial self-stimulation (ICSS) behavior. The present study investigated the specific contribution of dopamine D1 receptor (D1R) in mediating reward, locomotor activity, and spatial associative processes and in regulating NAc neural responses. In contrast to D2R-KO animals, here we find D1R-KO in mice selectively eliminated the prereward excitatory response and decreased place-field size of NAc neurons. Furthermore, D1R-KO impaired ICSS behavior, seriously reduced locomotor activity, and retarded acquisition of a place learning task. Thus, the present results suggest that D1R may be an important determinant in brain stimulation reward (ICSS) and participates in coding for a type of reward prediction of NAc neurons and in spatial learning.

Topographical effects of D1-like dopamine receptor agonists on orofacial movements in mice and their differential regulation via oppositional versus synergistic D1-like: D2-like interactions: cautionary observations on SK&F 82958 as an anomalous agent

Using a novel procedure, the regulation of individual topographies of orofacial movement in the mouse by oppositional versus cooperative/synergistic D1-like: D2-like dopamine receptor interactions was studied. The D1-like agonists SK&F 38393 and SK&F 83959 each induced vertical, but not horizontal, jaw movements, together with tongue protrusions and incisor chattering; however, SK&F 82958 induced a different profile which, consistent with other neurochemical and neurophysiological studies, suggests that this agent shows anomalous properties relative to other D1-like agonists. When given alone, the D2-like agonist quinpirole reduced horizontal jaw movements and incisor chattering. On coadministration, both SK&F 38393- and SK&F 83959-induced vertical jaw movements and tongue protrusions were inhibited by quinpirole, while SK&F 82958 again showed an anomalous profile. These findings indicate that, in the mouse, vertical jaw movements and tongue protrusions are regulated by oppositional D1-like: D2-like interactions, and appear to involve a D1-like receptor that is not coupled to adenylyl cyclase, whereas horizontal jaw movements are inhibited by D2-like receptors. Additionally, results obtained using SK&F 82958 as a probe for D1-like mechanisms should be treated with considerable caution until they are confirmed using other D1-like agonists.

Prefrontal, accumbal [shell] and ventral striatal mechanisms in jaw movements and non-cyclase-coupled dopamine D1-like receptors

The effect on jaw movements of intracerebral injections of the dopamine D1-like receptor agents SK&F 83959 (3-methyl-6-chloro-7,8-dihydroxy-1-[3-methylphenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine), SK&F 38393 ([R]-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) and SCH 23390 ([R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) and of injections of the dopamine D2-like receptor agonist quinpirole into the ventrolateral striatum, accumbens shell or prefrontal cortex were studied. SK&F 38393 and SK&F 83959 injected into the ventrolateral striatum synergised with i.v. quinpirole; in the shell of accumbens, SK&F 38393 evidenced weaker synergism with quinpirole, while SK&F 83959 did not synergise with it; neither agent synergised with quinpirole in the prefrontal cortex. Co-injection of SCH 23390 or SK&F 83959 into the prefrontal cortex antagonised jaw movements induced by injection of SK&F 83959 into the ventrolateral striatum in combination with i.v. quinpirole. Injection of SK&F 83959 + quinpirole into the ventrolateral striatum, but not into the accumbens shell, resulted in synergism. These findings indicate a primary, but not exclusive, role for ventral striatal, non-cyclase-coupled dopamine D1-like receptors in the induction of jaw movements. These processes appear to require tonic activity of prefrontal cyclase-linked dopamine D1A [and/or D1B] receptors.

Comparison of the discriminative-stimulus effects of SKF 38393 with those of other dopamine receptor agonists

The dopamine D(1)-like receptor agonists have traditionally been defined molecularly by their efficacy in stimulating adenylyl cyclase. However, evidence correlating the effectiveness of these drugs in behavioral assays and their effectiveness biochemically has not been forthcoming. The present study compared the discriminative-stimulus effects of the D(1)-like partial agonist SKF 38393 with several other D(1)-like agonists, an indirect agonist, cocaine, and a D(2)-like agonist, quinpirole. Rats were trained under a fixed-ratio 30-response schedule to discriminate SKF 38393 (5.6 mg/kg) from vehicle. Under this schedule, 30 consecutive responses on one of two keys were reinforced with food presentation after a pre-session injection of 5.6 mg/kg SKF 38393, and 30 consecutive responses on the alternative key were reinforced after saline injection. When daily performances were stable, substitution patterns for several compounds were assessed during test sessions in which 30 consecutive responses on either key were reinforced. Quinpirole and cocaine each produced saline-appropriate responding. In contrast, the D(1)-like agonists, SKF 75670 and SKF 77434, fully substituted for SKF 38393. Curiously, SKF 82958, which is considered a full agonist based on adenylyl cyclase assays, was less effective in substituting for SKF 38393 (maximum drug-appropriate responding 66%) than was the partial agonist SKF 75670. The present results suggest that second messenger effects other than stimulation of adenylyl cyclase may play an important role in the behavioral effects of dopamine D(1)-like agonists.

SKF83959 selectively regulates phosphatidylinositol-linked D1 dopamine receptors in rat brain

Previously a distinct D1-like dopamine receptor (DAR) that selectively couples to phospholipase C/phosphatidylinositol (PLC/PI) was proposed. However, lack of a selective agonist has limited efforts aimed at characterizing this receptor. We characterized the in vitro and in vivo effects of SKF83959 in regulating PI metabolism. SKF83959 stimulates (EC50, 8 micro m) phosphatidylinositol 4,5-biphosphate hydrolysis in membranes of frontal cortex (FC) but not in membranes from PC12 cells expressing classical D1A DARs. Stimulation of FC PI metabolism was attenuated by the D1 antagonist, SCH23390, indicating that SKF83959 activates a D1-like DAR. The PI-linked DAR is located in hippocampus, cerebellum, striatum and FC. Most significantly, administration of SKF83959 induced accumulations of IP3 in striatum and hippocampus. In contrast to other D1 DAR agonists, SKF83959 did not increase cAMP production in brain or in D1A DAR-expressing PC12 cell membranes. However, SKF83959 inhibited cAMP elevation elicited by the D1A DAR agonist, SKF81297, indicating that the compound is an antagonist of the classical D1A DAR. Lastly, we demonstrated that SKF83959 enhances [35S]guanosine 5'-O-(3-thiotriphosphate) binding to membrane Galphaq and Galphai proteins, suggesting that PI stimulation is mediated by activation of these guanine nucleotide-binding regulatory proteins. Results indicate that SKF83959 is a selective agonist for the PI-linked D1-like DAR, providing a unique tool for investigating the functions of this brain D1 DAR subtype.

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?

Using a novel system, the role of D2-like dopamine receptors in distinct topographies of orofacial movement was assessed in mutant mice with congenic D2 vs. D3 receptor knockout, and compared with findings in D1A mutants. Under spontaneous conditions, D2 mutants evidenced increased vertical jaw movements and unaltered horizontal jaw movements, with reductions in tongue protrusions and incisor chattering; in D3 mutants, only incisor chattering was reduced. Given previous evidence that D1A mutants show reduced horizontal but not vertical jaw movements, this indicates that apparent oppositional D1-like:D2-like interactions in the regulation of composited jaw movements may in fact reflect the independent actions of D2 receptors to inhibit vertical jaw movements and of D1A receptors to facilitate horizontal jaw movements. Effects of the D2-like agonist RU 24213 to exert greater reduction in horizontal than in vertical jaw movements were not altered prominently in either D2 or D3 mutants. The D1-like agonists A 68930 and SK&F 83959 induced vertical jaw movements, tongue protrusions, and incisor chattering; induction of tongue protrusions by A 68930 was reduced in D2 mutants. D2 receptors exert topographically specific regulation of orofacial movements in a manner distinct from their D1A counterparts, while D3 receptors exert only minor regulation of such movements.

Phenotypic, ethologically based resolution of spontaneous and D(2)-like vs D(1)-like agonist-induced behavioural topography in mice with congenic D(3) dopamine receptor "knockout"

Uncertainty as to the functional role of the D(3) dopamine receptor, due primarily to a paucity of selective agonists or antagonists, is being addressed in mice with targeted gene deletion ("knockout") thereof. This study describes, for the first time, the phenotype of congenic D(3)-null mice. Initially, 129/Sv x C57BL/6 D(3)-null mice were backcrossed 14 times onto C57BL/6; they were then assessed using an ethologically based approach which resolves all topographies of behaviour within the mouse repertoire. The ethogram of D(3)-null mice, on comparison with wildtypes, was characterised by no alteration in any topography of behaviour over an initial period of exploration; subsequent assessment over several hours revealed only increased rearing among females due to delayed habituation. Low doses of the selective D(2)-like agonist RU 24213 (0.016-0.25 mg/kg) inhibited topographies of exploratory behaviour; this effect was diminished in D(3)-null mice only when investigated following prolonged habituation, and then only for certain topographies of behaviour, primarily sniffing and rearing. High doses of RU 24213 (0.1-12.5 mg/kg) induced stereotyped sniffing and "ponderous" locomotion, while the selective D(1)-like agonist SK&F 83959 (0.016-2.0 mg/kg) promoted characteristic grooming syntax; these effects did not differ materially between the genotypes. When examined topographically on an essentially congenic C57BL/6 background (<0.005% 129/Sv), the resultant phenotype indicated essential conservation of the mouse ethogram, high-dose D(2)-like stimulatory effects, and D(1)-like stimulatory effects in the absence of D(3) receptors. A role for D(3) receptors in inhibitory processes appeared topographically circumscribed and only when baseline levels of behaviour were low.

Phenotypic resolution of spontaneous and D1-like agonist-induced orofacial movement topographies in congenic dopamine D1A receptor 'knockout' mice

A novel system was used to assess the role of D(1)-like dopamine receptors in distinct topographies of orofacial movements in mice with congenic D(1A) receptor knockout. Under spontaneous conditions, vertical jaw movements in wild-types declined with time at a rate that was reduced in D(1A) mutants, while horizontal jaw movements emerged progressively in wild-types but not in D(1A) mutants; tongue protrusions were absent in D(1A) mutants, while incisor chattering was initially reduced in D(1A) mutants but rose subsequently to reach the level of wild-types. D(1A) receptors exert a topographically specific role in regulating individual spontaneous orofacial movements, and these involve interactions with psychomotor processes which 'sculpt' behavioural change over time. The anomalous D(1)-like agonist SK&F 83959, which fails to stimulate, and indeed inhibits the stimulation of adenylyl cyclase induced by dopamine, readily stimulated vertical jaw movements, tongue protrusions and incisor chattering, and these response topographies were absent in D(1A) mutants. These results suggest that D(1A) receptors may exert some form of permissive role over orofacial topographies initiated via a novel, putative D(1)-like site not linked to adenylyl cyclase, or that some D(1A) receptors might be coupled to a transduction system other than adenylyl cyclase.