Drugs acting at D-1 and D-2 dopamine receptors induce identical purposeless chewing in rats which can be differentiated by cholinergic manipulation

A Subset of Purposeless Oral Movements Triggered by Dopaminergic Agonists Is Modulated by 5-HT2C Receptors in Rats: Implication of the Subthalamic Nucleus

Dopaminergic medication for Parkinson’s disease is associated with troubling dystonia and dyskinesia and, in rodents, dopaminergic agonists likewise induce a variety of orofacial motor responses, certain of which are mimicked by serotonin2C (5-HT_2C) receptor agonists. However, the neural substrates underlying these communalities and their interrelationship remain unclear. In Sprague-Dawley rats, the dopaminergic agonist, apomorphine (0.03–0.3 mg/kg) and the preferential D2/3 receptor agonist quinpirole (0.2–0.5 mg/kg), induced purposeless oral movements (chewing, jaw tremor, tongue darting). The 5-HT_2C receptor antagonist 5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxyl]-5-pyridyl]carbamoyl]-6-trifluoromethylindone (SB 243213) (1 mg/kg) reduced the oral responses elicited by specific doses of both agonists (0.1 mg/kg apomorphine; 0.5 mg/kg quinpirole). After having confirmed that the oral bouts induced by quinpirole 0.5 mg/kg were blocked by another 5-HT_2C antagonist (6-chloro-5-methyl-1-[6-(2-methylpiridin-3-yloxy)pyridine-3-yl carbamoyl] indoline (SB 242084), 1 mg/kg), we mapped the changes in neuronal activity in numerous sub-territories of the basal ganglia using c-Fos expression. We found a marked increase of c-Fos expression in the subthalamic nucleus (STN) in combining quinpirole (0.5 mg/kg) with either SB 243213 or SB 242084. In a parallel set of electrophysiological experiments, the same combination of SB 243213/quinpirole produced an irregular pattern of discharge and an increase in the firing rate of STN neurons. Finally, it was shown that upon the electrical stimulation of the anterior cingulate cortex, quinpirole (0.5 mg/kg) increased the response of substantia nigra pars reticulata neurons corresponding to activation of the “hyperdirect” (cortico-subthalamonigral) pathway. This effect of quinpirole was abolished by the two 5-HT_2C antagonists. Collectively, these results suggest that induction of orofacial motor responses by D2/3 receptor stimulation involves 5-HT_2C receptor-mediated activation of the STN by recruitment of the hyperdirect (cortico-subthalamonigral) pathway.

Chronic Exposure to Methamphetamine Disrupts Reinforcement-Based Decision Making in Rats

The persistent use of psychostimulant drugs, despite the detrimental outcomes associated with continued drug use, may be because of disruptions in reinforcement-learning processes that enable behavior to remain flexible and goal directed in dynamic environments. To identify the reinforcement-learning processes that are affected by chronic exposure to the psychostimulant methamphetamine (MA), the current study sought to use computational and biochemical analyses to characterize decision-making processes, assessed by probabilistic reversal learning, in rats before and after they were exposed to an escalating dose regimen of MA (or saline control). The ability of rats to use flexible and adaptive decision-making strategies following changes in stimulus-reward contingencies was significantly impaired following exposure to MA. Computational analyses of parameters that track choice and outcome behavior indicated that exposure to MA significantly impaired the ability of rats to use negative outcomes effectively. These MA-induced changes in decision making were similar to those observed in rats following administration of a dopamine D2/3 receptor antagonist. These data use computational models to provide insight into drug-induced maladaptive decision making that may ultimately identify novel targets for the treatment of psychostimulant addiction. We suggest that the disruption in utilization of negative outcomes to adaptively guide dynamic decision making is a new behavioral mechanism by which MA rigidly biases choice behavior.

Behavioral pharmacology of orofacial movement disorders

Dysfunction in orofacial movement is evident in patients with schizophrenia, Parkinson's disease and Huntington's disease. In animal studies on orofacial dyskinesia, these neurological disorders have been considered as a starting point to examine the pathophysiology and mechanisms underlying the symptoms. There is circumstantial evidence that orofacial dyskinesia in humans might be the consequence of hyperfunctioning mesolimbic-pallidal circuitry, in which the mesolimbic region occupies a central role, in contrast to typical Parkinson-like symptoms which involve hypofunction in the nigrostriato-nigral circuity. Studies in animals suffer from technical difficulties concerning the assessment of orofacial behaviors. There are some experimental designs that provide detailed information on the amplitude and the frequency of the jaw movements. By using such methods, the involvement of neurotransmitter systems and functional neural connections within the basal ganglia has been studied in rat rhythmical jaw movements. Regarding neurotransmitter systems, dopaminergic, cholinergic, γ-aminobutyric acid (GABA)ergic and glutamaterigic systems have been shown to be involved in rat rhythmical jaw movements. The involved neural connections have also been investigated, focusing on the differential role between the dorsal and ventral part of the striatum, the shell and core of the nucleus accumbens and the output pathways from the striatum and the nucleus accumbens. Taking available clinical and experimental evidence, the orofacial dyskinesias are thought to arise when hierarchically lower order output stations of the mesolimbic region start to dysfunction as a consequence of the arrival of distorted information sent by the mesolimbic region. This review seeks to provide an overview of prior and recent findings across several orofacial movement disorders and interpret new insights in the context of the limitations of behavioral pharmacology and prior knowledge of the regulation of behavior by dopamine receptors and other related neuronal systems.

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.

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.

Behavioral response profiles following drug challenge with dopamine receptor subtype agonists and antagonists in developing rat

As part of an investigation into the effects of gestational ethanol (ETOH) exposure on the developing dopamine (DA) system, pregnant Sprague-Dawley rats were exposed to one of three conditions: ETOH, pair-fed (PF) to the ETOH group, or ad libitum lab chow controls (LC). In this paper we report behavioral drug challenge effects for offspring of the two control groups (PF and LC). Male and female pups between postnatal days (PNDs) 21 and 23 in age were exposed to one of three intraperitoneal/subcutaneous doses of one of eight drugs chosen to assess the functional status of the DA D(1), D(2), and D(3) receptor subtype, or a saline control. Agonists were SKF 38393, apomorphine (APO), quinpirole (QUIN), and 7-hydroxy-N,N-di-n-propyl-2-amino-tetralin [7-OH-DPAT (DPAT)]; antagonists were spiperone (SPIP), SCH 23390, and two recently developed D(3) antagonists nafadotride (NAF) and PD 152255. Immediately following drug injection, pups were placed in observation cages, where eight behaviors (square entries, grooming, circling, rearing, sniffing, head and oral movements, and yawning) were scored at 3-min intervals for 30 min. Classic behavioral profiles were generally obtained for the high-dose mixed agonists APO, DPAT, and QUIN, which potently increased square entries, rearing, and sniffing, while reducing grooming and head movements. However, low-dose APO had no effect on behavior. The D(1) agonist, SKF 38393, had a strikingly different behavioral profile; it had no effect on square entries at any dose, while increasing grooming and sniffing at the medium dose. The D(1) antagonist, SCH 23390, profoundly decreased all behaviors except oral and head movements, especially at high doses. In contrast, the effects of the D(2) antagonist, SPIP, were limited to increasing sniffing at the medium dose. The two putative D(3) antagonists, NAF and PD 152255, presented strikingly different profiles. NAF induced a pattern of behavioral suppression that resembled the profile of high-dose SCH, while high-dose PD 152255 stimulated behavior. The failure of low-dose APO to have any effect on behavior suggests that the D(2) autoreceptor is not functional in preweanling rats. This hypothesis is further supported by the lack of behavioral suppression seen with low-dose QUIN and DPAT. Failure of NAF to produce behavioral activation at low doses and the stimulatory effects seen with PD 152255 suggests that either the D(3) autoreceptor, the postsynaptic D(3) receptor, or both are not fully functional at this age as well.

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 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.

Aberrant behavioral effects of a dopamine D1 receptor antagonist and agonist in monkeys: evidence of uncharted dopamine D1 receptor actions

BACKGROUND

Basic research indicates a role for dopamine (DA) D1 antagonism in the treatment of schizophrenia. Clinical trials have not confirmed any role. Besides the defining second messenger (adenylyl cyclase [AC]), DA D1 receptors are linked to other effectors (e.g., phospholipase C [PLC]). Differing actions of DA D1 antagonists upon differing effectors could explain conflicting results between the lab/clinic.

METHODS

In a monkey model in which behavioral effects of DA D1 antagonists/agonists have been well characterized we examined: 1) SKF 83959, biochemically, a DA D1 antagonist, behaviorally a DA D1 agonist, and 2) SKF 83822, biochemically, a DA D1 agonist, which, unlike all previously tested DA D1 agonists, does not also stimulate PLC. SKF 83959 and SKF 83822 were given alone and combined with DA D1 and D2 agonists, antagonists, and dextroamphetamine (AMP).

RESULTS

SKF 83959 acted as a DA D1 agonist (induced oral dyskinesia given alone, counteracted DA D1 antagonist [NNC 756], induced dystonia, and did not inhibit AMP induced behaviors). SKF 83822, unlike previously studied DA D1 agonists, did not induce dyskinesia, but resulted in a state of extreme arousal and locomotor activation without stereotypy, effectively counteracted by NNC 756, but not by SKF 83959 nor raclopride (DA D2 antagonist).

CONCLUSIONS

It is hypothesized that: 1) dyskinesia is linked to PLC stimulation; 2) DA D1 agonism can play a role in the induction of psychosis, via a mechanism linked neither to AC nor PLC, and 3) DA D1 antagonists differ in antipsychotic potential, possibly via this unidentified mechanism.

Ventral striatal vs. accumbal (shell) mechanisms and non-cyclase-coupled dopamine D(1)-like receptors in jaw movements

This study compared the effects of intracerebral injections of the dopamine D(1)-like receptor agents 3-methyl-6-chloro-7,8-dihydroxy-1-[3-methylphenyl]-2,3,4,5-tetrahydro-1H-3-benzazepine (SK&F 83959) and [R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390) into the ventrolateral striatum or the shell of the nucleus accumbens on the synergistic induction of jaw movements by intravenous (i.v.) co-administration of [R]-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SK&F 38393) or SK&F 83959 with the dopamine D(2)-like receptor agonist, quinpirole. In the ventrolateral striatum, SCH 23390 and SK&F 83959 each blocked jaw movements induced by i.v. SK&F 38393 with quinpirole, while only SCH 23390 blocked i.v. SK&F 83959 with quinpirole. SCH 23390 was less effective in the accumbens shell than in the ventrolateral striatum, and SK&F 83959 was ineffective to block i.v. SK&F 38393 with quinpirole, while neither SCH 23390 nor SK&F 83959 blocked i.v. SK&F 83959 with quinpirole. As SK&F 83959 inhibits the stimulation of adenylyl cyclase via dopamine D(1A) receptors but acts as an agonist at a putative dopamine D(1)-like receptor site not linked to cyclase, an important role is indicated for non-cyclase-coupled dopamine D(1)-like receptor sites as well as dopamine D(1A) receptors in the regulation of jaw movements via dopamine D(1)-like/D(2)-like receptor synergism, particularly in the ventrolateral striatum.

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

Delineation of the structural basis for the activation properties of the dopamine D1 receptor subtypes

To delineate the structural determinants involved in the constitutive activation of the D1 receptor subtypes, we have constructed chimeras between the D1A and D1B receptors. These chimeras harbored a cognate domain corresponding to transmembrane regions 6 and 7 as well as the third extracellular loop (EL3) and cytoplasmic tail, a domain referred herein to as the terminal receptor locus (TRL). A chimeric D1A receptor harboring the D1B-TRL (chimera 1) displays an increased affinity for dopamine that is indistinguishable from the wild-type D1B receptor. Likewise, a chimeric D1B receptor containing the D1A-TRL cassette (chimera 2) binds dopamine with a reduced affinity that is highly reminiscent of the dopamine affinity for the wild-type D1A receptor. Furthermore, we show that the agonist independent activity of chimera 1 is identical to the wild-type D1B receptor whereas the chimera 2 displays a low agonist independent activity that is indistinguishable from the wild-type D1A receptor. Dopamine potencies for the wild-type D1A and D1B receptor were recapitulated in cells expressing the chimera 2 or chimera 1, respectively. However, the differences observed in agonist-mediated maximal activation of adenylyl cyclase elicited by the D1A and D1B receptors remain unchanged in cells expressing the chimeric receptors. To gain further mechanistic insights into the structural determinants of the TRL involved in the activation properties of the D1 receptor subtypes, we have engineered two additional chimeric D1 receptors that contain the EL3 region of their respective cognate wild-type counterparts (hD1A-EL3B and hD1B-EL3A). In marked contrast to chimera 1 and 2, dopamine affinity and constitutive activation were partially modulated by the exchange of the EL3. Meanwhile, hD1A-EL3B and hD1B-EL3A mutant receptors display a full switch in the agonist-mediated maximal activation, which is reminiscent of their cognate wild-type counterparts. Overall, our studies suggest a fundamental role for the TRL in shaping the intramolecular interactions implicated in the constitutive activation and coupling properties of the dopamine D1 receptor subtypes.

The effect of novel antipsychotics in rat oral dyskinesia

1. The effect of the D1 agonist SKF38393 and the 5HT2C agonist m-CPP on repetitive jaw movements (RJM) was studied in rats. Acute administration of SKF38393 and/or m-CPP induced RJM in a dose dependent manner. In rats treated with both drugs, RJM responses were about equal to the sum of those obtained with each drug alone. 2. The induction of RJM by SKF38393 was somewhat lower in rats pretreated with 5HT2C receptor antagonist, mianserin, whereas mianserin severely reduced RJM induced by m-CPP alone. 3. D1 antagonist SCH23390 inhibited SKF38393 induced RJM but had no effect on m-CPP induced chewing behavior. 4. The present study confirms earlier evidence that D1 agonists used at optimal doses for the induction of RJM do not involve the serotonergic system in a significant way. It does, however, implicate the system in the emergence of drug induced oral behavior in rats. 5. The effect of the atypical antipsychotics, clozapine, olanzapine and risperidone was studied on SKF38393 and m-CPP induced RJM. Pretreatment with the atypical antipsychotics clozapine and olanzapine inhibit SKF38393 and m-CPP induced RJM. Pretreatment with risperidone inhibits m-CPP induced oral behavior in rats while increases dose dependently SKF38393 induced RJM.

SK&F 83959 and non-cyclase-coupled dopamine D1-like receptors in jaw movements via dopamine D1-like/D2-like receptor synergism

This study compared the effects of the dopamine D1-like receptor agents SK&F 83959 (3-methyl-6-chloro-7,8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro- 1 H-3-benzazepine), which inhibits the stimulation of adenylyl cyclase, and A 68930 ([1R,3S]-1-aminomethyl-5,6-dihydroxy-3-phenyl-isochroman), a full efficacy agonist, in regulating jaw movements in the rat by synergism with dopamine D2-like receptor agonism. When SK&F 83959 and A 68930 were given in combination with quinpirole, there was a synergistic induction of jaw movements. Responsivity to SK&F 83959 + quinpirole was antagonised by the dopamine D1-like receptor antagonists SCH 23390 ([R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-ben zaz epine) and BW 737C ([S]-6-chloro-1-[2,5-dimethoxy-4-propylbenzyl]-7-hydroxy-2-methyl- 1,2,3,4-tetrahydroisoquinoline); synergism was antagonised also by the dopamine D2-like receptor antagonist YM 09151-2 (cis-N-[1-benzyl-2-methyl-pyrrolidin-3-yl]-5-chloro-2-methoxy-4-++ +methyl-aminobenzamide). Responsivity to A 68930 + quinpirole was enhanced by low doses of SCH 23390, BW 737C and YM 09151-2, and antagonised by higher doses of SCH 23390 and YM 09151-2. These results implicate a novel, dopamine D1-like receptor that is coupled to a transduction system other than/additional to adenylyl cyclase, and suggest that its functional role extends to the regulation of jaw movements by synergistic interactions with dopamine D2-like receptors.

A phosphoinositide-linked dopamine D1 receptor mediates repetitive jaw movements in rats

BACKGROUND

We have demonstrated that rats injected with D1 agonists SKF 38393 or A68930 demonstrate repetitive jaw movements (RJM). These agonist-induced movements in rats are similar in their appearance to those induced in rats by long-term treatment with antipsychotic drugs. Over recent years D-1 receptors were discovered which showed linkage not only to c-AMP but also to PI hydrolysis. We examined the effect of EEDQ inactivation of D1 receptors on D-1 mediated PI hydrolysis and RJM.

METHODS

Twenty four hours following EEDQ or vehicle administration D-1 agonists or vehicle were administered. The number of RJM episodes was assessed in EEDQ and vehicle treated rats. D-1 receptor density and inositol phosphate formation were determined in the striata.

RESULTS

EEDQ administration resulted, 24 hours later, in 70-80% selective depletion of D-1 receptors in the striata but did not modify the rate of RJM induced by D-1 agonists. There was no significant difference in D-1 mediated PI hydrolysis in EEDQ treated rats when compared to vehicle treated group.

CONCLUSIONS

The present data support the earlier demonstration of D-1 agonist induced RJM, an effect mediated by a subpopulation of a D-1 receptor subtype and constitute the first behavioral evidence for the existence of a behavioral response mediated by D-1 like dopamine receptors linked to an alternate second messenger system-PI hydrolysis.

Tremulous jaw movements in rats: a model of parkinsonian tremor

Several pharmacological and neurochemical conditions in rats induce 'vacuous' or 'tremulous' jaw movements. Although the clinical significance of these movements has been a subject of some debate, considerable evidence indicates that the non-directed, chewing-like movements induced by cholinomimetics, dopamine antagonists and dopamine depletions have many of the characteristics of parkinsonian tremor. These movements occur within the 3-7 Hz peak frequency range that is characteristic of parkinsonian tremor. Tremulous jaw movements are induced by many of the conditions that are associated with parkinsonism, and suppressed by several different antiparkinsonian drugs, including scopolamine, benztropine, L-DOPA, apomorphine, bromocriptine, amantadine and clozapine. Striatal cholinergic and dopaminergic mechanisms are involved in the generation of tremulous jaw movements, and substantia nigra pars reticulata appears to be a major basal ganglia output region through which the jaw movements are regulated. Future research on the neurochemical and anatomical characteristics of tremulous jaw movements could yield important insights into the brain mechanisms that generate tremulous movements.

Behavioral and electromyographic characterization of the local frequency of tacrine-induced tremulous jaw movements

Rats were implanted with fine-wire electromyograph (EMG) electrodes and were videotaped to identify the local frequency characteristics and muscle activity associated with tacrine-induced tremulous jaw movements. All rats received intraperitoneal injections of 2.5 mg/kg tacrine. The videotape sessions were played back in slow motion (i.e., one-sixth normal speed), and an observer entered each jaw movement into a computer program that recalculated the interresponse time and the local frequency (in hertz) for each movement within a burst. Analyses of the distribution of frequencies showed that the peak frequency of jaw movements was in the 3- to 5-Hz frequency range, with an average frequency of 4.0 Hz. EMG electrodes were implanted into three jaw muscles: temporalis, anterior belly of digastricus, and masseter. Tremulous jaw movements were not accompanied by consistent changes in masseter activity. The anterior belly of digastricus showed bursts of EMG activity during some jaw movements, although the temporal relation between jaw movements and EMG activity was somewhat inconsistent. The muscle that showed activity most closely related to tremulous jaw movements was the temporalis. During bursts of jaw movements, temporalis muscles across several different rats showed bursts of EMG activity. Sections of videotape corresponding to bursts of EMG activity were reanalyzed by freeze-frame examination of the tape; typically, the temporalis showed a burst for each jaw movement, with the burst of activity occurring during the jaw-closing phase and the transition between jaw closing and opening. These results indicate that the local frequency of tremulous jaw movements is within the 3- to 7-Hz frequency that is typically associated with parkinsonian tremor. Moreover, the EMG data suggest that temporalis is a major contributor to the muscle activity that underlies tremulous jaw movements.

Tremulous jaw movements induced by the acetylcholinesterase inhibitor tacrine: effects of antiparkinsonian drugs

Several experiments were conducted to study the effects of established or potential antiparkinsonian drugs on the tremulous jaw movements induced by the anticholinesterase tacrine (9-amino-1,2,3,4-tetrahydroaminoacridine hydrochloride). In the first group of four experiments, separate groups of animals that received 2.5 or 5.0 mg/kg tacrine showed a dose-dependent decrease in tremulous jaw movements following co-administration of the non-selective dopamine receptor agonist apomorphine, the full dopamine D2 receptor agonist bromocriptine, and the full dopamine D1 receptor agonist APB (R(+)-6-bromo-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine). Co-administration of the partial dopamine D1 receptor agonist SKF 38393 (R(+)-2,3,4,5-tetrahydro-7,8-dihydroxy-l phenyl-1 H-benzazepine: 7.5-30.0 mg/kg) did not reduce tremulous jaw movements produced by 2.5 or 5.0 mg/kg tacrine. In animals treated with 2.5 mg/kg tacrine, co-administration of SKF 38393 resulted in a dose-related trend towards a potentiation of tremulous jaw movements. In the second group of experiments, all rats received 2.5 mg/kg tacrine. The dopamine precursor L-DOPA (L-3,4-dihydroxyphenylalanine), the dopamine and norepinephrine releasing agent amantadine, and the muscarinic receptor antagonist benztropine all reduced tremulous jaw movements induced by 2.5 mg/kg tacrine. Across all experiments, it was noted that apomorphine, bromocriptine and benztropine were more potent than amantadine and L-DOPA. These results are broadly consistent with the therapeutic doses of these agents noted in the clinical literature. The results of these experiments indicate that tremulous jaw movements in rats may be a useful model for evaluating potential antiparkinsonian agents.

Evidence for dopamine 'D1-like' receptor subtypes in the behavioural effects of two new selective antagonists, LY 270411 and BW 737C

A new, chemically distinct antagonist at dopamine 'D1-like' receptors, the thienoazepine LY 270411, ([+]-2(3-chloro-6-methyl-8-phenyl-5,6,7,8 -tetrahydro-4H-thieno[2,3d]azepin-2-yl)propan-2-ol) was compared with the isoquinoline BW 737C ([S]-6-chloro-1-[2,5-dimethoxy-4- propylbenzyl]-7-hydroxy-2-methyl-1,2,3,4-tetrahydroisoquinoline) and the benzazepine SCH 23390 ([R]-7-chloro-8-hydroxy-2,3,4,5-tetrahydro-3-methyl-1-phenyl-1 H-3-benzazepine) for effects on behavioural responses to the isochroman full efficacy dopamine 'D1-like' receptor agonist A 68930 ([1R,3S]-1-aminomethyl-5, 6-dihydroxy-3-phenylisochroman) vs. the dopamine 'D2-like' receptor agonist RU 24213 (N-n-propyl-N-phenylethyl-p-3-hydroxyphenylethylamine). Grooming responses to A 68930 were readily blocked by each of LY 270411, BW 737C and SCH 23390; however, the vacuous chewing response was blocked only by BW 737C. Sniffing and locomotor responses to RU 24213 were attenuated by BW 737C and SCH 23390 but not by LY 270411; furthermore, myoclonic jerking to RU 24213 was released by BW 737C and SCH 23390 but not by LY 270411. These findings indicate that grooming induced by dopamine 'D1-like' receptor agonism is blocked by all chemical classes of dopamine 'D1-like' receptor antagonist while vacuous chewing is blocked only by isoquinoline dopamine 'D1-like' receptor antagonism; this suggests that these behaviours may be mediated via functionally and pharmacologically distinct subtypes of dopamine 'D1-like' receptor. Furthermore, LY 270411 appears unique in its activity to readily block 'D1-like' receptor agonist-induced grooming without influencing behavioural responses to dopamine 'D2-like' receptor agonism; thus, the site mediating prototypical dopamine 'D1-like' receptor agonist-induced behaviours may be dissociable pharmacologically from dopamine 'D1-like' site(s) participating in functional interactions with dopamine 'D2-like' receptors.

Effects of ceruletide on perioral movements and the dopamine receptor-adenylate cyclase system in rats chronically treated with fluphenazine

The effects of repeated administration of ceruletide (100 micrograms/kg/perday, i.p. for 3 days) on perioral movements and the striatal dopamine receptor adenylate cyclase system were examined in rats chronically treated with fluphenazine enanthate (FPZ) (25 mg/kg i.m. every 3 weeks for 30 weeks) and sesame oil-treated (control) rats. After the tenth injection of fluphenazine, the rats started to display five types of perioral movements (teeth chattering, chewing, tongue protrusion, mouth opening and perioral tremors). Moreover, increases in SCH23390 binding and spiperone binding to striatal membranes, were found in the FPZ-treated rats. Furthermore, dopamine receptor-coupled adenylate cyclase activity was potentiated in striatal membranes. High amplitude EMG discharges (8-10 Hz), recorded from the masseter in the FPZ-treated rats occurred concurrently with perioral tremors. Repeated ceruletide (CLT) injections abolished perioral movements, and reversed both the elevated SCH23390 binding and the dopamine stimulated adenylate cyclase (AC) activity to the control level. The effect of CLT on perioral movements, D1 receptors and dopamine-stimulated AC activity continued for 6 days after the final CLT injection. These findings suggest that systemically administered CLT affects the D1 receptor adenylate cyclase system and that an increase of the D1 receptor mechanism may play an important role in the pathogenesis of tardive dyskinesia.

Comparison of the new atypical antipsychotics olanzapine and ICI 204,636 with clozapine on behavioural responses to the selective "D1-like" dopamine receptor agonist A 68930 and selective "D2-like" agonist RU 24213

The effects of the putative atypical antipsychotics olanzapine and ICI 204,636 on behavioural responses to the selective "D2-like" dopamine receptor agonist RU 24213 and to the selective "D1-like" agonist A 68930 were compared with those of the prototype atypical antipsychotic clozapine, the selective D1-like antagonist SCH 23390 and the selective D2-like antagonist YM 09151-2. Olanzapine (0.4-2.0 mg/kg) and ICI 204,636 (4.0-36.0 mg/kg), like clozapine (4.0-36.0 mg/kg) and SCH 23390 (0.01-1.0 mg/kg), effected at best modest reduction in typical sniffing and locomotor responses and, with the exception of ICI 204,636, released episodes of atypical myoclonic jerking to RU 24213 (12.5 mg/kg); a high dose of olanzapine (10.0 mg/kg), like YM 09151-2 (0.005-0.5 mg/kg), blocked all responsivity to RU 24213. Conversely, olanzapine (0.4-2.0 mg/kg) and ICI 204,636 (4.0-36.0 mg/kg), like clozapine (4.0-12.0 mg/kg) and SCH 23390 (0.01-0.1 mg/kg), readily blocked typical grooming responses to A 68930 (0.5 mg/kg); YM 09151-2 failed to block grooming and exerted more variable effects. Olanzapine and, to a lesser extent, ICI 204,636 share with clozapine a preferential action to attenuate D1-mediated function; given their lack of selective affinity for D1-like receptors, this common effect may be exerted at an alternative level of synaptic function. The action of olanzapine and particularly ICI 204,636 to release additional episodes of atypical vacuous chewing to A 68930 indicates some deviation from a wholly clozapine-like profile, the clinical significance of which remains to be specified.

Evidence for genetically mediated dysfunction of the central dopaminergic system in the stargazer rat

The stargazer rat is an autosomal recessive mutant (homozygous stg/stg) that displays abnormal behavior, characterized by stereotypic head-movement, circling, and a high level of ambulatory activity. Heterozygous (stg/+) littermates display normal spontaneous behaviors. In this study, stargazers and their unaffected littermates were compared in their behavioral responses to both stimulation and inhibition of dopamine D2/D3 receptors, using quinpirole and haloperidol. Stargazers were observed to yawn a significantly fewer number of times than littermates in response to (--)-quinpirole (50 mu g/kg, IP). Haloperidol (HAL 0.1 mg/kg and 0.3 mg/kg, SC) caused a decrease in stereotypic head-movement in the mutants that was both time- and dose-dependent. In normal littermates, HAL inhibited locomotor activity and produced catalepsy in a time- and dose-dependent manner. In stargazers, both doses of HAL inhibited locomotor activity to a similar degree as in the littermates. However, no catalepsy was detectable in the mutants using 0.1 mg/kg of HAL. A dose of 0.3 mg/kg HAL was only weakly cataleptogenic. Overall, the spectrum of abnormal behaviors expressed by the stargazers and the present evidence of D2/D3 receptor subsensitivity suggest that stargazers possess a genetically mediated dysfunction of the central dopaminergic system.

Pharmacological characterization of behavioural responses to SK&F 83959 in relation to 'D1-like' dopamine receptors not linked to adenylyl cyclase

1. Behavioural responses to the new benzazepine derivative, SK&F 83959, a compound that both fails to stimulate adenylyl cyclase and inhibits the stimulation of adenylyl cyclase induced by dopamine, were characterized in detail. 2. In rat striatal membrane preparations, radioligand binding studies with [3H]-SCH 23390 and [3H]-spiperone indicated SK&F 83959 had a high affinity and >250 fold selectivity for D1 over D2 receptors. 3. Using a rapid time-sampling behavioural check list technique, SK&F 83959 (0.01-1.25 mg kg(-1)) induced grooming in the manner of all known D1 receptor agonists, together with some vacuous chewing, which declined at higher doses with the emergence of directed chewing and rearing as an adjunct to prominent sniffing; no stereotyped behavioural was evident. 4. Grooming to SK&F 83959 (0.05 mg kg(-1)) was blocked by the selective D1 receptor antagonists, SCH 23390 (0.01-1.0 mg kg(-1)) and BW 737C (0.04-5.0 mg kg(-1)) and was attenuated by the selective D2 receptor antagonist, YM 09151-2 (0.005-0.5 mg kg(-1)); vacuous chewing to SK&F 83959 was not influenced by either SCH 23390 or BW 737C and was enhanced by YM 09151-2. 5. The paradoxical induction of typical D1 receptor agonist-induced grooming by SK&F 83959, an agent satisfying criteria for a D1 receptor antagonist as classically defined, together with its blockade by typical D1 antagonists, strongly suggests mediation via a 'D1-like' site that appears to respond similarly to agents independent of whether they exert agonist or antagonist actions at the classical adenylyl cyclase-coupled D1 receptor. This direct functional evidence for a 'D1-like' site that is not linked to adenylyl cyclase readily complements neurochemical data suggesting the existence of a cyclase-independent 'D1-like' receptor that may be coupled to phosphoinositide hydrolysis.

Behavioural pharmacology of 'D-1-like' dopamine receptors: further subtyping, new pharmacological probes and interactions with 'D-2-like' receptors

1. D-1 receptors are now recognised to play a critical psychopharmacological role in the regulation of unconditioned motor and numerous other aspects of behaviour. 2. There appears to exist a broad family of 'D-1-like' receptors in terms both of differential coupling to distinct messenger/transduction mechanisms and of gene cloning, whose behavioural roles remain to be clarified. 3. The adenylyl cyclase-inhibiting benzazepine SK&F 83959 induces behavioural responses in rats that are similar to those induced by the full efficacy cyclase-stimulating isochroman A 68930 but not to those induced by its high efficacy partial agonist benzazepine congener R-6-Br-APB; these data indicate roles for individual 'D-1-like' receptors in mediating distinct elements of dopaminergic behaviour. 4. The putative D-1 autoreceptor agonist B-HT 920 and the putative D-3 agonist 7-OH-DPAT demonstrate different behavioural profiles when given both alone and in combination with the selective 'D-1-like' antagonist BW 737C; D-3 receptors may participate in cooperative/synergistic but not in oppositional 'D-1-like': 'D-2-like' interactions. 5. Such interactions apparent at the level of behaviour are complemented by evidence for similar interactions at numerous alternative levels of function, though these may differ between rodent and primate species. 6. A broader range of more selective agonists and antagonists, able to distinguish between individual members of the 'D-1-like' and of the 'D-2-like' receptor families are needed to clarify these issues.

Selective dopamine antagonist pretreatment on the antiparkinsonian effects of benzazepine D1 dopamine agonists in rodent and primate models of Parkinson's disease--the differential effects of D1 dopamine antagonists in the primate

In rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle, pretreatment with the D1 DA antagonists, SCH 23390 (7-chloro-8-hydroxy-2,3,4,5-tetrahydro-3-methyl-1-phenyl-1H-3-benzazepin e) and A66359 (1- 2-bromo-4,5-dimethoxybenzyl]-7-hydroxy-6-methoxy-2-methyl- 1,2,3,4 tetrahydroisoquinoline), but not the D2 DA antagonist raclopride inhibited the contralateral circling induced by the benzazepine D1 DA agonists SKF 38393 (7-H, 3-H analogue of SCH 23390), SKF 80723 (7-H, 3-H, 6-Br analogue) and SKF 83959 (7-H, 6-Cl, 3'-CH3 analogue). In MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) treated common marmosets, administration of SKF 80723 and SKF 83959 increased locomotor activity and reversed the motor disability. Grooming and oral activities were also increased. Pretreatment with SCH 23390 and A66359 inhibited all the behavioural changes induced by both D1 DA agonists. In general, higher doses of A66359 and more especially SCH 23390 were needed to inhibit SKF 83959 and SKF 80723 induced increases in oral activity and grooming than locomotor activity. Raclopride pretreatment did not affect SKF 83959 and SKF 80723 induced oral activity and grooming, though it reduced the duration of the locomotor changes induced by the D1 DA agonists. These findings demonstrate that the behavioural effects of benzazepine D1 DA agonists in the 6-OHDA lesioned rat and MPTP-treated marmoset are mediated by D1 DA receptor sites, although in the primate, stimulation of D2 DA receptors by endogenous DA may be necessary in facilitating the antiparkinsonian effects of D1 DA agonists. The differential sensitivities of locomotor/motor disability and oral/grooming behaviours to antagonism by D1 DA antagonists may indicate the involvement of multiple D1 DA receptor subtypes in mediating benzazepine D1 DA agonist induced behaviours in the MPTP-treated marmoset.

The differential behavioural effects of benzazepine D1 dopamine agonists with varying efficacies, co-administered with quinpirole in primate and rodent models of Parkinson's disease

The effects of co-administration of quinpirole with benzazepine D1 dopamine (DA) agonists possessing full/supramaximal (SKF 80723 and SKF 82958), partial (SKF 38393 and SKF 75670) and no efficacies (SKF 83959) in stimulating adenylate cyclase (AC) were investigated in rodent and primate models of Parkinson's disease (PD). In rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the medial forebrain bundle, co-administration of SKF 38393 (7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine), SKF 75670 (3-CH3 analogue), SKF 80723 (6-Br analogue), SKF 83959 (6-Cl, 3-CH3, 3'-CH3 analogue) and SKF 82958 (6-Cl, 3-C3H5 analogue) strongly potentiated the contralateral circling induced by quinpirole. In MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) treated common marmosets, administration of quinpirole alone increased locomotor activity and reversed motor deficits. Grooming and oral activity were unaltered. Co-administration of SKF 38393 and SKF 75670 inhibited the quinpirole-induced changes in locomotor activity and motor disability. The combined treatment of SKF 80723 or SKF 82958 with quinpirole had no overall effect on locomotor activity or motor disability. In contrast, SKF 83959 extended the duration of the quinpirole-induced increase in locomotor activity with corresponding decreases in motor disability. Co-administration of high doses of SKF 82958 and more especially SKF 83959 and SKF 80723, with quinpirole induced hyperexcitability and seizures. Oral activity and grooming were unaltered following the co-administration of benzazepine derivatives with quinpirole. The ability of some benzazepine D1 DA agonists to prolong the antiparkinsonian effects of quinpirole in the MPTP-treated marmoset may indicate a role for certain D1 DA agonists in the clinical treatment of PD. In general, the behavioural responses to the combined administration of benzazepines with quinpirole in the 6-OHDA lesioned rat and more especially the MPTP-treated marmoset failed to correlate with their ability to stimulate AC. These observations further implicate a behavioural role for D1 DA receptors not linked to AC.

Differential anti-parkinsonian effects of benzazepine D1 dopamine agonists with varying efficacies in the MPTP-treated common marmoset

In common marmosets systemically treated with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), the behavioural effects of benzazepine D1 dopamine (DA) agonists with full/supramaximal (SKF 80723 and SKF 82958), partial (SKF 38393, SKF 75670 and SKF 83565) and no efficacies (SKF 83959) in stimulating adenylate cyclase (AC) activity were investigated. The benzazepine derivatives, with the exception of SKF 82958 (8 fold D1 DA receptor selectivity), demonstrated high D1 DA receptor affinity and selectivity (approximately 100 fold or more) in rat striatal homogenates. Administration of MPTP in marmosets induced locomotor hypoactivity, rigidity and motor disability. SKF 38393 (7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine) and SKF 75670 (3-CH3 analogue) further reduced locomotor activity (by -70 to -80%) and increased motor disability (by +22 to +67%) in these animals. SKF 83565 (6-Cl, 3-CH3, 3'-Cl analogue) and SKF 82958 (6-Cl, 3-C3H5 analogue) had only a slight effect on locomotor activity but decreased motor disability at high doses (-46 to -60%). In contrast, SKF 83959 (6-Cl, 3-CH3, 3'-CH3 analogue) and SKF 80723 (6-Br analogue) produced pronounced increases in locomotion (6-10 fold) and a reversal in motor disability (by -64 to -77%). Oral activity, consisting largely of abnormal, 'dyskinetic' tongue protrusions and vacuous chews, was increased in animals treated with SKF 38393, SKF 83565, SKF 82958 and more especially with SKF 80723 and SKF 83959. Grooming was increased with SKF 82958 and more especially with SKF 80723 and SKF 83959. In contrast, quinpirole (D2 DA agonist), reversed the MPTP-induced motor deficits in the marmoset, with no effect on grooming and oral activity. The present findings further demonstrate the antiparkinsonian actions of some D1 DA agonists in MPTP-treated primates. However, in general the behavioural effects of benzazepines failed to correlate with either their D1 DA receptor affinity/selectivity or their efficacy in stimulating adenylate cyclase (AC) activity. These observations further implicate a behavioural role for D1 DA receptors uncoupled to AC and/or a role for extrastriatal D1 DA receptors in mediating the behavioural response to D1 DA agonists.

Nicotine-induced purposeless chewing in rats: possible dopamine receptor mediation

Intraperitoneal (i.p.) administration of nicotine to rats induced purposeless chewing. The response induced by different doses of the drug (0.0001, 0.001, 0.01 and 0.1 mg/kg) seems to be dose dependent, with a maximum effect at 0.01 mg/kg and then decreasing at a higher dose (0.1 mg/kg). Pre-treatment of animals with the nicotine antagonist mecamylamine (0.01 and 0.1 mg/kg, 30 min) and the D-2 receptor antagonist sulpiride (12.5-100 mg/kg, 90 min), but not the D-1 antagonist SCH 23390 (0.01 and 0.05 mg/kg, 30 min), decreased the chewing induced by nicotine (0.01 mg/kg). When animals were pre-treated with propranolol (5 and 10 mg/kg) 60 min, reserpine (2.5 mg/kg) 18 h or α-methyl-p-tyrosine (α-MPT; 250 mg/kg) 60 min before nicotine, the effect of the drug was reduced. However, reserpine (2.5 mg/kg) at 18 h plus α-MPT (250 mg/kg) 60 min prior to nicotine completely inhibited the drug response. Pre-treatment of animals with phenoxybenzamine (2.5 and 5 mg/kg i.p., 60 min) or atropine (5 and 10 mg/kg) did not change the nicotine response significantly. It is concluded that nicotine- induced purposeless chewing is mediated through dopaminergic and nicotinic mechanisms.

Effects of chronic discontinuous and continuous treatment of rats with a dopamine D1 receptor antagonist (NNC-756)

Rats were treated intermittently or continuously with the dopamine D1 receptor antagonist NNC-756 for 15 weeks. Two weeks after withdrawal they were challenged with the dopamine D1 receptor agonist SK&F 38393, either alone or after pretreatment with NNC-756. Neither treatment regimen resulted in irreversible increases in oral activities when treated rats were compared with controls; however, transient elevations were observed in the beginning of treatment in the continuously treated group and in the withdrawal phase in the discontinuously treated group. Furthermore, discontinuous treatment resulted in within-group elevations in vacuous chewing movements and tongue protrusions after withdrawal. Dopamine D1 receptor supersensitivity was not observed after challenge with the dopamine D1 receptor agonist. NNC-756 efficiently blocked the behavioural response to stimulation with SK&F 38393. Both treatment regimens resulted in the development of rigidity and catalepsy. The present study suggests that treatment with selective dopamine D1 receptor antagonists is less likely to cause irreversible oral dyskinesia than is treatment with classical neuroleptic drugs.

Enhanced pilocarpine-induced oral activity responses in neonatal 6-OHDA treated rats

Neonatal destruction of rat nigrostriatal dopaminergic fibers results in an enhanced oral activity response to both dopamine (DA) D1 and serotonin (5-HT) agonists. Because cholinergic systems represent another one of the neural circuits involved in oral behavior, it was of interest to determine whether muscarinic receptors might also be sensitized in the lesioned rats. At 3 days after birth, rats were pretreated with desipramine HCl (20 mg/kg, IP) 1 h before 6-hydroxydopamine (6-OHDA) HBr (100 micrograms in each lateral ventricle) or saline-ascorbic acid (0.1%) vehicle. Between 2 and 4 months, behavioral supersensitivity to a D1 agonist (SK&F 38393) and 5-HT agonist (m-chlorophenylpiperazine; m-CPP) was established before rats were challenged with the muscarinic receptor agonist, pilocarpine HCl (0.125 to 10.0 mg/kg, IP). The pilocarpine dose-effect curve was shifted to the left, with a maximal effect of 63.7 +/- 8.6 oral movements being produced by a 1.0 mg/kg pilocarpine HCl dose in the 6-OHDA lesioned rats, versus 15.0 +/- 2.4 oral movements in the control group (p < 0.001). The enhanced response to pilocarpine was attenuated by the muscarinic receptor antagonist, scopolamine HCl (0.1 mg/kg IP). These findings indicate that neonatal 6-OHDA treatment produces supersensitization of muscarinic receptors in rats.

Involvement of the nucleus accumbens in oral behaviour in the freely moving rat

The role of the nucleus accumbens in oral behaviour was examined by intra-accumbens injections of a single dose of a selective dopamine D1 receptor agonist (SKF 38393: 5 micrograms/side), a selective dopamine D2 receptor agonist (quinpirole: 10 micrograms/side), and their combination in freely moving rats. Principal factor analysis revealed four factors to be involved in the scored behaviours, two of which concerned oral behaviour: a chew factor, comprising the behaviours chew, tongue protrusion, yawn and lick, and a groom factor, with high factor loadings of tremor and groom. The two remaining factors were the circle factor comprising circle, walk and rear, and the sniff factor comprising sniff, yawn and rear. Two-way ANOVA (independent variable D1 with H2O and SKF 38393 level; independent variable D2 with H2O and quinpirole level) of the factor scores revealed that SKF 38393 and quinpirole had similar or opposite effects which were additive or antagonistic, depending on which behaviour was studied. This study demonstrates that (a) the nucleus accumbens plays a major role in the oral behaviour of freely moving rats, and (b) an integrated study of all oral behavioural elements is necessary to describe the effects of drugs on oral behaviour.

Increases in rat striatal extracellular dopamine and vacuous chewing produced by two sigma receptor ligands

The present studies were carried out to analyze the neurochemical and behavioral effects of peripheral sigma ligand administration in the rat. Based upon previous studies which showed an increase in turning behavior following unilateral intranigral administration of sigma ligands, we determined the effects of two sigma ligands, 1,3-di-o-tolylguanidine (DTG) and (+)-pentazocine, on extracellular dopamine levels in the rat striatum. Dopamine levels were monitored via microdialysis in awake freely moving animals following i.p. injection of the ligands. Both DTG (1 and 3 mg/kg) and (+)-pentazocine (10 mg/kg) produced a significant (30-50%) increase in extracellular dopamine. Given the relatively high concentration of sigma receptors in brain nuclei involved in facial and mouth movements, we have also determined the effects of the two sigma ligands on facial movements. Both ligands produced a significant increase in vacuous chewing movements, suggesting that studies on the consequences of sigma receptor activation may have relevance to animal models of human dystonia and/or dyskinesia.

Biphasic locomotor effects of the dopamine D1 agonist SKF 38393 and their attenuation in non-habituated mice

The locomotor stimulatory effects of the dopamine D1 receptor partial agonist SKF 38393 were examined in male C57B1/6J mice. Non-habituated mice showed marked dose-related (3-300 mg/kg, SC) locomotor stimulation. The time-course effect was biphasic at very high doses (100-300 mg/kg), with dose-related locomotor depression followed by dose-related long-term hyperlocomotion. For all doses, locomotor effects were detectable throughout the 4-h test period. To determine whether these effects were mediated by D1 receptor stimulation, effects of SKF 38393 were assessed in combination with behaviorally inactive and active doses (0.1 and 0.2 mg/kg, respectively) of the selective D1 receptor antagonist SCH 39166. Both doses of SCH 39166 attenuated the hyperlocomotion induced by 30 mg/kg of the agonist to a similar degree. However, neither dose was able to reverse either the depressant or the stimulatory effects of 300 mg/kg SKF 38393. These results demonstrate effects of the prototypical D1 agonist previously unobserved, and raise questions concerning the nature of agonist/antagonist interactions at the D1 receptor subtype.

Persistent vacuous chewing in rats following neuroleptic treatment: relationship to dopaminergic and cholinergic function

In order to relate the effects of pharmacological intervention to neuroleptic induced increases in oral activity rats were treated continuously (7 mg/kg per week) or discontinuously (7 mg/kg per week or 2 mg/kg per week) with haloperidol for 6 months. Only the two intermittently treated groups developed persisting increases in vacuous chewing movements (VCM) following drug withdrawal. Opposed to control animals and continuously treated rats, the discontinuously treated groups demonstrated significant elevation in mouth movements following stimulation with the dopamine (DA) D1 receptor agonist SK&F 38393 (23 mg/kg), whereas they did not response to an acute challenge with the selective DA D1 receptor antagonist NNC-756 (0.1 mg/kg). The DA D2 receptor antagonist raclopride (1 mg/kg) provoked a general fall in VCM; however, this was only significant in rats treated intermittently with haloperidol 7 mg/kg per week and in control rats. Intermittent neuroleptic treatment also increased apomorphine-induced stereotypy. The effect of challenge with the anticholinergic drug scopolamine (0.25 mg/kg) was not related to oral activity; furthermore, the finding of severe agitation in rats tested with the latter drug points to caution in the interpretation of rating of rats treated with anticholinergics. These results support that intermittent ingestion of neuroleptic drugs lead to long-lasting increases in VCM. They also suggest a relation of persisting elevated oral activity to supersensitivity to DA receptor agonists, as opposed to subsensitivity to D1 receptor antagonists.

Electromyographical differentiation of the components of perioral movements induced by SKF 38393 and physostigmine in the rat

Facial electromyography (EMG) coupled with visual observation was used to investigate spontaneous and drug induced perioral movements in freely moving rats. Four separate perioral behaviours were identified; facial tremor, purposeless chewing, gaping and yawning. Facial tremor, yawning and gaping but not purposeless chewing produced characteristic EMG signals. Normal rats displayed a low level of purposeless chewing, occasional bursts of facial tremor but not gaping or yawning. Each burst of facial tremor was accompanied by a transient increase in purposeless chewing. Administration of the D1 agonist SKF 38393 induced a dose related increase in bursts of facial tremors and consequently an increase in the total number of purposeless chews. Gaping and yawning were not induced by SKF 38393 administration. Administration of the cholinesterase inhibitor physostigmine (0.1-0.4 mg/kg) induced a dose related increase in the total number of purposeless chews, but primarily these were not associated with facial tremor. Administration of physostigmine also increased gaping and yawning. Administration of the D1 antagonist SCH 23390 almost abolished facial tremor in normal treated rats but only partially reduced that induced by SKF 38393 and physostigmine. SCH 23390 reduced purposeless chewing in SKF 38393 treated rats but not in normal or physostigmine treated animals. Administration of the cholinergic antagonist atropine almost abolished facial tremor in normal and physostigmine treated rats, but only reduced by 46% that induced by SKF 38393. Atropine reduced purposeless chewing in normal, physostigmine and SKF 38393 treated animals. Physostigmine induced gaping and yawning were abolished by atropine administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioural evidence for "D-1-like" dopamine receptor subtypes in rat brain using the new isochroman agonist A 68930 and isoquinoline antagonist BW 737C

The full efficacy, high potency isochroman D-1 agonist A 68930 demonstrated greater than 220-fold selectivity for D-1 over D-2 receptors. A 68930 (0.06 and 0.25 mg/kg) readily induced intense grooming, together with vacuous chewing; these responses became less evident following higher doses (1.0 and 4.0 mg/kg) and sniffing became prominent. Intense grooming was blocked by three D-1 antagonists, the benzazepines SCH 23390 (0.01-1.0 mg/kg) and NNC-756 (0.01-1.0 mg/kg), and the isoquinoline BW 737C (0.2-5.0 mg/kg); however, vacuous chewing was not antagonised by SCH 23390 and NNC-756, but was blocked by BW 737C. Intense grooming was attenuated by the D-2 antagonist YM 09151 (0.005-0.5 mg/kg) while vacuous chewing was enhanced. These data suggest that intense grooming is mediated by a "D-1 like" receptor that recognises all known chemical classes of D-1-selective compounds, while vacuous chewing may be mediated by a pharmacologically distinct subtype of "D-1-like" receptor that recognises preferentially the isochromans and isoquinolines.

Effect of chronic trifluoperazine administration and subsequent withdrawal on the production and persistence of perioral behaviours in two rat strains

The effect of chronic administration of trifluoperazine on the perioral movement profile of Wistar and Sprague-Dawley rats was examined. Perioral movements were characterised by visual observations, coupled with electromyographic recording from the masseter muscle. In drug-naive animals from both strains the spectrum of perioral behaviours was essentially identical, primarily consisting of purposeless chewing, accompanied by occasional bursts of facial tremor and teeth chattering, with occasional yawning. Each burst of facial tremor was accompanied by a transient increase in the rate of purposeless chewing. Wistar rats exhibited a higher level of spontaneous purposeless chewing compared to Sprague-Dawley rats. In both strains, chronic administration of trifluoperazine (5 mg/kg per day, PO) for 5 months induced an increase in perioral behaviour, which primarily consisted of enhanced purposeless chewing. In Wistar rats the drug-induced increase in purposeless chewing was accompanied by an increase in the incidence of yawning, with no change in the incidence of either facial tremor or teeth chattering. In contrast, Sprague-Dawley rats displayed a drug-induced increase in purposeless chewing, accompanied by an increase in the incidence of facial tremor and teeth chattering, but not yawning. In Wistar rats withdrawal of trifluoperazine diminished but did not reverse the drug-induced increase in purposeless chewing. Drug withdrawal also precipitated a transient increase in the incidence of facial tremor and teeth chattering, but had no effect on yawning. In Wistar rats, the level of purposeless chewing and the incidence of yawning remained elevated above control levels for at least 13 weeks after drug withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient decrease in rat striatal D2 dopamine receptor mRNA level after acute haloperidol treatment

Acute haloperidol administration decreases the number of rat striatal D2 dopamine receptor (D2-receptor). The potential involvement of decreased D2-receptor gene transcription in the above process was examined using Northern blot analysis. There was a dose- and time-dependent transient decrement in the level of striatal D2-receptor mRNA after haloperidol. The decrease in transcription may be mediated via blockade of D2-receptor, since S(-)-sulpiride but not the inactive enantiomer R(+)-sulpiride produced the inhibition.

Cholinergic/dopaminergic interaction in the rat striatum assessed from drug-induced repetitive oral movements

The role of striatal dopaminergic/cholinergic interactions in the regulation of oral behaviour in rats was studied using methods which resolve distinct patterns of jaw movements, allowing a more accurate quantitative and qualitative analysis. Both dopamine and acetylcholine receptor agonists given either systemically or into the ventral striatum induced repetitive oral movements. However, the cholinergic movements differed from dopaminergic movements as to pattern of activity. Oral movements induced by apomorphine (0.2 mg/kg i.v.) were potentiated by carbachol (0.1 microgram/0.2 microliters) injected into the dorsal striatum, while inhibition was observed when carbachol was injected into the ventral striatum. Pilocarpine (4 mg/kg)-induced oral movements were reduced by injecting flupentixol (10 micrograms/0.2 microliters), but not a combination of SKF 38393 (3 micrograms)+quinpirole (10 micrograms/0.2 microliter), into either the dorsal or the ventral striatum. Oral movements induced by the injection of carbachol (1 microgram/0.2 microliter) into the ventral striatum were enhanced by previous injection of this combination of dopamine receptor agonists into the same site and were inhibited by flupentixol. These results suggest that cholinergic and dopaminergic oral movements are separate behaviors and that the striatal dopamine/acetylcholine interaction in their regulation is neither simply antagonistic or synergistic, nor reciprocal.