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

Cholecystokinin octapeptide and caerulein injection into the dorsomedial nucleus accumbens potentiate apomorphine-induced jaw movements in rats

The effects of bilateral intra-accumbal and intrastriatal injections of CCK-8 sulphate and its analogue, caerulein, on apomorphine-induced jaw movements were studied in ketamine-anaesthetized rats after C1 spinal transection. Jaw movements were detected by a photo-transducer attached to the mandible. CCK-8 (5, 10 and 20 ng) and its analogue, caerulein (1 and 5 ng), injected into the dorsomedial nucleus accumbens increased the frequency of apomorphine (0.2 mg/kg i.v.)-induced jaw movements. The potentiation was prevented by administration of a CCK-A receptor antagonist, lorglumide (5 ng), together with CCK-8 (20 ng) or caerulein (5 ng). Injection of lorglumide alone into the dorsomedial nucleus accumbens did not alter apomorphine (0.5 mg/kg i.v.)-induced jaw movements. Injections of CCK-8 (20 ng) and caerulein (5 ng) into adjacent sites (the ventrolateral nucleus accumbens, dorsal striatum and ventral striatum) did not affect the responses elicited by apomorphine (0.2 mg/kg i.v.). These results demonstrate that CCK-8 modulates responses elicited by a dopamine receptor agonist, apomorphine, in a region of the brain where CCK-8 is known to co-exist with dopamine.

Dopamine D1 receptors in the sub-commissural part of the globus pallidus and their role in oro-facial dyskinesia in cats

The possible role of dopamine D1 receptors in the sub-commissural part of the globus pallidus in the induction of oro-facial dyskinesia was studied in cats. The present study reveals two findings. Firstly, bilateral injections of the D1 agonist (+/-)-SK& F38393 into the ventral pallidal area elicited oro-facial dyskinesia, which was quantified in terms of numbers of tongue protrusions. The results show that the dose-effect curve was bell-shaped (1.0, 1.75, 2.5, 5.0 micrograms/0.5 microliters (+/-)-SK&F38393). The oro-facial dyskinesia elicited by (+/-)-SK&F38393 was highly comparable to the oro-facial dyskinesia elicited by injections of the GABA antagonist picrotoxin or the acetylcholine agonist carbachol into the sub-commissural part of the globus pallidus. Secondly, the inactive enantiomer of SK&F38393, i.e. S(-)-SK&F38393, was found to be ineffective in eliciting oro-facial dyskinesia when injected in a dose equivalent to 50% of the most effective dose of the racemic mixture of (+/-)-SK&F38393. Furthermore, the effect elicited by 2.5 micrograms/0.5 microliters (+/-)-SK&F38393 was significantly attenuated by local injection of the D1 antagonist R(+)-SCH23390 in a dose which had no effect itself (1.0 micrograms/0.5 microliters). These findings indicate that the effects elicited by (+/-)-SK&F38393 are D1-specific. The present results thus clearly indicate that dopamine D1 receptors within the sub-commissural part of the globus pallidus are involved in mediating oro-facial dyskinesia in cats.

Functional interaction between dopamine D1 and D2 receptors in rat jaw movements

The functional interaction between dopamine D1 and D2 receptors in dopamine-mediated jaw movements was studied in ketamine-anaesthetized rats after C1 spinal transection. Jaw movements were recorded by means of a light-emitting diode attached to the mandible; the method permits a detailed qualitative and quantitative analysis of jaw movements. D1 stimulation with SKF38393 (10 mg/kg i.v.) produced frequent bursts of teeth chattering, which were abolished by pretreatment with SCH23390 (0.25 mg/kg i.v.). D2 stimulation by quinpirole (1-10 mg/kg i.v.) produced infrequent bursts of jaw movements, which were characterized by low frequency jaw opening and closure movements from the rest position of the jaw, and absence of tongue protrusions. An additional stimulation of D1 receptors by giving SKF38393 30 min later produced an almost continuous pattern of jaw openings but less closure movements from the rest position, and the openings were accompanied by frequent tongue protrusions. These results clearly demonstrate that the type of oral behaviour produced by stimulation of D1 and D2 receptors together is qualitatively different from that produced by stimulation of either D1 or D2 receptors alone.

Role of neostriatum and nucleus accumbens in stepping induced by apomorphine and dexamphetamine

Systemic administration of apomorphine and dexamphetamine are known to produce circling in rats by changing the functioning of hindlimb stepping and forelimb stepping, respectively. In the present study intracranial injections of the dopamine antagonist sulpiride were used to study the involvement of the neostriatum and nucleus accumbens in these effects. It was found that injections of sulpiride into the neostriatum, but not the nucleus accumbens, dose-dependently (1-20 ng) reduced the number of apomorphine-induced hindlimb doublets without affecting the dexamphetamine-induced forelimb crossing steps. On the other hand, it was found that injections into the nucleus accumbens, but not the neostriatum, reduced the number of dexamphetamine-induced forelimb crossing steps without affecting the apomorphine-induced hindlimb doublets. This effect was not dose-dependent. The data suggest that the neostriatum, but not the nucleus accumbens, is primarily involved in the apomorphine-induced changes in hindlimb stepping, and that the nucleus accumbens, but not the neostriatum, is primarily involved in the dexamphetamine-induced changes in forelimb stepping.

Neurotoxicity induced by the D-1 agonist SKF 38393 following microinjection into rat brain

Microinjection of the D-1 agonist R-SKF 38393 into rat striatum resulted in extensive neurotoxic damage as revealed by the presence of large lesions upon histological analysis. These lesions were observed following a single injection of the drug into the ventrolateral striatum (30 micrograms/0.5 microliters) or nucleus accumbens (3.0 or 30 micrograms/0.5 microliters). This neurotoxic damage was also observed following microinjection of the inactive isomer S-SKF 38393. The mechanisms underlying these effects are presently unknown. The use of this compound for intracerebral microinjection studies should be re-evaluated. In view of the usefulness of central microinjections in studying the role of D-1 and D-2 receptors in behavior, it is suggested that alternative D-1 agonists, or ways of minimizing the toxicity of SKF 38393, should be considered.

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

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

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

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

Role of dopamine D-1 and D-2 receptors in the ventral striatum in the turning behaviour of rats

Systemically administered methamphetamine and apomorphine evoked characteristic turning when rats were pretreated with injections of D-1 and D-2 antagonists in the ventral but not in the dorsal striatum. The frequency of turning was greater for rats pretreated with D-2 antagonists (l-sulpiride and YM-09151-2) than for rats pretreated with a D-1 antagonist (SCH 23390). The responses were apparently additive when rats were pretreated with mixed D-1/D-2 antagonists, (cis(Z)-flupentixol and SCH 23390 + l-sulpiride). These results suggest that dopamine D-1 and D-2 receptors in the ventral striatum mediate turning behaviour through separate but cooperative mechanisms.

The role of D1 and D2 dopamine receptors in oral stereotypy induced by dopaminergic stimulation of the ventrolateral striatum

Microinjection of amphetamine into the ventrolateral region of the striatum results in compulsive and intense oral stereotypies in the rat. Although these stereotyped behaviors are known to be a direct result of excessive stimulation of the striatal dopamine neurons, the relative roles of the D1 and D2 receptors in oral stereotypies are not clearly understood. It is reported here that microinjection of the selective D1 agonist, SKF 38393 (0, 0.3, 3.0, 30.0 micrograms in 0.5 microliters vehicle) into the ventrolateral striatum resulted in no observable changes in behavior during the 30-min test period. However, it was observed that intense self-biting emerged 3-4 h following injection. Examination of histology from these animals revealed extensive tissue damage and the delayed onset of biting was hypothesized to result from a neurotoxic effect of SKF 38393. Infusion of quinpirole (0, 0.3, 3.0, 30.0 micrograms in 0.5 microliter vehicle), a selective D2 agonist, resulted in a dose-dependent increase in orofacial behaviors such as licking, wood-chip eating, head-down sniffing and mouth movements. Intense oral stereotypies such as biting or gnawing were not observed following treatment with quinpirole. Infusion of the mixed agonist dopamine (0, 2.0, 10.0, 20.0 micrograms in 0.5 microliter vehicle) into the ventrolateral striatum was found to elicit intense oral stereotypy. This behavior consisted almost exclusively of self-biting similar to that observed following amphetamine microinjection into this region. Haloperidol, when given as either a systemic (0.2 mg/kg) or intra-ventrolateral striatum (2.5 micrograms/0.5 microliter) pretreatment, effectively blocked oral stereotypies induced by amphetamine microinjection into the ventrolateral striatum. Pretreatment with either the D1 antagonist SCH 23390 (0, 0.01, 0.1 mg/kg, i.p.) or the D2 antagonist raclopride (0, 0.05, 0.50, 1.0 mg/kg, i.p.) antagonized amphetamine-induced oral stereotypy in a dose-dependent manner. These findings demonstrate that within the striatal site specifically implicated in oral behavior, concurrent stimulation of both receptor subtypes is necessary for the expression of intense oral stereotypies.