Selective protection from the inhibition by EEDQ of D1 and D2 dopamine agonist-induced rotational behavior in mice

Behavioral effects of dopamine receptor inactivation in the caudate-putamen of preweanling rats: role of the D2 receptor

RATIONALE

Inactivating dopamine (DA) receptors in the caudate-putamen (CPu) attenuates basal and DA agonist-induced behaviors of adult rats while paradoxically increasing the locomotor activity of preweanling rats.

OBJECTIVE

The purpose of this study was to determine (a) whether D1 or D2 receptor inactivation is responsible for the elevated locomotion shown by preweanling rats and (b) whether DA receptor inactivation produces a general state in which any locomotor-activating drug will cause a potentiated behavioral response.

METHODS

Dimethyl sulfoxide (DMSO) or N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) was bilaterally infused into the CPu on postnatal day (PD) 17. In experiment 1, DA receptors were selectively protected from EEDQ-induced alkylation by pretreating rats with D1 and/or D2 antagonists. On PD 18, rats received bilateral microinjections of the DA agonist R(-)-propylnorapomorphine into the dorsal CPu, and locomotor activity was measured for 40 min. In subsequent experiments, the locomotion of DMSO- and EEDQ-pretreated rats was assessed after intraCPu infusions of the selective DA agonists SKF82958 and quinpirole, the partial agonist terguride, or after systemic administration of nonDAergic compounds.

RESULTS

Experiment 1 showed that EEDQ's ability to enhance the locomotor activity of preweanling rats was primarily due to the inactivation of D2 receptors. Consistent with this finding, only drugs that directly or indirectly stimulated D2 receptors produced a potentiated locomotor response in EEDQ-treated rats.

CONCLUSIONS

These results show that DA receptor inactivation causes dramatically different behavioral effects in preweanling and adult rats, thus providing additional evidence that the D2 receptor system is not functionally mature by the end of the preweanling period.

Dopaminergic behaviors and signal transduction mediated through adenylate cyclase and phospholipase C pathways

We determined the relative effects of chemical receptor inactivation on dopaminergic signaling through adenylate cyclase and phospholipase C pathways and evaluated the behavioral implications of such receptor manipulations. Groups of rats were given intraperitoneal injections of 10 mg/kg N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), a reagent that differentially inactivates neurotransmitter receptors. Control and treated animals were used to assess dopaminergic-mediated behaviors or brain tissues were prepared from the animals and used to assay D1-like receptor binding and agonist-stimulated second messenger formation. EEDQ decreased by 75% the number of D1-like binding sites and completely abolished dopamine-stimulated cyclic AMP formation in striatal membranes. Conversely, dopamine-stimulated phosphoinositide hydrolysis was insensitive to inactivation by EEDQ as examined over different durations of EEDQ treatment, in different brain regions, or with different concentrations of the D1-like receptor agonist SKF38393. EEDQ-pretreated animals lost their stereotypic response to apomorphine but showed increased vacuous jaw movements in response to apomorphine or SKF38393. Basal catalepsy was increased and SCH23390 was unable to further enhance catalepsy beyond the basal levels in the lesioned animals. In naive animals, SCH23390 catalepsy was reversed by apomorphine, and apomorphine stereotypy was reversed by SCH23390. Taken together, the present results imply that the dopamine-sensitive phospholipase C system mediates a subset of dopaminergic behaviors, notably vacuous jaw movements, in contrast to stereotypy and catalepsy which appear to be respectively mediated through stimulation and inhibition of the adenylate cyclase-coupled dopaminergic system.

Dopaminergic and glutamatergic blocking drugs differentially regulate glutamic acid decarboxylase mRNA in mouse brain

Dopaminergic and glutamatergic inputs play an important role in regulating the activity of GABAergic neurons in basal ganglia. To understand more fully the biochemical interactions between these neurotransmitter systems, the effects of blocking dopamine and glutamate (N-methyl-D-aspartate) (NMDA) receptors on the expression of glutamic acid decarboxylase (GAD) mRNA were examined. Persistent blockade of dopamine receptors was achieved by daily injections of EEDQ, a relatively non-selective irreversible D1 and D2 dopamine receptor antagonist, or FNM, a relatively selective irreversible D2 dopamine receptor antagonist. Persistent blockade of NMDA receptors was achieved by continuously infusing dizocilpine (MK-801), a non-competitive NMDA receptor antagonist. The levels of GAD mRNA in mouse brain were measured by in situ hybridization histochemistry following treatment with these agents. Repeated administration of EEDQ increased the levels of GAD mRNA in corpus striatum and frontal and parietal cortex; the first significant effects were seen after 4 days of treatment. Treatment with FNM elicited effects similar to those produced by EEDQ, except FNM also significantly increased GAD mRNA in nucleus accumbens. Neither EEDQ nor FNM produced significant effects on GAD mRNA in olfactory tubercle or septum. Infusion of MK-801 produced a rapid and marked decrease in the levels of GAD mRNA in corpus striatum, nucleus accumbens, olfactory tubercle, septum and frontal and parietal cortex; significant changes were seen as early as 2 days of treatment. No significant effects were seen in globus pallidus. Cellular analysis of emulsion autoradiograms from corpus striatum revealed that MK-801 reduced the amount of GAD mRNA in individual cells as well as the proportion of cells expressing high levels of GAD mRNA. These results suggest that dopamine, though its interaction with D2 dopamine receptors, exerts an inhibitory effect on the expression of GAD mRNA, and that glutamate, though its interaction with NMDA receptors, exerts a stimulatory effect on GAD mRNA expression. They show further that the regulation of gene expression by dopamine receptors or NMDA receptors is different in different regions of the brain.

Irreversible blockade of D2 dopamine receptors by fluphenazine-N-mustard increases glutamic acid decarboxylase mRNA in rat striatum

The influence of dopaminergic activity on the function of GABAergic neurons in striatum was examined by administering rats the irreversible D2 dopamine receptor antagonist, fluphenazine-N-mustard (FNM), and determining the level of glutamic acid decarboxylase (GAD) mRNA in striatum. Rats were given either an acute single injection or chronic daily injections of FNM (20 mumol/kg, i.p.) for 6 days. The level of GAD mRNA in striatum was determined by in situ hybridization histochemistry. The results showed that acute treatment with FNM failed to significantly change striatal GAD mRNA. However, chronic FNM treatment significantly increased in the level of striatal GAD mRNA. These results demonstrate that irreversible blockade of D2 dopamine receptors increases the expression of GAD mRNA in rat striatum.

Role of dopamine receptors in the regulation of aggression in mice; relationship to genotype

The interline differences in the manifestation of aggression evoked by stimulation was studied in mice of eight inbred lines, and the role of different types of dopamine (DA) receptors in its manifestation was investigated. Aggression was assessed in a test involving the effect of a weak electrical stimulation through the floor of the cage. A significant relationship to the animals' genotype was demonstrated, and low-aggression (C3h/He, DD, BALB/c, and AKR) and high-aggression (CBA, DBA/2, and CC57Br) lines could be distinguished on the basis of the level of aggressivity. The mixed agonist of DA receptors, apomorphine, in a one-time administration activated aggressivity in the low-aggression mice. The selective stimulation of D2-receptors with bromocriptine substantially increased the evoked aggressivity in the low-aggression mice; the blockade of D2-receptors by sulpiride decreased or prevented the manifestation of aggressivity in the high-aggression lines. At the same time, the selective D1-agonist SKF 38393 and the selective D1-antagonist SCH 23390 did not exert a substantial influence on evoked aggressivity. Evidently the D2-receptors play a key role in the control of aggression evoked by stimulation, which constitutes a model of affective aggression.

Selective unilateral inactivation of striatal D1 and D2 dopamine receptor subtypes by EEDQ: turning behavior elicited by D2 dopamine receptor agonists

The unilateral intrastriatal injection of the irreversible dopamine (DA) receptor blocker N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) induces a marked decrease in the density of D1 (-48%) and D2 (-51%) DA receptors available for binding to [3H]SCH 23390 and [3H]raclopride, respectively. A challenge dose of the D2 agonist LY 171555 (1 mg/kg, i.p., 24 h after EEDQ) causes intensive ipsiversive circling behavior, whereas the selective D1 agonist SKF 38393 (20 mg/kg, i.p., 24 h after EEDQ) is unable to induce rotations. The density of D1 and D2 DA receptors returns to basal levels by 7 days after the intrastriatal infusion of EEDQ. This biochemical recovery is associated with a progressive decrease in the number of rotations elicited by a challenge dose of LY 171555, suggesting that EEDQ does not cause any relevant neuronal damage. A selective inactivation of striatal D1 or D2 DA receptors can be obtained by injecting EEDQ 30 min after the administration of the D2 antagonist raclopride (20 mg/kg, i.p.) or of the D1 antagonist SCH 23390 (2 mg/kg, s.c.), respectively. The intensity of the circling behavior induced by LY 171555 24 h after EEDQ in animals with a selective inactivation of D2 DA receptors is similar to that found in rats in which both D1 and D2 DA receptors have been inactivated. In contrast, LY 171555 does not cause rotations when the density of D1 DA receptors is selectively decreased by EEDQ in rats pretreated with raclopride.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral inactivation of dopamine receptors after intrastriatal injection of N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ): a novel rotational model to investigate dopamine receptor interactions

The interaction between D1 and D2 dopamine (DA) receptors was investigated in a novel rotational model. Rats were unilaterally injected into the striatum with the irreversible DA receptor blocker N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). This treatment induced a marked decrease in the density of D1 (-48%) and D2 (-45%) DA receptors available for binding to 3H-SCH 23390 and 3H-spiperone, respectively. Under these experimental conditions, the effect of DA receptor agonists were predominant on the intact side and resulted in rotations ipsilateral to the injected side. The effects of different agonists and antagonists for D1 and D2 DA receptors were evaluated 24 hr after EEDQ administration. The D2 agonist LY 171555 induced ipsilateral rotations in a dose-dependent manner (0.1-10.0 mg/kg, IP) in rats treated intrastriatally with EEDQ. In contrast, the D1 agonist SKF 38393 (1-20 mg/kg, IP) was unable to elicit circling behavior per se. However, SKF 38393 increased the number of rotations caused by LY 171555. The circling behavior induced by LY 171555 was blocked by the D2 antagonists (-)sulpiride and raclopride and by the D1 antagonist SCH 23390. Moreover, the inhibition of circling behavior induced by SCH 23390 was reversed by SKF 38393 in a dose-dependent manner. LY 171555 (1 mg/kg, IP) was unable to induce rotations in EEDQ-treated rats following DA depletion by alpha-methyl-p-tyrosine, whilst the combined administration of LY 171555 (1 mg/kg, IP) and SKF 38393 (10 mg/kg, IP) elicited intense circling behavior in DA depleted rats.(ABSTRACT TRUNCATED AT 250 WORDS)