The comparative effects of haloperidol, (-)-sulpiride, and SCH23390 on c-fos and c-jun mRNA expressions, and AP-1 DNA binding activity

Cocaine activates Homer1 immediate early gene transcription in the mesocorticolimbic circuit: differential regulation by dopamine and glutamate signaling

Homer proteins are intracellular scaffolding proteins that, among glutamate receptors, selectively bind to group1 metabotropic glutamate receptors and regulate their trafficking and intracellular signaling. Homer proteins have been implicated in synaptic and behavioral plasticity, including drug-seeking behavior after cocaine treatment. Homer1 gene activation leads to transcription of a variant mRNA (Homer1a), which functions as an immediate early gene. Homer1a competes with the constitutive Homer proteins (Homer1b/c/d, Homer2a/b, Homer3) for binding to group1 metabotropic glutamate and IP3 receptors. Binding of Homer1a to these proteins disrupts their association with the intracellular signaling scaffold and modulates receptor function. In this study, using RT-PCR, activation of Homer1a mRNA transcription in response to acute and repeated administration of cocaine was characterized in prefrontal cortex, nucleus accumbens, and ventral tegmental area, three mesocorticolimbic nuclei of the rat brain. Moreover, the dopaminergic and glutamatergic regulation of Homer1 gene activation by cocaine was investigated. Acute cocaine rapidly and transiently activated transcription of Homer1a mRNA in all three nuclei. However, repeated administration of cocaine was not effective in inducing the Homer1a mRNA transcription after various withdrawal times ranging from 2 h to 3 weeks. The acute cocaine-mediated activation of Homer1 gene was regulated by D1 but not D2 dopamine receptors. The blockade of AMPA or NMDA glutamate receptors did not prevent cocaine-mediated activation of Homer1 gene in the three mesocorticolimbic nuclei. These data indicate that acute administration of cocaine transiently activates Homer1 gene producing the immediate early gene Homer1a mRNA in the three mesocorticolimbic nuclei of the rat brain. Activation of Homer1 gene may contribute to the cocaine-mediated synaptic and behavioral plasticity.

Calcium-dependent, D2 receptor-independent induction of c-fos by haloperidol in dopamine neurons

Antipsychotic drugs such as haloperidol act as dopamine D2 receptor antagonists to produce a number of cellular effects including the induction of immediate-early genes such as c-fos. It has been hypothesized that blockade of D2 receptors by antipsychotics is responsible for the induction of c-fos, but the mechanism has not been determined. Using cultured ventral tegmental area (VTA) dopaminergic neurons as a model, we report that nanomolar concentrations of haloperidol cause a time-dependent increase in Fos expression in dopaminergic neurons.Surprisingly, this induction was not mimicked by sulpiride, a selective D2 receptor antagonist, and was not blocked by Rp-cAMPS, an antagonist of protein kinase A (PKA), thus suggesting that D2 receptors and the cAMP cascade are not required. The induction of Fos expression was blocked by tetrodotoxin, BAPTA and KN-93, thus showing that it is activity- and calcium-dependent and requires the activation of a calmodulin-dependent kinase (CaMK). Together, these results suggest that haloperidol induces Fos expression in dopaminergic neurons through a D2 receptor-independent increase in intracellular calcium, leading to CaMK activation.

Dopamine D4 receptor-mediated regulation of rod opsin mRNA expression in tiger salamander

Light stimulates dopamine release in the retina and has been shown to rapidly up-regulate rod opsin mRNA. In the present study, we tested the effect of dopamine on rod opsin mRNA expression and examined the hypothesis that dopamine can mediate a light-evoked increase in opsin gene expression. Northern blots showed that a 30-min light-exposure increased rod opsin mRNA expression 27%. In situ hybridization on isolated rods showed that 500 nM dopamine and 1 microM quinpirole (dopamine D2/D3/D4 agonist) increased opsin mRNA 45% and 26%, respectively. The effect of quinpirole was selectively blocked by the D4 antagonist, L750,667 (20 microM). In very low density cultures, quinpirole increased opsin expression 46%, suggesting a direct effect on rod photoreceptors. Consistent with a dopamine D4 receptor mechanism, 1 microM H-89 (protein kinase A inhibitor) increased opsin mRNA 39%. Finally, intravitreal injection of quinpirole increased opsin mRNA 21% whereas injection of L750,667 (10 microM) blocked the light-evoked increase in opsin expression. These data show that rod opsin mRNA is up-regulated by dopamine binding a D4-like receptor on rods, possibly through inhibition of protein kinase A, and that endogenous dopamine can mediate the light-evoked increase in opsin mRNA expression.

Comparative effects of dopamine D(1) and D(2) receptor antagonists on nerve growth factor protein induction

We previously reported that following acute administration of haloperidol or (-)-sulpiride, both dopamine D(2)-receptor antagonists, to mice induced nerve growth factor (NGF) gene expression, mediated by the interaction of c-fos with the AP-1 binding site present in the first intron on the NGF gene. In contrast, the D(1)-receptor antagonist R-(-)-8-chloro-2,3,4, 5-tetrahydro-3,1-methyl-5-phenyl-11-3-benzyoepine-7-ol (SCH23390) did not induce NGF mRNA expression. We report here immunohistochemical and Western blot analyses showing that following injection of these drugs for 14 consecutive days, the amount of NGF protein increased gradually and was induced significantly in the hippocampus, piriform cortex, amygdala, dorsal striatum, and nucleus accumbens neurons. NGF enhances the release of acetylcholine from these regions. Cholinergic innervation in the striatum and nucleus accumbens neurons is believed to be related to late-onset extrapyramidal symptoms, while in the hippocampus and piriform cortex it is involved in enhancing cognition. Thus, our data suggest that haloperidol- and (-)-sulpiride-induced NGF expression may be associated with both beneficial and adverse effects.

Comparison of the effects of dopamine D1 and D2 receptor antagonists on nerve growth factor mRNA expression

Regulation of the expression of the nerve growth factor (NGF) gene has been reported previously to be mediated by the interaction of c-fos with an activator protein-1 (AP-1) binding site present in the first intron on the NGF gene. Using an RNase protection assay and in situ hybridization, we examined the effects of dopamine D1 and D2 receptor antagonists on NGF mRNA. Haloperidol (0.1-8 mg/kg) and (-)-sulpiride (10-100 mg/kg), induced NGF mRNA in a dose-dependent fashion in the hippocampus, piriform cortex, striatum and nucleus accumbens. The haloperidol (1 mg/kg)- and (-)-sulpiride (20 mg/kg)-induced NGF mRNA expression attained a maximum level 120 min after injection and returned to control levels 24 h later. Prior administration of the protein synthesis inhibitor cycloheximide blocked the haloperidol- and (-)-sulpiride-mediated induction of NGF mRNA. In contrast, R-(-)-8-chloro-2,3,4,5-tetrahydro-3,1-methyl-5-phenyl-11-3-benzyoepin e-7-ol (SCH23390) did not induce NGF mRNA expression in either a dose-dependent or time-dependent manner. Our previous studies have shown that haloperidol and (-)-sulpiride induce the expression of c-fos and c-jun mRNAs and increase their AP-1 DNA binding activities. Thus, the data suggest that neuroleptics induce NGF gene expression by increasing AP-1 DNA binding activity.

Molecular and behavioral effects mediated by Gs-coupled adenosine A2a, but not serotonin 5-Ht4 or 5-Ht6 receptors following antipsychotic administration

Typical antipsychotic agents are potent antagonists of Gi-coupled dopamine D2 receptors, but their mechanisms of action following this initial blockade remain poorly understood. We hypothesized that in striatal neurons, interruption of this inhibitory dopamine D2 input would unmask endogenous striatal Gs-coupled receptors. An increase in cAMP levels generated by these unopposed receptors would then lead to the well-described behavioral and molecular effects of antipsychotic administration such as catalepsy and striatal c-fos and neurotensin gene transcription. We examined three striatal Gs-coupled receptor systems (serotonin 5-HT4, serotonin 5-HT6 and adenosine A2a) to assess their potential involvement in the mechanism of action of the typical antipsychotic haloperidol. Antagonists of each of these three receptor systems together with a 1 mg/kg dose of haloperidol were co-administered to Sprague-Dawley rats, and both the degree of catalepsy produced in the animals and the induction of striatal c-fos and neurotensin messenger RNAs were measured. Both the specific adenosine A2a antagonist 8-(3-chlorostyryl)-caffeine and the general adenosine antagonist theophylline reduced haloperidol-dependent induction of striatal neurotensin and c-fos messenger RNA. Administration of these agents also greatly reduced the degree of catalepsy induced by haloperidol. Antagonists of the 5-HT6 receptor failed to block the induction of striatal messenger RNAs, but the 5-HT6 antagonist clozapine (an important atypical antipsychotic agent in its own right) was a potent inhibitor of catalepsy. 5-HT4 agents were unable to alter haloperidol's effects on striatal messenger RNA levels or catalepsy. We conclude that the striatal Gs-coupled adenosine A2a receptor is an important mediator of the molecular and behavioral sequelae following haloperidol administration.

Distribution of Fos- and Jun-related proteins and activator protein-1 composite factors in mouse brain induced by neuroleptics

The mechanisms by which the direct actions of neuroleptics are translated into therapeutic effects are unknown. We immunocytochemically investigated the expression of Fos- and Jun-related proteins and examined activator protein-1 DNA-binding activity in ddY mouse brain 120 min after the administration of haloperidol (1 mg/kg), (-)-sulpiride (20 mg/kg) and a selective dopamine D1 receptor antagonist, SCH23390 (1 mg/kg). The densities of Fos-, FosB-, Fra-1-, Jun- and JunD-immunoreactive nuclei induced by haloperidol and sulpiride in the hippocampus, piriform cortex and accumbens nucleus were higher than those in the control groups. The same regions showed higher densities of FosB-, Fra-1- and JunD-immunoreactive nuclei induced by SCH23390 compared with the control groups. We investigated further the activator protein-1 composite factors using super gel shift assays. These results suggested that induced Fos, FosB, Fra-1, Jun and JunD proteins constitute the activator protein-1 complex after the administration of haloperidol and sulpiride. In contrast, FosB, Fra-1 and JunD appear to constitute the activator protein-1 complex after the administration of SCH23390. Therefore, the diversity of activator protein-1 composite factors suggests that various kinds of gene are induced to act by some neuroleptics.