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The dopamine receptor type 1 (D1R) and the dopamine receptor type 5 (D5R), which are often grouped as D1R-like due to their sequence and signaling similarities, exhibit high levels of constitutive activity. The molecular basis for this agonist-independent activation has been well characterized through biochemical and mutagenesis in vitro studies. In this regard, it was reported that many antipsychotic drugs act as inverse agonists of D1R-like constitutive activity. On the other hand, D1R is highly expressed in the medial prefrontal cortex (mPFC), a brain area with important functions such as working memory. Here, we studied the impact of D1R-like constitutive activity and chlorpromazine (CPZ), an antipsychotic drug and D1R-like inverse agonist, on various neuronal Ca V conductances, and we explored its effect on calcium-dependent neuronal functions in the mouse medial mPFC. Using ex vivo brain slices containing the mPFC and transfected HEK293T cells, we found that CPZ reduces Ca V 2.2 currents by occluding D1R-like constitutive activity, in agreement with a mechanism previously reported by our lab, whereas CPZ directly inhibits Ca V 1 currents in a D1R-like activity independent manner. In contrast, CPZ and D1R constitutive activity did not affect Ca V 2.1, Ca V 2.3, or Ca V 3 currents. Finally, we found that CPZ reduces excitatory postsynaptic responses in mPFC neurons. Our results contribute to understanding CPZ molecular targets in neurons and describe a novel physiological consequence of CPZ non-canonical action as a D1R-like inverse agonist in the mouse brain., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The dopamine receptor type 1 (D1R) and the dopamine receptor type 5 (D5R), which are often grouped as D1R-like due to their sequence and signaling similarities, exhibit high levels of constitutive activity. The molecular basis for this agonist-independent activation has been well characterized through biochemical and mutagenesis in vitro studies. In this regard, it was reported that many antipsychotic drugs act as inverse agonists of D1R-like constitutive activity. On the other hand, D1R is highly expressed in the medial prefrontal cortex (mPFC), a brain area with important functions such as working memory. Here, we studied the impact of D1R-like constitutive activity and chlorpromazine (CPZ), an antipsychotic drug and D1R-like inverse agonist, on various neuronal CaV conductances, and we explored its effect on calcium-dependent neuronal functions in the mouse medial mPFC. Using ex vivo brain slices containing the mPFC and transfected HEK293T cells, we found that CPZ reduces CaV2.2 currents by occluding D1R-like constitutive activity, in agreement with a mechanism previously reported by our lab, whereas CPZ directly inhibits CaV1 currents in a D1R-like activity independent manner. In contrast, CPZ and D1R constitutive activity did not affect CaV2.1, CaV2.3, or CaV3 currents. Finally, we found that CPZ reduces excitatory postsynaptic responses in mPFC neurons. Our results contribute to understanding CPZ molecular targets in neurons and describe a novel physiological consequence of CPZ non-canonical action as a D1R-like inverse agonist in the mouse brain. [ABSTRACT FROM AUTHOR]

Background and Purpose: CaV3.1‐3 currents differentially contribute to neuronal firing patterns. CaV3 are regulated by G protein‐coupled receptors (GPCRs) activity, but information about CaV3 as targets of the constitutive activity of GPCRs is scarce. We investigate the impact of D5 recpetor constitutive activity, a GPCR with high levels of basal activity, on CaV3 functionality. D5 recpetor and CaV3 are expressed in the hippocampus and have been independently linked to pathophysiological states associated with epilepsy. Experimental Approach: Our study models were HEK293T cells heterologously expressing D1 or D5 receptor and CaV3.1‐3, and mouse brain slices containing the hippocampus. We used chlorpromazine (D1/D5 inverse agonist) and a D5 receptor mutant lacking constitutive activity as experimental tools. We measured CaV3 currents and excitability parameters using the patch‐clamp technique. We completed our study with computational modelling and imaging technique. Key Results: We found a higher sensitivity to TTA‐P2 (CaV3 blocker) in CA1 pyramidal neurons obtained from chlorpromazine‐treated animals compared with vehicle‐treated animals. We found that CaV3.2 and CaV3.3—but not CaV3.1—are targets of D5 receptor constitutive activity in HEK293T cells. Finally, we found an increased firing rate in CA1 pyramidal neurons from chlorpromazine‐treated animals in comparison with vehicle‐treated animals. Similar changes in firing rate were observed on a neuronal model with controlled CaV3 currents levels. Conclusions and Implications: Native hippocampal CaV3 and recombinant CaV3.2‐3 are sensitive to D5 receptor constitutive activity. Manipulation of D5 receptor constitutive activity could be a valuable strategy to control neuronal excitability, especially in exacerbated conditions such as epilepsy. [ABSTRACT FROM AUTHOR]