D1/D5 Inverse Agonists Restore Striatal Cholinergic Interneuron Physiology in Dyskinetic Mice

Abstract

A BS TRACT: Background: In advanced stages of Parkinson's disease (PD), dyskinesia and motor fluctuations become seriously debilitating and therapeutic options become scarce. Aberrant activity of striatal cholinergic interneurons (SCIN) has been shown to be critical to PD and dyskinesia, but the systemic administration of cholinergic medications can exacerbate extrastriatal-related symptoms. Thus, targeting the mechanisms causing pathological SCIN activity in severe PD with motor fluctuations and dyskinesia is a promising therapeutic alternative. Methods: We used ex vivo electrophysiological recordings combined with pharmacology to study the alterations in intracellular signaling that contribute to the altered SCIN physiology observed in the 6-hydroxydopamine mouse model of PD treated with levodopa. Results: The altered phenotypes of SCIN of parkinsonian mice during the "off levodopa" state resulting from aberrant Kir/leak and Kv1.3 currents can be rapidly reverted by acute inhibition of cAMP-ERK1/2 signaling. Inverse agonists that inhibit the ligand-independent activity of D5 receptors, like clozapine, restore Kv1.3 and Kir/leak currents and SCIN normal physiology in dyskinetic mice. Conclusion: Our work unravels a signaling pathway involved in the dysregulation of membrane currents causing SCIN hyperexcitability and burst-pause activity in parkinsonian mice treated with levodopa (L-dopa). These changes persist during off-medication periods due to tonic mechanisms that can be acutely reversed by pharmacological interventions. Thus, targeting the D5-cAMP-ERK1/2 signaling pathway selectively in SCIN may have therapeutic effects in PD and dyskinesia by restoring the normal SCIN function.

Constitutive activity of the dopamine (D5) receptor, highly expressed in CA1 hippocampal neurons, selectively reduces CaV3.2 and CaV3.3 currents

“…In this line, a recent publication showed the impact of clozapine and flupenthixol, putative D 1 /D 5 receptor inverse agonists, on the electrical activity of striatal cholinergic interneurons in an animal model of dyskinesia (Paz et al, 2022). Moreover, the treatment with flupenthixol changes the firing pattern from a pathological burst to a physiological tonic firing in subthalamic nucleus (Chetrit et al, 2013).…”

“…Based on our data from Figure S1 showing that D 1 receptor coexpression reduces Ca V 3.3 and likely Ca V 3.2, chlorpromazine could also be acting on the D 1 receptor reducing its constitutive activity and further increasing Ca V 3 current. In this line, a recent publication showed the impact of clozapine and flupenthixol, putative D 1 /D 5 receptor inverse agonists, on the electrical activity of striatal cholinergic interneurons in an animal model of dyskinesia (Paz et al, 2022). Moreover, the treatment with flupenthixol changes the firing pattern from a pathological burst to a physiological tonic firing in subthalamic nucleus (Chetrit et al, 2013).…”

“…as inverse agonists (Paz et al, 2022;Zhang et al, 2014). In this respect, we previously used chlorpromazine to manipulate the constitutive activity of D 1 /D 5 receptors in the prefrontal cortex (McCarthy et al, 2020).…”

“…Finally, the binding of inverse agonists reduces the constitutively active levels of a GPCR (Costa & Cotecchia, 2005). In particular, for D 1 /D 5 receptor, it has been reported that some typical and atypical antipsychotics such as chlorpromazine, fluopentixol (flupenthixol) and clozapine function as inverse agonists (Paz et al, 2022; Zhang et al, 2014). In this respect, we previously used chlorpromazine to manipulate the constitutive activity of D 1 /D 5 receptors in the prefrontal cortex (McCarthy et al, 2020).…”

Striatal CDK5 Regulates Cholinergic Neuron Activation and Dyskinesia-like Behaviors through BK Channels

“…Abnormal activity of striatal cholinergic neurons has been identified to be essential to dyskinesia-like behaviors and motor symptoms of PD. The upregulation of regulator of G protein signaling 4 (RGS4) and the activation D5-cAMP-ERK1/2 signaling pathway are reported to mediate hyperexcitability of striatal cholinergic neurons [ 35 , 36 ]. Neuronal CDK5 is required for spatial learning and recurrent excitatory circuits in the hippocampus [ 37 , 38 ] and proper multipolar-to-bipolar transition in the cortex [ 39 ].…”