Long term chemogenetic suppression of spontaneous seizures in a mouse model for temporal lobe epilepsy

Abstract

Objective More than one‐third of patients with temporal lobe epilepsy (TLE) continue to have seizures despite treatment with antiepileptic drugs, and many experience severe drug‐related side effects, illustrating the need for novel therapies. Selective expression of inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) allows cell‐type‐specific reduction of neuronal excitability. In this study, we evaluated the effect of chemogenetic suppression of excitatory pyramidal and granule cell neurons of the sclerotic hippocampus in the intrahippocampal mouse model (IHKA) for temporal lobe epilepsy. Methods Intrahippocampal IHKA mice were injected with an adeno‐associated viral vector carrying the genes for an inhibitory DREADD hM4Di in the sclerotic hippocampus or control vector. Next, animals were treated systemically with different single doses of clozapine‐N‐oxide (CNO) (1, 3, and 10 mg/kg) and clozapine (0.03 and 0.1 mg/kg) and the effect on spontaneous hippocampal seizures, hippocampal electroencephalography (EEG) power, fast ripples (FRs) and behavior in the open field test was evaluated. Finally, animals received prolonged treatment with clozapine for 3 days and the effect on seizures was monitored. Results Treatment with both CNO and clozapine resulted in a robust suppression of hippocampal seizures for at least 15 hours only in DREADD‐expressing animals. Moreover, total EEG power and the number of FRs were significantly reduced. CNO and/or clozapine had no effects on interictal hippocampal EEG, seizures, or locomotion/anxiety in the open field test in non‐DREADD epileptic IHKA mice. Repeated clozapine treatment every 8 hours for 3 days resulted in almost complete seizure suppression in DREADD animals. Significance This study shows the potency of chemogenetics to robustly and sustainably suppress spontaneous epileptic seizures and pave the way for an epilepsy therapy in which a systemically administered exogenous drug selectively modulates specific cell types in a seizure network, leading to a potent seizure suppression devoid of the typical drug‐related side effects.

Pharmaco‐genetic inhibition of pyramidal neurons retards hippocampal kindling‐induced epileptogenesis

“…13 Many previous studies demonstrated that pharmaco-genetic inhibition of pyramidal neurons by engineered inhibitory Gi-coupled human muscarinic receptor hM4Di alleviated seizure severity in different types of epilepsy models in vitro and in vivo. [14][15][16][17] Meanwhile, we previously demonstrated that pharmaco-genetic activating parvalbumin neurons (a subtype of GABAergic neuron), with engineered excitatory Gqcoupled human muscarinic receptor hM3Dq, also produced seizure attenuation, 18 which may be a novel and promising approach for treating refractory TLE. Later study showed that pharmaco-genetic activating parvalbumin interneurons exhibited the better effect in reducing epileptiform activity than the other subtypes of GABAergic neurons.…”

Level of hM4D(Gi) DREADD Expression Determines Inhibitory and Neurotoxic Effects in the Hippocampus

“…It was recently demonstrated that selective hM4D(Gi) expression in principal hippocampal neurons results in seizure suppressing effects, both in chronic mouse and rat models for temporal lobe epilepsy (Desloovere et al, 2019;Goossens et al, 2021;Wang et al, 2018).…”

“…This approach represents one of the chemogenetic applications with therapeutic potential, e.g. in epilepsy (Chen et al, 2020;Desloovere et al, 2019;Goossens et al, 2021). The aim of this study was to vary hM4D(Gi) expression levels in hippocampal neurons by injecting different viral vector titers.…”

Chronic DREADD Isn’t As Bad As It Sounds

“…Above and beyond DREADD-mediated effects on normal physiology, clozapine (and CNO) may have DREADD-independent actions. 8 Reassuringly, Desloovere et al 11 found no effects of clozapine or CNO delivery on hippocampal activity or seizures in animals that did not express DREADD receptors and similarly found no effect of either drug in the open field task. While by no means a comprehensive assessment of potential off-target effects, these data nonetheless strengthen the case for this approach.…”

“…To evaluate longer term seizure suppression, Desloovere et al 11 carried out monitoring during 36-hour repeated clozapine dosing. As in the prior studies evaluating DREADDmediated seizure control in spontaneous models, 6,7 Desloovere used an on-off-on design.…”