Long-term effect of chemogenetic suppression of excitatory hippocampal neurons on spontaneous seizures in a rat model for temporal lobe epilepsy

Long-term effect of chemogenetic suppression of excitatory hippocampal neurons on spontaneous seizures in a rat model for temporal lobe epilepsy

M.G. GOOSSENS

, K. VONCK

, C. VAN DEN HAUTE

, V. BAEKELANDT

, W. WADMAN

, C. VANHOVE

, P. BOON

, R. RAEDT

14BRAIN, Department Head and Skin, Ghent University - Ghent, Belgium.

2 Leuven Viral Vector Core, Centre for Molecular Medicine, KU Leuven - Leuven, Belgium

3 MEDISIP, Department of Electronics and Information Systems, Ghent University - Ghent, Belgium

Corresponding author: MarieGabrielle.Goossens@UGent.be

Introduction

The hippocampus is believed to play a crucial role in seizure generation in temporal lobe epilepsy (TLE). Chemogenetic inhibition of excitatory neurons in the hippocampus using hM4Di, an inhibitory Designer Receptor Exclusively Activated by Designer Drugs (DREADD), can be used to suppress hippocampal excitability. In this study, we evaluated the potential of ligand-based activation of DREADD, selectively expressed in excitatory hippocampal neurons, as a tool to suppress epileptic activity in arat model for TLE.

Methods

Results

Activation of hM4Di DREADD suppresses evoked potentials in epileptic rats

Conclusion

Chemogenetic inhibition in an epilepsy model:

 Activated by subpharmacological doses of clozapine or olanzapine

 Suppression of dentate gyrus evoked potentials

 Reduction of seizures in IPKA rat model for TLE

 Observed tolerance towards end of treatment

 Further optimization is required

K4 K

Inhibitory DREADD

CamKIIα hM4Di ^mCherry

Cell Specific Promoter

Fluorescent Tag

Viral Vector

(AAV 2/7) 24

weeks

Kainic Acid

Chemogenetic modulation

Effect of hM4Di DREADD activation

> 20 weeks

Clozapine

0.1 mg/kg

7d Treatment (7d) ^7d

Clozapine or Olanzapine

0.4 mg/kg/24h Hippocampus

(right)

Spontaneous Seizures Epilepsy

model

Dentate Gyrus Evoked Potentials

Spontaneous seizures

Continuous activation of hM4Di DREADD suppresses chronic seizures in epileptic rats

Shown ratios calculated at I₇₀. Median ± IQR, symbols correspond to individual animals. Control: n=3, DREADD: n=10

n . s . n . s .

***

Seizure Frequency (#/day)

- 7 - 6 - 5 - 4 - 3 - 2 - 1 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3

0 5 0 1 0 0

1 5 0 C lo z a p in e t re a t e d B a s e lin e / W a s h o u t

** ^{n . s .}

*** ^{n . s .}

T im e r e la t iv e t o s t a r t t r e a t m e n t ( d a y s ) Seizure Frequency (#/day)

- 7 - 6 - 5 - 4 - 3 - 2 - 1 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3

0 5 0 1 0 0 1 5 0

B a s e lin e / W a s h o u t O la n z a p in e t r e a t e d

CLOZAPINEOLANZAPINE

Median ± IQR, lines correspond to individual animals. Clozapine: n=10, olanzapine: n=7. **: p < 0.01, ***: p < 0.001 funded by

Clozapine Olanzapine Natural

ligand

Decreased neuronal firing Synaptic silencing

hM4Di Gi signaling

Control group DREADD group

Ratio clozapine/baseline