Authors :
Presenting Author: Aaron Salisbury, BS – Johns Hopkins University School of Medicine
Michael Totty, PhD – Johns Hopkins University School of Public Health
Keri Martinowich, PhD – Lieber Institute for Brain Development; Johns Hopkins University School of Medicine
Rationale:
Cortistatin (CST) is a neuropeptide, similar in structure to somatostatin, primarily expressed in GABAergic neurons in the cortex and hippocampus. Ablating CST+ neurons in mice causes spontaneous, fatal seizures early in postnatal development, establishing their importance in regulating excitability. CST+ neurons show sexual dimorphism in regulating pituitary function, and may further show dimorphism in gating hyperexcitation. However, whether loss of CST+ neuron function after development influences seizure susceptibility, and whether restricting loss of CST+ neurons only to specific brain regions is sufficient to induce epilepsy, is unknown. Here, we investigate a role for CST+ neurons in the prelimbic cortex (PrL) of adult mice on susceptibility to PTZ-kindled seizures.
Methods:
12-16 week old Cst-T2A-Cre+/- mice on a C57BL/6J background were used for all experiments. For ablation experiments, mice (n = 16; 8M/8F) received bilateral intracranial injections (2.5E12 vg/mL, 350 nL) of either AAV5-flex-taCasp3-TEVp spiked with AAV5-flex-mCherry (10:1) (n=8) or AAV5-flex mCherry (n=8) in the PrL. 4 weeks post-infusion, PTZ was administered at varying concentrations (15-35 mg/kg, i.p.) across days and mice were observed for 20 minutes for seizures. Dosing was repeated over several days until seizures occurred. For DREAD-mediated inhibition of CST+ neuron activity, mice (n=24; 12M/12F) received bilateral injections (2.5E12 vg/mL, 350 nL) of either AAV8-hSyn-DIO-hM4D(Gi)-mCherry (n=12) or AAV8-hSyn-DIO-mCherry (n=12) in the PrL. 4 weeks post-infusion, the DREADD agonist CNO (5 mg/kg, i.p.) was administered followed 30 minutes later by PTZ (30 mg/kg, i.p.). Mice were then observed for 20 minutes and scored on a modified Racine scale for seizures. Viral expression was confirmed by immunohistochemistry.Results:
Ablating CST+ neurons in PrL is sufficient to elicit spontaneous seizures in a subset of mice (2/12), and increases susceptibility to PTZ-mediated kindling (2-Way ANOVA, F(1,41)=12.66, p< 0.0001). Mice with CST+ neuron ablation showed increased sensitivity to PTZ kindling. Acute, chemogenetic inhibition of CST+ neurons was also sufficient to potentiate development of PTZ-mediated kindling in female mice only (3-way ANOVA, F