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Updated: Aug 5, 2026

Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices
Published on: April 5, 2016
Modulation of in vitro Network Activity by Optogenetic Stimulation of Parvalbumin-positive Interneurons During
Fei Ran Li1, Maxime Lévesque1, Siyan Wang1
1Departments of Neurology & Neurosurgery, and Physiology, Montreal Neurological Institute-Hospital, McGill University, 3801 University Street, Montréal, Québec, H3A 2B4, Canada.
Background:
Catamenial epilepsy, which is defined as a periodicity of seizure exacerbation occurring during the menstrual cycle, has been reported in up to 70% of epileptic women. These seizures are often non-responsive to medication and our understanding of the relation between menstrual cycle and seizure generation (i.e. ictogenesis) remains limited.
Methods:
Here, we employed the in vitro 4-aminopyridine model of epileptiform synchronization, to analyze the effects induced by optogenetic activation of parvalbumin (PV)-positive interneurons at 8 Hz during estrous and non-estrous phases in female PV-ChR2 mice.
Results:
We found that: (i) optogenetic stimulation of PV-positive interneurons induced an initial interictal spike followed by field oscillations occurring more often in estrous (59%) than in non-estrous slices (17%); (ii) these oscillations showed significantly higher power in estrous compared to nonestrous slices (p < 0.001); (iii) significantly higher rates of interictal spikes and ictal discharges were identified in both estrous and non-estrous slices during optogenetic stimulation of PV-positive interneurons compared to periods of no stimulation (p < 0.05); and (iv) ictal events appeared to occur more frequently during optogenetic stimulation in estrous compared to non-estrous slices.
Conclusion:
Our findings show that optogenetic activation of PV-interneurons leads to more powerful network oscillations and more frequent ictal discharges in estrous than in non-estrous slices. We conclude that during the rodent estrous cycle, PV-interneuron hyperexcitability may play a role in epileptiform synchronization and thus in catamenial seizures.
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