Abstracts

This abstract has been invited to present during the Broadening Representation Inclusion and Diversity by Growing Equity (BRIDGE) poster session.

Rationale: The pedunculopontine nucleus (PPN) is a brainstem nucleus that regulates cortical rhythms through glutamatergic (Glu) and cholinergic (ACh) outputs to the thalamus, brainstem, and basal forebrain. Given its central role in arousal and potent effects on cortical synchronization, we tested whether activation or inactivation of GABA, ACh, and Glu neurons of the PPN would disrupt seizures._x000D_
Methods: Long Evans naïve and CRE(+) transgenic rats were injected with virus coding for either channelrhodopsin-2 or an archaerhodopsin-3 and implanted with fiber optics in the PPN and cortical EEG electrodes. They were tested on open-loop (i.e., continuous neuromodulation) and closed-loop (i.e., on-demand neuromodulation, stimulation at the time of seizure detection) stimulation paradigms after an acute induction of seizures either with systemic injection of gamma-butyrolactone (GBL 100 mg/kg) or pentylenetetrazol (PTZ, 32.5-40 mg/kg), using 5 Hz activation or 100 Hz inactivation frequencies. Additionally, adult genetically epilepsy-prone rats (GEPR-3) underwent into virus injection and fiber optic implantation surgery. Three weeks post-surgery, GEPR-3 rats were submitted to an acute audiogenic stimulation protocol. One hour after the first stimulation, the audiogenic stimulation was repeated with continues neuromodulation 30 s before and after the sound and during the seizure.

Results: Optogenetic activation of ACh neurons in the PPN reduced the total number of SWDs during open-loop stimulation. By contrast, on-demand neuromodulation was effective against GBL-induced SWD, when GABAergic or Glutamatergic cell populations were optogenetically activated. The optogenetic inactivation did not show anti-seizure effects. Optogenetic inactivation of PPN did not abolish seizures nor did the modulation of GABA, Glu and ACh reduce the intensity of the seizures. Optogenetic activation of Glu transmission in the GEPR-3 rats decreased the intensity of the audiogenic seizures, whereas inactivation was without effect._x000D_
Conclusions: Neuromodulation of the PPN exerts anti-seizure effects in a cell-type specific, and stimulation modality specific manner. On-demand stimulation was the optimal strategy when activating the GABA and Glu pathways, while activation of ACh has is effective only when applied continuously. This suggests that the pattern of stimulation may be a critical determinant of anti-seizure effects. _x000D_
Funding: NIH R01 NS09776204 (PAF), NIH F30 NS110318 (SKH)