Abstracts

Rationale: Supramammillary neurons project to the septal area and the hippocampus, with a targeted projection to the dentate gyrus dendritic zone along with a discrete projection to CA2, and the cerebral cortex. We hypothesized that activation of these neurons would result in increased fast EEG activity with wakefulness. Methods: We used the designer receptors exclusively activated by designer drug (DREADD) approach to selectively manipulate the activity of glutamatergic neurons of the supramammillary region. In vglut2-Cre mice, we stereotaxically injected a conditional adeno-associated virus that expressed either excitatory modified human M3 receptor, or a modified inhibitory glutamate-gated chloride channel, agonized by otherwise inert clozapine-N-oxide (CNO) or low-concentration ivermectin (IVM), respectively. Fluorescent labels allowed delineation of projections and transfected cells. Fluorescent labels allowed delineation of transfected cells and terminal fields. Headsets were affixed and video-EEG with EMG was recorded. Results: While mice receiving saline three hours after lights-on (typical sleep period) slept after 14 minutes, mice injected with CNO, remained awake for nine hours with a prominent spectral band at 10 Hz, along with gamma band activity (CNO: 540 208 (SD) versus saline: 13.7 5.42 minutes, t-test p = 0.0142, n = 4, 4;ANOVA p = 0.0014, Bonferoni p < 0.05 eight of nine hours). Ivermectin (at lights out, the normal wake period) suppressed wakefulness and 10 Hz activity, resulting in a level of sleep that would be typical of the light period (ANOVA p = 0.0464, n = 4, 4). Conclusions: This study demonstrates that glutamatergic neurons of the supramammillary region are capable of promoting fast EEG activity and prolonged wakefulness. Prominent 8-10 Hz activity recorded with intracranial cortical electrodes may correspond to a hippocampal rhythm.