Dysfunction of GABAergic neurons in the parafacial zone mediates sleep disturbances in a streptozotocin-induced rat model of sporadic Alzheimer’s disease

Sleep disturbances are prevalent among patients with Alzheimer’s disease (AD) and often precede the onset and progression of dementia. However, there are no reliable animal models for investigating sleep disturbances in patients with sporadic AD (sAD), which accounts for more than 90% of all AD cases. In the present study, we characterize the sleep/wake cycles and explore a potential mechanism underlying sleep disturbance in a rat model of sAD induced via intracerebroventricular (icv) injection of streptozotocin (STZ). STZ-icv rats exhibited progressive decreases in slow wave sleep (SWS) during the light phase and throughout the light/dark cycle beginning from 7 days after STZ-icv. Additionally, increased wakefulness and decreased rapid-eye-movement (REM) and non-REM (NREM) sleep were observed from 14 days after STZ-icv. Beginning on day 7, STZ-icv rats exhibited significant decreases in delta (0.5–4.0 Hz) power accompanied by increased power in the beta (12–30 Hz) and low gamma bands (30–50 Hz) during NREM sleep, resembling deficits in sleep quality observed in patients with AD. Immunohistochemical staining revealed a significant reduction in the ratio of c-Fos-positive GABAergic neurons in the parafacial zone (PZ) beginning from day 7 after STZ-icv. These results suggest that the STZ-icv rat model is useful for evaluating sleep disturbances associated with AD, and implicate the dysregulation of GABAergic neuronal activity in the PZ is associated with sleep disturbance induced by STZ.