Slow Wave Sleep Deficits in the Flinders Sensitive Line Rodent Model of Depression: Effects of Medial Forebrain Bundle Deep-Brain Stimulation.

Major Depressive Disorder (MDD) is an affective disorder typically accompanied by sleep disturbances. Deep brain stimulation (DBS) of the medial forebrain bundle (MFB) is an emerging intervention for treatment-resistant depression, but its effect on sleep has not been closely examined. Here we aimed to characterise sleep deficits in the Flinders sensitive line, an established rodent model of depression, and investigate the consequences of MFB stimulation on sleep-related phenotypes. Rats were implanted with bilateral stimulation electrodes in the MFB, surface electrodes to record electrocorticography and electromyography for sleep scoring and electrodes within the prelimbic cortex, nucleus accumbens (NAc) and dorsal hippocampus. Recordings of sleep and oscillatory activity were conducted prior to and following twenty-four hours of MFB stimulation. Behavioural anti-depressant effects were monitored using the forced swim test. Previously unreported abnormalities in the Flinders sensitive line rats were observed during slow wave sleep, including decreased circadian amplitude of its rhythm, a reduction in slow wave activity and elevated gamma band oscillations. Previously established rapid eye movement sleep deficits were replicated. MFB stimulation had anti-depressant effects on behavioural phenotype, but did not significantly impact sleep architecture; it suppressed elevated gamma activity during slow wave sleep in the electrocorticogram and prelimbic cortex signals. Diverse abnormalities in Flinders sensitive line rats emphasise slow wave sleep as a state of dysfunction in affective disorders. MFB stimulation is able to affect behaviour and sleep physiology without influencing sleep architecture. Gamma modulation may represent a component of antidepressant mechanism.