The formal properties of the circadian system of Siberian hamsters (a.k.a., Djungarian hamsters Phodopus sungorus) have been thoroughly characterized over the last 50 years, mainly as a model species for studies of melatonin signaling of daylength ( Bartness et al., 1993). The studies reviewed here show that DPS hamsters are a promising model for translational studies of adult onset circadian dysfunction in humans. By contrast, DPS hamsters have an intact, but arrhythmic, SCN which produces severe deficits in memory tasks that are accompanied by fragmentation of electroencephalographic theta oscillations, increased synaptic inhibition in hippocampal circuits, and diminished responsiveness to cholinergic signaling in the dentate gyrus of the hippocampus. As I show, SCN ablation has little to no effect on memory. In the area of learning and memory, DPS arrhythmia produces much different results than arrhythmia by surgical ablation of the SCN. The main advantage of this model for inducing arrhythmia is that the DPS protocol is non-invasive circadian rhythms are eliminated while leaving the animals neurologically and genetically intact. The DPS protocol uses room lighting to administer a phase-advancing signal followed by a phase-delaying signal within one circadian cycle to suppress clock gene rhythms in the SCN. The suprachiasmatic nucleus (SCN) of the Siberian hamster is a labile circadian pacemaker that is easily rendered arrhythmic (ARR) by a simple manipulation of ambient lighting.
In this article, I describe the development of the disruptive phase shift (DPS) protocol and its utility for studying how circadian dysfunction impacts memory processing in the hippocampus. Biology Department, Stanford University, Stanford, CA, United States.
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