Asymmetric propagation of spreading depression along the anteroposterior axis of the cerebral cortex in mice

The purpose of this study was to ascertain whether or not spreading depression (CSD) propagates symmetrically along the anteroposterior axis of the cortex of mice, and to determine where CSD should be elicited to achieve a uniform exposure of the cortex to this phenomenon. Experiments were performed in halothane-anesthetized mice, with three different locations aligned 1.5 min from the midline used for either KCI elicitation of CSD or the recording of its propagation. Our results demonstrated that, at least in the mouse cortex, CSD propagated much more effectively from posterior to anterior regions than in the opposite direction. This feature was due to a different efficacy of propagation in the two opposite directions, and not to a reduced susceptibility of occipital regions to CSD elicitation. Heterogeneous CSD propagation constitutes a potential pitfall for neurochemical studies of post-CSD changes in mice, as brain tissue samples collected for this purpose should be uniformly exposed to CSD. Occipital sites for CSD induction are clearly optimal for this purpose. If CSD propagation is confirmed to be more effective from posterior to anterior regions in other species, this may be relevant to the pathophysiology of classical migraine because the most frequent aura symptoms (i.e., visual disturbances) originate in the occipital cortex.