Spreading Depression: A Self-organized Excitation Depression Wave in Different Gravity Conditions

Abstract

The spreading depression is an excitation-depression wave that was first described by Leao in 1944 as a wave like spreading depression of neuronal activity in the central nervous system. The spreading depression waves travel over the cortex with a velocity of about 3mm/min, concomitant with a slow extra cellular negative potential shift about 10 to 30 mV. A very short hyper excitation at the wave front is followed by a complete suppression of electrical activity (Egert et al., 1995). The spreading depression itself is a fully reversible process without permanent damage of the neuronal tissue (Hansen und Nedergaard, 1988). Nearly at the same time as Leao discovered the cortical spreading depression, Lashley, a scientist suffering from migraine himself, described his own aura symptoms as patterns travelling over his field of vision. He postulated that these visual disorders are due to a neuronal inactivity which travels like a wave over the visual cortex at a velocity of about 3 mm/min (Lashley, 1941). For the first time in 1958 Milner linked these two phenomena (Milner, 1958). Not only the visual scotoma described by Lashley, but also other aura symptoms (e.g. somatosensory, somatomotory, auditive disorders) can be explained by spreading depression waves travelling over the corresponding cortex. Today the occurrence of spreading depression together with several neurological disorders is proven, e.g. for classical migraine (Welch et al., 1990; Welch et al., 1992), transient neurological disorders concomitant with ischemic attacks (Somjen et al., 1990), epilepsy (Marshall, 1959), transient global amnesia (Olesen et al., 1986) and brain traumata (Oka et al., 1977).