Microcirculatory and Ionic Responses to Ischemia in the Mongolian Gerbil

Abstract

The Mongolian gerbil (Meriones unguiculatus) is a very useful animal model for studying brain responses to partial or complete ischemia [1–5]. Various aspects of brain functions and responses have been studied in this model exposed to ischemic conditions. When cerebral blood flow diminished due to the ischemia [6], inhibition of the Na⁺K⁺ ATPase occurred and, as a result, extracellular K⁺ level increased [7, 8]. In 1978, we described the effects of ischemia on the metabolic activity in the gerbil brain using the surface fluorometry technique to monitor reduced nicotinamide adenine dinucleotide (NADH) redox state [9]. In ischemia, we described a new phenomenon defined as secondary reflectance increase (SRI), [10]; this event is associated with ionic homeostasis disturbances which occur under energy deprivation conditions. To study this microcirculatory phenomenon under ischemia, the multiparametric monitoring approach [8] was used. Metabolic activity was measured by monitoring tissue surface O₂ tension by a surface electrode. Intramitochondrial NADH redox state was evaluated by the surface fluorometry reflectometry technique described in detail previously [11]. The reflected light at the excitation wavelength (336 nm) measured simultaneously with the fluorescence light (450 nm) was used to correct the fluorescence signal for hemodynamic artifacts. This signal is largely dependent upon blood volume at the measurement site. Extracellular K⁺ activity was measured by a surface valinomycine electrode located in the multiprobe assembly.