Brain vasculature and mitochondrial responses to ischemia in gerbils. I. Basic anatomical patterns and biochemical correlates

A unique blood supply to the brain, the 'Circle of Willis' (COW), exists in all mammals except for the Mongolian gerbil (Meriones unguiculatus). This system is capable of compensating for a decrease in blood supply in one of the four arteries, which may occur during pathological conditions. The posterior connection between the basilar artery and the carotid artery system have been found to be missing in most gerbils. Furthermore, in some of the animals, the anterior communication was not complete, thus leading to partial ischemia following unilateral carotid artery occlusion. Due to those peculiar characteristics, the Mongolian gerbil today has become a widespread animal model for cerebral ischemia studies. M. unguiculatus has been used in most of the studies while the level of ischemia has been evaluated by the development of neurological symptoms created by the occlusion of the carotid arteries. In the present study we investigated the vasculature structure of the commonly used gerbil, M. unguiculatus (MU-TF) and compared it to the vasculature of the Israeli gerbil, Meriones tristrami as well as to that of the Albino rat. We determined the correlation between the anatomical pattern and the biochemical responses during partial or complete ischemia and anoxia by monitoring the oxidation-reduction state of the intramitochondrial NADH using an in vivo surface fluorescence technique. The corrected fluorescence signal was found to be inversely correlated with oxygen availability and could thus be used as an indicator for the level of ischemia developed after carotid artery occlusio. This is the first time that the brain vasculature of two lines of M. tristrami (MT-HU, MT-BD) has been investigated. It was found that the biochemical responses to ischemia may be used as a good indicator for the anatomical pattern of the COW in the gerbils as well as in rat. In most of the gerbils tested, a non-homogeneous metabolic response to unilateral carotid occlusion was found in various parts of the same hemisphere. We studied this phenomenon in detail by using a four light guide fluorometer reflectometer implanted across the brain midline (two on each hemisphere).