Meeting Abstract

23.4  Friday, Jan. 4  Natural Neuroprotection in the Brains of Marine Mammals: Why swimming dolphins don�t stroke WILLIAMS, T.M.**; ZAVANELLI, M.; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz williams@biology.ucsc.edu

Whereas neural impairment in human drowning victims can occur within a few minutes of submergence, extreme mammalian divers, most notably Weddell seals (Leptonychotes weddellii), elephant seals (Mirounga angustirostris), and sperm whales (Physeter macrocephalus) can remain underwater for more than 90 minutes with no apparent detrimental neural effects. Cardiovascular changes associated with the dive response have long been considered the main avenue for protecting the brain from hypoxic damage in these mammals. However, circulating oxygen levels during submergence appear inadequate for ensuring aerobic support of neural tissues. To determine how marine mammals avoid ischemic-hypoxic neural injury we evaluated the presence and concentration of oxygen-carrying globins in the cerebral cortex of 16 species of terrestrial and marine mammal. Globin protein concentrations were determined both spectrophotometrically and from mRNA expression patterns for neuroglobin and cytoglobin. We found a 9.5-fold difference in hemoglobin concentration between terrestrial and deep-diving mammals, and a nearly two-fold difference in resident cerebral globins (neuroglobin, cytoglobin) between terrestrial and swimming mammals. By safeguarding neural tissues challenged by oxygen deprivation, this array of concentrated globin proteins represents an important adaptation for maintaining sensory and locomotor function when marine mammals dive. Furthermore these results indicate the potential for novel mechanisms for averting oxygen-mediated neural injury as occurs in human drowning victims and stroke patients. (Supported by a grant from ONR).