Relationship between ion gradients and neurotransmitter release in the newborn rat striatum during anoxia

It has been well documented that mammalian newborns are more resistant to hypoxia than adults. The mechanisms for this tolerance has attracted considerable attention due to its clinical implications. Recently, there has been great interest in comparing the mechanisms involved in such tolerance with those of turtle brain, which has shown a remarkable tolerance to anoxia. In the latter, much attention has been paid to the role of neurotransmitters in regulating brain metabolic rate. In order to investigate this phenomenon in the mammalian neonate the pattern of neurotransmitter release with respect to pre- and postdepolarization stages was determined. Microdialysis was used to ascertain levels of neurotransmitters in the striatum of 5-day-old rats. Ion homeostasis was determined with a potassium-selective microelectrode. We report here that during anoxia at the predepolarization stage purines (inosine, hypoxanthine, xanthine and adenosine) were significantly released. However, amino acids (glutamate, gamma-amino butyric acid (GABA), aspartate and taurine) remained low during the first 30 min, but were released during anoxic depolarization. It was concluded that mammalian neonate brain differs from that of the turtle in hypoxic adaptations, which may be consequence of its comparatively undifferentiated state.