Effects of oxygen deprivation on parapyramidal neurons of the ventrolateral medulla in the rat

We characterized the electrophysiological properties and responses of neuro ns located in the parapyramidal region of the ventral aspect of the rat med ulla oblongata (parapyramidal neurons, PP neurons) to oxygen deprivation, i n order to understand the mechanisms involved in hypoxia induced respirator y depression. The responses of PP neurons to oxygen deprivation were compar ed to those of the functionally dissimilar neurons of the dentate gyrus (DG ). Neurons from the PP region were found to fire spontaneously with a frequ ency of 3-3.5 spikes/sec in both adults and neonates and responded to an an oxic insult with a complete loss of spontaneous firing. Discrete metabolite analysis showed a small (about 17%) decrease in tissue adenosine triphosph ate (ATP) levels of the PP neurons during an anoxic insult and the decrease was significantly smaller than in the DG cell region (28%). In contrast to the DG neurons, the PP neurons recovered from an anoxic insult lasting mor e than 30 min, indicating a greater survival capacity of the PP neurons dur ing oxygen deprivation, The PP neurons were also capable of withstanding su ccessive anoxic insults better than the DG cells as demonstrated by their c omplete recovery following reoxygenation. It is suggested that the PP neuro ns may depress their electrical activity as an energy conservation mechanis m, and thereby survive anoxic insults longer than the dentate neurons, wher eas the loss of cellular activity in the DG neurons may be a result of ener gy depletion. (C) 1999 Elsevier Science B.V. All rights reserved.