PLASTICITY OF TYROSINE-HYDROXYLASE GENE-EXPRESSION IN THE RAT NUCLEUS-TRACTUS-SOLITARIUS AFTER VENTILATORY ACCLIMATIZATION TO HYPOXIA

The aim of this study was to define the influence of long-term hypoxia on gene expression of tyrosine hydroxylase (TH) in the rat nucleus tr actus solitarius (NTS). Animals were exposed to normobaric hypoxia (10 % O-2 in nitrogen) for 2 weeks. At this time, the hypoxia-induced hype rventilation reached a plateau, indicating ventilatory acclimatization . In horizontal brainstem sections, hypoxia-induced changes in TH prot ein and TH mRNA were assessed by immunocytochemistry and in-situ hybri dization, respectively. Long-term hypoxia increased TH mRNA levels see n as both an increase in the number of grains per cell and an extensio n of the labeled area. The highest degree of labeling was found select ively located in caudal NTS. Hypoxia also enhanced TH immunoreactivity in the caudal NTS but this labeling extended more rostrally than that of TH mRNA. The data suggest that there is an hypoxia-induced plastic ity of gene expression at the gene level in the NTS, which is associat ed with ventilatory acclimatization. The hypoxia model described in th is study may serve as a framework for future regulatory studies.