Effects of carotid sinus nerve transection on changes in neuropeptide Y and indolamines induced by long-term hypoxia in rats

Long-term hypoxia induces changes in neuropeptide-Y-like immunoreactivity ( NPY-LI) and/or in the content of serotonin (5-HT) and its metabolite 5-hydr oxyindoleacetic acid (5-HIAA) at the central level. To determine whether th ese alterations depend on the integrity of carotid body (CB) chemoreceptors , intact rats or those whose carotid sinus nerve was transected (CSNT) were exposed to hypoxia (10% O-2) or to normoxia for 14 days. Thereafter, NPY-L I, 5-HT and 5-HIAA levels in discrete brain regions were determined. The in crease in NPY-LI in the ventrolateral medulla oblongata (VLM) of intact hyp oxic rats was mostly abolished after CSNT and therefore is mainly mediated by CB chemoreceptors. In contrast, other hypoxia-induced changes were simil ar or even enhanced in CSNT as compared to intact rats and therefore do not depend on the integrity of CB chemoreceptors. This was the case for the in crease of NPY-LI in the striatum and the caudal dorsomedian medulla oblonga ta (DMM), as well as for all the changes in 5-HT and 5-HIAA in the DMM, the VLM, the raphe nuclei, the striatum and the frontal cortex. We propose tha t longterm hypoxia alters brain NPY-LI and indolamine content through the s timulation of CB chemoreceptors or ancillary chemoreceptors, as well as thr ough local biochemical or morphological mechanisms.