Altered daily rhythms of brain and pituitary indolamines and neuropeptidesin long-term hypoxic rats

To determine whether sustained hypoxia alters daily rhythms in brain and pi tuitary neurotransmitters, the daily variations in vasoactive intestinal pe ptide-like immunoreactivity (VIP-LI), neuropeptide Y-like immunoreactivity (NPY-LI), serotonin (5-HT), and 5-hydroxyindole-3-acetic acid (5-HIAA) cont ent were determined in discrete brain regions, pineal gland and anterior pi tuitary of hypoxic (10% O-2; 14 days) and normoxic rats. Hypoxia suppressed daily variations in VIP-LI in the suprachiasmatic nuclei (SCN) and the ant erior pituitary, enhanced the daily rhythmicity in serotonergic elements of the caudal part of the dorsomedial medulla oblongata (DMMc), and even indu ced daily variations in NPY-LI in the DMMc as well as in the ventrolateral medulla oblongata. In addition, punctual alterations in the rhythmicity of 5-HT and 5-HIAA in the pineal gland and of plasma corticosterone were obser ved in hypoxic rats. Thus results of this study indicate that a permanent n onphotic stimulus, such as sustained hypoxia, may affect the functioning of the internal clock located in the SCN and may alter the daily rhythmicity in neurotransmitter content of some brain nuclei and the pituitary gland.