title: Effects of chronic hypoxia on MK-801-induced changes in the acute hypoxic ventilatory response.
abstract: Chronic hypoxia increases the sensitivity of the central nervous system to afferent input from carotid body chemoreceptors. We hypothesized that this process involves N-methyl-D-aspartate (NMDA) receptor-mediated mechanisms and predicted that chronic hypoxia would change the effect of the NMDA receptor blocker dizocilpine (MK-801) on the poikilocapnic hypoxic ventilatory response (HVR). Male Sprague-Dawley rats were studied before and after acclimatization to hypoxia (70 Torr inspiratory Po(2) for 9 days). We measured ventilation (VI) and the HVR before and after systemic MK-801 treatment (3 mg/kg ip). MK-801 resulted in a constant respiratory frequency (approximately 175 min(-1)) during acute exposure to 10% and 30% O(2) before and after acclimatization. MK-801 had no effect on tidal volume (VT) before acclimatization, but it significantly decreased Vt when the animals were breathing 10% O(2) after acclimatization. The net effect of MK-801 was to eliminate the O(2) sensitivity of Vi before (via changes in respiratory frequency) and after (via changes in VT) acclimatization. Hence, chronic hypoxia altered the effect of MK-801 on the acute HVR, primarily because of increased effects on Vt. This indicates that changes in NMDA receptor-mediated neurotransmission may be involved in ventilatory acclimatization to hypoxia. However, further experiments are necessary to determine the precise location of such plasticity in the central nervous system.
authors.affiliation: Dept. of Medicine, Univerity of Califronia, San Diego, La Jolla, CA, USA. sgreid@utsc.utoronto.ca
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Reid
authors.forename: Frank L
authors.initials: FL
authors.lastname: Powell
mesh_terms: D000081:Acetamides / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D000222:Adaptation, Physiological / Q000187:drug effects*; D000818:Animals; D002908:Chronic Disease; D016291:Dizocilpine Maleate / Q000008:administration & dosage*; D005998:Glycine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012123:Pulmonary Ventilation / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012119:Respiration / Q000187:drug effects*; D013990:Tidal Volume / Q000187:drug effects
chemical_list: D000081:Acetamides; C075144:N,N'-methylenediacetamide; D016291:Dizocilpine Maleate; D005998:Glycine