Chronic hypoxia modulates NMDA-mediated regulation of the hypoxic ventilatory response in an amphibian, Bufo marinus.
This study examined whether a hypoxia-tolerant amphibian, the Cane toad, undergoes mammalian-like ventilatory acclimatisation to hypoxia (VAH) and whether chronic hypoxia (CH) alters NMDA-mediated regulation of the acute hypoxic ventilatory response (HVR). Toads were exposed to 10 days of CH (10% O2) followed by acute hypoxic breathing trials or an intra-arterial injection of NaCN. Trials were conducted before and after i.p. treatment with an NMDA-receptor channel blocker (MK801). CH blunted the acute HVR but did not alter resting breathing. MK801 did not alter resting ventilation. In control animals, MK801 augmented breathing frequency (fR) during acute hypoxia by increasing the number of breaths per episode. This effect was attenuated following CH although MK801 did enhance the number of episodes per minute during acute hypoxia. MK801 enhanced the fR response to NaCN in both groups. The results indicate that CH did not produce mammalian-like VAH (i.e. increased resting ventilation and an augmented acute HVR) but did alter MK801-sensitive regulation of breathing pattern and the acute HVR.
McAneney
Jessica
J
Centre for the Neurobiology of Stress, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ont., Canada M1C 1A4.
Gheshmy
Afshan
A
Uthayalingam
Sarangan
S
Reid
Stephen G
SG
D000064:Acclimatization / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D002024:Bufo marinus; D003485:Cyanates / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D000860:Hypoxia / Q000503:physiopathology*; D016202:N-Methylaspartate / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology*; D012119:Respiration / Q000187:drug effects; D013997:Time Factors
D003485:Cyanates; D018691:Excitatory Amino Acid Antagonists; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; C009281:sodium cyanate