Yawning responses induced by local hypoxia in the paraventricular nucleus of the rat.
Yawing was induced by microinjections of L-glutamate, cyanide and a nitric oxide-releasing compound (NOC12) into the paraventricular nucleus of the hypothalamus (PVN) in anesthetized, spontaneously breathing rats. To evaluate physiological aspects of yawning, we monitored intercostal electromyogram (EMG) as an index of inspiratory activity, digastric EMG, blood pressure and electrocorticogram (ECoG). Microinjection of L-glutamate in the medial parvocellular subdivision (mp) elicited a stereotyped yawning response, i.e. an initial depressor response and an arousal shift in ECoG followed by a single large inspiration with mouth opening. The same sequential events were observed during spontaneous yawning, indicating that the mp is responsible for triggering yawning. Microinjection of cyanide into the mp caused the same yawning responses as the ones elicited by microinjection of L-glutamate, suggesting that the mp is sensitive to chemical hypoxia or ischemia within the PVN. Microinjection of NOC12 into the mp elicited a single large inspiration with a variable onset delay, suggesting that diffusible nitric oxide (NO) within the mp may act as a paracrine agent to cause a yawning response. We hypothesize that the mp of the PVN contains an oxygen sensor that causes a yawning response.
Kita
I
I
Department of Physiology, Toho University School of Medicine, 5-21-16, Omori-nishi, Ota-ku, 143-8540, Tokyo, Japan.
Sato-Suzuki
I
I
Oguri
M
M
Arita
H
H
D000818:Animals; D002545:Brain Ischemia / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D000860:Hypoxia / Q000139:chemically induced*; D008297:Male; D008845:Microinjections; D009569:Nitric Oxide / Q000378:metabolism / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000378:metabolism*; D009603:Nitroso Compounds / Q000378:metabolism*; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012684:Sensory Thresholds; D012966:Sodium Cyanide / Q000494:pharmacology*; D013239:Stereotyped Behavior; D015000:Yawning / Q000187:drug effects / Q000502:physiology*
C118603:NOC 12; D020030:Nitric Oxide Donors; D009603:Nitroso Compounds; D009569:Nitric Oxide; D018698:Glutamic Acid; D012966:Sodium Cyanide