Evidence for central chemoreception in the midline raphé.
We injected acetazolamide (AZ; 5 x 10(-6) M; 1 nl; n = 14), its inactive analogue 2-acetylamino-1,3,4-thiadiazole-5-sulfon-t-butylamide (5 x 10(-5) M; n = 6), or mock cerebrospinal fluid (n = 5) into the caudal raphé in the midline brain stem of anesthetized paralyzed ventilated rats. These AZ injections have been shown to produce a focal region of tissue acidosis with a radius < 350 microns and are used as a probe for sites of central chemosensitivity. Compared with control injections, AZ injection into the raphé, as demonstrated by anatomic analysis of injection location, significantly increased the amplitude of the integrated phrenic neurogram over 10-40 min. Not all raphé injections produced such a response. AZ injections identified as responders (n = 8 of 14) increased integrated phrenic amplitude 43.3 +/- 10.7% (SE) of baseline 20 min after the injection. We conclude that the midline caudal raphé contains sites of ventilatory chemoreception.
Bernard
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DG
Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03756-0001, USA.
Li
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A
Nattie
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EE
D000086:Acetazolamide / Q000494:pharmacology; D000138:Acidosis / Q000503:physiopathology; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008297:Male; D008845:Microinjections; D010791:Phrenic Nerve / Q000502:physiology; D011903:Raphe Nuclei / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015656:Respiratory Mechanics / Q000502:physiology; D014628:Vagotomy
D002257:Carbonic Anhydrase Inhibitors; D002245:Carbon Dioxide; D000086:Acetazolamide