Effect of alpha1-adrenergic receptor antagonist on the noradrenaline-induced facilitation in respiratory rhythm in newborn rat pons-medulla-spinal cord preparations.
We hypothesized that facilitation of respiratory rhythm by noradrenaline (NA) in rat pons-medulla-spinal cord preparations is mediated through alpha1-adrenergic receptors. In 0- to 4-day-old rats, the respiratory frequency (fR) was monitored at the C4 ventral root and trigeminal motor (VMO) outputs. fR at temperature (Te)=23 degrees C was lower than that at a higher Te (27 degrees C) and was increased by NA. At 23 degrees C, lower concentrations of NA were needed to produce the same increases in fR seen at 27 degrees C. With highest NA concentration we tested (50 microM), activity at C4 was maintained in all preparations at both Te, whereas that at VMO was maintained in 50% (27 degrees C) or 88% (23 degrees C) of the preparations. Particularly, tonic activity at C4 appeared in all preparations at both Te, but that at the VMO occurred in 0% (27 degrees C) or 18% (23 degrees C) of the preparations. Based on these results, we used the lower Te (23 degrees C) and applied a low concentration of NA (3 microM) to the preparations. We found that: (1) with the addition of NA, fR was increased without the occurrence of tonic activity and (2) NA-related fR facilitation was inhibited by pre-treatment with the alpha1-adrenergic receptor antagonist prazosin (2 microM). fR was increased by application of the alpha1-adrenergic receptor agonist phenylephrine (4 microM), and this response was inhibited by prazosin (4 microM). At Te=23 degrees C, fR facilitation by NA in newborn rat pons-medulla-spinal cord preparations was obtained by activation of alpha1-adrenergic receptors.
Makino
Masaya
M
Department of Pediatric Dentistry, Nippon Dental University, School of Dentistry at Tokyo, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan. m-masaya@tky.ndu.ac.jp
Saiki
Chikako
C
Matsumoto
Shigeji
S
D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D000818:Animals; D000831:Animals, Newborn; D004837:Epinephrine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D010507:Periodicity; D011149:Pons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012119:Respiration / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*
D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D004837:Epinephrine