Changes in baroreceptor vagal reflex performance in the developing rat.
Ontogenesis of both vagal control of heart rate and the baroreceptor vagal reflex were evaluated in rats at postnatal ages (P) of 5/6, 10, 15, 20, 25 and >>42 days anaesthetised with urethane (1.5 g/kg). Between P5/6 and P25 heart rate rose from 372 +/- 12 to 448 +/- 20 beats per minute and mean arterial pressure increased from 33.9 +/- 3.1 to 74.59 +/- 3.25 mm Hg (mean +/- SEM, n = 7 and 11 respectively). Cardiac vagal tone was absent at P10 but significant at P20 (P < 0.05) as revealed with atropine (0.5-1 mg/kg i.v.). Baroreceptor cardiac reflex sensitivity, tested with phenylephrine (10-50 microg/kg i.v.), was attenuated significantly in P10-20 rats compared with P5/6, P25 and mature animals. In P14-17 rats stimulation of neurones in either the solitary tract or ambiguual nuclei, by microinjection of L-glutamate (100-200 pmol), evoked an atropine-sensitive bradycardia indicating a functional integrity of central and peripheral efferent pathways mediating the baroreceptor reflex. Thus, the baroreceptor vagal reflex is functional in P5/6 rats but becomes attenuated between P10-P20, which is coincident with the maturational rise in arterial pressure.
Kasparov
S
S
Department of Physiology, School of Medical Sciences, University of Bristol, Bristol, BS8 1TD, UK.
Paton
J F
JF
D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development*; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure; D002628:Chemoreceptor Cells / Q000502:physiology; D005260:Female; D018698:Glutamic Acid / Q000494:pharmacology; D006329:Heart Conduction System / Q000254:growth & development / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology; D008845:Microinjections; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000502:physiology; D017552:Solitary Nucleus / Q000502:physiology; D013564:Sympathetic Nervous System / Q000254:growth & development / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology*
D018698:Glutamic Acid