Effects of unilateral lesions of the retrotrapezoid nucleus (rtn)
on breathing in awake rats breathing, rtn lesions, unanesthetized
rats.
Akilesh, Manjapra R., Matthew Kamper, Aihua Li, Eugene E. Nattie.
Department of Pediatrics, Dartmouth-Hitchcock Medical Center, and
Department of Physiology, Dartmouth Medical School, Lebanon, NH
03765
APStracts 3:0480A, 1996.
In anesthetized rats, unilateral RTN lesions decreased markedly
baseline phrenic activity and the response to CO2 (Resp. Physiol. 97:
63-77,1994). Here we evaluate the effects of such lesions on resting
breathing and on the response to hypercapnia and hypoxia in
unanesthetized, awake rats. We made unilateral injections (mean +/-
SEM) (24 +/- 7 nl) of ibotenic acid (IA; 50 mM), an excitatory amino
acid neurotoxin, in the RTN region (N = 7) located by stereotaxic
coordinates and by field potentials induced by facial nerve
stimulation. Controls (N=6) received RTN injections (80 +/- 30 nl) of
mock cerebrospinal fluid (mCSF). A second control consisted of 4
animals with IA injections (24 +/- 12 nl) outside the RTN region.
Injected fluorescent beads allowed anatomical identification of
lesion location. Using whole body plethysmography, we measured
ventilation in the awake state during room air, 7% CO2 in air and 10%
O2 breathing before and for 3 weeks after the RTN injections. There
was no statistically significant effect of the IA injections on
resting room air breathing, comparing lesion to control groups. We
observed no apnea. The response to 7% CO2, in the lesion group
compared to the control group, was significantly decreased, by 39% on
average, for the final portion of the 3 week study period. There was
no lesion effect on the ventilatory response to 10% O2 . In this
unanesthetized model, other areas suppressed by anesthesia, e.g. the
reticular activating system, hypothalamus, and perhaps the
contralateral RTN, may provide tonic input to the respiratory centers
that counters the loss of RTN activity.
Received 18 April 1996; accepted in final form 26 September 1996.
APS Manuscript Number A375-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996