Effects of unilateral lesions of retrotrapezoid nucleus on breathing in awake rats

• Published in: Journal of applied physiology (1985) 1997-02, Vol.82 (2), p.469-479
• Main Authors: Akilesh, Manjapra R, Kamper, Matthew, Li, Aihua, Nattie, Eugene E
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cardiorespiratory control. Arterial mecano- and chemoreceptor; Fundamental and applied biological sciences. Psychology; Male; Medulla Oblongata - physiology; Rats; Rats, Sprague-Dawley; Respiration - physiology; Vertebrates: respiratory system; Wakefulness - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1997.82.2.469

Manjapra R. Akilesh 1 , Matthew Kamper 2 , Aihua Li 2 , and Eugene E. Nattie 2 1  Department of Pediatrics, Dartmouth-Hitchcock Medical Center, and 2  Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03765 Received 18 April 1996; accepted in final form 26 September 1996. Akilesh, Manjapra R., Matthew Kamper, Aihua Li, and Eugene E. Nattie. Effects of unilateral lesions of retrotrapezoid nucleus on breathing in awake rats. J. Appl. Physiol. 82(2): 469-479, 1997. In anesthetized rats, unilateral retrotrapezoid nucleus (RTN) lesions markedly decreased baseline phrenic activity and the response to CO 2 (E. E. Nattie and A. Li. Respir. 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 [24 ± 7 (SE) 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. A second control consisted of four animals with IA injections (24 ± 12 nl) outside the RTN region. Injected fluorescent beads allowed anatomic identification of lesion location. Using whole body plethysmography, we measured ventilation in the awake state during room air, 7% CO 2 in air, and 10% O 2 breathing before and for 3 wk after the RTN injections. There was no statistically significant effect of the IA injections on resting room air breathing in the lesion group compared with the control groups. We observed no apnea. The response to 7% CO 2 in the lesion group compared with the control groups was significantly decreased, by 39% on average, for the final portion of the 3-wk study period. There was no lesion effect on the ventilatory response to 10% O 2 . 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. ventrolateral medulla; control of breathing; central chemoreceptors; carbon dioxide sensitivity; hypoxia; unanesthetized rats 0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society