Chemical lesions of the nucleus isthmi increase the hypoxic and hypercarbic drive to breathing of toads.
The nucleus isthmi (NI) is a mesencephalic structure of the amphibian brain that has recently been reported to participate in the hypoxic and hypercarbic drive to breathing. However, previous studies used electrolytic and kainic lesions, which causes diffuse and nonspecific destruction. Thus, in the present study, we assessed the participation of NI in the respiratory response to hypoxia and hypercarbia using lesions produced with ibotenic acid (a substance that selectively destroys cell bodies but spares fibers of passage) into the NI of toads (Bufo paracnemis). Our results demonstrated that, under resting breathing, NI plays no role in pulmonary ventilation. Hypoxia and hypercarbia caused hyperventilation in all groups. Chemical lesions in the NI elicited an increase in ventilatory response to hypoxia and hypercarbia, due to a higher tidal volume. We conclude that NI cell bodies do not participate in the control of pulmonary ventilation under resting conditions, but exert an inhibitory modulation of hypoxic and hypercarbic drive to breathing, acting on tidal volume.
Department of Physiology, Faculty of Medicine of Ribeirão Preto, Ribeirão Preto, Brazil.
Luciane H
LH
Gargaglioni
Norberto C
NC
Coimbra
L G S
LG
Branco
D000704:Analysis of Variance; D000818:Animals; D002025:Bufonidae; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D006935:Hypercapnia / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D006985:Hyperventilation; D000860:Hypoxia / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D007051:Ibotenic Acid / Q000633:toxicity; D008636:Mesencephalon / Q000166:cytology / Q000503:physiopathology*; D012123:Pulmonary Ventilation; D012016:Reference Values; D012119:Respiration; D013990:Tidal Volume
D018690:Excitatory Amino Acid Agonists; D007051:Ibotenic Acid