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J Appl Physiol (September 6, 2007). doi:10.1152/japplphysiol.00424.2007
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Submitted on April 18, 2007
Accepted on August 27, 2007

Raphe Magnus Nucleus is involved in ventilatory but not hypothermic response to CO2

Mirela Barros Dias1, Tatiane B. Nucci2, Lisandra Oliveira Margatho1, Jose Antunes-Rodrigues1, Luciane H. Gargaglioni3, and Luiz G. S. Branco4*

1 Department of Physiology, School of Medicine of Ribeirao Preto, University of Sao Paulo, Ribeirao Preto, Sao Paulo, Brazil
2 Physiology, School of Medicine of Ribeirao Preto, University of Sao Paulo, Ribeirao Preto, Sao Paulo, Brazil
3 Animal Morphology and Physiology, College of Agricultural and Veterinarian Sciences, Jaboticabal, Sao Paulo, Brazil
4 Department of Physiology, Dental School of Ribeirao Preto, University of Sao Paulo, Ribeirao Preto , Brazil

* To whom correspondence should be addressed. E-mail: branco{at}forp.usp.br.

There is evidence that serotonin [5-hydroxytryptamine (5-HT)] is involved in the physiological responses to hypercapnia. Serotonergic neurons represent the major cell type (comprising 15-20% of the neurons) in Raphe Magnus Nucleus (RMg), which is a medullary raphe nucleus. In the present study, we tested the hypothesis that (1) RMg plays a role in the ventilatory and thermal responses to hypercapnia, and that (2) RMg serotonergic neurons are involved in these responses. To this end, we microinjected (a) ibotenic acid to promote non-specific lesioning of neurons in the RMg, or (b) anti-SERT-SAP to specifically kill the serotonergic neurons in the RMg. Hypercapnia caused hyperventilation and hypothermia in all groups. RMg non-specific lesions elicited a significant reduction of the ventilatory response to hypercapnia due to lower tidal volume (VT) and respiratory frequency (f). Rats submitted to specific killing of RMg serotonergic neurons showed no consistent difference in ventilation during air breathing but had a decreased ventilatory response to CO2 due to lower VT. The hypercapnia-induced hypothermia was not affected by specific or non-specific lesions of RMg serotonergic neurons. These data suggest that RMg serotonergic neurons do not participate in the tonic maintenance of ventilation during air breathing but contribute to the ventilatory response to CO2 . Ultimately, this nucleus may not be involved in the thermal responses to CO2 .




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