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2. Ventilatory flow relative to intrabuccal and intraopercular volumes in the serrasalmid fish Piaractus mesopotamicus during normoxia and exposed to graded hypoxia

Author

KALININ, A. L., SEVERI, W., GUERRA, C. D. R., COSTA, M. J., and RANTIN, F. T.

Subjects
ventilatory parameters, hipóxia, buccal and opercular volumes, hypoxia, normoxia, volumes bucal e operculares, normóxia, parâmetros ventilatórios, Piaractus mesopotamicus
Abstract

Ventilation volume ( – mlH2O.min–1 ), respiratory frequency (fR – breaths.min–1) and tidal volume (V T – mlH2O.breath–1 ) were measured in a group of Piaractus mesopotamicus (650.4 ± 204.7 g; n = 10) during normoxia and in response to graded hypoxia. The fR was maintained constant, around 100 breaths.min–1, from normoxia until the O2 tension of the inspired water (PiO2) of 53 mmHg, below which it increased progressively, reaching maximum values (157.6 ± 6.3 breaths.min–1) at 10 mmHg. The V T rose from 1.8 ± 0.1 to 6.0 ± 0.5 and 5.7 ± 0.4 mlH2O. breath–1 in the PiO2 of 16 and 10 mmHg, respectively. The increased from 169.3 11.0 (normoxia) to 940.1 ± 85.6 mlH2O. min–1 at the PiO2 of 16 mmHg, below which it also tended to decrease. A second group of fish (29 to 1510.0 g, n = 34) was used for the evaluation of allometric relationships concerning ventilation and dimensions of the buccal and opercular cavities. At maximum , the V T corresponded to 93.2 ± 2.4% of the buccal volume and 94.9 2.3% of the opercular volume, suggesting that the of P. mesopotamicus is limited by the volumes of buccal and opercular cavities in severe hypoxia. Em um grupo de Piaractus mesopotamicus (Wt = 650,4 ± 204,7 g, n = 10) foram determinados a ventilação branquial ( – mlH2O. min–1), a freqüência respiratória (fR – ciclos respiratórios. min–1) e o volume ventilatório (V T – mlH2O. ciclo respiratório–1) em normóxia e em resposta à hipóxia gradual. A fR foi mantida constante, em torno de 100 ciclos respiratórios. min–1, de normóxia até a tensão de O2 da água inspirada (PiO2) de 53 mmHg, abaixo da qual aumentou progressivamente, atingindo seus valores máximos (157,6 ± 6,3 ciclos respiratórios. min–1) em 10 mmHg. O V T aumentou de 1,8 ± 0,1 para 6,0 ± 0,5 e 5,7 ± 0,4 mlH2O. ciclo respiratório–1 nas PiO2 de 16 e 10 mmHg, respectivamente. A aumentou de 169,3 ± 11,0 (normóxia) para 940,1 ± 85,6 mlH2O. min–1 na PiO2 de 16 mmHg, abaixo da qual também tendeu a diminuir. Um segundo grupo de peixes (29 to 1510,0 g, n = 34) foi utilizado para a avaliação das relações alométricas entre a ventilação e as dimensões das cavidades bucal e operculares. Na máxima, o V T correspondeu a 93,2 ± 2,4% do volume bucal e 94,9 ± 2,3% de volume opercular, sugerindo que a de P. mesopotamicus é limitada pelos volumes dessas cavidades durante hipóxia severa.

Published
2000

4. The role of the vagus nerve in the generation of cardiorespiratory interactions in a neotropical fish, the pacu, Piaractus mesopotamicus.

Author

Costa Leite, Cleo Alcantara, Taylor, E. W., Guerra, C. D. R., Florindo, L. H., Belão, T., and Rantin, F. T.

Subjects
CARDIOPULMONARY system, HEART beat, VAGUS nerve, BRADYCARDIA, MOTOR neurons
Abstract

The role of the vagus nerve in determining heart rate ( fH) and cardiorespiratory interactions was investigated in a neotropical fish, Piaractus mesopotamicus. During progressive hypoxia fH initially increased, establishing a 1:1 ratio with ventilation rate ( fR). Subsequently there was a hypoxic bradycardia. Injection of atropine abolished a normoxic inhibitory tonus on the heart and the fH adjustments during progressive hypoxia, confirming that they are imposed by efferent parasympathetic inputs via the vagus nerve. Efferent activity recorded from the cardiac vagus in lightly anesthetized normoxic fish included occasional bursts of activity related to spontaneous changes in ventilation amplitude, which increased the cardiac interval. Restricting the flow of aerated water irrigating the gills resulted in increased respiratory effort and bursts of respiration-related activity in the cardiac vagus that seemed to cause fH to couple with fR. Cell bodies of cardiac vagal pre-ganglionic neurons were located in two distinct groups within the dorsal vagal motor column having an overlapping distribution with respiratory motor-neurons. A small proportion of cardiac vagal pre-ganglionic neurons (2%) was in scattered positions in the ventrolateral medulla. This division of cardiac vagal pre-ganglionic neurons into distinct motor groups may relate to their functional roles in determining cardiorespiratory interactions. [ABSTRACT FROM AUTHOR]

Published
2009
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