Francisco Tadeu Rantin

The autonomic control and functional significance of the changes in heart rate associated with air breathing in the jeju, Hoplerythrinus unitaeniatus.

SUMMARY The jeju is a teleost fish with bimodal respiration that utilizes a modified swim bladder as an air-breathing organ (ABO). Like all air-breathing fish studied to date, jeju exhibit pronounced changes in heart rate (fH) during air-breathing events, and it is believed that these may facilitate oxygen uptake (MO2) from the ABO. The current study employed power spectral analysis (PSA) of fH patterns, coupled with instantaneous respirometry, to investigate the autonomic control of these phenomena and their functional significance for the efficacy of air breathing. The jeju obtained less than 5% of total MO2 (MtO2) from air breathing in normoxia at 26°C, and PSA of beat-to-beat variability in fH revealed a pattern similar to that of unimodal water-breathing fish. In deep aquatic hypoxia (water PO2=1 kPa) the jeju increased the frequency of air breathing (fAB) tenfold and maintained MtO2 unchanged from normoxia. This was associated with a significant increase in heart rate variability (HRV), each air breath (AB) being preceded by a brief bradycardia and then followed by a brief tachycardia. These fH changes are qualitatively similar to those associated with breathing in unimodal air-breathing vertebrates. Within 20 heartbeats after the AB, however, a beat-to-beat variability in fH typical of water-breathing fish was re-established. Pharmacological blockade revealed that both adrenergic and cholinergic tone increased simultaneously prior to each AB, and then decreased after it. However, modulation of inhibitory cholinergic tone was responsible for the major proportion of HRV, including the precise beat-to-beat modulation of fH around each AB. Pharmacological blockade of all variations in fH associated with air breathing in deep hypoxia did not, however, have a significant effect upon fAB or the regulation of MtO2. Thus, the functional significance of the profound HRV during air breathing remains a mystery.

Cardiorespiratory responses to hypoxia in the African catfish, Clarias gariepinus (Burchell 1822), an air-breathing fish

The African catfish, Clarias gariepinus, possesses a pair of suprabranchial chambers located in the dorsal-posterior part of the branchial cavity having extensions from the upper parts of the second and fourth gill arches, forming the arborescent organs. This structure is an air-breathing organ (ABO) and allows aerial breathing (AB). We evaluated its cardiorespiratory responses to aquatic hypoxia. To determine the mode of air-breathing (obligate or accessory), fish had the respiratory frequency (fR) monitored and were subjected to normoxic water (PwO2xa0=xa0140xa0mmHg) without becoming hyperactive for 30xa0h. During this period, all fish survived without displaying evidences of hyperactivity and maintained unchanged fR, confirming that this species is a facultative air-breather. Its aquatic O2 uptake (

The basis of vagal efferent control of heart rate in a neotropical fish,the pacu, Piaractus mesopotamicus

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The combined effect of copper and low pH on antioxidant defenses and biochemical parameters in neotropical fish pacu, Piaractus mesopotamicus (Holmberg, 1887).

) was maintained constant down to a critical PO2 (PcO2) of 60xa0mmHg, below which

Antioxidant defenses and biochemical changes in the neotropical fish pacu, Piaractus mesopotamicus: responses to single and combined copper and hypercarbia exposure.

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Autonomic control of heart rate during orthostasis and the importance of orthostatic-tachycardia in the snake Python molurus

declined linearly with further reductions of inspired O2 tension (PiO2). Just above the PcO2 the ventilatory tidal volume (VT) increased significantly along with gill ventilation (