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Extrabranchial chemoreceptors involved in respiratory reflexes in the neotropical fish Colossoma macropomum (the tambaqui)

William K. Milsom^1,*, Stephen G. Reid^1,, F. Tadeu Rantin² and Lena Sundin^1,

¹ Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z4
² Department of Physiological Sciences, Federal University of São Carlos, 13565-905 São Carlos SP, Brazil
Present address: Physiology Division, Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0623, USA
Present address: Department of Zoophysiology, Göteborg University, Box 463S-405 30, Göteborg, Sweden

View larger version (42K): [in a new window]   Fig. 1. Schematic diagram showing the cranial nerve roots relevant to this study. (A) The location of the nerves relative to the external anatomy of the fish. Scale bar, 5 cm. (B) An enlargement showing the origin of various cranial nerve roots. (C,D) Details of the branches of cranial nerves V, VII, IX and X.

View larger version (27K): [in a new window]   Fig. 2. Schematic diagram illustrating the different transections performed in various groups of fish in the different series of experiments. Control fish had all their cranial nerves intact (both series I and II). In the gill-denervated group, all branches of cranial nerves IX and X to the gills were sectioned where they enter the gills (series I). For the gill- and orobranchial-cavity-denervated group, all branches of cranial nerve V to the roof of the mouth as well as the palatine branches of VII and the opercular branches of VII to the floor of the mouth were also denervated (series I). In series II, the fish were decerebrate and spinalectomized, cranial nerves IX and X were transected where they originated from the brain within the cranium and cranial nerves V and VII were sectioned as in series I.

View larger version (29K): [in a new window]   Fig. 3. The effects on ventilation rate (percentage change from starting values) of graded hypoxia, hyperoxic hypercarbia, hyperoxia and injections of NaCN externally into the respiratory water. The data are shown as the mean + S.E.M. (N=8-12). In each graph, the different groups are C, control; GD, gills denervated; GOD, gills and orobranchial cavity denervated; DC, decerebrate control; DGD, decerebrate, gills denervated; DGOD, decerebrate, gills and orobranchial cavity denervated. Asterisks indicate values that are significantly different from resting values for fish within that group under normoxic normocapnic conditions (100 % value).

View larger version (30K): [in a new window]   Fig. 4. The effects on ventilation amplitude (percentage change from starting values) of graded hypoxia, hyperoxic hypercarbia, hyperoxia and injections of NaCN externally into the respiratory water. The data are shown as the mean + S.E.M. (N=8-12). In each graph, the different groups are C, control; GD, gills denervated; GOD, gills and orobranchial cavity denervated; DC, decerebrate control; DGD, decerebrate, gills denervated; DGOD, decerebrate, gills and orobranchial cavity denervated. Asterisks indicate values that are significantly different from resting values for fish within that group under normoxic normocapnic conditions (100 % value).

View larger version (32K): [in a new window]   Fig. 5. The effects on total ventilation (percentage change from the starting values) of graded hypoxia, hyperoxic hypercarbia, hyperoxia and injections of NaCN externally into the respiratory water. In each graph, the different groups are C, control; GD, gills denervated; GOD, gills and orobranchial cavity denervated; DC, decerebrate control; DGD, decerebrate, gills denervated; DGOD, decerebrate, gills and orobranchial cavity denervated. The data are shown as the mean + S.E.M. (N=8-12). Asterisks indicate indicates values that are significantly different from resting values for fish within that group under normoxic, normocapnic conditions (100 % value).

View larger version (23K): [in a new window]   Fig. 6. The effects on breathing frequency and amplitude (percentage change from the starting values) of superfusing the exposed brain of decerebrate fish for 15 min with various solutions (see text for details). The data are shown as the mean + S.E.M. (N=6).

View larger version (16K): [in a new window]   Fig. 7. The effects of systemic injection of different doses of adrenaline and of 100 nmol kg-1 adrenaline after pretreatment with sotalol (3 mg kg-1) on breathing frequency, breathing amplitude and total ventilation. The data are shown as the mean + S.E.M. (N=6). Asterisks indicate values that are significantly different from control values. All values were taken 30 s after injection except the 100 nmol kg-1 adrenaline+sotalol values, which were taken 120 s after injection.

View larger version (17K): [in a new window]   Fig. 8. The effects of graded hypoxia on breathing frequency before (filled circles) and after (open circles) pretreatment with sotalol. The data are shown as the mean ± S.E.M. (N=6). Asterisks indicate values that are significantly different from starting (18.7 kPa) values.