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N-methyl-D-aspartate receptors mediate chemoreflexes in the shorthorn sculpin Myoxocephalus scorpius

J. Turesson^* and L. Sundin

Department of Zoology, Göteborg University, Box 463, S-405 30 Gothenburg, Sweden

View larger version (114K): [in a new window]   Fig. 1. Micrographs showing planar and cross sections of the ganglion nodosum and the medulla, immunostained with glutamate or NMDAR1 antisera. (A) Glutamate-like immunoreactivity (IR) in vagal nerve fibres proximal to the ganglion nodosum. (B) Glutamate-like IR in numerous cell bodies (arrow) within the ganglion nodosum. (C) Glutamate-like IR in almost all vagal nerve fibres (arrow) in the medulla projecting toward the vagal sensory area (Xs). (D,E) NMDAR1-like IR in fibres (arrow, D) and cell bodies (arrow, E) in the intermediate Xs (see F). (F) Dorsal view of the sculpin hindbrain. VII, facial nerve; IX, glossopharyngeal nerve; X, vagus nerve (two major branches); ovals indicate the positions of the Xs columns on each side of the medulla (a, rostral; b, intermediate; c, caudal portion of the Xs). Arrowhead points towards the caudal end of the fourth ventricle (4V), the obex. (G) Nissl stained cross section through the intermediate Xs (indicated in F) showing the precise location of the Xs and the vagal motor area (Xm) in the medulla. Scale bars, 1 mm (F), 100 µm (A,C,G), 50 µm (B,D) and 10 µm (E).

View larger version (23K): [in a new window]   Fig. 2. Summary of hypoxia-elicited cardiorespiratory reflexes. Effects on ventilation rate (A), ventilation amplitude (B), ventral aortic pressure (C) and heart rate (D) in control fish (filled circles) and in MK801 treated fish (open circles). (E) Changes in partial oxygen tension (PO2) in the respiratory water during hypoxia. Values shown are means + S.E.M. (N=7). *A statistically significantly difference (P<0.05) from resting values; statistically significant difference (P<0.05) between control and MK801 treated fish. For abbreviations, see Table 3.

View larger version (24K): [in a new window]   Fig. 3. Summary of NaCN-induced respiratory reflexes. Effects of external NaCN injections into the respiratory water (A,C) or internal NaCN injections into the afferent branchial artery (B,D) on ventilation frequency and amplitude in control and MK801-treated fish (MK801) (means + S.E.M.; N=7). Open bars show the pre-exposure values; grey bars, the maximal response to NaCN. *A statistically significantly difference (P<0.05) from pre-exposed values; statistically significant difference (P<0.05) between control and MK801-treated fish. For abbreviations, see Table 3.

View larger version (22K): [in a new window]   Fig. 4. Summary of NaCN-induced cardiovascular reflexes. Effects on ventral aortic pressure and heart rate after NaCN injections either externally into the respiratory water (A,C) or internally into the afferent branchial artery (B,D) in control and MK801-treated fish (MK801) (means + S.E.M.; N=7). Open bars show the pre-exposure values; grey bars, the maximal response to NaCN. *A statistically significantly difference (P<0.05) from pre-exposure values. For abbreviations, see Table 3.

View larger version (36K): [in a new window]   Fig. 5. Original traces showing different types of breathing patterns occurring after treatment with MK801. (A) Normal breathing before MK801 treatment and (B) increased frequency after MK801 treatment. (C) Frequency cycling after MK801; (D) Episodic breathing after MK801.

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