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Distribution and effects of PACAP, VIP, nitric oxide and GABA in the gut of the African clawed frog Xenopus laevis

Catharina Olsson

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

View larger version (106K): [in a new window]   Fig. 1. PACAP and VIP immunoreactivities in the gastrointestinal tract of Xenopus laevis. (A,B) Extensive networks of PACAP-immunoreactive nerve fibres in the myenteric plexus of the distal intestine (A) and rectum (B). (C) PACAP-immunoreactive nerve cell body in the myenteric plexus of the pyloric stomach. (D) PACAP-immunoreactive endocrine cells (arrows) and nerve fibres (arrowhead) in the mucosa of the proximal intestine. (E) VIP-immunoreactive myenteric nerve cell in the distal intestine. Bars: 25 µm (C,E), 50 µm (A,D), 100 µm (B).

View larger version (115K): [in a new window]   Fig. 2. PACAP, VIP and helospectin immunoreactivities in the gastrointestinal tract of Xenopus laevis. (A,B) Double-staining of a section through the cardiac stomach showing a high degree of colocalisation between PACAP (A) and VIP (B) immunoreactivities in the myenteric plexus (mep), the circular muscle layer (cm) and submucosa (sm). (C,D) A high degree of colocalisation between PACAP (C) and VIP (D) immunoreactivities in nerve fibres in the myenteric plexus of the pyloric stomach. (E,F) Colocalisation between PACAP (E) and VIP (F) immunoreactivities in varicose nerve fibres in the circular muscle layer of the proximal intestine. (G,H) Colocalisation between helospectin (G) and VIP (H) immunoreactivities in varicose nerve fibres along the circular muscle fibres in the cardiac stomach. Bars: 25 µm (E-H), 50 µm (A-D).

View larger version (129K): [in a new window]   Fig. 3. NOS and VIP immunoreactivities and NADPH-diaphorase reactivity in the gastrointestinal tract of Xenopus laevis. (A,B) Double-staining of the myenteric plexus (mep) of the proximal intestine showing NOS- (A) and VIP-immunoreactive nerve fibres (B) but only NOS-immunoreactive nerve cell bodies. Most VIP-immunoreactive nerve fibres are not NOS-immunoreactive. (C) NOS-immunoreactive endocrine cell in the mucosa of the proximal intestine. (D,E) Section through the proximal intestine showing colocalisation between NOS- (D) and VIP-immunoreactive nerve fibres (E) in the circular muscle layer (cm). (F,G) Double-staining of the myenteric plexus of the distal intestine showing NOS- (F) and VIP-immunoreactive nerve fibres (G) but only NOS-immunoreactive nerve cells bodies. Most VIP-immunoreactive nerve fibres are not NOS-immunoreactive. (H) NOS-immunoreactive nerve cell body in the myenteric plexus of the rectum. (I) NADPH-diaphorasereactive nerve cell body and nerve fibres in the myenteric plexus of the rectum. Bars: 25 µm (D,E,H), 50 µm (A—C,F,G,I).

View larger version (138K): [in a new window]   Fig. 4. GABA and VIP immunoreactivities in the gastrointestinal tract of Xenopus laevis. (A) GABA-immunoreactive bipolar nerve cell body in the myenteric plexus of the cardiac stomach. (B) Extensive network of GABA-immunoreactive nerve fibres in the myenteric plexus of the rectum. (C,D) Double-staining of nerve fibres in the myenteric plexus of the rectum. Most GABA-immunoreactive nerve fibres are not VIP-immunoreactive and vice versa. Bars: 25 µm (A,C,D) 50 µm (B).

View larger version (17K): [in a new window]   Fig. 5. Original tracings showing the effect of PACAP 27 (A; 10-7 mol l-1), VIP (B; 10-6 mol l-1), NaNP (C; 10-7 and 10-6 mol l-1), GABA (D; 10-7-10-4 mol l-1) and L-NAME (E; 3x10-4 mol l-1) on the cardiac stomach of Xenopus laevis. The appearance of spontaneous activity varied between individual preparations. PACAP 27, VIP, NaNP and GABA reduced the resting tension while the NOS inhibitor L-NAME enhanced the activity.

View larger version (21K): [in a new window]   Fig. 6. The effect of PACAP 27 (10-7 mol l-1, N=8), VIP (10-7 and 10-6 mol l-1, N=6) and GABA (10-6-10-4 mol l-1, N=6) on the circular smooth muscles of the cardiac stomach of Xenopus laevis. PACAP 27, VIP and GABA reduced the mean force developed by the stomach. The results are presented as mean force developed (± S.E.M.) above resting level. Open bars represent values immediately before addition of drug. *P0.05 compared to the control (C).

View larger version (12K): [in a new window]   Fig. 7. The effect of NaNP (10-7 mol l-1, N=6; 10-6 mol l-1, N=8) and L-NAME (3x10-4 mol l-1, N=6) on the circular smooth muscles of the cardiac stomach of Xenopus laevis. NaNP reduced the mean force developed while L-NAME enhanced the force developed. The results are presented as mean force developed (± S.E.M.) above resting level. Open bars represent values immediately before addition of drug. *P0.05 compared to the control (C).

View larger version (24K): [in a new window]   Fig. 8. The effect of PACAP 27 (10-7 mol l-1, N=7), VIP (10-7 mol l-1, N=6; 10-6 mol l-1, N=5) and GABA (10-5 mol l-1, N=5; 10-4 mol l-1, N=6) on the longitudinal smooth muscles of the proximal intestine of Xenopus laevis. Neither PACAP 27 nor VIP nor GABA had any effect on the force developed by the intestine. The results are presented as mean force developed (± S.E.M.) above resting level. Open bars represent values immediately before addition of drug. *P0.05 compared to the control (C).

View larger version (10K): [in a new window]   Fig. 9. The effect of NaNP (10-6 mol l-1, N=6) and L-NAME (3x10-4 mol l-1, N=5) on the longitudinal smooth muscles of the proximal intestine of Xenopus laevis. Neither NaNP nor L-NAME had any effect on the force developed by the intestine. The results are presented as mean force developed (± S.E.M.) above resting level. Open bars represent values immediately before addition of drug. *P0.05 compared to the control (C).