doi:10.1016/j.peptides.2005.09.014
Copyright © 2005 Elsevier Inc. All rights reserved.
Effects of neuropeptide Y on food intake and brain biogenic amines in the rainbow trout (Oncorhynchus mykiss)
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M. Aldegunde
, 
and M. Mancebo
Laboratorio de Fisioloxía Animal, Dpto. de Fisioloxía, Facultade de Bioloxía, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
Received 5 July 2005;
revised 20 September 2005;
accepted 23 September 2005.
Available online 25 October 2005.
Abstract
Neuropeptide Y (NPY) is one of the most potent stimulants of food intake in mammals, but very little is known about NPY actions in fish. The present study investigated the role of NPY in food intake in the rainbow trout (Oncorhynchus mykiss). Food intake was monitored at different times after intracerebroventricular administration of porcine NPY (4 or 8 μg). Both doses significantly increased food intake at 2 and 3 h, and this effect was dose-dependent. However, 50 h after administration of NPY, food intake was significantly lower than in control fish, and cumulative food intake had returned to levels similar to those seen in the control group. The NPY antagonist (d-Tyr27,36, d-Thr32)-NPY (10 μg) inhibited food intake 2 h after icv administration, but did not block the orexigenic effect of NPY when administered jointly with 4 μg NPY. To identify the NPY receptor subtypes involved in the effects of NPY on food intake, we studied the effects of the Y1 receptor agonist (Leu31, Pro34)-NPY (4 μg), the Y2 receptor agonist NPY(3–36) (4 μg), and the highly specific Y5 receptor agonist (cPP1–7, NPY19–23, Ala31, Aib32, Gln34)-hPP (4 μg). Short-term (2 h) food intake was moderately stimulated by the Y1 agonist, more strongly stimulated by the Y2 agonist, and unaffected by the Y5 agonist. We found that administration of NPY (8 μg icv) had no effect on aminergic systems in several brain regions 2 and 50 h after NPY administration. These results indicate that NPY stimulates feeding in the rainbow trout, and suggest that this effect is cooperatively mediated by Y2- and Y1-like NPY receptors, not by Y5-like receptors.
Keywords: NPY; Food intake; Brain; Biogenic amines; Rainbow trout
Abbreviations: DA, dopamine; DOPAC, dihydroxyphenylacetic acid; 5-HIAA, 5-hydroxyindoleacetic acid; 5-HT, 5-hydroxytryptamine or serotonin; NA, noradrenaline; EDTA, ethylenediaminetetraacetic acid; FI, food intake; HPLC, high-performance liquid chromatography; icv, intracerebroventricular; MS 222, 3-aminobenzoic acid ethyl esther, methanesulfonate salt; NPY, neuropeptide Y
Fig. 1. Effects of icv administration of 1 μl of saline alone (control) or containing 4 μg of porcine NPY on food intake in rainbow trout. (A) Food intake is shown as mean ± SEM of food intake (g per kg body weight per 10 min assay) expressed as a percentage of the basal level (calculated as mean food intake over the 3 days prior to the experiment, g kg−1 per 10 min assay). (B) Cumulative food intake, obtained by cumulative summing of the mean values shown in (A). Values shown are for three replicate experiments with six fish per group (n = 3). Asterisk indicates a significant difference with respect to the corresponding control group (p < 0.05).
Fig. 2. Effects of icv administration of 1 μl of saline alone (control) or containing 8 μg of porcine NPY on food intake in rainbow trout. (A) Food intake is shown as mean ± S.E.M. of food intake (g per kg body weight per 10 min assay) expressed as a percentage of the basal level (calculated as mean food intake over the 3 days prior to the experiment, g kg−1 per 10 min assay). (B) Cumulative food intake, obtained by cumulative summing of the mean values shown in (A). Values shown are for three replicate experiments with six fish per group (n = 3). Asterisk indicates a significant difference with respect to the corresponding control group (p < 0.05).
Fig. 3. Effects of icv administration of (1) 1 μl of saline alone (control) or containing (2) 10 μg of the NPY antagonist d-NPY(27–36), (3) 4 μg of NPY, or (4) 10 μg of the NPY antagonist d-NPY(27–36) plus 4 μg of NPY on food intake in rainbow trout. Food intake is shown as mean ± SEM of food intake (g per kg body weight per 10 min assay) expressed as a percentage of the basal level (calculated as mean food intake over the 3 days prior to the experiment, g kg−1 per 10 min assay). Values shown are for three replicate experiments with six fish per group (n = 3). Bars with different letters do not differ significantly at the 5% level (NPY ant: NPY antagonist).
Fig. 4. Effects of icv administration of (1) 1 μl of saline alone (control) or containing (2) 4 μg of the Y1 receptor agonist (Leu31-Pro34)-NPY on food intake in rainbow trout. (A) Food intake is shown as mean ± S.E.M. of food intake (g per kg body weight per 10 min assay) expressed as a percentage of the basal level (calculated as mean food intake over the 3 days prior to the experiment, g kg−1 per 10 min assay). (B) Cumulative food intake, obtained by cumulative summing of the mean values shown in (A). Values shown are for three replicate experiments with six fish per group (n = 3). Asterisk indicates a significant difference with respect to the corresponding control group (p < 0.05).
Fig. 5. Effects of icv administration of (1) 1 μl of saline alone (control) or containing (2) 4 μg of the Y5 receptor agonist (cPP1–7, NPY19–23, Ala31, Aib32, Gln34)-hPP on food intake in rainbow trout. (A) Food intake is shown as mean ± S.E.M. of food intake (g per kg body weight per 10 min assay) expressed as a percentage of the basal level (calculated as mean food intake over the 3 days prior to the experiment, g kg−1 per 10 min assay). (B) Cumulative food intake, obtained by cumulative summing of the mean values shown in (A). Values shown are for three replicate experiments with six fish per group (n = 3). Asterisk indicates a significant difference with respect to the corresponding control group (p < 0.05).
Fig. 6. Effects of icv administration of (1) 1 μl of saline alone (control) or containing (2) 4 μg of the Y2 receptor agonist NPY(3–36) on food intake in rainbow trout. (A) Food intake is shown as mean ± S.E.M. of food intake (g per kg body weight per 10 min assay) expressed as a percentage of the basal level (calculated as mean food intake over the 3 days prior to the experiment, g kg−1 per 10 min assay). (B) Cumulative food intake, obtained by cumulative summing of the mean values shown in (A). Values shown are for three replicate experiments with six fish per group (n = 3). Asterisk indicates a significant difference with respect to the corresponding control group (p < 0.05).
Table 1.
Short-term effects of icv administration of porcine NPY on the levels of the biogenic amines 5-HT, 5-HIAA, DA, DOPAC and NA (pg mg−1) and 5-HIAA/5-HT and DOPAC/DA ratios in telencephalon, preoptic area and hypothalamus of rainbow trout
Fish received 1 μl of saline only or 1 μl of saline containing 8 μg of porcine NPY, and were killed for determination of amine levels 2 h later. Results shown are means ± S.E.M. for n = 8 fish.
Table 2.
Medium-term effects of icv administration of porcine NPY on the levels of the biogenic amines 5-HT, 5-HIAA, DA, DOPAC and NA (pg mg−1) and 5-HIAA/5-HT and DOPAC/DA ratios in telencephalon, preoptic area and hypothalamus of rainbow trout
Fish received 1 μl of saline only or 1 μl of saline containing 8 μg of porcine NPY, and were killed for determination of amine levels 50 h later. Results shown are mean ± S.E.M. for n = 8 fish.
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