In mammals, neuropeptide Y (NPY) is a potent orexigenic factor. In the present study, third brain ventricle (intracerebroventricular) injection of goldfish NPY (gNPY) caused a dose-dependent increase in food intake in goldfish, and intracerebroventricular administration of NPY Y1-receptor antagonist BIBP-3226 decreased food intake; the actions of gNPY were blocked by simultaneous injection of BIBP-3226. Goldfish maintained on a daily scheduled feeding regimen display an increase in NPY mRNA levels in the telencephalon-preoptic area and hypothalamus shortly before feeding; however, a decrease occured in optic tectum-thalamus. In both fed and unfed fish, brain NPY mRNA levels decreased after scheduled feeding. Restriction in daily food ration intake for 1 wk or food deprivation for 72 h resulted in increased brain NPY mRNA levels. Results from these studies demonstrate that NPY is a physiological brain signal involved in feeding behavior in goldfish, mediating its effects, at least in part, through Y1-like receptors in the brain.

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The effect of acute and chronic stress on the phagocytic activity of putative macrophages from the rainbow trout. Oncorhynchus mykiss has been assessed, using an in vitro phagocytic index, in which the average number of engulfed yeast cells in a population of phagocytes is determined. An injection stress given under light anaesthesia, or a longer noise stress combined with confinement, both significantly reduced, within 3 h, the level of phagocytic activity of macrophages from the spleen and pronephros. Daily injection stress over six days had a lesser effect on the proportion of phagocytically active cells even though plasma cortisol levels were equally raised. Daily dexamethasone injection depressed the proportion of phagocytically active cells more than saline injection. In these in vivo experiments, it was not possible to determine whether stress and steroids depressed the phagocytic activity of individual macrophages or caused the active macrophages to migrate out of the spleen and pronephros. Administration of cortisol (200 nM) to trout macrophages in vitro failed to depress phagocytic activity within a 3h period but both α- and β-adrenergic agonists (10 μM) were usually depressive. It is proposed that the autonomic nervous system may be an early regulator of macrophage phagocytosis following stress and that corticosteroids only exert their suppressive effect on macrophage activity in the longer term.

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Melanin-concentrating hormone (MCH) gene expression in the brain of rainbow trout, reared and maintained in either pale or black-coloured tanks, was studied using in situ hybridization histochemistry. MCH transcripts were most prevalent in the magnocellular neurones of the nucleus lateralis tuberis (NLT), which project to the pituitary gland. They were also present, although at much lower levels, in dorsally projecting parvocellular neurones, sited more posteriorly above the lateral ventricular recess (LVR). In the NLT the most intense hybridization signal was seen over the pituitary stalk; above the LVR, the most active neurones were located caudally. In both the NLT and above the LVR, MCH hybridization signal was 4-fold stronger in white-reared fish than in black-reared fish. There was also a marked diurnal variation in MCH expression in both sites, with high levels at 16.00 h and lower levels at 04.00 h. The results show that gene activity in both hormonal (NLT) and neuromodulator/neurotransmitter (LVR) MCH neurones is induced by pale environmental colour and that MCH gene activity is subject to pronounced diurnal variation.

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