Leonard, J.B.K.*; Plisetskaya, E.M.; Silverstein, J.T.: Effect of season and age on the hypothalamic neuropeptide Y mRNA response to fasting in channel catfish
While food intake is likely controlled by a variety of interacting neuroendocrine factors, neuropeptide Y (NPY) has repeatedly been implicated in this complex behavior. NPY’s affects on food intake in fish are likely localized to the hypothalamus and preoptic area. We investigated how hypothalamic NPY mRNA responds to fasting and how it differs between strains of fish known to grow differently. Fish of two strains of channel catfish (Ictalurus punctatus; Norris and USDA 103) were kept at constant 26oC and 12:12 LL:DD photoperiod from December (~ 7 g fish mass) until June and subjected to monthly, 1-week, fasting challenges. During the study, USDA 103s grew significantly faster than Norris. The expected elevation in NPY mRNA did occur in response to fasting in catfish, although this response was not demonstrated throughout the study. During spring (Apr, fish ~100 g), there was an elevation of hypothalamic NPY mRNA in fasted fish. In winter (Dec-Feb) and during the summer (May-June), there was no suggestion of this pattern. Plasma insulin levels also followed this general pattern of the maximum response to fasting (a decrease in this case) occurring in the spring. Our results suggest that 1) hypothalamically-produced NPY is important in the neural response to fasting, but that other areas of the brain are likely involved 2) the response of channel catfish to a fast varies with season and/or size 3) there are likely differences in the endocrine control of feeding between different strains of catfish. This work was supported in part by NSF grant #IBN-9722830.
