Regolazione della risposta alimentare in Carassius auratus: possibile interazione fra sistema endocannabinergico e fattore orexigenico NPY

The nervous system of non-mammalian vertebrates, such as fish, offers the opportunity to analyze comparative and functional aspects of neurotransmission/neuromodulation systems, in order to better understand the role of specific signalling molecules and exploit their potential, even in a therapeutic perspective. Thus, the teleost Carassius auratus could be a suitable and powerful model for studying food intake behaviour. Feeding control is a complex process mainly regulated by the hypothalamus and other CNS areas, by means of a number of neuromodulators, with both orexigenic or anorexigenic activities. Among them, Neuropeptide Y (NPY), one of the most powerful orexigenic factors in mammals, has been found in all the vertebrates, as well as in invertebrates, and does participate in food intake control also in goldfish. In order to confirm and extend previous data obtained in Carassius auratus, in the present work I analyzed the effect of fasting on NPY mRNA expression in the forebrain, which includes centers primarily involved in food intake regulation, such as the hypothalamus and the preoptic area. By means of quantitative Real-Time PCR, NPY mRNA levels were found to increase in response to food deprivation, in a time-dependent manner. Recently, an important role of the endocannabinoid system in food intake control has been suggested also in goldfish, in agreement with well-documented observations in mammals. Since an interplay of the endocannabinoid system and NPY has been reported in rat, the possibility that the endocannabinoid anandamide (AEA) could modify NPY expression was investigated in goldfish forebrain. AEA, intraperitoneally injected at two different doses (1pg/g bw and 10 pg/g bw) into satiated goldfish, shows a trend toward the reduction of NPY mRNA levels, in comparison to vehicle injected animals (controls). In order to investigate possible morphofunctional relationships between the endocannabinoid system and NPY, immunohistochemical techniques were used to evaluate the co-distribution/co-localization of CB1 cannabinoid receptors and NPY in the basal telencephalon/preoptic area and in the hypothalamus. NPY- immunopositive neurons were observed in the basal telencephalon together with a dense NPY innervation extended from the rostral telencephalon throughout the hypothalamus. In these same brain areas CB1-immunoreactive neurons and fibres were seen, suggesting a co- distribution of the two markers. Moreover, after the double immunofluorescence for both NPY and CB1 on the same section, the two immunolabelings were observed to co-localize in a few neurons along the basal telencephalon. In conclusion, my results, besides to confirm the orexigenic role of NPY in Carassius auratus, strongly suggest that NPY neurons might be modulated by the endocannabinoids through CB1 receptors.