Research in mammals has established the existence of a neuronal network that lies within the hypothalamus and that regulates energy homeostasis. However, it is unknown whether this system has been evolutionarily conserved. The objective of the present study was therefore to examine the influence of the agouti-related peptide (AGRP), pro-opiomelanocortin (POMC), prepro-orexin, and vasoactive intestinal polypeptide (VIP) genes on energy balance in birds by quantifying the effect of a 24-h fast on their expression in the hypothalamus of the Japanese quail. In situ hybridization revealed strong signals for AGRP and POMC mRNAs in the infundibular nucleus (IN), for prepro-orexin in the lateral hypothalamic area (LHy) and periventricular hypothalamic nucleus, and for VIP in the LHy. POMC mRNA was co-localized with alpha-melanocyte-stimulating hormone-like immunoreactivity in individual IN neurons. Compared with the ad-libitum-fed state, a 24-h fast resulted in a 2.2-fold increased expression of AGRP mRNA in the IN. However, fasting did not induce changes in POMC, prepro-orexin, or VIP mRNAs. The results suggest an involvement of the central melanocortin system in the regulation of energy balance in birds, as in mammals. In contrast, orexins in birds may be primarily involved in the control of physiological functions other than energy homeostasis.

Neuropeptide Y (NPY) has been implicated in the control of a number of physiological functions in birds including food intake and reproduction. In the present study, sites of NPY synthesis were localized in the brains of Japanese quail and domestic chickens by in situ hybridization histochemistry using a digoxigenin-labelled riboprobe. NPY mRNA was detected in three main cell groups in both species. The most prominent group was associated with structures in the lateral thalamus including the anterior lateral thalamic nucleus, lateral forebrain bundle, rotund nucleus, pretectal nucleus and occipitomesencephalic tract. Other major cell groups were detected in the hippocampus, and in the caudal linear nucleus and raphe nucleus of the brainstem. NPY mRNA was also present in the piriform cortex and taenial nucleus. Double-labelling of NPY mRNA and peptide was demonstrated in individual cells of the hippocampal, thalamic and brainstem cell groups, suggesting that NPY is synthesized and stored in these areas. However, the identity of other cell groups, notably in the hyperstriatal, archistriatal and neostriatal regions of the telencephalon, which exhibit NPY-immunoreactive cell bodies but no NPY mRNA, remains to be determined.

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In domestic juvenile chickens kept on short days, photoinduced luteinsing hormone (LH) release, and by inference gonadotrophin-releasing hormone (GnRH) release, are readily detectable within 4 days of photostimulation.2 The molecular mechanisms responsible for the rapid photoinduced release of LH and GnRH in avian species are unknown. It has been suggested that it might involve a cascade of gene expression associated with an increase in cfos in the basal hypothalamus and glial cells in the median eminence.1 A microarray was made consisting of known genes of interest and clones obtained from a hypothalamic short day/long day subtractive library. An experiment was undertaken to determine if this reproductive neuroendocrine microarray could detect new targets for study in the chicken model of photostimulated GnRH release. The microarray was interrogated with hypothalamic RNA from juvenile chickens showing an increase in plasma LH after 4 days of photostimulation. Six genes were identified as showing changes in expression after photostimulation on the microarray. However, only one gene, encoding heat shock protein 108 (HSP108), could be confirmed by quantitative competitive RT-PCR. The expression of this gene decreased both in the hypothalamus and the optic tectum. Treatment of short day juvenile chickens with thyroxine, to mimic the effects of photostimulation, resulted in LH release and depression of HSP108 expression in the anterior but not the basal hypothalamus. Immunocytochemical analyses showed that HSP108 is widely distributed in the brain including glial-like cells with terminals in the median eminence. HSP108 is suggested as a candidate protein involved in the regulation of gonadotrophin release from the median eminence by glial cells. (1)Meddle SL and Follett BK (1995) Photoperiodic activation of fos-like immunoreactive protein in neurones within the tuberal hypothalamus of Japanese quail. Journal of Comparative Physiology [A] 176(1), 79–89.(2)Sreekumar KP and Sharp PJ (1998) Ontogeny of the photoperiodic control of prolactin and luteinizing hormone secretion in male and female bantams (Gallus domesticus). General and Comparative Endocrinology 109(1), 69–74.