Abstract
The expression of the recently identified neuropeptide, amylin, is restricted in rodents to the postpartum preoptic area and may play a role in the control of parental behaviours and food intake. These processes are substantially different between bird and rodent parents as birds do not lactate but often show biparental care of the offspring. To establish the presence and role of amylin in the bird brain, in the present study, we investigated the distribution of amylin in brains of adult male and female zebra finches in three different reproductive stages (i.e. paired without young, incubating eggs or provisioning nestlings) and in unpaired control birds living in same sex flocks. Amylin mRNA was identified in the hypothalamus of zebra finch by RT-PCR, which was also used to produce probes for in situ hybridisation. Subsequently, in situ hybridisation histochemistry was performed in brain sections, and the labelling signal was quantified and compared between the groups. Amylin showed a much wider brain distribution than that of rodents. A strong and, in some regions, sexually dimorphic label was found in the striatum and several brain regions of the social behavioural network in both males and females. Many regions responsible for the learning of birdsong also contained amylin-positive neurons, and some regions showed sex differences reflecting the fact that vocalisation is sexually dimorphic in the zebra finch: only males sing. Area X (Ar.X), a striatal song centre present only in males, was labelled in paired but not unpaired male. Ar.X, another song centre, the lateral part of the magnocellular nucleus of the anterior nidopallium (lMAN) also contained amylin and had higher amylin label in paired, as opposed to unpaired birds. The wider distribution of amylin in birds as compared to rodents suggests a more general role of amylin in social or other behaviours in avian species than in mammals. Alternatively, parental care in birds may be a more complex behavioural trait involving a wider set of brain regions. The sex differences in song centres, and the changes with reproductive status suggest a participation of amylin in social behaviours and related changes in the singing of males.
Highlights
Amylin, or islet amyloid polypeptide, is a 37 amino acid peptide belonging to the calcitonin family of peptides (Hay et al, 2015)
Amylin may exert its potential modulatory actions via the amylin receptor, which has been detected in the brain of chicken and the Japanese quail (C. japonica) implying that the receptor may be present in the zebra finch based on its presence in the zebra finch genome
No detailed mapping of the amylin or its receptor is available in precocial birds, the amylin expression found in the zebra finch might be specific to altricial birds rather than a general pattern in the avian species
Summary
Islet amyloid polypeptide, is a 37 amino acid peptide belonging to the calcitonin family of peptides (Hay et al, 2015). It is released from the pancreas and plays a role as a satiating hormone (Leffert et al, 1989; Ogawa et al, 1990). A number of neurons are activated in the preoptic area in rat and mouse dams in response to pup exposure (Numan, 2007; Matsushita et al, 2015). Amylin neurons were shown to be activated by pup exposure suggesting a role of amylin in controlling maternal behaviours (Szabó et al, 2012). Amylin was induced in maternally sensitised nulliparous rats, which showed maternal behaviour without lactation, but not in mother rats at late pregnant stage implying that amylin is more likely to play a Abbreviations: A, arcopallium; Ac, nucleus accumbens; Ar.X, Area X; BST, bed nucleus of the stria terminalis; BSTm, medial part of the bed nucleus of the stria terminalis; CA, anterior commissure; Cb, cerebellum; CDL, dorsolateral corticoid area; CO, optic chiasm; CP, posterior commissure; dmSt, dorsomedial striatum; E, entopallium; EA, extended amygdala; FA, frontoamygdaloid tract; FLM, longitudinal medial tract; FRL, lateral reticular formation; GCt, central grey; GP, globus pallidus; HA, apical hyperpallium; HF, hippocampal formation; HVC, proper name; INP, intrapeduncular nucleus; IO, isthmo-optic nucleus; IP, interpeduncular nucleus; ICo, intercollicular nucleus; LHy, lateral hypothalamic area; lMAN, lateral part of the magnocellular nucleus of the anterior nidopallium; LSt, lateral striatum; LrSt, lateral rostral striatum; M, mesopallium; MAN, medial anterior nidopallium; Md.Th, mediodorsal thalamus; MLd, the dorsal part of the lateral mesencephalic nucleus; Mm, medial mesopallium; MSt, medial striatum; N, nidopallium; nBOR, nucleus of the basal optic root/nucleus ectomamamillaris; Nc, caudal nidopallium; NCL, caudalateral nidopallium; NIII, oculomotor nerve; nPrV, principal nucleus of the trigeminal nerve; OM, tractus occipito-mesencephalicus; POM, medial preoptic nucleus; R, raphe nucleus; ROI, region of interest; Rot, nucleus rotundus; RS, thalamic superior reticular nucleus; RT-PCR, real-time polymerase chain reaction; S, septum; SN, substantia nigra; St, striatum; TeO, optic tectum
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