Distribution of vasotocin- and vasoactive intestinal peptide-like immunoreactivity in the brain of penduline tit

Penduline tits are songbirds, used as model animals in numerous studies of sexual conflict. Nevertheless, the distribution of neuropeptides in the brain of this avian species remains largely unknown. Here we present some of the first results on distribution of vasotocin (AVT) and vasoactive intestinal peptide (VIP) in the brain of this songbird species, using immunohistochemical mapping. The bulk of AVT-like cells are found in the hypothalamic supraoptic, paraventricular and suprachiasmatic nuclei, medial bed nucleus of the stria terminalis, and along the lateral forebrain bundle. Most AVT-like fibres course toward the median eminence, but also in the medial bed nucleus of the stria terminalis, preoptic area and lateral septum. Further terminal fields occur in the dorsal thalamus, ventral tegmental area and pretectal area. Most VIP-like cells are in the lateral septal organ and arcuate nucleus. VIP-like fibres are distributed extensively in the hypothalamus, preoptic area, lateral septum, nucleus of the diagonal band. They are also found in the medial bed nucleus of the stria terminalis, amygdaloid nucleus of taenia, robust nucleus of the arcopallium, caudo-ventral hyperpallium, nucleus accumbens and the brainstem. The results indicate a high degree of conservatism in both AVT and VIP neuropeptidergic systems across avian species, as well as the different vertebrate taxa. The anatomical distribution of AVT and VIP in the penduline tit supports an involvement of these peptides in reproductive behaviours and social decision making, widely studied in this wild bird species.