Seasonal neuronal plasticity in song‐control and auditory forebrain areas in subtropical nonmigratory and palearctic‐indian migratory male songbirds

Abstract

This study examines whether differences in annual life-history states (LHSs) among the inhabitants of two latitudes would have an impact on the neuronal plasticity of the song-control system in songbirds. At the times of equinoxes and solstices during the year (n = 4 per year) corresponding to different LHSs, we measured the volumetric changes and expression of doublecortin (DCX; an endogenous marker of the neuronal recruitment) in the song-control nuclei and higher order auditory forebrain regions of the subtropical resident Indian weaverbirds (Ploceus philippinus) and Palearctic-Indian migratory redheaded buntings (Emberiza bruniceps). Area X in basal ganglia, lateral magnocellular nucleus of the anterior nidopallium (LMAN), HVC (proper name), and robust nucleus of the arcopallium (RA) were enlarged during the breeding LHS. Both round and fusiform DCX-immunoreactive (DCX-ir) cells were found in area X and HVC but not in LMAN or RA, with a significant seasonal difference. Also, as shown by increase in volume and by dense, round DCX-ir cells, the neuronal incorporation was increased in HVC alone during the breeding LHS. This suggests differences in the response of song-control nuclei to photoperiod-induced changes in LHSs. Furthermore, DCX immunoreactivity indicated participation of the cortical caudomedial nidopallium and caudomedial mesopallium in the song-control system, albeit with differences between the weaverbirds and the buntings. Overall, these results show seasonal neuronal plasticity in the song-control system closely associated with annual reproductive LHS in both of the songbirds. Differences between species probably account for the differences in the photoperiod-response system between the relative refractory weaverbirds and absolute refractory redheaded buntings. J. Comp. Neurol. 524:2914-2929, 2016. © 2016 Wiley Periodicals, Inc.

Iterative Metaplasticity Across Timescales: How Circadian, Ultradian, and Infradian Rhythms Modulate Memory Mechanisms

“…Circannual variations in songbird song learning have received a great deal of attention. For instance, brain nuclei important for song learning grow in volume during breeding season in a variety of species (Tramontin and Brenowitz, 2000; Van Meir et al, 2006; Surbhi et al, 2016), owing in part to neurogenesis (Nottebohm, 1989). In addition, the maintenance of new neural cells is enhanced at the beginning of the breeding season (Larson et al, 2019).…”

“…Non-circadian forms of iterative metaplasticity that are also endogenously generated may be viewed to niche memory function on non-daily timescales. That songbirds are best at song learning during mating season is a fitting illustration (Van Meir et al, 2006; Surbhi et al, 2016; Cornez, Collignon, et al, 2020). Whereas endogenously generated forms of iterative metaplasticity support predictive homeostasis, environmentally generated forms of iterative metaplasticity may instead support reactionary homeostasis, the better known type of homeostasis (Moore-Ede, 1986).…”