Seasonal Changes in Brain GnRH Immunoreactivity and Song-Control Nuclei Volumes in an Opportunistically Breeding Songbird

Abstract

White-winged crossbills (Loxia leucoptera) are opportunistic breeders that can nest at almost any time of year if there is sufficient food. Other cardueline finches that have been shown to breed on a strictly seasonal schedule become absolutely refractory to the stimulatory effects of long-day photoperiod, dramatically down-regulate hypothalamic gonadotropin-releasing hormone (GnRH), and reduce the volume of several song-control nuclei in autumn. This study examined whether changes in photoperiod modify the GnRH and song-control systems in white-winged crossbills. Adult male and female crossbills were captured and held on a naturally changing photoperiod. Brains of male and female birds were collected in May, October, and January. GnRH content was assessed by immunocytochemistry and the volumes of Nissl-defined song-control nuclei (HVc, Area X, and the robust nucleus of the archistriatum) were reconstructed. In contrast to other cardueline finches, GnRH immunoreactivity was relatively stable across the year, exhibiting only modest seasonal variation. The song control system, on the other hand, exhibited large seasonal changes as well as sex differences. Thus, crossbills appear to maintain hypothalamic GnRH content year round, perhaps to facilitate a rapid response to favorable breeding conditions, even on short days. However, song control nuclei are dramatically affected by photoperiod. Future work should examine these systems in crossbills breeding on short days to compare photoperiod-dependent and -independent effects on neural plasticity.

Recent advances in behavioral neuroendocrinology: Insights from studies on birds

“…For example, seasonal plasticity of the GnRH system is greater in taxa that become absolutely photorefractory, such as European starlings and house finches (Carpodacus mexicanus), than in those that do not, such as quail and crossbills (Loxia sp.) (Foster et al, 1987(Foster et al, , 1988Cho et al, 1998;MacDougall-Shackleton et al, 2001;Pereyra et al, in press). These differences are correlated with the degree of reproductive flexibility displayed MacDougall-Shackleton et al, 2005).…”

Photoperiodic induced changes in reproductive state of border canaries (Serinus canaria) are associated with marked variation in hypothalamic gonadotropin-releasing hormone immunoreactivity and the volume of song control regions

“…Within the cardueline subfamily, that includes canaries, species variation in the degree of breeding flexibility is associated with species variation in the neuroendocrine plasticity in the hypothalamo-pituitary-gonadal axis (MacDougall-Shackleton et al, 2001, Hahn et al, 2004, Pereyra et al, 2005. Species in which photostimulation solely can instate vernal breeding activity tend to exhibit marked declines in preoptic-hypothalamus area during the non-breeding season of the key releasing peptide that controls gonadotropin function, gonadtrophin-releasing hormone-I (GnRH; e.g.…”

Reduction of Brain Volume Correlates with Behavioral Changes in Queen Ants

“…Such neuronal modifications have been documented in different animal systems and are perhaps best understood in birds. Breeding and seasonal singing activities in songbirds are controlled by hormones [DeVoogd and Nottebohm, 1981] and may be triggered by day length and other factors [reviewed by Bottjer and Johnson, 1997;MacDougall-Shackleton et al, 2001]. Seasonal singing activity correlates with robust changes in the volume of brain centers that underlie singing behavior [Nottebohm, 1981;Bottjer et al, 1986;Bernard et al, 1996; Alvarez-Buylla and Kirn, 1997;MacDougall-Shackleton et al, 2001].…”