Hormonal and environmental control of song control region growth and new neuron addition in adult male house finches, Carpodacus mexicanus

Abstract

In songbirds, testosterone (T) mediates seasonal changes in the sizes and neuroanatomical characteristics of brain regions that control singing (song control regions; SCRs). One model explaining the mechanisms of the growth of one SCR, the HVC, postulates that in the spring increasing photoperiod and circulating T concentrations enhance new neuron survival, thus increasing total neuron number. However, most research investigating the effects of T on new neuron survival has been done in autumn. The present study investigated the effects of photoperiod and T treatment on SCR growth and new neuron survival in the HVC in photosensitive adult male House Finches, Carpodacus mexicanus, under simulated spring-like conditions. Birds were castrated, given T-filled or empty Silastic capsules and maintained on short days (SD; 8L:16D) or long days (LD; 16L:8D). To mark new cells, birds received bromodeoxyuridine injections 11 days after experimental manipulations began and were sacrificed 28 days later. Testosterone treatment increased the sizes of two SCRs, the HVC and Robust nucleus of the arcopallium (RA). Exposure to LD did not affect HVC volume, but did increase RA volume. Testosterone treatment increased the total number of HVC neurons, but did not affect the number of new HVC neurons. Thus, T initiates SCR growth and increases neuron survival, but effects of T on new neuron incorporation may be limited in photosensitive birds under spring-like conditions. These results provide new insight into the effects of photoperiod and T treatment on vernal SCR growth and new neuron incorporation and support current models explaining this growth.

Reversing song behavior phenotype: Testosterone driven induction of singing and measures of song quality in adult male and female canaries (Serinus canaria)

“…Multiple studies later showed that treatment with exogenous T of photoregressed or gonadectomized subjects of both sexes largely mimics this effect therefore demonstrating the causal role of T in this aspect of neuroplasticity (Sartor et al, 2005; Smith et al, 1997; Strand and Deviche, 2007). However, no study has to our knowledge directly tested whether identical treatments with exogenous T have identical effects on the morphology of the song-control system in both male and female canaries.…”

Seasonal-like growth and regression of the avian song control system: Neural and behavioral plasticity in adult male Gambel’s white-crowned sparrows

“…In castrated male starlings, American tree sparrows, and dark-eyed juncos and Gambel's whitecrowned sparrows, LD photoperiod is sufficient to promote at least partial growth of some song control system nuclei volumes (Bernard et al, 1997;Smith et al, 1997;Bentley et al, 1999;Dloniak and Deviche, 2001). In castrated male house finches, LD photoperiod is sufficient to induce growth of RA but not HVC (Strand and Deviche, 2007). More recent data testing this hypothesis comes from Gambel's white-crowned sparrows, where LD photoperiod accelerates the systemic T-induced increase in spontaneous firing rate and soma size in the nucleus RA (Meitzen et al, 2007a).…”

Territorial Behavior and Cortical Brain Plasticity in Adult Male Sceloporus Occidentalis

“…In some species these brain regions are also responsive to changes in photoperiod absent from changes in T (Nottebohm, 2002;Strand & Deviche, 2007;Strand et al, 2009;Ball & Balthazart, 2010). Still, T directly affects these song control regions, independent from photoperiod, to modulate plasticity and induce singing behaviors (Dloniak & Deviche, 2001).…”

“…This increase in neuron lifespan leads to larger numbers of neurons in the HVC where they can induce changes to behavior such as the seasonal increases in song. After the breeding season, T levels drop and apoptosis increases within the HVC which attenuates male songbird singing behavior (Rasika et al, 1994;Kirn et al, 1994;Nottebohm, 2002;Strand & Deviche, 2007). The neuroplasticity within the song control nuclei is therefore mediated by seasonal and hormonal changes, and these changes in the brain can lead to changes in behavior.…”

“…and/or internal (hormone levels, reproductive state, etc.) environment can cause growth or regression of the song control nuclei (Gulledge & Deviche, 1998;Dloniak & Deviche, 2001;Strand & Deviche, 2007;Ball & Balthazart, 2010).…”