Song Control Regions Research Articles

The effects of systemic androgen treatment on androgen accumulation in song control regions of the adult female canary brain

Systemic treatment of adult female canaries (Serinus canarius) with testosterone (T) induces song and increases the size of song control regions (SCRs) in the brain. We used autoradiographic techniques to determine whether systemic T treatment also changes the accumulation of tritiated T or its metabolites by SCR cells. T treatment did not change the proportion of T target cells in SCRs, nor did it change the degree of cellular accumulation of T or its metabolites. Neuronal density was not altered by T treatment in any SCR sampled. In HVc (caudal nucleus of the ventral hyperstriatum) and RA (robust nucleus of the archistriatum), cell size did not differ between T-treated and control females. However, systemic T did increase the mean sizes of labelled cells and of all cells sampled in MAN (magnocellular nucleus of the anterior neostriatum). The results support the hypothesis that the induction of song in female canaries by T relates to increases in the absolute numbers of neurons and of T target neurons in SCRs.

Cell death during development of a forebrain nucleus involved with vocal learning in zebra finches

Lateral MAN (magnocellular nucleus of the anterior neostriatum) is a forebrain nucleus that is known to be importantly involved with vocal learning in juvenile male zebra finches only during a restricted period of the learning process: lesions of lMAN completely disrupt song behavior in zebra finches prior to 50 days of age but have little or no effect in older juvenile or adult birds. The development of lMAN, as of other song-control regions, is delayed until the time that song behavior is being learned. Lateral MAN undergoes a substantial loss of neurons between 25 and 55 days of age, a time that encompasses initial stages of vocal production as well as the interval during which lMAN lesions become ineffective. In this study, we measured both the time course of neuronal loss and the incidence of pyknotic cells within lMAN during the period of cell loss. There is a pronounced loss of neurons from lMAN between 20 and 35 days, after which the adult number of neurons is established. The incidence of pyknosis is greatest at 20 days, around the time when the loss of live cells is also most pronounced, suggesting that the loss of neurons from lMAN is attributable to cell death. The loss of neurons occurs well before lesions of lMAN become ineffective in disrupting vocal behavior. Thus the neurons remaining in lMAN after the period of cell loss apparently undergo a substantial change in function at the time lesions lose effectiveness (about 55-60 days).

Paradoxical hypermasculinization of the zebra finch song system by an antiestrogen

Exogenous estrogens, when administered to hatchling female zebra finches, masculinize the morphology and function of their neural vocal control system. The first of two experiments evaluated whether tamoxifen citrate is an antiestrogen in zebra finches, and the second determined whether it would block the masculinization hypothesized to be caused in hatchling males by the males' endogenous estradiol. In the first experiment adult female zebra finches were ovariectomized and injected for 10 days with estradiol benzoate (EB), tamoxifen, EB and tamoxifen combined, or vehicle (control). The dependent variable was oviduct weight. The EB-stimulated growth of the oviduct was blocked by tamoxifen, which had no effects when administered alone. Thus, tamoxifen acts as an antiestrogen in the zebra finch oviduct. In Experiment 2, male and female zebra finches were treated with tamoxifen or vehicle for the first 20 days after hatching. The males were castrated at 20 days. At 60 days we compared the song control regions of experimental and control males and females. In both sexes tamoxifen increased the somatic areas of neurons in RA (robust nucleus of the archistriatum), HVc (caudal nucleus of the ventral hyperstriatum), and MAN (magnocellular nucleus of the anterior neostriatum). Tamoxifen also increased the volumes of HVc, RA, MAN, and Area X in males. Thus, tamoxifen failed to block masculinization of males, but masculinized females and hypermasculinized males. Tamoxifen's hypermasculinization of the male and masculinization of the female song system is paradoxical given that (1) estradiol does not have similar effects on the male song system, and (2) tamoxifen antagonizes the effects of EB in the oviduct.

Immunohistochemical localization of neuropeptides in the vocal control regions of two songbird species

Immunohistochemistry was used to map the distribution of four neuropeptides in song control regions of two songbird species, the European starling (Sturnus vulgaris) and the song sparrow (Melospiza melodia). We searched for positively stained cell bodies or apparent terminals containing vasoactive intestinal peptide (VIP), methionine-enkephalin (MET), cholecystokinin (CCK), and substance P (SUB P). Intraventricular colchicine pretreatment was administered to enhance the visualization of peptide-containing cell bodies. Four areas implicated in the central control of song were examined. Three of these areas are sexually dimorphic telencephalic nuclei characteristic of songbirds: the caudal nucleus of the ventral hyperstriatum (HVc), the robust nucleus of the archistriatum (RA), and the magnocellular nucleus of the anterior neostriatum (MAN). The fourth region is the mesencephalic nucleus intercollicullaris (ICo), common to all birds, which contains the dorsomedial nucleus (DM) that appears to be specifically involved in the motor control of song. The pattern of neuropeptide localization was similar between the two species. However, the neuropeptides were heterogeneously dispersed among the four areas. VIP and MET were the most widely distributed, whereas CCK and SUB P were seen only in DM. MAN and HVc revealed remarkably similar patterns of staining for both MET and VIP. Fine varicosities immunolabeled for both these peptides appear to encircle nonreactive somata. In both these nuclei positively stained somata were observed for MET but not for VIP. In RA there was a dense accumulation of MET-positive multipolar cell bodies. VIP-containing neurons were seen in the surrounding archistriatum and caudal neostriatum but not in RA itself. Cell bodies and fibers for all four peptides were observed in DM; in no case were they limited to this subregion, but rather seemed to encompass the surrounding intercollicular area as well. The widespread distribution of VIP and MET strongly suggests a role for these peptides in the acquisition or production of passerine song.

Estrogen accumulation in zebra finch song control nuclei: implications for sexual differentiation and adult activation of song behavior.

In zebra finches the gonadal steroid estradiol (E2) directs the sexual differentiation of neural regions controlling song and synergizes with androgens to stimulate song in adulthood. To identify regions where E2 may act to exert these effects, steroid autoradiographic techniques were used to assess cellular accumulation of 3[H]-E2 or its metabolites within various nuclei of the zebra finch brain. In Experiment 1 we examined brains from juvenile females, still within the critical period for E2's effect on sexual differentiation. In Experiment 2 the pattern and extent of labeling in adult male brains was determined following injection of 3[H]-E2, 3[H]-testosterone, or 3[H]-dihydrotestosterone. The results suggest that, both during development and in adulthood, most song-control nuclei contain few E2-accumulating cells. In contrast, many cells densely labeled by 3[H]-E2 or its metabolites are present in the hypothalamus and in close proximity to one song-control region, the hyperstriatum ventralis pars caudalis (HVc). The distribution of these latter cells overlaps with cells that project to another song-related nucleus, Area X. Thus, in Experiment 3 fluorescent retrograde tracing and steroid autoradiographic techniques were combined to determine if E2-accumulating cells project to Area X in adult males. Although a few retrogradely labeled cells were lightly labeled by 3[H]-E2 or its metabolites, for the most part these appear to be two distinct populations of cells. The sparse accumulation of E2 in the zebra finch song system contrasts with that described in other song birds and has important implications as to the mechanism of E2 action on the developing and mature song system.

Interspecific comparisons of the size of neural song control regions and song complexity in duetting birds: evolutionary implications

Previous studies have demonstrated a correlation between song repertoire size and volume of song control regions (SCRs) in the brains of songbirds. In the present study we demonstrate that 2 congeneric species of tropical duetting wrens, the rufous-and-white wren (Thryothorus rufalbus) and the bay wren (T. nigricapillus), share the same relationship between SCR volume and vocal complexity. In each species, females sing in elaborate duets with males. Males of these species have similar song repertoire sizes; there is no significant difference between heterospecific males in the volumes of SCRs. Female rufous-and-white wrens have less than half as large a song repertoire as female bay wrens, and all of their SCRs measured are significantly smaller than those of bay wren females. This interspecific equivalence of the relationship between SCR volume and repertoire size suggests that the neural system regulating vocal behavior in songbirds is evolutionarily conservative in the manner in which it encodes song complexity.

Changes in neuronal number, density and size account for increases in volume of song-control nuclei during song development in zebra finches

The caudal nucleus of the ventral hyperstriatum (HVc) and the robust nucleus of the archistriatum (RA) are two anatomically discrete brain regions that are known to be involved with song production in adult passerine birds. Both the HVc and RA increase greatly in volume during a restricted period of song development in male zebra finches, while brain regions not involved with song control show little or no increase in size. We report here that the increased volume of the HVc is attributable to an increase in the number of neurons during this period of song learning, whereas the growth of the RA is due to an increase in the somal size of neurons and a decrease in neuronal density. The pattern of results described is consistent with the idea that the HVc matures prior to the RA, and that the development of the RA may depend on the ingrowth of axons from the HVc and other song-control regions.

Neural correlates of female song in tropical duetting birds

Duetting involves production of song by female and male birds in close temporal coordination. We studied the neural network controlling song in 3 tropical duetting species. The volumes of song control regions (SCRs) in the brain, neuronal density in nucleus robustus of the archistriatum (RA) which is one of these SCRs, total number of neurons in RA, and somal size of neurons in RA were measured and compared to values published for zebra finches and canaries in which only males sing. The extent of sexual dimorphism in SCR volumes, RA neuronal density, and total neuronal number in RA varied in a graded fashion across species and was correlated with extent of sexual dimorphism in song repertoire size in any one species. Somal size of RA neurons was identical in males and females of each duetting species, regardless of relative repertoire size. Of all SCRs, the caudal nucleus of the ventral hyperstriatum appeared to have the greatest relative size in the song system of duetting birds compared to non-duetting species.