Joint hormonal and sensory stimulation modulate neuronal number in adult canary brains

Treatment of adult female canaries with testosterone (T) causes them to produce male-typical vocalizations and results in striking growth of brain nuclei that control song behavior (Nottebohm, 1980). The song-control nucleus HVc (caudal nucleus of the ventral hyperstriatum) contains cells that concentrate testosterone or its metabolites, suggesting that steroid hormones may induce the growth of HVc directly by regulating the expression of specific genes in those HVc neurons that have steroid receptors. However, we have previously provided evidence that is inconsistent with the idea that steroids promote growth of HVc solely via a direct action on hormone receptors: testosterone treatment of deafened adult females results in very little growth of HVc, relative to T-treated hearing birds (Bottjer et al., 1986b). Thus, birds in the former group undergo very little overall growth of HVc despite high circulating levels of hormone. We show here that the slightly increased size of HVc in T-treated deaf birds is attributable to an increase in neuronal spacing; the greatly increased size of HVc in T-treated hearing birds is due to an increase in neuronal number as well as spacing. There was virtually no increase in number of HVc neurons in T-treated deafened birds relative to control groups, whereas T-treated hearing birds showed a marked increase in neuron number. The song-control nucleus RA (robust nucleus of the archistriatum), which receives direct afferent input from HVc, also increases in size in response to testosterone treatment. However, the volume of RA increases in both hearing and deafened birds; this increase is primarily due to an increase in neuronal spacing as well as a small increase in neuron number. These results demonstrate that the number of neurons in a specific vocal-control nucleus (HVc) can change dramatically in adult canaries and suggest that some synergistic action of hormonal and sensory stimulation is necessary to induce such a change.     

Differential estrogen accumulation among populations of projection neurons in the higher vocal center of male canaries

The higher vocal center (HVC) of adult male canries undergoes a seasonal change in volume that corresponds to seasonal modifications of vocal behavior: HVC is large when birds produce stereotyped song (spring) and is small when birds produce plastic song and add new song syllables into their vocal repertoires (fall). We reported previously that systemic exposure to testosterone (T) produces an increase in the volume of HVC similar to that observed with long-day photoperiods. T-induced growth of HVC occured regardless of wheter the borders of HVC were defined by Nissl-staining, the distribution of androgen-concentrating cells, or the distribution of projection neurons [separate neuronal populations within HVC project to the robust nucleus of the archistriatum (RA) and to Area X of the avian striatum (X)]. In the present study we used steroid autoradiography to determine whether T can influence the distribution of HVC cells that bind estrogen, and we combined estrogen autoradiography with retrograde labeling to determine whether HVC neurons that project to RA versus X differ in their ability to accumulate estrogen. Results showed that T increased the volume of Nissl-defined HVC and although HVC contained a low density of estrogen-concentrating cells, T increased the spatial distribution of these cells to match the Nissl borders of HVC. We also identified a region containing a high density of estrogenconcentrating cells located medial to HVC [we call this region paraHVC (pHVC)], and T also increased the volume of pHVC. pHVC also contained numerous X-projecting neurons, but few if any RA-projecting neurons. Double-labeling analysis revealed the RA-projecting neurons did not accumulate estrogen, a small percentage of X-projecting neurons in HVC accumulated estrogen, and the majority of X-projecting neurons in pHVC showed heavy accumulation of estrogen. The data reported here and in our previous article suggest distinct roles for gonadal steroids within the HVC-pHVC complex: estrogens are concentrated by neurons that project to a striatal region that influences vocal production during song learning (X), whereas androgens are concentrated primarily by neurons that project to a motor region that is involved in vocal production during both song learning and the recitation of already-learned song (RA). © 1995 John Wiley & Sons, Inc.     

Testosterone and the incidence of hormone target cells in song-control nuclei of adult canaries.

Adult male canaries learn to produce high-amplitude complex courtship songs each breeding season, whereas females do not, and brain nuclei involved with the production of song behavior are much larger in breeding males than in nonbreeding males or females (Nottebohm, 1980, 1981). However, treatment of adult females with testosterone (T) causes them to produce male-like song and stimulates pronounced growth of some song-control brain nuclei such as the caudal nucleus of the ventral hyperstriatum (HVc). We reexamined the effects of T on song-control nuclei in deafened birds. In order to examine whether the pattern of hormone accumulation varies as a function of circulating testosterone levels we described the distribution of testosterone-concentrating cells in HVc and the magnocellular nucleus of the anterior neostriatum (MAN) in hearing adult male, female, and T-treated female canaries, as well as in deaf T-treated and untreated females. In contrast to our previous findings (Bottjer, Schoonmaker, and Arnold, 1986a), we observed no tendency in this study for testosterone-induced growth of HVc to be attenuated in deafened birds. There was no difference between deaf and hearing birds in the incidence of labeled cells within HVc. We also observed no sex or hormone-induced differences in the percentage of hormone-concentrating cells in HVc: normal females have approximately the same proportion of hormone target cells as do males and T-treated females. However, males normally have many more neurons in HVc than do control females, and systemic exposure to testosterone induces a pronounced increase in the number of HVc neurons of adult females. Therefore, the absolute number of hormone target cells in HVc is likely to be much greater in males and T-treated females than in normal females. As in HVc, there were no differences among groups in the proportion of labeled cells within lateral MAN (IMAN), a nucleus that has been implicated in song learning (Bottjer, Miesner and Arnold, 1984). In contrast, the incidence of hormone target cells in medial MAN (mMAN) did vary as a function of hormonal condition: although mMAN of normal females is rarely visible in Nissl-stained sections and cells in this region are not hormone labeled, mMAN is clearly visible in Nissl-stained sections of males and T-treated females and contains many hormone-labeled cells. This testosterone-induced change in the phenotype of mMAN cells suggests a possible role for mMAN in learned song behavior.     

Testosterone and the incidence of hormone target cells in song-control nuclei of adult canaries

Adult male canaries learn to produce high-amplitude complex courtship songs each breeding season, whereas females do not, and brain nuclei involved with the production of song behavior are much larger in breeding males than in nonbreeding males or females (Nottebohm, 1980, 1981). However, treatment of adult females with testosterone (T) causes them to produce male-like song and stimulates pronounced growth of some song-control brain nuclei such as the caudal nucleus of the ventral hyperstriatum (HVc). We reexamined the effects of T on song-control nuclei in deafened birds. In order to examine whether the pattern of hormone accumulation varies as a function of circulating testosterone levels we described the distribution of testosterone-concentrating cells in HVc and the magnocellular nucleus of the anterior neostriatum (MAN) in hearing adult male, female, and T-treated female canaries, as well as in deaf T-treated and untreated females. In contrast to our previous findings (Bottjer, Schoonmaker, and Arnold, 1986a), we observed no tendency in this study for testosterone-induced growth of HVc to be attenuated in deafened birds. There was no difference between deaf and hearing birds in the incidence of labeled cells within HVc. We also observed no sex or hormone-induced differences in the percentage of hormone-concentrating cells in HVc: normal females have approximately the same proportion of hormone target cells as do males and T-treated females. However, males normally have many more neurons in HVc than do control females, and systemic exposure to testosterone induces a pronounced increase in the number of HVc neurons of adult females. Therefore, the absolute number of hormone target cells in HVc is likely to be much greater in males and T-treated females than in normal females. As in HVc, there were no differences among groups in the proportion of labeled cells within lateral MAN (IMAN), a nucleus that has been implicated in song learning (Bottjer, Miesner and Arnold, 1984). In contrast, the incidence of hormone target cells in medial MAN (mMAN) did vary as a function of hormonal condition: although mMAN of normal females is rarely visible in Nissl-stained sections and cells in this region are not hormone labeled, mMAN is clearly visible in Nisslstained sections of males and T-treated females and contains many hormone-labeled cells. This testosterone-induced change in the phenotype of mMAN cells suggests a possible role for mMAN in learned song behavior.     

Coordinated and dissociated effects of testosterone on singing behavior and song control nuclei in canaries (Serinus canaria)

Temperate zone songbirds that breed seasonally exhibit pronounced differences in reproductive behaviors including song inside and outside the breeding season. Springlike long daylengths are associated with increases in plasma testosterone (T) concentrations, as well as with increases in singing and in the volume of several brain nuclei known to control this behavior. The mechanisms whereby T can induce changes in behavior and brain, and whether or not these effects are differentially regulated, have recently begun to be examined, as has the question of the relative contributions of T and its androgenic and estrogenic metabolites to the regulation of this seasonal behavioral and neural plasticity. In this experiment, we examined the effects of T, 5alpha-dihydrotestosterone, or 17beta-estradiol treatment on castrated male canaries housed on short days and compared neural and behavioral effects in these males to similarly-housed males given only blank implants. We observed that only T treatment was effective in eliciting significant increases in singing behavior after 11 days of hormone exposure. In addition, T alone was effective in increasing the volume of a key song production nucleus, HVC. However, at this time, none of the steroids had any effects on the volumes of two other song control nuclei, Area X of the medial striatum and the robust nucleus of the arcopallium (RA), that are efferent targets of HVC, known to be regulated by androgen in canaries and also to play a role in the control of adult song. T can thus enhance singing well before concomitant androgen-induced changes in the song control system are complete.     

Social context affects testosterone-induced singing and the volume of song control nuclei in male canaries (Serinus canaria)

The contribution of social factors to seasonal plasticity in singing behavior and forebrain nuclei controlling song, and their interplay with gonadal steroid hormones are still poorly understood. In many songbird species, testosterone (T) enhances singing behavior but elevated plasma T concentrations are not absolutely required for singing to occur. Singing is generally produced either to defend a territory or to attract a mate and it is therefore not surprising that singing rate can be influenced by the sex and behavior of the social partner. We investigated, based on two independent experiments, the effect of the presence of a male or female partner on the rate of song produced by male canaries. In the first experiment, song rate was measured in dyads composed of one male and one female (M-F) or two males (M-M). Birds were implanted with T-filled Silastic capsules or with empty capsules as control. The number of complete song bouts produced by all males was recorded during 240 min on week 1, 2, 4, and 8 after implantation. On the day following each recording session, brains from approximately one-fourth of the birds were collected and the volumes of the song control nuclei HVC and RA were measured. T increased the singing rate and volume of HVC and RA but these effects were affected by the social context. Singing rates were higher in the M-M than in the M-F dyads. Also, in the M-M dyads a dominance-subordination relationship soon became established and dominant males sang at higher rates than subordinates in T-treated but not in control pairs. The differences in song production were not reflected in the size of the song control nuclei: HVC was larger in M-F than in M-M males and within the M-M dyads, no difference in HVC or RA size could be detected between dominant and subordinate males. At the individual level, the song rate with was positively correlated with RA and to a lower degree HVC volume, but this relationship was observed only in M-M dyads, specifically in dominant males. A second experiment, carried out with castrated males that were all treated with T and exposed either to another T-treated castrate or to an estradiol-implanted female, confirmed that song rate was higher in the M-M than in the M-F condition and that HVC volume was larger in heterosexual than in same-sex dyads. The effects of T on singing rate and on the volume of the song control nuclei are thus modulated by the social environment, including the presence/absence of a potential mate and dominance status among males.     

Birth,migration, incorporation,and death of vocal control neurons in adult songbirds

Neurogenesis continues in the brain of adult birds. These cells are born in the ventricular zone of the lateral ventricles. Young neurons then migrate long distances guided, in part, by radial cell processes and become incorporated throughout most of the telencephalon. In songbirds, the high vocal center (HVC), which is important for the production of learned song, receives many of its neurons after hatching. HVC neurons which project to the robust nucleus of the archistriatum to form part of the efferent pathway for song production, and HVC interneurons continue to be added throughout life. In contrast, Area X-projecting HVC cells, thought to be part of a circuit necessary for song learning but not essential for adult song production, are only born in the embryo. New neurons in HVC of juvenile and adult birds replace older cells that die. There is a correlation between seasonal cell turnover rates (addition and loss) and testosterone levels in adult male canaries. Available evidence suggests that steroid hormones control the recruitment and/or survival of new HVC neurons, but not their production. The functions of neuronal replacement in adult birds remain unclear. However, rates of HVC neuron turnover are highest at times of year when canaries modify their songs. Replaceable HVC neurons may participate in the modification of perceptual memories or motor programs for song production. In contrast, permanent HVC neurons could hold long-lasting song-related information. The unexpected large-scale production of neurons in the adult brain holds important clues about brain function and, in particular, about the neural control of a learned behavior—birdsong. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 585–601, 1997     

白腰文鸟发声行为的性别差异及其机制

通过声谱分析,研究了５－１２０日龄雌、雄白腰文鸟（Lonchura striata swinhoei)的声谱变化,及该时段３个主要发声控制核团）ＨＶＣ、ＲＡ、Ａrea X)体积、睾丸（睾酮）的相应改变。结果如下：①４５日龄以前,雌雄鸟只能发出简单鸣叫（call),鸣声基本不会鸣唱。②雄性ＨＶＣ,ＲＡ,ＡreaX体积均比雌性大２－６部。３个核团的大小发育不完全一致。各核团的快速生长期与鸣唱学习的主要时段（６０－１２０日龄）不同步,说明核团的个体发育可能不完全受发声行为的影响。③睾丸的充分发育（１２０日龄后）及血液中具有较高的睾酮水平是雄鸟发出成熟鸣唱语句的重要条件。     

Effects of early song experience on song preferences and song control and auditory brain regions in female house finches (Carpodacus mexicanus)

We examined the effects of song tutoring on adult song preferences, volume of song-control brain regions, and activity of auditory brain regions in female house finches (Carpodacus mexicanus). Hand-reared females were tutored with local songs, foreign songs, or no song. We then examined adult song preferences, determined the Nissl-defined volume of the song-control nuclei HVc, Area X, and RA, and compared the number of cells immunoreactive for Zenk protein in the auditory regions NCM and cmHV, following playback of songs heard early in life (Tutor/Playback Match) versus not heard (Tutor/Playback Nonmatch). All hand-reared birds exhibited preferences for locally recorded song over foreign or heterospecific song. We found no difference in the volume of song-control nuclei among the three groups. As well, we found no difference in the number of Zenk immunoreactive cells in NCM and cmHV between females in the Tutor/Playback Match group and females in the Tutor/Playback Nonmatch group. Isolate-reared birds showed greater Zenk immunoreactivity following song playback than either tutored group. Thus, early auditory experience may not play a role in adult geographic song preferences, suggesting that genetic factors can lead to preferences for songs of local dialects. Song tutoring did not influence the size of song-control regions nor Zenk induction levels following song playback, suggesting that early experience with particular songs does not influence Zenk expression. However, overall greater activation in isolate females in auditory areas suggests that exposure to song early in life may increase the selectivity of Zenk activation to song playback in auditory areas.     

白腰文鸟发声行为的神经发育

本文研究了 5～ 15 0日龄雄性白腰文鸟 (Lonchurastriataswinhoei)不同年龄段的声谱变化以及这种变化的神经调制机制。结果如下 :(1)HVC、RA和AreaX三个发声核团的神经联系基本接近成年鸟的水平后 ,幼鸟才开始学习鸣叫 (约 45日龄 ) ;(2 )HVC、RA和AreaX达到成年核团体积时 (约 80日龄 ) ,幼鸟才具有成年雄鸟的鸣叫模式 ;(3)发声控制核团的发育与核团间的神经支配有关 ,而基本不受鸣唱行为的影响 ,HVC、RA和AreaX的最快增长时间段各不相同 ,三个核团随年龄增长而呈现体积增长的显著变化 (one wayANOVA ,P <0 0 5 ) ,但各核团在任意两个时间段的体积差异并不都显著。结果提示 :发声行为产生的时间和发展与发声控制核团的发育、核团间的神经联系有关 ,最终的体积发育程度受内在遗传力的作用 ,同时可能还受神经核团建立正常神经联系时间的影响     

Castration and antisteroid treatment impair vocal learning in male zebra finches.

Both song behavior and its neural substrate are hormone sensitive: castrated adult male zebra finches need replacement of gonadal steroids in order to restore normal levels of song production, and sex steroids are necessary to establish male-typical neural song-control circuits during early development. This pattern of results suggests that hormones may be required for normal development of learned song behavior, but evidence that steroids are necessary for normal neural and behavioral development during song learning has been lacking. We addressed this question by attempting to eliminate the effects of gonadal steroids in juvenile male zebra finches between the time of initial song production and adulthood. Males were castrated at 20 days of age and received systemic implants of either an antiandrogen (flutamide), an antiestrogen (tamoxifen), or both drugs. The songs of both flutamide- and tamoxifen-treated birds were extremely disrupted relative to normal controls in terms of the stereotypy and acoustic quality of individual note production, as well as stereotypy of the temporal structure of the song phrase. We did not discern any differences in the pattern of behavioral disruption between birds that were treated with either flutamide, tamoxifen, or a combination of both drugs. Flutamide treatment resulted in a reduced size of two forebrain nuclei that are known to play some role unique to early phases of song learning [lateral magnocellular nucleus of the anterior neostriatum (IMAN) and area X (X)], but did not affect the size of two song-control nuclei that are necessary for normal song production in adult birds [caudal nucleus of the ventral hyperstriatum (HVc) and robust nucleus of the archistriatum (RA)]. In contrast, treatment with tamoxifen did not result in any changes in the size of song-control nuclei relative to normal controls, and it blocked the effects of flutamide on the neural song-control system in birds that were treated with both drugs. Castration and antisteroid treatment exerted no deleterious effects on the quality of song behavior in adult birds, indicating that gonadal hormones are necessary for the development of normal song behavior during a sensitive period.     

Hormone-induced changes in identified cell populations of the higher vocal center in male canaries

Male canaries revise their vocal repertoire every year. Early work indicated that the volume and neuron number of the song-control nucleus HVC (Higher Vocal Center) declined in late-summer/fall as birds added and deleted syllables from their repertoire, and increased in spring as the set of song syllables stabilized to a fixed number. Seasonal variation in serum testosterone levels suggested that these changes in brain and behavior were regulated by testosterone (T). However, although initial studies describing growth and regression of HVC used Nissl-staining to define its borders, recent experiments that have measured the distribution of identified populations of HVC cells (projection neurons, hormone target cells) suggest that there are no seasonal changes in HVC volume or neuron number. In order to clarify the role of T in the regulation of HVC morphology, we castrated male canaries, maintained them on short (fall-like) days, and treated them with either T, antisteroid drugs, or nothing. After 1 month of treatment, we used a double-labeling technique to characterize HVC projection neurons and androgen target cells. The results showed that hormonal manipulation influenced HVC volume, the density and size of HVC cells, and the absolute number and percentage of androgen target cells in HVC. Hormonal manipulation did not influence the absolute number of cells in HVC. Moreover, the distribution of projection neurons, androgen target cells, and the Nissl-defined borders of HVC were closely aligned in all experimental groups, indicating that exposure to T and/or its metabolites (estradiol and dihydrotestosterone) regulates the overall size of HVC by affecting the distributions of both projection neurons and androgen target cells. Analysis of double-labeling results suggests that T specifically influences both cell size and the ability to accumulate androgen among HVC neurons that project to the robust nucleus of the archistriatum (RA). The results of this study show that steroid hormones exert potent effects on HVC morphology in male canaries, but differences between our results and studies of seasonal males suggest there may be additional factors that can regulate HVC morphology. © 1993 John Wiley & Sons, Inc.     

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.     

Lack of a synergistic effect between estradiol and dihydrotestosterone in the masculinization of the zebra finch song system

Previous studies have suggested that both major active metabolites of testosterone, estradiol (E₂) and dihydrotestosterone (DHT), are needed for complete masculinization of the brain regions that control song in passerine birds. However, DHT treatment of hatchling female zebra finches has only small masculinizing effects on the song system. To assess whether E₂ and DHT have a synergistic effect on the masculinization of the zebra finch song system, female zebra finches were given Silastic implants of E₂ on the day of hatching (day 1) either without any additional hormone treatment or in combination with DHT on days 1, 14, or 70. At 105 to 110 days of age, we measured the volumes of Area X, higher vocal center (HVC), robust nucleus of the archistriatum (RA), soma sizes in HVC, RA, and the lateral magnocellular nucleus of the neostriatum (lMAN), and neuron density and number in RA. E₂ masculinized all of the measures in the song system with the exception of the number of neurons in RA. DHT did not synergize with E₂ to produce any additional masculinization of the attributes measured. These data demonstrate that the combination of E₂ and DHT did not result in the complete masculinization of the song control nuclei and argue against the importance of androgen in sexual differentiation of the song system. © 1995 John Wiley & Sons, Inc.     

Forebrain circuits underlying the social modulation of vocal communication signals

Across vertebrate species, signalers alter the structure of their communication signals based on the social context. For example, male Bengalese finches produce faster and more stereotyped songs when directing song to females (female‐directed [FD] song) than when singing in isolation (undirected [UD] song), and such changes have been found to increase the attractiveness of a male's song. Despite the importance of such social influences, little is known about the mechanisms underlying the social modulation of communication signals. To this end, we analyzed differences in immediate early gene (EGR‐1) expression when Bengalese finches produced FD or UD song. Relative to silent birds, EGR‐1 expression was elevated in birds producing either FD or UD song throughout vocal control circuitry, including the interface nucleus of the nidopallium (NIf), HVC, the robust nucleus of the arcopallium (RA), Area X, and the lateral magnocellular nucleus of the anterior nidopallium (LMAN). Moreover, EGR‐1 expression was higher in HVC, RA, Area X, and LMAN in males producing UD song than in males producing FD song, indicating that social context modulated EGR‐1 expression in these areas. However, EGR‐1 expression was not significantly different between males producing FD or UD song in NIf, the primary vocal motor input into HVC, suggesting that context‐dependent changes could arise de novo in HVC. The pattern of context‐dependent differences in EGR‐1 expression in the Bengalese finch was highly similar to that in the zebra finch and suggests that social context affects song structure by modulating activity throughout vocal control nuclei. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 47–63, 2016     

Castration and antisteroid treatment impari vocal learning in male zebra finches

Both song behavior and its neural substrate are hormone sensitive: Castrated adult male zebra finches need replacement of gonadal steroids in order to restore normal levels of song production, and sexsteroids are necessary to establish male-typical neural song-controlcircuits during early development. This pattern of results suggests that hormones may be required for normal development of learned songbehavior, but evidence that steroids are necessary for normal neuraland behavioral development during song learning has been lacking. Weaddressed this question by attempting to eliminate the effects of gonadal steroids in juvenile male zebra finches between the time of initial song production and adulthood. Males were castrated at 20 daysof age and received systemic implants of either an antiandrogen (flutamide). an antiestrogen (tamoxifen), or both drugs. The songs of both flutamide-and tamoxifen-treated birds were extremely disrupted relative to normal controls in terms of the stereotypy and acoustic quality of individual note production, as well as stereotypy of the temporal structure of the song phrase. We did not discern any differences in the pattern of behavioral disruption between birds that were treated with either flutamide, tamoxifen, or a combination of both drugs. Flutamide treatment resulted in a reduced size of two forebrain nuclei that are known to play some role unique to early phases of song learning [lateral magnocellular nucleus of the anterior neostriatum (IMAN) and area X (X)], but did not affect the size of two song-control nuclei that are necessary for normal song productionin adult birds [caudal nucleus of the ventral hyperstriatum (HVc) and robust nucleus of the archistriatum (RA)]. In contrast, treatment with tamoxifen did not result in any changes in the size of song-control nuclei relative to normal controls, and it blocked the effects of flutamide on the neural song-control system in birds that were treated with both drugs. Castration and antisteroid treatment exerted no deleterious effects on the quality of song behavior in adult birds, indicating that gonadal hormones are necessary for the development of normal song behavior during a sensitive period. © 1992 John Wiley & Sons, Inc.     

10种鸣禽鸣唱复杂性与发声核团体积的聚类分析

选用捕自野外和人工繁殖的10种雄性成鸟(一年龄以上)作为实验材料。当鸟适应环境后录音,用VS-99语音工作站软件进行声谱分析。鸣唱的复杂性采用语句短语总数、短语的音节数之和、短语的音节种类数之和、每个短语中所含的平均音节数、每个短语中所含的平均音节种类数、每种鸣禽最长短语的音节数和最长短语的音节种类数7项指标表示。然后测定前脑的上纹状体腹侧尾端(HVC)、古纹状体粗核(RA)以及嗅叶的X核(Areax)3个主要鸣唱控制核团的体积。最后分别对10种鸣禽3个发声控制核团体积和鸣唱复杂性的7项指标进行聚类分析。10种鸣禽的7项指标值相差较大,即使同一科也如此。蒙古百灵的3种核团体积比值均最大,其次是金丝雀和黄喉鹉。10种鸣禽鸣唱语句复杂性的7个指标和3种核团体积聚类分析树形图显示的结果各不相同;仅RA和Areax核团体积的树形图显示蒙古百灵远离其他9种鸣禽,与现代分类学和DNA分析得到的进化树一致。     

Social context affects testosterone‐induced singing and the volume of song control nuclei in male canaries (Serinus canaria)

The contribution of social factors to seasonal plasticity in singing behavior and forebrain nuclei controlling song, and their interplay with gonadal steroid hormones are still poorly understood. In many songbird species, testosterone (T) enhances singing behavior but elevated plasma T concentrations are not absolutely required for singing to occur. Singing is generally produced either to defend a territory or to attract a mate and it is therefore not surprising that singing rate can be influenced by the sex and behavior of the social partner. We investigated, based on two independent experiments, the effect of the presence of a male or female partner on the rate of song produced by male canaries. In the first experiment, song rate was measured in dyads composed of one male and one female (M‐F) or two males (M‐M). Birds were implanted with T‐filled Silastic capsules or with empty capsules as control. The number of complete song bouts produced by all males was recorded during 240 min on week 1, 2, 4, and 8 after implantation. On the day following each recording session, brains from approximately one‐fourth of the birds were collected and the volumes of the song control nuclei HVC and RA were measured. T increased the singing rate and volume of HVC and RA but these effects were affected by the social context. Singing rates were higher in the M‐M than in the M‐F dyads. Also, in the M‐M dyads a dominance‐subordination relationship soon became established and dominant males sang at higher rates than subordinates in T‐treated but not in control pairs. The differences in song production were not reflected in the size of the song control nuclei: HVC was larger in M‐F than in M‐M males and within the M‐M dyads, no difference in HVC or RA size could be detected between dominant and subordinate males. At the individual level, the song rate with was positively correlated with RA and to a lower degree HVC volume, but this relationship was observed only in M‐M dyads, specifically in dominant males. A second experiment, carried out with castrated males that were all treated with T and exposed either to another T‐treated castrate or to an estradiol‐implanted female, confirmed that song rate was higher in the M‐M than in the M‐F condition and that HVC volume was larger in heterosexual than in same‐sex dyads. The effects of T on singing rate and on the volume of the song control nuclei are thus modulated by the social environment, including the presence/absence of a potential mate and dominance status among males. 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

Rapamycin blocks the neuroprotective effects of sex steroids in the adult birdsong system

In adult songbirds, the telencephalic song nucleus HVC and its efferent target RA undergo pronounced seasonal changes in morphology. In breeding birds, there are increases in HVC volume and total neuron number, and RA neuronal soma area compared to nonbreeding birds. At the end of breeding, HVC neurons die through caspase‐dependent apoptosis and thus, RA neuron size decreases. Changes in HVC and RA are driven by seasonal changes in circulating testosterone (T) levels. Infusing T, or its metabolites 5α‐dihydrotestosterone (DHT) and 17 β‐estradiol (E2), intracerebrally into HVC (but not RA) protects HVC neurons from death, and RA neuron size, in nonbreeding birds. The phosphoinositide 3‐kinase (PI3K)‐Akt (a serine/threonine kinase)‐mechanistic target of rapamycin (mTOR) signaling pathway is a point of convergence for neuroprotective effects of sex steroids and other trophic factors. We asked if mTOR activation is necessary for the protective effect of hormones in HVC and RA of adult male Gambel's white‐crowned sparrows (Zonotrichia leucophrys gambelii). We transferred sparrows from breeding to nonbreeding hormonal and photoperiod conditions to induce regression of HVC neurons by cell death and decrease of RA neuron size. We infused either DHT + E2, DHT + E2 plus the mTOR inhibitor rapamycin, or vehicle alone in HVC. Infusion of DHT + E2 protected both HVC and RA neurons. Coinfusion of rapamycin with DHT + E2, however, blocked the protective effect of hormones on HVC volume and neuron number, and RA neuron size. These results suggest that activation of mTOR is an essential downstream step in the neuroprotective cascade initiated by sex steroid hormones in the forebrain.