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.     

Testosterone-induced changes in adult canary brain are reversible

Brain nuclei that control song are larger in male canaries, which sing, than in females, which sing rarely or not at all. Treatment of adult female canaries with testosterone (T) induces song production and causes song-control nuclei to grow, approaching the volumes observed in males. For example, the higher vocal center (HVC) of adult females approximately doubles in size by 1 month following the onset of T treatment. Male HVC projects to a second telencephalic nucleus, RA (the robust nucleus of the archistriatum), which projects in turn to the vocal motor neurons. Whether HVC makes a similar connection in female canaries is not known, although HVC and RA are not functionally connected in female zebra finches, a species in which testosterone does not induce neural or behavioral changes in the adult song system. This experiment investigated whether HVC makes an efferent projection to RA in normal adult female canaries, or if T is necessary to induce the growth of this connection. In addition, we examined whether T-induced changes in adult female canary brain are reversible. Adult female canaries received systemic T implants that were removed after 4 weeks; these birds were killed 4 weeks after T removal (Testosterone-Removal, T-R). Separate groups of control birds received either (a) T implants for 4 weeks which were not removed (Testosterone-Control, T-C) or (b) empty implants (Untreated Control, øO-C). Crystals of the fluorescent tracer DiI were placed in the song-control nucleus HVC in order to anterogradely label both efferent targets of HVC, RA and Area X. Projections from HVC to RA and Area X were present in all treatment groups including untreated controls, and did not appear to differ either qualitatively or quantitatively. Thus, formation of efferent connections from HVC may be prerequisite to hormone-induced expression of song behavior in adult songbirds. The volumes of RA and Area X were measured using the distribution of anterograde label as well as their appearance in Nissl-stained tissue. RA was larger in T-treated control birds than in untreated controls. Experimental birds in which T was given and then removed (T-R) had RA volumes closer in size to untreated controls (ø-C). Because the volume of RA in T-treated controls (T-C) was larger than that of birds that did not receive T (ø-C), we conclude that the volume of RA increased in both T-C and T-R birds but regressed upon removal of T in T-R birds. Surprisingly, the volume of Area X did not increase in T-treated birds. Birds in this study were maintained on short days, suggesting that T-induced growth of Area X reported previously may have resulted from an interaction between T and another seasonal or photoperiodic factor induced by exposure to long daylengths. © 1993 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     

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.     

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.     

The distribution of tyrosine hydroxylase immunoreactivity in the brains of male and female zebra finches

A system of brain nuclei controls song learning and behavior in zebra finches (Poephila guttata). The size of song-control nuclei are much larger in males, which sing, than in females, which do not sing. This study examined the distribution of fibers, terminals, and cell bodies that are immunoreactive for tyrosine hydroxylase (TH) (the rate-limiting enzyme in the synthesis of catecholamines) in song-control nuclei of adult males and females and juvenile males. In addition, the broad pattern of TH staining throughout the brain was described. There was a sex difference in TH immunoreactivity within song-control nuclei: males had light to moderate staining in all three cortical nuclei examined, whereas females had little or no label in corresponding areas [lateral magnocellular nucleus of the anterior neostriatum (IMAN), higher vocal center (HVC), and robust nucleus of the archistriatum (RA)]. The song-control nucleus area X (X), located in the striatum of avian basal ganglia, was more darkly stained than the surrounding striatum only in males; X was not defined by more intense immunoreactivity in females and hence could not be visualized. There were no apparent differences in TH staining in males ranging in age from 50 days to adulthood (>90 days). Outside of the song-control system there were no substantive differences as a function of sex or age in the pattern or intensity of TH labeling. Major areas of telencephalic staining included the striatal region of basal ganglia, which was covered with dense, fine-grained label, and the septum, where cell bodies were encircled by extremely well-labeled thick processes. In the diencephalon, the preoptic area and hypothalamus included a complex pattern of darkly stained somata and fiber and terminal labeling. Darkly stained somata surrounded the pretectal nucleus, and labeled processes ramified throughout the superficial layers of the optic tectum. The midbrain and hindbrain contained a dense plexus of extremely dark cell bodies corresponding to mammalian substantia nigra, adjacent tegmental areas, and locus ceruleus. Labeled hindbrain cells were also seen in the pontine region, around nucleus solitarius, and in the ventrolateral medulla. © 1993 John Wiley & Sons, Inc.     

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.     

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.     

Hormone accumulation in song regions of the canary brain.

[3H]Testosterone (T) was injected into male and female canaries (Serinus canarius), a species in which females are able to sing but do so more rarely and more simply than males. Autoradiographic analysis revealed that males and females have equal proportions of cells labeled by T or its metabolites in four song control nuclei: the high vocal center (HVC), the lateral portion of the magnocellular nucleus of the anterior neostriatum (IMAN), the robust nucleus of the archistriatum (RA), and the hypoglossal motor nucleus (nXII). Labeled cells were also observed in both sexes in the medial portion of MAN, and in hypothalamic nuclei. In both sexes, labeled cells in HVC, IMAN, RA, and nXII were larger than unlabeled cells. There were no sex differences in the size of either labeled or unlabeled cells in these song nuclei. The density of labeled cells per unit volume of tissue did not differ between the sexes in any song nucleus analyzed. However, because males have larger HVC and RA than females, males have a greater total number of hormone-sensitive cells in these regions than do females. Comparison of these results with measures of hormone accumulation in zebra finches and tropical duetting wrens suggests that the complexity of song that a bird can produce is correlated with the total number of hormone-sensitive cells in song nuclei.     

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.     

Hormone accumulation in song regions of the canary brain

[³H]Testosterone (T) was injected into male and female canaries (Serinus canarius), a species in which females are able to sing but do so more rarely and more simply than males. Autoradiographic analysis revealed that males and females have equal proportions of cells labeled by T or its metabolites in four song control nuclei: the high vocal center (HVC), the lateral portion of the magnocellular nucleus of the anterior neostriatum (IMAN), the robust nucleus of the archistriatum (RA), and the hypoglossal motor nucleus (nXII). Labeled cells were also observed in both sexes in the medial portion of MAN, and in hypothalamic nuclei. In both sexes, labeled cells in HVC, IMAN, RA, and nXII were larger than unlabeled cells. There were no sex differences in the size of either labeled or unlabeled cells in these song nuclei. The density of labeled cells per unit volume of tissue did not differ between the sexes in any song nucleus analyzed. However, because males have larger HVC and RA than females, males have a greater total number of hormone-sensitive cells in these regions than do females. Comparison of these results with measures of hormone accumulation in zebra finches and tropical duetting wrens suggests that the complexity of song that a bird can produce is correlated with the total number of hormone-sensitive cells in song nuclei. © 1992 John Wiley & Sons, Inc.     

Testosterone metabolism in the avian hypothalamus

Many central actions of testosterone (T) require the transformation of T into several metabolites including 5-dihydrotestosterone (5-DHT) and estradiol (E₂). In birds as in mammals, 5-DHT and E₂, alone or in combination, mimic most behavioral effects of T. The avian brain is, in addition, able to transform T into 5β-DHT, a metabolite which seems to be devoid of any behavioral or physiological effects, at least in the context of reproduction. By in vitro product-formation assays, we have analyzed the distribution, sex differences and regulation by steroids of the 3 main T metabolizing enzymes (aromatase, 5- and 5β-reductases) in the brain of the Japanese quail (Coturnix c. japonica) and the zebra finch (Taeniopygia guttata castanotis). In the hypothalamus of quail and finches, aromatose activity is higher in males than in females. It is also decreased by castration and increased by T. The activity of the 5-reductase is not sexually differentiated nor controlled by T. The 5β-reductase activity is often higher in females than in males but this difference disappears in gonadectomized birds and no clear effect of T can be observed at this level. The zebra finch brain also contains a number of steroid-sensitive telencephalic nuclei [e.g. hyperstriatum ventrale, pars caudale (HVc) and robustus archistriatalis (RA)] which play a key role in the control of vocalizations. These nuclei also contain T-metabolizing enzymes but the regulation of their activity is substantially different from what has been observed in the hypothalamus. Aromatase activity is for example higher in females than in males in HVc and RA and the enzyme in these nuclei is not affected by castration nor T treatment. In these nuclei, the 5-reductase activity is higher in males than in females and the reverse is true for the 5β-reductase. These sex differences in activity are not sensitive to gonadectomy and T treatment and might therefore be organized by neonatal steroids. We have been recently able to localize aromatase-immunoreactive (AR-ir) neurons by ICC in the brain of the quail and zebra finch. Positive cells are found in the preoptic area, ventromedial and tuberal hypothalamus. AR-ir material is found in the perikarya of cells and fills the entire cellular processes including axons. At the electron microscope level, immunoreactive material can clearly be observed in the synaptic boutons. This observation raises questions concerning the mode of action of estrogens produced by central aromatization of T.     

A direct comparison of the masculinizing effects of testosterone,androstenedione, estrogen,and progesterone on the development of the zebra finch song system

To assess which hormones are capable of masculinizing the neural song system of zebra finch hatchlings, we implanted female hatchlings with estrogen (estradiol [E2], 75 μg, n = 9), testosterone (T, 75–88 μg, n = 13), androstenedione (AE, 75 μg, n = 7), progesterone (P, 117 μg, n = 10), or nothing (Blanks, n = 10) and compared these to unimplanted males (n = 7). Implants, consisting of a hormone and Silastic mixture encased in polyethylene tubing, were placed under the skin of the breast on the day of hatching. Birds were killed when they were subadult (58 to 68 days old). We measured volumes of area X, the higher vocal center (HVC), and the robust nucleus of the archistriatum (RA); measured soma sizes in the lateral magnocellular nucleus of the neostriatum (IMAN), HVC, and RA: and counted RA neurons. E2 masculinized all measures in the song system and nearly sex-reversed the size of RA neurons. T masculinized volumes of nuclei and soma sizes but not the number or spacing of RA neurons. E2 was always at least as effective as T in masculinizing measures of the song system and was usually more effective. AE and P did not significantly masculinize any measure. These data suggest that E2 is more potent than aromatizable androgens or P in masculinizing the female song system in development and that the action of E2 alone may be sufficient to masculinize the volume of song control nuclei and the size and number of neurons. © 1995 John Wiley & Sons, Inc.     

A comparison of aromatase, 5 alpha-, and 5 beta- reductase activities in the brain and pituitary of male and female quail (C. c. japonica)

In numerous vertebrate species including Japanese quail (Coturnix coturnix japonica), actions of testosterone (T) on neuroendocrine target tissues are mediated in part by conversion to estrogenic and androgenic metabolites. In order to assess which pathways were favored in each identified androgen target area in quail brain and whether there were discernible sex differences, we developed an assay for simultaneously quantifying aromatase, 5 alpha-, and 5 beta-reductase. In addition, we made the first definitive identification of aromatase in quail pituitary and compared all three enzyme activities in the pituitary of males and females. Enzymes were measured in tissue homogenates by the conversion of [3H]androstenedione to [3H]estrone, [3H]5 alpha-androstanedione, and 5 beta-androstanedione. Aromatase activity was restricted to limbic tissues (anterior hypothalamus greater than posterior hypothalamus greater than septum greater than archistriatum containing nucleus taenia) while hyperstriatum, cerebellum, and midbrain containing nucleus intercollicularis were aromatase-negative. Quail pituitary aromatized androgen at rates equivalent to anterior hypothalamus/pre-optic area (aHPOA). 5 alpha- and 5 beta-reductase were present in all tissues tested. Aromatase was significantly higher in aHPOA and pituitary of males, whereas 5 alpha-reductase was significantly higher in female pituitary. These data suggest that a complex of androgen-metabolizing enzymes controls the neuroanatomic (spatial) distribution of active hormone in neuroendocrine tissues and that quantitative differences between males and females may account for sex differences in behavior.     

Distribution and onset of retinaldehyde dehydrogenase (zRalDH) expression in zebra finch brain: lack of sex difference in HVC and RA at early posthatch ages

Using in situ hybridization to detect the expression of the retinoic acid synthesizing enzyme (retinaldehyde dehydrogenase: zRalDH) mRNA, we mapped the distribution of its expression in adult zebra finch brain. In the neural song circuit, strong expression was found in high vocal center (HVC), para-HVC, and at a very low level in the robust nucleus of the arcopallium (RA). The expression in HVC and RA was found in both males and females. Outside of the song system, major areas of expression were in medial nidopallium (N), hyperpallium apicale (HA), mesopallium ventrale (MV), taenial amygdala (TnA), cerebellar Purkinje cells, and nucleus isthmo-opticus (IO). In nestlings, we found zRalDH mRNA expression in HVC and RA as early as posthatch day 4 or 5 (P4-5), although the expression varied among individuals. Thus, retinoic acid synthesis in HVC and RA could participate in song system formation and development. However, we found no sex difference in volume or intensity of zRalDH and androgen receptor (AR) expression in HVC and RA at P11 prior to the development of significant size dimorphisms in these nuclei. The size of HVC in females at P11 defined by zRalDH expression was greater than that in adult females, suggesting that HVC might experience net cell loss between P11 and adulthood.     

Female marsh wrens do not provide evidence of anatomical specializations of song nuclei for perception of male song

In songbirds the forebrain nuclei HVC (high vocal center) and RA (robust nucleus of the archistriatum) are larger in individuals or species that produce larger song repertoires, but the extent to which the size of these nuclei reflects a need for either producing or perceiving large repertoires is unknown. We, therefore, tested the hypothesis that species differences in the size of song nuclei reflect a commitment of “brain space” to the perceptual processing of conspecific song. The two species of marsh wren (Cistothorus palustris western and eastern) provide a good test case. Western males produce larger song repertoires, and have larger HVC and RA than do eastern males. Female marsh wrens do not sing, and if they use their song nuclei to assess conspecific male song repertoires, then we predicted that measurable cellular and nuclear parameters of HVC and RA would be greater in western than eastern female wrens. For males we confirmed that the volumes of HVC and RA, and cellular parameters of HVC, are greater in western than in eastern birds. These nuclei were also considerably larger in males than in conspecific females. Western and eastern female wrens, however, did not differ in any measured parameters of HVC or RA. Females of these wren species thus do not provide any direct evidence of anatomical specializations of song nuclei for the perceptual processing of conspecific male song. 1994 John Wiley & Sons, Inc.     

雌性斑胸草雀发育和成体期发声核团LMAN中神经元数量的高水平维持

鸟类的发声和发声学习涉及处于脑中不同水平的相互联系的一些发声核团。在很多鸟类中, 仅雄性鸣啭, 例如在斑胸草雀(Taeniogygia guttata) 中, 雌雄个体间存在显著的性差异, 雌性发声系统和发声核团中的神经元数量显著少于雄性。推测这种性差异也可能存在于弓状皮质前部大细胞外侧核(LMAN), 但有关这方面的报道还很少。为探讨雌雄鸣禽脑中神经元数量发育的规律, 我们应用半薄切片对斑胸草雀发育不同阶段的神经元数量和密度的变化进行了数量分析。结果表明, 在全部实验组中, 发育10 d和成体雌性LMAN中神经元的密度和神经元数量均无明显变化, 神经元的数量维持在一个较高水平。在雄鸟中, 我们发现在发育早期神经元的数量有极为显著的减少, 这与已有的报道, 即应用非类固醇技术获得的结果相似。LMAN中神经元数量的减少(57%) 一直持续到成体。因此, 成年雌鸟LMAN中的全部神经元数量是雄鸟的4 倍(P<0 001)。推测雌鸟脑中存在较多的神经元数量可能与其在发育和成体期间需维持适当的神经网络有关, 这种神经构筑对于动物种间识别等功能可能具有特殊意义。