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G F Ball

Publications and source records attributed to G F Ball.

At least 73 records · Page 4Linked to original sources
PubMed1998

Distribution of androgen receptor-immunoreactive cells in the quail forebrain and their relationship with aromatase immunoreactivity.

The distribution of androgen receptor-like immunoreactive (AR-ir) cells in the quail brain was analyzed by immunocytochemistry with the use of the affinity-purified antibody PG-21-19A raised against a synthetic peptide representing the first 21 N-terminal amino acids of the rat and human AR. This antibody is known to bind to the receptor in the absence as well as in the presence of endogenous ligands, and it was therefore expected that a more complete and accurate characterization of AR-ir cells would be obtained in comparison with previous studies using an antibody that preferentially recognizes the occupied receptor. Selected sections were double labeled for aromatase (ARO) by a technique that uses alkaline phosphatase as the reporter enzyme and Fast blue as the chromogen. AR-ir material was detected in the nucleus of cells located in a variety of brain areas in the preoptic region and the hypothalamus including the medial preoptic (POM), the supraoptic, the paraventricular (PVN), and the ventromedial (VMN) nuclei, but also in the tuberculum olfactorium, the nucleus accumbens/ventral striatum, the nucleus taeniae, the tuberal hypothalamus, the substantia grisea centralis (GCt), and the locus ceruleus. Cells exhibiting a dense AR-ir label were also detected in the nucleus intercollicularis. Preincubation of the primary antibody with an excess of the synthetic peptide used for immunization completely eliminated this nuclear staining. A significant number of AR-ir cells in the POM, VMN, PVN, and tuberal hypothalamus also contained ARO-ir material in their cytoplasm. These data confirm and extend previous studies localizing AR in the avian brain, and raise questions about the possible regulation by androgens of the metabolizing enzyme aromatase.

Animals↗
PubMed1997

Induction of the Zenk protein after sexual interactions in male Japanese quail.

We mapped cells immunoreactive (ir) for the protein encoded by the immediate early gene zenk in the brains of male Japanese quail after they engaged in either appetitive or consummatory sexual behavior (i.e. copulation). Castrated males treated with testosterone were either allowed to copulate with a female or exhibited a learned social proximity response indicative of appetitive sexual behavior, and were compared with control males in their home cage or in the experimental chamber but not exhibiting the proximity response. Copulation increased the number of ZENK-ir cells in the nucleus striae terminalis and the nucleus intercollicularis, while both copulation and the proximity response induced increases in the medial and anterior ventral hyperstriatum. These results indicate that zenk is induced in the context of sexual behavior.

Analysis of Variance↗
PubMed1997

Testis-dependent and -independent effects of photoperiod on volumes of song control nuclei in American tree sparrows (Spizella arborea).

Songbirds exhibit seasonal changes in the volumes of song control nuclei. Birds on long, spring-like days have larger nuclei than do birds on short, winter-like days. The mechanisms mediating volumetric changes have not been determined unequivocally, but testosterone (T) is probably involved. This study examined whether testicular factors are uniquely responsible for seasonal changes in the song system, or whether photoperiod has testis-independent effects. Male American tree sparrows were exposed to one of three photoperiodic conditions: (1) Photosensitive birds were retained on short days (8L:16D). Plasma T is rarely detected in such birds. (2) Photosensitive birds were moved from short days to long days (20L:4D) and photostimulated for three weeks. Photostimulation elevates circulating T in photosensitive birds. (3) Photorefractory birds were held at least four months on 20L:4D. Such birds seldom have detectable levels of T, even though they are on long days. In each condition, there were both intact and castrated birds. Castration typically removes circulating T in tree sparrows. The volumes of the high vocal center (HVC), nucleus robustus archistriatalis (RA), and area X were measured. Song nuclei were largest in intact photostimulated birds. Other long-day birds (i.e. castrated photostimulated, and intact and castrated photorefractory groups) had larger song nuclei than did short-day intact or castrated photosensitive birds and did not differ from each other. These data indicate that photoperiod has both testis-dependent and -independent effects on the volumes of song control nuclei.

Animals↗
PubMed1997

Photoperiodic condition modulates the effects of testosterone on song control nuclei volumes in male European starlings.

Songbirds possess a specialized network of brain nuclei mediating song learning and production, the song system. In many species, the nuclei in this circuit are larger in volume in males housed on long photoperiods than in males housed on short photoperiods. Exposure to long days initially leads to increases in circulating levels of testosterone (T) and it is generally believed that volume changes in the song system are controlled by T-dependent effects of photoperiod. However, a growing body of evidence indicates that photoperiod can also have T-independent effects on song system morphology. Previous work in our laboratory suggested that photoperiodic condition may modulate the effects of exogenous testosterone on the volumes of song control nuclei in male European starlings (Sturnus vulgaris). In the present report, we tested the hypothesis that photorefractoriness attenuates the effects of T on the volumes of song control nuclei in starlings. One group of long-day photorefractory males (16L:8D) was exposed to exogenous T and two groups of short-day photosensitive birds (8L:16D) were either implanted with T or blank (control) capsules. After 8 weeks, T levels were elevated in both groups of T-implanted birds and were undetectable in control animals. Volumes of the high vocal center were larger in T-implanted photosensitive birds than in both T-implanted photorefractory and control photosensitive males, which did not differ. These results suggest that photorefractoriness renders the song nuclei of starlings less sensitive to stimulatory effects of T. Plasticity in the starling song system appears to require the coordination of the appropriate hormonal milieu with a permissive photoperiodic condition.

Animals↗
PubMed1997

Differential effects of D1 and D2 dopamine-receptor agonists and antagonists on appetitive and consummatory aspects of male sexual behavior in Japanese quail.

Pharmacological studies in Japanese quail based on behavioral tests with a variety of dopaminergic compounds suggest that the activation of D2 dopamine receptors inhibits, and the activation of D1 dopamine receptors enhances, appetitive and consummatory components of male sexual behavior. This hypothesis was tested by studying the behavioral effects of specific D1 and D2 dopaminergic-receptor agonists and antagonists in castrated male Japanese quail chronically treated with exogenous testosterone (subcutaneous Silastic implants). The effects of 5 compounds were tested: 1 D1 (SKF38393) and 2 D2 (PPHT and quinpirole) agonists, and 1 D1 (SCH23390) and 1 D2 (Spiperone) antagonist. All compounds were tested at a low and a high dose (0.1 and 1 mg/kg, respectively, for all drugs, except spiperone where the doses were 2 and 10 mg/kg). A consistent effect of all drugs on consummatory sexual behavior was observed: it was stimulated by the D1 agonist and the D2 antagonist, but inhibited by the D1 antagonist and the D2 agonists. Far fewer effects of the treatments were detected on the measures of appetitive behavior. Measures of appetitive behavior were decreased by the 2 D2 agonists, but not affected by the other treatments. These data suggest that male copulatory behavior in quail is stimulated by dopamine acting on D1 receptors, but inhibited by activation of the D2 receptor subtype. The partial dissociation observed between the effects of the same treatments on appetitive and consummatory aspects of sexual behavior also suggests that these 2 behavioral systems may be controlled by the action of dopamine on different neuronal systems.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1997

Effects of dopamine agonists on appetitive and consummatory male sexual behavior in Japanese quail.

The effects of pharmacological manipulations of dopaminergic transmission on appetitive and consummatory aspects of male sexual behavior were investigated in castrated male Japanese quail treated with exogenous testosterone. Appetitive male sexual behavior was assessed by measuring a learned social proximity response and consummatory behavior was assessed by measuring copulatory behavior per se. The nonselective dopamine receptor agonist, apomorphine, inhibited in a dose-dependent manner both components of male sexual behavior. Two indirect dopamine agonists were also tested. Nomifensine, a dopamine re-uptake inhibitor, decreased appetitive sexual behavior but increased the frequency of mount attempts, a measure of consummatory sexual behavior. Amfonelic acid, a compound that enhances dopaminergic tone by a complex mechanism, increased aspects of both appetitive and consummatory behaviors. These data suggest that, in quail, as in rodents, increases in dopaminergic tone facilitate both appetitive and consummatory aspects of male sexual behavior. Apomorphine may be inhibitory in quail because it acts primarily on D2-like receptors, unlike in rats, where it stimulates sexual behavior and acts primarily on D1-like receptors at low doses but interacts with D2-like receptors at higher doses. This is supported by the observation that stereotyped pecking, a behavior stimulated selectively in quail by D2 agonists, was increased by apomorphine but not by the two indirect agonists. The observed partial dissociation between the effects of these dopaminergic agonists on appetitive and consummatory sexual behaviors suggests that these two components of male sexual behavior may be controlled by the action of dopamine through different neuronal systems.

Animals↗
PubMed1997

Aromatase inhibition blocks the activation and sexual differentiation of appetitive male sexual behavior in Japanese quail.

Two experiments investigated the role of estrogens in the activation and sexual differentiation of appetitive sexual behavior (ASB) in Japanese quail (Coturnix japonica) as measured by a learned social proximity response. Injection of the aromatase inhibitor R767 13 in castrated, testosterone (T)-treated male quail completely suppressed ASB, confirming that, like consummatory sexual behavior, ASB is mediated by T aromatization. ASB is not observed in female quail, even if they are treated with T as adults. The role of embryonic estrogens in the sexual differentiation of ASB was tested by blocking estrogen synthesis in ovo. Control male and T-treated female quail deprived of estrogens during embryonic life learned the social proximity response used to assess ASB, whereas control female quail did not, despite the presence of high T. Thus, ASB is demasculinized by the action of embryonic estrogens during ontogeny as is consummatory behavior.

Animals↗
PubMed1996

Age- and behavior-related variation in volumes of song control nuclei in male European starlings.

There is considerable interindividual variation in the volumes of song control nuclei. Sex and physiological condition appear to contribute to these differences; however, these factors alone do not account for all of the variation. Studies have attempted to relate differences in song behavior (i.e., song repertoire size) to variation in song nucleus volume, but have met with mixed success. In this article, two studies are presented that used male European starlings (Sturnus vulgaris) to explore the relationship between song nuclei volumes and age-related differences in song behavior and interindividual variation in song behavior in adults. The results of the first study showed that song repertoire size and song bout length were significantly greater in older adult than in yearling males. In addition, the volumes of the high vocal center (HVC) and nucleus robustus archistriatalis (RA) were significantly larger in older adults than yearlings. Area X of the parolfactory lobe did not differ significantly in volume between the two age classes. In the second study, both HVC and RA volume correlated positively with song bout length but not repertoire size among adult birds. Based on these results a new hypothesis is presented that states that variation in song nuclei volumes in starlings relates more to the amount of song produced than to the number of song types stored in memory.

Aging↗
PubMed1996

Distribution of aromatase-immunoreactive cells in the forebrain of zebra finches (Taeniopygia guttata): implications for the neural action of steroids and nuclear definition in the avian hypothalamus.

Cells immunoreactive for the enzyme aromatase were localized in the forebrain of male zebra finches with the use of an immunocytochemistry procedure. Two polyclonal antibodies, one directed against human placental aromatase and the other directed against quail recombinant aromatase, revealed a heterogeneous distribution of the enzyme in the telencephalon, diencephalon, and mesencephalon. Staining was enhanced in some birds by the administration of the nonsteroidal aromatase inhibitor, R76713 racemic Vorozole) prior to the perfusion of the birds as previously described in Japanese quail. Large numbers of cells immunoreactive for aromatase were found in nuclei in the preoptic region and in the tuberal hypothalamus. A nucleus was identified in the preoptic region based on the high density of aromatase immunoreactive cells within its boundaries that appears to be homologous to the preoptic medial nucleus (POM) described previously in Japanese quail. In several birds alternate sections were stained for immunoreactive vasotocin, a marker of the paraventricular nucleus (PVN). This information facilitated the clear separation of the POM in zebra finches from nuclei that are adjacent to the POM in the preoptic area-hypothalamus, such as the PVN and the ventromedial nucleus of the hypothalamus. Positively staining cells were also detected widely throughout the telencephalon. Cells were discerned in the medial parts of the ventral hyperstriatum and neostriatum near the lateral ventricle and in dorsal and medial parts of the hippocampus. They were most abundant in the caudal neostriatum where they clustered in the dorsomedial neostriatum, and as a band of cells coursing along the dorsal edge of the lamina archistriatalis dorsalis. They were also present in high numbers in the ventrolateral aspect of the neostriatum and in the nucleus taeniae. None of the telencephalic vocal control nuclei had appreciable numbers of cells immunoreactive for aromatase within their boundaries, with the possible exception of a group of cells that may correspond to the medial part of the magnocellular nucleus of the neostriatum. The distribution of immunoreactive aromatase cells in the zebra finch brain is in excellent agreement with the distribution of cells expressing the mRNA for aromatase recently described in the finch telencephalon. This widespread telencephalic distribution of cells immunoreactive for aromatase has not been described in non-songbird species such as the Japanese quail, the ring dove, and the domestic fowl.

Animals↗
PubMed1996

Testosterone induction of male-like vocalizations in female budgerigars (Melopsittacus undulatus).

Budgerigars possess a complex learned vocal repertoire that includes a long rambling song called warble. While both males and females can warble, there are marked sex differences in the amount of song produced. Males generally warble daily at a high rate, while females rarely sing. Both the quantity and the quality of male warble are influenced by circulating levels of testosterone. Males have higher circulating levels of testosterone than females. In this study we asked whether administering testosterone to adult female budgerigars would activate male-like vocal behavior. Four females were implanted with 8-mm Silastic implants filled with testosterone and recorded before and after implantation. Within 10-14 days, all four birds showed: (1) changes in there color to the male-like condition (blue), (2) male-typical patterns of precopulatory behavior, and (3) an increase in their rate of warbling to male-like levels. Sound analysis revealed that the acoustic structure of the testosterone-induced female warble is similar to the male warble. These data indicate that sex differences in budgerigar vocal behavior are not based on early organizational effects of steroid hormones, but rather are probably the result of adult sex differences in circulating testosterone levels.

Animals↗
PubMed1996

Early administration of 17beta-estradiol partially masculinizes song control regions and alpha2-adrenergic receptor distribution in European starlings (Sturnus vulgaris).

The vocal control system in many songbird species is a sexually dimorphic neural circuit that mediates learning and production of song. The mechanism by which this system is sexually differentiated has been investigated in only one species, the zebra finch (Taeniopygia guttata). Estradiol may be involved in the sexual differentiation of this system, as female zebra finches treated with estradiol as nestlings develop a male-like song system; however, blocking estradiol action in embryonic and nestling male zebra finches does not demasculinize the song system. Therefore, the role of estradiol in song system development is unclear. The role of estradiol in song system sexual differentiation was assessed in European starlings (Sturnus vulgaris). This species is of potential interest because it is less extreme in the degree of sexual dimorphism of the song system and song behavior than zebra finches. While in the field, starling nestlings were implanted with 500 microg of estradiol at 3 days of age. These birds were brought into the laboratory at Day 11 and hand-reared. In females, estradiol produces significant increases in the volumes of song control regions defined by Nissl stain, as well as by autoradiography for alpha2-adrenergic receptors; however, these estradiol-treated females have song systems that more closely resemble those of control females than control males. Estradiol-treated males exhibit significant hypermasculinization at 210 days of age, but this effect is transient and hypermasculinization is no longer evident at Day 345. The role of estradiol in sexual differentiation of the neural circuit mediating song behavior remains enigmatic.

Animals↗
PubMed1996

Do sex differences in the brain explain sex differences in the hormonal induction of reproductive behavior? What 25 years of research on the Japanese quail tells us.

Early workers interested in the mechanisms mediating sex differences in morphology and behavior assumed that differences in behavior that are commonly observed between males and females result from the sex specificity of androgens and estrogens. Androgens were thought to facilitate male-typical traits, and estrogens were thought to facilitate female-typical traits. By the mid-20th century, however, it was apparent that administering androgens to females or estrogens to males was not always effective in sex-reversing behavior and that in some cases a "female" hormone such as an estrogen could produce male-typical behavior and an androgen could induce female-typical behavior. These conceptual difficulties were resolved to a large extent by the seminal paper of C. H. Phoenix, R. W. Goy, A. A. Gerall, and W. C. Young in (1959, Endocrinology 65, 369-382) that illustrated that several aspects of sexual behavior are different between males and females because the sexes have been exposed during their perinatal life to a different endocrine milieu that has irreversibly modified their response to steroids in adulthood. Phoenix et al. (1959) therefore formalized a clear dichotomy between the organizational and activational effects of sex steroid hormones. Since this paper, a substantial amount of research has been carried out in an attempt to identify the aspects of brain morphology or neurochemistry that differentiate under the embryonic/neonatal effects of steroids and are responsible for the different behavioral response of males and females to the activation by steroids in adulthood. During the past 25 years, research in behavioral neuroendocrinology has identified many sex differences in brain morphology or neurochemistry; however many of these sex differences disappear when male and female subjects are placed in similar endocrine conditions (e.g., are gonadectomized and treated with the same amount of steroids) so that these differences appear to be of an activational nature and cannot therefore explain sex differences in behavior that are still present in gonadectomized steroid-treated adults. This research has also revealed many aspects of brain morphology and chemistry that are markedly affected by steroids in adulthood and are thought to mediate the activation of behavior at the central level. It has been explicitly, or in some cases, implicitly assumed that the sexual differentiation of brain and behavior driven by early exposure to steroids concerns primarily those neuroanatomical/neurochemical characteristics that are altered by steroids in adulthood and presumably mediate the activation of behavior. Extensive efforts to identify these sexually differentiated brain characteristics over the past 20 years has only met with limited success, however. As regards reproductive behavior, in all model species that have been studied it is still impossible to identify satisfactorily brain characteristics that differentiate under early steroid action and explain the sex differences in behavioral activating effects of steroids. This problem is illustrated by research conducted on Japanese quail (Coturnix japonica), an avian model system that displays prominent sex differences in the sexual behavioral response to testosterone, and in which the endocrine mechanisms that control sexual differentiation of behavior have been clearly identified so that subjects with a fully sex-reversed behavioral phenotype can be easily produced. In this species, studies of sex differences in the neural substrate mediating the action of steroids in the brain, including the activity of the enzymes that metabolize steroids such as aromatase and the distribution of steroid hormone receptors as well as related neurotransmitter systems, did not result in a satisfactory explanation of sex differences in the behavioral effectiveness of testosterone. Possible explanations for the relative failure to identify the organized brain characteristics responsible for behavio

Animals↗
PubMed1995

Assessment of volumetric sex differences in the song control nuclei HVC and RA in zebra finches by immunocytochemistry for methionine enkephalin and vasoactive intestinal polypeptide.

In this study we assessed sex differences in the volume of two vocal control nuclei, the high vocal center (HVC) and the robust nucleus of the archistriatum (RA) in zebra finches (Taeniopygia guttata) exposed to various endocrine treatments (neonatal treatment with an aromatase inhibitor and/or an adult treatment with testosterone). The boundaries of these nuclei were defined in sections stained for Nissl substance and compared to alternate sections stained with an immunocytochemical procedure for two neuropeptides, methionine enkephalin and vasoactive intestinal polypeptide. A high density of immunoreactive fibers for methionine enkephalin and vasoactive intestinal polypeptide completely covered the high vocal center in male and female zebra finches and these fibers were not observed in the surrounding neostriatum. With the use of these markers to define the boundary of the high vocal center, it became possible to reconstruct its volume. Positively staining perikarya were not apparent within the boundaries of this nucleus. Immunoreactive fibers for vasoactive intestinal polypeptide and enkephalin also allowed one to define the boundary of the robust nucleus of the archistriatum but they did not fill the entire area of the nucleus as is the case for the high vocal center. When the volumes of both nuclei were reconstructed based on enkephalin or vasoactive intestinal polypeptide immunoreactivity, the presence of a marked sex difference in the volume of these nuclei was confirmed. Neonatal and adult endocrine manipulations did not affect the volumes of these two nuclei measured in Nissl-stained material nor did they affect the volumes as defined based on the peptidergic innervations of the nuclei. Also, the volumetric estimates of these two nuclei derived from sections stained by immunocytochemistry were in good agreement in all groups of birds with the values obtained based on an analysis of the Nissl-stained material. These results illustrate the usefulness of employing a variety of histochemical markers to define a brain area when investigating brain variation and plasticity.

Animals↗
PubMed1995

Two histological markers reveal a similar photoperiodic difference in the volume of the high vocal center in male European starlings.

Most studies of seasonal changes in the avian song control system have used Nissl stains to characterize the nuclei. More recent work has indicated that changes in nucleus volume evident in Nissl-stained tissue are not always apparent when investigated with other histochemical criteria. In this experiment, we used two different markers (Nissl stain and alpha 2-adrenergic receptor autoradiography) to characterize changes in the song system of European starlings (Sturnus vulgaris). Fluctuating levels of circulating testosterone (T) appear to be causally related to seasonal changes in the song system. Therefore, we used photoperiod manipulations to place male starlings into different physiological conditions. Photosensitive male starlings were placed on 11L:13D or 16L:8D photoperiods for at least 5 months. Birds on 11L:13D have enlarged gonads and circulating T. In contrast, starlings maintained on 16L:8D initially show marked gonadal growth. However, after about 6-8 weeks the birds are photorefractory (i.e., the gonads are regressed and T falls to undetectable levels). The volume of the high vocal center (HVC) was 44% larger in the 11L:13D than in 16L;8D birds in Nissl-stained tissue. The density of alpha 2-adrenergic receptors as determined by in vitro receptor autoradiography with [3H]p-amino-clonidine (PAC) is higher in HVC than in the surrounding neostriatum, clearly delineating the boundaries of the nucleus. We reconstructed the volume of HVC using PAC stained tissue. Thus, two histochemical markers indicate a photoperiodic difference in HVC volume of male starlings.

Animals↗
PubMed1995

Peptidergic delineations of nucleus interface reveal a sex difference in volume.

Nucleus interface (Nif) is a song bird vocal control nucleus located in the neostriatum. In zebra finches (Taeniopygia guttata), high densities of fibers immunoreactive for the vasoactive intestinal polypeptide (VIP) and methionine enkephalin (ENK) define the boundaries of this nucleus. The volume of Nif measured using this pattern of peptidergic immunoreactivity was greater in males than in females. This difference was also found in gonadectomized, testosterone-treated birds that had similar levels of circulating steroids, suggesting that it is organizational in nature. These data show that Nif may form part of the neural substrate underlying sex differences in song behavior. They also provide further evidence that VIP and ENK may play a role in the activation of bird song.

Animals↗
PubMed1995

The effects of photoperiod on olfactory c-fos expression in prairie voles, Microtus ochrogaster.

Reproduction stops among the majority of prairie voles (Microtus ochrogaster) during the winter. Short day lengths suppress male reproductive function dramatically in the laboratory, but photoperiod exerts only subtle effects on female reproductive function. Thus, the regulation of seasonal breeding in this species remains partially unspecified. In contrast to commonly studied rodents, female prairie voles do not undergo spontaneous estrous cycles; rather, they are induced into estrus by exposure to chemosignals expressed in conspecific male urine. In the present study, the hypothesis was tested that seasonal breeding among female prairie voles in the field reflects photoperiod-mediated changes in the responsiveness of the chemosensory system to male urine. Responsiveness was assessed by localizing the product of the c-fos immediate early gene with an immunocytochemical procedure. Female prairie voles were maintained in either long (LD 16:8) or short (LD 8:16) photoperiods from birth until adulthood, and exposed to either male urine or skim milk. Immunocytochemistry for fos protein revealed an increased number of immunoreactive cells within the accessory olfactory system of female prairie voles, including the accessory olfactory bulbs, granule cell layer, as well as the medial and cortical divisions of the amygdala 1 h after exposure to a single drop of urine as compared to individuals exposed to skim milk. The number of immunoreactive fos cells induced in females by conspecific male urine was also affected by photoperiod; short day females displayed fewer immunoreactive fos neurons in the accessory olfactory system as compared to long-day animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Amygdala↗
PubMed1995

Changes in brain GnRH associated with photorefractoriness in house sparrows (Passer domesticus).

Temperate zone birds terminate reproduction when they become photorefractory. In many species, refractoriness is "absolute" in that gonadal regression occurs before day length declines, and individuals are reproductively unresponsive even to continuous light. Based on studies of a few species, this form of refractoriness appears to be associated with a reduction (compared with breeding and/or photosensitive birds) in numbers of hypothalamic cells and fibers that are immunoreactive for gonadotropin releasing hormone (GnRH). Some species display "relative" refractoriness, in that day length must decline before gonadal regression occurs, and individuals never lose the capacity to respond to very long days. A few reports suggest that GnRH levels in the brain do not change in relatively refractory birds. House sparrows (Passer domesticus) regress their gonads sooner when day length declines during summer than they do if photoperiod is not permitted to decline after the summer solstice (i.e., they appear to be "relatively" refractory). However, if held on long days they eventually regress the gonads despite no decline in photoperiod (they appear to be "absolutely" refractory). In this experiment, we tested whether gonadal regression was associated with changes in hypothalamic GnRH in adult male house sparrows. We used immunocytochemistry (primary antibody sensitive to both forms of avian GnRH) to compare the distribution and number of GnRH-immunoreactive cells and fibers among reproductively active individuals on long days, "absolutely" refractory individuals on long days, and presumably "relatively" refractory individuals induced to regress by shortened days. Similar reductions in ir-GnRH cell number and cell size occurred in both groups of refractory birds compared with birds still in breeding condition. Gonadal regression also was correlated with reduced staining intensity of cell bodies and reduced fiber staining, but these reductions were somewhat more pronounced in the "absolutely" than the "relatively" refractory birds. We discuss these results in light of other studies of avian GnRH changes with reproductive stage. Our results are consistent with the idea that house sparrows become absolutely refractory, regardless of whether exposed to a decline in photoperiod. However, the results also suggest that relative refractoriness may induce gonadal regression through a cessation of GnRH secretion, whereas absolute refractoriness involves down-regulation of peptide production as well.

Animals↗