Hypertrophy of gonadotropin releasing hormone-containing neurons after castration in the teleost, Haplochromis burtoni.

In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11KT) and testosterone (T)], as well as 17 beta-estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males.     

Castration Lowers Aggression but not Social Dominance in Male Haplochromis burtoni (Cichlidae)

Adult males of the African cichlid fish Haplochromis burtoni are either territorial or nonterritorial. In nature and aquaria, only territorial males breed and they have markedly more developed testes than do nonterritorial males. Territorial males are clearly dominant over nonterritorial males of the same age and size, and also exhibit higher levels of aggression. In this study, territorial males were gonadectomized in order to assess the effects of lowered androgen levels on their aggression and dominance status. Completely castrated males showed a pronounced reduction in both testosterone and 11-ketotestosterone, as well as significantly lower aggression scores than sham-operated males. Partially castrated males (> 0.005 g gonadal tissue remaining at autopsy) exhibited intermediate levels of both androgen levels and aggression. Surprisingly, in dyadic encounters with normal nonterritorial males of the same size, castrated territorial males retained their dominance despite decreased androgen levels and aggression.     

Number of preoptic GnRH-immunoreactive cells correlates with sexual phase in a protandrously hermaphroditic fish, the dusky anemonefish (Amphiprionmelanopus)

The populations of gonadotropin-releasing hormone (GnRH)-producing cells within the preoptic area (POA) and terminal nerve (TN) of the brain have been suggested as the neuronal systems mediating social control of sex and gonadogenesis in sequentially hermaphroditic teleosts. In the present study, the number and soma size of GnRH-immunoreactive (GnRH-ir) cells in the POA and TN were studied in male, female and juvenile individuals of the dusky anemonefish (Amphiprionmelanopus), a species which displays both male to female sex change and socially controlled sexual maturation. The results showed that the number of POA (but not TN) GnRH-ir cells differ significantly between sexual phases, with males displaying higher cell numbers than both females and juveniles. Soma sizes of POA and TN GnRH-ir cells were larger in females than in males and juveniles. However, this relationship was fully explained by differences in body size. The results indicate that high POA GnRH cell numbers are part of a masculinizing mechanism and support the hypothesis that the POA GnRH cell population plays a central role in initiating or mediating the process of socially induced gonadal and/or behavioural transformations in sequential hermaphrodites. Accepted: 9 June 1997     

Social regulation of the electrical properties of gonadotropin-releasing hormone neurons in a cichlid fish (Astatotilapia burtoni)

Variation in reproductive capacity is common across the lives of all animals. In vertebrates, hypothalamic neurons that secrete GnRH are a primary mediator of such reproductive plasticity. Since social interactions suppress gonadal maturity in the African cichlid fish, Astatotilapia (Haplochromis) burtoni, we investigated whether the electrical properties of GnRH neurons were also socially regulated. Adult A. burtoni males are either territorial (T) and reproductively active or nonterritorial (NT) and reproductively regressed, depending upon their social environment. We compared the basic electrical properties of hypothalamic GnRH neurons from T and NT males using whole-cell electrophysiology in vitro. GnRH neurons were spontaneously active and exhibited several different activity patterns. A small fraction of neurons exhibited episodic activity patterns, which have been described in GnRH neurons from mammals. The type of activity pattern and spontaneous firing rate did not vary with reproductive capacity; however, several basic electrical properties were different. Neurons from T males were larger than those from NT males and had higher membrane capacitance and lower input resistance. In neurons from NT males, action potential duration was significantly longer and after-hyperpolarization characteristics were diminished, which led to a tendency for neurons from NT males to fire less rapidly in response to current injection. We predict this could serve to decrease GnRH release in NT males. These data are the first electrophysiological characterization of hypothalamic GnRH neurons in a nonmammalian species and provide evidence for several changes in electrical properties with reproductive state.     

Gonadotropin releasing hormone (GnRH) neurones of triploid catfish,Heteropneustes fossilis (Bloch): an immunocytochemical study

Gonadotropin-releasing hormone (GnRH), a regulator of gonadal maturation in vertebrates, is primarily secreted by neurosecretory cells of the pre-optic area (POA) in the forebrain of teleosts. GnRH-immunoreactive (GnRH-ir) cells of this area demonstrate positive correlation in number and size of soma with gonadal maturity and directly innervate the pituitary in most teleosts. Gonadal development in triploid fish remains impaired due to genetic sterility. The gonadal immaturity in triploid fish may be due to low levels of gonadotropin and sex steroids during the vitellogenic phase of reproductive cycle. However, the nature of GnRH-ir cells in triploid fish is not yet known. Triploid catfish (H. fossilis) showed significant decrease (P<0.001) in size and number of immunoreactive-GnRH cells of POA and low immunoreactivity in pituitary in comparison to their diploid full-sibs during the late pre-spawning phase of ovarian cycle. This study suggests that low activity of GnRH-cells in triploid may be due to lack of positive feedback stimulation by sex steroids and/or reduced responsiveness of sensory cells to environmental cues required for gonadal maturation in teleosts.     

Effects of neonatal gonadal steroids on adult CA3 pyramidal neuron dendritic morphology and spatial memory in rats

The hippocampus is implicated in spatial cognition, which is sexually dimorphic and developmentally sensitive to gonadal steroids. Previously we have shown a sex difference in CA3 pyramidal cell layer volume and neuronal soma size that was reversible with neonatal castration in males or prenatal treatment of females with either testosterone propionate (TP) or a nonaromatizable androgen, dihydrotestosterone propionate, but not estradiol benzoate, all of which correlated with adult water maze navigation. The present study further investigates developmental androgen sensitivity of CA3 pyramidal neurons by measuring dendritic morphology and its relation to adult spatial ability. Female rats were injected with TP on postnatal day (P) 3 and P5 or ovariectomized (OVX) on P2, and male rats were castrated on P2, with or without testosterone replacement (Cas+T). Sham surgery controls were also included. Animals were tested on a water maze in adulthood, sacrificed, and CA3 pyramidal neurons were Golgi-stained and reconstructed in three dimensions using a computer-interfaced morphometry system. High-androgen groups (control males, Cas+T, TP females) performed better in spatial navigation and exhibited CA3 neurons with longer dendrites, a larger number of dendritic branches, and volumes of influence compared to low-androgen groups (control females, castrated males, OVX). Collectively, these findings indicate that the critical time period for organizational effects of androgens on the CA3 pyramidal neurons includes both prenatal and postnatal life, during which time androgens regulate developmental events such as somal growth and neuronal differentiation, all of which significantly contribute to establishing the sex difference in adult spatial navigation.     

Testosterone implanted in the preoptic area of male Japanese quail must be aromatized to activate copulation

Intracranial implantation of minute pellets of gonadal steroids was combined with aromatase inhibitor treatment to determine if aromatization within the preoptic area (POA) is necessary for androgens to activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, implantation of pellets of testosterone propionate (TP) or estradiol benzoate (EB) in the POA of castrated males restores male-typical copulatory behavior. In Experiment 1, adult male castrated quail were implanted intracranially with 200-micrograms pellets of equimolar mixtures of crystalline TP + cholesterol (CHOL), TP + 1,4,6-androstatriene-3,17-dione (ATD, an aromatase inhibitor), EB + ATD, or CHOL and behavior-tested with intact males and females. Copulation was stimulated by POA implants containing TP or EB (three of six CHOL + TP males and two of seven ATD + EB males copulated vs zero of four CHOL males), but copulation was not inhibited by combining ATD with TP (three of four ATD + TP males copulated). In Experiment 2, adult male castrated quail were injected systemically with ATD or oil for 6 days prior to and 14 days after intracranial implantation of 200-micrograms pellets containing the same amounts of TP or EB as in Experiment 1. The ATD injections completely blocked copulatory behavior in males with TP implants in the POA such that ATD/TP and Oil/TP mount frequencies differed significantly, but failed to block copulation in males with EB implants in the POA (proportions of males copulating were ATD/EB, 6/8; ATD/TP, 0/6; Oil/TP, 4/7). The cloacal foam gland, an androgen-sensitive secondary sex character, was unaffected by the dose of ATD used. We conclude that activation of copulatory behavior by TP implants in the POA is not due to nonspecific effects of high local testosterone concentrations but rather to aromatization. These results support the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to activation of male-typical copulatory behavior.     

Sexually dimorphic effects of morphine and MK-801: sex steroid-dependent and -independent mechanisms.

Rats show gender differences in responses to morphine and the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801); the role of sex steroids in mediating these differences is unclear. We tested the overall hypothesis that circulating gonadal steroids determine the gender differences in morphine- and MK-801-induced behavior and c-Fos expression. Morphine caused a greater expression of c-Fos in the striatum of intact males than of that females, which was independent of sex steroids. MK-801 completely inhibited morphine-induced c-Fos in intact females but only caused partial inhibition in intact males; castrated males showed complete inhibition, which was reversed by testosterone, but gonadal steroids had no effect on this response in females. In thalamus, there was a large sex difference in the response to MK-801 that was independent of gonadal steroids. Behavioral responses to morphine were greater in males, but responses to MK-801 were greater in females; both were sex steroid independent. These findings show significant sex differences in response to morphine and MK-801 that are mediated by sex steroid-dependent and -independent mechanisms, which may be important in treatment outcomes of drug addiction.     

Members of opposite sex mutually regulate gonadal recrudescence in the lizard Calotes versicolor Agamidae)

Adult males and females of the seasonally breeding lizardCalotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17β-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in theC. versicolor.     

Sexual dimorphism of gonadotropin-releasing hormone type-III (GnRH3) neurons and hormonal sex reversal of male reproductive behavior in Mozambique tilapia

In tilapia, hormone treatment during the period of sexual differentiation can alter the phenotype of the gonads, indicating that endocrine factors can cause gonadal sex reversal. However, the endocrine mechanism underlying sex reversal of reproductive behaviors remains unsolved. In the present study, we detected sexual dimorphism of gonadotropin-releasing hormone type III (GnRH3) neurons in Mozambique tilapia Oreochromis mossambicus. Our immunohistochemical observations showed sex differences in the number of GnRH3 immunoreactive neurons in mature tilapia; males had a greater number of GnRH3 neurons in the terminal ganglion than females. Treatment with androgen (11-ketotestosterone (11-KT) or methyltestosterone), but not that with 17β-estradiol, increased the number of GnRH3 neurons in females to a level similar to that in males. Furthermore, male-specific nest-building behavior was induced in 70% of females treated with 11-KT within two weeks after the onset of the treatment. These results indicate androgen-dependent regulation of GnRH3 neurons and nest-building behavior, suggesting that GnRH3 is importantly involved in sex reversal of male-specific reproductive behavior.     

Activation of sexual behavior by implantation of testosterone propionate and estradiol benzoate into the preoptic area of the male Japanese quail (Coturnix japonica)

Intracranial implantation of minute pellets of gonadal steroids was performed to determine neuroanatomical loci at which steroids activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, systemic treatment of castrated males with either testosterone propionate (TP) or estradiol benzoate (EB) restores male-typical copulatory behavior (head grabbing, mounting, and cloacal contact movements). In addition, EB activates female-typical receptive behavior (crouching). Adult male castrated quail were implanted intracranially with 300-micrograms pellets containing TP, EB, or cholesterol (CHOL) and behavior was tested with intact males and females. Either TP or EB pellets in the preoptic area (POA) activated male-typical copulatory behavior. Mounting was specifically activated without concomitant activation of other steroid-sensitive sexual and courtship behaviors. TP and EB implants in adjacent nuclei containing receptors for these steroids and CHOL implants in POA had no effect on male-typical copulatory behavior. Eighteen percent of all males tested for female-typical receptivity crouched, but no specific effect of EB was seen at any site. The similarity of the POA sites for activation of mounting by TP and EB is consistent with the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to behavioral activation.     

Courtship interactions stimulate rapid changes in GnRH synthesis in male ring doves

Many birds and mammals show changes in the hypothalamo-pituitary-gonadal (HPG) axis in response to social or sexual interactions between breeding partners. While alterations in GnRH neuronal activity play an important role in stimulating these changes, it remains unclear if acute behaviorally-induced alterations in GnRH release are accompanied by parallel changes in GnRH synthesis. To investigate this relationship, we examined changes in the activity of GnRH neurons in the brains of male ring doves following brief periods of courtship interactions with females. Such interactions have been previously shown to increase plasma LH in courting male doves at 24 h, but not at 1 h, after pairing with females. In the first study, males allowed to court females for 2 h had 60% more cells that showed immunocytochemical labeling for GnRH-I in the preoptic area (POA) of the hypothalamus than did control males that remained isolated from females. To determine whether an increase in GnRH gene expression preceded this increase in GnRH immunoreactivity in the POA, changes in the number of cells with detectable GnRH-I mRNA in the POA were measured by in situ hybridization following a 1 h period of courtship interactions with females. In this second study, courting males exhibited 40% more cells with GnRH-I in this region than did isolated control males. GnRH-immunoreactive neurons in two other diencephalic regions failed to show these courtship-induced changes. Plasma LH was not elevated after 1 or 2 h of courtship. These results demonstrate that the release of GnRH-I in the POA that is presumably responsible for courtship-induced pituitary and gonadal activation is accompanied by a rapid increase in GnRH synthesis that occurs before plasma LH levels increase. We suggest that this increase in GnRH synthesis is necessary to support the extended period of HPG axis activation that is seen in this species during the 5–10 day period of courtship and nest building activity.     

Courtship interactions stimulate rapid changes in GnRH synthesis in male ring doves

Many birds and mammals show changes in the hypothalamo-pituitary-gonadal (HPG) axis in response to social or sexual interactions between breeding partners. While alterations in GnRH neuronal activity play an important role in stimulating these changes, it remains unclear if acute behaviorally-induced alterations in GnRH release are accompanied by parallel changes in GnRH synthesis. To investigate this relationship, we examined changes in the activity of GnRH neurons in the brains of male ring doves following brief periods of courtship interactions with females. Such interactions have been previously shown to increase plasma LH in courting male doves at 24 h, but not at 1 h, after pairing with females. In the first study, males allowed to court females for 2 h had 60% more cells that showed immunocytochemical labeling for GnRH-I in the preoptic area (POA) of the hypothalamus than did control males that remained isolated from females. To determine whether an increase in GnRH gene expression preceded this increase in GnRH immunoreactivity in the POA, changes in the number of cells with detectable GnRH-I mRNA in the POA were measured by in situ hybridization following a 1 h period of courtship interactions with females. In this second study, courting males exhibited 40% more cells with GnRH-I in this region than did isolated control males. GnRH-immunoreactive neurons in two other diencephalic regions failed to show these courtship-induced changes. Plasma LH was not elevated after 1 or 2 h of courtship. These results demonstrate that the release of GnRH-I in the POA that is presumably responsible for courtship-induced pituitary and gonadal activation is accompanied by a rapid increase in GnRH synthesis that occurs before plasma LH levels increase. We suggest that this increase in GnRH synthesis is necessary to support the extended period of HPG axis activation that is seen in this species during the 5–10 day period of courtship and nest building activity.     

To be or not to be? Mating success and survival trade‐offs when switching between alternative reproductive tactics

Hormones underlie the decision of assuming a territorial or a nonterritorial role, with territorial individuals usually having higher hormonal levels than nonterritorial individuals. As a territorial status is linked to higher mating opportunities, it is unclear why animals do not keep high hormonal levels and one explanation is that this would imply survival costs. We have tested this using males of the territorial damselfly Argia emma in the field. We increased juvenile hormone (JH) levels using methoprene in both territorial and nonterritorial males and predicted that: (i) males will keep (the case of territorial males) or become (the case of nonterritorial males) territorial after hormonal increase, and (ii) there will be an increase in mating success for nonterritorial males only and an impaired survival for both male tactics. Hormonally treated males remained or became territorial but had their survival impaired compared with control groups. Also, hormonally treated, ex‐nonterritorial males increased their mating success compared with the other control, nonterritorial males. The reduced survival can be explained proximally by the energy devoted either to the enhanced aggression showed during territory defence or immune function (as detected previously in damselflies). Although nonterritorial males may increase their mating success by switching to a territorial tactic, they are possibly unable to do it naturally as JH is dietary dependent and usually nonterritorial animals are in poorer condition than territorial animals.     

Variability of GnRH secretion in two goby species with socially controlled alternative male mating tactics

Male reproductive phenotypic plasticity related to environmental-social conditions is common among teleost fish. In several species, males adopt different mating tactics depending on their size, monopolizing mates when larger, while parasitizing dominant male spawns when smaller. Males performing alternative mating tactics are often characterized by a strong dimorphism in both primary and secondary reproductive traits. According to studies on sex-changing species and on species where only one male morph is reproductively active, male alternative phenotypes are expected to vary also in gonadotropin-releasing hormone (GnRH) neurons in forebrain preoptic area (POA). Here, we compared the intra- and inter-sexual variations in number and size of GnRH neurons, along with gonads and male accessory structure investment, in two goby species, the grass goby, Zosterisessor ophiocephalus, and the black goby, Gobius niger, characterized by male alternative mating phenotypes. In both species, older and larger males defend nests, court and perform parental care, while younger and smaller ones try to sneak territorial male spawning. We found that grass goby and black goby have different patterns of GnRH expression. Grass goby presents a clear intra-sexual dimorphism in GnRH expression, related to the occurrence of alternative mating tactics, while in the black goby, only inter-sexual differences are observed. The inter- and intra-specific variability in the GnRH neurons in these two goby species is discussed in light of the differences in migratory behavior, nest type, and mating system.     

Linking alternative reproductive tactics and habitat selection in Northern chamois

In polygynous ungulates, males may achieve fertilization through the use of alternative reproductive tactics (ARTs), discrete phenotypic variations evolved to maximize fitness. ARTs are often associated with different male spatial strategies during the rut, from territoriality to female‐following. Although variation in space use patterns of rutting male ungulates is known to be largely affected by the spatial distribution of females, information on the year‐round habitat selection of alternative reproductive types is scant. Here, we investigate the seasonal variation in habitat choice of a large mammal with ARTs (territoriality and nonterritoriality), the Northern chamois Rupicapra rupicapra. Global Positioning System (GPS) data on 28 adult males were collected between February 2010 and December 2013 in the Gran Paradiso National Park (Italy) and used to fit resource selection functions to explore the ART‐specific use of key topographic features, such as elevation, aspect, and slope, and vegetation phenology expressed as NDVI values. Territorial and nonterritorial chamois profoundly differed in their habitat selection not only during the rutting season. Compared to nonterritorial males, territorial males used lower elevations in summer and autumn, preferred southern slopes in spring and summer, and used steeper areas in summer but not in winter. We found no difference in seasonal selection of NDVI values between males adopting ARTs. Our results suggest that territorial males tend to occupy warmer, lower‐food‐quality habitats in late spring and summer, whereas nonterritorial males are free to follow and exploit vegetation phenology and more favorable temperatures. Different patterns of habitat selection may reflect different trade‐offs between the optimization of energy balances throughout the year and the increase of mating opportunities during the rut in males adopting alternative reproductive tactics.     

Sex differences and hormone influences on tyrosine hydroxylase immunoreactive cells in the leopard frog

We examined sex differences in tyrosine hydroxylase immunoreactive (TH-ir) cell populations in the preoptic area (POA), suprachiasmatic nucleus (SCN), posterior tuberculum (TP), and caudal hypothalamus (Hy) in the leopard frog (Rana pipiens), in addition to the effects of natural variation in sex steroid hormones on these same populations in both sexes. All four of these populations have been shown to be dopaminergic. Gonadal sex, androgens, and estrogen all influenced TH-ir cell numbers, but in a complicated pattern of interactions. After factoring out the effects of sex steroids by multiple regression, TH-ir cell numbers in all four areas differed between the sexes, with males having a greater number of TH-ir cells. The influence of androgens and estrogen differed by region and sex of the animals. Androgens were the main influence on TH-ir cell numbers in the POA and SCN. Plasma androgen concentrations were positively correlated with TH-ir cell numbers in both areas in males. In females, androgen concentration was negatively correlated with TH-ir cell numbers in the POA; there was no significant relationship in the SCN in females. In the more caudal populations, estrogen (E2) levels were positively correlated with TH-ir cell numbers in the TP of both males and females. In the caudal hypothalamus, E2 levels were positively correlated with TH-ir cell numbers in females, but there was no significant correlation in males. The results indicate that gonadal sex imposes a baseline sex difference in the four TH-ir (dopamine) populations, resulting in a higher number of such cells in males. Individual and sex-linked differences in gonadal steroid hormones lead to variation around this baseline condition, with androgens having a greater influence on rostral populations and estrogen on caudal populations. Last, an individual's gonadal sex determines the effect that androgens and estrogen have on each population.     

The role of endogenous gonadotropin-releasing hormone in the control of luteinizing hormone and testosterone secretion in the juvenile male monkey, Macaca fascicularis

To determine what changes occur in the activity of gonadotropin-releasing hormone (GnRH) neurons during pubertal development in primate species we tested the hypotheses that there are morphologic differences between GnRH-containing neurons in juvenile versus adult monkeys, and the low activity of the reproductive axis is governed by hypothalamic GnRH release in monkeys prior to puberty. We removed the brains from 5 juvenile and 5 adult male monkeys (Macaca fascicularis) and blocked, sectioned, and prepared each hypothalamus for light microscopic immunocytochemistry for GnRH-containing cells. The distribution and number of GnRH-containing neurons were similar in adult and juvenile brains; however, GnRH-containing perikarya in adult brains were significantly larger in total cross-sectional area (200 +/- 12 vs. 169 +/- 8 micron 2, P less than 0.05) and in cross-sectional area of the cytoplasm (139 +/- 2 vs. 88 +/- 6 micron 2, P less than 0.05) than in juvenile brains. In another group of 10 juvenile male macaques, we administered an antiserum to GnRH (Fraser #94; 2 ml/kg, i.v.) and monitored the effects on plasma luteinizing hormone (LH) and testosterone concentrations. The percentage of plasma samples with detectable LH levels decreased significantly (from 26.67 +/- 8.3% to 5.3 +/- 3.4%, P less than 0.05) after GnRH antiserum administration; however, plasma testosterone concentrations (0.08 +/- 0.02 ng/ml) remained unchanged. We conclude that during pubertal maturation in primate species there is increased synthesis and release of GnRH from a population of GnRH neurons that are active prior to puberty.     

Territorial songs indicate male quality in the sac-winged bat Saccopteryx bilineata (Chiroptera, Emballonuridae)

Defense of territories in many animal species involves the advertisementof territory holder quality by acoustic signaling. In the sac-wingedbat Saccopteryx bilineata, males engage in territorial countersingingwhen reoccupying their day-roost territories in the morningand in the evening before abandoning the roost for the night.Females roost mainly in male territories, and territory holdersare reproductively more successful than nonterritorial males.In territorial songs of male S. bilineata, we distinguished6 syllable types and parameterized their acoustic properties.The analysis of 11 microsatellite loci allowed assignments ofjuveniles to their parents. Males had a higher reproductivesuccess both when they uttered more territorial songs per dayand when their long buzz syllables had a lower end frequencyof the fundamental harmonic. Long buzzes had a harsh qualitydue to a pulsation of the fundamental frequency at the syllableonset and also had the highest sound pressure level of all syllabletypes in most territorial songs. Territorial songs and especiallylong buzz syllables are thus likely to advertise territory holderquality and competitive ability.     

Relation of the pituitary gland to gonadal hormone effects on the adrenocortical 11beta-hydroxylase system in rats.

Studies were conducted to further examine the mechanisms responsible for gonadal hormone effects on the rat adrenocortical 11beta-hydroxylase system. Despite higher concentrations of cytochrome P-450 and larger 11-deoxycorticosterone (DOC)-induced difference spectra in adrenal mitochondria from females than males, no sex difference in 11beta-hydroxylase activity was observed. The pregnenolone-induced difference spectrum, indicative of cholesterol binding to cytochrome P-450, also was similar in males and females. Testosterone administration to castrated males lowered both 11beta-hydroxylase activity and mitochondrial cytochrome P-450 content. Estradiol produced the opposite effects in castrated females. However, when given to ACTH-replaced hypophysectomized rats, neither testosterone nor estradiol affected cytochrome P-450 levels or the rate of 11beta-hydroxylation. These observations, taken with the known effects of estradiol and testosterone on ACTH secretion in rats and the effects of ACTH on 11beta-hydroxylation, indicate that gonadal hormone effects on the 11beta-hydroxylase system are mediated by ACTH.