Endocrine disruption in sexual differentiation and puberty. What do pseudohermaphroditic polar bears have to do with the practice of pediatrics?

What do pseudohermaphroditic polar bears and girls with premature breast development have in common? Hormones. Sexual differentiation and the initiation of secondary sexual characteristics, such as breast growth, are both under the control of the sex hormones estrogen and androgen. Abnormal differentiation of the internal or external genitalia in bears and early onset of breast development in girls also may have a common element--exposure to environmental hormones.

Expression of mu-opioid receptor mRNA in the medial preoptic area of juvenile rats.

Previous studies indicate that the latency to initiate parental behavior in both male and female rats increases with age; weanling (21 days old) rats display parental behavior 0-2 days after exposure to newborn pups, while older juveniles (30 days old) require 5-6 days of pup exposure before they express the behavior. Furthermore, activation of mu-opioid receptors inhibits parental behavior in juvenile and adult rats. We hypothesized that the age-related increase in behavioral latency could be modulated by the induction of mu-receptor expression in the medial preoptic area (MPOA), a region in which mu-receptors regulate parental behavior. In situ hybridization histochemistry was used to measure mu-receptor mRNA expression in the MPOA of male and female Sprague-Dawley rats that were 21, 24, 27, 30, or 33 days old. Using autoradiographic film analysis, we observed that neurons within part of the MPOA expressed very dense mu-receptor mRNA. Comparison of mRNA distribution with histological boundaries indicated that neurons within the medial preoptic nucleus (MPN), excluding the central part, exhibited the highest density of mu-receptor mRNA within the MPOA. High densities of mu-receptor mRNA extended dorsolaterally and caudally from the MPN toward the bed nucleus of the stria terminalis. MPN mu-receptor mRNA expression was not altered with age and no sex difference was observed. The dense presence of mu-receptor mRNA in the MPN suggests that ample substrate exists on which mu-receptor ligands could modulate the latency to begin parental behavior in juvenile rats, but such behavioral expression apparently is not mediated by a change in mu-receptor mRNA production.

Vocal control region sizes of an adult female songbird change seasonally in the absence of detectable circulating testosterone concentrations.

Previous research established that in several species of seasonally breeding oscine birds, brain areas [vocal control regions (VCRs)] that control vocal behavior learning and expression exhibit seasonal plasticity, being larger during than outside the reproductive period. In adult males, this seasonal decrease correlates with circulating testosterone (T) concentrations. VCRs contain androgen receptors and T plays an important role in neural plasticity and in the control of singing behavior. In behaviorally dimorphic species, VCRs are larger in males than females and change seasonally also in females, but the dependency of these changes on circulating T levels in females has not been established. In free-living adult dark-eyed juncos (Junco hyemalis), a species in which females do not normally sing, the sizes of three VCRs (high vocal center, robust nucleus of the archistriatum, and Area X) were larger in males than females and decreased between summer and fall in both sexes. In males, this decrease was associated with changes in circulating T concentrations. Females, however, had on average undetectable T levels throughout the breeding season. Seasonal changes in VCR volumes in adult females may depend on very low (below detection limit) circulating T concentrations, on nonandrogenic plasma steroids, on androgen (or androgen metabolites) produced in brain tissues, and/or on nonsteroidal factors such as photoperiod or social interactions with conspecific birds.

Age- and sex-related differences in opioid receptor densities in the songbird vocal control system.

Avian vocal control regions of adult male songbirds contain opioid peptides and receptors, suggesting that opioids play a role in avian vocal behavior control. In a previous study, we found no difference in opioid receptor densities in singing versus nonsinging adult male dark-eyed juncos (Junco hyemalis), leading us to hypothesize that opioids are not involved in controlling song production. To assess whether opioids may be involved in other aspects of vocal behavior, we used quantitative in vitro autoradiography to compare mu and delta opioid receptor densities in vocal control regions of singing adult males with those of adult females and adolescent (about 3 months old) males and females. We found mu and delta receptors in all vocal control regions measured. Adolescents had significantly higher opioid receptor densities than did adults in area X (delta), robust n. of the archistriatum (delta and mu), and n. intercollicularis (mu), suggesting a developmental role for opioids in the vocal control system. Based on opioid roles in other animal models, we propose that opioids may be involved in song learning, auditory processing, and/or vocal control system development.

Photoperiod and testosterone independently affect vocal control region volumes in adolescent male songbirds.

Previously, we found that, unlike adults, adolescent male dark-eyed juncos (Junco hyemalis) maintained large Area X volumes despite having low plasma testosterone concentrations. Other studies indicate that photoperiod may act independently of testosterone to modulate vocal control region (VCR) volumes in adult songbirds. In the present study, we investigated the effects of testosterone and photoperiod on the volumes of four VCRs in adolescent male juncos. To test the hypothesis that VCR volumes in these males are testosterone independent, we treated birds exposed to short days with testosterone and later compared their VCR volumes with those of birds exposed to short days without testosterone. To examine whether photoperiod alone could affect VCR volumes independent of testosterone, we measured these volumes in photorefractory birds exposed to long photoperiod without testosterone. Administering testosterone induced singing, yet increased the volume of only one VCR, the robust nucleus of the anterior neostriatum (RA). In contrast, long photoperiod increased several VCR volumes (Area X, higher vocal center, and RA) despite low testosterone levels, but did not induce singing. Our results suggest a limited role for testosterone, but an important role for photoperiod, in controlling VCR volumes in adolescent male juncos. In addition, the results demonstrate that singing behavior can be induced in adolescent males without a concomitant increase in most VCR volumes.

Androgen control of vocal control region volumes in a wild migratory songbird (Junco hyemalis) is region and possibly age dependent.

Previous laboratory studies have shown that photoperiodic adult songbirds experience seasonal variations in singing frequency that correlate with plasma androgen levels, as well as changes in the brain regions that control singing (vocal control regions). The present study investigates naturally occurring seasonal changes in the sizes of these regions in a wild migratory species (dark-eyed junco, Junco hyemalis), with samples from adolescence to post-breeding fall migration. In adult males, the volumes of the vocal control regions area X and the higher vocal center (HVC) were large during the breeding season when birds were singing and androgen levels were high, and decreased in size after the breeding season when singing had stopped and androgen levels were low. HVC volume in adolescent males caught in the fall (no singing), when plasma androgen levels were low, was smaller than in breeding adults, thereby following the seasonal pattern of change in plasma androgen levels. In adolescent males, however, area X volume was the same as in breeding adults. Thus, area X size in adolescent male juncos may be testosterone independent. The seasonal pattern of robust nucleus of the archistriatum volume was similar to that of the HVC. The volumes of neither the magnocellular nucleus of the anterior neostriatum nor the nucleus rotundus, a control region, differed seasonally. Castration of breeding adult males caused both area X and HVC volumes to decrease compared to castrated controls with testosterone replacement, indicating that maintenance of these two region volumes is testosterone dependent in adults.

Autoradiographic localization of opioid receptors in vocal control regions of a male passerine bird (Junco hyemalis).

Previous studies have found opioid peptide-like immunoreactivity in avian vocal control regions, but whether these regions contain receptors for opioid peptides has not been examined. To address this question, we used quantitative in vitro autoradiography to determine the anatomical distribution and to measure the densities of mu, delta, and kappa opioid receptors in vocal control regions (area X, higher vocal center, and nucleus intercollicularis) of adult male dark-eyed juncos (Junco hyemalis). To evaluate whether opioid receptor densities in these regions depend on the activity of the reproductive system, we also measured these densities in birds collected during the spring, summer, and fall. We found area X, the higher vocal center, and nucleus intercollicularis to contain the three receptor types under study, but opioid receptor densities did not vary seasonally in any of these regions. The presence of specific opioid receptors in avian vocal control regions suggests the participation of opioids in the control of vocal behavior. This participation may consist of short-term (e.g., auditory processing) and/or long-term (e.g., neuronal plasticity) influences.

Identification, partial characterization, and hypothalamic distribution of kappa, mu, and delta opioid receptors in a passerine songbird (Junco hyemalis).

Brain tissues obtained from a passerine songbird (dark-eyed junco, Junco hyemalis) were used to identify and partially characterize central opioid receptors. We found that [3H]EKC (putative kappa ligand), [3H]DAMGO (putative mu ligand), and [3H]DPDPE and [3H]pCl-DPDPE (two putative delta ligands) bind to brain tissue preparations specifically, in a time-dependent fashion, and with a high affinity (Kd's < or = 5 nM). Binding sites are present at low concentrations (Bmax < 120 fmol/mg protein), and they are pharmacologically selective. In vitro autoradiography studies revealed a high density of delta receptors in hypothalamic regions (ventromedial and lateral hypothalamus) that regulate feeding behavior. Together with previous studies, these observations suggest that the central influence of opioids on avian food consumption depends on mechanisms located in hypothalamic regions.

Chromatographic-fluorometric analysis of antileprotic sulfones.

Modifications to the power supply system of a spectrophotofluorometer are described. These modifications stabilize the output of the xenon are lamp and permit the determination of nanogram quantities of antileprotic sulfones. The sulfones are removed from plasma by a single extraction with ethyl acetate, then separated by high-pressure liquid chromatography on silica, and detected in the effluent by their fluorescence. The method is specific, rapid, and reproducible.