Characterization and properties of steroid binding protein in Bufo arenarum serum

Serum steroid binding properties of mature Bufo arenarum females were studied. Binding data obtained using charcoal adsorption assay and equilibrium dialysis methods indicates a single protein, named Bufo arenarum sex binding protein (Ba SBP), which binds 5 α-dihydrotestosterone (DHT), testosterone (T), and estradiol-17β (E₂) with high affinity (10⁷ M^?1 – 10⁸ M^?1) and fair capacity (10^?6 M). Scatchard plot analysis demonstrated the coexistence of two binding sites. Ba SBP has a sedimentation coefficient of 5.2 S in sucrose gradient centrifugation in low salt and under steady-state conditions. The specificity of this protein, determined by competitive binding experiments, is comparable to human SBP. DHT and T bind with higher affinity than E₂. Estriol and estrone competed poorly, while diethylstilbestrol and C₂₁ steroids did not compete. The binding capacity of this protein is under estrogenic control. © 1994 Wiley-Liss, Inc.     

Advances in understanding neuronal somatostatin receptors

It has long been considered that somatostatin acts as a neuromodulator in the mammalian central nervous system but its precise physiological roles remain elusive. Early studies to identify somatostatin-binding sites revealed a widespread heterogeneous pattern, especially in the CNS. More recently, a family of somatostatin receptors have been identified, of which five genes (sst_1–5) have been cloned. In this review, we discuss current data describing the localisation of the five receptor types. Recent progress in understanding their function has been made using high-affinity, selective receptor ligands and transgenic animal technology. Finally, the therapeutic potential for somatostatin receptor-selective compounds as analgesics is considered.     

Hormonally mediated epigenetic changes to steroid receptors in the developing brain: Implications for sexual differentiation

The establishment of sex-specific neural morphology, which underlies sex-specific behaviors, occurs during a perinatal sensitive window in which brief exposure to gonadal steroid hormones produces permanent masculinization of the brain. In the rodent, estradiol derived from testicular androgens is a principal organizational hormone. The mechanism by which transient estradiol exposure induces permanent differences in neuronal anatomy has been widely investigated, but remains elusive. Epigenetic changes, such as DNA methylation, allow environmental influences to alter long-term gene expression patterns and therefore may be a potential mediator of estradiol-induced organization of the neonatal brain. Here we review data that demonstrate sex and estradiol-induced differences in DNA methylation on the estrogen receptor α (ERα), estrogen receptor β (ERβ), and progesterone receptor (PR) promoters in sexually dimorphic brain regions across development. Contrary to the overarching view of DNA methylation as a permanent modification directly tied to gene expression, these data demonstrate that methylation patterns on steroid hormone receptors change across the life span and do not necessarily predict expression. Although further exploration into the mechanism and significance of estradiol-induced alterations in DNA methylation patterns in the neonatal brain is necessary, these results provide preliminary evidence that epigenetic alterations can occur in response to early hormone exposure and may mediate estradiol-induced organization of sex differences in the neonatal brain.     

Altered patterns of filopodia production in CHO cells heterologously expressing zebra finch CB1 cannabinoid receptors

Recent findings indicate that cannabinoid-altered vocal development involves elevated densities of dendritic spines in a subset of brain regions involved in zebra finch song learning and production suggesting that cannabinoid receptor activation may regulate cell structure. Here we report that activation of zebra finch CB₁ receptors (zfCB₁, delivered by a lentivector to CHO cells) produces dose-dependent biphasic effects on the mean length of filopodia expressed: Low agonist concentrations (3 nM WIN55212-2) increase lengths while higher concentrations reduce them. In contrast, treatment of zfCB₁-expressing cells with the antagonist/inverse agonist SR141716A causes increases in both mean filopodia length and number at 30 and 100 nM. These results demonstrate that CB₁ receptor activation can differentially influence filiopodia elongation depending on dose, and demonstrate that manipulation of cannabinoid receptor activity is capable of modulating cell morphology.     

Cannabinoid mitigation of neuronal morphological change important to development and learning: Insight from a zebra finch model of psychopharmacology

Normal CNS development proceeds through late-postnatal stages of adolescent development. The activity-dependence of this development underscores the significance of CNS-active drug exposure prior to completion of brain maturation. Exogenous modulation of signaling important in regulating normal development is of particular concern. This mini-review presents a summary of the accumulated behavioral, physiological and biochemical evidence supporting such a key regulatory role for endocannabinoid signaling during late-postnatal CNS development. Our focus is on the data obtained using a unique zebra finch model of developmental psychopharmacology. This animal has allowed investigation of neuronal morphological effects essential to establishment and maintenance of neural circuitry, including processes related to synaptogenesis and dendritic spine dynamics. Altered neurophysiology that follows exogenous cannabinoid exposure during adolescent development has the potential to persistently alter cognition, learning and memory.     

Altered patterns of filopodia production in CHO cells heterologously expressing zebra finch CB1 cannabinoid receptors

Recent findings indicate that cannabinoid-altered vocal development involves elevated densities of dendritic spines in a subset of brain regions involved in zebra finch song learning and production suggesting that cannabinoid receptor activation may regulate cell structure. Here we report that activation of zebra finch CB₁ receptors (zfCB₁, delivered by a lentivector to CHO cells) produces dose-dependent biphasic effects on the mean length of filopodia expressed: Low agonist concentrations (3 nM WIN55212-2) increase lengths while higher concentrations reduce them. In contrast, treatment of zfCB₁-expressing cells with the antagonist/inverse agonist SR141716A causes increases in both mean filopodia length and number at 30 and 100 nM. These results demonstrate that CB₁ receptor activation can differentially influence filiopodia elongation depending on dose, and demonstrate that manipulation of cannabinoid receptor activity is capable of modulating cell morphology.     

Single-cell responses in the ectostriatum of the zebra finch

The responses of single cells to computer-generated spots, bars, gratings, and motion-in-depth stimuli were studied in the ectostriatum and the adjacent neostriatum of the zebra finch, Taeniopygia guttata. No differences in neuronal properties could be detected between ectostriatum and neostriatum. The receptive fields of ectostriatal neurons are large, often extending over the entire visual field of the contralateral eye, and have oddly defined borders. The centers of the receptive fields, located in the foveal region, generally yielded better responses than the periphery, and exhibited different subdivisions. Neurons responded selectively to moving bars, preferring those moving parallel to their longest axis. An SDO (sensitivity, direction, orientation) analysis of responses to sinusoidal gratings showed that all orientations were equally represented by ectostriatal neurons, while there was a slight preference for forward and upward movements. The neurons also showed preferences for gratings of a particular spatial frequency, and responded vigorously to stimuli moving towards the eye (looming). Our results indicate that the ectostriatum is involved in both detecting displacement of the surround and in stimulus identification. By comparison with results obtained in the extrastriate cortex of mammals, it is concluded that the homology of the ectostriatum with the extrastriate cortex of mammals, which was proposed on the basis of hodological findings, is supported by our study.Abbreviations Di index of directionality - HW HH half-width at half-height - PLLS posterolateral lateral suprasylvian cortex - PMLS posterior medial lateral suprasylvian area - PSTH poststimulus time histogram - SDO sensitivity, direction, orientation     

Caffeine analogs: effects on ryanodine-sensitive calcium-release channels and GABAA receptors

1. Caffeine at 0.3–10 mM enhanced the binding of [³H]ryanodine to calcium-release channels of rabbit muscle sarcoplasmic reticulum. A variety of other xanthines were as efficacious as caffeine or nearly so, but none appeared markedly more potent.2. Caffeine at 1 mM markedly inhibited binding of [³H]diazepam to GABA_A receptors in rat cerebral cortical membranes.3. Other xanthines also inhibited binding with certain dimethylpropargylxanthines being nearly fivefold more potent than caffeine.4. Caffeine at 1 mM stimulated binding of [³⁵S]TBPS to GABA_A receptors as did certain other xanthines.5. The dimethylpropargylxanthines had little effect. 1,3-Dipropy1-8-cyclopentylxan- thine at 100 M had no effect on [³H]diazepam binding, but markedly inhibited [³⁵S]TBPS binding.6. Structure–activity relationships for xanthines do differ for calcium-release channels and and for different sites on GABA_A receptors, but no highly selective lead compounds were identified.     

Testosterone implants alter the frequency range of zebra finch songs

To investigate whether changes in testosterone alter the frequency range in which a zebra finch produces song, we assigned male zebra finches to two groups, one of which received testosterone implants and the other empty silastic capsule implants. We then recorded songs up to 52 weeks after the surgery and measured frequency changes in the fundamental frequencies of arbitrarily chosen harmonic stacks in the songs of birds in either group. We found statistically significant decreases after 5 weeks in the songs of the testosterone-treated birds. No changes were found in the fundamental frequencies of the control group. The frequency change remained after the apparent effects of the testosterone implants ended. These data show that high levels of testosterone can lower the frequencies of elements in zebra finch songs.     

Delayed behavioral effects of postnatal exposure to corticosterone in the zebra finch (Taeniopygia guttata)

Early developmental conditions can significantly influence the growth and survival of many animal species. We studied the consequences of exposure to corticosterone (CORT), a stress hormone, during the nestling stage on two behavioral traits (neophobia, social dominance) measured when the birds had reached independence. Nestling zebra finches (Taeniopygia guttata) were exposed twice daily to exogenous CORT via oral administration for a 12-day period up until fledging. Experimental CORT administration depressed nestling growth rates, confirming results previously obtained in this species. Our data on neophobic behavior revealed a significant interaction between sex and treatment, with CORT-dosed males showing reduced latencies to approach a novel object, while there was little effect of corticosterone treatment on female neophobia. There was no significant effect of age (30 or 50 days), however, there was a non-significant trend towards an interaction between treatment and age, with neophobia increasing with age in the CORT-dosed birds, but decreasing in controls. At 50 days of age previous exposure to corticosterone resulted in reduced success in competitions for a non-food-based resource (a perch) in both sexes. There were no effects of brood size on any behavioral traits measured here, but this may be due to the small range in brood size used. Our results show that elevated levels of stress hormones during postnatal development can have significant effects on important behavioral traits, i.e., neophobia and dominance. Moreover, they confirm the importance of rearing conditions in shaping adult phenotypes.     

Synthesis and in vivo evaluation of 11-substituted estradiol derivatives as anti-implantation agents

Synthesis of 11-substituted estradiol derivatives (12–17) has been carried out by the Grignard reaction with alkyl, allyl, and benzyl halides on 17β-hydroxy-3-methoxy-11-oxo-estra-1,3,5(10),8(9)-tetraene (10). The novel compounds (10 and 12–17) were evaluated for their preliminary post-coital contraceptive (anti-implantation) activity in Sprague–Dawley rats. The tested compounds were administered orally and showed significant anti-implantation activity. Compound 13 is the most potent compound in the series which showed 100% contraceptive efficacy at 1.25 mg kg⁻¹.     

Characterization of insect neuronal octopamine receptors (OA3 receptors)

Octopamine receptors in the nervous tissue of insects were investigated using a ligand-receptor assay with [³H]NC-5Z or [³H]octopamine as the radioligands. Both ligands recognized a homogenous class of binding sites with the properties of an octopamine receptor. This receptor has been characterized pharmacologically. Both high-affinity agonists (e.g. NC 7, K₁=0.3 nM) and antagonists (e.g. maroxepine, K₁=1.02 nM) were investigated. The neuronal octopamine receptor belongs to a receptor class that can easily be distinguished from peripheral octopamine receptors. Initial investigations of the localization of octopamine receptors within the insect nervous tissue show the greatest receptor density in the optic lobes.     

Costly steroids: egg testosterone modulates nestling metabolic rate in the zebra finch

The transfer of non-genetic resources from mother to the offspring often has considerable consequences for offspring performance. In birds, maternally derived hormones are known to influence a variety of morphological, physiological and behavioural traits in the chick. So far, the range of these hormonal effects involves benefits in terms of enhanced growth and competitive ability as well as costs in terms of immunosuppression. However, since yolk hormones can enhance growth and begging activity, high levels of these hormones may also involve energetic costs. Here, we show experimentally that elevated levels of prenatal testosterone increase resting metabolic rate in nestling zebra finches (Taeniopygia guttata). Surprisingly, however, elevation of prenatal testosterone did not result in higher growth rates and, thus, differences in resting metabolism do not seem to be linked to nestling growth. We conclude that apart from immunosuppressive effects, high levels of egg steroids may also entail costs in terms of increased energy expenditure.     

Effects of testosterone and corticosterone on immunocompetence in the zebra finch

The original immunocompetence handicap hypothesis (ICHH) suggested that testosterone has a handicapping effect in males by both promoting the development of sexual signals and suppressing immune function. A modified version, the stress-linked ICHH, has recently proposed that testosterone is immunosuppressive indirectly by increasing production of corticosterone. To test both the original and stress-mediated versions of the ICHH, we implanted male zebra finches taken from lines selected for divergent maximum stress-induced levels of corticosterone (high, low and control) with either empty or testosterone-filled implants. Their humoral and cell-mediated immune responses were then assessed by challenge with diphtheria:tetanus vaccine and phytohemagglutinin respectively. We found no effect of the hormone manipulations on either PHA or tetanus antibody responses, but found a significant interaction between titers of both testosterone and corticosterone on diphtheria secondary antibody response; antibody response was greatest in individuals with high levels of both hormones. There was also a significant interactive effect between testosterone treatment group and corticosterone titer on body mass; the body mass of males in the elevated testosterone treatment group decreased with increasing corticosterone titer. These results suggest that, contrary to the assumption of the stress-mediated version of the ICHH, high plasma levels of corticosterone are not immunosuppressive, but are in fact immuno-enhancing in the presence of high levels of plasma testosterone. Equally, the central assumption of the ICHH that testosterone is obligately immunosuppressive is also not supported. The same individuals with the highest levels of both hormones and consequently the most robust antibody response also possessed the lowest body mass.     

Localization of steroid hormone receptors in the apocrine sweat glands of the human axilla

The apocrine axillary glands, regarded as pheromone-producing scent glands, do not begin to function until puberty. Accordingly, sex hormones should have an impact on their activity, and the present study was designed to investigate the localization of androgen receptor (AR) and estrogen receptors (ER and ER) in those glands. Strong nuclear immunoreactivity for AR and ER was found in the secretory epithelium. In AR especially, staining intensity was correlated with the height of the epithelium with more intense immunoreactivity in tall segments. Since the lower epithelium has been considered inactive or resting, our results suggest a correlation between steroid-receptor expression and secretory activity. Androgens are known to upregulate the cholesterol biosynthesis, and cholesterol may be used as precursor for pheromones. Accordingly, the results of this study establish a possible link between steroid hormone action and induction of pheromone production in the apocrine axillary glands.     

Glucocorticoid receptors: relations between steroid binding and biological effects

Steroid binding has been studied in cytoplasmic extracts of cultured rat hepatoma cells to investigate the mechanism of enzyme induction by glucocorticoids. The affinity of inducer steroids for the specific receptors contained in the extracts is directly related to the potency of these steroids as inducers of tyrosine amino-transferase. The ability of anti-inducer steroids to compete with inducers for binding is similar to their ability to inhibit induction. Furthermore, the affinity of an anti-inducer for the receptors can be predicted from its ability to inhibit inducer binding. These and other correlations allow distinction between the specific cytoplasmic receptors and a number of other molecules, includingplasma transcortin, which also bind glucocorticoid hormones.