Sexual maturation in the female ferret: circumventing the gonadostat.

The purpose of this study was to examine the role of circulating 17 beta-estradiol in the regulation of pituitary gonadotropin secretion and, hence, ovarian maturation in immature female ferrets. The hypersensitive negative feedback relationship between the ovaries and the hypothalamo-pituitary axis in developing ferrets was disrupted by infusion of a specific antiserum to 17 beta-estradiol. The effect of this treatment on gonadotropin secretion and ovarian morphology was contrasted with that observed in intact age-matched control females treated with a nonimmune gamma-globulin preparation. Infusion of the antibody into intact immature ferrets caused, within 48 h, an increase in pulsatile secretion of LH to 0.67 +/- 0.06 pulses/h over that observed in intact females treated with control gamma-globulin (0.13 +/- 0.06 pulses/h). This increase in pulse frequency was similar to that observed 48 h after ovariectomy of young animals (0.70 +/- 0.12 pulses/h). Furthermore, this level of gonadotropin secretion in antibody-treated animals resulted in stimulation of antral follicle growth in ovaries of these females. Ferrets treated with specific antiserum to 17 beta-estradiol showed a significant increase in numbers of ovarian follicles greater than 0.3 mm in diameter compared to those in ovaries of females treated with control gamma-globulin. These data strongly suggest that the limiting event at puberty in the ferret is the rise in gonadotropin secretion which is allowed by the pubertal decrease in efficacy of 17 beta-estradiol to inhibit gonadotropin secretion.

A modification of the glyoxylic acid induced histofluorescence technique for demonstration of catecholamines and serotonin in tissues of Aplysia californica.

A modified glyoxylic acid technique was used to examine central and peripheral nervous tissues in Aplysia californica. In addition to confirming the distribution of catecholamines and serotonin in the central nervous system, the method demonstrated the presence of monoamines in the opaline gland and bag cell clusters where they may act as transmitters. In conjunction with electrophysiological techniques this method may be useful to identify other monoamine-containing neurons in Aplysia.

Selective effects of fetal alcohol exposure on rat thymocyte development.

The thymoproliferative response to concanavalin A (ConA) following fetal alcohol exposure (FAE) is higher than control (149%) on day 44, is lower than control (64%) by day 51, and normalizes by day 69 (88% of controls). The ontogeny of HLA-Dr and transferrin receptor (CD71) expression in response to anti-CD3 stimulation is similar among the groups, but is distinct from that of ConA proliferation. The ontogeny of glucocorticoid cytoplasmic receptor (GCCR) sites per thymocyte is also different from the ontogeny of the ConA response. The number of GCCR sites rises sharply (2.5-fold) in control rat thymocytes between days 30 and 44, and remains at that level at later time points. By contrast, the number of GCCR sites per FAE thymocytes rises nearly linearly and normalizes by day 72. Our data support the notion that prenatal alcohol exposure significantly alters thymic development and indicates that the relationship between the development of thymocyte functional responses and that of GCCR is more complex than initially hypothesized.

Effects of prenatal alcohol and pair feeding on lipopolysaccharide-induced secretion of TNF-alpha and corticosterone.

Fetal alcohol exposure (FAE) produces profound alterations in immunological and neuroendocrine functions. The present study examined the effects of FAE on the secretion of tumor necrosis factor (TNF-alpha) and corticosterone following administration of lipopolysaccharide (LPS) in normal (N) adult rats, in adult offspring of dams fed a liquid diet supplemented with ethanol (E), and in pair-fed control offspring (P). LPS-induced TNF-alpha secretion was not affected by either gender or prenatal treatment. In contrast, LPS-induced corticosterone secretion was significantly greater in female than in male rats, and at 60-min post-LPS was significantly higher in E and P, compared to N females. Ovariectomy significantly inhibited LPS-induced TNF-alpha secretion in E, but not in P and N, rats and chronic replacement with 17-beta-estradiol markedly inhibited TNF-alpha secretion in ovariectomized E and N, but not in P, rats. In contrast, ovariectomy reduced the effects of LPS on corticosterone secretion in all groups, and chronic replacement with 17-beta-estradiol reversed this effect. These findings indicate that LPS-induced secretion of corticosterone, but not TNF-alpha, is affected by prenatal manipulations and by gender. In addition, alterations in the hormonal environment in females modulate LPS-induced corticosterone secretion in all prenatal treatment groups, but differentially influence TNF-alpha secretion in rats exposed to alcohol, restricted feeding, or normal diets in utero.

Motor controls of opaline secretion in Aplysia californica.

1. Using combined morphological and electrophysiological techniques, we have identified motor neurons in the right pleural ganglion of Aplysia californica that contribute to the release of opaline from the opaline gland. 2. Three pleural ganglion neurons were found to meet the requirements for identification as opaline gland motor neurons by a) sending processes in nerve P5, which innervates the gland; b) producing contractions of the gland in the absence of central synaptic activity; and c) producing excitatory junctional potentials (EJPs) in cells making up the opaline gland itself. The neurons can be reliably located and have been designated PLR1, PLR2, and PLR3. 3. When gland contraction is measured by the change in luminal pressure, the gland response is a graded function of low-frequency spike activity in the motor neurons. 4. Presumptive EJPs recorded from opaline gland cells are reversibly decreased in size by high extracellular Mg2+ and reversibly increased in size by raising the concentration of extracellular Ca2+. These results suggest that the presumptive EJPs are chemically mediated. The presumptive EJPs show facilitation and posttetanic potentiation. 5. The identified opaline motor neurons may constitute a significant portion of the motor input to the opaline gland via nerve P5 since hyperpolarization of the cells prevents the opaline gland response elicited by right connective stimulation in vitro. 6. We have compared the properties of the opaline motor neurons with the previously identified properties of the ink motor neurons (6--9, 19). Like the ink motor neurons, the opaline motor neurons have high resting potentials, are electrically coupled, and have no spontaneous spike activity. They also receive a slow and long-lasting evoked depolarizing synaptic input, which appears to be mediated by a decreased conductance mechanism. The firing pattern of the opaline motor neurons produced by synaptic input shows the same delayed bursting pattern previously described for the ink motor neurons. 7. The biophysical properties and synaptic input to the ink motor neurons have been shown to affect the features of inking behavior (4, 6--9, 19). The opaline motor neurons share some of these biophysical characteristics and mediate a defensive behavior similar to ink release. Further comparisons of these behaviors and their underlying neural circuits may provide a better understanding of the extent to which cellular biophysical properties and patterns of synaptic input influence the features of the behaviors that individual neurons mediate.

Neurotransmitters producing and modulating opaline gland contraction in Aplysia californica.

1. Opaline release in Aplysia provides a simple model system for examining the biochemical and electrophysiological mechanisms underlying glandular secretion and its modulation. The opaline gland is a large multivesicular structure, which is innervated by at least three large identified motor neurons located within the right pleural ganglion (28). In this paper we have investigated the roles of dopamine (DA), acetylcholine (ACh), and serotonin (5-HT) in this simple neural system. 2. DA infusion produces a gland contraction that is similar to the response produced by neural activity in the previously identified opaline motor neurons. 3. The gland response to DA infusion is not affected by blocking synaptic transmission in the gland, suggesting that DA acts directly on muscle cells surrounding the gland and not through interposed interneurons. 4. In addition to its effect of producing contractions of the gland, DA enhances the size of subsequent neurally evoked gland contractions and increases the size of excitatory junctional potentials (EJPs) recorded from the opaline gland. Thus DA may have an additional modulatory role in opaline release. 5. DA antagonists such as fluphenazine and haloperidol inhibit the gland response to DA and also block the gland contraction produced by neural activity in the identified motor neurons. In addition, the DA antagonists reversibly block the EJPs recorded from the gland cells. Compounds known to block the effects of ACh or 5-HT have no effect on the dopamine-induced gland contractions, the contractions produced by firing the motor neurons, or the EJPs evoked by motor neuron stimulation. These results suggest that DA may be the neurotransmitter used by the identified opaline motor neurons. 6. ACh produces a decrease in pressure recorded from the lumen of the opaline gland that can be blocked by hexamethonium. 7. While 5-HT does not directly produce a contraction, treatment of the gland with the transmitter increases the size of subsequent gland responses produced either by DA infusion or activity in the opaline motor neurons. This enhancement has a relatively slow onset and long duration and persists for more than 15 min after the serotonin is washed out. In 60% of the experiments 5-HT also increased the size of the EJPs recorded from the opaline gland. The results suggest a modulatory role for serotonin in opaline secretion similar to the one it plays in other neural systems in Aplysia.

Adrenalectomy but not adrenal demedullation during pregnancy prevents the growth-retarding effects of fetal alcohol exposure.

Growth retardation, both in the prenatal and the early neonatal period, is a consistent feature of fetal alcohol exposure, but the mechanism by which alcohol affects growth has not been elucidated. Because other stressors--such as maternal restraint and neonatal glucocorticoid treatment--can also affect growth, we examined the effect of ethanol on pup birthweight under two experimental conditions that altered maternal adrenal function. In the first study when dams were adrenalectomized and given low replacement doses of dexamethasone, the ethanol-exposed offspring of the adrenalectomized dams had birthweights similar to those of dams maintained on regular lab chow diets. In a second study, we found that maternal adrenal demedullation did not alter the reduction in birthweight produced by fetal ethanol exposure. The results suggest that the effects of ethanol on fetal growth may be mediated in part through ethanol-induced changes in the function of the maternal adrenal cortex.

Fetal alcohol exposure augments the blunting of tumor necrosis factor production in vitro resulting from in vivo priming with lipopolysaccharide in young adult male but not female rats.

We previously reported altered responses of thymocytes and splenocytes to mitogen stimulation in fetal alcohol-exposed (FAE) male Sprague-Dawley rats. We also reported enhanced neuroendocrine responses to stressful stimuli in these animals. The experiments we describe herein aimed at testing whether young adult FAE rats manifest a notable dysregulation in the neuroendocrine-immune response to pathogen administration. We tested the effect of in vivo priming of the animal with a low dose of endotoxin [lipopolysaccharide (LPS), 5 micrograms/kg], considered to be suboptimal from the perspective of mounting detectable levels of circulating monokines several hours after administration, upon the production of immunoreactive tumor necrosis factor (TNF-alpha) in response to a further in vitro challenge of peripheral blood mononuclear cells with 2.5 micrograms/ml of LPS 90 min after priming. We show that the response to the LPS pathogen in vitro after priming is significantly blunted (p < 0.01) in male rats exposed prenatally to alcohol, compared with control male animals. FAE female rats and FAE ovariectomized female rats do not show significant differences in the priming response, compared with control animals. We also show that there is no correspondence between plasma corticosterone levels and TNF-alpha production after priming in any of the groups tested.