Multicomponent mutual diffusion in the warm, dense matter regime.

We present the formulation, simulations, and results for multicomponent mutual diffusion coefficients in the warm, dense matter regime. While binary mixtures have received considerable attention for mass transport, far fewer studies have addressed ternary and more complex systems. We therefore explicitly examine ternary systems utilizing the Maxwell-Stefan formulation that relates diffusion to gradients in the chemical potential. Onsager coefficients then connect the macroscopic diffusion to microscopic particle motions, evinced in trajectories characterized by positions and velocities, through various autocorrelation functions (ACFs). These trajectories are generated by molecular dynamics (MD) simulations either through the Born-Oppenheimer approximation, which treats the ions classically and the electrons quantum-mechanically by an orbital-free density-functional theory, or through a classical MD approach with Yukawa pair-potentials, whose effective ionizations and electron screening length derive from quantal considerations. We employ the reference-mean form of the ACFs and determine the center-of-mass coefficients through a simple reference-frame-dependent similarity transformation. The Onsager terms in turn determine the mutual diffusion coefficients. We examine a representative sample of ternary mixtures as a function of density and temperature from those with only light elements (D-Li-C, D-Li-Al) to those with highly asymmetric mass components (D-Li-Cu, D-Li-Ag, H-C-Ag). We also follow trends in the diffusion as a function of number concentration and evaluated the efficacy of various approximations such as the Darken approximation.

Endogenous opioids participate in the regulation of the hypothalamus-pituitary-luteinizing hormone axis and testosterone's negative feedback control of luteinizing hormone.

Two narcotic antagonists, naloxone and naltrexone, significantly elevated serum LH levels in male rats within minutes after their sc injection. The peak increase in serum LH occurred 20 min after the injection. Naloxone increased LH levels up to a dose of 1 mg/kg, after which no further increases were found. A dose of 0.35 mg/kg produced a half-maximal response. The exogenous opioid morphine blocked the increase in LH produced by naloxone in a dose-dependent fashion, suggesting that the specific receptor-blocking effects of the antagonist could account for its enhancement of serum LH levels. The locus of action of naloxone within the hypothalamic-pituitary-LH axis appeared to be at the level of the hypothalamus since the drug had no effect on LHRH-stimulated release of LH by the anterior pituitary and did not block dihydrotestosterone's suppression of pituitary LH release in vitro. Naloxone also prevented testosterone's negative feedback inhibition of serum LH in the castrated male rat. The results of these studies suggest that endogenous opioids exist in brain tissue which normally inhibit activity in the hypothalamic-pituitary-LH axis and participate in the androgen-dependent feedback control of LH elaboration by this axis.

Effects of morphine and methadone on serum testosterone and luteinizing hormone levels and on the secondary sex organs of the male rat.

The effects of morphine and methadone on the endocrine control of the male rat's sexual function were examined. The results indicate that these narcotics markedly reduce the structural and functional integrity of the secondary sex organs by producing a pronounced reduction in serum testosterone levels. Serum levels of luteinizing hormone (LH) were not detectable in narcotic-treated animals, whereas serum levels of the follicle stimulating hormone (FSH) were unaltered. On the basis of these observations, it seems reasonable to conclude that the narcotics inhibit the secretion of LH, by an action either in the hypothalamus (e.g., suppression of LH-releasing hormone) or directly in the pituitary gland, which leads to a reduction in serum testosterone levels and a subsequent reduction in the wet-tissue weight and secretory activity of the secondary sex organs.

Paternal alcohol consumption in the rat impairs spatial learning performance in male offspring.

Pubescent (30 day old) male rats were maintained on an alcohol liquid diet containing 35% ethanol-derived calories (ALC) for 39 days or were pairfed an isocaloric control diet (PF). The concentration of alcohol in the diet was gradually increased to permit adaptation, then stabilized and then gradually tapered to prevent an alcohol withdrawal syndrome. Following a drug-free period (2 weeks), the males were mated with nontreated females. Offspring were evaluated on several developmental indices and on various learning/memory tasks to assess functional deficits in adulthood. Offspring sired by ALC-treated males did not differ from the offspring of PF males on several developmental parameters including body weights, when developmental landmarks appeared, or on tests of sensorimotor development. As adults, male offspring groups did not differ on tests of activity or on an object exploration/recognition task. However, male offspring of ALC-treated males demonstrated impaired acquisition performance (days and errors to criterion) on a win-shift spatial discrimination in an eight-arm radial maze and on a win-stay discrimination (days to criterion) conducted in a T-maze at a later age. The radial maze results were replicated in a subsequent experiment using different groups of rats.

Morphine exerts testosterone-like effects in the hypothalamus of the castrated male rat.

Previous research has indicated that endogenous opioids participate in the regulation of activity in the hypothalamic-pituitary-luteinizing hormone (LH) axis and mediate the negative feedback control exerted by testosterone. If this assumption is correct, then two predictions can be made. First, the effects of testosterone should be competitively inhibited by narcotic antagonists; and, second, opiates should mimic the acute and chronic effects of testosterone in the castrated male rat. The results of the present investigations support both of these predictions. We found that naloxone competitively antagonized the depressive effects of testosterone on serum LH in the castrated rat and, conversely, that testosterone competitively antagonized the LH-releasing properties of naloxone. In addition, morphine and testosterone both depressed serum LH levels in a dose-dependent fashion in the acutely castrated animal. Moreover, morphine was just as effective as testosterone in reversing the castration-induced fall in hypothalamic-LH-releasing hormone (LH-RH), which occurs in the chronically castrated male rat. On the other hand, morphine failed to reverse the long-term changes in pituitary LH content and increase in serum LH, which is consistent with prior observations that morphine affects only the hypothalamic aspect of the hypothalamic-pituitary-LH axis in the male rat. These results, thus, support the concept that an as yet unidentified opioid-containing neuronal system regulates activity in the hypothalamic-pituitary-LH axis and mediates the effects of testosterone on this axis.

Exogenous and endogenous opioid-induced enhancements of naloxone's effects on serum luteinizing hormone levels in the male rat.

We have previously shown that brief periods of exposure to opiate alkaloid drugs markedly enhance the subsequent effects of the opiate antagonist, naloxone, on serum luteinizing hormone (LH) levels in the male rat. In the present studies, we have found that this phenomenon is not simply a property of opiate drugs, but can be produced by a metabolically stable analog of an endogenously occurring opioid peptide, methionine enkephalin (FK 33-824). These findings suggest that alterations in the sensitivity of those opioid receptors involved in LH-releasing hormone (LHRH) generated in our experimental paradigm may occur under in vivo conditions, particularly since it now appears that endogenous opioids are released in an episodic manner like most neurotransmitter/neuromodulators. We also attempted to more fully characterize the factors responsible for the development of opiate-induced enhancements of naloxone's effects on LH. We found that this effect was produced only by those doses of morphine which initially suppressed serum LH levels, followed by a "rebound" increase in the gonadotropin 6-8 h later. A modest facilitation of LHRH-evoked increases in serum LH was also observed, but our data suggest that this represents only a minor component of opiate-induced enhancements of naloxone's effects. These data indicate that hypothalamic or suprahypothalamic sites are the major loci involved, but no differences in the uptake or regional distribution of naloxone in brain have been previously found, as a function of morphine pretreatment, nor were we able to demonstrate any alterations in opiate binding sites in the hypothalamus or whole brain. Thus, the mechanisms involved in this effect remain unclear.

Characterization and possible opioid modulation of N-methyl-D-aspartic acid induced increases in serum luteinizing hormone levels in the developing male rat.

It has been previously reported that the excitatory amino acid, N-methyl-D-aspartic acid (NMDA), elicits prompt increases in serum luteinizing hormone (LH) levels in young male rats. The present studies were carried out to determine whether the effects of NMDA on LH were mediated by the release of LHRH from the hypothalamus. We also examined whether NMDA-sensitive neuronal pathways interacted with the endogenous opioid system regulating LHRH release and the ontogeny of NMDA-evoked increases in serum LH. We found that the age-response curve for NMDA-induced increases in LH was an inverted U; at early ages (10 and 15 days) the amino acid was marginally effective in increasing LH levels, it became maximally effective from post-natal days 20-40 and thereafter rapidly lost its efficacy such that it was virtually inactive in adult animals. Dose-response curves revealed that adult animals were more than 10-fold less sensitive to NMDA than their younger counterparts. Our studies also demonstrated that NMDA increased LH via a direct effect on the hypothalamic release of LHRH since a potent LHRH antagonist competitively inhibited the effects of NMDA. Finally, we observed that morphine competitively inhibited the effects of NMDA on LH release, suggesting a relationship between NMDA-sensitive neuronal pathways and those endogenous opioid-containing systems which are known to regulate LH release.

Testosterone does not influence opiate binding sites in the male rat brain.

It has been reported previously that castration produces testosterone-reversible increases in the density of 3H-naltrexone binding sites in the male rat brain. Unfortunately, we were unable to replicate these observations in a comprehensive series of studies. Specifically, we found that castration failed to produce changes in the Kd or Bmax of opiate binding sites in whole male rat brain, or in the hypothalamus, utilizing 3H-dihydromorphine (a mu receptor ligand), 3H-D-alanine, D-leucine enkephalin (delta) or 3H-naltrexone (ubiquitous). Furthermore, we found that the relative proportion of mu and delta binding sites in brain was unchanged by castration. The reasons for the discrepancy between the present results and those previously reported are unclear, but it appears that the provocative hypothesis that testosterone influences opioid receptors in brain must be carefully reevaluated.

Inhibition of the morphine withdrawal syndrome by a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester.

The hypothesis that an arginine-nitric oxide (NO) synthase-NO system mediates the morphine abstinence syndrome was tested in adult male rats implanted subcutaneously for 3 days with one morphine (75 mg) pellet followed by naloxone-precipitated withdrawal (0.5 mg/kg). Injection with a NO synthase inhibitor, NG-nitro-L-arginine methyl ester (NAME, 100 mg/kg subcutaneous), shortly before naloxone-induced withdrawal significantly inhibited abstinence signs by 25-80%. Continuous infusion of NAME via subcutaneous osmotic pumps during the development of morphine physical dependence and during naloxone-precipitated withdrawal also inhibited morphine abstinence signs. In addition, treatment with isosorbide dinitrate, a NO donor, induced a quasi morphine-abstinence syndrome (QMAS) that was significantly suppressed by implantation of a morphine pellet 3 days before isosorbide dinitrate treatment. These results indicate that NO mediates part of the expression of the morphine abstinence syndrome.

Enhancement of opiate-induced depressions in serum luteinizing hormone levels by the prior administration of naloxone in the male rat.

The effects of naloxone pretreatment on opiate agonist-induced depressions in serum luteinizing hormone (LH) levels were examined in male rats. Our results demonstrated a pronounced enhancement of morphine's actions 6 hours after the administration of naloxone (0.5 mg/kg). This effect was characterized by a 10 fold reduction in the ED50 (1.26 mg/kg versus 0.13 mg/kg in saline- and naloxone-pretreated rats, respectively) and much greater depressions in serum LH levels at each dose of morphine. The actions of naloxone were not confined to morphine, since similar increased potencies were found for opioid agonists with selectivity for a variety of opioid receptor subtypes. Because naloxone did not alter the uptake of subsequently administered morphine into brain, our results cannot be explained on the basis of an increased availability of the agonist. Rather, it appears that naloxone pretreatment induces a change in the sensitivity of those receptors involved in the effects of opioid agonists on LH.

Luteinizing hormone releasing hormone mediates naloxone's effects on serum luteinizing hormone levels in normal and morphine-sensitized male rats.

Naloxone produces large increases in serum luteinizing hormone (LH) levels in normal males and females, supporting a role for endogenous opioids (EOP) in the tonic inhibition of LH. Since the antagonist apparently exerts no important effects on the pituitary, the reasonable assumption has been made that it elevates gonadotropin levels by affecting the release of LH-releasing hormone (LHRH) from the hypothalamus. However, at present there is no direct in vivo evidence supporting this widely-held view. In an attempt to directly demonstrate that naloxone increases the secretion of LHRH, and thereby elevates serum LH levels, we examined whether a potent synthetic antagonist of LHRH ( [D-p Glu1, D-Phe2, D-Trp3,6]-LHRH, GPT-LHRH) blocked the effects of naloxone in male rats with a normal response to naloxone and in those with a markedly enhanced sensitivity to the drug induced by a brief period of morphine pellet implantation. Our results demonstrated that GT-LHRH antagonized equipotent doses of LHRH (100 ng/kg) and naloxone (0.5 mg/kg) over a similar time course with approximately the same AD50. Most importantly, however, we showed that the GPT-LHRH produced equivalent, parallel shifts to the right in the dose-response curves for LHRH and naloxone, indicative of competitive inhibition. We also found that GPT-LHRH completely abolished the enhanced response to naloxone's effects on LH which occurs in morphine-pretreated rats. Since we observed no competition between LHRH and naloxone for their binding sites in pituitary or brain, the only viable interpretation of our results is that naloxone increases LH by inducing the release of LHRH.

Acute paternal alcohol exposure impairs fertility and fetal outcome.

An acute injection of an intoxicating dose of alcohol to male rats 24 hours prior to breeding with drug-naive females produced no discernible effect on copulatory activity, as reflected in vaginal plugs, but resulted in markedly (> 50%) reduced pregnancy rates. Fetal outcome was also markedly affected in offspring sired by alcohol-treated males: litter sizes were appreciably smaller (30%) and fetal mortality was more than 2 times higher than in controls. These results suggest that paternal alcohol use, like maternal alcohol abuse, may adversely affect fertility and fetal outcome.

Acute alcohol exposure markedly influences male fertility and fetal outcome in the male rat.

Although it is recognized that drugs ingested by pregnant females produce marked cognitive and physiological deficits in their offspring, the possibility that paternal exposure to drugs prior to mating may have adverse effects on fertility and fetal outcome has not received much attention. The purpose of the present studies was to examine whether a single, acute exposure to alcohol influences the subsequent ability of adult male rats to mate and produce healthy and viable litters. Our results showed that a relatively large dose of alcohol 24 hours prior to breeding had little effect on the mating behavior of male rats, but there were markedly fewer pregnancies in females mated with alcohol-exposed male rats than in controls. Of equal importance, we found that, even when conception occurred and live births were produced, there were striking differences in fetal outcome. Alcohol-treated males sired many fewer pups than control males and there was a markedly enhanced mortality rate in their offspring. Collectively, these data suggest that acute paternal alcohol administration 24 hours prior to breeding does not affect mating behavior, but results in a greatly diminished fertility rate and fewer and less viable offspring. These studies suggest that paternal alcohol use may be as important as maternal alcohol abuse as a negative variable in pregnancy and fetal outcome.

Gender differences in the reinforcing properties of morphine.

The purpose of the present studies was to examine whether gender differences could be observed in an important aspect of morphine's pharmacology: its reinforcing properties. Our results showed that morphine served as a positive reinforcing agent in both male and female rats in a place conditioning paradigm, but that the dose-response curves displayed marked sex-related differences. At doses from 0.2 up to 10.0 mg/kg, morphine induced an equally strong preference for the drug-associated chamber in males and females. However, as the dose was increased from 10-17.5 mg/kg, morphine ceased to act as a positive reinforcer in males. In contrast, a very strong preference for the morphine-associated chamber was still observed in females at doses up to 30 mg/kg. No gender differences in the blood and brain levels of morphine were observed subsequent to morphine administration during the conditioning phase, suggesting that pharmacokinetic factors were not involved in the sex-related differences observed. Consequently, these results suggest that there are intrinsic sex-linked differences in the doses of morphine that can induce a preference for the drug-associated chamber in a place-conditioning paradigm that are most likely related to differences in the sensitivity of the central nervous system to morphine's reinforcing properties in males and females.

Chronic opiate exposure in the male rat adversely affects fertility.

We examined whether morphine administration to adult male rats adversely affected pregnancy outcome after mating with drug-naive females and at what point in the complex series of steps leading to viable offspring it exerted its actions. The results indicate that chronic paternal morphine exposure markedly influenced fertility measures in a number of important ways. There was a pronounced increase in pseudopregnancies in females mated with males treated chronically with morphine (40%) when compared to controls (<6%), indicating that vaginal penetration occurred, but successful impregnation failed; only 33% of matings between drug-naive females and morphine-treated males resulted in pregnancies, as compared to 74.5% in controls. In addition, there were fewer implantation sites in gravid females mated with morphine-treated males than in controls. Taken together, these observations suggest that morphine-exposed male rats were apparently able to copulate, but there was a failure in successful impregnation of the females. These findings suggest a primary defect in either the quality of male sexual behavior or a complete failure of the fertilization or conception processes in females mated with morphine-exposed males. This potentially important effect of paternal morphine administration on conception and/or preimplementation loss of embryos has not been previously noted and deserves more systematic study.

Precision spectroscopy of polarized molecules in an ion trap.

Polar molecules are desirable systems for quantum simulations and cold chemistry. Molecular ions are easily trapped, but a bias electric field applied to polarize them tends to accelerate them out of the trap. We present a general solution to this issue by rotating the bias field slowly enough for the molecular polarization axis to follow but rapidly enough for the ions to stay trapped. We demonstrate Ramsey spectroscopy between Stark-Zeeman sublevels in (180)Hf(19)F(+) with a coherence time of 100 milliseconds. Frequency shifts arising from well-controlled topological (Berry) phases are used to determine magnetic g factors. The rotating-bias-field technique may enable using trapped polar molecules for precision measurement and quantum information science, including the search for an electron electric dipole moment.