Insulin-like growth factor-I, insulin-like growth factor-binding proteins, and gonadotropins in the hypothalamic-pituitary axis and serum of nutrient-restricted ewes

Body condition scores (BCS) of ovariectomized estradiol-treated ewes were controlled to examine effects of suboptimum BCS on insulin-like growth factor (IGF)-I, IGF-binding proteins (IGFBPs), and LH in the anterior pituitary gland, hypophyseal stalk-median eminence (SME), and circulation. Serum LH increased in ewes with BCS (1 = emaciated, 9 = obese) > 3 (HIGH-BCS), but not in ewes with BCS </= 3 (LOW-BCS), after onset of the breeding season. Concentrations of LH and LHbeta subunits in anterior pituitary glands were lower in LOW-BCS than in HIGH-BCS ewes. Serum IGF-I was lower in LOW-BCS than in HIGH-BCS ewes but did not differ in SME or anterior pituitary glands. In serum, the 44-kDa IGFBP-3 and 24-kDa IGFBP-4 were lower in LOW-BCS than in HIGH-BCS ewes. In anterior pituitary glands, IGFBP-2 tended to be higher in LOW-BCS than in HIGH-BCS ewes. In the SME, IGFBP-2, -3, and -5 were lower in LOW-BCS than in HIGH-BCS ewes. Low body condition may inhibit the increased secretion of LH associated with the onset of the breeding season by altering relative amounts of IGFBPs within the hypothalamic-pituitary axis.

CB1 cannabinoid receptor antagonist-induced opiate withdrawal in morphine-dependent rats

Recent reports have provided evidence of a link between the endogenous brain cannabinoid system and the endogenous central opioid systems. Here we report that the selective CB1 receptor antagonist SR 141716A induced behavioral and endocrine alterations associated with opiate withdrawal in morphine-dependent animals in a dose-dependent manner and that naloxone induced an opiate withdrawal syndrome in animals made cannabinoid-dependent by repeated administration of the potent cannabinoid agonist HU-210. Additionally CB1 and mu-opioid receptor mRNAs were co-localized in brain areas relevant for opiate withdrawal such as the nucleus accumbens, septum, dorsal striatum, the central amygdaloid nucleus and the habenular complex. These results suggest that CB1 cannabinoid receptors may play a role in the neuroadaptive processes associated with opiate dependence, and they lend further support for the hypothesis of a potential role of cannabinoid receptors in the neurobiological changes that culminate in drug addiction.

Estrous cycle effects on operant responding for ethanol in female rats

Human females have been reported to be uniquely sensitive to the deleterious effects of ethanol, thus it is important to study the characteristics of and mechanisms underlying alcohol consumption that may be specific to females. Models of ethanol self-administration in female rats that take into consideration the estrous cycle have the potential to provide important information concerning these characteristics and mechanisms. The purpose of this study was to explore the effect of the cycle on ethanol self-administration using a limited access operant paradigm. Female Wistar rats were trained to lever press for 10% ethanol versus water using a saccharin fading procedure. Responses were examined across the four phases of the estrous cycle. No effects of estrous cycle phase were observed when these rats were allowed to cycle freely. Subsequently, estrous phase effects were investigated in females whose cycles had been synchronized. Under this condition, an effect of estrous phase was present, with lower ethanol intake observed in estrus (and in some cases proestrus). Synchronized rats all showed at least one very clear 4-day estrous cycle, whereas free-running rats' cycles ranged from 3 to 5 days. Thus, it is more likely that synchronized rats were tested in the identical portion of each phase, when hormone levels were less variable. These results suggest that ethanol may be more reinforcing during diestrus than proestrus and estrus in female rats.

Characterization of insulin-like growth factor-binding proteins in the uterus and conceptus during early conceptus elongation in cattle

As a first step in determining the role that insulin-like growth factor (IGF)-binding proteins (BPs) may have in regulating initial stages of conceptus elongation in cattle, the type and relative abundance of IGFBPs in serum, uterine tissues, and uterine fluid from pregnant and noninseminated cows on Days 13 and 15 postestrus and in Day 15 conceptuses was evaluated. Uterine and serum samples contained IGFBPs 2, 3, 4, and 5 as determined by immunoprecipitation followed by Western ligand blots of precipitates. Compared with those in uterine and serum samples, IGFBPs in conceptuses and conceptus-conditioned culture media were only faintly detectable. The percentage of the total IGF-I binding activity attributed to IGFBP-3 was greater (p < 0.05) in myometrium, serum, and uterine fluid (> 50%) than in inter- (40%) and intracaruncular (37%) endometrium. Percentage of total binding attributed to IGFBP-2 was greater (p < 0.05) in endometrium and serum ( approximately 30%) than in myometrium (16%) and uterine fluid (9%). Binding activity of certain IGFBPs varied due to day of the estrous cycle or due to pregnancy status. Concentrations of IGF-I in serum were greater (p < 0.05) in nonpregnant (52 +/- 2 ng/ml) than in pregnant (40 +/- 4 ng/ml) cows. Concentration of IGF-I in uterine fluid did not differ due to pregnancy status or stage of cycle (4.4 pg IGF-I/ microg uterine protein). Northern blots revealed mRNAs for IGFBPs 1, 2, 3, 4, and 5 in uterine tissues but not in conceptuses. In situ hybridization indicated that IGFBP-1 mRNA was primarily localized in luminal epithelium of endometrium; IGFBP-2 mRNA was in luminal epithelium and dense stromal cells adjacent to endometrial epithelium; and IGFBP-3 mRNA was in vascular endothelial cells and was more prevalent in myometrium than in endometrium. Tissue specificity and changes in abundance of IGFBPs in the uterus during early conceptus elongation indicate the potential importance of IGFBP regulation of uterine IGFs during this time period.

Growth, body composition, and endocrine responses to chronic administration of insulin-like growth factor I and(or) porcine growth hormone in pigs

The actions of IGF-I, alone and in combination with porcine growth hormone (pGH), on growth and circulating endocrines and metabolites important in growth were investigated in peripubertal-age Meishan barrows. Pigs were assigned to four treatments: control, buffer; IGF-I, 33 microg rhIGF-I/kg BW injected twice daily; pGH, 33 microg rpGH/kg BW injected once daily; and IGF-I+pGH, 33 microg rhIGF-I/kg BW injected twice daily plus 33 microg rpGH/kg BW injected once daily. Treatments were administered for 28 d. Feed intake, BW, and backfat were recorded and blood samples were collected weekly. At slaughter, organ and primal cut weights were recorded. Offal and half the carcass were ground for chemical analysis. Serum concentrations of IGF-I on d 7, 14, 21, and 28 in the IGF-I, pGH, and IGF-I+pGH groups were increased 60, 107, and 131%, respectively, compared with those of the control group. Administration of pGH increased gain 43%, feed efficiency 60%, carcass protein accretion 88%, and trimmed lean cuts 16%, whereas IGF-I administration increased gain 22%, carcass protein accretion 33%, and trimmed lean cuts 5%. There was little difference in responses to administration of IGF-I+pGH and pGH alone except that coadministration of IGF-I with pGH reduced the ability of pGH to suppress backfat gain (P < .02). Even though administration of IGF-I resulted in a 60% increase in chronic nadir serum concentrations of IGF-I, only a few growth and carcass measures were changed when compared with control pigs. These included increased (P < .05) weight of body, leaf fat, kidneys, and belly. The actions of pGH on growth of pigs were not mimicked, and some were countermanded by administration of IGF-I at a dose that produces significantly increased serum concentrations of IGF-I.

Estradiol increases relative amounts of insulin-like growth factor binding protein (IGFBP)-3 in serum and expression of IGFBP-2 in anterior pituitaries of ewes

This study determined whether estradiol regulates insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBPs) in the pituitary gland, hypophyseal stalk median eminence (SME), and circulation concomitantly with effects on LH. Ovariectomized ewes received an estradiol implant or no implant during the anestrous season and were slaughtered 80 days later. Estradiol suppressed serum LH to a greater extent during anestrus than after onset of the breeding season (Days 60 and 75). Amounts of mRNA for LHbeta subunit were decreased by estradiol, but mRNA for alpha and FSHbeta subunits were not affected. Estradiol increased serum IGF-I, IGFBP-3, and IGFBP-4 throughout the treatment period, but it did not influence other IGFBPs in serum. In response to estradiol, pituitary IGFBP-2 tended to increase and mRNA for IGFBP-2 increased twofold. Other IGFBPs in the pituitary gland were not influenced by estradiol. In the SME, IGFBP-2, IGFBP-5, and the 40-kDa IGFBP-3 were increased by estradiol. Thus, estradiol influences both the IGF and gonadotropin systems in sheep. Estradiol influences on gonadotroph function may be mediated by alterations in the IGF system.

Substance dependence as a compulsive behavior

A compulsion to take a drug combined with a loss of control in limiting intake is the defining feature of substance dependence or addiction, and is the conceptual framework for the criteria of substance dependence or addiction outlined by the World Health Organization and the American Psychiatric Association. However, defining exactly what constitutes loss of control and compulsive drug taking at the level of animal models is a daunting task, and it is clear that no validated animal model exists for the whole syndrome of addiction. The present discussion redefines loss of control as a narrowing of the behavioral repertoire toward drug-seeking behavior and suggests that there are many sources of reinforcement that contribute to this behavioral focus on drug seeking. Evidence is presented demonstrating separate animal models for many of these sources of reinforcement as well as for most of the criteria for substance dependence. Evidence is also presented showing that the brain neurochemical systems involved in processing drug reward are altered by chronic drug exposure to contribute additional sources of reinforcement. Challenges for the future involve not only elucidation of the neurobiological substrates of the different behavioral components of addiction, but better animal models of these components with which to effect such studies.

Effects of amperozide, 8-OH-DPAT, and FG 5974 on operant responding for ethanol

Both 5-HT1A and 5-HT2A receptors have been implicated in modulating ethanol self-administration. A novel serotonergic compound, FG 5974, with combined 5-HT1A agonist/5-HT2A antagonist activities, has shown effects in decreasing ethanol consumption in two-bottle choice paradigms. In the present study, the effect of this compound on operant responding for ethanol (as well as water and a saccharin solution) was compared to compounds possessing the separate neuropharmacological effects of this drug (the 5-HT1A agonist, 8-OH-DPAT, and the 5-HT2A antagonist, amperozide). While all three serotonergic compounds decreased operant responding for ethanol, only FG 5974 had no effect on water and saccharin responding. These results suggest that combined 5HT1A agonist/5-HT2A antagonist activity provides a more selective effect on ethanol reinforcement than either neuropharmacological action alone. Therefore, further analysis of mixed serotonergic compounds in general, and FG 5974 in particular, is warranted as they offer potential treatments for alcoholism.

Neurocircuitry targets in ethanol reward and dependence

Alcoholism is a complex behavioral disorder characterized by excessive consumption of ethanol, a narrowing of the behavioral repertoire toward excessive consumption, the development of tolerance and dependence, and impairment in social and occupational functioning. Animal models of the complete syndrome of alcoholism are difficult if not impossible to achieve, but validated animal models exist for many of the different components of the syndrome. Recent work has begun to define the neurocircuits responsible for the two major sources of reinforcement key to animal models of excessive ethanol intake: positive and negative reinforcement. Ethanol appears to interact with ethanol-sensitive elements within neuronal membranes that convey the specificity of neurochemical action. Ethanol reinforcement appears to be mediated by an activation of GABA-A receptors, release of opioid peptides, release of dopamine, inhibition of glutamate receptors, and interaction with serotonin systems. These neurocircuits may be altered by chronic ethanol administration as reflected by opposite effects during acute ethanol withdrawal and by the recruitment of other neurotransmitter systems such as the stress neuropeptide corticotropin-releasing factor. Future challenges will include a focus on understanding how these neuroadaptive changes convey vulnerability to relapse in animals with a history of ethanol dependence.

Relationships of light and heavy fetuses to uterine position, placental weight, gestational age, and fetal cholesterol concentrations

With emphasis on increasing litter size to improve productivity and profitability, lightweight pigs born will increase in number as litter size increases and may be problematic due to reduced neonatal survival of lightweight pigs. To study developmental aspects of lightweight fetuses, fetal and placental weights were evaluated at three stages of pregnancy (30, 70, and 104 d) from white composite gilts (n = 88, 123, and 135, respectively) in relation to uterine position of light and heavy fetuses. Fetal cholesterol concentrations were analyzed at the beginning (d 70) and end (d 104) of the in utero growth phase (last third of gestation). At 30 d of gestation, no differences were noted between fetal weight and position within the uterine horn, but at 70 d and 104 d of pregnancy, heavy fetuses were found at the tubal ends and light fetuses at the cervical ends of the uterus. Using the criteria of +/- 1 SD or +/- 2 SD of the mean and lower and upper 10 or 20% of fetal weights for each gestational age, light and heavy fetuses in conjunction with their placentas were different from population means at all stages of gestation. Cholesterol concentrations were lower in light fetuses (d 104) and increased in heavy fetuses. In 28 litters (d 104) selected for extremes in within-litter fetal weights, concentrations of IGF-I increased with fetal weight (P < .01), which suggests that growth and development of lightweight pigs may be limited by critical endocrine components.

Behavioral sensitization to ethanol: genetics and the effects of stress

Some aspects of drug abuse syndromes may be influenced by sensitization to some drug effects. This enhancement of drug effect has been associated with prior drug exposure and with exposure to stressful stimuli. It has been postulated that sensitization to psychomotor stimulant drug effects influences sensitivity to drug reward. The drugs of abuse best characterized for sensitization phenomena include cocaine, amphetamine, and morphine. In general, ethanol's molecular mechanisms of action have been difficult to define relative to drugs with known receptor or transporter binding sites and, likewise, ethanol sensitization has been less thoroughly examined. Evidence supporting the existence of behavioral sensitization to ethanol, for genetic differences in the occurrence of ethanol sensitization, and for the influence of corticosterone on the development of ethanol sensitization is reviewed herein. There appear to be different genetic determinants of acute drug sensitivity and sensitization. Cross-sensitization between stress and ethanol suggest a potential role for hypothalamic-pituitary-adrenal (HPA) axis associated changes in ethanol sensitization, consistent with mechanisms likely contributing to sensitization to other abused drugs. Furthermore, glucocorticoid receptors appear to mediate both ethanol- and stress-induced sensitization to ethanol. A biological link between drug reward and drug sensitization involving HPA axis hormones may exist and, thus, study of the sensitization process may elucidate mechanisms relevant to drug abuse.

Circulating insulin-like growth factor I, insulin-like growth factor binding proteins, growth hormone, and resumption of estrus in postpartum cows subjected to dietary energy restriction

The objective of this study was to determine whether serum concentrations of growth hormone (GH), IGF-I, IGF binding proteins (IGFBP), and glucose at wk 2 and 10 postpartum were associated with the ability of postpartum beef cows to resume cycling when maintained on a limited nutrient environment. Cows (n = 29) were individually fed either 130 or 170 kcal ME x BW-75 x d-1 during nonlactation and 170 or 210 kcal ME x BW-75 x d-1 during lactation for an average of 4.1 yr before sample collection. The proportion of cows that resumed estrus within 20 wk after parturition was less (P < .05) at the lower feeding rate (5 of 14) than at the higher feeding rate (11 of 15). Concentrations of IGF-I increased from wk 2 to 10 in cows that resumed cycling but not in cows that remained anestrous and were less (P < .05) at wk 2 and 10 in cows that remained anestrous compared to cows that resumed cycling. Circulating amounts of IGFBP-2 at wk 2 were greater (P < .05) and IGFBP-3 concentrations were lower (P < .05) in cows that remained anestrous compared to cows that resumed cycling. Cows on the lower feeding rate that did not cycle had lower body condition scores and greater concentrations of GH compared (P < .05) to other cows. At the higher feeding rate, body condition score and concentrations of GH did not differ between cows that did or did not resume cycling. Circulating concentrations of IGF-I and IGFBP-2 and -3 at wk 2 postpartum were indicators of the capacity of energy-restricted cattle to resume cycling after parturition.

Intravenous self-administration of heroin, cocaine, and the combination in Balb/c mice

Polydrug abuse, including the abuse of cocaine + heroin combinations (or 'speedballs') is an increasingly significant problem. The use of genetically defined populations of mice has the potential to add considerably to the study of polydrug abuse. Balb/cByJ (Balb/c) mice have been shown to self-administer opiates, but not cocaine, therefore these mice were chosen for the initial characterization of intravenous self-administration of cocaine + heroin combinations. Mice were implanted with chronic indwelling jugular catheters and given the opportunity to self-administer heroin, cocaine or heroin + cocaine combinations. Heroin was self-administered, while, under the same conditions, none of the mice tested acquired cocaine self-administration. However, heroin + cocaine combinations were self-administered in naive mice as well as in mice that had failed to self-administer cocaine alone. The heroin + cocaine combination dose-effect curve resembled the heroin dose-effect curve. It is hypothesized that heroin may interact with effects of cocaine that function to limit self-administration in Balb/c mice, facilitating the acquisition and maintenance of self-administration of cocaine + heroin combinations.

Effect of gonadotropin treatment on size, number, and cell proliferation of antral follicles in cows

To determine the effects of gonadotropins on the size, number, and cell proliferation of antral ovarian follicles, cows received FSH-P or vehicle beginning on Day 2 after estrus, and ovaries were collected 6, 12, 24, or 48 hr after the initiation of FSH-P treatment or 24 or 48 hr after the initiation of vehicle treatment. Ovaries also were collected from untreated cows on Day 2 after estrus (pretreatment). Before fixation, all visible antral follicles were counted and their surface diameters were recorded. Proliferating cells were immunolocalized in fixed follicles by using a specific primary antibody against proliferating cell nuclear antigen (PCNA), and the labeling index (LI; percentage of cells staining positively for PCNA) was determined for granulosa and thecal cells. After 48 hr of treatment, FSH-P-treated cows had fewer (P < 0.01) small antral follicles and more medium and large antral follicles (P < 0.01 and P < 0.05, respectively) compared with vehicle-treated cows. Granulosa cell LI was negatively correlated (P < 0.05) with follicular diameter for vehicle-treated but not for FSH-P-treated cows. Analysis of covariance using follicular diameter as a covariate to adjust to a common diameter indicated that granulosa cell LI was greater (P < 0.05) at 24 and 48 hr in FSH-P-treated than in vehicle-treated cows; conversely, thecal cell LI was greater (P < 0.01) at 48 hr in FSH-P-treated compared with vehicle-treated cows but did not differ at 24 hr. Across all groups, the LI of cells located within the antral half of the granulosa cell layer was greater (P < 0.01) than that of cells located within the basal half. In conclusion, the stimulation of follicular development by exogenous gonadotropins increased or maintained the proliferation of granulosa and thecal cells concomitant with continued follicular growth. Therefore, enhanced follicular cell proliferation may be an important mechanism by which FSH-P superinduces the growth of antral follicles in cows.

Genetic differences in behavioral sensitivity to a neuroactive steroid

Recent work found that lower endogenous levels of the gamma-aminobutyric acid-agonist, neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) may be correlated with increased ethanol withdrawal severity in the selectively bred Withdrawal Seizure-Prone and -Resistant mice. The present studies were conducted to determine whether decreased sensitivity to 3alpha,5alpha-THP was correlated with ethanol withdrawal hyperexcitability in another genetic mouse model, namely the C57BL/6 (B6) and DBA/2 (D2) inbred strains. These strains also differ in ethanol withdrawal severity (D2 >> B6). B6 and D2 male mice were injected with 3alpha,5alpha-THP (0-10 mg/kg i.p.) 15 min before the timed tail vein infusion of pentylenetetrazol. B6 mice were more sensitive than D2 animals to the anticonvulsant effect of 3alpha,5alpha-THP. Subsequent studies measured sensitivity to several of the pharmacological effects of 3alpha,5alpha-THP. B6 and D2 male mice were injected with 3alpha,5alpha-THP (0-32 mg/kg) before testing for locomotor activation (total number of entries) and anxiolysis (percent open arm entries) on the elevated plus maze, muscle relaxation (impairment of forelimb grip strength), ataxia (impairment of Rotarod performance) and seizure susceptibility to pentylenetetrazol. B6 mice were more sensitive than D2 animals to the anxiolytic, locomotor stimulant and anticonvulsant effects of 3alpha,5alpha-THP. In contrast, D2 mice were more sensitive than B6 mice to 3alpha,5alpha-THP-induced muscle relaxation and ataxia. Plasma 3alpha,5alpha-THP levels did not differ in the B6 and D2 mice injected with this steroid, suggesting that the strain differences were not pharmacokinetic. Collectively, the results in selectively bred Withdrawal Seizure-Prone and -Resistant mice and B6 and D2 inbred strains suggest that genetic differences in neuroactive steroid sensitivity and biosynthesis may contribute to ethanol withdrawal severity.

The neurobiology of addiction: an overview

Addiction can be defined in part as a compulsion to use alcohol or other drugs and the occurrence of withdrawal symptoms when long-term consumption ceases. In addition to physical symptoms related to nervous system hyperexcitability, withdrawal includes changes in mental state that may motivate renewed AOD consumption. The manifestations of addiction are associated with changes in nerve cell function by which the brain attempts to adapt to a drug's presence. These functional changes modulate a person's initial response to a drug, the establishment of long-term craving for the drug (i.e., addiction), and the persistent sense of discomfort that leads to relapse after abstinence has been achieved. Research is beginning to reveal how specific brain regions may be integrated to form neural circuits that modulate aspects of addiction.

Insulin-like growth factor I and insulin-like growth factor-binding proteins in bovine serum and follicular fluid before and after the preovulatory surge of luteinizing hormone

Previous studies have shown that concentrations of insulin-like growth factor (IGF)-binding proteins (BPs) in bovine follicles before the preovulatory surge of LH are inversely associated with estradiol concentrations, such that decreases in IGFBPs occur with advanced development of antral follicles and atresia is associated with increases in IGFBPs. In the present study, we evaluated serum and follicular fluid at different times after the preovulatory surge of LH to determine whether changes in IGF-I and IGFBPs are associated with the marked changes in the steroidogenic capacity that occur in follicle during this period. Serum and fluid from small follicles (> or = 5-mm diameter) and the preovulatory follicle were collected from cows at the onset of standing estrus or 8.5 and 20.5 h after administration of 100 micrograms GnRH at the onset of estrus (n = 4/time). Concentrations of IGF-I (determined by RIA) did not differ (p > 0.10) among times but were lower (p < 0.05) in fluid from small and preovulatory follicles than those in serum. Profiles of IGFBPs (evaluated by ligand blot analysis) differed among serum and fluid from small and preovulatory follicles. Preovulatory follicles contained IGFBP-3 with little or no other IGFBPs detected. Amount of IGFBP-3 and progesterone did not differ with time of sample collection, but a 13- to 15-fold reduction in estradiol-17 beta and androstenedione occurred between 8.5 and 20.5 h after the LH surge. Small follicles contained IGFBP-2, -3, -4, and -5 (determined by immunoprecipitation). The amount of 28-29-kDa IGFBPs (small form of IGFBP-5 and [or] glycosylated form of IGFBP-4) was inversely associated with concentrations of androstenedione. The 31-kDa form of IGFBP-5 was positively correlated with concentration of progesterone. Serum contained IGFBP-2, -3, and -4, but not IGFBP-5. Circulating IGFBP-2, but not other IGFBPs, decreased by 50% from estrus to 20.5 h after GnRH. In summary, amounts of IGF-I or IGFBPs in preovulatory follicular fluid did not change in response to an LH surge, even though estradiol and androstenedione decreased markedly. The absence of IGFBPs other than IGFBP-3 in bovine preovulatory follicles may allow for increased availability of IGF-I, which is proposed to be important for oocyte maturation and ovulation.

Intra-amygdala muscimol decreases operant ethanol self-administration in dependent rats

Dependence is an important factor motivating continued alcohol use in human alcoholics. Development of a model of ethanol (EtOH) consumption in dependent animals would advance the understanding of reinforcement after chronic EtOH exposure and allow for the investigation of the neuropharmacological mechanisms mediating reinforcement in dependent versus nondependent animals. In the present study, rats were trained to lever press for 10% EtOH, surgically implanted with bilateral guide cannulae in the amygdala, and either made dependent on EtOH by exposure for 2 weeks to EtOH or exposed to air in identical vapor chambers. Upon removal, the rats were placed in operant boxes and allowed to respond on levers for 10% EtOH or water during a 12-hr period. Rats were removed briefly at approximately 6.5 hr for intra-amygdala injections of saline or the GABAA receptor agonist muscimol. After the test period, rats were returned to the vapor chambers for 4 days before retest. EtOH-dependent animals responded more for EtOH across the 12-hr test period than did air control nondependent rats; this difference became more pronounced with repeated test sessions. Intra-amygdala muscimol significantly decreased responding for EtOH in EtOH-dependent rats, but had no effect in nondependent controls. These data suggest that the reinforcing effects of EtOH and neurotransmitter pathways mediating reward are altered after the development of dependence, and they support the use of this paradigm for further investigations into the neuropharmacology of EtOH dependence.

Genetic analysis of the corticosterone response to ethanol in BXD recombinant inbred mice

The genetic control over the corticosterone response to ethanol (EtOH) and its possible relationship to other EtOH-related traits was examined using BXD recombinant inbred (RI) strains derived from an F2 cross of C57BL/6J (B6) and DBA/2J (D2) progenitor strains. Quantitative trait locus (QTL) analysis of corticosterone levels 1 hr following EtOH suggested the influence of a single major gene on this trait. Two loci were predicted to account for 47% of the genetic variance in plasma corticosterone levels 6 hr following EtOH, whereas 3 loci were predicted to account for 78% of the genetic variance in corticosterone levels 7 hr following EtOH. Markers associated with corticosterone levels 7 hr following EtOH and corrected corticosterone levels 6 hr post-EtOH overlapped with ones found to influence acute and chronic EtOH withdrawal severity, suggesting some degree of common genetic determination between these traits. Overall these results indicate that gene action significantly influences stress responsiveness and suggest possible chromosomal locations of these genes.

Preparation and measurement of artificial enamel lesions, a four-laboratory ring test

Transversal microradiography is the most widely accepted method used to study changes in mineral content profiles. In spite of its widespread use, relatively little information is available on its validity and reproducibility. Following the recommendation of the Consensus Conference on Intraoral Model Systems, this study was designed to explore reproducibility of lesion analysis within a laboratory and comparability of analysis among various laboratories. Incipient enamel lesions were produced by four research groups using both a common ('standard') and a local ('preferred') protocol. Sections were produced by each group and allocated to 'mixed' bags of specimens, which were analysed by the groups. With the chosen scheme some sections were analysed six times by the same group (as an internal reference standard) while others were analysed by all four groups. The data for the mineral content profiles were expressed as the integrated mineral loss (IML) value and lesion depth. The results showed the lesions produced with the standard protocol to be in the range 2,000-3,000 vol% mineral x microns for IML. The IML of the lesions produced with the preferred protocol varied between 1,800 and 6,300 vol% mineral x microns. Variation in IML values could be attributed to the biological variation between lesions, but also to time (of microradiograph production) and measurement effects, calibration of the magnification of the specimens, and the parameters used in the algorithm to calculate IML. Some of these parameters also affected the lesion depth. It is advised to standardise (or at least report) the method of calculation of IML, and to include a reference lesion between analyses in a longitudinal study as an internal standard. With the data produced, it was calculated that the number of lesions required to differentiate between preventive treatments varied substantially among laboratories. The recommendations given will improve the power of the screening methods for caries-preventive agents for which microradiography is an essential analytical method.

Genetic analysis of the corticosterone response to ethanol in BXD recombinant inbred mice

The genetic control over the corticosterone response to ethanol (EtOH) and its possible relationship to other EtOH-related traits was examined using BXD recombinant inbred (RI) strains derived from an F2 cross of C57BL/6J (B6) and DBA/2J (D2) progenitor strains. Quantitative trait locus (QTL) analysis of corticosterone levels 1 hr following EtOH suggested the influence of a single major gene on this trait. Two loci were predicted to account for 47% of the genetic variance in plasma corticosterone levels 6 hr following EtOH, whereas 3 loci were predicted to account for 78% of the genetic variance in corticosterone levels 7 hr following EtOH. Markers associated with corticosterone levels 7 hr following EtOH and corrected corticosterone levels 6 hr post-EtOH overlapped with ones found to influence acute and chronic EtOH withdrawal severity, suggesting some degree of common genetic determination between these traits. Overall these results indicate that gene action significantly influences stress responsiveness and suggest possible chromosomal locations of these genes.

Role of models in assessing new agents for caries prevention--non-fluoride systems

While fluoride is an effective anti-caries agent, the search for more effective alternative therapies continues. A wide range of non-fluoride anti-caries agents has been postulated, and this paper reviews some of the pre-clinical models that have been utilized in their evaluation and some of the pitfalls that must be avoided. Using data on the potential anti-caries efficacy of phosphopeptides obtained from casein, the caution that must be applied in extrapolating laboratory data to predict clinical performance is discussed. Evaluation strategies that focus on only one potential mode of action (e.g., inhibition of demineralization) may overestimate the true clinical efficacy which may arise from a combination of two or more effects (e.g., inhibition of demineralization and stimulation of remineralization). Although laboratory and in situ data predict anti-caries efficacy for sodium trimetaphosphate in combination with fluoride, this was not found in three-year clinical trials. A possible reason for this, the lack of suitable calibration methods, is discussed. Finally, some comments on the appropriateness of laboratory evaluation strategies are made.