Milk-fat globule epidermal growth factor 8 (MFGE8) is expressed at the embryo- and fetal-maternal interface in equine pregnancy.

Milk-fat globule epidermal growth factor (EGF) 8 protein (MFGE8), also known as lactadherin, promotes cell adhesion in an Arg-Gly-Asp (RGD)-dependent modus via integrins. In the present study, the expression of MFGE8 was examined in equine endometrium during oestrus and at Days 12 and 16 after ovulation in pregnant and non-pregnant mares and in mares during the 5th month of gestation. Results demonstrated that MFGE8 is expressed at the embryo- and fetal-maternal interface in equine pregnancy. In non-pregnant endometrium its expression was upregulated by oestrogen, a finding that was confirmed using endometrial explant culture. MFGE8 was expressed at similar levels by conceptuses collected 13 and 14 days after ovulation and by allantochorion sampled during the 5th month of gestation. Pericytes of endometrial blood vessels displayed strong MFGE8 expression upon in situ hybridisation. During the 5th month of gestation, the fetal side of the allantochorionic villi in particular displayed pronounced staining upon in situ hybridisation, confirming that MFGE8 expression is not restricted to early pregnancy but persists and is present at the fetal-maternal interface. Potential roles of MFGE8 in equine pregnancy include mediating cell-cell adhesion, promotion of angiogenesis and placental transfer of fatty acids.

Using life-histories to predict and interpret variability in yolk hormones.

Variation in yolk hormones is assumed to provide the plasticity necessary for mothers to individually optimize reproductive decisions via changes in offspring phenotype, the benefit being to maximise fitness. However, rather than routinely expecting adaptive variation within all species, the pattern and magnitude of yolk hormone deposition should theoretically relate to variation in life-histories. Here we present data on intra-clutch variation in yolk corticosterone in three species along a developmental continuum (European starling (Sturnus vulgaris): fully altricial; black guillemot (Cepphus grylle): semi-precocial; common eider (Somateria mollissima): fully precocial) to examine how and why variation in life-histories might relate to the evolution of variation in yolk steroids. Starlings and guillemots showed a significant increase in yolk corticosterone across the laying sequence; however, we found no pattern within eider clutches. Moreover, starlings showed the largest difference (94.6%) in yolk corticosterone between first- and last-laid eggs, whereas guillemots showed a moderate difference (58.9%). Despite these general species-specific patterns, individuals showed marked variation in the intra-clutch patterns of yolk corticosterone within each species indicating potential differences in intra-clutch flexibility among females. It is well documented that exposure to elevated yolk glucocorticoids reduces offspring quality at birth/hatching in many taxa and it has therefore been proposed that elevated yolk levels may modulate offspring competition and/or facilitate brood reduction under harsh conditions in birds. Our data suggests that intra-clutch variation in yolk corticosterone has the potential to act as an adaptive maternal effect in species where modulation of competition between nest-bound offspring would benefit mothers (starlings and guillemots). However, in precocial species where mothers would not benefit from a modulation of offspring quality, intra-clutch variation in yolk hormones may play little or no adaptive role. While future phylogenetically-controlled studies will be helpful in examining questions of adaptive mechanisms once more data on yolk corticosterone becomes available, our results nonetheless suggest that research on the evolutionary role of yolk hormones can benefit by a priori incorporating species-specific life-history-driven hypotheses.

Stressful Life Events Prior to Depression Onset and the Cortisol Response to Stress in Youth with First Onset Versus Recurrent Depression.

The strongest proximal predictors of depression onset in adolescence are stressful life events (SLEs). Changes in the hypothalamic-pituitary-adrenal (HPA) axis response to stress are theorized to mediate the etiological effect of SLEs on depression onset. The goal of the current study was to examine differences in the cortisol response to a laboratory-induced stressor between youth with versus without at least one SLE in the etiologically-central 3-month period prior to depression onset. One hundred adolescents (24 first-onset depression, 18 recurrent depression, and 58 non-depressed controls) had five salivary cortisol samples collected over the course of the Trier Social Stress Test (TSST). SLEs were assessed using a rigorous contextual interview and rating system. Among those with an SLE, youth on their first onset of depression had a flatter cortisol reactivity slope relative to non-depressed adolescents, and youth on a recurrent episode of depression had a steeper recovery slope relative to first-onsets and non-depressed adolescents. In contrast, no between-group differences were found among those with no SLE prior to onset. These results suggest that differences in the HPA axis response pattern may represent a neurobiological mechanism that distinguishes depressed and non-depressed groups but only for adolescents whose depression is precipitated by SLEs. Further, this neurobiological mechanism may play a different role in the very first episode of depression than it does in recurrent episodes.

Male and female prolactin receptor mRNA expression in the brain of a biparental and a uniparental hamster, phodopus, before and after the birth of a litter.

Prolactin receptor (PRL-R) mRNA transcript level was quantified in the choroid plexus (ChP) of a naturally biparental hamster, Phodopus campbelli, and its otherwise similar, yet nonpaternal, sibling species, Phodopus sungorus. Pair-housed males and females on the day before the birth of their first litter (G17), the day after birth (L1), lactation day 5 (L5), and unpaired animals that were sexually naïve, were tested. PRL-R mRNA transcript level relative to total RNA, was evaluated by reverse transcriptase-polymerase chain reaction using primers common to the long- and short-form of the PRL-R in Phodopus. In the ChP, a region implicated in prolactin transport into the central nervous system, females had the expected increase in PRL-R mRNA transcript from dioestrus to L5, consistent with known actions of prolactin. As predicted, males and females of the biparental species were similar, although PRL-R mRNA in naive males was higher than in dioestrus females. Males of the two species also differed as predicted. PRL-R mRNA transcript levels were higher in the biparental males. In addition, P. campbelli males had low PRL-R mRNA at G17 compared to L5. By contrast, non-paternal P. sungorus males had elevated PRL-R mRNA transcript levels on G17 relative to unpaired males. We conclude that PRL-R mRNA in the ChP is differentially regulated before and after birth in a paternal and a nonpaternal male.

Cyclic Djungarian hamsters, Phodopus campbelli, lack the progesterone surge normally associated with ovulation and behavioral receptivity.

Serum levels of 17 beta-estradiol and progesterone were assayed at 4- to 5-h intervals across the estrous cycle in female Djungarian hamsters, Phodopus campbelli. The pattern of secretion for estradiol is similar to that described for the rat and the Syrian hamster, rising slowly from a baseline of 54 +/- 2 pg/ml during the morning of estrus to a peak of 187 +/- 16 pg/ml in the early afternoon of proestrus, then falling rapidly back to baseline levels. The pattern of progesterone secretion is significantly different from that of any estrous cycle previously described for a 4-day cyclic mammal. There is no evidence for a significant peak in serum progesterone levels associated with ovulation and receptivity. The highest levels of serum progesterone occur during the early afternoon of diestrous day 2 (8046 +/- 1063 pg/ml). The lowest levels of serum progesterone occur in the early morning of proestrus (720 +/- 125 pg/ml). During the period of sexual receptivity only 2504 +/- 654 pg/ml progesterone are found in the serum. Ovariectomized females show behavioral receptivity after 48 h of treatment with 50 micrograms estradiol benzoate/kg BW in sesame oil. Progesterone is not necessary for receptivity and will not facilitate receptivity when administered in conjunction with a subthreshold dose of estrogen. The presence of tubular ova confirms the time of ovulation to be a period of approximately 7 h between 2200 h on proestrus and 0500 h on estrus. Histological examination of ovarian sections from each of the 4 days of the estrous cycle shows follicular development to differ from that in the Syrian hamster in that the total number of follicles in the ovary is variable and low, and the ovulated follicles (new corpora lutea) are blood filled. Djungarian hamster primary follicles averaged 83 +/- 2 microns in diameter, and preovulatory follicles averaged 455 +/- 17 microns in diameter. The total number of intact follicles per ovary rose from 21 +/- 5 on the evening of estrus to 73 +/- 29 on the evening of diestrous day 2, then fell to 32 +/- 26 by the evening of proestrus. Preovulatory follicles increased in number from 1.0 +/- 0.6/ovary early on estrus to a maximum of 4 +/- 1 on the evening of diestrous day 2. However, at ovulation a combined total of only 5.1 +/- 0.8 ova are shed.

Evolutionary biology of plant defenses against herbivory and their predictive implications for endocrine disruptor susceptibility in vertebrates.

Hormone disruption is a major, underappreciated component of the plant chemical arsenal, and the historical coevolution between hormone-disrupting plants and herbivores will have both increased the susceptibility of carnivores and diversified the sensitivities of herbivores to man-made endocrine disruptors. Here I review diverse evidence of the influence of plant secondary compounds on vertebrate reproduction, including human reproduction. Three of the testable hypotheses about the evolutionary responses of vertebrate herbivores to hormone-disrupting challenges from their diet are developed. Specifically, the hypotheses are that a) vertebrate herbivores will express steroid hormone receptors in the buccal cavity and/or the vomeronasal organ; b) absolute sex steroid concentrations will be lower in carnivores than in herbivores; and c) herbivore steroid receptors should be more diverse in their binding affinities than carnivore lineages. The argument developed in this review, if empirically validated by support for the specific hypotheses, suggests that a) carnivores will be more susceptible than herbivores to endocrine-disrupting compounds of anthropogenic origin entering their bodies, and b) diverse herbivore lineages will be variably susceptible to any given natural or synthetic contaminant. As screening methods for hormone-disrupting potential are compared and adopted, comparative endocrine physiology research is urgently needed to develop models that predict the broad applicability of those screening results in diverse vertebrate species.

Changes in testosterone, cortisol, and estradiol levels in men becoming fathers.

OBJECTIVE: To quantify longitudinally steroid hormone (testosterone, cortisol, and estradiol) concentrations in men becoming fathers for the first time ("dads"). SUBJECTS AND METHODS: Volunteer study subjects were recruited from first-trimester prenatal classes in Kingston, Ontario, in February 1999. Twenty-three dads provided saliva samples from recruitment through 3 months after the birth of their children. Fourteen men who were not fathers were recruited from the general population to serve as age-matched controls for season and time of day. Estradiol, testosterone, and cortisol levels were quantified. RESULTS: After controlling for effects of time of day and season, dads had lower mean +/- SE testosterone (6.5+/-0.7 vs 10.0+/-0.9 ng/dL; P<.005) and cortisol (morning values, 0.30+/-0.05 vs 0.53+/-0.05 microg/dL; P<.005) concentrations, a higher proportion of samples with detectable estradiol concentrations (68% [308/454] vs 57% [87/154]; P=.01), and higher estradiol concentrations in those detectable samples (3.81+/-0.09 pg/mL [13 dads] vs 3.26+/-0.11 pg/mL [9 controls]; P<.002) than did control men. Within 10 individual dads with frequent samples before and after the birth, the percentage of samples with detectable estradiol was lower during the month before the birth than during the month after (51% vs 71%; P=.02), and cortisol concentration was increased in the week before the birth (to a mean of 0.16 microg/dL). In each of 13 dads providing frequent samples, testosterone concentration and variance were low immediately after the birth (no change from previous levels in 5, decrease after prebirth increase in 3, and decrease relative to all other times in 5). CONCLUSIONS: In this population of Canadian volunteers attending prenatal classes, expectant fathers had lower testosterone and cortisol levels and a higher proportion of samples with detectable estradiol concentrations than control subjects. Individual patterns of testosterone variance relative to the birth and estradiol and cortisol concentrations immediately before the birth may be worthy of further investigation. The physiologic importance of these hormonal changes, if any, is not known. However, they are hormones known to influence maternal behavior.

Photoperiodic control of oestrous cycles in Syrian hamsters: mediation by the mediobasal hypothalamus.

To assess whether the mediobasal hypothalamus (MBH) is necessary for photoperiodic control of oestrous cycles and prolactin secretion, we tested intact female Syrian hamsters (controls) and those that had sustained unilateral or bilateral lesions of the MBH. All hamsters displayed 4-day oestrous cycles postoperatively in the long-day photoperiod (14 h light/day); control females and those with unilateral MBH damage ceased to undergo oestrous cycles approximately 8 weeks after transfer to a short-day photocycle (10 h light/day), whereas 12 of 15 females with bilateral MBH lesions continued to generate 4-day oestrous cycles throughout 22 weeks in short days. Serum prolactin concentrations were either undetectable or low in all hamsters 8 or 14 weeks after the transfer to short-day lengths, but increased above long-day baseline values by week 22. We conclude that melatonin-binding sites in the MBH mediate suppression of oestrous cycles but not prolactin secretion by short-day lengths; recovery of prolactin secretion in females during prolonged exposure to short-day lengths reflects development of refractoriness to melatonin in a substrate distinct from the MBH. These findings suggest that separate neural pathways mediate photoperiodic control of gonadotropin and prolactin secretion in female hamsters.

Photorefractoriness of immune function in male Siberian hamsters (Phodopus sungorus).

Short days induce multiple changes in reproductive and immune function in Siberian hamsters. Short-day reproductive inhibition in this species is regulated by an endogenous timing mechanism; after approximately 20 weeks in short days, neuroendocrine refractoriness to short-day patterns of melatonin develops, triggering spontaneous recrudescence of the reproductive system. It is unknown whether analogous mechanisms control immune function, or if photoperiodic changes in immune function are masked by prevailing photoperiod. In Experiment 1, 3 weeks of exposure to long days was not sufficient to induce long-day-like enhancement of in vitro lymphocyte proliferation in short-day adapted male Siberian hamsters. Experiment 2 tested the hypothesis that immunological photorefractoriness is induced by prolonged exposure to short days. Adult male hamsters were gonadectomized or sham-gonadectomized and housed in long (14 h light/day) or short (10 h light/day) photoperiods for 12, 32 or 40 weeks. Somatic and reproductive regression occurred after 12 weeks in short days, and spontaneous recrudescence was complete after 32-40 weeks in short days, indicative of somatic and reproductive photorefractoriness. In gonad-intact hamsters, 12 weeks of exposure to short days decreased the number of circulating granulocytes and increased the number of B-like lymphocytes. After 32 weeks in short days, these measures were restored to long-day values, indicative of photorefractoriness; castration eliminated these effects of photoperiod. In both intact and castrated hamsters, in vitro proliferation of splenic lymphocytes was inhibited by 12 weeks of exposure to short days. After 40 weeks in short days lymphocyte proliferation was restored to long-day values in intact hamsters, but remained suppressed in castrated hamsters. These results suggest that short-day-induced inhibition of lymphocyte function does not depend on gonadal regression, but that spontaneous recrudescence of this measure is dependent on gonadal recrudescence. In Experiment 3, in vitro treatment with melatonin enhanced basal proliferation of lymphocytes from male hamsters exposed to short days for 12 weeks, but had no effect on lymphocytes of photorefractory hamsters or long-day control hamsters. Lymphocytes of castrated hamsters were unresponsive to in vitro melatonin, suggesting that photoperiodic changes in gonadal hormone secretion may be required to activate mechanisms which permit differential responsiveness to melatonin depending on phase in the annual reproductive cycle. Together, these data indicate that, similar to the reproductive system, the immune system of male Siberian hamsters exhibits refractoriness to short days.

Differential effects of paternal presence on pup survival in two species of dwarf hamster (Phodopus sungorus and Phodopus campbelli).

The effect of the presence or absence of the male, and of decreased ambient temperature (21 degrees C vs. 4 degrees C) on litter survival, pup survival and pup growth was measured from birth through day 18 after birth in Siberian (P. sungorus) and Djungarian (P. campbelli) hamsters. Siberian hamsters were not significantly affected by the experimental manipulations. In contrast, whereas 100% of litters and 95% of pups were successfully raised to weaning at 21 degrees C by paired Djungarian hamsters, survival fell to 47% when the mate was absent and even further, to 32%, when the ambient temperature was lowered. No significant differences in litter size or pup weight at birth were detected between species at the warmer temperature. However, P. sungorus pups gained weight significantly faster through day 12 after birth (while dependence upon the mother for food was absolute) than P. campbelli pups under all experimental conditions. Although the species are closely related, these data show that male Djungarian hamsters are essential to offspring survival under conditions where Siberian hamsters do not require conspecific help. Species differences in metabolism and thermoregulation may account for the differential pup survival.

Thermal constraints on maternal behavior during reproduction in dwarf hamsters (Phodopus).

The chronic hyperthermia of lactating dwarf hamster (Phodopus) dams may constrain maternal behavior if contact with the litter further increases their body temperature, forcing the termination of nest bouts to dissipate the heat load. Changes in female body temperature and nest attendance in two species of dwarf hamster (P. campbelli and P. sungorus) were recorded each minute over the reproductive cycle. As the pups develop from naked poikilotherms to well-insulated thermoregulators, they function as heat sinks and heat sources. This role of pup development in maternal thermoregulation interacts with the dam's activity, primarily nocturnal wheel running, to produce a complex pattern of heating and cooling in each species. Contact with the pups is more constrained by maternal temperature during the inactive phase (day), and more constrained in P. campbelli than in P. sungorus. The interspecific difference in pup development or maternal thermoregulation is consistent with predictions based on biparental care, and a thermoregulatory role for the male in P. campbelli, but not in P. sungorus. These data suggest that environmental temperature and water availability are ecological variables that affect maternal thermoregulation, reproductive success, and the need for biparental care.

Disruption of body temperature and behavior rhythms during reproduction in dwarf hamsters (Phodopus).

The internal gestation and subsequent lactation of mammalian reproduction represent a considerable physiological challenge. The extent of disruption in the daily rhythm of four parameters, core body temperature, nest attendance, activity, and wheel running, was monitored in Djungarian hamster (Phodopus campbelli) and Siberian hamster (P. sungorus) females implanted intraperitoneally with biotelemetric thermistors. The amplitude of each rhythm decreased during late gestation, culminating in a substantial disruption at parturition, and did not begin a recovery until the latter third of lactation. In each species, the change in the core body temperature rhythm was primarily the result of an elevation in light phase body temperature to approximate the normally occurring dark phase temperature, although the disruption was more extensive in P. sungorus than in P. campbelli. As this maternal hyperthermia is associated with the provision of essential heat to the altricial liter, these species differences in the vulnerability to hyperthermia may constrain the reproductive success of these extreme cold adapted small mammals.

Paternal care reduces maternal hyperthermia in Djungarian hamsters (Phodopus campbelli).

Throughout lactation, maternal body temperature, nest attendance, activity level and reproductive success of solitary female Djungarian hamsters housed at the recommended ambient temperature of 23 degrees C (Canadian Council on Animal Care guidelines) were compared with those of paired females housed at the same temperature and with solitary females housed at the natural burrow temperature of 18 degrees C. As expected, cooler ambient temperature improved pup survival and weaning weight. Likewise, paternal presence largely compensated for the poor pup growth typical at 23 degrees C. However, the mechanisms were not the same. Females at reduced ambient temperatures were as hyperthermic as females at the higher temperature and spent the same proportion of their day at very high body temperatures. However, the steeper temperature gradient available for passive cooling allowed those females to enhance maternal care by shortening their nest bout absences. In contrast, body temperatures of paired females were tightly regulated compared to the hyperthermia of solitary females and rarely included the highest body temperatures. This alleviation of maternal hyperthermia was not achieved through a reduction in nest attendance. Therefore, maternal hyperthermia in Djungarian hamsters is not essential and may be considered a substantial cost to females when males are not present.

Maternal and pup contributions to different patterns of pup growth in Phodopus species.

A cross-fostering approach was used to compare and quantify patterns of pup growth in Phodopus sungorus and P. campbelli. Standard litters of five pups were reared by a foster mother of the same or the opposite species. Individual pups were weighed daily, and maternal and pup body condition were quantified. Studies were conducted at an ambient temperature of 23 degrees C, which constrains maternal contact with pups in P. campbelli but not P. sungorus, to maximize the difference in pup growth curves between the species. Results confirmed that the similar Day 18 weights in the two species of Phodopus were a complex result of laboratory conditions that masked different patterns of pup growth. The primary determinants of that pup growth were 1) constraints on maternal investment by P. campbelli mothers, which arose from the thermoregulatory stresses of a 23 degrees C ambient temperature and may have involved different milk energetic value or water content; 2) an intrinsic pup difference in the threshold weight for independent thermoregulation, which increased energetic expenditures for P. sungorus pups several days earlier than for P. campbelli pups; and 3) a longer lactation in P. campbelli, which improved access to dry food. Results also confirmed that within-litter variation in pup weights was considerably larger in P. campbelli, but forced rejection of the hypothesis that the difference arose from different maternal investment strategies during lactation. Species-typical patterns of variation were already established on Day 1 after birth.

Ontogeny of thermoregulation in the Djungarian hamster (Phodopus campbelli).

At birth, altricial Djungarian hamster pups require exogenous heat to grow and gain little benefit from huddling with their littermates. By day 6 huddled pups begin effective thermogenesis although isolated pups do not show spontaneous increases in temperature until day 9. On day 12, isolated pups can resist cooling for short periods of time and huddles do not cool within a 15 min test. By day 15, isolated pups can thermoregulate, although at a lower core body temperature than is typical of adults, and both huddling contact with littermates and direct contact with the dam are reduced. At weaning, pups are effectively thermally independent. This ontogeny is correlated with behavioral, morphological and physiological changes during pup development including brown adipose tissue (BAT) thermogenesis, pelage development and body size. The onset of thermogenesis, and then thermoregulation, causes temporary reductions in pup growth rate on days 6 and 7 and again on days 12 and 13. Body weight, rather than pup age, appears critical for independent thermoregulation. These results are discussed relative to the extent of maternal hyperthermia and the physiological demands of the concurrent gestation characteristic of reproduction in Djungarian hamsters.

Induced components in the spontaneous ovulatory cycle of the Djungarian hamster (Phodopus campbelli).

Although Djungarian hamsters, Phodopus campbelli, show regular, 4-day spontaneous estrous cycles when tested for behavioral receptivity, this study shows that over 50% of 624 virgin females paired with males show their first behavioral estrous on the third day after pairing. The observed pattern is compared against predictions of estrous synchrony and/or estrous cycle suppression models. They fail to explain the high incidence of mating on the third day, and are incompatible with our current understanding of the natural history of the species. An alternative hypothesis, that Djungarian hamsters fail to cycle in the absence of a male, but are rapidly induced into a succession of 4-day cycles by his presence, appears to explain both the pattern of matings and earlier observations that estrous cycles could not be monitored by vaginal smear or lavage, only by interactions with a male. These analyses, thus, conclude that Djungarian hamster females may require a signal from a male to initiate and maintain successive 4-day estrous cycles.

Earlier thermoregulation and consequences for pup growth in the Siberian versus Djungarian dwarf hamster (Phodopus).

In spite of the shared reproductive timetable and phenotypic similarity of the two Phodopus species, previous studies had suggested that P. sungorus pups might thermoregulate at an earlier age and might experience decreases in growth rate as a consequence of that energetic demand. The current study investigated thermogenesis and thermoregulation in single pups and huddles separated from adults. Thermoregulation was earlier (Day 9 vs Day 12 for the earliest individuals) in P. sungorus than in P. campbelli and occurred at a lower body weight (6 vs. 8 g). Earlier development of insulating pelage in P. sungorus was not responsible. Both guard and underhair components of the pelt were completed earlier in P. campbelli development. Pup weights from five independent studies of each species were used to compare patterns of growth. Although birthweights were similar, P. sungorus pups grew faster during early lactation. Nest temperatures were probably involved in that faster growth. Maternal hyperthermia raised nest temperatures > or =4 degrees C above nonbreeding levels and left P. sungorus huddles 1.0 degrees C warmer than P. campbelli huddles throughout lactation. Comparisons between studies also suggested that laboratory conditions adversely affected pup growth in each species. In P. campbelli, cool ambient temperatures and biparental care improved early growth. In P. sungorus, providing fresh apple as a water source prevented a major decline in pup growth rate during mid to late lactation. Thus, as predicted, P. sungorus pups grow faster, thermoregulate earlier, and weigh more at Day 18 (when water is available to the pups).

Male-female interactions across the female estrous cycle: a comparison of two species of dwarf hamster (Phodopus campbelli and Phodopus sungorus).

Recent studies in our laboratory have suggested that monogamy may be the preferred mating system in the Djungarian hamster (Phodopus campbelli), whereas the available evidence for the closely related Siberian hamster (P. sungorus) does not show the same pattern. Here we examine the behavior of male-female dyads of both species interacting during 1-hr tests in large, familiar habitats containing defensible nest boxes, food, and water. Levels of aggression within pairs were low, compared with those seen during brief intrasexual encounters, whereas affiliative behaviors, such as sniffs, were high. P. campbelli scent marked more than twice as frequently as P. sungorus. Females of both species scent marked at a constant rate irrespective of their location in the habitat, whereas males scent marked at a higher rate in the female's home area. Two major features of the copulatory pattern differed between the two species: (a) The duration of the ejaculatory lock was five times longer in P. sungorus than in P. campbelli. (b) Both species had approximately the same number of mounts in each ejaculatory series, but the intromission/mount ratio was significantly higher in P. sungorus.

Cortisol and prolactin concentrations during repeated blood sample collection from freely moving, mouse-sized mammals (Phodopus spp.).

BACKGROUND AND PURPOSE: Validation of a method for obtaining blood samples that does not change cortisol or prolactin concentrations yet allows serial blood samples to be collected from animals under anesthesia, without prior handling, from freely interacting social groups of small mammals. METHODS: Results from five experiments are reported. Male dwarf hamsters (Phodopus spp.) were housed in modified home cages under continuous flow of compressed air that could be switched to isoflurane in O2 vehicle without approaching the cages. RESULTS: Dwarf hamsters respond to manual restraint with behavioral distress and increase in the concentration of the dominant glucocorticoid, cortisol, and decrease in prolactin concentration. Both effects are evident within one minute. In contrast, when this new method was used, neither cortisol nor prolactin changed in response to repeated sample collection (up to 8 successive samples at 2 hour intervals), prolonged isoflurane exposure, or substantial blood volume reduction (30%). Prolactin concentration was suppressed and cortisol concentration was increased in response to stimuli from other hamsters tested without anesthesia. Suppression of prolactin concentration was graded in response to the degree of stress and equaled the pharmacologic reduction caused by bromocryptine mesylate (50 microg of CB154 x 3 days). CONCLUSIONS: The technique is superior to alternatives for studies of behavioral endocrinology of freely interacting small mammals.

neuroendocrinological responses to alcohol intoxication in healthy males: relationship with impulsivity, drinking behavior, and subjective effects.

Ambiguous biochemical and subjective responses to alcohol may relate to preexisting individual differences in alcohol expectations, experience, or impulsivity. This study examined cortisol and alpha-amylase responses to alcohol and their association with trait impulsivity, alcohol expectancy, and subjective reports of alcohol's effects. Eighty-seven males assigned to an alcohol, sober, or placebo group provided biochemical and self-report measures. Both cortisol and alpha-amylase increased following alcohol administration. Impulsivity correlated with cortisol changes, and the greatest rise in cortisol correlated with high stimulating effects in the alcohol group. These findings emphasize the importance of individual differences in alcohol responses and support a relationship between hormonal responses and alcohol use.