Endocrinological responses during suckling in Hatano high- and low-avoidance rats

Maternal traits during lactation period reduce the anxiety-related behavior in male offspring: Results from a fostering study in Hatano rats

The Hatano strains of the Sprague Dawley rats have been selectively bred to create high- (HAA) and low- (LAA) active avoidance variants. We previously reported that HAA rats display more anxiety-related behavior than LAA rats, but whether this strain difference is affected by postnatal environmental factors remains unclear. In this study, we performed in- and cross-fostering between the HAA and LAA strains and investigated the effect of postnatal maternal traits on the emotional responses in each strain of the male offspring. We evaluated the effect of the fostering treatment on the emotional responses of the male offspring using the elevated plus maze test. The male LAA offspring reared by HAA dam showed higher anxiety-related behavior than those reared by LAA dam. Next, we quantified and typed various maternal behavior under the in- and cross-fostering conditions during the lactation period using a snapshot sampling method. This method allowed us to evaluate potential maternal traits that may influence the emotional responses of the offspring observed in our first experiment. We found that HAA dams showed long-term resting without offspring and offspring arrangement compared with LAA dams. These findings suggest that postnatal environmental factors may alter anxiety-related behavior in the male LAA offspring and that less direct contact with their offspring during the lactation period may induce anxiety-related behavior in male offspring.

Hatano rats selectively bred for high- and low-avoidance learning: an overview

This review compiles the results of a series of studies on Hatano high- and low-avoidance animals (HAA and LAA, respectively) established at the Hatano Research Institute, Food and Drug Safety Center, Japan. The HAA and LAA lines were selected and bred from Sprague Dawley rats for high and low avoidance learning, respectively, in a shuttlebox task since 1985. Although Hatano rats were selected only based on their behavioral traits in the active avoidance task, strain differences between the HAA and LAA lines were also observed in their stress responses and reproductive functions. However, the most noticeable finding of Hatano rats is a matched result in both active and passive avoidance tasks. The HAA and LAA lines are useful for next-generation toxicological studies, because the hereditary characters of behaviors or endocrine functions are well controlled.

Night eating model shows time-specific depression-like behavior in the forced swimming test

The circadian clock system is associated with feeding and mood. Patients with night eating syndrome (NES) delay their eating rhythm and their mood declines during the evening and night, manifesting as time-specific depression. Therefore, we hypothesized that the NES feeding pattern might cause time-specific depression. We established new NES model by restricted feeding with high-fat diet during the inactive period under normal-fat diet ad libitum. The FST (forced swimming test) immobility time in the NES model group was prolonged only after lights-on, corresponding to evening and early night for humans. We examined the effect of the NES feeding pattern on peripheral clocks using PER2::LUCIFERASE knock-in mice and an in vivo monitoring system. Caloric intake during the inactive period would shift the peripheral clock, and might be an important factor in causing the time-specific depression-like behavior. In the NES model group, synthesis of serotonin and norepinephrine were increased, but utilization and metabolism of these monoamines were decreased under stress. Desipramine shortened some mice’s FST immobility time in the NES model group. The present study suggests that the NES feeding pattern causes phase shift of peripheral clocks and malfunction of the monoamine system, which may contribute to the development of time-specific depression.

Annual ovarian activity monitored by the noninvasive measurement of fecal concentrations of progesterone and 17β-estradiol metabolites in rusa deer (Rusa timorensis)

To clarify the reproductive cycle of female Rusa deer (Rusa timorensis), the fecal concentrations of progesterone and 17β-estradiol metabolites were measured. Fecal samples were collected on a weekly basis for one year (between October, 2012 and September, 2013) from five healthy adult hinds in Thailand. At the beginning of the study, three hinds were pregnant. Two hinds delivered one healthy offspring, and one hind delivered a stillborn calf. The mating period of Rusa hinds in Thailand is from November to April. In pregnant hinds, fecal progesterone metabolite concentration was high in late pregnancy and abruptly declined to the baseline around parturition, suggesting that the placenta secretes a large amount of progesterone. Fecal 17β-estradiol metabolite concentration remained elevated around the day of parturition. Both concentrations of fecal progesterone and 17β-estradiol metabolites in non-lactating hinds were significantly higher than those in lactating hinds, indicating that ovarian activity of lactating hinds is suppressed by the suckling stimulus of fawn during lactation. The present study demonstrated that monitoring of fecal steroid hormones is useful method for assessing ovarian function in this species.

Effects of an extended photoperiod on gonadal function and condition of hair coats in Thoroughbred colts and fillies

The effects of an extended photoperiod (EP) in Thoroughbreds colts and fillies from winter at one year old to spring at two years old on the gonadal functions, coat condition, and endocrine changes were investigated. Sixty-two Thoroughbreds (31 colts and 31 fillies) reared in the Hidaka Training and Research Center (Hidaka), Japan Racing Association were used. Thirty of them (15 colts and 15 fillies) were reared under EP conditions from December 20 to April 10, and the remaining 32 horses were reared under natural light alone as a control group. For EP, a 100-watt white bulb was set near the ceilings of stalls, and lighting conditions of 14.5-hr light and 9.5-hr dark periods were established. Blood was collected from the jugular vein once a month from October at one year old to February at two years old in both colts and fillies, and then twice a month in colts and weekly in fillies after March, and the coat condition was evaluated in January and April in 56 horses. To investigate endocrine changes, the plasma concentrations of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), immunoreactive (ir-) inhibin, testosterone, estradiol-17β and progesterone were measured. No significant difference was noted in the coat condition between the two groups in January, but they changed from winter to summer coats (molting of winter coats) in April in the EP group compared with the control group. Regarding endocrine changes, the plasma concentrations of prolactin, FSH, ir-inhibin and testosterone were significantly higher in the EP colts than in the control group from January to April. The plasma concentrations of LH tended to rise in the EP colts from January to April compared with the control group. In the EP fillies, the plasma concentrations of prolactin, LH, ir-inhibin, estradiol-17β and progesterone were significantly higher during January and April, but a significantly high level of FSH was noted in the control than EP group in January. The ovulation day was advanced in the EP fillies compared with the control group. The present study clearly demonstrated that EP treatment during rearing advanced the molting of winter coats in both colts and fillies. These results suggested to be due to the action of prolactin being increased by EP treatment. In addition, EP treatment stimulated the hypothalamus-pituitary-gonadal axis even in yearlings, and advanced ovulation in fillies. Since EP treatment-induced changes in the yearlings were within the physiological range, and the method is safe and simple, EP treatment may be an effective technique in horse husbandry.

Male Hatano high-avoidance rats show high avoidance and high anxiety-like behaviors as compared with male low-avoidance rats

Our prime objective was to establish an optimal model animal for studying avoidance learning and memory in rodents. The two-way rat inbred strains of Hatano high- (HAA) and low-avoidance (LAA) animals were originally selected and bred in accordance with their high or low performance respectively in the shuttle-box active avoidance task. Previous studies demonstrated that they have clear strain differences in endocrine stress response, which is related to acquisition of aversive learning and emotional reactivity. To evaluate the effect of selection by the shuttle-box task on avoidance performance and emotional reactivity, male Hatano rats underwent passive avoidance, open field and elevated plus maze tests. The present results show that the avoidance performance in the passive task was significantly greater in HAA rats than in LAA rats. Furthermore, HAA rats showed high anxiety-like behaviors compared with LAA rats in open field and elevated plus maze tests. Taken together, this study demonstrated that 1) selection and breeding of Hatano HAA and LAA strain rats by shuttle-box task had been properly carried out with the criterion of high and low avoidance performance respectively and that 2) HAA rats were predisposed to high anxiety compared with LAA rats. These results indicated that Hatano HAA and LAA rats can be useful models for studying avoidance learning and memory.

Estrogenic regulation of Kiss1 mRNA variants in Hatano rats

Differences in reproductive endocrinology distinguish Hatano high-avoidance animals (HAA) from low-avoidance animals (LAA). Compared to HAA rats, female LAA rats secrete low levels of basal luteinizing hormone (LH) and a reduced LH surge. To investigate the underlying cause of the differences between the two strains, levels of the following mRNAs were measured in the hypothalamus of intact and ovariectomized (OVX) females treated with vehicle control or estradiol-17β (E2): gonadotropin-releasing hormone (Gnrh), newly isolated rat kisspeptin (Kiss)1 mRNA variant-1 (Kiss1V1) and variant-2 (Kiss1V2) and estrogen receptor (Er) α. In OVX-HAA rats, the levels of Gnrh mRNA in the preoptic area (POA) 30 h after E2 treatment were significantly higher than in OVX-LAA rats. For HAA rats, the levels of Kiss1V1 and Kiss1V2 mRNA in the anteroventral periventricular nucleus (AVPV) were significantly higher in the E2-treated group than in the vehicle-treated group. In the arcuate nucleus (Arc) of HAA rats, Kiss1V1 and Kiss1V2 expression was significantly lower in E2-treated females compared to vehicle-treated females. Kiss1V2 expression was significantly higher than Kiss1V1 expression in intact HAA rats. In E2-treated OVX-LAA rats, there were no changes in the expression levels of Gnrh, Kiss1V1 or Kiss1V2. In intact LAA rats, no differences were observed in the expression levels of Kiss1V1 or Kiss1V2 in the AVPV, but the expression levels of these mRNAs in the Arc were significantly lower in E2-treated OVX-LAA rats. Additionally, no strain differences were observed for Erα mRNA expression in either the AVPV or Arc. These results indicate that the failure of estrogenic regulation of GnRH neurons in the POA and of kisspeptin neurons in the AVPV of LAA rats causes low LH secretion and reduced reproductive function.

Lactation deficit in OFA hr/hr rats may be caused by differential sensitivity to stress compared with Wistar and Sprague Dawley rats

OFA hr/hr (OFA) rats present a major lactation deficit that impairs offspring survival. To explore whether abnormal stress responsiveness causes this deficit, we compared their hormonal (prolactin, progesterone, and corticosterone) responses to stress (room change and 2-min ether exposure) with those of Wistar and Sprague Dawley (SD) rats. We tested responses during the estrous cycle, pregnancy, lactation, after ovariectomy, and ovarian steroid hormone priming, and responses to suckling. We evaluated hypothalamic expression of receptors for prolactin (PRLRlong) and the isoforms of receptors for progesterone (PRA and B) and estrogen (ERα and β) in late pregnancy. We tested whether administration of an anxiolytic (diazepam) improved lactation. Ether exposure increased circulating levels of the three hormones in the three strains of rats, cycling and ovariectomized, but was less effective in pregnancy and lactation. Elevated estrogen level (estrus and estradiol-treated ovariectomized rats) potentiated the prolactin response more in SD and OFA rats than in Wistar rats. Elevated progesterone level (late pregnancy, lactation, progesterone-treated ovariectomized rats) inhibited the prolactin response less in OFA than in SD or Wistar rats. Ether exposure inhibited the prolactin and oxytocin responses to suckling only in OFA rats. Diazepam treatment increased pup survival rate and the prolactin response to suckling. Hypothalamic total PR mRNA content, assayed by RT-PCR, was higher in pregnant OFA rats compared with SD and Wistar rats, but the PRB/PRA protein ratio determined by Western blot was lowest in Wistar rats, intermediate in OFA rats, and highest in SD rats. The heightened sensitivity to stress of lactating OFA rats may contribute to their lactational deficit and be caused by a combination of hypoprolactinemia and reduced inhibitory capacity of progesterone.

Endocrinological differences between Hatano high- and low-avoidance rats during early two-way avoidance acquisition

Hatano high (HAA)- and low (LAA)-avoidance rats were selected from Sprague-Dawley rats genetically on the basis of their active avoidance behavior in a shuttle-box test. The purpose of this study was to investigate stress-related alterations of hormones corticotropin-releasing hormone (CRH), arginine-vasopressin (AVP), prolactin, and adrenocorticotropin (ACTH) in the brain and blood during early avoidance acquisition using two lines of Hatano rats. In paraventricular nucleus (PVN) of the hypothalamus, the CRH levels in HAA rats were significantly increased after shuttle-box tasks compared with before the tasks, whereas the CRH levels in LAA rats significantly decreased after shuttle-box tasks compared with before the tasks. In the HAA rats, the CRH and AVP levels in the median eminence decreased after shuttle-box tasks, whereas there were no significant differences in the levels between before and after shuttle-box tasks in LAA rats. The plasma concentrations of ACTH were significantly higher in HAA rats than in LAA rats after shuttle-box tasks. These results show that the response of CRH-ACTH was higher in HAA rats than in LAA rats. This phenotype may be an important reason for the high avoidance rates of shuttle-box tasks in HAA rats. These endocrine differences in early avoidance acquisition may be involved in regulation of their avoidance responses in the shuttle-box task.

The secretory pattern and source of immunoreactive prolactin in pregnant African (Loxodonta africana) and Asian (Elephas maximus) elephants

The objective of the present study was to define the secretion of prolactin (PRL) in pregnant African and Asian elephants. Levels of immunoreactive (ir-) PRL in serum and placental homogenates were measured by a heterologous radioimmunoassay (RIA) based on an ovine and human RIA system, and the localization of ir-PRL in the placenta was detected by immunohistochemistry using anti-human PRL. Circulating ir-PRL clearly showed a biphasic pattern during pregnancy in African and Asian elephants. Serum levels of ir-PRL started to increase from the 4 - 6th month of gestation and reached the first peak level around the 11-14th month. A second peak of circulating ir-PRL levels was observed around the 18-20th month of gestation followed by an abrupt decline after parturition. In contrast, in a case of abortion of an African elephant, the second peak of ir-PRL was not observed, and the levels remained low for about four months until parturition. The weight of the fetus delivered at the 17th month of gestation was 23.5 kg, which was quite small compared with normal fetuses in previous reports. Ir-PRL was detected in placental homogenates, and immunolocalization was observed in trophoblasts in both the African and Asian elephants, indicating that the placenta is the source of ir-PRL during pregnancy in elephants. The present results clearly demonstrated that circulating ir-PRL shows a biphasic pattern during normal pregnancy and that the placenta appears to be an important source of circulating ir-PRL during pregnancy in both African and Asian elephants.

Follicular turnover and hormonal association in postpartum goats during early and late lactation

To clarify the effect of lactation period on ovarian follicular activity and associated hormonal levels in goats, six goats were monitored daily by ultrasonographic examination with blood sampling during early (Days 5 to 25; Day 0 was the day of kidding) and late (Days 40 to 60) lactation. While the presence of a corpus luteum of pregnancy retarded follicular growth in the ipsilateral ovary until Days 11-13 postpartum, the total follicular number (TFN) and area (TFA) increased during late lactation due to the significant increase in the number of medium- and large-sized follicles and decrease in the number of small follicles. Four goats showed a similar pattern of follicular development during the period studied characterized by the emergence of five and six waves during the early and late lactation, respectively. The largest follicle diameter of the first three waves monitored during early lactation was significantly smaller as compared with the diameter of those existing during late lactation. TFN showed a positive correlation with FSH but showed a negative correlation with immunoreactive (ir-) inhibin and estradiol during the postpartum period. TFA was positively correlated with ir-inhibin, estradiol and PRL and negatively correlated with FSH during the monitored periods. The plasma levels of ir-inhibin and progesterone were significantly higher during late lactation compared with the levels recorded during early lactation. Ir-inhibin levels showed a significant positive correlation with LH and estradiol during early and late lactation but showed a negative correlation with FSH during the whole lactation period. LH was positively correlated with estradiol and PRL during early and late lactation, respectively. These results suggest that the lactation period has a detrimental effect on ovarian activity during the early postpartum period in goats.

Corticosterone as a marker of susceptibility to oxidative/nitrosative cerebral damage after stress exposure in rats

There are important individual differences in susceptibility to stress-induced diseases, most of them associated to the hypothalamic-pituitary and sympatho-medullo-adrenal axis functioning. Characterization of individual differences in animals may help to find the origin of this susceptibility. In order to study differences in oxidative and neuroinflammatory consequences in brain after stress exposure, we used an adult, male, outbred (Wistar:Hannover) population of 60 rats. Animals were subjected to 6h of immobilisation stress. Basal (1 week before stress) and post-stress (immediately after stress) plasma corticosterone (CC) was measured for each animal from the tail vein (basal: 239.74+/-19.44 ng/ml at 1500 h). Group H was assigned to animals with 33% higher levels of CC (>279.53 ng/ml) and group L to animals with 33% lower levels of CC (<199.09 ng/ml). After stress, animals with higher plasma CC levels in basal conditions showed higher adrenal response (higher post-stress CC levels) than rats with lower levels of basal CC. Furthermore, rats from H group are more vulnerable to accumulation of oxidative/nitrosative mediators in brain (higher calcium-independent nitric oxide activity and higher lipid peroxidation, by malondialdehyde determination, MDA) and also to the accumulation of proinflammatory mediators (higher PGE(2) levels) whereas showing less antiinflammatory protection (less 15-deoxy-PGJ(2) levels). Statistical analysis, by using ROC curves revealed cut-off values of basal plasma CC predicting animals with higher post-stress MDA and PGE(2) and lower PGJ(2) levels in brain. These data indicate that plasma basal levels of CC are an easily detectable and reproducible parameter for predicting the response of the individuals after an acute stress, providing further support for studies on individual differences.

Adrenal 20alpha-hydroxysteroid dehydrogenase in the mouse catabolizes progesterone and 11-deoxycorticosterone and is restricted to the X-zone

The enzyme 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) is a progesterone-catabolizing enzyme that is highly expressed in mouse ovaries and adrenals. Although the functional significance of ovarian 20alpha-HSD for the induction of parturition has been defined, regulation and distribution of 20alpha-HSD in the adrenal gland has not been determined. We demonstrate that the expression of adrenal 20alpha-HSD is restricted to the X-zone, a transient zone between the adrenal cortex and the medulla of yet unknown function. Adrenal 20alpha-HSD activity in male mice peaks at 3 wk of age and disappears thereafter, whereas 20alpha-HSD enzyme activity is maintained in adrenals from nulliparous female animals. Testosterone treatment of female mice induces rapid involution of the X-zone that is associated with the disappearance of the 20alpha-HSD-positive cells. Conversely, reappearance of 20alpha-HSD expression and activity in male animals is evident after gonadectomy. Moreover, pregnancy, but not pseudopregnancy, is accompanied by X-zone regression and loss of 20alpha-HSD activity. Pregnancy-induced X-zone regression and -abolished 20alpha-HSD expression is partially restored in animals that were kept from nursing their pups. We found that in addition to its progesterone-reducing activity, 20alpha-HSD also functions as an 11-deoxycorticosterone-catabolizing enzyme. The unaltered growth kinetics of the X-zone in 20alpha-HSD knockout animals suggests that 20alpha-HSD is not required for the regulation of X-zone growth. However, 20alpha-HSD expression and enzymatic activity in all experimental paradigms is closely correlated with the presence of the X-zone. These findings provide the basis for 20alpha-HSD as a reliable marker of the murine X-zone.