Clomiphene citrate treatment during perinatal development alters adult partner preference, mating behaviour and androgen receptor and vasopressin in the male mandarin vole Microtus mandarinus.

During development, many aspects of behaviour, including partner preferences and sexual behaviour, are "organized" by neural aromatization of androgen and oestrogen. This study aimed to analyse these processes in the mandarin vole (Microtus mandarinus); this is a novel mammalian model exhibiting strong monogamous pair bonds. Male pups were treated daily with a sesame oil only (MC) or the oestrogen receptor blocker-clomiphene citrate sesame oil mixture (MT) from prenatal day 14 to postnatal day 10. Female pups were treated daily with sesame oil only (FC). Partner preferences, sexual behaviour, and the expression of androgen receptor (AR) and arginine vasopressin (AVP) were examined when animals were 3 months old. The MT and FC groups exhibited male-directed partner preferences and feminized behaviour. AR-immunoreactive neurons (AR-IRs) in the medial preoptic area (mPOA), bed nucleus of stria terminalis (BNST), and medial amygdaloid nucleus (MeA) were reduced in MT males compared to MC males, and there was no significant difference in the number of AR-IRs between MT males and FC females. AVP-immunoreactive neurons (AVP-IRs) in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) were reduced in MT males compared to MC males, and there were no significant differences in the number of AVP-IRs between MT males and FC females. The results indicate a significant role of hormone signalling in the development of male mate preference in the novel monogamous mammal model.

Methamphetamine Consumption Inhibits Pair Bonding and Hypothalamic Oxytocin in Prairie Voles.

Methamphetamine (MA) abuse has been linked to violence, risk-taking behaviors, decreased sexual inhibition, and criminal activity. It is important to understand mechanisms underlying these drug effects for prevention and treatment of MA-associated social problems. Previous studies have demonstrated that experimenter-administered amphetamine inhibits pair bonding and increases aggression in monogamous prairie voles. It is not currently known whether similar effects on social behaviors would be obtained under conditions during which the drug is voluntarily (actively) administered. The current study investigated whether MA drinking affects pair bonding and what neurocircuits are engaged. In Experiment 1, we exposed male and female voles to 4 days each of 20 and 40 mg/L MA under a continuous 2-bottle choice (2BC) procedure. Animals were housed either singly or in mesh-divided cages with a social partner. Voles consumed MA in a drinking solution, but MA drinking was not affected by either sex or housing condition. In Experiment 2, we investigated whether MA drinking disrupts social bonding by measuring aggression and partner preference formation following three consecutive days of 18-hour/day access to 100 mg/L MA in a 2BC procedure. Although aggression toward a novel opposite-sex animal was not affected by MA exposure, partner preference was inhibited in MA drinking animals. Experiment 3 examined whether alterations in hypothalamic neuropeptides provide a potential explanation for the inhibition of partner preference observed in Experiment 2. MA drinking led to significant decreases in oxytocin, but not vasopressin, in the paraventricular nucleus of the hypothalamus. These experiments are the first investigation into how voluntary pre-exposure to MA affects the development of social attachment in a socially monogamous species and identify potential neural circuits involved in these effects.

Effects of dietary tannic acid on the growth, hepatic gene expression, and antioxidant enzyme activity in Brandt's voles (Microtus brandti).

This study was designed to investigate the physiological and biochemical responses of Brandt's voles to the persistent presence of dietary tannic acid. The diet for animals in the experimental group was supplemented with 3% dietary tannic acid for 5weeks. The control group received a commercial lab chow. No significant differences were detected in body weight, organ (heart, kidney, and liver) weights, and organ parameters between animals from two groups. However, voles in the experimental group had significantly higher daily food intake, increased contents of proline and histidine in saliva and feces after protein hydrolysis, and elevated hepatic expression of transferrin than the control. Our results suggested the existence of adaptive strategies developed in Brandt's voles to overcome the adverse effects of dietary tannic acid. (1) Food consumption was increased to satisfy their nutritional demands. (2) The secretion of tannic-acid-binding salivary proteins was promoted. (3) The absorption of iron was enhanced. These alterations contributed to neutralize the negative effects of tannic acid and maintain body mass in animals supplemented with tannic acid. As the result of the consumption of tannic acid, hepatic expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase was significantly decreased, while the overall potential of the antioxidant system, characterized by increased hepatic enzymatic activities of catalase and glutathione peroxidase, was enhanced. Our results also implied the involvement of tannic acid in the regulation of lipid metabolism and oxidative stress in voles.

Manifestations of fasting-induced fatty liver and rapid recovery from steatosis in voles fed lard or flaxseed oil lipids.

Long-chain n-3 polyunsaturated fatty acids (PUFA) can have beneficial effects against fat deposition, cardiovascular diseases, and liver steatosis. We investigated how diets based on lard (predominantly saturated and monounsaturated fatty acids) or flaxseed oil (rich in 18:3n-3) affect liver fat-% and fatty acid profiles of tundra voles (Microtus oeconomus). We also studied potential participation of hyaluronan (HA) in the pathology of fatty liver and whether the development and recovery of fasting-induced steatosis are influenced by n-3 PUFA. The dietary fatty acid composition was manifested in the liver fatty acid signatures. Fasting for 18 h induced macrovesicular steatosis and the liver fat-% increased to 22% independent of the preceding diet. Fasting-induced steatosis did not involve inflammation or connective tissue activation indicated by the absence of both leukocyte accumulation and increased HA. Food deprivation modified the liver fatty acid signatures to resemble more closely the diets. Fasting reduced the proportions of long-chain n-3 PUFA in both dietary regimes and n-3/n-6 PUFA ratios in the lard-fed voles. Decreases in long-chain n-3 PUFA may promote lipid accumulation by modulating the expression of lipid-metabolizing genes. Dietary 18:3n-3 did not prevent the development or attenuate the manifestation of steatosis in the fasted voles or promote the recovery.

Comparative distribution of central neuropeptide Y (NPY) in the prairie (Microtus ochrogaster) and meadow (M. pennsylvanicus) vole.

Neuropeptide Y (NPY) has been implicated as a modulator of social behavior, often in a species-specific manner. Comparative studies of closely related vole species are particularly useful for identifying neural systems involved in social behaviors in both voles and humans. In the present study, immunohistochemistry was performed to compare NPY-like immunoreactivity (-ir) in brain tissue of the socially monogamous prairie vole and non-monogamous meadow vole. Species differences in NPY-ir were observed in a number of regions including the cortex, extended amygdala, septal area, suprachiasmatic nucleus, and intergeniculate leaf. Meadow voles had higher NPY-ir in all these regions as compared to prairie voles. No differences were observed in the striatum or hippocampus. The extended amygdala and lateral septum are regions that play a key role in regulation of monogamous behaviors such as pair bonding and paternal care. The present study suggests NPY in these regions may be an additional modulator of these species-specific social behaviors. Meadow voles had moderately higher NPY-ir in a number of hypothalamic regions, especially in the suprachiasmatic nucleus. Meadow voles also had much higher levels of NPY-ir in the intergeniculate leaflet, another key region in the regulation of circadian rhythms. Overall, species differences in NPY-ir were observed in a number of brain regions implicated in emotion, stress, circadian, and social behaviors. These findings provide additional support for a role for the NPY system in species-typical social behaviors.

Strong pituitary and hypothalamic responses to photoperiod but not to 6-methoxy-2-benzoxazolinone in female common voles (Microtus arvalis).

The annual cycle of changing day length (photoperiod) is widely used by animals to synchronise their biology to environmental seasonality. In mammals, melatonin is the key hormonal relay for the photoperiodic message, governing thyroid-stimulating hormone (TSH) production in the pars tuberalis (PT) of the pituitary stalk. TSH acts on neighbouring hypothalamic cells known as tanycytes, which in turn control hypothalamic function through effects on thyroid hormone (TH) signalling, mediated by changes in expression of the type II and III deiodinases (Dio2 and Dio3, respectively). Among seasonally breeding rodents, voles of the genus Microtus are notable for a high degree of sensitivity to nutritional and social cues, which act in concert with photoperiod to control reproductive status. In the present study, we investigated whether the TSH/Dio2/Dio3 signalling pathway of female common voles (Microtus arvalis) shows a similar degree of photoperiodic sensitivity to that described in other seasonal mammal species. Additionally, we sought to determine whether the plant metabolite 6-methoxy-2-benzoxazolinone (6-MBOA), described previously as promoting reproductive activation in voles, had any influence on the TSH/Dio2/Dio3 system. Our data demonstrate a high degree of photoperiodic sensitivity in this species, with no observable effects of 6-MBOA on upstream pituitary/hypothalamic gene expression. Further studies are required to characterise how photoperiodic and nutritional signals interact to modulate hypothalamic TH signalling pathways in mammals.

Litter size variation in hypothalamic gene expression determines adult metabolic phenotype in Brandt's voles (Lasiopodomys brandtii).

BACKGROUND: Early postnatal environments may have long-term and potentially irreversible consequences on hypothalamic neurons involved in energy homeostasis. Litter size is an important life history trait and negatively correlated with milk intake in small mammals, and thus has been regarded as a naturally varying feature of the early developmental environment. Here we investigated the long-term effects of litter size on metabolic phenotype and hypothalamic neuropeptide mRNA expression involved in the regulation of energy homeostasis, using the offspring reared from large (10-12) and small (3-4) litter sizes, of Brandt's voles (Lasiopodomys brandtii), a rodent species from Inner Mongolia grassland in China. METHODOLOGY/PRINCIPAL FINDINGS: Hypothalamic leptin signaling and neuropeptides were measured by Real-Time PCR. We showed that offspring reared from small litters were heavier at weaning and also in adulthood than offspring from large litters, accompanied by increased food intake during development. There were no significant differences in serum leptin levels or leptin receptor (OB-Rb) mRNA in the hypothalamus at weaning or in adulthood, however, hypothalamic suppressor of cytokine signaling 3 (SOCS3) mRNA in adulthood increased in small litters compared to that in large litters. As a result, the agouti-related peptide (AgRP) mRNA increased in the offspring from small litters. CONCLUSIONS/SIGNIFICANCE: These findings support our hypothesis that natural litter size has a permanent effect on offspring metabolic phenotype and hypothalamic neuropeptide expression, and suggest central leptin resistance and the resultant increase in AgRP expression may be a fundamental mechanism underlying hyperphagia and the increased risk of overweight in pups of small litters. Thus, we conclude that litter size may be an important and central determinant of metabolic fitness in adulthood.

Central vasopressin and oxytocin receptor distributions in two species of singing mice.

The neuropeptides arginine vasopressin (AVP) and oxytocin (OT) are key modulators of vertebrate sociality. Although some general behavioral functions of AVP and OT are broadly conserved, the detailed consequences of peptide release seem to be regulated by species-specific patterns of receptor distribution. We used autoradiography to characterize central vasopressin 1a receptor (V1aR) and OT receptor (OTR) distributions in two species of singing mice, ecologically specialized Central American rodents with a highly developed form of vocal communication. While both species exhibited high V1aR binding in the auditory thalamus (medial geniculate), binding in structures involved in vocal production (periaqueductal gray and anterior hypothalamus) was significantly higher in the more vocal species, Scotinomys teguina. In S. xerampelinus, receptor binding was significantly higher in a suite of interconnected structures implicated in social and spatial memory, including OTR in the hippocampus and medial amygdala, and V1aR in the anterior and laterodorsal thalamus. This pattern is concordant with species differences in population density and social spacing, which should favor enhanced sociospatial memory in S. xerampelinus. We propose that V1aR and OTR distributions in singing mice support an integral role for the AVP/OT system in several aspects of sociality, including vocal communication and sociospatial memory.

[The dynamics of tundra vole populations and accumulation of natural radionuclides in the territories with increased level of radioactive pollution].

The analysis of natural radionuclide (226Ra) contamination and tundra vole (Microtus oeconomus Pall.) relative number (from the sixties of 20-th century to 2007) reveals the impotent role of murine rodents in radionuclide migration. As a result of their pawing and of radionuclides carry-over by plants on the soil surface since the beginning of 1990 to present time the increase of 226Ra content in animals from control and radioactive plots have been ascertain. In the plots under study tundra vole number was half as much from 1993 to 2007. Simultaneous rotation of population cycle stages noticed in the control plot and in the plot with radium contamination, and long periods of low number was recorded in the plot with radium and thorium contamination, which are typical for border and impact populations.

Voles on small islands: effects of food limitation and alien predation.

Ecosystems of three trophic levels may be bottom-up (by food-plant availability) and/or top-down (by predators) limited. Top-down control might be of greater consequence when the predation impact comes from an alien predator. We conducted a replicated two-factor experiment with field voles (Microtus agrestis) during 2004-2005 on small islands of the outer archipelago of the Baltic Sea, south-west Finland, manipulating both predation impact by introduced American mink (Mustela vison) and winter food supply. In autumn 2004, we live-trapped voles on five islands from which mink had been consistently removed, and on four islands where mink were present, and provided half of these islands with 1.8 kg oats per vole. Body mass of female voles increased as a response to supplementary food, whereas both food supplementation and mink removal increased the body mass of male voles in subsequent spring. During winter, there was a positive effect of supplementary food, but in the subsequent summer, possible positive long-term impacts of food supplementation on field voles were not detected. Mink removal appeared not to affect density estimates of field voles during the winter and summer immediately after food addition. Trapping data from 2004 to 2005 and 2007 suggested, however, that in two out of three summers densities of voles were significantly higher in the absence than in the presence of mink. We conclude that vole populations on small islands in the archipelago of the Baltic Sea are mainly bottom-up limited during winter (outside the growing season of food plants), when food availability is low, and limited by mink predation during summer which slows population growth during the reproductive season of voles.

Hypothalamic suppressor-of-cytokine-signalling 3 mRNA is elevated and pro-opiomelanocortin mRNA is reduced during pregnancy in Brandt's voles (Lasiopodomys brandtii ).

Leptin acts within the hypothalamus to diminish food intake. In Brandt's voles (Lasiopodomys brandtii), both circulating leptin levels and food intake are elevated during pregnancy, suggesting an ineffectiveness of leptin to reduce food intake. Diminished hypothalamic leptin receptors and impaired leptin signal transduction are characteristic of central leptin resistance. The present study aimed to determine whether these characteristic modulations of leptin sensitivity occurred in pregnant Brandt's voles. The mRNA expression of the long form of the leptin receptor (Ob-Rb), suppressor-of-cytokine-signalling 3 (SOCS3), neuropeptide Y (NPY), agouti-related protein (AgRP), pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) in the hypothalamus were examined on dioestrous, day 5, day 10 and day 18 of pregnancy. Compared to controls, there was no significant change in hypothalamic Ob-Rb mRNA during the pregnancy. SOCS3 mRNA was increased significantly by 68% on day 10% and 93% on day 18 of pregnancy compared to controls. Despite elevated leptin levels, POMC mRNA was decreased significantly by 60% on day 18 of pregnancy, whereas no differences were found in the mRNA expression of NPY, AgRP and CART in pregnant voles compared to controls. The elevation of SOCS3 mRNA together with disrupted leptin regulation of neuropeptides in the hypothalamus suggests that leptin resistance may develop in pregnant Brandt's voles.

Sex-biased maternal investment in voles: importance of environmental conditions.

Adaptive bias in sex allocation is traditionally proposed to be related to the condition of mothers as well as to the unequal fitness values of produced sexes. A positive relationship between mother condition and investment into male offspring is often predicted. This relationship was also recently found to depend on environmental conditions. We studied these causalities experimentally using a design where winter food supply was manipulated in eight outdoor-enclosed populations of field voles Microtus agrestis. At the beginning of the breeding season in spring, food-supplemented mothers seemed to be in a similar condition, measured as body mass, head width, body condition index and parasite load (blood parasite Trypanosoma), to non-supplemented mothers. Food supplements affected neither the litter size, the reproductive effort of mothers, nor the litter sex ratios at birth. However, food supplementation significantly increased the birth size of male offspring and improved their condition, as indicated by reduced parasite loads (intestinal Eimeria). Interestingly, mothers in good body condition produced larger male offspring only when environmental conditions were improved by food supplements. Although the adaptiveness of variation in mammalian sex ratios is still questionable, our study indicates that mothers in good condition bias their investment towards male offspring, but only when environmental conditions are favourable.

Phytosterols affect endocrinology and metabolism of the field vole (Microtus agrestis).

Phytosterols or plant sterols (PS) enter the ecosystem via pulp mill effluents. They are also consumed by the general population of developed countries in natural remedies and margarines to lower elevated serum cholesterol levels. This study screened the endocrine and enzymatic parameters of the field vole (Microtus agrestis) for the effects of subchronic PS exposure at three doses (0, 5, or 50 mg of PS kg(-1) day(-1)). PS at 5 or 50 mg kg(-1) day(-1) decreased the relative liver weight of the voles. The kidney glycogen phosphorylase activity decreased at 5 or 50 mg kg(-1) day(-1), but the liver glycogen phosphorylase activity increased at 5 mg kg(-1) day(-1). The plasma estradiol and testosterone concentrations of males were higher due to PS supplement at 5 mg kg(-1) day(-1). This can be due to increased sex steroid synthesis from PS precursors. Biotransformation enzyme activities were not affected. PS caused multiple, previously unreported effects that were more pronounced at a low dose. As 5 mg PS kg(-1) day(-1) is the recommended dose for various health products, a thorough risk assessment of the effects and interactions of PS is warranted.

[The variability of the biochemical status of populations of the bank vole (Clethrionomys glareolus) subjected to the chronic action of ionizing radiation in relation to the time of their inhabiting radionuclide-contaminated areas]. / Izmenchivost' biokhimicheskogo statusa populiatsii ryzhikh polevok (Clethrionomys glareolus), podvergshikhsia khronicheskomu deistviiu ioniziruiushchei radiatsii, v zavisimosti ot vremeni ikh obitaniia na territoriiakh, zagriaznennykh radionuklidami.

The existence of a population of bank voles in the course of long time (50-60 years) in conditions of chronic ionizing radiation at low doses, promoted adaptation of this populations of rodents to the action of this factor. As opposed to, in a population of bank voles, living radionuclide-contaminated areas during 8-years after the Chernobyl accident, adaptation was not observed.

Transfer coefficient of 226Ra from vegetation to meadow voles, Microtus pennsylvanicus, on U mill tailings.

The 226Ra level in vegetation growing on U mine tailings in Elliot Lake, Ontario, Canada, was 211 + 22 mBq g-1 (dry weight) compared to less than 7 mBq g-1 (dry weight) in material from a control site. Skeletons of meadow voles (Microtus pennsylvanicus) established on the tailings had concentrations of 226Ra of 6,083 +/- 673 mBq per animal in winter; 7,163 +/- 1,077 mBq per animal in spring; 1,506 +/- 625 mBq per animal in summer; and 703 +/- 59 mBq per animal in fall, compared to less than 7 mBq per animal in controls. The 226Ra transfer coefficient from vegetation to voles (defined as total millibecquerels of 226Ra in adult vole per total millibecquerels of 226Ra consumed by the vole in its lifetime) was calculated as 4.6 +/- 2.9 X 10(-2) in summer and 2.8 +/- 0.6 X 10(-2) in fall.

Effect of copulation on the hypothalamic content of gonadotrophic hormone-releasing hormone in the vole, Microtus agrestis.

There was a drop of 56% in the hypothalamic content of Gn-RH in female voles 5 min after mating compared with that in unmated but receptive animals. This suggests that the surge of LH in vole plasma associated with reflex ovulation is evoked by a massive release of Gn-RH.

Are certain peculiarities in the distribution of somatostatin-like immunoreactivity (SLI) in the brain of sand rats (Psammomys obesus) possibly connected with an altered carbohydrate metabolism?

The hypothalamic and extrahypothalamic distribution of somatostatin-like immunoreactivity (SLI) was investigated in fed adult sand rats (Psammomys obesus) of both sexes using the immunofluorescence technique. Blood glucose and insulin concentrations were determined in these animals prior to decapitation. In a blind study, the amount of immunofluorescence of certain CNS areas and the glucose: Insulin ratio were compared and found to be connected: High amounts of SLI were detected in the dorsal hippocampus, in some hypothalamic nuclei and the median eminence of rats displaying low glucose levels. Sand rats with high blood glucose values did not show SLI in the hippocampal formation and the immunofluorescence of the circumventricular (hypothalamic) regions and the Eminentia mediana was drastically reduced. A possible correlation of SLI with insulin concentrations in the blood could not be revealed. The data obtained are discussed as a possible expression of a CNS influence on glucoregulation in this species.