Dwarf Hamster Research Articles

Seasonal changes of steroid levels in blood plasma of three phodopus species (Mammalia, Cricetinae)

Seasonal change of the base plasma level of testosterone and cortisol in males and progesterone, estradiol, and cortisol levels in females were analyzed in three Phodopus species: Ph. campbelli (Campbell's dwarf hamster), Ph. sungorus (Russian dwarf hamster), and Ph. roborovskii (Roborovski's dwarf hamster). Our results showed a significant difference in the seasonal plasma level of testosterone and cortisol in males and cortisol in females of all Phodopus species, though the rhythms of breeding activity were similar. The results are discussed in the context of adaptive differences between hormonal patterns of evolutionarily young species (Campbell's dwarf hamster and Russian dwarf hamster) and the evolutionarily old Roborovski's dwarf hamster, the phylogenic position of which is currently under discussion.

Endocrine mechanisms of seasonal adaptation in small mammals: from early results to present understanding

Seasonal adaptation is widespread among mammals of temperate and polar latitudes. The changes in physiology, morphology and behaviour are controlled by the photoneuroendocrine system that, as a first step, translates day lengths into a hormonal signal (melatonin). Decoding of the humoral melatonin signal, i.e. responses on the cellular level to slight alterations in signal duration, represents the prerequisite for appropriate timing of winter acclimatization in photoperiodic animals. Corresponding to the diversity of affected traits, several hormone systems are involved in the regulation downstream of the neural integration of photoperiodic time measurement. Results from recent studies provide new insights into seasonal control of reproduction and energy balance. Most intriguingly, the availability of thyroid hormone within hypothalamic key regions, which is a crucial determinant of seasonal transitions, appears to be regulated by hormone secretion from the pars tuberalis of the pituitary gland. This proposed neuroendocrine pathway contradicts the common view of the pituitary as a gland that acts downstream of the hypothalamus. In the present overview of (neuro)endocrine mechanisms underlying seasonal acclimatization, we are focusing on the dwarf hamster Phodopus sungorus (long-day breeder) that is known for large amplitudes in seasonal changes. However, important findings in other mammalian species such as Syrian hamsters and sheep (short-day breeder) are considered as well.

Operant behavior in dwarf hamsters (Phodopus campbelli): Effects of rate of reinforcement and reinforcer flavor variety

We investigated operant behavior in a novel species, the dwarf hamster (Phodopus campbelli). In two experiments, hamsters were trained to lever-press for food reinforcement. In Experiment 1, rate of reinforcement was manipulated across conditions using four variable-interval schedules of reinforcement (delivering one to eight reinforcers per min). As predicted, within-session decreases in responding were steepest on the richest schedule. In Experiment 2, lever-pressing was reinforced by either a constant or a variety of flavored food pellets. Within-session decreases in responding were steeper when the reinforcer flavor remained constant than when it was varied within the session. In both experiments, subjects hoarded most reinforcers in their cheek pouches rather than consuming them in the operant chambers. These results are incompatible with post-ingestive satiety variables as explanations for within-session decreases in operant responding and suggest that habituation to repeatedly presented reinforcers best accounts for subjects' response patterns. Additionally, a mathematical model that describes behavior undergoing habituation also described the present results, thus strengthening the conclusion that habituation mediates the reinforcing efficacy of food.

Complete Ablation of Vertical Auditive Conduct and Ear Pinna in a Dwarf Hamster ( Phodopus sungorus) with an Aural Spontaneous Squamous Cell Carcinoma

Abstract A 1-year-old male dwarf hamster ( Phodopus sungorus) with an inflammation of 7 days' duration in the right ear was examined. Abnormalities noted on physical examination were limited to the right ear and an anal mass. The right ear showed swollen skin and a yellowish secretion. The pinna presented scabs and ulcers, probably secondary to the scratching. Cytological examination of the secretion revealed rod-shaped bacteria and neutrophils. The anal mass was a freely movable nodule 1 mm in diameter attached to the anal skin. Initial treatment consisted of antibiotics and antiinflammatory drugs. After an incomplete response to the treatment, surgery was proposed. The surgical procedures consisted of right ear pinna and vertical canal ablation, and excision of the anal mass. The animal recovered uneventfully. All the samples were submitted for histologic examination. The diagnosis was aural squamous cell carcinoma (SCC) and anal papilloma. Although many neoplasias have been described in laboratory rodents, cutaneous SCC is underreported in rodents kept as pets, especially in hamsters. The case here describes an aural SCC that caused a nonresponsive otitis externa in a dwarf hamster. The tumor was successfully removed and the otitis resolved completely. To the authors' knowledge, this is the first report of ear SCC resolved after surgery in a dwarf hamster.

Circadian activity rhythms of dwarf hamsters (Phodopus spp.) under laboratory and semi-natural conditions

Circadian activity rhythms of dwarf hamsters (Phodopus spp.) under laboratory and semi-natural conditions

Film Review ETIENNE!: A Film about the Little Things in Life

I have to admit that I had no intention of reviewing this film for publication. My journey to the hostel on the beach in Sausalito was meant purely to be a fun night out at a special event with a colleague when she made the comment, “You’re reviewing this movie tonight, aren’t you?” The thought had never occurred to me. Why would a bona fide clinical ethicist want to review a movie about the end-of-life vacation of a hamster with terminal cancer? I mean really, I have to be serious about my work! Then the film started rolling ... Etienne, a dwarf hamster with a diagnosis of terminal cancer, isn’t the star of the film as I assumed; rather, Richard, loving owner, is the star. Richard’s goofiness and nerdy appearance is captivating. He takes you on his (mostly) bicycle journey from Laguna Beach in Southern California to Sausalito in Northern California, with a hand-crafted basket carrying Etienne hanging from the handlebars. In the days prior, Richard, who is taking a “sabbatical” from his mixed media art classes, has been informed that his best friend has terminal cancer. The veterinarian’s advice is euthanasia as soon as possible; however, the office receptionist suggests that Etienne “live life out loud” till its natural end. Richard opts for plan B and the adventure begins. Etienne’s “vacation” is Richard’s attempt to show the hamster how much he/she is loved and valued; it is also meant to be Etienne’s last hurrah. Up until now, Etienne’s life had been lived out in a series of hand-crafted domiciles, built by Richard with the best of design intent, but not always with structural integrity. Now, the hamster is running the beach and hiking the trails. In life and in death, Richard sets out to ensure that Etienne will shine. Convinced he cannot cure the disease, he aims to give total comfort and serenity during Etienne’s last days of life. Toward the end of the movie, somewhat awkwardly, a new character enters: Elodie. Her plight as a jilted college student who is also on “sabbatical” makes the two stories eventually collide. In some ways, Elodie can be a bit distracting, but she is a thread that pulls the movie together at its conclusion. The parallel to what is often seen when human patients are transitioned to comfort care is vivid. On the other hand, the caring images in the film between owner and animal also bring to mind the painfully difficult images encountered in hospitals when families refuse to transition their loved ones to comfort care and instead insist on their continued torture with needles, knives, and tubes of all sorts at the end of life. It seems that, sometimes, pets can get better endof-life care than genetic relations. This film affirms the importance of the “little things in life”, but what are these “little things” that the movie refers to? Rather than give up the plot, you will have to see the movie for yourself, as I suspect Bioethical Inquiry (2009) 6:513–514 DOI 10.1007/s11673-009-9189-7

Neurochemistry of Olivocochlear Neurons in the Hamster

The present study was conducted to characterize the superior olivary complex (SOC) of the lower brain stem in the pigmented Djungarian hamster Phodopus sungorus. Using Nissl-stained serial cryostat sections from fresh-frozen brains, we determined the borders of the SOC nuclei. We also identified olivocochlear (OC) neurons by retrograde neuronal tracing upon injection of Fluoro-Gold into the scala tympani. To evaluate the SOC as a putative source of neuronal nitric oxide synthase (nNOS), arginine-vasopressin (AVP), oxytocin (OT), vasoactive intestinal polypeptide (VIP), or pituitary adenylate cyclase-activating polypeptide (PACAP) that were all found in the cochlea, we conducted immunohistochemistry on sections exhibiting retrogradely labeled neurons. We did not observe AVP-, OT-, or VIP-immunoreactivity, neither in OC neurons nor in the SOC at all, revealing that cochlear AVP, OT, and VIP are of nonolivary origin. However, we found nNOS, the enzyme responsible for nitric oxide synthesis in neurons, and PACAP in neuronal perikarya of the SOC. Retrogradely labeled neurons of the lateral olivocochlear (LOC) system in the lateral superior olive did not contain PACAP and were only infrequently nNOS-immunoreactive. In contrast, some shell neurons and some of the medial OC (MOC) system exhibited immunofluorescence for either substance. Our data obtained from the dwarf hamster Phodopus sungorus confirm previous observations that a part of the LOC system is nitrergic. They further demonstrate that the medial olivocochlear system is partly nitrergic and use PACAP as neurotransmitter or modulator.

Intraspecific organization of dwarf hamsters Phodopus campbelli and Phodopus sungorus (Rodentia: Cricetinae) basing on mtDNA analysis

35 Two dwarf hamster species of the genus Phodopus —Djungarian hamster ( Ph. sungorus ) and Campbell’ hamster (Ph. campbelli )—have been widely used since 1960s in many laboratories of the world as model objects for studying various aspects of physiology, behavior, and seasonal changes in the organism. We were the first to perform analysis of mitochondrial DNA polymorphism of these two species, which revealed different phylogenetic lines separated by significant genetic distances. This finding is indicative of a long-term isolated existence of groups of hamster populations in different parts of their range and their independent evolution. This fact should be taken into account in interpreting the results of laboratory experiments and field observations. The sample of Campbell’ hamsters consisted of 24 animals from 13 geographic sites encompassing the major part of their range: Chuya and Kurai steppes (Russia), western and central areas of Mongolia, Inner Mongolia (China), and Chita region (Russia). We also analyzed the nucleotide sequences of hamsters from the vivarium of the Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences. The sample of Djungarian hamsters consisted of 18 animals, nine of which were caught in three sites of the main part of their range (Northern and Eastern Kazakhstan and Novosibirsk region (Russia)), and nine were caught in an isolated part of the range in the Minusink Basin (Russia). In addition, we analyzed the nucleotide sequences of mtDNA of Djungarian hamsters from vivariums of the Severtsov Institute of Ecology and Evolution (Russian Academy of Sciences) and the Institute of Animal Breeding and Husbandry (MartinLuther-University, Halle, Germany).

Social cues influence foraging in dwarf hamsters (Phodopus campbelli).

In 2 experiments, dwarf hamsters (Phodopus campbelli) were trained to find palatable foods in an open field. The location of each food patch remained the same throughout each experiment, and only 1 food was available per day. Once subjects had been trained to find each food in its unique location, they progressed to a testing phase in which subjects' mates were allowed to eat and hoard the food that was available in the open field each day. The foods that subjects' mates brought back to the home cages then served as discriminative stimuli signaling which food could be obtained in the open field. Subjects generally approached the patch containing the food hoarded by their mates, suggesting that dwarf hamster burrows could function as information centers.

In Three Brain Regions Central to Maternal Behaviour, Neither Male Nor Female Phodopus Dwarf Hamsters Show Changes in Oestrogen Receptor Alpha Distribution with Mating or Parenthood

Oestrogen receptor (ER)alpha immunoreactivity in three brain regions relevant to maternal behaviour (medial preoptic area, bed nucleus of the stria terminalis and medial amygdala) was measured in two species of dwarf hamster that both mate during a postpartum oestrous but differ in expression of paternal behaviour. Male and female Phodopus campbelli and Phodopus sungorus were sampled as sexually naive adults, following mating to satiety, and as new parents. In all brain regions, females expressed higher levels of ER alpha than males. Species did not have an effect on ER alpha distribution except in the medial amygdala, where P. sungorus females had higher expression levels than all other groups. Behavioural status was not associated with altered ER alpha expression. These results were not expected for females and suggest that a primary activational role for oestrogen, acting through ER alpha in these regions, does not generalize to maternal behaviour in Phodopus. In males, these results are consistent with previous manipulations of the ER alpha ligand, oestrogen, and suggest that paternal behaviour in P. campbelli is likely to be regulated by developmental effects of oestrogen on the brain during early life (similar to Microtus ochrogaster), rather than through activation by oestrogen at the time of fatherhood (similar to Peromyscus californicus).

Why we need rats: What it is like to use animals in neurobiological research in the UK?

I'm a big fan of rodents. As a kid, I had two pet mice (called Pip and Marty). As a teenager, I had four Russian dwarf hamsters (Sex, Drugs, Rock and Roll) and, as a student, I had a couple of piebald rats (Chicken and Noodle). Now, as a neuroscientist at a UK university, I have a colony of rats with numbers instead of names. It's a dilemma that many researchers face: how to reconcile their empathy with animals with their desire to develop safe and effective therapies for diseases or injuries. It is ethically challenging: for 7 years, I was simultaneously a vegetarian and vivisector.

Aromatase inhibition during adolescence reduces adult sexual and paternal behavior in the biparental dwarf hamster Phodopus campbelli

Previous studies have failed to identify an activational role for estradiol in the paternal behavior of Phodopus campbelli fathers. However, none of these studies addressed a developmental role that estradiol might play in establishing paternal behavior in this species. Males were orally administered the aromatase inhibitor letrozole (1 mg/kg/day) for three days at 18, 34, or 90 days of age. As adults, males were tested for paternal and sexual behavior. Letrozole treatment at 18 days resulted in males that spent less time huddling over pups during the birth, and had higher pup losses and male-biased pup survival for the first litter. Letrozole treatment at 34 days resulted in males that had altered sexual behavior; males had a longer interval between mounts and between intromissions, and took longer to achieve ejaculations over the first three ejaculatory series. Furthermore, these males sired smaller first litters and produced second litters with a male-biased sex ratio. Males treated with letrozole as adults showed a modest increase in paternal care during the birth, but pup development and survival were not altered. There was no effect of treatment on attack or retrieval behavior either as sexually naive adults or as new fathers. Thus, the results of the present study suggest that estradiol acts during adolescence to establish the normal expression of midwifery behavior and sexual behavior during adulthood.

Comparative analysis of the effect of predator odor on morphological and physiological parameters of adult male Campbell hamsters (Phodopus campbelli) and dwarf hamsters (Phodopus sungorus)

The effect of long-term exposure to natural excretions of the European polecat on the morphological parameters and hormonal status of adult male Campbell hamsters (Phodopus campbelli) and dwarf hamsters (Ph. sungorus) was studied. Exposure to volatile components of natural excreta of a potential predator did not have any significant effect on hamsters. The combined influence of volatile and nonvolatile components of the polecat’s excretions caused physiological stress in Ph. campbelli, while in Ph. sungorus, on the contrary, an increase in thymus weight and the plasma testosterone level was recorded.

Bacterial pseudomycetoma in dwarf hamster, Phodopus sungorus

A case of a dwarf hamster with two progressively growing nodules on the right fore limb is described. These were excised following ineffective medical treatment and were submitted for histopathological examination, which revealed bacterial pseudomycetoma in both nodules. To the authors' knowledge this is the first reported case of bacterial pseudomycetoma in a dwarf hamster.

In uniparental Phodopus sungorus, new mothers, and fathers present during the birth of their offspring, are the only hamsters that readily consume fresh placenta

Placentophagia is common among parturient female mammals but non-parturient females generally refuse placenta. Biparental male dwarf hamsters (Phodopus campbelli) readily consume placenta. The present study quantified placentophagia and liver acceptance in the closely related Siberian hamster P. sungorus in which males do not participate in the birth and are not responsive to a displaced pup. Sexually naïve P. sungorus males and females refused both placenta and liver (all groups <10%). Reproductive females specifically consumed placenta on the day before (G17), and the day of, parturition (G18) (>80%). Males rejected both tissues on G17 and accepted placenta soon after the birth (G18) (80%) only if they were present during the birth. Palatability of the placenta was not responsible for the species difference as P. campbelli accepted P. sungorus placenta. Results are consistent with a neophobic reaction to both placenta (conspecific or heterospecific) and liver as P. sungorus also rejected P. campbelli placenta.

Individual variation in cortisol responses to acute ‘on-back’ restraint in an outbred hamster

An outbred species of dwarf hamster (Phodopus campbelli) was used to assess between-individual variability in the response to, and recovery from, a one-time stressor of 6 min of physical restraint in a subordinate, on-back, position. Four repeated plasma samples were drawn under home-cage isoflurane anesthesia from 33 males and 38 females 50 min before, and then 10, 60, and 120 min after the stress onset. Plasma cortisol concentrations were higher in females than males, but there was no evidence for a sex difference in response to the stressor. The expected cross-sectional increase (∼50 ng/ml) in response to the stressor, followed by recovery, was seen. However, there was extensive individual variation, ranging from no reaction to continuous decline from the initial to the final sample. Results were expressed in four ways (absolute concentration, relative concentration, and area under the curve relative to ground and relative to the stress-induced increase) and also standardized and subjected to hierarchical cluster analysis. Clusters failed to effectively partition the between-individual variation and did not cluster by sex, age, or housing conditions. The current study cautions against ignoring individual differences and suggests that outbred animal models might be particularly relevant to understanding stress-related pathological conditions.

Species differences among various rodents in the conversion of 7α-hydroxycholesterol in liver microsomes

Our previous study demonstrated that there are species differences among vertebrates in their conversion of 7α-hydroxycholesterol (7HC) to 7-ketocholesterol (7KC). To examine this further, we investigated the differences in the products of 7α-hydroxycholesterol in various species of male muroid rodents. Adult male Syrian hamsters ( Mesocricetus auratus), dwarf hamsters ( Phodopus rovolovskii), Djungarian hamsters ( Phodopus sungorus), Chinese hamsters ( Cricetulus griseus), rat-like hamsters ( Tscherskia triton), and hispid cotton rats ( Sigmodon hispidus) were used. Microsomal fractions were prepared from their livers, and the activities of the enzymes that participate in the dehydrogenation of 7α-hydroxycholesterol were determined by measuring the products using high-performance liquid chromatography. 7α-hydroxycholesterol was converted to both 7α-hydroxy-4-cholesten-3-one (7HCO) and 7-ketocholesterol in all of the hamsters tested. However, in the rat-like hamster and the hispid cotton rat, 7α-hydroxycholesterol was converted mostly to 7α-hydroxy-4-cholesten-3-one, as also observed in the rat ( Rattus norvegicus). The results suggest that microsomal enzyme activity in the conversion of 7α-hydroxycholesterol to 7-ketocholesterol varies considerably, even within the subfamily Cricetinae and the family Muridae.

Castration reduces male testosterone, estradiol, and territorial aggression, but not paternal behavior in biparental dwarf hamsters ( Phodopus campbelli)

Biparental male hamsters, Phodopus campbelli, act as midwives during the birth of their litter and are highly responsive to an experimentally displaced pup. They also have high peripheral concentrations of estradiol, a hormone with known roles in maternal behavior. Surgical castration during the gestation of their first litter was used to investigate the source of that estradiol and the functional role of testicular sex steroids in paternal responsiveness. In Experiment I, castration reduced both testosterone and estradiol concentrations, confirming that the testes were the primary source of estradiol. However, neither paternal responsiveness nor multiple measures of reproductive success were altered by the castration. Aggression directed towards an intruder, however, was reduced by castration. In Experiment II, removal of prior experience with birth or pups also failed to alter paternal responsiveness in castrated males. Although the present results do not preclude a role for local estradiol synthesis in the brain, results do not support an association between high circulating estradiol in males and their paternal behavior.

Ontogeny of the transition from killer to caregiver in dwarf hamsters (Phodopus campbelli) with biparental care

Biparental Phodopus campbelli and uniparental P. sungorus juvenile litters (2 males, 2 females) both consumed amniotic fluid and placenta during the birth of younger siblings. Three days later, P. campbelli juveniles were most responsive to a displaced younger sibling. Thus, P. campbelli are responsive to pups as juvenile alloparents and as new parents; however, at intervening ages, infanticidal attack (bite) was seen. At 5, 7, 9, 11, or 13 weeks of age, male and female P. campbelli were given a 5-min test with an unrelated, 3-day-old, anesthetized pup. Females attacked more often than males, yet pup-retrieval rates did not differ. Female aggression increased with age and was replaced by retrieval behavior 3 days after parturition. Male attack ceased after a birth, but parental behavior did not increase, remaining below the rate for new fathers tested with their own awake pup. Over repeated testing, behavior in one test did not predict behavior in another. Transitions from caregiving alloparent to infanticidal adult and back to parental care were clear in females, but less discrete with this stimulus paradigm in these highly paternal males.

High maternal aggression in dwarf hamsters (Phodopus campbelli andP. sungorus)

:::::::::::::::: :::::::::::::::: : The defense of offspring, termed maternal aggression, is a highly conserved behavior in mammals, including rodents. This study examined relative levels of maternal aggression in two closely related dwarf hamster species, Phodopus campbelli and P. sungorus, that normally inhabit high latitude, boreal environments. When tested with first litters and with the breeder male remaining with the female (for P. campbelli the male is necessary for successful rearing of offspring), both species exhibited high levels of maternal aggression with average duration of aggressive behavior480 sec for a 10 min test. For P. sungorus, males are not required to rear offspring. P. sungorus females with either one or multiple litters (singly housed after impregnation) exhibited significantly higher levels of aggression (4300 sec) relative to females co-housed with the sires. In terms of species differences in attack style, P. campbelli exhibited a boxing or clawing strategy for B50% of total attack time, but for P. sungorus, this form of attack occurredo5% of the time. For P. sungorus, attacks to the vulnerable belly and flank constituted490% of all attacks, but these regions were attacked B50% of the time for P. campbelli. A survey of levels of maternal aggression of rodents in other genera suggests that maternal aggression in Phodopus is at the high end of the spectrum. Results of this study suggest that the presence of the breeder male may actually suppress aggression in P. sungorus. This fact, as well as its high level of aggression and its distant relationship to mice and rats, suggest P. sungorus as a possible model for future studies on the neurobiological basis of maternal aggression. The relationship between the high rates of maternal aggression and life history strategy in Phodopus is discussed. Aggr. Behav. 31:294–302, 2005. r 2005 Wiley-Liss, Inc.