Beta-adrenoceptor blockade and open-field behavior in male golden hamsters.

Open-field behavior was compared between untreated, saline-treated, and butoxamine (a beta-2-adrenoceptor antagonist) treated (15 and 5 mg/kg body weight) male golden hamsters (Mesocricetus auratus). Butoxamine-treated males spent significantly more time self-grooming than saline-treated and untreated males. Especially, untreated males and very similar saline control males showed a clear time sequential structure of behavior with two axes: a grooming-grooming sequence and a highly organized flankmark followed by scrape axis. The degree of this organization was markedly decreased in the butoxamine-treated males, showing an increase in organization of the transition between grooming acts. In general, these males displayed a more stereotypic pattern of behavior than the other. To reveal a systematic relation between the flankmark-scrape response and the exposition to butoxamine and to keep the numbers of experimental animals low, mixed samples were created through consecutive summing of the individual transition matrices of six males treated with 5 mg/kg b.wt. butoxamine to the 15 mg/kg b.wt. sample. By analyzing all samples separately, a positive linear relation between the number of low dosed males in the samples and the degree of organization of the flankmark-scrape sequence was found. The results suggest that the analysis of the transitional structure of behavior during short-term challenges can considerably contribute to an estimation of the coping style and seems to be a more sensitive method than comparing frequencies of behavioral indicators of stress.     

Copulatory behavior of golden hamsters: effects on pregnancy.

Two experiments were conducted to study the role of male copulatory behavior in initiating physiological responses necessary for pregnancy in female hamsters. In Experiment 1, it was found that copulation beyond the first ejaculatory series is critical to attainment of maximal probabilities of pregnancy. Whereas all females became pregnant when mated to a criterion of sexual satiety, only 20 percent were pregnant after one ejaculatory series. The relationship between increased copulatory stimulation and increased probability of pregnancy was further refined in Experiment 2. Females required more than 4 ejaculatory series to maximize the probability of pregnancy. Mounts without intromission had no effect. Neither parturition number of ova shed, nor little size appeared affected by amount of copulatory stimulation. A coadaptation between the copulatory pattern of the males and the response systems of the females of several rodent species appears to have evolved and to aid successful reproduction.     

Lead exposure alters the development of agonistic behavior in golden hamsters

We tested the effects of exposure to different doses of lead acetate (either 0, 25, 100, or 400 ppm) on the development of aggressive behavior in male golden hamsters. Pups were tested for offensive responses across puberty, as they were maturing from play fighting to adult aggression. Our data show a dose-specific effect of lead exposure on the development of aggression during puberty at doses resulting in blood levels well below 20 microg/dl. Animals exposed to 25 ppm lead acetate were faster and performed more than twice as many attacks on intruders by late puberty. They were also twice as likely to initiate adult instead of play-fighting attacks around mid-puberty. These observations were independent of any effect on growth. Thus, exposure to low doses of lead enhanced aggression and accelerated its maturation. As such, our data support the association between exposure to low doses of lead and aggressive behavior in boys.     

Dehydroepiandrosterone and exercise in golden hamsters.

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are adrenal androgens that have been associated with a sense of well-being in humans. We describe two experiments done to test the hypothesis that an increase in DHEA or DHEAS secretion is associated with the inclination to exercise using a hamster model. In the first experiment, morning blood samples were obtained from adult male golden hamsters at various intervals after being placed in cages with (EX group) or without (SED group) access to running wheels. The EX group had lower DHEA (6, 12, and 14 weeks; p < 0.05) and DHEAS (13 and 16 weeks; p < 0.01) levels than the SED hamsters. In the second experiment, the number of wheel revolutions was monitored in castrated adult male hamsters implanted with Silastic capsules containing no hormone (blank control group), testosterone, or DHEA. The number of wheel revolutions in the group receiving DHEA was not significantly different than the blank control group, whereas testosterone increased wheel running at 4, 5, and 7 weeks (p < 0.05). These results indicate that DHEA and DHEAS levels decrease with exercise in male golden hamsters and that exogenous DHEA does not enhance the tendency to run on wheels.     

The ependyma of ventriculus mesencephali in golden hamsters.

The ventriculus mesencephali of golden hamsters protrudes, in the form of a short channel, from the upper wall of the aquaeductus Sylvii in dorsal direction, between the third and fourth ventricle. It is lined with ependymal cells of cubic to cylindrical forms. Some of the ependymal cells possess basal processes. On the cell surface, there are cilia, microvilli and protoplasmatic protrusions. The cells contain relatively few endoplasmatic reticulum, a poorly developed Golgi apparatus, free and bound ribosomes and critiform mitochondria. The cell nuclei have round to oval shapes. Supraependymally, there are homogenous globules and intraventricular nerve fibres. The morphological characteristics of ependyma in the region of ventriculus mesencephali, as well as the close contact of the ependymal cells with capillaries, allow to suppose an active participation of these cells in the exchange of various substances also in this part of the brain ventricle system.     

Serotonin regulation of aggressive behavior in male golden hamsters (Mesocricetus auratus).

These studies examined the neurochemistry and neuroanatomy of the serotonin (5-HT) system innervating the anterior hypothalamus (AH) and the interaction of 5-HT receptor agonists with arginine vasopressin (AVP) in the regulation of offensive aggression in golden hamsters. Because specific 5-HT1A, 5-HT1B, and AVP V1A binding sites were observed within the AH by in vitro autoradiography, the hamsters were tested for offensive aggression after microinjections of AVP in combination with either the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetraline (DPAT) or the 5-HT1B agonist CGS-12066A (CGS) directly within the AH. Though treatment with DPAT resulted in a dose-dependent inhibition of AVP-facilitated offensive aggression, CGS was ineffective. In addition, a retrograde tracer was injected within the AH to localize the distribution of 5-HT neurons projecting to the area. Retrogradely labeled 5-HT neurons were found within the dorsal, median, and caudal linear raphe nuclei and are suspected to inhibit AVP-facilitated offensive aggression by an activation of 5-HT1A receptors in the AH.     

Obesity without overeating in golden hamsters

When male golden hamsters were switched from a diet of Purina rodent chow to a calorically-dense high-fat diet or were given ad lib access to a 32% sucrose solution in addition to chow, they adjusted their food intakes rapidly (within 24 hr) and did not overeat. Nevertheless, the fat-fed hamsters tripled their rate of weight gain and nearly doubled their carcass fat content after one month on the diet. Resting oxygen consumption (animals awake but quiet) was significantly lower in fat-fed animals than in chow-fed controls. Sucrose feeding had no effect on food intake, body weight gain, carcass composition or oxygen consumption. Thus, whereas rats exhibit dietary obesity in spite of increases in energy expenditure (diet-induced thermogenesis), fat-fed hamsters seem to become obese because of decreases in energy expenditure. However, although actual energy expenditure is reduced, fat-fed hamsters exhibit an enhanced thermogenic capacity. Interscapular brown adipose tissue mass, protein content, and DNA content as well as norepinephrine-stimulated oxygen consumption were all significantly elevated in fat-fed hamsters. The significance of these concurrent diet-induced decreases in energy expenditure and increases in thermogenic capacity is not clear, but they could be of some value in preparing the hamster for winter.     

Endotoxin-induced hyperthermia in pregnant golden hamsters

The degree of elevation and the duration of induced fever following endotoxin treatment of pregnant golden hamsters were examined. A radiothermistor was surgically implanted in the abdomen of each animal on day 6 of pregnancy. The animals were intravenously treated with a bolus injection of saline or endotoxin (1, 10, 20, or 200 micrograms/kg) on the morning of day 8 of gestation. Abdominal temperatures were monitored at 15-minute intervals on days 8 and 9 and at 1-hour intervals on days 10 through 14 of gestation. The mean temperature of the saline-treated control animals was 37.2 degrees C with a range from 36.5 to 38.2 degrees C. The total number of viable fetuses, and the mean fetal weight of the 1-microgram/kg group were not significantly different from those of the saline controls, although a statistically significant monophasic temperature elevation did occur between 3 and 9 hr post-treatment. Three of seven females that received 10 micrograms/kg had viable litters and exhibited a monophasic fever. The remaining four animals exhibited a biphasic fever and total resorption of all implanted fetuses. The first phase began 2.5 hr post-treatment and lasted for 3-6 hr. The second phase began 12-15 hr post-treatment and lasted for 15 to 25 hr. All animals receiving 20 or 200 micrograms/kg demonstrated similar multiple temperature elevations. Treatment of animals with greater than 20 micrograms/kg resulted in total resorption of all implanted fetuses and maternal weight loss. Nonpregnant females treated with 20 micrograms/kg of endotoxin exhibited a biphasic temperature elevation; thus the second phase of the fever response can not be attributed to embryo death and resorption.     

Polycystic liver disease in golden hamsters

Seven cases of multiple hepatic cysts of varying sizes and shapes were recorded in a closed colony of golden hamsters. Ante-mortem examination failed to show any clinical signs except for abdominal enlargement in one hamster. Multiple, thin-walled cysts of varying sizes (0.25 to 3.0 cm) and shape were observed in the liver. The larger cysts protruded from the liver surfaces and contained a colourless, clear, serous fluid and caused pathological change in 5-60 per cent of the hepatic parenchyma. Microscopically, the cysts were uni- or multilocular and lined by low cuboidal or flattened epithelial cells. The hepatic parenchyma around cysts showed pressure atrophy, necrosis, engorged sinusoids or other blood vessels or even haemorrhages, mild to extensive fatty or vacuolar degenerative changes and occasionally proliferation of biliary ducts.     

The effect of photoperiod on development of sexual behavior and fertility in golden hamsters

Male hamsters were raised on short (SD) or long (LD) photoperiods from birth, and the expression of sexual behavior at 6, 7, 10, and 14 weeks was compared. Neither mounting, intromissions, ejaculations, nor ultrasonic vocalizations differed in the two groups until 14 weeks of age, when these behaviors were performed more often by LD males. Sperm appeared in daily penile smears at an earlier age in SD than LD males, but LD males had larger flank glands and testes beginning at 6 and 7 weeks, respectively. Female siblings of the males in this study were mated around 7 weeks of age to adult males. Almost all females on both photoperiods conceived normally, and greater than 90% of the offspring delivered survived to weaning in both groups. Together, these results show that hamsters reared on SD are behaviorally and physiologically capable of reproducing for a period of time after puberty. The possibility that social influences or environmental factors other than photoperiod act on the juvenile hamster to retard reproductive development is discussed.     

Effect of systemic BCG infection in syrian golden hamsters.

The response of Syrian golden hamsters to systemic infection with several doses of Mycobacterium bovis (strain BCG) was assessed. Large numbers of organisms (10(7)), injected intravenously, were lethal for hamsters, whereas all animals survived infection with 10(4) colony-forming units of BCG. Animals responded immunologically to purified protein derivative as assessed by increased footpad swelling and splenic lymphocyte proliferation. The immediate cause of death was a diffuse granulomatous interstitial pneumonia.     

Maturation of olfactory exploration in golden hamsters

Following placement into a test cage filled with pine shavings, a litter of 7-8 golden hamster pups (aged 3-18 days postnatal: P3-18) initially displays a period of locomotion which ends reliably in huddling. The latency to establish a huddle (i.e., the duration of locomotion) is significantly longer in the presence of novel odors (fresh or lemon shavings) than more familiar odors (slightly soiled fresh or lemon shavings) but only in pups aged P12 or older. Pups aged P9 or younger do not locomote differentially in the presence of novel or familiar odors. This age difference represents the emergence of olfactory exploration in hamsters between P9 and P12. Exploration of novel odors interferes with initial attempts to establish a single huddle site by a litter, but does not preclude the ultimate aggregation of all pups at a single site as guided by conspecific odors and possibly thermotactile cues as well. Such shifts in the control of behavior by non-nest and nest-related, conspecific stimuli correspond well with the first occurrence of nest exits at P11-12 (e.g., Dieterlen, 1959) coupled with the persistent return of hamster pups to the maternal nest for as long as it is maintained (Rowell, 1961).     

Control of protein intake in golden hamsters

Experiments were performed to investigate the behavioural responses of golden hamsters to manipulations of dietary protein availability. In the first experiment, hamsters were maintained on a protein-free diet and a powdered diet containing 64.8% protein (P64.8). When the P64.8 diet was progressively diluted with cornstarch, hamsters increased their intake of this diet fraction, but protein intake nevertheless declined. When the protein content of the diet was 16.2%, animals derived only 6% of total calories from protein and lost weight despite normal intake of calories. In the remaining experiments, hamsters were maintained on a self-selection regimen of high-protein chow, pure carbohydrate (sugar cubes), and pure fat (vegetable shortening). When high-protein chow was removed for either 5 or 10 days, total caloric intake and body weight declined, and hamsters selectively increased protein intake for several days after high-protein chow was returned. Hamsters allowed access to high-protein chow for only one hour each day markedly increased the amount of high-protein chow they ate during this hour as protein-restriction continued, but still consumed only about 10% of their normal daily protein intake on this schedule and lost 20% of starting body weight in two weeks; when free access to high-protein chow was restored, these animals selectively increased their protein intake above pre-restriction levels. Hamsters given access to high-protein chow only on alternate days demonstrated a relatively modest and slowly developing increase in protein intake, perhaps because they incurred only a moderate protein deficit. The results suggest that when protein intake falls below normal minimum requirements, hamsters will demonstrate an adaptive protein hunger but make only a limited adjustment to the dilution of a protein-containing diet fraction.     

Developmental changes in open-field behavior in the kitten

Seventy-eight kittens from 3 to 7 weeks of age were studied in an open-field arena. Three major age-dependent changes were noted: (1) the number of floor squares entered was markedly higher for 5- and 6-week-olds than for younger animals, and slightly lower for 7-week-olds than for 5- and 6-week-olds; (2) the tendency to backtrack from 1 square to a just-vacated square decreased with age, the largest change occurring between 4 and 5 weeks of age; (3) the within-session decrement in locomotion was largest for 3-week-old kittens but was smallest for 4-week-olds and increased monotonically with age thereafter. The results suggest a possible role of hippocampal maturation.     

Dietary self-selection in chronically insulin-treated golden hamsters

Adult male golden hamsters were maintained on either Purina Rat Chow (chow group) or a self-selection diet consisting of high-protein chow, pure carbohydrate, and pure fat (choice group). Animals were injected for 12 consecutive days with either long-acting insulin (20 U/kg for 4 days, 60 U/kg for 4 days, and 100 U/kg for 4 days) or physiological saline. Insulin-injected hamsters under both dietary conditions increased their total caloric consumption by up to 33% and gained significantly more weight than saline-injected controls. Choice hamsters increased their fat intake in response to the 60 and 100 U/kg doses of insulin, but carbohydrate and protein consumption increased only in response to the 100 U/kg dose. Choice hamsters derived approximately 65% of the excess calories ingested during insulin administration from fat, but only 20% from carbohydrate and 15% from protein. Results are related to those previously observed in other species.     

SV40 lymphomagenesis in Syrian golden hamsters

Simian virus 40 (SV40) isolates differ in oncogenic potential in Syrian golden hamsters following intraperitoneal inoculation. Here we describe the effect of intravenous exposure on tumor induction by SV40. Strains SVCPC (simple regulatory region) and VA45-54(2E) (complex regulatory region) were highly oncogenic following intravenous inoculation, producing a spectrum of tumor types. Three lymphoma cell lines were established; all expressed SV40 T-antigen, were immortalized for growth in culture, and were tumorigenic following transplantation in vivo. New monoclonal antibodies directed against hamster lymphocyte surface antigens are described. The cell lines expressed MHC class II and macrophage markers and were highly phagocytic, indicating a histiocytic origin. Many hamsters that remained tumor-free developed SV40 T-antigen antibodies, suggesting that viral replication occurred. This study shows that route of exposure influences the pathogenesis of SV40-mediated carcinogenesis, that SV40 strain VA45-54(2E) is lymphomagenic in hamsters, that hamster lymphoid cells of histiocytic origin can be transformed in vivo and established in culture, and that reagents to hamster leukocyte differentiation molecules are now available.     

Photoperiodic modulation of steroid-induced lordosis in golden hamsters

The photoperiodic modulation of steroid-induced receptive behavior was investigated using ovariectomized female hamsters (Mesocricetus auratus) kept in short (6 hr of light/day) or long (16 hr of light/day) photoperiods. When a low dose of estradiol (E) was used, a significantly larger percentage of animals housed in long days displayed lordosis behavior than did animals housed in short days in tests with intact males as stimuli. This effect of photoperiod was reduced when a high dose of E was employed and was absent when E treatment was supplemented with progesterone. These observations suggest that a reduction in behavioral sensitivity to E may contribute to the reproductive quiescence induced by short photoperiods.     

Neural circuitry of play fighting in golden hamsters

In hamsters, play fighting matures gradually into adult aggression. As these two behaviors share many similarities in this species, we predicted that a single neural circuitry controls their offensive component. The goal of the present study was to identify neural systems associated with offensive play fighting in male juvenile golden hamsters. The neural circuitry related to this behavior was identified through quantification of c-Fos immunolabeling. We also looked for vasopressin cells possibly associated with play fighting. We found that areas previously associated with offensive aggression in adult hamsters, including the ventrolateral hypothalamus, the medial amygdala, and the bed nucleus of the stria terminalis, also showed enhanced c-Fos expression after play fighting. In addition, vasopressin neurons in the nucleus circularis and the medial division of the supraoptic nucleus expressed enhanced c-Fos immunolabeling in juveniles after play fighting, as previously reported in adult hamsters after aggression. Finally, enhanced c-Fos expression associated with play fighting was also found in areas previously unexplored in adult hamsters, such as the prefrontal cortex. Together, our results support the hypothesis of a single core neural circuitry controlling the offensive components of play fighting and adult aggression throughout puberty in hamsters.     

Occurrence of the parathyroid cyst in golden hamsters

Parathyroid cyst is a rare lesion, but has clinical significance because of it's ability to mimic a thyroid mass and it's association with hyperparathyroidism. The occurrence and morphology of parathyroid cysts in golden hamsters from neonatal to senile periods were investigated using light and electron microscopy. The results demonstrate the presence of chief cell cysts in the parathyroid glands of 5-day-old hamsters. Some chief cells lining the cyst wall showed mitosis and apoptosis. The existence of chief cell cysts may represent the rapid proliferation of the parathyroid chief cells in 5-day-old hamsters. Ciliated cysts were observed in the parathyroid glands of 5-day-, 1- and 3-month-old hamsters. Three cell types were distinguished in the wall of the ciliated cyst: Ciliated, mucous and basal cells. Ciliated cysts possessed the features of the pharyngeal epithelia without endocrine cells and may arise from embryological remnants of pharyngeal pouches in the neck undergoing cystic degeneration and entrapping portions of parathyroid tissue. The frequency of parathyroid cysts decreased with age.