Naive Hamsters Research Articles

Social experience and social context alter the behavioral response to centrally administered oxytocin in female Syrian hamsters

The type of social behavior displayed by an individual is profoundly influenced by its immediate social environment or context and its prior social experience. Although oxytocin is important in the expression of social behavior in several species, it is not known if social factors alter the ability of oxytocin to influence behavior. The purpose of the present study was to test the hypothesis that social experience and social context alter the ability of oxytocin to regulate flank marking (a form of scent marking) in female Syrian hamsters. Oxytocin was microinjected into the medial preoptic anterior hypothalamic continuum (MPOA-AH) of socially experienced, dominant female hamsters which were then tested with either a subordinate partner, with a novel partner, or alone. Oxytocin induced flank marking in a dose-dependent manner but only when the experienced dominant hamsters were tested with their familiar, subordinate partners. Oxytocin did not induce flank marking when injected into socially naive female hamsters that were tested with an opponent or alone. In males, by contrast, oxytocin induced flank marking in dominant hamsters when they were tested with their subordinate partner or alone. These data support the hypothesis that social experience and social context interact to regulate the ability of oxytocin to stimulate flank marking by its actions in the MPOA-AH in female hamsters.

Actions of Testosterone in Prepubertal and Postpubertal Male Hamsters: Dissociation of Effects on Reproductive Behavior and Brain Androgen Receptor Immunoreactivity

This study was conducted to determine whether there is a increase in responsiveness to the activating effects of testosterone on male reproductive behavior during puberty in male golden hamsters and whether responsiveness to behavioral actions of testosterone is correlated with the ability of testosterone to upregulate brain androgen receptor immunoreactivity (AR-ir). Sexually naive male hamsters were castrated at 21 or 42 days of age and implanted subcutaneously with a pellet containing 0, 2.5, or 5 mg of testosterone. One week later, males were given a 10-min mating test with a receptive female. Animals were euthanized 1 hr after the behavioral test, and blood samples and brains were collected. Plasma testosterone levels were equivalent in prepubertal and adult males that had been administered the same dose of testosterone. However, adult males exhibited more mounts, intromissions, and ejaculations than prepubertal males, demonstrating that postpubertal males are more responsive than prepubertal males to the effects of testosterone on sexual behavior. In both age groups, testosterone increased the number of AR-ir cells per unit area in several brain regions involved in male sexual behavior, including the medial preoptic nucleus (MPN), medial amygdala, posteromedial bed nucleus of the stria terminalis, and magnocellular preoptic nucleus (MPNmag). Surprisingly, testosterone increased AR-ir in the latter three regions to a greater extent in prepubertal males than in adults. Thus, prepubertal males are more responsive to the effects of testosterone on AR-ir in these regions. In a separate experiment, a pubertal increase in the number of AR-ir cells per unit area was found in both the MPN and MPNmag of intact male hamsters. These results indicate that a testosterone-dependent increase in brain AR during puberty may be necessary, but is not sufficient, to induce an increase in behavioral responsiveness to testosterone.

Evaluation of selected antiprotozoal drugs in the Babesia microti-hamster model.

The presently used therapy for Babesia microti infections, a combination of quinine and clindamycin, does not always result in parasitologic cures. To identify possible alternative chemotherapeutic agents for such infections, we screened, in the hamster-B. microti system, 12 antiprotozoal drugs that have either recently been released for human use or were in experimental stages of development at the Walter Reed Army Institute of Research for the treatment of malaria and leishmaniasis. Several well-recognized antimalarial drugs, such as mefloquine, halofantrine, artesunate, and artelenic acid, exhibited little or no effect on parasitemia. Two 8-aminoquinolines, WR006026 [8-(6-diethylaminohexylamino)-6-methoxy-4-methylquinoline dihydrochloride] and WR238605 [8-[(4-amino-1-methylbutyl)amino]-2,6-dimethoxy-4-methyl-5 -(3-trifluoromethylphenoxy-7) quinoline succinate], produced clearance of patent parasitemia. Furthermore, blood from infected hamsters treated with WR238605 via an intramuscular injection failed to infect naive hamsters on subpassage, thus producing a parasitologic cure. These two compounds merit further screening in other systems and may prove useful in treating human babesiosis.

Resistance to tick-borne spirochete challenge induced by Borrelia burgdorferi strains that differ in expression of outer surface proteins.

Hamsters were immunized with thimerosal-killed Borrelia burgdorferi 297 or a mutant of 297 (M297) that lacks the 49-kb linear plasmid and expression of outer surface proteins A and B (OspA and OspB). Ixodes scapularis nymphs infected with either the B. burgdorferi sensu stricto strain 297 or JMNT, similar in OspA and OspB but differing in OspC expression, were used to evaluate protection. In a homologous challenge, 24 hamsters were vaccinated, 8 each with 297 or M297 and 8 sham (adjuvant)-vaccinated controls. Hamsters vaccinated with either bacterin were completely protected against a natural tick bite or subcutaneous (s.c.) inoculation of 297. Borreliae were effectively eliminated from 80 to 90% of the 297-infected ticks that fed on four hamsters immunized with the 297 bacterin. Cultures of spirochetes isolated from the ticks that remained infected were infectious and induced joint inflammation in naive hamsters. There was no reduction of strain 297 spirochetes in ticks that fed on four hamsters immunized with M297, but the hamsters were protected. Results with the M297 bacterin indicate that proteins other than OspA or OspB can protect hamsters against a tick challenge without eliminating B. burgdorferi in the tick. In a heterologous challenge, 36 hamsters were vaccinated, 12 with each bacterin and 12 controls. None of the hamsters immunized with either bacterin were protected from a challenge involving JMNT-infected ticks, while two of four were protected against an s.c. challenge. Hamsters challenged s.c. with strain 297 spirochetes were protected. There was partial elimination of JMNT spirochetes in ticks that fed on the group of four hamsters immunized with the 297 bacterin, and infection rates were reduced by 50 to 60%. JMNT spirochetes reisolated from the ticks that fed on 297-vaccinated hamsters also remained infectious for hamsters. In the JMNT-infected ticks that fed on four M297-immunized hamsters, there was no decline in the proportion of infected ticks. Destruction of spirochetes in ticks that fed on the hamsters vaccinated with the 297 bacterin suggests that antibodies to OspA and OspB may have been responsible, since the mutant did not induce this activity.

Role of L3T4+ and 38+ T-cell subsets in resistance against infection with Treponema pallidum subsp. pertenue in hamsters

The protective immunity conferred by T-cell subsets against infection with Treponema pallidum subsp. pertenue was studied. We demonstrated that hamster T cells can be separated into two subsets by monoclonal antibody (MAb) GK 1.5 (anti-L3T4) and MAb 38. Eighty-five percent of hamster thymocytes were L3T4+ and 87% were 38+ cells; 84% were dual positive for MAbs anti-L3T4 and 38. In the peripheral lymph nodes, however, the L3T4+ and 38+ T cells were mutually exclusive according to two-color immunofluorescence analysis. The two T-cell subsets were found to be functionally distinct according to their secretion of interleukin 2 (IL-2) when stimulated with concanavalin A. The L3T4+ cells secreted IL-2 and had characteristics of T helper cells, while the 38+ cells did not secrete IL-2 and appeared to be T cytotoxic-suppressor cells. Transfer of 4 x 10(6) helper or cytotoxic-suppressor T lymphocytes from T. pallidum subsp. pertenue-immune hamsters protected irradiated naive hamsters against challenge with this subspecies. IL-2 production could still be detected in the irradiated recipients 12 days after irradiation of naive recipients, although at a low level. This suggests that the remaining lymph node cells could support the survival and expansion of the infused cytotoxic-suppressor T cells. No accumulation of macrophages was observed in regional lymph nodes of immune T-cell recipients within 10 days of infection. Instead, there was an influx of polymorphonuclear neutrophils in all animals injected with T. pallidum subsp. pertenue. This report demonstrates that hamster T cells can be separated into two phenotypically and functionally distinct subsets and that both T-cell subsets confer protection against challenge with T. pallidum subsp. pertenue.

The outer bilayer of the adult schistosome tegument surface has a low turnover rate in vitro and in vivo

An immunoradiometric assay has been used to determine the rate of loss of host erythrocyte antigen from the tegumental surface of adult Schistosoma mansoni. Host antigens were lost from the parasite surface with a half-time of up to 45 h during chase incubation in vitro, and with a half-time of about 5 days during residence in vivo in naive recipient hamsters. Since the host antigens were associated intimately with the outer bilayer of the tegument surface, it is suggested that the rate of surface turnover may similarly be very low. The implications of these findings for immune evasion by the adult parasite are discussed.

Ancylostoma ceylanicum: migratory behaviour in golden hamsters after oral and parenteral infection

The infectivity and migratory pattern of Ancylostoma ceylanicum infective larvae (L3) were investigated in hamsters infected by various routes. Following oral administration 40-70% of L3 attained maturity and there was no tissue migration. Following subcutaneous inoculation a small number (1-1.2%) of L3 attained maturity in the intestine after completing the broncho-oesophageal journey. Larvae which penetrated the skin also became adult in the intestine. Most of the larvae entering parenterally remained at the site of infection and in the tracheal region for more than 100 days without undergoing any development, other than desheathment. Those transmitted orally to naive hamsters developed in the normal way. Larvae inoculated parenterally into female hamsters were able to infect offspring in milk, but could not cross the placental barrier.

Langerhans Cell Function Dictates Induction of Contact Hypersensitivity or Unresponsiveness to DNFB in Syrian Hamsters

The relationship between distribution and function of Langerhans cells within the epidermis and the capacity of cutaneous surfaces to promote the induction of contact hypersensitivity to DNFB have been examined in inbred Syrian hamsters. In a manner very similar to previous findings in mice, the results indicate that hamster cutaneous surfaces deficient in normally functioning Langerhans cells, naturally (cheek pouch epithelium) or artificially (after perturbation with ultraviolet light), are inefficient at promoting DNFB sensitization. Instead, DNFB applied to these regions of skin results in the induction of a state of specific unresponsiveness. Viable lymphoid cells from unresponsive hamsters can transfer the unresponsiveness to naive hamsters suggesting that active suppression is at least partly responsible, probably mediated by T lymphocytes.

Contact hypersensitivity, humoral immunity, and specific unresponsiveness can be induced in Syrian hamsters with simple haptens.

Several inbred strains of Syrian hamsters have been immunized by skin painting with highly reactive haptens. Classical contact hypersensitivity has been assayed by the ear swelling response: the response is hapten-specific, exaggerated after re-immunization with the original hapten, and can be transferred adoptively to naive syngeneic hamsters with viable lymphoid cells, suggesting that contact hypersensitivity is mediated in hamsters by T lymphocytes. Moreover, skin painting with hapten induces significant serum titers of anti-hapten antibodies, indicating that antigen-specific B lymphocytes are also activated. Hamsters can be rendered unresponsive to these same haptens by conventional methods: 1) i.v. inoculation of the soluble hapten sulfonate or 2) inoculation of hapten-derivatized syngeneic lymphoid cells. Hamsters treated with these "tolerizing" maneuvers develop profound hapten-specific unresponsiveness that can be adoptively transferred to naive recipients with living lymphoid cells. "Unresponsive" animals, however, make strong anti-hapten antibody responses that rival the humoral immune responses found after skin sensitization. The data suggest that an active process is involved in the induction and maintenance of the unresponsive state, but responsibility can not be assigned firmly to putative suppressor T cells or to an antibody-mediated B suppressor modality.

Reinforcement and the organization of behavior in golden hamsters: Brain stimulation reinforcement for seven action patterns.

Golden hamsters were reinforced with intracranial electrical stimulation of the lateral hypothalamus (ICS) for spending time engaging in one of seven topographically defined action patterns (APs). The stimulation used as reinforcer elicited hoarding and/or feeding and supported high rates of bar pressing. In Experiment 1, hamsters were reinforced successively for digging, open rearing, and face washing. Digging increased most in time spent, and face washing increased least. Experiments 2-5 examined these effects further and also showed that "scrabbling," like digging, was performed a large proportion of the time, almost without interruption, for contingent ICS but that scratching the body with a hindleg and scent-marking showed relatively little effect of contingent ICS, the latter even in an environment that facilitated marking. In Experiment 6, naive hamsters received ICS not contingent on behavior every 30 sec (fixed-time 30-sec schedule). Terminal behaviors that developed on this schedule were APs that were easy to reinforce in the other experiments, but a facultative behavior, face washing, was one not so readily reinforced. Experiment 7 confirmed a novel prediction from Experiment 6--that wall rearing, a terminal AP, would be performed at a high level for contingent ICS. All together, the results point to both motivational factors and associative factors being involved in the considerable differences in performance among different reinforced activities.

The attractiveness of Harderian gland smears to sexually naive and experienced male golden hamsters

The Harderian gland of the golden hamster shows pronounced sexual dimorphism in histology and products. Sexually experienced or inexperienced males were attracted to fresh smears of female and male Harderian gland as opposed to a control. Female smears were investigated significantly more than male smears. Control smears of quadriceps muscle proved unattractive. Neither category of male preferred oestrus to mid-cycle Harderian smears, and attractiveness did not correlate with protoporphyrin content. Males were unattracted to protoporphyrin solution. Cephalic olfactory cues, such as Harderian secretions, may be of importance in tunnel-dwelling rodents.

Induction of maternal behavior in nulliparous golden hamsters ( Mesocricetus auratus)

The purposes of this study were to determine: (1) if naive hamsters could be induced to behave maternally through exposure to pups (i.e., to become “sensitized”); (2) if previous exposure to pups had any effect on the latency to sensitize; and (3) the differences in the latency to sensitize between males and females. Naive females sensitized with a mean latency of 18 hr; previously sensitized females, 28 hr; and males 72 hr. The female groups did not differ from each other, and naive females differed significantly from naive males.

Sexual and olfactory preferences of naive and experienced male hamsters

The olfactory preferences and behavioural responses of sexually naïve and sexually experienced male hamsters ( Mesocricetus auratus) towards anaesthetized conspecifics were investigated. Olfactory preference tests, in which the odours of a pair of anaesthetized stimulus animals were presented in a two-choice olfactometer, revealed that both sexually inexperienced and experienced males preferred female (oestrous and dioestrous) to male conspecific odours, but did not discriminate between the odours of receptive and non-receptive females. Similar results were obtained when a pair of unfamiliar anaesthetized conspecifics were presented in a neutral arena (supine test) to sexually naïve and experienced male hamsters. Experienced males directed significantly more mounts to anaesthetized females than did sexually inexperienced males.

The Ontogeny of Predatory Behaviour in the Golden Hamster (Mesocricetus a. Auratus). IV. Effects of Prolonged Exposure, Iti, Size of Prey and Selective Breeding

As an outgrowth of previous experimental work (POLSKY, 1977a, 1977b, 1977c) this paper presents findings which examined the influence of the following variables on the development of predatory behaviour in golden hamsters (M. a. auratits) : (a) prolonged exposure to the prey; (b) the interval between successive prey presentations (ITI) ; (c) the size of prey, and (d) selective breeding. Nymphs of Locusta migratoria served as prey. The basic methodology consisted of testing naive hamsters individually for the capture of a locust in their own home compartment. The principal measure was latency to capture; in addition, in Experiment 3 the frequency of exploration of the prey, withdrawal from the prey, nip at the prey and unsuccessful capture were recorded. Results showed: 1. Increasing familiarization with the prey via prolonged exposure resulted in an increase in the incidence of capture. 2. Latency to capture decreased significantly with repeated testing when the prey was presented at intervals of five or ten days; no significant decrease occurred when the prey was presented at intervals of one day. Further, the response of capture remained intact in established captors after a period of seventy days without the opportunity for capture. 3. Large prey were captured with relatively high latencies by forty day old hamsters; overall, forty day old hamsters, when compared with seventy day old hamsters, also showed a greater frequency of the behaviours associated with capture. 4. Prey capture was susceptible to the effects of selective breeding. The above results were discussed within the framework of habituation (Experiment i), methodological procedures and the stability of the prey capture response (Experiment 2), the relative size between predator and prey (Experiment 3) and genetic predispositions for capture (Experiment 4). Areas for future research were suggested.

The Ontogeny of Predatory Behaviour in the Golden Hamster (Mesocricetus a. Auratus). Iv. Effects of Prolonged Exposure, Iti, Size of Prey and Selective Breeding

As an outgrowth of previous experimental work (POLSKY, 1977a, 1977b, 1977c) this paper presents findings which examined the influence of the following variables on the development of predatory behaviour in golden hamsters (M. a. auratus) : (a) prolonged exposure to the prey; (b) the interval between successive prey presentations (ITI) ; (c) the size of prey, and (d) selective breeding. Nymphs of Locusta migratoria served as prey. The basic methodology consisted of testing naive hamsters individually for the capture of a locust in their own home compartment. The principal measure was latency to capture; in addition, in Experiment 3 the frequency of exploration of the prey, withdrawal from the prey, nip at the prey and unsuccessful capture were recorded. Results showed: 1. Increasing familiarization with the prey via prolonged exposure resulted in an increase in the incidence of capture. 2. Latency to capture decreased significantly with repeated testing when the prey was presented at intervals of five or ten days; no significant decrease occurred when the prey was presented at intervals of one day. Further, the response of capture remained intact in established captors after a period of seventy days without the opportunity for capture. 3. Large prey were captured with relatively high latencies by forty day old hamsters; overall, forty day old hamsters, when compared with seventy day old hamsters, also showed a greater frequency of the behaviours associated with capture. 4. Prey capture was susceptible to the effects of selective breeding. The above results were discussed within the framework of habituation (Experiment 1), methodological procedures and the stability of the prey capture response (Experiment 2), the relative size between predator and prey (Experiment 3) and genetic predispositions for capture (Experiment 4). Areas for future research were suggested.

The Ontogeny of Predatory Behaviour in the Golden Hamster (M. a. Auratus). Iii. Sensory Preexposure

This paper represents a continuation in a series of experimental studies (POLSKY, 1977a, 1977b) on the ontogeny of predation in the golden hamster (M.a. auratus). The variable under scrutiny in the two experiments reported was sensory preexposure. Sensory preexposure was defined as exposure to the sensory characteristics of the prey without the concomitant opportunity for This was accomplished by inserting the prey (Locusta migratoria) into specially constructed perspex cubes into which naive hamsters could see and/or smell. Control subjects were exposed to empty cubes. Subjects were housed singly and each lived continuously with the appropriate type cube which was positioned on the floor of their testing compartment. Subsequently, subjects were tested for the capture of a fourth instar nymph. The principal measure was latency to capture; additional measures were exploration of the prey, withdrawal from the prey, nip at the prey, and unsuccessful capture. Collectively the results showed: 1. Preexposure enhanced the tendency for capture; 2. Preexposure through olfaction appeared to be the chief mediator of the effect; 3. The interval between preexposure and test was of minor importance; 4. The effects of preexposure early in ontogeny (26-31 days) were minimal if coupled with an early test (31 days) ; however, with the administration of a relatively late test (51 days), preexposure early in ontogeny was as affective as late preexposure (46-51 days). The above findings, along with the data from the other behaviours recorded, support the theory of a dichotomous function for what has been termed the experience. One of the mechanisms of the pre-capture experience, that of fear habituation through sensory exposure, was then discussed in relation to priming studies in other rodent species.

Aggressive behavior in female hamsters: The hormonal basis for fluctuations in female aggressiveness correlated with estrous state.

The frequency and sequencing of aggressive behaviors by naive female hamsters change during series of brief encounters, probably because of the lack of stable dominance relations. Such initial encounters seem most representative of interactions likely in free-ranging hamsters and have been emphasized in studies of the hormonal mediation of female aggression. Nonestrous females exhibit intense aggression toward conspecifics of either sex. Estrous females are not aggressive and spend much time in lordosis, indicative of sexual receptivity. The inhibition of fighting on estrous day depends on estrogen and progesterone. Whereas oil-injected adrenalectomized-ovariectomized females fight at high levels, comparable with intact nonestrous females, the combination of 17 beta-estradiol benzoate and progeterone suppresses fighting completely. In contrast, replacement of estradiol, progesterone, or testosterone propionate individually has on consistent effect. Hypophysectomized females also fight at high levels, indicating that pituitary hormones are not required for vigorous aggression. Further, individual anterior pituitary hormones did not produce marked changes in fighting. These results emphasize the roles of estrogen and progesterone in synchronizing aggression with current reproductive state.

The role of dark chest patches and upright postures in the agonistic behavior of male hamsters, Mesocricetus auratus

Dyeing the chests of socially naive male hamsters black, and thus enlarging and darkening their normal dark brown chest patches, gives such males an advantage in initial aggressive encounters with partners matched in weight and age. This effect disappears if such initial encounters occur in the dark, indicating the importance of visual cues. Video and film analysis demonstrated that, contrary to previous claims, the normal chest patches were not displayed in threat postures prior to fighting, but rather were displayed by losers of fights in an upright posture with clearly defensive functions. It is suggested that the chest patches may have evolved in conjunction with this defensive posture for use in both intra- and interspecific conflict; the possible reasons for the effectiveness of larger and darker chest patches in interspecific aggression are discussed.

Sexual excitation function of hamster vaginal secretion

Sexually naive male hamsters were paired with ovariectomized females or with castrated males. On half of the trial days, the stimulus animals were scented with vaginal secretion from estrous females, and on half of the trials they were left unscented. Added vaginal secretion resulted in an increased frequency of mounting and decreased latency to mount, and an increase in the amount of time the males remained near the stimulus animals. These results demonstrate that the vaginal secretion has attractant and sexual excitant effects on naive males and thus is a source of sex pheromones. Presence of the secretion also resulted in a decrease in some measures of agonistic behavior, suggesting anti-aggressive functions as well.

Central stimulant drugs on avoidance behaviour in hamsters

Summary Central stimulant drugs have been tested on naive hamsters in a shuttle box situation. Facilitating effects are evident after Amphetamine, Methamphetamine and Cocaine administration, while Nicotine, Strichnine, Pentylentetrazol and Caffeine are ineffective. The role of adrenergic mechanism in the action of the facilitating drugs is discussed.