Stimuli contributing to the decrement in sexual receptivity of female golden hamsters (Mesocricetus auratus)

Stimuli capable of altering sexual receptivity in the female golden hamster were examined. Females receiving full copulatory stimulation from a normal male hamster or a combination of mounting by a male and mechanical vagino-cervical stimulation were almost totally unreceptive upon retest. Mounting alone or mechanical stimulation alone produced significantly smaller depressions in receptivity, but females receiving these treatments were less receptive than unmated females. The amount of stimulation received during intromissions-only from a male was also positively related to a depression in female receptivity. Thirty-six intromissions were adequate to produce maximal changes in receptivity. Ejaculation was not necessary to alter female behaviour. Increases in fighting generally accompanied decreases in receptivity.     

Neural connections between the brain and the pineal gland of the golden hamster (Mesocricetus auratus)

Summary Neurons projecting from the brain to the pineal gland via the pineal stalk were investigated in the golden hamster with the use of the retrograde horseradish-peroxidase tracing method both in vivo and in vitro. Labelled perikarya were observed in the medial and lateral habenular nuclei as well as in the posterior commissure. Single cells located in the ependymal lining of the pineal- and suprapineal recesses were also retrogradely labelled. These results show that a distinct central innervation of the pineal gland exists in the golden hamster, in agreement with findings in other mammalian species investigated by means of a similar methodology. In addition, also direct signals from the cerebrospinal fluid to the parenchyma might be conducted via cells located within the ependymal layer of the pineal- and suprapineal recesses.This study was supported by grants from the Deutscher Akademischer Austauschdienst to M.M. (312/dk-4-is), the Deutsche Forschungsgemeinschaft to H.W.K. (Ko 758/2-2, 2-3), and the Carlsberg Foundation     

Synaptic ribbons during postnatal development of the pineal gland in the golden hamster (Mesocricetus auratus)

Summary Synaptic ribbons, functionally enigmatic structures of mammalian pinealocytes, were studied during the postnatal development of the pineal gland in the golden hamster (Mesocricetus auratus). On day 4 post partum, synaptic ribbons appear in cells that have already started to differentiate into pinealocytes. Between days 4 and 9, an increase in the number of synaptic ribbons occurs, concomitant with the continuing differentiation of the pineal tissue. Between days 9 and 16, when differentiation of this tissue is almost completed, the number of synaptic ribbons decreases and approaches that characteristic of the adult pineal gland. During development, the synaptic ribbons increase in length, and dense core vesicles are frequently found in the vicinity of these structures. It is assumed that a functional relationship exists between dense core vesicles and the synaptic ribbons, which are considered to be engaged in a certain form of secretory activity of the mammalian pineal gland.Supported by the Deutsche Forschungsgemeinschaft     

Asynchrony in the estrous cycles of golden hamsters (Mesocricetus auratus)

The golden hamster has been described as exhibiting estrous cycle synchrony caused by social dominance. This has recently been reexamined by J. C. Schank (2000, Horm. Behav. 38, 94-101) with the aid of computer simulations. He concluded that there is no evidence for cycle synchrony among golden hamsters. In the present article we confirm this theoretical approach with the help of long-term experiments. Indeed, estrous cycle asynchrony was observed. Singly housed female golden hamsters in phase with their neighbors and in physical contact desynchronized their 4-day cycles after 2 or 3 weeks. Asynchrony was caused mainly by stochastic 5-day cycles. Statistical analysis was performed using a Monte-Carlo bootstrap approach. Based on the empirical data, an individual-based computer model was developed to simulate the dynamics of cycle desynchronization. Potential advantages were deduced for the population level. It emerged that estrous cycle asynchrony led to higher reproductive success for females where the probability of fertilization was low (e.g., after hibernation, poor habitat).     

Pineal melatonin in hibernating and aroused golden hamsters (Mesocricetus auratus)

Daily changes of pineal melatonin content were determined in warm-adapted nonhibernating and cold-adapted hibernating golden hamsters (Mesocricetus auratus). Pineal melatonin in nonhibernating golden hamsters showed marked daily rhythm with the night values about 20 times higher than the daytime ones. In hamsters hibernating for 2 and 3 days the melatonin rhythm was abolished, since no increase of pineal melatonin over basal levels occurred throughout 24 hr period. After arousal from hibernation melatonin increased rapidly regardless whether the hamsters were provoked to arousal during day or night.     

Electroencephalography in the diagnosis of hydrocephalus in golden hamsters (Mesocricetus auratus)

The golden hamster (Mesocricetus auratus) is a popular laboratory animal and is used in a multitude of behavioural studies. However, it has been shown that it suffers from different forms of hereditary hydrocephalus, which may result in behavioural changes. This prospective study was designed to look into the usefulness of electroencephalography (EEG) measurements in the diagnosis of hydrocephalus in hamsters. The EEGs of the hydrocephalic hamsters were evaluated double-blind and showed a high-voltage slow wave activity, with a fast activity superimposed onto it. This pattern has already been well described in other hydrocephalic species and differed significantly from the EEGs that were obtained from the normal hamsters. It was concluded from our study that a background activity with an amplitude over 50 muV in combination with a frequency of < or =5 Hz was highly indicative of hydrocephalus in young hamsters. We believe that the EEG could be a very useful diagnostic tool in the screening for hydrocephalus in hamsters.     

Arrest of the circadian pacemaker driving the pineal melatonin rhythm in hibernating golden hamsters, Mesocricetus auratus

Pineal melatonin rhythm in golden hamsters was abolished during hibernation. After arousal in darkness, pineal melatonin increased rapidly regardless of whether the arousal was induced during the day or at night. Rapid increase of pineal melatonin after arousal was markedly diminished in animals exposed to light. In hamsters aroused at midnight, the melatonin rhythm in constant darkness ran with the reversed phase relative to hamsters aroused at noon. Since after arousal the melatonin rhythm obviously starts anew from the same phase, we conclude that the circadian pacemaker driving the rhythm might be arrested during hibernation at the day-time phase.     

Whole blood folate values in normal female hamsters (Mesocricetus auratus)

Whole blood folate estimations in adult female hamsters, using radioassay kits gave values similar to human data and comparable with previously reported serum folate levels measured using microbiological techniques.     

Hereditary hydrocephalus internus in a laboratory strain of golden hamsters ( Mesocricetus auratus)

Golden hamsters of one common laboratory strain had a high incidence of hydrocephalus internus. When a severity score of hydrocephalus was used, a major autosomal recessive locus could be identified. However, when a binary score (hydrocephalus, no hydrocephalus) was used, no such major locus could be detected and results of test matings were not consistent with Mendelian inheritance. Golden hamsters with severe forms of hydrocephalus had a dorsally compressed and ventrally intact hippocampus. Implications for the behavior and well-being of affected hamsters are unknown but researchers using this strain should be aware of the likely presence of hydrocephalus.     

Predictors of social dominance in the adult female golden hamster (Mesocricetus auratus)

Adult female golden hamsters exhibit smaller and less pigmented flank glands than do males. Nevertheless, as has been found in male hamsters, variations in these parameters of the flank glands correlate highly (r_s=0·78) with social rank attained in a group of four females. Ovariectomy and subsequent replacement with a graded series of testosterone propionate doses produces a directly related response in the flank gland and in the social rank attained in all-female groups (r_s=0·72). Body weight of females also correlates directly with social status (r_s=0·74), but, when body weight is held constant, social rank can still be predicted from measures of the flank gland. Oestrous-related fluctuations in aggressive behaviour of females did not alter dominance relationships.