Effects of long-term treatment with melatonin or melatonin plus ectopic pituitary transplants on testicular LH/hCG and prolactin receptors in juvenile Syrian hamsters (Mesocricetus auratus)

Juvenile hamsters were injected daily with melatonin and some were also given transplants of 2 pituitaries under the kidney capsule. Weights of the testes and the accessory reproductive glands were reduced after 8 and after 12 weeks of melatonin treatment, but remained unaltered in animals treated with ectopic pituitary transplants. Levels of testicular LH/hCG receptors were significantly reduced by daily melatonin injections for 8 and 12 weeks. The presence of pituitary transplants in melatonin-injected hamsters prevented these reductions, and increased LH/hCG receptors above control levels. These changes in testicular LH/hCG receptors were closely related to alterations in serum prolactin concentration induced by melatonin and pituitary transplants. After 8, but not after 12 weeks of treatment, testicular prolactin receptor levels were reduced by melatonin and maintained by the presence of pituitary transplants. We conclude that: juvenile male hamsters become sensitive to the effects of daily melatonin injections when they reach maturity; daily melatonin injections can reduce the levels of testicular LH/hCG and prolactin receptors; and the effects of melatonin on LH/hCG and prolactin receptors are probably due to suppression of endogenous prolactin release.     

Effects of photoperiod and hCG on the regulation of testicular LH/hCG receptors in Syrian hamsters (Mesocricetus auratus)

The regulation of testicular LH/hCG receptors was studied in Syrian (golden) hamsters with testicular atrophy induced by exposure to short photoperiod (5L:19D) and in gonadally active hamsters kept in a long photoperiod (14L:10D). By 24 h after injection of hCG, long-photoperiod hamsters showed a dose-related decrease in the number of testicular LH/hCG receptors. At 48 and 72 h, there was a recovery from this 'down-regulation'. The recovery was much faster than has been reported for the rat and mouse, and it resulted in elevation of testicular LH/hCG receptor concentrations above basal values. Hamsters with short photoperiod-induced testicular atrophy showed an increase in testicular LH/hCG receptors after injection of hCG, except for animals injected with a very high dose. The hCG-induced increase in testicular LH/hCG binding in these animals was associated with reappearance of testosterone responses to subsequent hCG stimulation. Response of testicular LH/hCG receptors to hCG in prepubertal hamsters resembled that measured in animals with short photoperiod-induced gonadal atrophy.     

The effect of pinealectomy, melatonin and leptin hormones on ovarian follicular development in female Syrian hamsters (Mesocricetus auratus)

We studied the effects of melatonin and leptin hormones on ovarian follicular development in intact and pinealectomized female Syrian hamsters. We first monitored the oestrous cycle of the hamsters by the vaginal smear samples throughout a ten day period to start the injections simultaneously in all groups and performed saline, melatonin and leptin hormone injection groups for both control and pinealectomized hamsters. Then the injections were applied for four days starting the oestrus phase of the cycle and the ovaries were removed for preparation of histological analysis. We measured the diameters and the numbers of the follicles and we classified the follicles according to the number of the granulosa cell layer. Leptin hormone injection increased melatonin hormone injection decreased the number and the diameter of the follicles. The stimulating effect of the leptin hormone was more pronounced in the pinealectomized group. The results of the present study indicate that the removal of the pineal gland and leptin hormone administration are playing a stimulatory while melatonin hormone administration is playing an inhibitory role on the follicular development in female Syrian hamsters.     

Regulation of testicular LH/hCG receptors in golden hamsters (Mesocricetus auratus) during development

During prepubertal development in the golden hamster, there are major age-related changes in the number of testicular LH/hCG receptors. Between 22 and 35 days of age, there was greater than 10-fold increase in testicular LH/hCG receptors, followed by a decrease at Day 37. Concomitant with, but preceding slightly, the changes in receptors, were increases in plasma LH and FSH and most noticeably prolactin concentrations, between Days 10 and 20 of age. Inhibition of the increases in plasma levels of prolactin by daily injections of bromocriptine, between 14 and 31 days of age, resulted in suppressed testicular and seminal vesicle weights, and decreased content and concentration of testicular LH/hCG receptors. Similarly, the premature increase in plasma prolactin concentrations in prepubertal hamsters between 6 and 20 days of age, by means of ectopic pituitary transplants, resulted in increased testicular and seminal vesicle weights, as well as an increase in the concentration of testicular LH/hCG receptors. These results strongly suggest that increases in plasma prolactin values during development are important in enhancement of the development of testicular LH/hCG receptors.     

Short days and exogenous melatonin increase aggression of male Syrian hamsters (Mesocricetus auratus)

Many nontropical rodent species rely on photoperiod as a primary cue to coordinate seasonally appropriate changes in physiology and behavior. Among these changes, some species of rodents demonstrate increased aggression in short, "winter-like" compared with long "summer-like" day lengths. The precise neuroendocrine mechanisms mediating changes in aggression, however, remain largely unknown. The goal of the present study was to examine the effects of photoperiod and exogenous melatonin on resident-intruder aggression in male Syrian hamsters (Mesocricetus auratus). In Experiment 1, male Syrian hamsters were housed in long (LD 14:10) or short (LD 10:14) days for 10 weeks. In Experiment 2, hamsters were housed in long days and half of the animals were given daily subcutaneous melatonin injections (15 microg/day in 0.1 ml saline) 2 h before lights out for 10 consecutive days to simulate a short-day pattern of melatonin secretion, while the remaining animals received injections of the vehicle alone. Animals in both experiments were then tested using a resident-intruder model of aggression and the number of attacks, duration of attacks, and latency to initial attack were recorded. In Experiment 1, short-day hamsters underwent gonadal regression and displayed increased aggression compared with long-day animals. In Experiment 2, melatonin treatment also increased aggression compared with control hamsters without affecting circulating testosterone. Collectively, the results of the present study demonstrate that exposure to short days or short day-like patterns of melatonin increase aggression in male Syrian hamsters. In addition, these results suggest that photoperiodic changes in aggression provide an important, ecologically relevant model with which to study the neuroendocrine mechanisms underlying aggression in rodents.     

Age affects hibernation in Syrian hamsters (Mesocricetus auratus)

In this study, we aimed to show how age affects hibernation in the Syrian hamster. Experimentally, we used 30 male animals differing in age. The old animals were 20 months of age and the adults were 8 months of age at the end of the test. The young animals were 3 weeks old at the start of testing and 5 months old at the end of the testing period. The torpor observation started October 15, 1996, and ended March 11, 1997, in the laboratory colony maintained under natural photoperiod and outdoor air. Observations were performed around noon daily. Three measures (i.e., prehibernation period [hibernation latency], proportion of hibernation spent in torpor, and proportion of animals in torpor), all of which reflect the strength of occurrence of hibernation, indicated that the older hamsters (1) started hibernation earlier, (2) spent more time in torpor, and (3) had a higher chance of being in torpor than the younger ones during the hibernation season. (Chronobiology International, 17(5), 623-630, 2000)     

Experimental iron deficiency in Syrian hamsters (Mesocricetus auratus)

An animal model was developed in which the effect of iron deficiency on the oral mucosa could be studied. Iron deficiency was induced by feeding hamsters a low-iron powdered diet together with withdrawal of 0.5 ml of blood weekly, for a period of 9 weeks. At the end of this period the mean haematological values for control animals were, Hb 15.9 g/dl, plasma iron 40.3 mumol/l, TIBC 90.5 mumol/l and transferrin saturation 44.5%, compared with 7.4, 7.2, 111.4 and 6.5 respectively for experimental animals. These results were reproducible in successive groups of animals and indicate that this is a useful model for the study of iron deficiency anaemia.     

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.     

Effects of a circadian mutation on seasonality in Syrian hamsters (Mesocricetus auratus).

In Syrian hamsters, exposure to short photoperiods or constant darkness induces a decrease in gonadotrophin secretion and gonadal regression. After 10-12 weeks, animals undergo spontaneous gonadal reactivation, gonadotrophin concentrations rise, and in males, testes size increases and spermatogenesis resumes. The tau mutation shortens the period of circadian wheel-running activity by 4 h in the homozygote. Here, we examine the impact of this mutation on the reproductive response to photoperiod change. Seventeen adult tau mutant and nine adult wild-type males were housed in complete darkness for 25 weeks and testes size determined at weekly intervals. Gonadal regression and subsequent recrudescence occurred in both groups of animals. Regression occurred more rapidly in tau mutants, with a nadir significantly earlier than wild-types but after a similar number of circadian cycles. Rates of testicular recrudescence were similar in both groups. Our data suggest that an acceleration of the circadian period increases the rate of reproductive inhibition in animals exposed to inhibitory photoperiods. Once initiated, the rate of spontaneous reactivation may be independent of the circadian axis.     

Pathophysiological studies of trinitrobenzene sulfonic acid-induced colitis in Syrian hamsters (Mesocricetus auratus)

We developed a colitis model in Syrian hamsters (Mesocricetus auratus) to investigate the relationship between colitis and neutrophil elastase (NE). Colitis was induced by a single intracolonic dose of trinitrobenzene sulfonic acid (TNBS; 90 mg/ml) dissolved in 15% (vol/vol) ethanol. The ulcer area, tissue myeloperoxidase (MPO) activity, and luminal NE activity all were increased on Days 1 and 5, corresponding with the acute inflammatory histopathological changes. These acute inflammatory parameters subsequently decreased by Day 14, and chronic inflammatory histopathological changes became evident. Recurrence of inflammation was not observed during the period up to Day 28. To evaluate our colitis model, the effects of prednisolone were examined. Prednisolone was administered orally once on the day before induction of colitis, and animals were treated twice daily thereafter. Although prednisolone had little effect on the tissue MPO activity, prednisolone inhibited the ulcer area and NE activity. In addition, the effects of an NE-specific inhibitor (ONO-6818) on our TNBS-induced colitis model were examined. In the subcutaneous treatment study, ONO-6818 was administered once before the induction of colitis. Although ONO-6818 had little effect on the tissue MPO activity, the ulcer area and NE activity were decreased in the ONO-6818-treated group. The inhibitory effects on the ulcer area and NE activity were confirmed after oral treatment with ONO-6818 after induction of colitis. We conclude that our colitis model is useful for investigating the relationship between colitis and NE, and inhibition of NE activity can prevent the progression of ulceration.     

Routine chromosome screening in Syrian hamsters (Mesocricetus auratus) using orbital sinus blood

Blood from the posterior orbital sinus of Syrian hamsters, obtained under halothane anaesthesia, can be cultured to give large numbers of metaphase chromosome spreads for analysis. The procedure has been used for rapid routine screening of the karyotypes of all offspring in a breeding colony where translocations are present. Results can be obtained within 3 days of collecting the blood sample.     

Isolation of Corynebacterium kutscheri from aged Syrian hamsters (Mesocricetus auratus).

Corynebacterium kutscheri was isolated from the oral cavities of 12 male Syrian hamsters (Mesocricetus auratus) which were about 12 months old. At 1, 5, and 9 months after initial isolation of C. kutscheri from the oral cavity, hamsters were euthanatized, and attempts were made to culture C. kutscheri from 13 additional sites. Corynebacterium kutscheri was isolated from nine hamsters, and regardless of the hamsters' ages, the organisms were most frequently isolated from the oral cavity (100%), esophagus (100%), cecal content (100%), and colon and rectum (88.9%). Isolation rates in the nasal cavity were 66.7%, followed by 55.5% in the trachea and 33.3% in the submaxillary lymph nodes. The number of the organisms found in the submaxillary lymph nodes and esophagus was 10(3) to 10(4) CFU/g. The number found in the cecal content and in the colon and rectum was 10(2) to 10(5) CFU/g. The organisms were not isolated from lung, stomach, kidney, spleen, and mesenteric lymph node tissues. The hamsters had neither clinical signs nor lesions. However, 7 of 12 animals had low agglutinating antibody titers. The Syrian hamster can therefore be an asymptomatic carrier of C. kutscheri.     

Volitional ethanol consumption affects overall serotonin metabolism in Syrian golden hamsters (Mesocricetus auratus)

Methods were established for the determination of serotonin (5-HT)(1) metabolites 5-hydroxyindole-3-acetic acid (5-HIAA) and 5-hydroxytryptophol (5-HTOL) in the urine of Syrian golden hamsters (Mesocricetus auratus) and used to study the effect of volitional ethanol consumption on overall 5-HT metabolism in this ethanol-preferring rodent. The basal levels of 5-HIAA and 5-HTOL in 24-h urine of ethanol-naive hamsters were 300 +/- 101 and 4.96 +/- 1. 06 nmol (n = 8), respectively. Given free choice between water and a 15% ethanol solution, these hamsters chose to consume increasing amounts of ethanol. The increase was accompanied by a concomitant decrease in urine 5-HIAA and increase in urine 5-HTOL, indicating that volitional ethanol intake diverted part of the 5-HT metabolic flux from an oxidative into a reductive pathway. In a separate experiment, the amounts of ethanol consumed by and blood ethanol concentrations attained in ethanol-drinking golden hamsters were determined at 5 different time intervals between 6 PM and 7 AM when most feeding activities occurred. Except in the first hour after lights were turned off, ethanol was consumed at a relatively even pace throughout the night (2-3 g/kg/3 h) and blood ethanol levels were maintained at the low mM range which rarely exceeded 2 mM. These results suggest that the biochemical pathway that catalyzes 5-HT metabolism is extremely sensitive to ethanol and can play an important role in mediating the reported clinically beneficial action of a low concentration of ethanol during alcohol detoxification.     

Reproductive effects of 6-chloromelatonin implants and/or injections in male and female Syrian hamsters (Mesocricetus auratus)

Adult female hamsters were injected each afternoon for 9 weeks with 2.5, 15 or 25 micrograms of melatonin or 6-chloromelatonin (CM). Each drug resulted in a significant dose-related depression in uterine, ovarian and anterior pituitary gland weights. Additionally, plasma and pituitary concentrations of prolactin fell with increasing dose of either indole whereas pituitary levels of LH and FSH were positively correlated with dose. There was no difference in effectiveness between the two drugs. Adult male hamsters treated for 10 weeks with daily afternoon injections of melatonin and a blank beeswax pellet had depressed testicular and accessory organ weights and plasma and pituitary concentrations of prolactin. Implantation of a 1 mg melatonin or CM beeswax pellet in hamsters concurrently receiving daily afternoon injections of melatonin prevented the organ weight and hormonal changes, except for plasma prolactin. Adult male hamsters treated for 10 weeks with daily afternoon injections of CM and a blank beeswax pellet had depressed reproductive organ weights and pituitary and plasma concentrations of prolactin; this depression in hormonal values and organ weights was totally prevented if the CM-injected hamsters were also bearing a beeswax-melatonin pellet. In conclusion, 6-chloromelatonin is as effective as melatonin with regards to antigonadotrophic and counter-antigonadotrophic effects in male and female Syrian hamsters.     

Daily rhythm in serum melatonin and leptin levels in the Syrian hamster (Mesocricetus auratus)

Melatonin is produced and secreted by the pineal gland in a rhythmic manner; circulating levels are high at night and low in the day. Leptin is a hormone secreted by adipocytes as a product of the obese gene and plays an important role in regulating body energy homeostasis and reproductive function in rodents and humans. The present study was conducted to examine daily fluctuations in serum levels of melatonin and leptin in Syrian hamster. We measured serum leptin and melatonin levels by ELISA in (a) intact and pinealectomized (pinx) male hamsters kept under long daylight conditions [14 h of light (14L)]; (b) intact and pinx hamsters under short daylight (10L); and (c) intact hamsters in constant light (24L). Blood samples were obtained every 2 h throughout a 24-h period. Statistically significant circadian variations were found in both melatonin and leptin profiles. Their relationship was inverse, i.e. when melatonin was high in the serum, leptin was comparably low. These results suggest that there is a rhythm in leptin levels in the adult male Syrian hamster and this rhythm is pineal gland (melatonin) and/or photoperiod dependent.     

Effects of different numbers of ectopic pituitary transplants on regulation of testicular LH/hCG and prolactin receptors in the hamster (Mesocricetus auratus)

Adult male hamsters were given transplants of 1/2, 1, 2, 3 or 4 pituitaries under the kidney capsule and were killed 4 weeks later. Pituitary transplants produced a significant, dose-related increase in plasma prolactin levels, no changes in plasma LH and an increase in plasma FSH. Concentration of LH/hCG receptors in the testes was significantly increased in animals with 2 or 3 transplants and concentration of testicular prolactin receptors was significantly increased in those given 2 transplants. The apparent stimulatory effects of 1/2, 1 or 4 transplants on testicular LH/hCG and prolactin binding were not statistically significant. Some of the animals were injected with 0.3 i.u. hCG/g body weight 24 h before being killed. This produced a significant reduction in the levels of prolactin receptors and an apparent reduction in the levels of LH/hCG receptors in the testes. Elevation of plasma testosterone concentrations in response to hCG was significantly greater in animals given 3 or 4 pituitary transplants than in the remaining groups. These results provide further evidence that prolactin increases the number of LH/hCG and prolactin receptors in the hamster testis and suggest that changing the number of ectopic pituitary transplants may result in biphasic effects on the testis, with 2 or 3 transplants being maximally stimulatory.     

Suprachiasmatic nuclei may regulate the rhythm of leptin hormone release in Syrian hamsters (Mesocricetus auratus)

The suprachiasmatic nuclei (SCN) generate the circadian rhythm of many hormones. The hormone leptin is a metabolic signal that informs the brain about fat and energy stores of the body. We investigated whether the rhythm of leptin hormone release in Syrian hamsters is directly controlled by the SCN. Three experiments were performed: in the first, hamsters were SCN-lesioned; in the second, hamsters were exposed to different feeding regimes; and in the third, hamsters were adrenalectomized and implanted with cortisol capsules to maintain constant glucocorticoid release. Blood samples were collected before and after the experiments at different clock times and examined for leptin levels by enzyme-linked immunosorbant assay (ELISA). Different feeding regimes and constant glucocorticoid release did not alter the rhythm of leptin release; whereas, SCN lesions abolished the rhythm. The results of the present study suggest the rhythm in leptin release in Syrian hamsters may be controlled by the SCN.     

Intravenous injection of unanesthetized hamsters (Mesocricetus auratus)

A rubber band tourniquet was applied to the proximal portion of the foreleg of unanesthetized male and female golden hamsters followed by intravenous injection in the cephalic vein using a 25 gauge needle. Volumes up to 0.3 ml could be injected easily.     

Ontogeny of oral function in hamsters (Mesocricetus auratus)

The oral apparatus of neonatal and juvenile golden hamsters was investigated by clearing and staining of whole crania, videotaping of behavior, and electromyography of several jaw muscles. Chewing developed during the first postnatal week and matured in the second; however, suckling was still the primary mode of feeding. Micromovements of the jaws occurred early when the osseous skeleton and joints developed. Macromovements correlated well with EMG records and were limited to jaw opening at birth. Muscles of the oral floor generated large bursts of activity during jaw opening and tongue protrusion from 0 days postnatal (dpn), when simple and stereotyped gaping was induced, until 14 dpn, when movements were spontaneous and not stereotyped nor inducible. However, adductor muscle activity was brief, low in amplitude, and primarily involved with jaw stabilization until 4 dpn, when these muscles became active during closing the jaws; closing activity increased in frequency and amplitude until the end of the second week. Development of frequent, coordinated macromovements of chewing was associated with the refinement of joint structure and dental occlusion and with the growth of the craniofacial skeleton. Jaw movements and associated EMG's correlated better with available data on development of neural circuitry than with that for musculoskeletal development.     

Auditory brainstem responses in Golden Syrian hamsters (Mesocricetus auratus) affected with the Wh gene.

BACKGROUND AND PURPOSE: The anophthalmic white (Wh) gene in Golden Syrian hamsters (Mesocricetus auratus) is autosomal semi-dominant and causes several developmental defects, including hearing loss. The Wh mutation is thought to be homologous to Waardenburg syndrome in humans, apparently affecting similar developmental processes. The purpose of this study was to assess the hearing of hamsters in the AN/As-Wh strain. METHODS: Using auditory brainstem responses, electrophysiologic activity was determined in 20 hamsters of the AN/As-Wh strain, with the aim of elucidating hearing status. Hamsters were classified into five genotypes and were evaluated by use of click stimuli. RESULTS AND CONCLUSION: Hamsters assigned to the genotypes differed in their hearing sensitivity and could be classified into categories of normal hearing, moderate hearing loss, and profound hearing loss.