Blinded Hamsters Research Articles

Melatonin: reproductive effects.

N-acetyl-5-methoxytryptamine, melatonin, is synthesized within and secreted from the pineal gland. Although the concentration of this constituent in the blood is diminished after surgical removal of the pineal gland it does not completely disappear. Other potential contributors to blood titers of melatonin include the retinas, the Harderian glands and the gastro-intestinal tract. Melatonin has a potent antigonadotrophic action in the Syrian hamster ( a highly photosensitive species) provided the indole is given during a restricted portion of the light phase of the light-dark cycle. This so-called sensitive period falls late in the light phase; melatonin acutely administered at other times has virtually no inhibitory influence on the reproductive physiology of hamsters. When melatonin is continuously available (from a subcutaneous deposit) it counteracts the antigonadotrophic influence of the pineal gland in light restricted or blinded hamsters, i.e., it causes a "functional pinealectomy". Furthermore, chronically available melatonin negates the antigonadotrophic capability of acute melatonin injections.

Testicular involution following optic enucleation: the Leydig cell.

The testes of Syrian hamsters underwent pronounced involution within six weeks after blinding. The seminiferous tubules were devoid of all stages of spermatid development and mature spermatozoa were absent from the tubule lumina. The diameter of of the Leydig cells was 25% less than that of controls. Examination with the electron microscope revealed thick bundles of collagen fibrils interspersed between Leydig cells and surrounding Leydig cells in the blinded hamsters. The Leydig cell nuclei were shrunken and highly infolded. Lipid droplets that were often seen in normal Leydig cells were absent in the involuting Leydig cells. The size of the Golgi complex and the amount of smooth endoplasmic reticulum were reduced. Results of the present experiment confirm that inactivity of the Leydig cells is the reason for the decline in serum testosterone levels in blinded hamsters.

Effects of blinding, pinealectomy and superior cervical ganglionectomy on free thyroxine index of male golden hamsters.

Blinding young male golden hamsters led to a depression of the plasma free thyroxine index after an 8 week period. Removal of either the pineal gland or the superior cervical ganglia of blind hamsters reversed the effects of blinding on free thyroxine index. No significant effects were observed 2 weeks after treatment. Previously reported effects of blinking, and removal of the pineal gland or the superior cervical ganglia on testicular weight were confirmed. A similar mechanism of pineal inhibition of thyroid function and gonadal function is suggested.

Estradiol shortens the period of hamster circadian rhythms.

Continuous administration of estradiol benzoate by means of subcutaneously implanted capsules shortened the free-running circadian period of locomotor activity of blind hamsters (Mesocricetus auratus) that had had their ovaries removed. Estradiol also advanced the phase of the wheel running of sighted female hamsters without ovaries that were entrained to a photoperiod with 12 hours of light and 12 of darkness. These results, and findings from hamsters undergoing natural estrous cycles, indicate that endogenous estradiol is involved in the regulation of circadian periodicity.

Heavy water as a tool for study of the forces that control length of period of the 24-hour clock of the hamster.

In alternating 12-hr periods of light and darkness, start of the dark period entrains the hamster's 24-hr clock. Blinding or constant darkness frees the clock of entrainment by allowing it to run faster or slower than 24 hr. Constant light frees the clock from entrainment and permits it to run slower than 24 hr--that is, lengthening its period. Heavy water given in drinking water linearly lengthens the period of the 24-hr clock of blinded hamsters or of hamsters kept in constant darkness in direct proportion to concentration of heavy water (1--50%). Heavy water (1-35%) has very different effects on length of the periods of the 24-hr clock when given under conditions of alternating 12-hr periods of light and darkness. Under these conditions, length of the period is controlled by three factors: (i) heavy water which slows the 24-hr clock; (ii) constant light which also slows the 24-hr clock; (iii) the counteracting effects of entrainment. It is thus possible to observe the effects of all three forces simultaneously in the same animal. The clock slowed by heavy water (1--20%) showed a strong tendency to return to a 24-hr entrainment whenever possible. On a 50% concentration of heavy water, the length of period of the clock became markedly lengthened but very constant and apparently independent of all external and internal disturbances.

Free thyroxin index in normal, melatonin-treated and blind hamsters.

The administration of melatonin to young male hamsters depressed thyroxin levels, as measured by radioimmunoassay, by 38.5% of saline controls. Free thyroxin index was also signficantly depressed by melatonin injections. The depression of thyroxin and free thyroxin index by melatonin injections was more effective in intact than in pinealectomized animals. Blinding of hamsters also reduced both thyroxin and free thyroxin index.

Restoration of fertility in light-deprived female hamsters by chronic melatonin treatment

Blinding young adult female hamsters was followed by functional involution of the ovaries and uteri and by the cessation of cyclic vaginal phenomena. Light deprivation was also accompanied by elevated plasma and pituitary levels of luteinizing hormone and depressed levels of prolactin in both the blood and the pituitary gland. Only one of 15 blinded hamsters became pregnant when they were exposed to fertile males for 30 days. Both pinealectomy or chronic melatonin treatment (1 mg melatonin implanted subcutaneously per week in beeswax) prevented the changes in the reproductive organs and in pituitary hormone levels attendant on light-deprivation. Both treatment also returned vaginal cycles to normal and restored plasma prolactin titers. Unlike hamsters that were blinded only, light deprived hamsters that were either pinealectomized or melatonin treated were capable of reproducing when they were caged with fertile males. The reproductive capability (i.e., percent of animals that become pregnant and the sizes of their litters) of these animals was equivalent to that of the untreated control hamsters. This is the first report that chronic melatonin treatment restores fertility in blinded female hamsters.

Fine structural changes in the hamster pineal gland after blinding and superior cervical ganglionectomy

Pineal glands of male hamsters 8 weeks after removal of both eyes or both superior cervical ganglia and those of untreated animals were studied by electron microscopy. In the blinded hamsters the reproductive organs were remarkably involuted, whereas the pinealocytes enlarged and were characterized by a tremendous hypertrophy of the smooth-surfaced endoplasmic reticulum, in the mesh of which some dense cored vesicles were distributed. In constrast the pinealocytes of ganglionectomized hamsters atrophied and were noted by a large number of lysosomes and sparsity of the agranular reticulum, the testes being significantly larger than the controls. The findings were interpreted to be compatible with the view that the pineal capability of producing antigonadal substance is augmented by blinding and is suppressed by cervical ganglionectomy due to the impairment of normal functioning of the pineal by denervation. It is assumed that the degree of development of the smooth endoplasmic reticulum in the pinealocyte is parallel to, and reflects that of the pineal activity. Probably the membranous organelle is involved in the elaboration of the pineal antigonadal substance.

Melatonin-pineal relationships in female golden hamsters.

Light deprivation by blinding in female hamsters was followed by a regression of the reproductive organs, an elevation of pituitary LH concentration and a depression of pituitary prolactin levels. Pinealectomy negated almost completely the effects of light deprivation on the neuroendocrine-reproductive axis. Weekly subcutaneous implants of a melatonin:beeswax pellet completely prevented the pineal gland from inhibiting reproductive physiology in blinded hamsters. The findings suggest that melatonin is not pineal antigonadotrophic factor in female golden hamsters. Melatonin implanted hamsters also had higher than normal levels of plasma prolactin.

Studies on the minimal dosage of melatonin required to inhibit pineal antigonadotrophic activity in male golden hamsters.

Blinding adult male golden hamsters was followed by atrophy, within 12 weeks, of the testes and accessory sex organs (seminal vesicles and coagulating glands) and by a significant reduction in pituitary prolactin levels. In experiment 1 blind hamsters received subcutaneously implanted melatonin-beeswax (1:24 mg) pellets at the following intervals: once per week, per 2, 3, 4, 6 weeks, or only one pellet during the 12-week experimental period. The melatonin-beeswax pellets, regardless of the frequency of implantation, overcame completely the inhibitory effects of blinding on reproduction and nearly completely the depressant action of light deprivation on pituitary prolactin levels. In the second study the melatonin-beeswax pellets were implanted subcutaneously into blind hamsters every 2 weeks. The pellets contained either 1 mg, 500, 100, 50, or 1 mug melatonin. With the exception of the 1-mug dosage, melatonin again negated almost totally the inhibitory action of darkness on the gonads and accessory organs and also, for the most part, prevented the drop in pituitary prolactin levels. Based on these studies, when melatonin is chronically administered subcutaneously in a beeswax pellet the minimal dosage of melatonin required to counteract the inhibitory effect of darkness on reproduction seems to be less than 3.6 mug/day. The effects of chronic melatonin treatment are similar to those of pinealectomy.

Pineal Regulation of Immunoreactive Luteinizing Hormone and Prolactin in Light-Deprived Female Hamsters

The influence of light deprivation pinealectomy and pineal denervation on pituitary and plasma levels of luteinizing hormone (LH) and prolactin in 62 adult female hamsters was studied. 46 of the hamsters were blinded by bilateral orbital enucleation. 10 of the blinded animals were pinealectomized and 11 were superior cervical ganglionectomized. After 8 weeks 12 blinded and 8 intact hamsters received 4-mcg LH-releasing hormone (RH)/day for 1 week after which all animals were necropsied. Immunoreactive LH and prolactin levels were determined by double antibody radioimmunoassays. The blinded hamsters had significantly higher levels of LH within the pituitary than the normal controls (p less than .001). Pituitary prolactin levels in the blinded were significantly decreased (p less than .001). LH-RH treatment did not markedly alter LH or prolactin levels in the pituitary. Plasma LH of the blinded hamsters was about twice as high as the controls. LH-RH did significantly raise plasma LH in the intact and blinded (p less than .01 and p less than .02 respectively). Blinded hamsters that were pinealectomized or ganglonectomized had LH and prolactin levels comparable to the controls. Plasma prolactin levels were only slightly altered among the 6 experimental groups.

Pineal influence on the Harderian glands of female golden hamsters.

AbstractThe effects of blinding on cellular structure and porphyrin pigment content were studied in Harderian glands of pinealectomized and non‐pinealectomized adult female golden hamsters. Uterine weights were used as a criterion for pineal activity. Five weeks post‐operatively, no significant changes were observed in the Harderian glands or in the uterine weights of animals in either group. Eleven weeks post‐operatively, the blinded hamsters with intact pineal glands had significantly lowered uterine weights and Harderian glands that exhibited diminished amounts of porphyrin pigments and cellular characteristics of the male hamster. Harderian glands and reproductive organs from the 11‐week blinded‐pinealectomized hamsters did not differ from those of untreated controls.

Pineal gland: Evidence for an influence on ethanol preference in male syrian hamsters

1. 1. If adult male hamsters kept in light: dark cycles of 14: 10 are given a choice to drink water or 5% ethanol, they show a preference for the alcohol solution. Hamsters that are pinealectomized exhibit a reduced preference for ethanol. 2. 2. Blinded hamsters show an exaggerated ethanol preference which is also reduced by either pinealectomy or decentralization of the superior cervical ganglia. 3. 3. Daily melatonin injections of subcutaneously implanted melatonin-beeswax pellets do not influence ethanol preference in hamsters.

Light-dark rhythms in hamster eating, drinking and locomotor behaviors

Adult hamsters were exposed to alternating 12-hr periods of light (L) and darkness; 99% of daily wheel running activity occurred in the 12-hr dark (D) period. Water intake and food consumption also occurred more commonly in the dark but the extent to which these behaviors were displayed nocturnally, 85% and 58%, respectively, was significantly less than for wheel running. Activity cycles modulate drinking rhythms; nocturnal water intake was substantially reduced in hamsters with access to wheels while drinking during the light period was unaffected. Nocturnal drinking rhythms of hamsters phase-shifted very slowly after the L-D cycle was inverted; females required more than 40 days, whereas males re-established their normal nocturnal drinking rhythms in approximately 25 days. This sex difference disappeared after males and females were gonadectomized. Wheel running behavior of hamsters phase-shifted by 12 hr within 6–9 days of inversion of the L-D cycle. The great disparity in the rate of phase-shifting of hamster activity and drinking rhythms suggests different central pacemakers for these behaviors or different sensitivities to changes in the light-dark cycle in their respective phase-shifting and coupling mechanisms. Eating and drinking rhythms of blind hamsters were described and compared to those of blind rats. Constant illumination (L-L) decreased water intake of male and female hamsters; loss of entrainment to the previous L-D cycle occurred more slowly than for rats maintained in L-L. These findings are consistent with the differential effects of constant light on rhythmic reproductive phenomena in the two species. Hamster drinking and wheel-running behaviors are particularly appropriate endpoints for the analysis of neural and endocrine bases of circadian rhythmicity.

Lack of pineal-induced gonadal regression in dark-exposed or blind hamsters after surgical isolation of the medial-basal hypothalamus

Blinding or exposing hamsters to increased dark periods (L:D::1:23) caused involution of the reproductive organs. Involution of reproductive organs was absent in hamsters that were pinealectomized or subjected to complete surgical isolation of the medial-basal hypothalamus. This observation suggests that isolation of the medial-basal hypothalamus may have destroyed pathways which serve to transmit photic information to the pineal (e.g., medial forebrain bundle) or the site of action of the substance secreted by the pineal in blind or dark-exposed hamsters is outside of the cut, located in a neural structure responsible for inhibition of gonadotropin release.

Ultrastructural features of the pineal gland in normal and light deprived golden hamsters.

Although current physiological findings imply that the mammalian pineal organ liberates an antigonadal agent, microscopic examinations of this organ have afforded little information regarding the possible storage and release of such a substance. Since it is known that light deprivation for six weeks results in pineal-induced atrophy of certain reproductive organs in adult golden hamsters, one might expect that any morphological manifestations of this activity in the pineal organ would be enhanced in hamsters which had heen deprived of light for that length of time. A comparison at the ultrastructural level of pineal glands from normal and experimentally blinded hamsters revealed that pineal cells from the blinded animals exhibited a greater number of vesicles and contained complex membranous whorls. The possible significance of the vesicles and lamellar whorls is discussed in terms of similar structures found in other tissues.

Effect of biogenic amines on the endocrine axis and esterase activity of hamster testes.

Pinealectomy reverses the loss of testis and seminal vesicle weights of blinded hamsters. Treatment with moderate doses of serotonin and melatonin does not cause further decrease in reproductive organ weights, or appreciably affect adrenal and pituitary gland weights of blinded hamsters. The seminiferous tubules of blinded hamsters exhibit primarily spermatogonia containing lipid aggregations and numerous lysosomal bodies. Blinded hamsters have significantly higher levels of testicular esterase activity than do control, pinealectomized, and blinded and pinealectomized hamsters. This suggests that the higher esterase activity results from greater lysosomal activity.

Pineal-induced alteration of estrous cycles in blinded hamsters

Estrous cycles, as evaluated by vaginal smears of adult hamsters, were examined under a variety of experimental conditions. Normal females cycled regularly with oval and elongate nucleated epithelial cells usually observed one of every four days. Cycles of blinded hamsters did not vary from those of normal or blinded-pinealectomized hamsters until approximately 7 weeks after eye removal. Thereafter, blinded hamsters became acyclic, exhibiting a vaginal smear which contained cornified cells predominantly and varying numbers of leukocytes. An absence of follicles and corpora lutea also was observed in the ovaries of blinded hamsters. In addition, blinded hamsters possessed smaller than normal uteri. Cycles of blinded-pinealectomized hamsters never varied from those of normal hamsters; in each of these groups approximately 25% of the smears were routinely of the estrous type. Bilateral ovariectomy in animals blinded for 7 weeks had no effect on pattern of vaginal smears. Ovariectomy in normal and blinded-pinealectomized hamsters induced a cessation of cyclic epithelial changes and thereafter the smears appeared similar to those obtained from blinded or blinded-ovariectomized hamsters.

Morphological studies on the reproductive organs of blinded male hamsters and the effects of pinealectomy or superior cervical ganglionectomy.

AbstractThe testes, seminal vesicles and coagulating glands of hamsters subjected to bilateral optic enucleation (blinding) involuted within 6–8 weeks. During the first several weeks after blinding there was relatively little change in the weights of the reproductive organs, however, between 4–6 weeks the weights of these organs declined precipitously. Finally, the testes and accessory sex organs of 8‐week blinded hamsters were about one‐tenth and one‐third their normal size, respectively. The atrophic testes exhibited a complete loss of spermatogensis and an apparent diminished secretion of androgens since the seminal vesicles and coagulating glands also regressed significantly. Despite the involution, the testes showed a high degree of deoxyribonucleic acid synthesis as evidenced by the large number of spermatogenic cells which took up tritiated thymidine. These findings indicate that the testes retained a certain level of regenerative capacity even in the presence of advanced tubular damage.If hamsters blinded for 9 weeks, had either their pineal gland or superior cervical ganglia removed, the involuted testes and accessory organs regenerated and returned to the normal size, and presumed function, within approximately 8 weeks. Regenerated testes were histologically indistinguishable from those of normal animals. Eyeless hamsters killed after 17 weeks still possessed involuted reproductive organs.

Failure of the pineal gland to prevent gonadotrophin-induced ovarian stimulation in blinded hamsters.

Failure of the pineal gland to prevent gonadotrophin-induced ovarian stimulation in blinded hamsters.