Lack of gonadotrophin-releasing hormone (GnRH) neuron response to decreasing photoperiod in thyroidectomized male starlings (Sturnus vulgaris)

Exposure of starlings to long days initially causes reproductive maturation, but eventually leads to photorefractoriness. During photorefractoriness, gonadotrophin-releasing hormone (GnRH) decreases in the GnRH cell bodies and fibers emanating from these to the median eminence, circulating gonadotrophin concentrations decrease to a minimum, and the gonads regress. Thyroidectomy profoundly affects these photoperiodic responses. In chronically thyroidectomized starlings, gonadal responses to changes in day length are attenuated. This investigation was conducted to determine whether, in the absence of gonadal responsiveness, the GnRH system of chronically thyroidectomized starlings responds to changes in day length. Two groups of thyroidectomized male starlings were transferred from short days (8L:16D) to long days (18L:6D) for four weeks, and testicular volume increased. One group was kept on long days (TxLD) and the other was returned to short days (TxSD). Testicular volume did not decrease in the TxSD group. The GnRH neurons of the two thyroidectomized groups were compared to those of two groups of intact starlings, one of them on long days and photorefractory (ILD), the other on short days and photosensitive (ISD). Group ILD had lower numbers of GnRH-stained cells than groups TxLD, TxSD and ISD, which did not differ in this respect. Similar differences were observed for GnRH cell size in the pre-optic area (POA) and for density of staining of GnRH fibers in the median eminence. The results confirm that thyroidectomy attenuates gonadal responses to change in day length and suggest that this results from an effect upon the central nervous system rather than a peripheral effect.     

Short photoperiod-induced gonadal regression: effects on the gonadotropin-releasing hormone (GnRH) neuronal system of the white-footed mouse, Peromyscus leucopus

The peroxidase-antiperoxidase method was used to determine quantitatively the effect of short photoperiod-induced gonadal regression on the immunoreactive gonadotropin-releasing hormone (GnRH) neuronal system of female Peromyscus leucopus. In mice exposed to either long (16L:8D) or short (8L:16D) photoperiod, immunoreactive cell bodies were loosely organized into six groups: olfactory peduncle, diagonal band of Broca, septum, preoptic area (POA), anterior hypothalamus (AH), and basal hypothalamus. The POA and AH contain the largest number of cell bodies, which supply the major GnRH innervation to the median eminence (ME) and several extrahypothalamic brain sites. Exposure to short photoperiod increased the number of immunoreactive cell bodies within the anterior hypothalamus and preoptic area (AHPOA) and also increased the optical density for staining of immunoreactive cell bodies in the AHPOA and olfactory peduncle. The ME of mice exposed to short photoperiod had a higher density of GnRH fibers relative to that of mice exposed to long photoperiod, and the content of GnRH fibers in the rostral ME was correlated with the optical content for immunostaining of cell bodies in the AHPOA. These results are evidence that gonadal regression induced by short photoperiod (mediated by the pineal gland) involves alterations of GnRH neuronal activity. Notably, data from this study are consistent with the hypothesis that suppressed release of GnRH from neurovascular terminals in the ME, rather than lack of availability of the decapeptide, promotes gonadal regression.     

Circannual rhythms in European starlings: Why do they stop under long photoperiods?

Summary In European starlings (Sturnus vulgaris) exposed in winter to photoperiods of 12 1/2 h or more, testes go through a cycle of growth and regression but then stay inactive for many months. Under a photoperiod of 12 h, in contrast, testes usually go through repeated circannual cycles. We have tested the hypothesis that the failure of starlings held under long photoperiods to initiate a second testicular cycle is a consequence of the fact that photorefractoriness is not broken under photoperiods longer than 12 h. The results of 2 experiments are consistent with this hypothesis: whereas the testes of starlings held continuously in a 13-h photoperiod or in continuous light, remained inactive after an initial testicular cycle, testicular growth was re-initiated after birds were exposed for 4 to 8 weeks to a short 8-h photoperiod.     

Differential responses of the photoperiodic clock in two passerine birds possessing a strongly self-sustained circadian system

To investigate whether the photoperiodic clocks of species possessing strongly self-sustaining circadian clocks share identical features, we compared the full response cycle (initiation and termination of the response) in body mass and testes of the non-migratory house sparrow (Passer domesticus) with that of the migratory redheaded bunting (Emberiza bruniceps) under Nanda-Hamner experiments. Birds were exposed to a 36 h day (L:D=6:30 h), controls exposed to a 24 h day (L:D=6:18 h), for a period of 31 weeks. By week 18 of L:D=6:18 h, there was a small increase in body mass among sparrows, but not among buntings, and the testes of bunting did not grow, while those of sparrow grew slightly. The response to L:D=6:30 h is of particular interest. There was a rapid gain and subsequent loss in the body mass of bunting, but not of sparrows. Further, both species underwent a testicular cycle as if they were exposed to long days, but the response of sparrows was slower and hence delayed the attainment of peak testicular size. Such a differential response to exotic light cycles between these two photosensitive species, despite their similar circadian oscillatory properties (strong self-sustainment), could suggest a species-specific adaptation of the endogenous clock involved in photoperiodic regulation of avian seasonality.     

Immunocytochemistry of luteinizing hormone-releasing hormone during spontaneous and thyroxine-induced metamorphosis of bullfrogs

Double-bridge peroxidase-antiperoxidase immunocytochemistry was used to compare the developmental appearance of immunoreactive LH-RH (ir-LH-RH) in brains of bullfrog (Rana catesbeiana) tadpoles during either spontaneous or thyroxine-induced metamorphosis. During spontaneous metamorphosis, ir-LH-RH was localized in fibers of the external layer of the median eminence (ME) of stage XIII-XXV animals, while immunoreactive perikarya and other immunostained brain structures were absent. The extent and intensity of ME immunostaining increased concomitantly with measured ME morphological development. Tadpoles induced with thyroxine to metamorphic stages XIX-XXI exhibited ME structural development and neurohypophysial neurosecretory staining similar to spontaneously metamorphosed individuals of equal stages. However, comparable ME ir-LH-RH immunostaining and gonadal size were both less developed in thyroxine-treated animals, although increased relative to non-metamorphic vehicle-injected controls. These results indicate that the hypothalamic LH-RH system changes concurrently with ME structural development during spontaneous metamorphosis. Reduced ME ir-LH-RH staining and gonadal size in thyroxine-treated animals suggest that during prometamorphosis, factors other than thyroxine alone may coordinate the normal maturation of the hypothalamo-pituitary-gonadal axis of the bullfrog.     

Short days induce premature reproductive maturation in juvenile starlings, Sturnus vulgaris

Castration of juvenile and photorefractory adult starlings caused no immediate increase in circulating concentrations of LH. In castrated juveniles and adults exposed to natural changes in daylength, plasma LH increased between mid-October and mid-November, although the increase was more rapid in adults. In castrated photorefractory adults, plasma LH increased 3-5 weeks after transfer to artificial short days (8L:16D). In castrated juvenile starlings plasma LH increased 4-6 weeks after transfer to 8L:16D, irrespective of the age of the birds. Birds as young as 17 weeks had high LH concentrations. These results suggest that the reproductive system of juvenile starlings is in the same state as that of photorefractory adults, and therefore the activation of the hypothalamo-pituitary axis for the first time in juveniles is analagous to the termination of photorefractoriness in adults.     

Stable daily light regimens as inductive factors of endogenous testicular cycles in the European starling,Sturnus vulgaris

European starlings (Sturnus vulgaris ) maintained under chronic 12L:12D exhibit testicular cycles with a periodicity of 9–10 months. These circannual testicular cycles incorporate all of the physiologically distinct phases observed during gonadal cycles in starlings under temperate-zone photoperiods. Starlings maintained under chronic 6L-18D also undergo testicular cycles but these cycles: (a) have a relatively short periodicity (about 6 months); (b) include periods of testicular involution, though not to the minimal quiescent level for this species; and (c) do not include the physiologically distinct photorefractory phase separating testicular cycles in starlings under chronic 12L:12D and under temperate-zone photoperiods. While it is possible that testicular cycles in starlings under certain daily light regimens of fixed duration are a function of an endogenous circannual reproductive rhythm, we believe that the testicular cycles generated under both 12L:12D and 6L:18D are the product of gonadotropin secretion rates controlled by circadian (not circannual) oscillations periodically entrained by these chronic photoperiods.     

Seasonality in a temperate zone bird can be entrained by near equatorial photoperiods

Birds use photoperiod to control the time of breeding and moult. However, it is unclear whether responses are dependent on absolute photoperiod, the direction and rate of change in photoperiod, or if photoperiod entrains a circannual clock. If starlings (Sturnus vulgaris) are kept on a constant photoperiod of 12h light:12h darkness per day (12L:12D), then they can show repeated cycles of gonadal maturation, regression and moult, which is evidence for a circannual clock. In this study, starlings kept on constant 11.5L:12.5D for 4 years or 12.5L:11.5D for 3 years showed no circannual cycles in gonadal maturation or moult. So, if there is a circannual clock, it is overridden by a modest deviation in photoperiod from 12L:12D. The responses to 11.5L:12.5D and 12.5L:11.5D were very different, the former perceived as a short photoperiod (birds were photosensitive for most of the time) and the latter as a long photoperiod (birds remained permanently photorefractory). Starlings were then kept on a schedule which ranged from 11.5L:12.5D in mid-winter to 12.5L:11.5D in mid-summer (simulating the annual cycle at 9 degrees N) for 3 years. These birds entrained precisely to calendar time and changes in testicular size and moult were similar to those of birds under a simulated cycle at 52 degrees N. These data show that birds are very sensitive to changes in photoperiod but that they do not simply respond to absolute photoperiod nor can they rely on a circannual clock. Instead, birds appear to respond to the shape of the annual change in photoperiod. This proximate control could operate from near equatorial latitudes and would account for similar seasonal timing in individuals of a species over a wide range of latitudes.     

The effect of duration and time of food availability on the photoperiodic response in the male house sparrow, Passer domesticus

We investigated the effects of food availability on the seasonal testicular growth in the photoperiodic house sparrow (Passer domesticus). Two experiments were performed, each lasting 4 weeks. In experiment 1, sparrows were exposed to natural (NDL; group 1), short (8L:16D; group 2) and long (16L:8D; groups 3-5) day lengths with access to food ad libitum (groups 1-3) or for 10 h (zeitgeber time (zt) 0-10, group 4; zt 0 is the time of light onset) or for 8 h (zt 8-16, group 5). Testes recrudesced under long, but not short and natural, day lengths, and the recrudescence under long days was influenced by the duration of food availability. In experiment 2, the sparrows were exposed to short (8L:16D, group 1) and long (16L:8D, groups 2-5) day lengths with access to food ad libitum (for groups 1 and 2) or for 6 h (for groups 3-5) at different times during the 16 h light period (group 3- zt 0-6, group 4- zt 5-11, group 5- zt 10-16). As the expected, the testes recrudesced only under long lengths, but the photoinduction was variable among the 4 groups. The testes grew to full size in groups 2 and 3 that received food either ad libitum or for 6 h at zt 0-6, but to sub-maximal size in the groups that received 6 h food either at zt 5-11 (group 4) or at zt 10-16 (group 5). Altogether, these results support the idea that the photoperiodic regulation of reproduction in a seasonally breeding species is influenced both by the duration and the time of food availability.     

Photoperiodic variations of somatic and germ cell populations in the Soay ram testis

Seasonal changes in the Leydig, Sertoli and stem cells (undifferentiated A0 and cyclic A1) spermatogonia and the daily spermatid production were analysed in the testes of adult Soay rams exposed to short days (8L:16D) or long days (16L:8D) for 12 weeks. The total numbers of Leydig, Sertoli and stem cells (A0 + A1) were not affected by the treatments, but the size of the Leydig and the Sertoli cells, the efficiency of spermatogenesis (i.e. the number of male gametes produced by an A1 spermatogonium) and the daily sperm production were all significantly reduced in the rams exposed to long days. There was a positive correlation between the concentration of FSH and testosterone and many of the cytological changes consistent with a causal role for these hormones in mediating the effects of photoperiod on the testicular function in the ram.     

A histochemical study on the effects of photoperiod on gonadal and adrenal function in the male bank vole (Clethrionomys glareolus).

NADH- and NADPH-diaphorases, 3alpha-, delta5-3beta-, 11beta- and 17beta-hydroxy-steroid dehydrogenases (HSD) and lipids were studied histochemically in the testes and adrenals of male bank voles kept in a long (16L:8D) or a short (8L:16D) photoperiod (Groups L and S, respectively). At 67 days of age the Group L males were heavier and had active and significantly larger testes than Group S males. The testes of Group S males were regressed and were also significantly smaller than those of 18-day-old animals born and reared in a 18L:6D photoperiod. Lipid droplets were detected in the Leydig cells and intratubular spaces in the testes of Group L animals, but were absent from those of Group S voles. The adrenal cortex of the Group L animals was virtually devoid of lipids, but large lipid inclusions were present in the basal zona fasciculata of the Group S voles. In the Group L testes the diaphorase activities were more intense and the difference in enzymic activity between the seminiferous epithelium and the Leydig cells was more pronounced (especially for NADH-diaphorase) than that in the testes of Group S animals. Moreover, the 3alpha-- and delta5-3beta-HSD activities were much stronger in the testes of sexually active animals; 17beta-HSD activity was present in the Leydig cells of the active testes, and absent in the regressed testes. There was no marked difference between the two groups of animals with regard to the distribution or intensity of diaphorases, 3alpha-, delta5-3beta-, 11beta- or 17beta-HSD in the adrenal cortex. It is concluded that a decline in steroid synthesis occurs in the testes of voles kept in a short photoperiod. The large lipid inclusions observed in the adrenal cortex of such animals suggest decreased corticosteroid synthesis and/or secretion.     

Quantitative immunocytochemistry of pituitary receptors for luteinizing hormone-releasing hormone

In Araldite sections of male rat pituitaries, stained after embedding by the unlabeled antibody enzyme method with antisera to native luteinizing hormone-releasing hormone (LH-RH) or LH-RH azo-conjugated to bovine serum albumin, localization is confined mainly to the interior of the large, and to a lesser extent to that of the small, secretion granules of the gonadotrophic cells. Plasma membranes are not demonstrated. Except for weak staining in the granules of corticotrophs, no other pituitary cell is stained. Pretreatment of sections with LH-RH (to dilutions of 4 pg/mul) increases staining intensity in the gonadotrophic granules. Other cells are unaffected. The lesser the gonadotroph staining intensity without pretreatment, the greater the increase (more than 23-fold reactivity). Augmented staining is measurable (P less than 0.001) to antiserum dilutions of 1:240000. Pretreatment with des-Glu-1-LH-RH, porcine corticotropin or rat prolactin has no effect. LH-RH-Gly-10(des-amide) inhibits. Rat glycoprotein hormones enhance staining with anti-azo-conjugated LH-RH. With antinative LH-RH these hormones enhance weak staining, but inhibit strong staining. Thick vibrotome sections of male rat or rabbit pituitaries stained before embedding reveal specific localization on plasma membrane and gonadotrophic secretion granules provided the sections have been pretreated with LH-RH (250 pg/mul). The data show that LH-RH after reaction with receptor is not sterically hindered from binding specific antibodies. Receptor may be found in secretion granules, both in the free state or combined with LH-RH. Plasma membrane receptor, on the other hand, was free under the conditions of the experiments. Immunization with LH-RH elicits not only heteroimmune antibodies specific for LH-RH, but also a group of still ill defined autoimmune antibodies, some of which may conceivably be reactive with glycoprotein hormone alpha-chains.     

Photosensitivity in body mass and testicular activity of brahminy myna, Sturnus pagodarum

This study analyzed photoperiodic sensitivity of brahminy myna (Sturnus pagodarum), which is a seasonally breeding bird species. During regression phase of the reproductive cycle (in early September), groups of myna were exposed to artificial photoperiods that were either close to or longer than those brahminy myna experiences at this time in wild at 29 degrees N. Following a 14-week exposure to such photoperiods (hours of light: hours of darkness; 13L:11D, 12L:12D, 11.5L:12.5D and 11L:13D), the birds were subjected to a longer day length (16L:8D) for another 9 weeks to test whether pre-treatment with varying photoperiods had an effect on subsequent long day photostimulation. There was a progressive increase in body mass under different pre-treatment photoperiods, with a faster increase in 11L:13D and 11.5L:12.5D than in 12L:12D and 13L:11D. When subjected to 16L: 8D, however, all groups showed decline in body mass. By contrast, the testes were not stimulated under 11L:13D and 11.5L:12.5D, and only one individual of the groups under 12L:12D and 13L: 11D showed a small testis recrudescence. All birds except one individual of the 13L:11D group, however, showed testis recrudescence when subjected to 16L:8D. These results suggest that body mass and testes have a different profile of photoperiodic response and appear to have two different threshold photoperiods for dissipating the post-reproductive refractoriness.     

Photoperiodic control of meiosis in the male Syrian hamster (Mesocricetus auratus)

Male Syrian hamsters exposed to short photoperiods of 6 h light/day (6L:18D) show regression of the testes within 12 weeks. Chromosome preparations of the meiotic stages (pachytene, metaphase I (MI) and metaphase II (MII)), testicular weights relative to body weights, sperm counts, seminiferous tubule diameter and histological appearance were examined at intervals during regression and subsequent recovery in a long photoperiod (14L:10D). The fall of testicular weight was associated with the decrease in tubule diameter. Spermatogenesis and sperm count were reduced rapidly and finally ceased after 10 weeks in short days. The numbers of MI and MII cells relative to 100 pachytene cells progressively decreased during the short-day treatment, although the ratio of MI:MII stayed constant whenever there was meiotic activity (except in the first week of the recovery phase). This suggests that an increasing proportion of pachytene cells did not progress to MI with increased time in short days, but cells which did reach MI progressed to MII in the same proportions as in the control testes. Meiosis ceased after 10 weeks in short days. Recovery in the long days was marked by a peak in the number of MI and MII cells/100 pachytene cells soon after the return to long days. This preceded the return (to control values) of the sperm count by 10 weeks. Initial recovery in the first 3 weeks was very rapid in all the determined values.     

Environmental regulation of the reproductive system in a flexibly breeding Sonoran Desert bird, the Rufous-winged Sparrow, Aimophila carpalis

We investigated reproductive regulation in male Rufous-winged Sparrows, Aimophila carpalis, a Sonoran Desert passerine that breeds after irregular summer rains. Field and captive data demonstrate that increased photoperiod stimulates testicular development in March and maintains it until early September. Free-living birds caught in July and placed on captive long days (16L: 8D) maintained developed testes for up to 7 months, and free-living birds caught in September, during testicular regression, redeveloped testes when placed on captive long days, indicating that these birds were still photosensitive. Captive birds on long days maintained testicular development when exposed to temperatures mimicking those occurring during regression in free-living birds. In free-living birds, testicular development was observed during spring and summer, but unless this was associated with rainfall, breeding (indicated by juveniles) did not occur. Large increases in plasma luteinizing hormone (LH) in free-living males were correlated with heavy rainfall in July/August, when the birds bred, and in November, when they did not breed. In captive birds, plasma LH concentrations were unresponsive to photoperiodic changes, but may have responded to social cues. Plasma prolactin concentrations were directly correlated with photoperiod in free-living birds, but an effect of photoperiod on prolactin secretion was not seen in captive birds. It is concluded that male Rufous-winged Sparrows use long photoperiods to stimulate and maintain testicular development, but exposure to long photoperiods does not terminate breeding by inducing absolute photorefractoriness. The specific timing of reproductive behaviors is apparently determined by elevated plasma LH coinciding with long day stimulated gonad development.     

Areas of asbestoid (amianthoid) fibers in human thyroid cartilage characterized by immunolocalization of collagen types I,II, IX,XI and X

The distribution of type I, II, IX, XI and X collagens in and close to areas of asbestoid (amianthoid) fibers in thyroid cartilages of various ages was investigated in this study. Asbestoid fibers were first detected in thyroid cartilage from a 3-year-old male child. Areas of asbestoid fibers functionally appear to serve as guide rails for vascularization of thyroid cartilage. Alcian blue staining in the presence of 0.3 M MgCl₂ revealed a loss of glycosaminoglycans in areas of asbestoid fibers. In addition, the fibers reacted positively with antibodies against collagen types II, IX and XI, but showed no staining with antibodies to collagen types I and X. Territorial matrix of adjacent chondrocytes showed the same staining pattern. In addition to staining for type II, IX and XI collagens, asbestoid fibers showed strong immunostaining for type I collagen after puberty but not for type X collagen. However, groups of chondrocytes within areas of asbestoid fibers reacted strongly with antibodies to type X collagen, suggesting that this collagen plays an important role in matrix of highly differentiated chondrocytes. The finding that these type X collagen-positive chondrocytes also revealed immunostaining for type I collagen confirms previous studies showing that hypertrophic chondrocytes can further differentiate into cells that are characterized by the synthesis of type X and I collagens.     

Fas-Fas ligand system as a possible mediator of spermatogenic cell apoptosis in human maturation-arrested testes

To elucidate the mechanism of maturation arrest, known as one of the male infertility, we addressed whether germ cell apoptosis occurs during maturation arrest, and if so, whether Fas and Fas ligand expressions are involved in the apoptosis. By electron microscopy and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), typical apoptotic features were frequently found around the spermatocytic stage in maturation arrest, compared to that in normal testes. When paraffin-embedded sections reacted with anti-Fas antiserum, staining for Fas was found in the plasma membranes of spermatocytes in the maturation-arrested testes, while no positive spermatogenic cells were seen in the normal testes. On the other hand, positive immunostaining for Fas ligand was restricted to Sertoli cells in the maturation-arrested testes as well as in the normal testes, although the intensity of staining for Fas ligand in normal testicular Sertoli cells was much weaker than that of maturation-arrested ones. Thus, these findings demonstrate that "maturation arrest" is characterized by frequent apoptosis of spermatocytes, and that Fas and Fas ligand staining are associated with a high frequency of apoptosis.     

Regulation of seasonality in the migratory male blackheaded bunting (Emberiza melanocephala)

The present study was carried out on a Palearctic-Indian migratory species, the blackheaded bunting (Emberiza melanocephala), to understand the importance of photoperiodism and circannual rhythms in determining seasonality in changes in body mass and testis size in birds. An initial experiment determined the effects of duration and intensity of light on photoperiodic induction. The birds were exposed to different photoperiods (hours of light:hours of darkness; 11.5L:12.5D, 12L:12D, 12.5L:11.5D and 13L:11D) at the same (approximately 450 lux) light intensity, and to 13L:11D at different light intensities (50-, 100-, 400-, 800- and 1000-lux). The induction and subsequent regression of photoperiodic responses were dependent upon duration and intensity of the light period until these reached threshold. A second experiment investigated if an endogenous seasonal rhythm underlies photoperiodism in buntings. Birds maintained since February on a 8L: 16D photoperiod (a non-inductive short day length invariably used to ensure photosensitivity in photoperiodic species) were subjected periodically to 16L:8D (a long day length), one group every month from mid-March to mid-August. The magnitude of long day response in body mass and testes decreased as the duration of the short days progressed, but testicular response was restored in birds that were exposed to long days in July and August. The birds exposed simultaneously to short, long, and natural day lengths for 32 weeks underwent an induction-regression cycle under long days and natural day lengths, but not under short days in which a decrease in body mass occurred after about 20 weeks. The last experiment examined the importance of latitudinal migration on photoperiodism, by comparing the response to long days of three groups which included birds from populations those were held in the outdoor aviary for 1 or 2 years at 27 degrees N and those immediately arrived from their breeding grounds (approximately 40 degrees N). There was no difference in the photoperiodic induction among the three groups, indicating that neither experience to changing photoperiods during a migratory journey, nor to long photoperiods at breeding grounds, were critical for a subsequent response (initiation-termination-reinitiation) cycle. Taken together, these findings suggest that (1) the blackheaded bunting has its own endogenous timing program, which is regulated by the photoperiod, and (2) the photoperiodic programs of bunting are flexible enough to accommodate variations in the amplitude of environmental cycles. Thus, it appears that photoperiodism has evolved independently of the evolution of migration in this species.     

Effect of long-term pinealectomy on serum LH levels and on cerebral serotonin metabolism in adult male rats

Two months after pinealectomy carried out in adult male rats previously exposed to a long photoperiod (L:D 14:10) during 10 weeks, the weight of seminal vesicles significantly increased in comparison with Sham-operated animals. Nevertheless, the weights of testes and ventral prostate did not change significantly. The serum LH concentration increased significantly by pinealectomy. The levels of serotonin and 5-hydroxiindolacetic acid significantly decreased in the hypothalamus and midbrain after pinealectomy.     

Effect of photoperiod on the size of the Leydig cell population and the rate of recruitment of Leydig cells in adult Syrian hamsters

The number of Leydig cells was determined by stereologic procedures in adult Syrian hamsters housed in long days (14L:10D) to maintain testicular activity (active), in short days (5L:19D) for 12-13 wk to induce testicular regression (photoperiod-induced regressed), or in short days for a period of 21 wk or more to allow spontaneous gonadal recrudescence (spontaneously recrudesced). Testes were removed, sliced, fixed, embedded in Epon 812, and observed by bright-field microscopy. Testicular and seminal vesicle weights, plasma testosterone concentration, total Leydig cell volume per testis, and volume of single Leydig cell were greater (p less than 0.01) in active and recrudesced animals than in regressed animals. The density of Leydig cells was greater in the regressed testes, but the total number per testis was not influenced by photoperiod. In Experiment 2, the rate of recruitment of Leydig cells was determined in 5 adult hamsters exposed to long days (active) or 5 hamsters whose testes were regressed by exposure of animals to short days for 13 wk followed by long-day exposure to initiate testicular growth (photoperiod-induced recrudescing). Hamsters were injected for 3 days/wk for 3 wk with tritiated thymidine, 0.5 or 1 microCi/g body weight. Testes were fixed and tissues prepared, as above, and processed for autoradiography. Again, the photoperiod did not influence the number of Leydig cells per testis. Labeling of Leydig cell nuclei revealed that recruitment of new Leydig cells occurred at approximately 1.3% per day in recrudescing testes but also occurred at approximately 0.6% per day in active testes. Without change in the total number of Leydig cells, new Leydig cells were added continually to the existing population in adult hamsters with either recrudescing or active testes.