Effect of 12 hr temporal relation of serotonin and dopamine precursor drugs (5-HTP and L-DOPA) on photosexual responses of immature Japanese quail

To study the interaction of photoperiod and circadian neurotransmitter activity, L-DOPA L-dihydroxyphenylalanine, dopamine precursor) was administered daily, 12 hr after 5-HTP (5-hydroxy tryptophan, serotonin precursor) in sexually immature Japanese quail, raised under short photoperiod (LD8:16) since hatching. The 12 hr treatment of 5-HTP and L-DOPA was given under continuous condition of light for 11 days. After treatment the quail were transferred to intermediate day length (LD 13.5:10.5). The cloacal gland size of drug treated group increased significantly in comparison to control. The quail were then transferred to short photoperiod (LD 8:16). The cloacal gland size of both the groups started decreasing gradually but the rate was significantly low in drug treated quail in comparison to control. The results indicate that the endogenous mechanism controlling seasonality may be reset by drugs that influence serotonergic and dopaminergic activity. The 12 hr relation between the two drugs is stimulatory for gonadal growth under intermediate day length and retards the rate of regression when transferred to short days.     

Correlation of nitric oxide (NO) activity and gonadal function in Japanese quail, Coturnix coturnix japonica following temporal phase relation of serotonergic and dopaminergic oscillations

Nitric oxide (NO), a highly reactive and short-lived radical, is considered to be an important trigger molecule for several physiological mechanisms including gonadotrophin releasing hormone (GnRH) secretion in mammals, although there is no such information in avian literature. On the other hand, specific temporal phase relation of circadian neural (serotonergic and dopaminergic) oscillations is reported to modulate reproductive activity in many avian species including Japanese quail. The present study was undertaken to investigate the correlation of NO activity and gonadal function of Japanese quail. In experiment I, the effect of serotonin and dopamine precursors, (5-hydroxytryptophan (5-HTP) and L-dihydroxyphenyalanine (L-DOPA) respectively; 5 mg per 100g body weight) administered at intervals of 8 or 12h over a period of 13 days, was studied on reproductive responses and NO activity. Measurements of body weight, cloacal gland size, testosterone concentration, spermatogenesis, nitrite-nitrate concentration in plasma, hypothalamus and testes, and NADPH-diaphorase (NADPH-d) activity in testes were made on the 2nd, 3rd, 6th and 11th days of treatment and 2nd and 30th day post-treatment. In experiment II, quail were divided into five groups including the control. One experimental group received 13 daily injections of 5-HTP and L-DOPA at intervals of 8h along with 0.1 ml of normal saline administered orally (8-hr+Veh), while another group of 8-hr quail received NO donor (sodium nitroprusside (SNP), 5 mg per 100 g body weight) orally (8-hr+SNP). The third experimental group received 5-HTP and L-DOPA at intervals of 12h along with normal saline (12-hr+Veh), while the fourth group of quail along with 5-HTP and L-DOPA at intervals of 12h also received the NOS inhibitor (N-nitro-L-arginine methyl ester, L-NAME, 25 microg per 100 g body weight) intraperitoneally (12-hr+L-NAME) for 13 days. This experiment was terminated after 21 days of the treatment. Results indicate that 5-HTP and L-DOPA administered 8h apart (8-hr) suppressed but if given 12h apart (12-hr) stimulated the reproductive system and NO activity compared to the control. These effects were apparent on the 6th day of injections and were maintained 30 days following the termination of the treatment. A significant decrease in nitrite and nitrate concentration and NADPH-d activity in reproductively inhibited 8-hr group and an increase in reproductively stimulated 12-hr quail was also evident. In contrast, these activities were stimulated in 8-hr+SNP quail and were suppressed in 12-hr+L-NAME group quail. It is concluded that activity of the reproductive system and NO activity waxes and wanes simultaneously in Japanese quail. Moreover, experimental modulation of gonadal activity (following changes in the phase relation of serotonergic and dopaminergic activity) or NO activity (following the administration of NO modulator or inhibitor) affects each other maintaining a parallel relation between the two systems. Further, it is interesting to note that the gonado-stimulatory effect of SNP overpowers the gonado-inhibitory effects of the 8-hr time interval and inhibitory effects of L-NAME mask the stimulatory effects of 12-hr temporal relation of 5-HTP and L-DOPA administration. These findings strongly suggest that reproductive effects may be induced via changes in NO activity, however the exact mechanism by which NO drives gonadal axis needs to be ascertained.     

Influence of different photoperiods on development of gonad, cloacal gland and circulating thyroid hormones in male Japanese quail Coturnix coturnix japonica.

One day old chicks of Japanese quail were exposed to different photoperiods (LD, 8:16, 13.5:10.5, 16:8 and LL) and observations (testes weight, cloacal gland size, body weight and circulating thyroxine and triiodothyronine) were taken at the age of 3, 5, 7, 9 and 16 weeks. Results indicate that immediate reproductive development occurred in birds exposed to long photoperiods (greater than 12 hr). Growth under LD 8:16, was not apparent till 7th week and by 16 weeks, degree of gonadal development was similar in all the birds, irrespective of photoperiodic treatment. Whereas body weight of the intermediate and long day (LD 13.5:10.5, 16:8 and LL) treated birds increased upto 5th week and remained constant thereafter. But the chicks maintained under short day length (LD 8:16), showed spontaneous increase till the end of the study and birds were much heavier compared to all other groups. Plasma T4 concentration increased with increasing age till 9th week and remained unaltered thereafter. On the other hand T3 level did not change till 7th week followed by a decline. It is suggested that the initiation and degree of gonadal growth in quail depends on the availability of daily photoperiod, until the achievement of full breeding condition. Peak level of T4 observed in 9 week old birds may be involved in the development of photorefractoriness at that age.     

Age, photoperiod and estrogen dependent variations in the shell gland and the expression of AVT in the ovary of Japanese quail

Present work was undertaken to describe (i) age dependent (prepuberal-3, 4, 5 and 6 weeks old, puberal and actively laying 8 and 12 weeks old and aged 78 weeks old) (ii) photoperiodic response dependent (photosensitive and photorefractory) and sex steroid dependent (estradiol benzoate and its antagonist tamoxifen treated) variation in the ovary and shell gland activity of Japanese quail (Coturnix coturnix japonica). Further, in view of the role of neurohypophysial peptide arginine vasotocin (AVT) in many physiological processes including age/reproduction related oviposition, expression of ir-AVT was also monitored in the ovary of quail. All the parameters associated with histodifferentiation increased rapidly during the developing stages followed by a decrease in old age, which also increased in reproductively quiescent photorefractory birds following estradiol treatment and decreased in reproductively active photosensitive quail following tamoxifen treatment. Using AVT-specific antibody, expression of immunoreactive AVT (ir-AVT) observed in the ovary of photosensitive quail was not detected in the photorefractory quail. However, administration of estrogen in the photorefractory quail stimulated the growth and activity of ovary and shell gland also resulted in the expression of ovarian ir-AVT. On the other hand, tamoxifen eliminated the localization of ir-AVT in the ovary of photosensitive quail in addition to a decrease in the shell gland protein and alkaline phosphatase activity. It is concluded that estrogen not only affects the growth and differentiation of ovary and oviduct including shell gland but also regulates the expression of ovarian AVT. It is also suggested that in addition to reported paracrine effect of AVT in the shell gland of Japanese quail for oviposition, ovarian AVT may also affect ovarian function (ovulation), and in part, this regulation is estrogen dependent.     

Testosterone induction of song in photosensitive and photorefractory male sparrows

Song in male songbirds is activated by the sex steroid testosterone (T). Using male song sparrows (Melospiza melodia), we compared effects of T in the normal spring state of photosensitivity (i.e., when the pituitary-gonadal axis is sensitive to stimulation by increasing daylength) and in the late summer-early fall state of photorefractoriness (i.e., when they are insensitive to increasing daylength). Photosensitive males experienced short days for 8 weeks and then long days for another 22 weeks to induce photorefractoriness. T implants were given to the birds twice, first when on short days and photosensitive, and second when on long days and photorefractory. Song rates were compared among 5 conditions: (1) photosensitive, short days, low T titers; (2) photosensitive, short days, high T titers; (3) photosensitive, long days, high T titers; (4) photorefractory, long days, low T titers; and (5) photorefractory, long days, high T titers. Plasma levels of T were monitored throughout the experiment by radioimmunoassay. T was equally effective in inducing song in both the photosensitive and photorefractory conditions. Thus, no seasonal change was found in the sensitivity to hormone action of the neural target sites mediating this behavior in song sparrows. Photosensitive birds sang at a higher rate when on long days than when on short days, however, even though there was no concomitant increase in plasma levels of T. This finding suggests that environmental factors can alter the expression of song activated by similar levels of T.     

Relationship of cloacal gland with testes, testosterone and fertility in different lines of male Japanese quail

An attempt has been made to investigate the relationship of cloacal gland with testes, testosterone and fertility in different lines of Japanese quail (Coturnix coturnix japonica). For this study, three lines of healthy adult male Japanese quails (<12 weeks) viz., heavy body weight (HB), white breasted (WB), and white egg shell (WES) were taken. They were housed in individual cages under uniform husbandry conditions and were provided with normal quail breeder ration and water ad libitum, with 14 h light/day. The experimental birds were selected from each of these three lines and categorized into different groups (15 birds/group) based on the increasing order of the area of cloacal gland. At the end of this experiment (24 weeks) the data indicated that size of the cloacal gland was directly proportional to foam discharge, foam weight, testicular weight, fertility and testosterone concentration in plasma. From this study it may be concluded that area of cloacal gland in Japanese quail is positively correlated with testicular weight, level of testosterone in plasma and fertility. Visual examination of cloacal gland and cloacal foam may provide a valuable non-invasive tool for predicting the fertilizing ability of individual male bird.     

Effects of surgical deafening and exposure to continuous darkness on cloacal gland size in scotorefractory Japanese quail

Adult male quail were transferred to short days (SD) and exposed simultaneously to conspecific vocalizations of males on long days (CVMLD). Cloacal glands did not regress in some males while in others their glands regressed then spontaneously recrudesced. Of the birds that exhibited cloacal gland regression, 80% recrudesced by 8 weeks and all birds recrudesced by 25 weeks on SD. Three experiments are reported. The first experiment analyzed the effects of transfer to SD. The remaining two experiments examined the role of auditory stimuli. In Experiment 2, deafening males whose cloacal glands had not regressed after 17 days exposure to SD and CVMLD produced a significant decrease in cloacal gland size. In Experiment 3, quail whose cloacal glands had regressed and recrudesced while exposed to SD and CVMLD were deafened and/or transferred to complete darkness (DD). Cloacal gland size was significantly smaller in deafened males kept on SD or kept in DD than in sham controls retained on SD. Surprisingly, the cloacal glands of sham controls in DD were similar to those of intact birds which remained on SD. These results suggest that scotorefractoriness which has been attributed to an insensitivity to short photoperiods may be due to a sensitivity to vocalizations of birds on LD. Perhaps there is a hierarchy of physical and social cues so that a decrease in the photoperiod unmasks the effects of auditory stimuli. Furthermore, an interval timer mechanism or some alternative to the external coincidence model of time keeping seems to account for the refractoriness to SD.     

Reproductive phase dependent circadian variation in hypothalamic concentration of serotonin, dopamine and peripheral thyroxine levels in Japanese Quail following 5-HTP and L-DOPA administration at specific time intervals

Temporal phase relations of circadian hypothalamic neurotransmitters are reported to regulate seasonal reproduction in some avian species. Present experiments were designed to study circadian variation in the hypothalamic concentration of neurotransmitters (serotonin and dopamine) and the plasma thyroxine level in sexually active (long day) and inactive (short day) Japanese Quail. A significant circadian cycle was noted in the hypothalamic content of both serotonin and dopamine, but with different patterns. In breeding Quail, peak activity of serotonin and dopamine was noted at 10.00 A.M. and 10.00 P.M. respectively i.e. at the interval of 12 hours. However, during sexually quiescent condition, peaks of both neurotransmitters occurred at 2.00 P.M. i.e. having a 0-hour temporal relationship. During the breeding phase, the plasma thyroxine level showed a biphasic pattern with two circadian peaks at 10.00 A.M. and 10.00 P.M. whereas in the non-breeding condition a single peak was observed at 10.00 A.M. In the second experiment, to study the effect of temporal synergism of neurotransmitter precursor drugs on circadian cycles, two groups of Quail were administered daily with serotonin precursor 5-HTP (5-hydroxytryptophan) and dopamine precursor L-DOPA (L-dihydroxyphenylalanine) (5 mg/100 g body weight) 12 hour (12-hr) and 8 hour (8-hr) apart over a period of 11 days under continuous conditions of light and then transferred to long day length for 15 days when the experiment was terminated. When compared to controls, the 12-hr condition induced breeding while the 8-hr condition led to a non-breeding condition. The circadian pattern of serotonin levels of control and 12-hr Quail was similar to that of a normal sexually active bird, while that of the 8-hr Quail showed the pattern of a sexually inactive bird. The plasma thyroxine level exhibited a biphasic pattern in 12-hr Quail, which was similar to a normally breeding bird, whereas unlike sexually inactive birds, the thyroxine concentration in 8-hr Quail was relatively low and did not show significant cyclicity. Interestingly, the plasma testosterone level of 12-hr Quail followed a more or less similar pattern with peak activities coinciding with that of thyroxine i.e. biphasic in the sexually active condition (12-hr and control) but a single peak in the quiescent (8-hr) condition. These findings suggest that the temporal phase relation of circadian serotonergic and dopaminergic oscillator varies as a function of reproductive status of the bird, and breeding/non-breeding conditions may be induced experimentally by changing the phase relation of these oscillations.     

Isolation of E. coli from foam and effects of fluoroquinolones on E. coli and foam production in male Japanese quail

Sexually active male Japanese quail (Coturnix coutrnix Japonica) produce a foamy substance from their cloacal gland. It was postulated that bacteria played an important role in production of foam. The primary objective of this study was to isolate and identify bacteria present in the cloacal foam. The secondary objective was to evaluate the effect of fluoroquinolone treatment on bacterial counts and foam production. Healthy adult Japanese quail were maintained in individual cages under uniform husbandry conditions and allocated arbitrarily into three groups (each group consisted of 12 male and 12 female birds). Foam was collected from the cloacal gland of male birds of each group separately into sterile petri dishes and was cultured to isolate and identify bacteria and to determine their sensitivity to various antibiotics. Escherichia coli bacteria, sensitive to various antibacterials (including the fluoroquinolones ciprofloxacin and pefloxacin), were isolated. In the second part of the study, male quails of Group I (control) received I mL vehicle (normal saline 0.9% (w/v) NaCl) daily (via the intraperitoneal route) for 12 days. Male birds from groups II and III were treated intraperitoneally with ciprofloxacin or pefloxacin at the rate of 10 mg and 12 mg per/kg body weight respectively, for 12 days. In antibiotic-treated birds, there was a gradual reduction in foam production during treatment. At the end of treatment, the cloacal gland area was smaller (P < 0.05) in pefloxacin-treated birds compared to the other groups. Furthermore, a trend towards decreasing body weight and fertilizing ability was noted in the same group. A drastic reduction in bacterial counts of foam was recorded only in fluoroquinolone-treated groups during treatment period. After cessation of treatment, all end points were increasing back to pre-treatment levels. In conclusion, E. coli were present in the foam of the cloacal gland of Japanese quail and may have a role in foam production.     

Effect of daylength on the rate of recovery of photosensitivity in male starlings (Sturnus vulgaris).

Four groups of castrated photorefractory starlings were transferred from a photoperiod of 18 h light/day (18 L) to photoperiods of 6 L, 8 L, 11 L or 12 L. A control group was kept on 18 L. Plasma concentrations of luteinizing hormone (LH) were low in all groups initially. The first significant increase in LH, which signals the recovery of photosensitivity, occurred after 4 weeks in the groups on 6 L and 8 L, after 8 weeks in the 11 L group and after 13 weeks in the 12 L group. There was no increase in the group on 18 L. The rate of recovery of photosensitivity is therefore inversely proportional to daylength, for daylengths between 8 L and 12 L.     

Changes in the daily rhythm of plasma corticosterone concentration related to seasonal conditions in the white-throated sparrow, Zonotrichia albicollis.

Circadian variations in concentrations of plasma corticosterone were investigated in the white-throated sparrow maintained on short (10-hr) or long (16-hr) daily photoperiods. In addition, the plasma concentrations of corticosterone were determined throughout a day in birds that were in the reproductively photosensitive spring migratory condition, the reproductively photorefractory post nuptial molt condition, and the fall migratory condition. Distinct unimodal rhythms were found in photosensitive birds. The daily rise occurred 12 hr after the offset of light in birds kept on both the short and the long photoperiodic regimens. There was no discernible daily variation in photorefractory birds kept on a 16 hr daily photoperiod and there was a bimodal rhythm in the birds that were in the fall migratory condition. The results are consistent with an hypothesis that assigns an important role to the circadian rhythm of corticosteroid concentration in the photoperiodic mechanism controlling seasonal reproductive and migratory conditions in the white-throated sparrow.     

Termination of photorefractoriness in the brahminy myna, Sturnus pagodarum: role of photoperiods and gonadal hormones.

In brahminy myna a photosensitive species, long days caused full gonadal development followed by rapid regression, whereas short days inhibited these responses. Experiments were performed to investigate the effects of duration of photoperiod and gonadal hormones on the recovery of photosensitivity to long photoperiods in male birds. Groups of photorefractory birds were subjected to 8-, 9- or 11-hr daily photoperiods for 45 (6.5 weeks) or 63 (9 weeks) days and then transferred to 15 h daily photoperiods for 60 days to check for the regaining of photoresponsivity. A control group was held under 15L:9D throughout the period of study. Another experiment included three groups of photorefractory males, which were maintained on 9L:15D for 9 weeks and administered with, birth-1day-1 alternately for first 30 days olive oil or different doses (10 or 100 micrograms) of testosterone propionate (TP)/bird/day alternately for first 30 days, and then transferred to 15L:9D for another 30 days to test the recovery of photosensitivity. The results indicated that (i) a period of exposure to short daylengths is required to dissipate photorefractoriness, (ii) termination of photorefractoriness is dependent on the length and duration of photoperiods and (iii) TP inhibits the recovery of photosensitivity in a dose dependent manner.     

The quail's eye: a biological clock

The site (intraocular vs. extraocular) of the biological clock driving a rhythm in melatonin content in the eyes of Japanese quail was investigated by alternately patching the left and right eyes of individual birds, otherwise held in constant light, for 12-hr periods. This patching protocol, therefore, exposed each eye to a light-dark cycle (LD 12:12) 180 degrees (12 hr) out of phase with the LD cycle experienced by the other eye. The optic nerves to both eyes were transected prior to initiating the patching protocol. The ocular melatonin rhythm (OMR) of the left eyes of quail could be entrained by this procedure 180 degrees out of phase with the rhythm expressed by the right eyes. Since optic nerve section would have deprived any putative extraocular clocks of photic entrainment information, the results show conclusively that the clock driving the OMR is located within the eye itself. In addition, the OMR of Japanese quail is remarkably unaffected by removing two potential neural inputs to the eye (sympathetic innervation from the superior cervical ganglia, and input from the isthmo-optic nucleus of the midbrain); this suggests that these inputs are not required to maintain the OMR. Finally, the clock driving the OMR of one eye does not appear to be coupled to the clock driving the OMR in the other eye, since permanently patching one eye abolished the ability of the patched eye to re-entrain to an 8-hr shift in the phase of an LD 12:12 cycle, whereas the exposed eye rapidly re-entrained to the phase-shifted cycle.     

Temporal synergism of neurotransmitters (serotonin and dopamine) affects testicular development in mice

The temporal phase relation of circadian oscillations is reported to regulate reproduction in many seasonally breeding avian and mammalian species, but its role in the reproductive regulation of continuous breeders is not yet known. Hence in the present study, six experimental groups of 3-week-old male Parkes strain mice, Mus musculus, were injected with 5-hydroxytryptophan (5-HTP, serotonin precursor) and l-dihydroxyphenylalanine (l-DOPA, dopamine precursor) at intervals of 0, 4, 8, 12, 16 or 20 hr (5 mg/100 g body weight per day for 13 days). Control mice received two daily injections of normal saline. When observed 24 days post-treatment, 8-hr mice exhibited low body weight and suppression of gonadal activity (spermatogenesis, sperm count/motility/viability and plasma testosterone concentration), while body weight and degree of gonadal development were higher in the 12-hr mice as compared to the controls. It is concluded that normal somatic and gonadal growth of pre-puberal mice may be suppressed with an 8-hr phase relation of circadian serotonergic and dopaminergic oscillations. On the other hand, a 12-hr phase relation accelerated the rate of gonadal maturation, while other relations led to more or less similar gonadal development as in the control mice. This study suggests the importance of circadian organization as a function of specific temporal phase relations of neural oscillations in the maturation of gonads. Although the exact mechanism still needs to be investigated, this seems to be mediated via effects on the neuroendocrine axis.     

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.     

Effects of hemicastration and castration on foam production and its relationship with fertility in male Japanese quail

Healthy heavy body weight strain of adult male Japanese quail (Coturnix coturnix Japonica) of the same age were used in this study to observe the effect of hemicastration and castration on the frequency of foam discharges from cloacal gland and other related parameters. The quails were housed in individual cages and divided into four groups: control (intact birds), sham-operated control (intact birds with incision), hemicastrated, and castrated groups of birds. Hemicastration and castration were carried out surgically at 10 and 13 weeks of age, respectively. Subsequently, 3 weeks after castration birds were examined for different parameters. Hemicastration caused a significant (P < 0.05) drop in the foam discharge frequency, weight of the foam, and the level of testosterone in the plasma, whereas in castrated group these variables were observed nil or negligible as compared to both of the controls. A suppressive effect of hemicastration was also noticed on the body weight, area of the cloacal gland, as well as percent fertility. Castration induced the drastic regression of the cloacal gland and a significant reduction (P < 0.05) of the body weight was also noted as compared to other groups. Frequencies of foam discharges were twice the number in daytime (06:00-18:00 h) than night, irrespective of the groups. In another study, the effect of characteristics of foam or foam glands on fertility was examined in 77 male birds paired with females. Several characteristics of foam and foam glands were examined for infertility, such as light yellow foam, dark yellow foam, smaller area of foam gland (below 225 mm2), hardness of foam gland and certain unknown factors that contributed 0.23, 0.68, 5.23, 2.27 and 3.64% infertility, respectively. An overall 12.1% birds were found to be infertile. This data indicated that smaller sizes of foam glands might reflect the poorest fertilizing ability of the male birds. From this study, it may be concluded that the cloacal gland may be considered as an external indicator of testicular function of the birds. Characteristics of the cloacal gland or foam or both may be used as a simple and effective tool to predict the fertilizing ability of an individual male in view of the very small semen ejaculate that is very difficult to collect and evaluate for fertility.     

The effects of combined serotonin and dopamine precursor application during testicular photosensitivity vs photorefractoriness of the red headed bunting (emberiza bruniceps)

Abstract

A study of the temporal synergism of serotonergic and dopaminergic activity in the regulation of reproductive seasonality of photosensitive and photorefractory migratory Red headed bunting was undertaken. In experiment 1, groups of birds kept in natural day length (NDL) in their photosensitive phase (April) received daily injections of L‐DOPA (L‐dihydroxyphenylalanine, a dopamine precursor) at 8 and 12 hr after 5‐HTP (5 hydroxytryptophan, a serotonin precursor) administration. One control group received two daily injections of saline. The injections with 12‐hr temporal relation induced early recrudescence and full gonadal growth was achieved much in advance to that of control birds. The applications with 8‐hr temporal relation suppressed the testicular growth initially but later on this effect was eliminated by NDL of May‐June. In Experiment 2, photorefractory birds also received the treatments but the temporal relation of 5‐HTP and L‐DOPA had no effect on the regressed gonads of these birds.

This study indicates that injections with specific phase relations of dopamine and serotonin precursors may alter seasonal reproductive conditions only in the photosensitive phase but had no effect in photorefractory birds.     

Altered brain metabolism of testosterone is correlated with reproductive decline in aging quail

In aging quail, an increasing proportion of males show no sexual behavior. A decrease in the mean size of the tests, cloacal gland, and sternotracheal muscles is also observed. In both sexually active and inactive males, plasma testosterone decreases with age but more so in inactive birds. The behavioral and morphological changes observed during aging are correlated with shifts in the intracellular testosterone metabolism resulting in a change in the ratio of active versus inactive metabolites. In the hypothalamus there is a steady decrease with age of 5 beta-reductase activity in all birds and an increase in 5 alpha-reductase activity only in the birds which remain sexually active. In the cloacal gland, the 5 beta-reductase activity markedly increases with age but more so in the birds which become sexually inactive. These data support the notion that the effects of testosterone are controlled by enzymatic shifts which could modulate the sensitivity to the hormone at the cellular level.     

Thyroxine treatment prevents the development of photosensitivity in european starlings (Sturnus vulgaris)

Summary In starlings, the breeding season is terminated by a state of photorefractoriness. Birds remain completely reproductively inactive as long as long days are maintained, and only exposure to short days restores photosensitivity. Two experiments investigated the role of different doses of thyroxine in the development of photosensitivity in castrated starlings. First, photorefractory castrated male starlings were moved from long (18L:6D) to short (8L:16D) days, and received in the drinking water either 1 or 10 mg · 1^-1 thyroxine for the first 7 weeks of a 14-week observation period. Control birds regained photosensitivity after 5 weeks of short days, as signaled by a spontaneous increase in plasma LH, whereas the return to photosensitivity was delayed until weeks 7 and 9 in the 1- and 10-mg · 1^-1 thyroxine-treated birds, respectively. In the second experiment, the effect of different doses of thyroxine was explored at the level of the hypothalamic Gn-RH neurosecretory neurones. The acquisition of photosensitivity in control birds transferred from long to short days was characterized by a marked increase in hypothalamic Gn-RH content (while long-day controls maintained low Gn-RH content). Doses of 10 and 20 mg · 1^-1 of thyroxine completely prevented the return to photosensitivity, as seen through changes in either plasma LH concentrations or hypothalamic Gn-RH content, while a dose of 1 mg · 1^-1 allowed a partial recovery of photosensitivity, as hypothalamic Gn-RH content increased to an intermediate level and the spontaneous rise in plasma LH occurred slowly but steadily.Abbreviations Gn-RH gonadotrophin-releasing hormone - LH luteinizing hormone - LHRH-I luteinizing hormone releasing hormone