Genes controlling polyunsaturated fatty acid synthesis are developmentally regulated in broiler chicks.

1. The objective of this study was to characterise the regulation of the pathways that synthesise long-chain polyunsaturated fatty acids (PUFA) on developing adipose deposits in broiler embryos and chicks. Subcutaneous adipose depots were harvested from embryos and embryonic d E13, E15 and E17. Subcutaneous, abdominal and crop (neck) adipose, as well as liver, were collected at 7 and 14 d post-hatch. 2. Targeted RNA sequencing was used to quantify expression of 6 elongation of very long-chain fatty acid (ELOVL) genes, two isoforms of stearoyl-CoA desaturase (SCD and SCD5), and three fatty acid desaturases (FADS1, FADS2, and FADS6) in each depot and in the liver. Expression levels of marker genes for fatty acid oxidation and adipogenesis (peroxisome proliferator-activated receptor gamma (PPARG)) were quantified. Fatty acid composition of subcutaneous adipose was analysed using gas chromatograph-mass spectrometry (GC/MS). 3. Genes in the PUFA synthetic pathway were differentially expressed across developmental ages and between depots. These include elongase and desaturase genes, that have not previously been characterised in chicken. Correlation analyses identified subsets of co-regulated genes and fatty acids and highlighted relationships that may influence adipose metabolism and development. 4. It was concluded that PUFA synthesis is an active and dynamically regulated pathway in developing adipose deposits in the broiler chick. These data highlighted potential novel roles for specific elongase and desaturase genes in adipose deposition and metabolism.

Neuropeptide Y inhibits estrous behavior and stimulates feeding via separate receptors in Syrian hamsters.

Central injections of neuropeptide Y (NPY) increase food intake in Syrian hamsters; however, the effect of NPY on sexual behavior in hamsters is not known nor are the receptor subtypes involved in feeding and sexual behaviors. We demonstrate that NPY inhibits lordosis duration in a dose-related fashion after lateral ventricular injection in ovariectomized, steroid-primed Syrian hamsters. Under the same conditions, we compared the effect of two receptor-differentiating agonists derived from peptide YY (PYY), PYY-(3-36) and [Leu(31),Pro(34)]PYY, on lordosis duration and food intake. PYY-(3-36) produced a 91% reduction in lordosis duration at 0.24 nmol. [Leu(31),Pro(34)]PYY was less potent, producing a reduction in lordosis duration (66%) only at 2.4 nmol. These results suggest NPY effects on estrous behavior are principally mediated by Y2 receptors. PYY-(3-36) and [Leu(31),Pro(34)]PYY stimulated comparable dose-related increases in total food intake (2 h), suggesting Y5 receptors are involved in feeding. The significance of different NPY receptor subtypes controlling estrous and feeding behavior is highlighted by results on expression of Fos immunoreactivity (Fos-IR) elicited by either PYY-(3-36) or [Leu(31),Pro(34)]PYY at a dose of each that differentiated between the two behaviors. Some differences were seen in the distribution of Fos-IR produced by the two peptides. Overall, however, the patterns of expression were similar. Our behavioral and anatomic results suggest that NPY-containing pathways controlling estrous and feeding behavior innervate similar nuclei, with the divergence in pathways controlling the separate behaviors characterized by linkage to different NPY receptor subtypes.

The effect of antiplatelet drugs, heparin, and preanalytical variables on platelet function detected by the platelet function analyzer (PFA-100).

The platelet function analyzer (PFA)-100 is a newly developed instrument that provides a rapid, in vitro, quantitative measurement of platelet adhesion and aggregation in whole blood flowing through a small aperture under high shear conditions. Thirty patients undergoing percutaneous transluminal coronary angioplasty (PTCA) and ten normal individuals were included in this study. In vitro and in vivo studies were conducted to discern the effect of combinations of antiplatelet drugs (aspirin, ticlopidine, abciximab) and heparin on the performance of the device as well as the effects of preanalytical variables, such as method of sample collection and ex vivo anticoagulants. Studies were also conducted examining the effect of aperture size (standard 150 microns vs. smaller 120 microns) on the ability of the device to detect the effect of antiplatelet drugs. There was no difference in mean PFA-100 closure time with citrate versus PPACK anticoagulants or with venipuncture vs. sheath sampling. Closure times did not vary with heparin administration. Closure times were slightly longer for patients taking aspirin plus ticlopidine compared to aspirin alone (p = NS). In contrast adenosine disphosphate (ADP) induced platelet aggregation was significantly less in patients that took aspirin plus ticlopidine vs. aspirin alone (p = .0005). In vitro, there was a dose-dependent increase in closure time for both aperture sizes with increasing abciximab concentration. Although both cartridges showed infinite closure times at an abciximab concentration of 2.25 micrograms/mL, there was a slight benefit to using the 120 microns aperture cartridges at abciximab concentrations of 1.75 to 2.0 micrograms/mL. In ten patients who were followed during abciximab therapy to assess the effect of aperture size, the PFA-100 was able to detect in vivo platelet inhibition by abciximab, but detection of recovery from abciximab-induced platelet dysfunction was slightly better for the PFA-100 with the 120 microns aperture compared to the standard 150 microns aperture collagen/ADP cartridge.

AP lesions block suppression of estrous behavior, but not estrous cyclicity, in food-deprived Syrian hamsters.

Food deprivation inhibits ovulatory cycles and estrous behavior in Syrian hamsters. Lesions of the area postrema (AP) prevented the suppression of estrous behavior in food-deprived hamsters, but they did not prevent the suppression of estrous cyclicity or the increase in running-wheel activity caused by food deprivation. Food deprivation or treatment with pharmacological inhibitors of glycolysis and fatty acid oxidation decreased estrogen-receptor immunoreactivity (ERIR) in the ventromedial hypothalamus (VMH), increased ERIR in the arcuate nucleus (Arc) and the posterior parvicellular paraventricular nucleus (PaPo), but had no effect on ERIR in the posterodorsal medial amygdala or the anterior parvicellular paraventricular nucleus. Lesions of the AP prevented the food deprivation-induced decrease in VMH ERIR and the increase in Arc ERIR, but they did not prevent the increase in ERIR in the PaPo. Thus, whatever physiological cues are produced by food deprivation, an intact AP is required for their transmission to the neural circuits controlling estrous behavior, VMH ERIR, and Arc ERIR. The AP is not essential for transmission of this information to the neural circuits controlling estrous cyclicity, running-wheel activity, or PaPo ERIR.

Effect of photoperiod on neural estrogen and progestin receptor immunoreactivity in female Syrian hamsters.

This study explored the possibility that reduced behavioral responsiveness to estradiol and progesterone in female Syrian hamsters exposed to a short photoperiod is associated with a reduction in the concentration of neural steroid receptors. The effects of long and short photoperiod (LP; SP) exposure on steroid receptor immunoreactivity were examined in the ventromedial hypothalamus (VMH), medial tuberal region (mTu), medial preoptic area (mPOA), medial nucleus of the amygdala (mAMYG), and the arcuate nucleus (ARC) of ovariectomized hamsters. In Experiment 1, exposure to SP for ten weeks attenuated the lordosis response following sequential treatment with estradiol and progesterone. In a separate group of animals not given hormones, SP decreased the staining intensity of estrogen receptor immunoreactive (ERIR) cells in the mPOA while increasing the number of detectable ERIR cells in part of the mAMYG. In Experiment 2, SP diminished the lordosis response as it did in Experiment 1. One week later, the same females were administered estradiol systemically to induce progestin receptors (PR). Animals housed in SP showed significantly reduced progestin receptor immunoreactivity (PRIR) in the VMH, mTu, mPOA, mAMYG, and ARC. Experiment 3 examined whether the results of Experiment 2 might have been influenced by photoperiodic effects on peripheral metabolism of estradiol. Among hamsters housed in LP or SP, PRs were induced by estradiol implanted unilaterally in the medial basal hypothalamus, thus bypassing possible photoperiodic effects on peripheral estradiol availability. This treatment resulted in significantly fewer cells with detectable PRIR in the VMH and mPOA of SP females, suggesting that the photoperiodic influences on PR induction observed in Experiment 2 do not depend on alterations in the peripheral availability of estradiol.

Effects of photoperiod duration and melatonin signal characteristics on the reproductive system of male Syrian hamsters.

Three experiments tested effects of photoperiod and the pineal hormone melatonin (MEL) on reproductive function among male Syrian-hamsters. In Experiment 1, hamsters were exposed for 32 weeks to 1 of 4 short photoperiods which varied in duration (11.5 L; 10 L; 8 L; 6 L). A fifth group was shifted from 11.5 L to 6 L after 6 weeks. Shorter photoperiods were associated with more rapid regression of the testes, but all groups eventually regressed to the same extent. In contrast, the temporal profile of testicular recrudescence, expressed as males became photorefractory, was not significantly different between groups. A decrease in photoperiod from 11.5 L to 6 L after 6 weeks did not delay the onset of recrudescence. The 11.5 L group was subdivided at week 32 and transferred to either 13 L or 16 L for the next 8 weeks to break photorefractoriness. Upon subsequent exposure to 8 L, both subgroups regressed their testes in similar fashion over weeks 40-52, indicating that the two long photoperiods were equally effective in breaking photorefractoriness. Nevertheless, FSH and prolactin were more consistently suppressed in the 16 L group following the switch to 8 L. Experiment 2 tested whether differing durations of MEL, administered s.c. each night for 9 weeks, elicit graded rates of reproductive regression in pinealectomized males. Testicular regression was more rapid in the group receiving MEL for 12 h than it was in the group receiving MEL for 8.5 h, thus supporting the hypothesis that the faster rates of testicular regression in the shorter photoperiods of Experiment 1 were due to their concomitant longer durations of nightly MEL secretion. Experiment 3 tested the hypothesis that rates of testicular regression in males receiving exogenous MEL would be affected by their prior photoperiodic history. Males were exposed to 18 L or 14 L for 7 weeks, then pinealectomized and administered 9.5 h MEL infusions s.c. each night for 9 weeks. In contrast to predictions, photoperiodic history had only transitory effects on MEL-induced testicular regression. Although the differences in MEL duration that accompany different short photoperiods have reproductive consequences (Experiment 1), the extent to which MEL duration expands during the transition from stimulatory to inhibitory photoperiods appears to be a less significant variable (Experiment 3).

Food deprivation and the facilitatory effects of estrogen in female hamsters: the LH surge and locomotor activity.

Two experiments investigated short-term food deprivation effects on neuroendocrine processes influenced by estrogen. These studies were prompted by prior work indicating that food deprivation increased the number of immunocytochemically identified cells containing estradiol receptors in the medial preoptic area of ovariectomized female hamsters. Presumably, this is one way that changes in metabolic fuel availability might alter the responsiveness of one or more systems to estradiol. The purpose of this study was to investigate two effects of estradiol that might be affected by food deprivation; these were 1) the positive feedback effects of estradiol on the luteinizing hormone (LH) surge, and 2) the facilitating effects of estradiol on locomotor activity. In Experiment 1, ovariectomized hamsters were administered estradiol, before or after 48 h of food deprivation. Two days after hormone treatment, blood was obtained by cardiac puncture, once in the morning (1100 h) and twice during the afternoon (1600-1800 h). These times were chosen to best characterize the magnitude of the LH surge. Food deprivation enhanced the amplitude of the LH surge in response to estradiol when this treatment preceded, but not when it followed, the administration of estradiol. However, there was variability in the dose of estradiol at which this effect of food deprivation occurred. In Experiment 2, the locomotor (running wheel) activity of two groups of gonadally intact female hamsters was quantified; one group was tested during the early (days 1 + 2; low estradiol) part of the estrous cycle, and the other group was tested during the late (days 3 + 4; high estradiol part of the estrous cycle. In both groups, testing was performed first under ad lib feeding conditions and again during 48 h of food deprivation. On average, the days 3 + 4 group was more active than the days 1 + 2 group, reflecting their differing levels of endogenous estradiol. Food deprivation significantly increased locomotor activity, independently of the stage of the estrous cycle during which it was imposed. These results are discussed in terms of the influence that altered estradiol receptor expression in the medial preoptic area might play in generating the effects we observed following short-term food deprivation.

Interactive effects of food deprivation and exercise on reproductive function in female hamsters.

Two experiments evaluated the combined effects of food deprivation and runningwheel access on estrous cycles and estrous behavior of female hamsters. In experiment 1, food deprivation on days 1 and 2 of the estrous cycle disrupted the next expected ovulation, and this effect was more, rather than less, robust in females allowed to exercise in running wheels while they were deprived. In experiment 2, a similar protocol was used except the females were ovariectomized and received sequential injections of estradiol benzoate (EB; 5 micrograms) and progesterone (P; 200 micrograms) separated by 48 h to induce lordosis, which was tested 4-5 after P. Food deprivation concomitant with hormonal treatment diminished lordosis durations, but this effect was significant only among the females that were permitted to run in activity wheels. Previous findings demonstrated that access to running wheels attenuated the inhibitory effects of short photoperiod exposure on hamster estrous cycles. In contrast, the present results indicate that this same manipulation exaggerates rather than diminishes the inhibitory effects of food deprivation on estrous cycles and hormone-induced behavioral estrus.

ICI 182,780 antagonizes the effects of estradiol on estrous behavior and energy balance in Syrian hamsters.

Three experiments examined the effects of ICI 182,780, a steroidal "pure" antiestrogen that is thought to be active peripherally but not in the brain when given systemically, on energy balance, estrous behavior, and in vivo cell nuclear binding of [3H]estradiol in Syrian hamsters. Pretreatment with ICI 182,780 reduced in vivo uptake of [3H]estradiol in uterus but not in pooled hypothalamus-preoptic area. Ovariectomized Syrian hamsters were treated with estradiol benzoate (EB, 5 micrograms/day), ICI 182,780 (250 micrograms/day), or both EB and ICI 182,780 for 4 wk. Estradiol treatment caused significant decreases in food intake, body weight and fat content, and linear growth. Given alone, ICI 182,780 had no effect on these measures. When they were given concurrently, ICI 182,780 attenuated the effects of estradiol on body weight, growth, and fat content but not on food intake. Treatment with ICI 182,780 significantly diminished estrous behavior induced with either EB plus progesterone or with EB alone. These findings support the hypothesis that, in addition to its actions in the brain, estradiol acts peripherally to modulate estrous behavior and energy balance.

The timed infusion paradigm for melatonin delivery: what has it taught us about the melatonin signal, its reception, and the photoperiodic control of seasonal responses?

This review summarizes the evidence showing that the duration of the nocturnal secretory profile of pineal melatonin (MEL) is critical for eliciting seasonally appropriate reproductive physiological and behavioral responses in mammals. We review experiments using the timed infusion paradigm (TIP) to deliver MEL either systemically or centrally to pinealectomized hamsters and sheep. In this paradigm, MEL is infused, usually once daily, for a specific number of hours and at a predetermined time of day. This experimental strategy tests most directly those features of the MEL signal that are necessary to trigger photoperiodic responses. The data suggest that the duration of the MEL stimulation is the critical feature of the MEL signal for both inhibitory and stimulatory effects of the hormone on the photoperiodic control of reproductive development in juvenile Siberian hamsters, and for the photoperiodic control of reproductive and metabolic responses in adult Siberian and Syrian hamsters and sheep. The use of the TIP reveals the importance of the frequency of the signal presentation of MEL and suggests the importance of a period of low-to-absent circulating concentrations of the hormone. The TIP also reveals that the characteristics of the MEL signal that regulate male sexual behavior are similar to those that are critical for reproductive and metabolic responses in Syrian hamsters. We summarize the locations of possible functional MEL target sites identified by combining the TIP with traditional brain lesion techniques. Evidence from such studies suggests that the integrity of the suprachiasmatic nucleus (SCN) region in Siberian hamsters and the anterior hypothalamus in Syrian hamsters is necessary for the response to short-day MEL signals. The TIP has been used to deliver MEL to putative target sites for the hormone in the brain of juvenile and adult Siberian hamsters. The results of these preliminary experiments suggest that the regions of specific MEL binding in this species, especially the SCN, are effective sites where MEL may stimulate short-day-type responses. In contrast, results from intracranial application of MEL in sheep suggest the medial basal hypothalamus as a critical site of action. Finally, we also discuss potential applications of the TIP for identification of brain MEL target sites, understanding of other photoperiodic phenomena and responses, and resolution of the cellular/molecular basis underlying the reception and interpretation of MEL signals.(ABSTRACT TRUNCATED AT 400 WORDS)

Tamoxifen antagonizes the effects of estradiol on energy balance and estrous behavior in Syrian hamsters.

Ovariectomized Syrian hamsters were treated with estradiol benzoate (5 micrograms/day for 4 wk), tamoxifen (500 micrograms/day), an antiestrogen that competes with estradiol for central and peripheral estrogen receptors, or both estradiol benzoate and tamoxifen. As expected, estradiol treatment caused significant decreases in body weight and fat content without affecting food intake. Given alone, tamoxifen had no effect on body weight or composition, but when given concurrently, tamoxifen significantly attenuated the effects of estradiol. These results stand in contrast to findings in rats where nonsteroidal antiestrogens, including tamoxifen, mimic the effects of estradiol on body weight and energy metabolism and are completely devoid of any antiestrogenic actions. As in rats, tamoxifen was a potent inhibitor of estrous behavior, whether induced with estradiol alone or with sequential treatment with estradiol and progesterone. Again, as in rats, tamoxifen acted as an antagonist and a weak estrogen agonist on uterine weight. These findings support the notion that the relative agonistic and antagonistic actions of tamoxifen, and other antiestrogens, vary with species and with the estrogen-sensitive endpoint being investigated.

Photoperiodic and pineal influences on estrogen-stimulated behaviors in female Syrian hamsters.

Three experiments investigated the effects of short photoperiod exposure on the estrogenic facilitation of locomotor activity and lordosis. In Experiment 1, ovariectomized female hamsters were administered exogenous estrogen to stimulate locomotor activity in running wheels. Estrogen was effective in the long photoperiod group but did not stimulate running-wheel activity in the short photoperiod group. In Experiment 2, the role of the pineal gland in mediating photoperiodic influences on female hamster behavior was examined. Both estrogen-induced locomotor activity and estrogen+progesterone-stimulated lordosis behavior were significantly reduced in short photoperiod females. Both these photoperiodic effects were absent in pinealectomized hamsters. Sham-pinealectomized, short photoperiod females expressed behavioral deficits; pinealectomized hamsters in the short photoperiod did not. Experiment 3 investigated lordosis only and used hormone injections rather than silastic implants to administer estrogen. The photoperiodic and pineal effects observed in Experiment 2 were replicated in Experiment 3. Additionally, the suppression of lordosis responsiveness by short photoperiod exposure was estrogen dose dependent. Photoperiodic effects were present when 2 micrograms estradiol cypionate was used but absent when higher estrogen doses were used. These findings are discussed in the context of other results that suggested photoperiodic effects on hamster lordosis were pineal independent.

The effect of signal frequency on the gonadal response of male Syrian hamsters to programmed melatonin infusions.

The aim of this study was to investigate which characteristics of the nocturnal melatonin signal, in addition to its duration, convey photoperiodic information to the reproductive axis. To achieve control over the pattern of circulating melatonin, male Syrian hamsters held under stimulatory long daylengths (16h light:8h dark) were pinealectomized to remove the principal source of circulating endogenous hormone and then fitted with chronic subcutaneous cannulae through which programmed infusions of melatonin solution or vehicle could be delivered. Experiment 1 tested whether long intervals between successive melatonin signals impaired the photoperiodic response. Animals which received a short day-like melatonin infusion of 10 h duration once every 24 h (T = 24) for 6 weeks underwent gonadal atrophy. When the same number of signals (42) was delivered at a frequency of once every 32 h (T = 32), they were ineffective and animals remained gonadally active. Two infusion patterns were used to determine if the loss of response to 10 h signals given at T = 32 h was a consequence of the frequency per se or the long interval between signals (22 h). In the first, a 'chimaeric' signal which combined a long duration i.e. short day-like 18 h melatonin signal with a short day-like melatonin-free interval of 14 h (combined signal T = 32 h) was able to induce significant, but only partial, gonadal atrophy. Second, when the 22-h interval between 10-h melatonin signals was interrupted by a short (2 h) melatonin pulse, significant but partial gonadal regression again occurred. Moreover, the response depended upon the timing of the 2 h pulse. When this fell early in the melatonin-free interval, leaving a large portion of it intact, it had no effect on gonadal condition. In contrast, a pulse delivered in the middle of the interval, which divided it up into two short day-like segments of 10 h each, was partially effective in restoring a short day response. The second experiment tested whether melatonin signals delivered at a high frequency would induce a photoperiodic response. A 10 h infusion delivered once every 24 h caused gonadal atrophy. The same melatonin infusion delivered at a periodicity of 20 h (T = 20) was also very potent as a short day stimulus. However, when 10-h signals were delivered at the higher frequencies of once every 18 or 16 h, they were less effective. Only a minority of animals exhibited gonadal atrophy and overall the group means were not significantly different from those of saline-infused controls, but were significantly greater than those of the 24 and 20 h groups. These data demonstrate that the photoperiodic response to the melatonin signal is sensitive to the frequency at which the signal is received. However, there is no evidence for a circadian basis to this sensitivity, nor a dependence upon the relationship between the endocrine stimulus and the light-dark cycle, insofar as signals encountered at a non-circadian period of 20 h are very effective. Moreover, the effectiveness of signals encountered at longer periodicities can be modified by manipulation of the uninterrupted duration of the interval free of melatonin, demonstrating a role in photoperiodic time measurement for the duration of the interval between signals.

Influence of daylength on male hamster sexual behavior: masking effects of testosterone.

Exposure of male hamsters to short photoperiods for 6-8 weeks cause deficits in sexual behavior with receptive females. The present experiment tested the hypothesis that short photoperiodic effects on behavior could be masked in the presence of chronic and stable levels of testosterone. Males were castrated and administered Silastic capsules of testosterone while housed in long (16L:8D) or short (8L:16D) photoperiodic conditions for 7 weeks. Sexual behavior tests at this time indicated that the short photoperiod males copulated less well, but group differences were not robust. Testosterone capsules were then removed and half the animals in both 16L:8D and 8L:16D were transferred to the opposite photoperiod. Sexual behavior was tested 18 days later as the effects of this functional castration developed. These tests indicate that photoperiodic effects were much more obvious in the absence of testosterone than they were during week 7 tests when testosterone was still present. The behavior of the males that were transferred from one photoperiod to the other demonstrated that exposure to the short photoperiod for only 18 days was not sufficient to generate short photoperiod-like sexual behavior deficits. In contrast, exposure to the long photoperiod for 18 days was sufficient to reverse short photoperiodic effects that had already developed.

Brain aromatization of testosterone in the male Syrian hamster: effects of androgen and photoperiod.

Estrogen formed by aromatization of testosterone (T) is involved in the activation of sexual behavior and control of the neuroendocrine system in the male Syrian hamster. Our study examined whether daylength influences formation of estrogen in the preoptic area (POA) and other neuroendocrine areas (anterior hypothalamus, AHT, and medial amygdala, MA) which are targets for T in behaviorally active males. Estrogen formation in individual brain samples was assayed in vitro using the stereospecific production of 3H2O from (1 beta-3H) T as a measurement of aromatase activity. Serum levels of PRL, LH, FSH and T were compared with brain aromatase activity. Groups of intact, castrated and T-treated (chronic silastic T implants) male hamsters, previously selected on behavioral criteria as being sexually active, were maintained on long (16:8LD) or short (8:16LD) daylength for 16 weeks. Two further groups of males either intact or castrated and T-treated were shifted after 7 weeks from the long photoperiod to 12:12LD. POA, AHT and MA areas of sexually active males contained active aromatase systems which converted 3H-T to estrogens. Enzyme activity differed between the areas (POA, MA greater than AHT). Aromatase activity was low in medial septum and cerebral samples. Castration, which reduced serum T to undetectable levels and elevated LH and FSH, had no effect on preoptic aromatase activity. Although estrogen formation in POA did not differ between 8:16LD and 16:8LD males, castration reduced aromatase activity in AHT of both short- and long-day groups. Aromatase activity in AHT was also significantly reduced in photo-inhibited 12:12LD intact males. There was no analogous decrease in 5 alpha-reductase or 17 beta-hydroxysteroid dehydrogenase (HSD) activity, indicating a specific effect on the aromatase. The effect of photoperiod on aromatase activity was not reversed by T treatment. Therefore, photoinhibition acts in part through the effects of reduced T levels on the anterior hypothalamus, but it also acts independently of circulating T. Our results suggest that both androgen and photoperiod may regulate the AHT aromatase system and that this occurs by different mechanisms. The more active aromatase system in POA is insensitive to both castration and photoperiod. Behavioral deficits in short-day males are not due to changes in the preoptic aromatase system, but may be related to changes in aromatase activity within AHT. We conclude that there is a difference in the regulation of two locally active aromatase systems within the preoptic-anterior hypothalamic complex of the male hamster.

Melatonin and the coding of day length in male Syrian hamsters.

Two experiments investigated the response of the pituitary-gonadal axis of pinealectomized male Syrian hamsters to programmed systemic administration of melatonin. In the first experiment, castrated male Syrian hamsters were housed in a short photoperiod (8L:16D) and maintained on subcutaneous testosterone implants for 7 weeks. These males were then pinealectomized or sham-pinealectomized and their testosterone capsules removed. Daily infusions of melatonin 250 ng/infusion) or its vehicle were administered for 3 weeks; infusion duration was long (11 or 12 hr) or short (6 hr). Measurement of serum luteinizing hormone (LH) following this 3-week period indicated that long-duration melatonin infusions mimicked short-day conditions (LH levels were low), but short-duration infusions did not (LH levels were significantly elevated). In the second experiment, pinealectomized, gonadally intact males were housed in a 12L:12D photoperiod and injected once daily with melatonin or its vehicle, either 3 or 5 hr after dark onset for 11 weeks. These times were chosen to coincide with the light:dark cycle phase that according to published reports is optimally responsive to exogenous melatonin for the induction of short-photoperiodic effects. Melatonin injections did not induce gonadal regression in pinealectomized hamsters. Melatonin and vehicle-treated males responded similarly; their testis widths and serum testosterone levels were not significantly different at the end of the experiment. These results support the hypothesis that the duration of melatonin secretion each night is an important variable in conveying photoperiodic information, but that the circadian phase during which melatonin is present is not.

Occlusion of the melatonin-free interval blocks the short day gonadal response of the male Syrian hamster to programmed melatonin infusions of necessary duration and amplitude.

Abstract Photoperiodic control of the neuroendocrine axis is mediated by changes in the duration of the nocturnal melatonin signal. This study tested the hypothesis that reading of the signal depends upon the presence of a period free of melatonin between successive signals. Adult male Syrian hamsters were pinealectomized and received chronic subcutaneous infusions of melatonin or saline for 6 weeks. Animals which received saline had large testes. Those which received a single daily infusion which lasted for 10 h (50 ng/h) followed by 14 h without infusion underwent gonadal atrophy. Other animals received a compound melatonin signal in which the melatonin-free interval was occluded by a continuous infusion (25 ng/h). Superimposed upon this was a 10 h phasic increase in infusion rate such that the maximum rate of infusion was equivalent to that observed in controls (25 ng/h increase, 50 ng/h peak rate), or the increase in rate over the baseline was the same as in controls (50 ng/h increase, 75 ng/h peak rate). In neither group did the animals undergo gonadal regression. Analysis of iodomelatonin binding sites by in vitro autoradiography failed to reveal any systematic difference between animals which did and did not respond to melatonin and so the absence of a response could not be attributed to loss of receptors. These data demonstrate that the photoperiodic system cannot identify the melatonin signal solely upon the features of nocturnal peak height or amplitude of the peak over baseline. They are consistent with the hypothesis that the melatonin-free interval plays a significant role in photoperiodic time measurement.

Pinealectomy prevents short photoperiod inhibition of male hamster sexual behavior.

The role of the pineal gland in mediating photoperiodic influences on copulatory behavior (CB) of male hamsters (Mesocricetus auratus) was assessed in the presence and absence of testosterone (T). The results demonstrate that the pineal gland is necessary for short photoperiod exposure to alter CB. Sexually experienced males were exposed to either long (14L:10D; LP) or short (8L:16D; SP) photoperiods for 13 weeks; after the first 2 weeks of exposure, all animals were castrated and then either pinealectomized (PINX) or sham operated (SHAM PINX). CB tests over an 8-week period following surgery indicated that copulatory impairments developed in all animals, but deficits occurred more rapidly among short photoperiod males with intact pineal glands (SP-SHAM PINX), compared to pinealectomized males housed in either the long (LP-PINX) or short photoperiod (SP-PINX). LP-PINX and SP-PINX animals were not statistically different on any of the CB measures examined. Nine weeks after castration (11 weeks of photoperiod exposure), all hamsters were given a T-filled Silastic capsule to restore CB. Restoration of sexual behavior was less rapid and less complete among SP-SHAM PINX hamsters. Additionally, males in this group took longer to initiate copulation relative to the pinealectomized hamsters. These findings are compared to other reports suggesting that photoperiodic effects on the sexual behavior of female hamsters do not require an intact pineal gland.

Photoperiod history, melatonin, and reproductive responses of male Syrian hamsters.

The action of melatonin (MEL) in mediating photoperiodic history (PPH) effects among male Syrian hamsters was investigated. In Exp. 1, pineal intact males in LD 14:10 received daily injections of MEL (15 micrograms) or ethanol:saline vehicle (SAL) 1 h before lights off for 8 wk to generate two groups experiencing identical photoperiods but distinctly different MEL histories. Following the cessation of injections, males were transferred to either LD 12:12 or LD 8:16 for 8 wk to evaluate whether their reproductive response to the new photoperiod would be more influenced by prior PPH or prior MEL history; MEL history was the significant variable. LD 12:12 caused gradual recrudescence in hamsters that were gonadally regressed following MEL injections. In contrast, LD 12:12 caused gonadal regression in hamsters that had large testes following SAL injections. Exp. 2 evaluated whether PPH influences might be mediated by aftereffects on the period (tau) of the circadian pacemaker regulating many behavioral and physiological rhythms. Pineal intact hamsters were exposed to long or short T cycles consisting of an 8 h photoperiod, repeated every 24.67 h (long T) or 23.33 h (short T) to mimic the aftereffects generated by short or long photoperiods. After 5 wk in these T-cycle conditions, all males were transferred to LD 12:12 for 11 wk. The reproductive response to LD 12:12 was modestly influenced by T-cycle history, even though each T-cycle generated different patterns of entrainment to LD 12:12. These findings support the hypothesis that the response of the reproductive system of male hamsters to an intermediate-duration photoperiod depends upon the duration of nocturnal melatonin secretion associated with hamsters' previous PPH.

Short photoperiods affect male hamster sociosexual behaviors in the presence and absence of testosterone.

Male hamsters were exposed to long (LD 14:10) or short (LD 8:16) photoperiods (LP; SP) to evaluate the effects of these environmental conditions on sociosexual behaviors. In Experiment 1, gonadally intact males in SP exhibited deficits in sexual behavior, reflected both in performance as well as initiation measures. Some aspects of the males' chemoinvestigation of females or their odors were also significantly different between LP and SP hamsters. In Experiment 2, castration resulted in the development of copulatory impairments, but they occurred more rapidly among males in SP conditions. Subsequent testosterone (T) replacement restored mounts, intromissions and ejaculations on tests given 2 and 4 weeks after T, but this happened more quickly in the LP group. SP males were still slower than LP males to initiate mounts and intromissions on their second test. These influences of photoperiod are discussed in the context of steroid-independent and steroid-dependent effects on behavior and the role of impaired processing of chemosensory information is evaluated.