Papers by Stephan Steinlechner
Journal of neuroendocrinology, Jan 6, 2015
The timing of growth in seasonal mammals is inextricably linked to food availability. This is exe... more The timing of growth in seasonal mammals is inextricably linked to food availability. This is exemplified in the Siberian hamster (Phodopus sungorus) which uses the annual cycle of photoperiod to optimally programme energy expenditure in anticipation of seasonal fluctuations in food resources. During the autumn, energy expenditure is progressively minimized by physiological adaptations including a 30% reduction in body mass, comprising of a reduction in both fat and lean tissues. However, the mechanistic basis of this adaptation is still unexplained. We hypothesised that growth hormone (GH) was a likely candidate to underpin these reversible changes in body mass. Administration of pasireotide, a long acting somatostatin receptor agonist developed for the treatment of acromegaly, to male hamsters in long-day photoperiod (LD) produced a body weight loss. This comprised of a reduction in lean and fat mass, including kidneys, testes, and brown adipose tissue typically found in short-day...
Chronobiology International, 2008
Djungarian hamsters (Phodopus sungorus) exhibit pronounced winter acclimatization with changes in... more Djungarian hamsters (Phodopus sungorus) exhibit pronounced winter acclimatization with changes in body mass, gonads, fur, and thermogenic capacity induced by decreasing daylength. To determine whether the annual activity pattern reflects the crucial role of the photoperiod for the hamsters' seasonality, animals with and without access to a running wheel (RW) were exposed to natural lighting conditions (approximately 52 degrees N) and ambient temperatures. Registration of locomotion in hamsters with a RW revealed a clear activity pattern closely related to dusk and dawn throughout the year. In contrast, animals without RW access showed a less stable phase relationship between the activity and the day-night cycle in autumn and winter. During these seasons, the activity phase either exceeded the dark phase or even became indistinguishable from the rest phase. This correlated not only with increased locomotion during the light phase but also over the whole 24 h period, especially in autumn. In RW hamsters, a similar but attenuated trend was found that possibly reflects foraging due to increased food hoarding before winter. The more stable correlation between activity time and night length in RW hamsters might be explained by a suppressing effect of light on wheel-running behavior (negative masking) and/or a stabilizing effect of running exercise on rhythmicity. In a further experiment, the phase-reference points lights-off and lights-on within artificial light-dark (LD) cycles were compared to sunset and sunrise in an intermediate ratio of light and dark and in long days. With respect to the defined phase-reference points of the zeitgeber, the phase relation between activity and the LD cycle was similar in natural and corresponding artificial lighting conditions, and dependent on the LD ratio.
Naturwissenschaften, 2014
The secondary plant metabolite 6-methoxy-2benzoxazolinone (6-MBOA) is abundant in vegetative part... more The secondary plant metabolite 6-methoxy-2benzoxazolinone (6-MBOA) is abundant in vegetative parts of monocotyledons emerging in spring. This grazing protective has been shown to promote gonadal growth and, thus enable precise alignment of reproductive activity with favorable environmental conditions in a variety of seasonally breeding rodent species. Feeding and breeding ecology make the Djungarian hamster (Phodopus sungorus) a potential candidate using 6-MBOA as an acute environmental cue to optimize reproductive timing when photorefractoriness induces reproductive recrudescence. Therefore, four different experiments were designed to examine whether the hamsters' reproductive organs are responsive to oral 6-MBOA administration under different photoperiodic conditions. Only under a long photoperiod, we found a slight increase in uterine weights. In a short photoperiod, 6-MBOA-treated hamsters showed a slight body weight gain without a change in uterine weights. However, these marginal effects are likely not to be of ecophysiological significance for reproductive timing. The results are in agreement with the common view that the annual changes in photoperiod length are not only the predominant environmental cue for Djungarian hamsters, but are also sufficient to synchronize reproductive efforts with favorable breeding conditions in highly predictable climates like the continental Asian steppes.
Journal of Comparative Physiology B, 2008
Djungarian hamsters (Phodopus sungorus) were exposed to artiWcial short days either with access t... more Djungarian hamsters (Phodopus sungorus) were exposed to artiWcial short days either with access to a running wheel (RW) or without. Within 6 weeks RW hamsters considerably increased their body mass, whereas controls showed the typical body mass reduction. Estimation of paired testis weights indicated a decelerated testis regression in RW hamsters. Subsequent locking of RWs for 9 weeks led to a decline in body mass of RW animals in parallel to controls. Daily torpor was almost completely missing in hamsters with initially unlocked wheels. During the Wnal phase when RWs were again unlocked (3 weeks), body mass of exercising hamsters increased again, while controls reached the nadir in body mass. In comparison to equiponderate long-day (LD) controls the relative liver weight of RW hamsters was signiWcantly increased unlike the relative heart weight. However, the latter tended to be higher than in sedentary LD hamsters. A growth-stimulating eVect of wheel running was proven by elongated femora in exercising short-day (SD) hamsters compared to SD controls and suggested by exercise-induced elevation of body mass in a further experiment under continuous LD conditions, indicating a growth-promoting eVect of wheel running independent from the photoperiod.
Journal of Thermal Biology, 2015
In addition to morphological and physiological traits of short-day acclimatisation, Djungarian ha... more In addition to morphological and physiological traits of short-day acclimatisation, Djungarian hamsters (Phodopus sungorus) from Central Asia exhibit spontaneous daily torpor to decrease energy demands during winter. Environmental factors such as food scarcity and low temperatures have been shown to facilitate the use of this temporal reduction in metabolism and body temperature. We investigated the effect of a daily cycle in ambient temperature on short-day acclimation and torpor expression in juvenile and adult Djungarian hamsters. The animals were exposed to a cold dark phase (6°C) and a warmer light phase (18°C) and were compared with control hamsters kept at a constant ambient temperature of 18°C. Under constant conditions, torpor expression did not differ between adult and juvenile hamsters. Although the daily temperature cycle evoked an increased metabolic rate in adult and juvenile hamsters during the dark phase and strengthened the synchronization between torpor entrance and the beginning of the light phase, it did not induce the expected torpor facilitation. In adult hamsters, torpor expression profiles did not differ from those under constant conditions at all. In contrast, juvenile hamsters showed a delayed onset of torpor season, a decreased torpor frequency, depth and duration, as well as an increased number of early torpor terminations coinciding with the rise in ambient temperature after the beginning of the light phase. While the temperature challenge appeared to be of minor importance for energy balance and torpor expression in adult hamsters, it profoundly influenced the overall energy saving strategy of juvenile hamsters, promoting torpor-alleviating active foragers over torpor-prone energy-savers. In addition, our data suggest a more efficient acclimation in juvenile hamsters under additional energy challenges, which reduces the need for torpor expression.
The Journal of experimental biology, Jan 15, 2014
Essential polyunsaturated fatty acids (PUFA) have been shown to play a beneficial role in hiberna... more Essential polyunsaturated fatty acids (PUFA) have been shown to play a beneficial role in hibernating mammals. High amounts of dietary PUFA led to an earlier hibernation onset, deeper and longer hibernation bouts and a higher proportion of hibernating animals in several species. In contrast, the relevance of dietary PUFA for daily heterotherms exhibiting only brief and shallow torpor bouts is less well studied. Therefore, diets differing in PUFA composition were used to examine the effects on the frequency of spontaneous daily torpor in Djungarian hamsters (Phodopus sungorus). In contrast to earlier studies, we were interested in whether the ratio of n-6 to n-3 PUFA affects torpor expression, and in comparison with a diet rich in monounsaturated fatty acids (MUFA). Although we found a positive effect on torpor frequency in hamsters fed a diet rich in n-6 PUFA compared with the groups fed diets either rich in n-3 PUFA or MUFA, the latter two groups did not show unusually low torpor f...
The Journal of experimental zoology, 1993
We investigated the influence of ambient temperature (Ta) and food availability on seasonal timin... more We investigated the influence of ambient temperature (Ta) and food availability on seasonal timing and extent of physiological responses to short photoperiod (SP), in particular daily torpor, in Djungarian hamsters (Phodopus sungorus). Exposure of hamsters to cold temperature (Ta = 5 degrees C), relative to warm Ta (23 degrees C), resulted in: 1) a significant advance (P < 0.05) of the first occurrence of torpor among cold-exposed hamsters (days 52-97 vs. days 83-99 in SP); 2) a higher (P < 0.01) incidence of torpor (48% vs. 20% torpid animals/day); 3) a higher (P < 0.05) degree of molt into the winter pelt; and 4) an accelerated reduction of body weights (P < 0.001). However, within SP/cold-Ta exposed groups, individual hamsters clearly showed different tendencies for torpor (torpor on 0-95% of days observed). Therefore, we evaluated the effects of small changes in Ta on torpor frequency and extension by subjecting the same SP-adapted individuals to varying temperatures...
Journal of pineal research, 1984
The nighttime rise in pineal melatonin levels can be blocked by administration of the beta-adrene... more The nighttime rise in pineal melatonin levels can be blocked by administration of the beta-adrenergic receptor antagonist, propranolol, in both Syrian hamsters and rats. Although the administration of beta-adrenergic receptor agonists such as norepinephrine or isoproterenol stimulates pineal melatonin production in the rat, these drugs are without apparent effect on indole production in the Syrian hamster. To determine whether this lack of stimulatory effect in the Syrian hamster is characteristic of this species, a comparison of the effects of norepinephrine and isoproterenol on pineal serotonin N-acetyltransferase activity and melatonin content was conducted. In contrast to their lack of effect in the Syrian hamster, norepinephrine and isoproterenol stimulated pineal serotonin N-acetyltransferase activity and melatonin content in the Djungarian hamster. Hourly injection of norepinephrine during a continuation of light into the normal dark period stimulated increases in the activit...
PLoS ONE, 2014
The Siberian hamster (Phodopus sungorus) is a seasonal mammal responding to the annual cycle in p... more The Siberian hamster (Phodopus sungorus) is a seasonal mammal responding to the annual cycle in photoperiod with anticipatory physiological adaptations. This includes a reduction in food intake and body weight during the autumn in anticipation of seasonally reduced food availability. In the laboratory, short-day induction of body weight loss can be reversed or prevented by voluntary exercise undertaken when a running wheel is introduced into the home cage. The mechanism by which exercise prevents or reverses body weight reduction is unknown, but one hypothesis is a reversal of short-day photoperiod induced gene expression changes in the hypothalamus that underpin body weight regulation. Alternatively, we postulate an exercise-related anabolic effect involving the growth hormone axis. To test these hypotheses we established photoperiod-running wheel experiments of 8 to 16 weeks duration assessing body weight, food intake, organ mass, lean and fat mass by magnetic resonance, circulating hormones FGF21 and insulin and hypothalamic gene expression. In response to running wheel activity, short-day housed hamsters increased body weight. Compared to shortday housed sedentary hamsters the body weight increase was accompanied by higher food intake, maintenance of tissue mass of key organs such as the liver, maintenance of lean and fat mass and hormonal profiles indicative of long day housed hamsters but there was no overall reversal of hypothalamic gene expression regulated by photoperiod. Therefore the mechanism by which activity induces body weight gain is likely to act largely independently of photoperiod regulated gene expression in the hypothalamus. Citation: Petri I, Dumbell R, Scherbarth F, Steinlechner S, Barrett P (2014) Effect of Exercise on Photoperiod-Regulated Hypothalamic Gene Expression and Peripheral Hormones in the Seasonal Dwarf Hamster Phodopus sungorus. PLoS ONE 9(3): e90253.
Klinische Neurophysiologie, 2010
ABSTRACT Introduction: In response to short day (SD) lengths, Phodopus sungorus reduces body mass... more ABSTRACT Introduction: In response to short day (SD) lengths, Phodopus sungorus reduces body mass, size and activity of the gonads and changes into a whitish winter pelage. In previous studies we reported a reversal of the seasonal reduction in body mass and an impairment of seasonal gonadal regression in Phodopus with access to a running wheel (RW) in SDs. However, the seasonal change to a whitish winter fur was not affected by RW activity, suggesting that the SD signal can be read, but is overridden by a physiological response to RW activity. To understand how RW activity influences the occurrence of SD physiology, we examined its effect on physiological parameters and genes regulated by photoperiod that are important for the seasonal adaptation of Phodopus sungorus. Methods: Expt 1. The effect of photoperiod on the activity pattern of Phodopus with and without access to a RW was recorded by infrared motion detectors under natural photoperiod and ambient temperature. Expt 2. Hamsters were housed in artificial SD for 8 weeks with or without a RW. At the end of the experiment food intake was measured before the hamsters were killed. Liver glucose and lipids were determined by a colorimetric assay. VGF, DIO3 and SRIF mRNA levels in the dmpArc, ependymal layer of the third ventricle and ARC, respectively, were quantified by in situ hybridization. The effect of photoperiod and activity on growth hormone (GH) was determined by Northern blot analysis, carried out on RNA extracted from pituitary glands. Results: Expt 1. In exercising hamsters the annual activity pattern shows an entrained and well-defined rhythm throughout the year. However, hamsters without a RW show a tendency towards an indistinct rhythm during times of decreasing photoperiod in autumn and winter months. Expt 2. With access to a RW, the typical SD decrease in testes and body mass is attenuated and food intake is nearly doubled. SRIF gene expression is decreased and VGF gene expression is further increased by RW activity in SD, whereas DIO3 gene expression is not affected. Liver glucose levels are increased by RW activity and GH expression in the pituitary is increased in SD. Conclusions: The annual activity pattern and DIO3 gene expression of the RW hamsters demonstrates that the SD signal is perceived, but the hamsters show an altered physiological response. Expressions of VGF and SRIF are affected by RW activity. The latter may contribute to an increased release of GH to increase body mass, and an increase in GnRH might cause the delay of testes regression.
Birds are generally thought to have excellent vision with high spatial resolution. However, spati... more Birds are generally thought to have excellent vision with high spatial resolution. However, spatial contrast sensitivity of birds for stationary targets is low compared to other animals with similar acuity, such as mammals. For fast flying animals body stability and coordination are highly important, and visual motion cues are known to be relevant for flight control. We have tested five budgerigars (Melopsittacus undulatus) in behavioural discrimination experiments to determine whether or not stimulus motion improves contrast sensitivity. The birds were trained to distinguish between a homogenous grey field and sine-wave gratings of spatial frequencies between 0.48 and 6.5 cyc/deg, and Michelson contrasts between 0.7% and 99%. The gratings were either stationary or drifting with velocities between 0.9 and 13 deg/s. Budgerigars were able to discriminate patterns of lower contrast from grey when the gratings were drifting, and the improvement in sensitivity was strongest at lower spatial frequencies and higher drift velocities. Our findings indicate that motion cues can have positive effects on visual perception of birds. This is similar to earlier results on human vision. Contrast sensitivity, tested solely with stationary stimuli, underestimates the sensory capacity of budgerigars flying through their natural environments.
Science, 1981
discharge per unit width, 0 is the inclination of water surface, and v is mean runoff velocity. 1... more discharge per unit width, 0 is the inclination of water surface, and v is mean runoff velocity. 15. Spatially and temporally averaged runoff power per unit area is P = r0v = pgq(sin 9), where re is mean bed shear stress and p is fluid density. R.
Oecologia, 1981
In Phodopus sungorus spontaneous shallow daily torpor occurred only during winter. Frequency of t... more In Phodopus sungorus spontaneous shallow daily torpor occurred only during winter. Frequency of torpor was not affected by low ambient temperature but the seasonal cueing seems primarily dependent on photoperiodic control. Maximum torpor frequency was found in January with 30% of all hamsters living inside or outside being torpid at a time. It is calculated that torpor will reduce long term energy requirements of Phodopus by only 5%. Therefore it is concluded that torpor is not primarily aimed to reduce energy requirements but to guarantee survival of a fraction of a population during short periods of extreme cold load or inaccessability of food.
Neuroendocrinology, 1990
In the rat pineal gland, the activity of serotonin N-acetyltransferase (NAT) and the concentratio... more In the rat pineal gland, the activity of serotonin N-acetyltransferase (NAT) and the concentration of melatonin are normally high at night; conversely, the concentration of serotonin (5-HT), the precursor of melatonin, is low. Since tryptophan administration increases the concentration of pineal 5-HT at night, we examined its effect of melatonin production. Nighttime tryptophan loading led to substantial increases in pineal 5-hydroxytryptophan, 5-hydroxyindole acetic acid (5-HIAA), and 5-HT but a highly significant reduction in NAT activity in comparison to saline-injected controls. In contrast to other measured indoles, melatonin levels also were significantly diminished by tryptophan loading. Nocturnally high pineal norepinephrine levels were unaltered by tryptophan administration. The idea that high concentrations of 5-HT could lead to substrate inhibition of NAT activity was not supported by kinetic analysis of control NAT levels versus tryptophan-inhibited NAT activity under varied substrate concentrations. Hypotheses to explain these results include the possibility that tryptophan inhibition of melatonin synthesis is mediated by the release of 5-HT from the pinealocyte and its subsequent autocrine action on melatonin production.
Life Sciences, 1987
In an attempt to clarify further the role of the hypothalamic paraventricular nuclei (PVN) in the... more In an attempt to clarify further the role of the hypothalamic paraventricular nuclei (PVN) in the control of pineal function, the effects of 2 min electrical stimulation of these nuclei were investigated in acutely blinded, adult, male Sprague-Dawley rats. Pineal serotonin-N-acetyltransferase (NAT) activity, melatonin content and catecholamine levels were measured by means of radio-enzymatic, radioimmunoassay and high-performance liquid-chromatography methods, respectively. All three pineal parameters underwent significant declines following brief PVN stimulation during the night time. These observations lend credence to the view that the neural pathways transmitting light information to the sympathetic innervation controlling pineal melatonin synthesis.
Life Sciences, 1983
Wild-captured cotton rats (Sigmodon hispidus) trapped and tested in September and October exhibit... more Wild-captured cotton rats (Sigmodon hispidus) trapped and tested in September and October exhibited a rapid reduction in pineal N-acetyltransferase (NAT) activity and melatonin levels after exposure to a light irradiance of 300 microW/cm2 during the dark period. The half-time for the depression of both NAT and melatonin was on the order of 2 min. The exposure of cotton rats during darkness to much lower irradiances of light, i.e., 5.0, 0.04, 0.03 or 0.01 W/cm2, for 32 min also greatly diminished pineal NAT activity and radioimmunoassayable melatonin levels; however, a light irradiance of 0.005 microW/cm2 failed to significantly depress either the acetylating enzyme or the melatonin content of the pineal gland. The results show that the pineal gland of the wild-captured cotton rat, as judged by NAT activity and melatonin levels, is inhibited even by very low irradiances of light.
Life Sciences, 1983
Pineal melatonin levels were compared in laboratory-raised or wild-captured 13-lined ground squir... more Pineal melatonin levels were compared in laboratory-raised or wild-captured 13-lined ground squirrels (Spermophilus tridecemlineatus) that were either exposed to 10 h of darkness at night or to light which had an irradiance of 400 microW/cm2. In laboratory-born squirrels the period of darkness was associated with a gradual rise in pineal melatonin levels with peak values being reached at 0200 h, 6 h after darkness onset. Thereafter, melatonin levels decreased and were back to low daytime levels by 0800 h, 2 h after light onset. The exposure of laboratory-raised animals to an irradiance of 400 microW/cm2 during the night totally prevented the nocturnal rise in pineal melatonin levels in these animals. In wild-captured ground squirrels the period of darkness at night was associated with a rapid rise in pineal melatonin such that by 2200 h, 2 h after lights out, peak melatonin values were already attained; additionally, melatonin levels remained high throughout the period of darkness but returned to daytime values by 0800 h. Exposure of wild-captured squirrels to a light irradiance of 400 microW/cm2 during the normal dark period was completely incapable of suppressing pineal melatonin levels. The difference in the sensitivity of the pineal gland of laboratory-raised and wild-captured ground squirrels may relate to their previous lighting history.
Journal of Pineal Research, 1984
The purpose of the present studies using artificial light was to determine how the timing and dur... more The purpose of the present studies using artificial light was to determine how the timing and duration of exposure influence the light-induced suppression of pineal melatonin levels in hamsters. An 8;min exposure to 0.186 pWlcm2 of cool white fluorescent light caused a continued depression of pineal melatonin even when animals were returned to darkness. In addition, the pineal gland does not appear to change its sensitivity to light throughout the night. A 20-min exposure to 0.019 pW/cm* of cool white fluorescent light did not significantly suppress pineal melatonin during any time of the melatonin peak, whereas a 20-min exposure to 0.186 pWlcm2 was capable of always suppressing melatonin. Furthermore, increasing the duration of 0.019-pW/cm2 exposure to 30, 60, 120, or 180 min does not increase the capacity of this irradiance to depress melatonin. Similar to artifical light, natural light has a variable capacity for suppressing nocturnal levels of pineal melatonin. Twilight irradiances of 0.138 pW/cm2 or less did not suppress nocturnal melatonin whereas twilight irradiances of 3.0 pW/ cm2 or greater did suppress pineal melatonin. A few animals did have lower melatonin after a 40-min exposure to full moonlight during July (0.045 pW/cm2) or January (0.240 pW/cm2). However, pineal melatonin levels remained high in the majority of animals exposed to full moonlight.
Journal of Pineal Research, 1984
The nighttime rise in pineal melatonin levels can he blocked by administration of the 0-adrenergi... more The nighttime rise in pineal melatonin levels can he blocked by administration of the 0-adrenergic receptor antagonist, propranolol, in both Syrian hamsters and rats. Although the administration of P-adrenergic receptor agonists such as norepinephrine or isoproterenol stimulates pineal melatonin production in the rat, these drugs are without apparent effect on indole production in the Syrian hamster. To determine whether this lack of stimulatory effect in the Syrian hamster is characteristic of this species, a comparison of the effects of norepinephrine and isoproterenol o n pineal serotonin N-acetykransferase activity and melatonin content was conducted. In contrast to their lack of effect in the Syrian hamster, norepinephrine and isoproterenol stimulated pineal serotonin N-acetyltransferase activity and melatonin content in the Djungarian hamster. Hourly injection of norepinephrine during a continuation of light into the normal dark period stimulated increases in the activity of serotonin N-acetyltransferase and melatonin content in the Djungarian hamster but was without effect o n these pineal parameters in the Syrian hamster.
Journal of Pineal Research, 1996
Sulphatoxymelatonin secretion in different locomotor activity types of the blind mole rat Spalax ... more Sulphatoxymelatonin secretion in different locomotor activity types of the blind mole rat Spalax ehrenbergi.
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Papers by Stephan Steinlechner