The effect of α- and β-adrenergic blockade on daily rhythms of body temperature, urine production, and urinary 6-sulfatoxymelatonin of social voles Microtus socialis (original) (raw)
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Life Sciences, 1997
a-adrenergic stimulation induces melatonin synthesis and non-shivering thermogenesis (NST) in rodents. The golden spiny mouse, Acomys rzcssatus is a nocturnal species capable of diurnal activity when coexisting with its congenitor the common spiny mouse A. cahirinus. We have investigated the impact of oadrenergic blockade on 6-sulphatoxymelatonin (6-SMT-a metabolite and index of melatonin production) and body temperature (Tb) daily rhythms in male A. russatus. Mice were acclimated to an ambient temperature (T,) of 28"C, under two photoperiod regimes (16L:8D; 8L:16D). The daily rhythms of Tb and urinary 6-SMT were measured for a period of 30 h at intervals of 4 h. Propranolol (4.5 mg/kg, i.p.) was administered one hour before lights went off (i.e. when p blockade does not affect NST in this species) and both variables were measured for another 30 h. The 0 blocker markedly augmented melatonin output of A. russatus under both photoperiod regimes. The elevation in melatonin secretion was accompanied with an increase in Tb of only 16L:8Dacclimated mice (i.e. shorten duration of melatonin peak). However, in 8L: 16Dacclimated mice, a phase advance of about 4 h was noted in 6-SMT daily rhythm. These results indicate that the role of sympathetic innervation in regulation of melatonin synthesis in A. rzrssatus differs from that in the rat. In addition, these data are compatible with the hyperthermic action of melatonin in this species. Therefore, it is suggested that in A. russatus, other neural pathways are involved in its pineal regulation.
Chronobiology International, 2007
In mammals, nocturnal light pulses (NLP) have been demonstrated to affect physiology and behavior. However, the impact of NLP as a stressor has been less broadly examined. The purpose of this study was to examine the effect of NLP (three 15 min 450 lux light pulses) during each scotophase on both thermoregulation and endocrine stress responses under short-day (SD; 8L:16D) acclimation. Voles were acclimated to either SD (SD voles) or SD þ NLP (NLP voles). Resistance to cold was estimated by measurements of body temperature (T b) during cold exposure (58C). Daily rhythms of energy expenditure (calculated from oxygen consumption), urine production, and urinary adrenaline and serum cortisol levels were measured. T b values of SD voles were generally unaffected by the cold stimulus, whereas in NLP voles, resistance to cold was markedly lowered. While SD-and NLP voles showed similar ultradian characteristics in energy expenditure with a period of 3.5 h, mean energy expenditure levels were lowest for voles exposed to NLP-treatment. In SD voles, but not in NLP voles, urine production rates showed clear time variations and were consistently highest for SD voles, with significant differences during the scotophase. Both mean total urinary adrenaline and serum cortisol levels were significantly elevated in NLP-treated voles compared with the control group. Taken together, the results suggest that NLP negatively affects winter acclimatization of thermoregulatory mechanisms of M. socialis, probably by mimicking summer acclimatization, and consequently the thermoregulatory mechanisms respond inappropriately to ambient conditions. One important finding of this study is that NLP may act as a stressor and
General and Comparative Endocrinology, 2012
The annual cycle of changing day length (photoperiod) is widely used by animals to synchronise their biology to environmental seasonality. In mammals, melatonin is the key hormonal relay for the photoperiodic message, governing thyroid-stimulating hormone (TSH) production in the pars tuberalis (PT) of the pituitary stalk. TSH acts on neighbouring hypothalamic cells known as tanycytes, which in turn control hypothalamic function through effects on thyroid hormone (TH) signalling, mediated by changes in expression of the type II and III deiodinases (Dio2 and Dio3, respectively). Among seasonally breeding rodents, voles of the genus Microtus are notable for a high degree of sensitivity to nutritional and social cues, which act in concert with photoperiod to control reproductive status. In the present study, we investigated whether the TSH/Dio2/Dio3 signalling pathway of female common voles (Microtus arvalis) shows a similar degree of photoperiodic sensitivity to that described in other seasonal mammal species. Additionally, we sought to determine whether the plant metabolite 6-methoxy-2-benzoxazolinone (6-MBOA), described previously as promoting reproductive activation in voles, had any influence on the TSH/Dio2/Dio3 system. Our data demonstrate a high degree of photoperiodic sensitivity in this species, with no observable effects of 6-MBOA on upstream pituitary/hypothalamic gene expression. Further studies are required to characterise how photoperiodic and nutritional signals interact to modulate hypothalamic TH signalling pathways in mammals.
Age, Photoperiodic Responses, and Pineal Function in Meadow Voles, Microtus pennsylvanicus
Journal of Pineal Research, 1989
We tested whether juvenile males of Microtus pennsylvanicus were more sensitive than adults to the suppressive effects of short photoperiods. Voles were transferred to short photoperiods (10L:14D) at 20 or 80 d of age, and 60 d later (i.e., at 80 or 140 d) the animals were killed at intervals throughout the day and night. Pineal glands were collected for measurement of melatonin, and the testes were weighed. There were no dlfferences in paired testicular weights of 80 and 140 d old animals held on long days (median testicular weights: 1,953 and 1,843 mg). In contrast, median testicular weights of voles held on short days were 504 and 1,112 mg, respectively, at 80 and 140 d of age; the testicular weights of both groups were significantly different from their age-matched controls (P < ,001, two-sample t-tests on log transformed data). The responses of the two age groups were compared by normalizing the individual values by the mean and variance of the respective long-day controls. This comparison suggests that the responsiveness to photoperiod decreases as the animals age (t-test, P = .0l). Duration and amplitude of the nocturnal rise in pineal melatonin content were similar in differently aged animals. In two experiments, voles were injected daily with melatonin from 20 to 80 or 80 to 140 d of age. Melatonin-injected animals had smaller testes than did saline-injected controls (ANOVA: P = .OI), and injections were more effective in the afternoon than in the morning (P = .Ol). Comparison of the effectiveness of short day and melatonin injections in juvenile and adult voles suggests that while short days inhibited testicular development of young animals more than it induced regression of adults, this decrease in responsiveness may involve factors other than alterations in the nocturnal pattern of melatonin production.
Physiology & behavior, 1998
Body temperature (Tb) daily rhythms and the effects of alpha and beta blockade were studied in the South African diurnal striped mouse Rhabdomys pumilio. Eleven mice (8 males and 3 females) with a body mass of 42.7+/-7.8 g (mean +/- SD) were tested. Mice were acclimated to a 13 h:11 h light-dark photoperiod at an ambient temperature of 25 degrees C. To assess the daily rhythm of pineal melatonin secretion, urinary 6-sulfatoxymelatonin (6-SMT) was determined. Mice displayed a robust Tb daily rhythm with an acrophase in the dark period, which is unexpected for a diurnal species. The nocturnal increase in Tb was accompanied by a significant rise in urinary 6-SMT. The beta blocker propranolol (4.5 mg/kg), injected 1 h before lights-off, resulted in a higher Tb value, whereas the alpha blocker prazosin (1 mg/kg) blocked the increase of Tb during the dark period. Prazosin also significantly attenuated the nocturnal increase of urinary 6-SMT. These results are in agreement with those obtai...
Physiology & Behavior, 2007
For meadow voles, Microtus pennsylvanicus, seasonal differences exist in self-grooming and in odor preferences for conspecifics, two behaviors which facilitate sexual interactions in this species. Both behaviors are mediated by photoperiodically-induced changes in circulating gonadal steroid hormone titers which, in turn, can be transduced by the duration of the melatonin signal that a seasonally breeding animal receives. The goal of this study was to determine whether exogenous melatonin administration affects circulating gonadal steroid hormone titers in meadow voles, and whether it influences their odor preferences and self-grooming behavior to same-and opposite-sex conspecifics. Long-photoperiod voles that did not receive exogenous melatonin had higher testosterone (males) and estradiol (females) titers than did short-photoperiod voles and long-photoperiod voles treated with melatonin for 12 weeks; the latter had similar estradiol and testosterone titers. Long-photoperiod voles that did not receive melatonin preferred the scent marks of long-photoperiod opposite-sex conspecifics and spent more time self-grooming in response to their odors than those of either longphotoperiod same-sex, short photoperiod same-sex, or short-photoperiod opposite-sex conspecifics. Long-photoperiod voles that received melatonin, however, no longer preferred the marks of longphotoperiod opposite-sex conspecifics and no longer spent more time self-grooming in response to their odors, not unlike the odor preferences and self-grooming behavior of short-photoperiod voles. As a whole, the data suggest that the duration of the melatonin signal is likely involved in mediating the photoperiodically-induced changes in gonadal steroid hormones that mediate a meadow vole's odor preferences for opposite-sex conspecifics and its self-grooming response to those marks.
- Measurements of VO 2 and T b daily rhythms in T. nigricauda were conducted. (2) Three different effects on VO 2 and T b were assessed: alpha and beta blockade, time of the day, and photoperiod regime. (3) Results show that in T. nigricauda, the response of T b and VO 2 differs significantly under the different photoperiod regimes. Rats acclimated to 16L:8D increased T b values as a response to beta blockade, while alpha blockade caused a decrease in T b . (4) VO 2 values of T. nigricauda acclimated to 11.5L:12.5D responded differently to alpha and beta blockade. It can be assumed that the thermoregulatory responses with beta blockade are through a decrease in heat production, rather than through heat dissipation. However, in the case of alpha blockade, it may be assumed that heat dissipation, through vasodilation, is the cause for the decrease in T b values. #
Journal of Experimental Biology, 2003
We examined the effect of increasing photoperiod, at a constant low temperature, on the body mass and energy budget of the bank vole Clethrionomys glareolus. Simultaneously, we determined the hypothalamic gene expression of neuropeptides and receptors known to be involved in short-term energy balance. Despite an increase in body mass (approximately 10% of initial mass), we found no significant changes in any energetic parameters (food intake, energy assimilation rate, resting metabolic rate and total daily energy expenditure by doubly-labelled water). Apparent energy assimilation efficiency was higher in voles exposed to long-days (LD) compared to short-days (SD). Surprisingly, gene expression of corticotrophin releasing factor (CRF; in the paraventricular nucleus), and the melanocortin-3 receptor (in the arcuate nucleus), both known to be involved in appetite suppression and elevation of energy expenditure in short-term energy balance, were higher in voles kept in LD compared to SD. CRF expression was also elevated in females compared to males. These paradoxical data suggest an alternative mechanism for the control of seasonal body mass changes compared to short-term body mass changes, and between male and female voles. Furthermore, they highlight the need for studies to perform simultaneous measurements at both the molecular and whole animal levels.