RESUMEN
It has been suggested that epidermal growth factors (EGF) are responsible for the inhibition of locomotion by light (i.e., masking) in nocturnal rodents (Kramer et al., 2001). The poor masking response of waved-2 (Egfr(wa2)) mutant mice, with reduced EGF receptor activity, was adduced in support of this idea. In the present work, we studied the responses to light over a large range in illumination levels, in a variety of tests, with pulses of light and with ultradian light-dark cycles in Egfr(wa2) mutant mice. No evidence suggested that normal functioning of epidermal growth factor receptors was required, or even involved, in masking.
Asunto(s)
Receptores ErbB/genética , Actividad Motora/fisiología , Animales , Ritmo Circadiano/genética , Cartilla de ADN , Iluminación , Ratones , Ratones Mutantes , Reacción en Cadena de la PolimerasaRESUMEN
Light influences mammalian circadian rhythms in two different ways: (1) It entrains endogenous oscillators (clocks), which regulate physiology and behavior; and (2) it affects directly and often immediately physiology and behavior (these effects are also referred to as masking). Masking effects of light on pineal melatonin, locomotor activity, and the sleep-wake cycle in mammals and man are reviewed. They seem to represent a universal response in this group. The review reveals that the mechanism of photic inhibition of melatonin is fairly well understood, whereas only little is known about the influence of light on other circadian rhythm outputs, such as locomotor activity.
Asunto(s)
Ritmo Circadiano/fisiología , Ritmo Circadiano/efectos de la radiación , Fenómenos Fisiológicos del Sistema Nervioso , Animales , Fenómenos Cronobiológicos , Cuerpos Geniculados/fisiología , Cuerpos Geniculados/efectos de la radiación , Humanos , Luz , Melatonina/metabolismo , Actividad Motora/fisiología , Actividad Motora/efectos de la radiación , Células Fotorreceptoras de Vertebrados/fisiología , Células Fotorreceptoras de Vertebrados/efectos de la radiación , Glándula Pineal/metabolismo , Área Preóptica/fisiología , Área Preóptica/efectos de la radiación , Sueño/fisiología , Sueño/efectos de la radiación , Núcleo Supraquiasmático/fisiología , Corteza Visual/fisiología , Corteza Visual/efectos de la radiaciónRESUMEN
The inhibition of locomotion by light (masking) was investigated in Syrian hamsters. When 1-h pulses of light were presented in the early night, activity was strongly suppressed by irradiances of about 1 lx or greater. Ultradian light-dark cycles were used as another way to study masking. Hamsters were unable to entrain to 3.5:3.5-h light-dark cycles, thus permitting the masking and the entraining effects of light to be distinguished. Light had greater suppressive effects on activity in home cages than on activity in novel running wheels. Moreover, in home cages activity remained very low for about 30 min after lights were turned off. Post-pulse suppression of activity was not simply a consequence of reduced running, as shown by experiments in which running was temporarily prevented by locking the wheels. A phase response curve for masking was obtained by placing hamsters in novel wheels for 3-h periods at various times throughout their circadian cycles, and then superimposing a 30-min light pulse. The suppressive effect of light was maximal around the onset of activity, which normally coincides with dusk in hamsters. This may have adaptive value in limiting foraging to the hours of darkness.
Asunto(s)
Ritmo Circadiano/fisiología , Actividad Motora/fisiología , Ciclos de Actividad/fisiología , Animales , Cricetinae , Masculino , Mesocricetus , Estimulación LuminosaRESUMEN
Inhibition of wheel running by light (masking) was investigated in Syrian hamsters with suprachiasmatic nucleus or sham lesions. Approximately 90% of the wheel revolutions made by hamsters with complete suprachiasmatic nucleus lesions, as judged by histology and power spectrum analysis of their wheel running, occurred during the dark phases of an ultradian light-dark cycle (3.5 h light, 3.5 h dark). This was demonstrated for two illumination levels (380 lx and 6 lx). Similar results were obtained with sham-operated animals. In further tests, the hamsters with lesions also retained a strong preference for the dark side of a box divided into dark and light sides. These results demonstrate that the suprachiasmatic nucleus is not necessary for masking by light or the preference for a dark over a light compartment. Evidently the direct effects of light can substitute for the endogenous control by the suprachiasmatic nucleus to maintain appropriate behaviour in time and space.
Asunto(s)
Ritmo Circadiano/fisiología , Actividad Motora/fisiología , Núcleo Supraquiasmático/fisiología , Ciclos de Actividad/fisiología , Animales , Cricetinae , Masculino , Mesocricetus , Estimulación LuminosaRESUMEN
Syrian hamsters with intergeniculate leaflet or sham lesions were given tests with a series of light pulses of gradually decreasing intensities. The light pulses were given early in the night, at zeitgeber time 14-15. The amount of wheel running during the pulses was compared to that in the same hour on a night with no light pulses. Hamsters with intergeniculate leaflet lesions showed a significantly greater suppression of their wheel running in response to light than the sham-lesioned animals. The lesioned animals also had larger negative phase angles of entrainment to the 14:10-h light-dark cycle than sham-operated controls. However, phase shifting in response to light pulses at either zeitgeber time 14 or 18 was not significantly altered by the lesions. Preferences for spending more time in a dark than a light area were not abolished by the lesions. It is concluded that the intergeniculate leaflet in the Syrian hamster cannot be of paramount importance for masking of locomotor activity by light but may play a modulating role.
Asunto(s)
Ritmo Circadiano/fisiología , Cuerpos Geniculados/fisiología , Actividad Motora/fisiología , Ciclos de Actividad/fisiología , Animales , Cricetinae , Oscuridad , Inmunohistoquímica , Luz , Masculino , Mesocricetus , Estimulación LuminosaRESUMEN
Djungarian hamsters (Phodopus sungorus) from a long day photoperiod (16:8 h light-dark cycle) were either pinealectomized (PINX; n = 7) or sham-pinealectomized (SHAM; n = 6). One week after surgery coronal brain slices (500 microm), containing the suprachiasmatic nucleus (SCN), were prepared. The firing-rate rhythm of SCN neurons was recorded over at least a 22 h period. The amplitude of the firing rhythm for SHAM slices (3.42 +/- 0.26 Hz) was not significantly different from PINX slices (3.45 +/- 0.29 Hz). Maxima and minima of the firing rhythms also could not be distinguished statistically between PINX and SHAM groups. However, two-way ANOVA of 2 h firing-rate averages indicated a statistically significant effect of pinealectomy on the firing rhythm (P < 0.01). The results show that pinealectomy one week prior to brain slice preparation only had a minor effect on the in vitro neuronal firing rhythm in the SCN. In this study, SCN firing-rate rhythm in the Djungarian hamster is largely independent of endogenous melatonin secretion.
Asunto(s)
Glándula Pineal/fisiología , Núcleo Supraquiasmático/fisiología , Análisis de Varianza , Animales , Cricetinae , Electrofisiología , Técnicas In Vitro , Glándula Pineal/cirugíaRESUMEN
Phase shifts resulting from nonphotic events can be accompanied by sizable changes in the free-running period. This study examined the relationship between tau changes and phase shifts produced by confining Syrian hamsters to a novel running wheel in the mid-subjective day. Both phase shifting and tau lengthening were higher in animals that made a high number of wheel turns in the 3 h in the novel wheel. Hamsters that ran little during the activity pulse, and did not subsequently exhibit either phase shifts or tau lengthening, had low baseline activity and long taus before the pulse. However, long taus did not preclude hamsters from running in a novel wheel and subsequently phase shifting. This was demonstrated by finding the phase shifts after activity pulses in animals whose tau had already been lengthened by previous activity pulses in novel wheels. The possibility is discussed that feedback from locomotor activity influences the period of the clock in hamsters, but it is concluded that, in addition, there must be other mechanisms accounting for the relationships between activity and tau.
Asunto(s)
Ritmo Circadiano/fisiología , Locomoción/fisiología , Animales , Cricetinae , Retroalimentación/fisiología , MasculinoRESUMEN
A synopsis of the effects of exercise on the circadian system in nocturnal rodents is followed by a review of the few studies investigating the influence of exercise on the human circadian system. It is premature to make specific recommendations about using exercise to promote synchronization in people because of the lack of information on the best times of exercise, the amounts required, and interactions between nonphotic and photic zeitgebers.
Asunto(s)
Ritmo Circadiano , Ejercicio Físico , Animales , Oscuridad , Humanos , Luz , Melatonina/sangre , Melatonina/metabolismo , Actividad Motora , RoedoresRESUMEN
The aim of this study was to determine whether the circadian cycle of core temperature (Tc) and oxygen consumption (VO2) in juvenile rats is correlated with changes in the thermogenic activity of brown adipose tissue (BAT). Nine-day-old rat pups derived from two colonies with 12:12 h light-dark cycles 180 degrees out of phase were artificially reared in continuous light for 12-48 h while Tc and VO2 were recorded. For measurement of GDP binding half the pups from each colony were killed during the maximum phase of their circadian Tc cycle and the other half during the minimum phase. During the maximum phase (0.5-2 h after lights-off in the colony of origin), when Tc was 36.1 +/- 0.1 degrees C, GDP binding (pmol/mg protein) was 575 +/- 31 (n = 19). During the minimum phase (0.5-2 h after lights-on), when Tc was 32.9 +/- 0.5 degrees C, GDP binding was 361 +/- 47 (n = 19). Moreover, the correlations between Tc, VO2, and GDP binding determined during the maximum plateau of the circadian cycle differ substantially from those determined during the minimum phase. Consequently, developmental studies of thermoregulation and BAT activity in suckling pups are seriously compromised if circadian phase is neglected.
Asunto(s)
Tejido Adiposo Pardo/fisiología , Regulación de la Temperatura Corporal , Ritmo Circadiano , Tejido Adiposo Pardo/efectos de los fármacos , Tejido Adiposo Pardo/metabolismo , Animales , Temperatura Corporal/efectos de los fármacos , Guanosina Difosfato/metabolismo , Consumo de Oxígeno/efectos de los fármacos , Propranolol/farmacología , Ratas , Ratas Zucker , Maduración SexualRESUMEN
The importance of the sympathetic innervation in the regulation of 5'-deiodinase activity in the interscapular brown adipose tissue (BAT) of the Djungarian hamster was studied. Interscapular BAT of Djungarian hamsters was either unilaterally or bilaterally denervated, and thereafter the animals were maintained at thermoneutral temperature or exposed to 0 degree C for 24 h. Denervation reduced the norepinephrine content to 2-10% of the level in the control groups. Unilateral denervation was as effective as bilateral denervation in depressing the norepinephrine content of the interscapular BAT. Cold exposure for 24 h resulted in a pronounced 5'-deiodinase activation. Denervation reduced, but did not completely prevent, the cold-induced increase in 5'-deiodinase activity. The basal level of 5'-deiodinase activity at thermoneutral temperature was not reduced by denervation. We conclude that cold-induced activation of BAT 5'-deiodinase primarily depends on the intact sympathetic innervation.
Asunto(s)
Tejido Adiposo Pardo/enzimología , Yoduro Peroxidasa/metabolismo , Tejido Adiposo Pardo/inervación , Tejido Adiposo Pardo/metabolismo , Animales , Frío , Cricetinae , Desnervación , Activación Enzimática , Femenino , Masculino , Norepinefrina/metabolismo , Sistema Nervioso Simpático/fisiologíaRESUMEN
Young adult male and female Djungarian hamsters were exposed to ambient temperatures of 23 or 0 C for 12 h; half of the animals in each group were treated with iopanoic acid to suppress the peripheral conversion of T4 to the thermotropically active thyroid hormone T3 by the enzyme 5'-deiodinase (5'D). Brown adipose tissue (BAT) mRNA for uncoupling protein (UCP), BAT lipoprotein lipase (LPL) activity, and 5'D activity were measured at the conclusion of the study. A temperature of 0 C produced large rises in 5'D and LPL activities and a similar large increase in UCP mRNA within the 12-h exposure period. When 5'D activity was inhibited with iopanoic acid, mRNA for UCP was reduced, while LPL activity was unaffected. The results show that the optimal production of mRNA for BAT UCP depends on the availability of T3; however, T3 is not required for the cold-induced activation of LPL activity in BAT.