Meal feeding schedule and ventromedial hypothalamic lesions do not affect rhythm of pineal serotonin N-acetyltransferase activity in rats

Effects of meal feeding schedule and bilateral lesions of the ventromedial hypothalamus (VMH) on the circadian rhythm of pineal serotonin N-acetyltransferase (SNAT) activity were examined in rats, under LD (12:12) condition. Neither meal feeding nor VMH lesions affected the phase of the circadian rhythm of pineal SNAT activity, but the VMH lesions reduced the level. Meal feeding caused a shift of the phases of the daily rhythms of phosphoenolpyruvate carboxykinase and tyrosine aminotransferase activities in the liver. These findings suggest that the circadian rhythm of pineal SNAT activity is not entrained by the food intake, and that the VMH does not function as a master oscillator of the rhythm.     

Melatonin and corticosterone regulation: Feeding time or the light:Dark cycle?

Under ad libitum feeding, male rats exhibit a marked rhythm of plasma and pineal melatonin; levels are low during the day and high at night. Restricting food availability to a 2 hour period during the light or dark does not markedly influence the melatonin rhythm, both groups having a crest in circulating melatonin during the dark. In contrast, plasma corticosterone levels are influenced by both the light-dark cycle and feeding. Animals fed early in the light period exhibit a biomodal corticosterone secretory pattern, with high steroid levels immediately prior to feeding and again just before lights-out, animals fed early in the dark have a single crest, just before food presentation. These data provide evidence for the dissociation of melatonin and corticosterone secretory patterns, providing support for the hypothesis that multiple regulators control neuroendocrine rhythmicity.     

Serum melatonin and pineal indoleamine metabolism in a species with a small day/night N-acetyltransferase rhythm

Ovine serum and pineal melatonin levels are low during the day, increase five to ten-fold at night, decrease during a light pulse at night, and rapidly increase to night levels following the light-dark transition. N-Acetyltransferase activity increases three-fold at night, falls significantly in response to the light pulse, but does not increase following the light pulse. No significant change in N-acetylserotonin occurs under these conditions. These results suggest that the biochemical mechanisms controlling pineal melatonin synthesis in the sheep pineal gland may be different from those in the rat.     

Food availability affects circadian clock-controlled activity and Zugunruhe in the night migratory male blackheaded bunting (Emberiza melanocephala)

This study investigated the functional linkage between food availability and activity behavior in the Palaearctic Indian night migratory blackheaded bunting (Emberiza melanocephala) subjected to artificial light-dark (LD) cycles. Two experiments were performed on photosensitive birds. In the first one, birds were exposed to short days (LD 10/14; Experiment 1A), long days (LD 13/11; Experiment 1B), or increasing daylengths (8 to 13?h light/d; Experiment 1C) and presented with food either for the whole or a restricted duration of the light period. In Experiments 1A and 1B, illumination of the light and dark periods or of the dark period, alone, was changed to assess the influence of the light environment on direct and circadian responses to food cycles. In the second experiment, birds were exposed to LD 12/12 or LD 8/16 with food availability overlapping with the light (light and food presence in phase) or dark period (light and food presence in antiphase). Also, birds were subjected to constant dim light (LL(dim)) to examine the phase of the activity rhythms under synchronizing influence of the food cycles. Similarly, the presentation of food ad libitum (free food; FF) during an experiment examined the effects of the food-restriction regimes on activity rhythms. A continuous measurement of the activity-rest pattern was done to examine both the circadian and direct effects of the food and LD cycles. Measurement of activity at night enabled assessment of the migratory phenotype, premigratory restlessness, or Zugunruhe. The results show that (i) light masked the food effects if they were present together; (ii) birds had a higher anticipatory activity and food intake during restricted feeding conditions; and (iii) food at night alone reduced both the duration and amount of Zugunruhe as compared to food during the day alone. This suggests that food affects both the daily activity and seasonal Zugunruhe, and food cycles act as a synchronizer of circadian rhythms in the absence of dominant natural environmental synchronizers, such as the light-dark cycle.     

Working for food shifts nocturnal mouse activity into the day

Nocturnal rodents show diurnal food anticipatory activity when food access is restricted to a few hours in daytime. Timed food access also results in reduced food intake, but the role of food intake in circadian organization per se has not been described. By simulating natural food shortage in mice that work for food we show that reduced food intake alone shifts the activity phase from the night into the day and eventually causes nocturnal torpor (natural hypothermia). Release into continuous darkness with ad libitum food, elicits immediate reversal of activity to the previous nocturnal phase, indicating that the classical circadian pacemaker maintained its phase to the light-dark cycle. This flexibility in behavioral timing would allow mice to exploit the diurnal temporal niche while minimizing energy expenditure under poor feeding conditions in nature. This study reveals an intimate link between metabolism and mammalian circadian organization.     

ROLE OF ADENOSINE 3'', 5''-MONOPHOSPHATE IN THE REGULATION OF CIRCADIAN OSCILLATION OF SEROTONIN N-ACETYLTRANSFERASE ACTIVITY IN CULTURED CHICKEN PINEAL GLAND

—When pineal glands of 10–12-day-old chicks were organ-cultured in darkness, serotonin N-acetyltransferase activity was low during the daytime, increased at midnight and then decreased to the daytime level the next morning. The pattern of increase and decrease of enzyme activity in cultured pineal glands was comparable to the circadian rhythm of N-acetyltransferase activity in vivo. When pineal glands were kept at a low temperature for 5 h prior to culture, the phase of autonomous rhythm of enzyme activity was delayed. When chicken pineal glands were cultured during the daytime for 6 h, derivatives of adenosine 3′, 5′-monophosphate (cyclic AMP), cholera toxin, a high concentration of KCl and phosphodiesterase inhibitors increased N-acetyltransferase activity 3–7-fold, indicating an involvement of cyclic AMP in the regulation of N-acetyltransferase activity in chicken pineal gland as has been shown in rat pineal gland. When pineal glands were cultured at night in darkness, cholera toxin or a high KCl did not enhance the night-time increase of the enzyme activity. Derivatives of cyclic AMP or phosphodiesterase inhibitors enhanced the autonomous night-time increase of N-acetyltransferase activity in an additive or more than additive manner in cultured pineal glands. These observations suggest that adenylate cyclase of pinealocytes is inactive during daytime, but is activated at night in darkness, which is transduced to the synthesis of N-acetyltransferase molecules. Catecholamines suppressed the basal level and the nocturnal increase of N-acetyltransferase activity via α-adrenergic receptor. The nocturnal increase of enzyme activity was prevented by cycloheximide or actinomycin D. Cocaine, which stabilizes cell membrane potential or light exposure, blocked the nighttime increase of N-acetyltransferase activity in cultured chicken pineal glands.     

Day-night differences in the response of the pineal gland to swimming stress

The effect of swimming stress on pineal N-acetyltransferase activity, hydroxyindole-O-methyltransferase (HIOMT) activity, and melatonin content was studied during the day and night in adult male rats. At night, elevated pineal activity was suppressed by light exposure before the animals swam. During the day, swimming for 2 hr did not stimulate NAT activity unless the animals were pretreated with desmethylimipramine (DMI), a norepinephrine uptake blocker. Pineal melatonin content after daytime swimming exhibited a weak rise, unless DMI was injected, in which case melatonin levels showed a highly significant increase. Swimming at night caused a greater (compared to daytime levels) increase in NAT activity in both noninjected and DMI-injected rats. Melatonin levels at night were highly significantly stimulated (compared to daytime values) even without pretreatment of the rats with DMI. The greater response of the rat pineal to swimming stress at night may relate either to an increase in the number of beta-adrenergic receptors in the pinealocyte membrane at night or to a reduced capacity of the sympathetic neurons in the pineal to take up excess circulating catecholamines. Pineal HIOMT activity was not influenced by swimming (with or without DMI) either during the day or at night.     

结节乳头体在小鼠运动和摄食中的作用及机制研究

目的:探讨结节乳头体在小鼠运动和摄食中的作用及机制。方法:选择雄性ddy小鼠,180-200 g,通过单侧植入电极损毁TMN-E2区。采用荧光金逆行追踪方法检测小鼠Me5与TMN之间的神经纤维联系;采用免疫组化方法检测小鼠TMN中组氨酸脱羧酶(HDC)免疫反应阳性细胞数;采用旷场试验箱记录小鼠全天、夜间以及白天的自主活动和摄食摄水;采用PCR检测小鼠穹窿周和下丘脑外侧区的orexin m RNA的表达。结果:荧光金逆行追踪实验显示小鼠Me5可向TMN-E2发出神经纤维投射。单侧TMN损毁,两侧TMN中HDC反应阳性细胞显著减少(P0.05),且损毁侧比未损毁侧HDC免疫反应阳性细胞数减少(P0.05)。TMN损毁对小鼠24 h自主活动和摄食摄水无明显影响。单侧TMN损毁,小鼠从暗期到光期的自主活动和摄食摄水显著减少(P0.05)。单侧TMN损毁,小鼠正常昼夜活动摄食节律无显著改变。单侧TMN损毁,小鼠穹隆周和下丘脑外侧区白天的orexin m RNA表达显著减少(P0.05)。结论:Me5与TMN之间存在神经通路,该通路可能通过调节穹隆周区或下丘脑外侧区的orexin神经元的激活从而调控摄食及相关行为的昼夜节律。     

Vitamin A deficiency reduces the responsiveness of pineal gland to light in Japanese quail (Coturnix japonica)

Synthesis of melatonin in pineal gland is under the control of light environment. The recent finding of the presence of rhodopsin-like photopigment (pinopsin) and retinal in the avian pinealocytes has led to a hypothesis that vitamin A is involved in photoresponses of the pineal gland. We have thus analyzed the effect of vitamin A deficiency on the regulatory system of melatonin synthesis in the pineal gland of Japanese quail. Depletion of vitamin A from Japanese quails was attained by feeding them with a vitamin A-free diet supplemented with retinoic acid. In the vitamin A-deficient birds, diurnal rhythm in melatonin production persisted such that the phase of the wave was similar to that seen in the control birds. However, the amplitude of the nighttime surge of pineal melatonin was damped by vitamin A deficiency. When the control birds were briefly exposed to light at night, pineal melatonin dropped to the daytime level. In contrast, only slight decrease was observed in the vitamin A-deficient quails. The light responsiveness was restored after feeding the vitamin A-deficient quails with the control diet for 1 week. These results indicate that vitamin A plays essential roles in maintaining sufficient responsiveness of the avian pineal gland to photic input.     

Suppression of food intake and body weight gain by naloxone in rats

The effect of acute and chronic administration of naloxone on food acquisition and weight gain in rats was studied in 3 experiments. One injection of a sparingly-soluble salt of naloxone in slow-release vehicle markedly lowered mean food intake over that of control rats injected with the vehicle only. Mean body weight of the naloxone-injected rats was significantly lower than that of the control group for one week.Repeated evening injections (2000 h) of naloxone hydrochloride in saline tended to reduce the night-time feeding below control levels throughout the 10-day period of naloxone administration. Food intake was significantly lower in the 4- and 8-h periods after the first injection of naloxone than that on the preceding saline control night. The initial decreases were offset by increased day-time feeding so that total daily food intake was not significantly altered over the 10 days. When saline was substituted for naloxone, food intake increased.Rats given naloxone following 24 h of fasting consumed significantly less food and gained less weight during 4 h of access to food compared to those receiving saline. After a 48-h fast naloxone-treated rats also gained significantly less body weight than those given saline, but the reduction in food intake was not statistically significant. These results suggest the possibility that endorphins may have a modulating effect on feeding activity.     

Effect of neonatal MSG treatment on day-night alkaline phosphatase activity in the rat duodenum

The day-night variation of food intake and alkaline phosphatase (AP) activity was studied in the duodenum of rats neonatally treated with monosodium glutamate (MSG) and saline-treated (control) rats. The animals were kept under light-dark conditions (light phase from 09:00 h to 21:00 h) with free access to food. AP activity was cytophotometrically analyzed in the brush-border of enterocytes separated from the tip, middle and cryptal part of the villi every 6 h over a 24-hour period. In comparison with the controls, MSG-treated rats consumed about 40% less food during the dark period and their 24-hour food intake was thus significantly lowered (P<0.001). On the other hand, the nocturnal feeding habit showed a similar pattern: food consumption was high during the night (65% vs. 75%) and the lowest consumption was found during the light phase (35% vs. 25%) in MSG-treated and control rats, respectively. In agreement with the rhythm of food intake, the highest AP activity was observed during the dark phase and was lowest during the light phase in both groups of animals. These significant day-night variations showed nearly the same pattern in the enterocytes of all observed parts along the villus axis. In comparison with the controls, a permanent increase of AP activity was observed in neonatal MSG-treated rats. This increase was more expressive during the dark phase of the day in the cryptal (P<0.001) and middle part of the villus (P<0.01). From the viewpoint of feeding, this enzyme in MSG-treated rats was enhanced in an inverse relation to the amount of food eaten i.e. despite sustained hypophagia the mean AP activity in the enterocytes along the villus axis was higher than in the control animals during all investigated periods. The present results suggest that the increased AP activity in MSG-treated rats is probably not a consequence of actual day-night eating perturbations but could be a component of a more general effect of MSG. This information contributes to better understanding of the function of intestinal AP and its relation to day-night feeding changes especially in connection with the MSG syndrome.     

Trade-off between energy budget, thermogenesis and behavior in Swiss mice under stochastic food deprivation

(1) The role of metabolic rate, thermogenesis and behavior in trade-off strategy was examined in Swiss mice under stochastic food deprivation (FD).

(2) For the mice under severe FD, food intake on feeding days increased, and basal metabolic rate (BMR) and nonshivering thermogenesis decreased significantly. The duration of activity decreased but resting behavior increased significantly on feeding days.

(3) It suggested that a trade-off between increased food intake and decreased energy expenditure related to lower BMR, thermogenesis and activity might be employed to meet reduced calorie intake caused by unpredictable FD.

Time-dependent effects of leptin on food intake and locomotor activity in goldfish

The present study investigates the possible circadian dependence of leptin effects on food intake, locomotor activity, glycemia and plasma cortisol levels in goldfish (Carassius auratus). Fish were maintained under 12L:12D photoperiod and subjected to two different feeding schedules, one group fed during photophase (10:00) and the other one during scotophase (22:00). Leptin or saline were intraperitoneally injected at two different times (10:00 or 22:00), coincident or not with the meal time. To eliminate the entraining effect of the light/dark cycle, goldfish maintained under 24 h light (LL) were fed and leptin-injected at 10:00. A reduction in food intake and locomotor activity and an increase in glycemia were found in goldfish fed and leptin-injected at 10:00. No significant changes in circulating cortisol were observed. Those effects were not observed when leptin was administered during the scotophase, regardless the feeding schedule; neither in fish maintained under LL, suggesting that a day/night cycle would be necessary to observe the actions of leptin administered during the photophase. Changes in locomotor activity and glycemia were only observed in goldfish when leptin was injected at daytime, coincident with the feeding schedule, suggesting that these leptin actions could be dependent on the feeding time as zeitgeber. In view of these results it appears that the circadian dependence of leptin actions in goldfish can be determined by the combination of both zeitgebers, light/dark cycle and food. Our results point out the relevance of the administration time when investigating regulatory functions of hormones.     

Antagonistic effects of naloxone on CCK-octapeptide induced satiety and rumino-reticular hypomotility in sheep

Continuous intracerebroventricular (ICV) infusion of CCK-octapeptide (CCK8) was performed in ewes fitted with a permanent cannula into the lateral cerebral ventricle and Nichrome electrodes on the reticulum in order to record its electrical activity. In the first series of experiments, subsequently repeated in 12 h fasted animals, CCK8 was infused during the first hour of a 3 hour period of feeding at 2.5, 5 and 10 ng.kg-1.min-1. The same series of infusion were performed 20 min after ICV injection of 2.4 and 10 micrograms.kg-1 of naloxone. CCK8 reduced significantly in a dose related manner the food intake (r = 0.95; P less than 0.01) and the frequency of cyclic spike bursts associated to biphasic contractions of the reticulum observed during feeding (r = 0.89; P less than 0.01). At 5 and 10 ng.kg-1.min-1, the reduction of food intake reached 46.2 and 52.6% during the period of infusion; the basal and stimulated (feeding) frequency of reticular contractions were nearly halved. Previous ICV administration of naloxone (2.4 micrograms.kg-1) partially blocked the effects of CCK8 infusion on both food intake (72%) and reticular frequency (54% basal, 67% stimulated). The CCK8 induced effects on both food intake and frequency of reticular contraction were completely abolished after a previous 10 micrograms.kg-1 injection of naloxone. These results suggest that the central effects of CCK8 on feeding behavior and forestomach motility involve similar central structures and are mediated through opiate receptor structures.     

A selective orexin-1 receptor antagonist reduces food consumption in male and female rats

A variety of evidence implicates the orexins, especially orexin-A, in the regulation of food intake, but it has not been established whether this effect is mediated by the orexin-1 or orexin-2 receptor. In the present study, a selective orexin-1 receptor antagonist, 1-(2-methylbenzoxazol-6-yl)-3-[1,5]naphthyridin-4-yl urea hydrochloride (SB-334867-A), was administered intraperitoneally to rats under various conditions, and food consumption was subsequently measured over 24 h. In male rats, a single dose of SB-334867-A (30 mg/kg, i.p.) given during the light phase reduced both orexin-A-induced food intake (7 nmol, i.c.v.) and feeding stimulated by an overnight fast for 4 h. When given at the start of the dark phase, food consumption was reduced in both male and female rats over 24 h. Daily injections at the start of the dark phase for 3 days reduced natural feeding in male rats over 24 h on days one and three. These findings demonstrate direct inhibition of orexin-A induced food intake with a selective orexin-1 receptor antagonist. Furthermore, the suppression of nocturnal feeding and food intake stimulated by an overnight fast supports other evidence that orexin-A is involved in the regulation of natural feeding and suggests that orexin-1 receptor antagonists could be useful in the treatment of obesity.     

Pineal N-acetyltransferase, pineal and serum melatonin response to isoproterenol stimulation in underfed male rats

Adult male rats were subjected to 4 weeks of 50% food restriction under lighting regimen of 14 h light and 10 h dark. The pineal response to isoproterenol (ISO) was determined. In the time-course study, animals were injected with 0.5 mg/Kg ISO subcutaneously (SC) and killed at different times up to 180 min post injection. In the dose-response study, various doses of ISO (0.2 mg/Kg to 5.0 mg/Kg) were injected intraperitoneally (IP) and animals were killed 120 min post injection. Body weight, pineal N-acetyltransferase (NATase), pineal and serum melatonin (MT) were determined. After 4 weeks of restricted feeding, body weight was reduced by 40%. In the time-course study, peak pineal NATase occurred 120 min post injection in the ad libitum fed animals. By contrast, the food restricted animals showed a gradual increase of pineal NATase up to 180 min post injection. In the dose-response study, the ad libitum fed animals demonstrated a dose dependent increase of pineal NATase up to 5 mg/kg dose. The food restricted animals, however, achieved their maximal pineal NATase at 1 mg/Kg dose with no further increment at 5 mg/Kg dose. These differences in responsiveness were also reflected in pineal and serum MT levels. These results indicate that underfed animals have abnormal pineal NATase, pineal and serum MT responses to ISO stimulation.     

Differential responses of rat pineal thyroxine type II 5′-deiodinase andN-acetyltransferase activities to either light exposure,isoproterenol, phenylephrine,or propranolol

1. Compared to pineal N-acetyl transferase (NAT) activity, which exhibited a dramatic drop following acute light exposure at night, nocturnal rat pineal thyroxine type II 5'-deiodinase (5'-D) activity was minimally influenced by the same light exposure. The injection of cycloheximide, a potent inhibitor of protein synthesis, although it did curtail the rise in NAT activity for at least 2 hr, did not elicit decreases in the activities of either 5'-D or NAT enzymes. Propranolol, a beta-adrenergic blocker, either delayed the continued nocturnal rise in 5'-D activity when injected at 0000 hr or slightly enhanced the fall in 5'-D activity when injected at 0200 hr. These results suggest that interruption of the synthesis of proteins is responsible for the slow deterioration of 5'-D activity induced by either light or propranolol. 2. The slight fall in 5'-D activity induced by light at night was prevented by isoproterenol; phenylephrine, however, did not prevent the fall and the effect of isoproterenol + phenylephrine was similar to that obtained with isoproterenol alone. On the other hand, the light-inhibited NAT activity recovered after the injection of isoproterenol; phenylephrine did not elicit any effect, but the injection of both isoproterenol and phenylephrine simultaneously caused a greater NAT response than that induced by isoproterenol alone. 3. When injected during the day, phenylephrine had no effect on either pineal 5'-D or NAT activities; however, the injection of either isoproterenol alone or isoproterenol + phenylephrine elicited 5-fold and 10-fold increases in nocturnal, light-suppressed 5'-D and NAT activities, respectively. During the day, phenylephrine did not potentiate the effects of isoproterenol on NAT activity as it did at night. When the effects of isoproterenol on the 5'-D activity were compared to rats exposed to light during the day and at night, the activity of 5'-D reached a higher level at night than during the day.     

Photoneural Regulation of Rat Pineal Nitric Oxide Synthase

Abstract: We report here a photoneural regulation of nitric oxide synthase (NOS) activity in the rat pineal gland. In the absence of the adrenergic stimulation following constant light exposure (LL) or denervation, pineal NOS activity is markedly reduced. A maximal drop is measured after 8 days in LL. When rats are housed back in normal light-dark (LD) conditions (12:12), pineal NOS activity returns to normal after 4 days. A partial decrease in pineal NOS activity is also observed when rats are placed for 8 days in LD 18:6 or shorter dark phases, indicating that pineal NOS activity reflects the length of the dark phase. Because it is known that norepinephrine (NE) is released at night from the nerve endings in the pineal gland and this release is blocked by exposure to light, our data suggest that NOS is controlled by adrenergic mechanisms. Our observation may also explain the lack of cyclic GMP response to NE observed in animals housed in constant light.     

Avian Melatonin Synthesis: Photic and Circadian Regulation of Serotonin N-Acetyltransferase mRNA in the Chicken Pineal Gland and Retina

Abstract: The circadian rhythms in melatonin production in the chicken pineal gland and retina reflect changes in the activity of serotonin N -acetyltransferase (arylalkylamine N -acetyltransferase; AA-NAT; EC 2.3.1.87). Here we determined that the chicken AA-NAT mRNA is detectable in follicular pineal cells and retinal photoreceptors and that it exhibits a circadian rhythm, with peak levels at night. AA-NAT mRNA was not detected in other tissues. The AA-NAT mRNA rhythm in the pineal gland and retina persists in constant darkness (DD) and constant lighting (LL). The amplitude of the pineal mRNA rhythm is not decreased in LL. Light appears to influence the phase of the clock driving the rhythm in pineal AA-NAT mRNA in two ways: The peak is delayed by ∼6 h in LL, and it is advanced by >4 h by a 6-h light pulse late in subjective night in DD. Nocturnal AA-NAT mRNA levels do not change during a 20-min exposure to light, whereas this treatment dramatically decreases AA-NAT activity. These observations suggest that the rhythmic changes in chicken pineal AA-NAT activity reflect, at least in part, clock-generated changes in mRNA levels. In contrast, changes in mRNA content are not involved in the rapid light-induced decrease in AA-NAT activity.     

Predator–prey interactions between larval damselflies and mining larvae of Glyptotendipes gripekoveni (Chironomidae): reduction in feeding activity as an induced defence

1. The feeding methods and intensity of predation by larvae of the damselfly Erythromma najas on leaf‐mining larvae of the chironomid Glyptotendipes gripekoveni were examined in artificial habitats differing in complexity. The experiments assessed the influence of chemical stimuli from the predator, light and the concentration of suspended food on the feeding activity of G. gripekoveni inside and outside of the mine.
2.  Erythromma najas preyed upon G. gripekoveni as the latter grazed outside mines. The intensity of this predation decreased significantly at night in a habitat offering alternative prey.
3. When the food concentration for the chironomid was high, it significantly reduced both filtering activity and activity outside mines in response to the kairomone produced by E. najas . Feeding activity did not change when food was scarce.
4. The induced reduction in filter‐feeding and deposit‐feeding activity probably reduced predator success by reducing the probability of long‐distance detection of a mine and location of the chironomid's hole.
5. The predator can detect and catch mining prey in either the light (visually) or dark (mechanically). This may explain the lack of diel periodicity in the chemically induced differences in prey activity.
6. Reduced feeding activity of mining larvae in the chemically simulated presence of a larval damselfly can be explained as an induced antipredator behaviour, illustrating the trade‐off between feeding demands and predation risk in a poorly known link of the littoral foodweb.