Food intake and growth of rats fed with adiurnal periodicity

The effects of adiurnal periodicity of feeding on the food intakes and growth of rats kept under a 12-hr light-dark cycle or continuous light were examined. When rats were fed for 5 hr once every 20 hr or for 7 hr once every 28 hr, they ate less food and grew more slowly than rats that were fed for 6 hr once every 24 hr, regardless of the lighting conditions. The data are discussed in terms of the relation between the feeding cycle and the internal circadian clock.     

Circadian feeding rhythm after hypothalamic knife-cut isolating suprachiasmatic nucleus

Bilateral parasagittal knife-cut between the suprachiasmatic nucleus (SCN) and lateral hypothalamic area (LH) or coronal knife-cut between the SCN and ventromedial hypothalamic nucleus (VMH) resulted in a partial loss of the circadian feeding rhythm in rats; after either operation the rats consumed about 30% of their total daily food intake during the light period. However, after the parasagittal and coronal knife-cuts were made in combination, the circadian feeding rhythm was completely lost (50% food intake during the light period). Rats which lost the circadian feeding rhythm partially or completely showed neither obesity nor anorexia. These findings suggest that there are dual informational pathways from the SCN, possibly between the SCN and LH and between the SCN and VMH, through which circadian time signals generated in the SCN are transmitted to the LH and VMH to drive the circadian feeding rhythm.     

Entrainment of anticipatory activity to various durations of food access

Rats with lesions of the suprachiasmatic nuclei (SCN) and intact rats were maintained on restricted feeding with the duration of food access ranging from 4 to 12 hr. All rats with SCN lesions displayed at least some anticipatory activity (AA) at all food access durations. The amount of AA diminished when food access was extended to 12 hr and was lowest in a group that was exposed only to a 10-hr access period. The onset of AA (phase angle of entrainment) appeared to be more sensitive to the time of food availability than to its termination. Most intact rats maintained in constant light displayed some AA at food access durations between 4 and 10 hr. In most cases the period of the free running rhythm increased as it crossed food access and the free running rhythm became increasingly disrupted as the experiment progressed in all rats. In some cases the free running rhythm appeared to force AA out of entrainment. These results demonstrate that AA occurs in conditions that impose only minor deficits on the energy balance of rats. Furthermore, they provide additional evidence of interactions between two separate circadian pacemaking systems.     

Circadian rhythm of feeding induced changes in hypothalamic Met-enkephalin concentrations

Accumulating evidence suggests that opioid peptides play an important role in the hunger component of the control of food intake. The enkephalins, one of the opioid peptide families, stimulate feeding when injected into specific hypothalamic areas and endogenous concentrations change with the fed/fasted condition of rats and sheep and with phase of circadian cycle. To demonstrate a possible circadian rhythm in feeding-induced changes in Met-enkephalin (MEK), 54 male rats initially weighing 255 +/- 3 g were adapted to a 12-hr fast during the light (light-fasted) or dark (dark-fasted) phase of the circadian cycle, then sacrificed before (non-fed) or after (fed) being allowed to eat a meal. In non-fed compared with fed rats, MEK concentrations were higher in the paraventricular nucleus (PVN, 170 vs. 109 pg/mg tissue, p less than 0.05) and ventromedial hypothalamus (VMH, 209 vs. 161 pg/mg tissue, p less than 0.05) in the dark (light-fasted) but not light (dark-fasted), even though rats ate a larger meal in the light (8.6 vs. 5.0 g, p less than 0.01). In rats fed the same amount of food in the light (dark-fasted) as ad lib fed rats in the dark (light-fasted), MEK concentrations did not differ in the PVN or VMH, suggesting that circadian rhythm is more important than meal size. Rats gavaged with an amount of milk equal in calories to dark ad lib-fed rats (light-fasted) had MEK concentrations not different from light-fasted non-fed rats (216 vs. 209 pg/mg tissue, NS) suggesting that feeding behavior, pregastric stimuli and/or form of diet is important for influencing MEK concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suprachiasmatic nuclei lesions do not eliminate the circadian rhythms of electrolyte excretion in the rat

The 24-hour variations in 2-hour diuretic and saluretic action of furosemide (4 mg/kg) given at 8, 12, 16, 20, 24 or 4 hr and the circadian rhythms of food and water intake, urine and electrolyte excretion followed for two consecutive days at 4-hour intervals were investigated in suprachiasmatic nuclei (SCN)-lesioned or sham-operated male Wistar rats. The results showed that: a distinct 24-hour rhythm in furosemide-induced urine, sodium and chloride excretion persisted after SCN lesions, and the lesions abolished the circadian rhythms of food and water intake but only desynchronized the individual 24-hour variations in electrolyte excretion. We concluded that SCN play a role as a central synchronizer but not as a major oscillator of the circadian rhythms of electrolyte excretion in the rat.     

Entrainment of methamphetamine-induced locomotor activity rhythm to feeding cycles in SCN-lesioned rats.

Suprachiasmatic nuclei (SCN)-lesioned rats, showing a locomotor activity rhythm with a circadian period by chronic methamphetamine treatment, were subjected to the periodic food restriction (RF) of 4 h per every 27 h and 24 h. All rats were phase set by the feeding schedule of both 24-h and 27-h periods. Phase angle differences between the activity onset and food presentation were more positive under the RF with a period of 27 h than that of 24 h. Methamphetamine-induced locomotor rhythm showed a stable entrainment to RF of the 27-h period in all rats. Under the RF of the 24-h period, on the other hand, some rats showed circabidian rhythms, i.e., an activity band appeared at every second food presentation. After the termination of feeding schedule, the locomotor rhythm started to free-run from the phase set by the previous feeding schedule in all rats examined. Methamphetamine-induced locomotor rhythm was shown to be entrained by the RF with a predictable manner of an oscillation theory.     

Phase shifts of circadian rhythms in activity entrained to food access

Rats anticipate daily 2 hr meals with a sharp increase in activity several hours prior to food availability. The present experiment examined the response to phase shifts of food access in rats with lesions of the suprachiasmatic nuclei (SCN). Following entrainment of activity to 2 hr of food per day, food access was phase delayed or phase advanced by 4, 6, or 8 hr. All rats responded to phase delays of 4 or 6 hr with an increase in the duration of anticipatory activity so that transients appeared mostly in activity onset. Following 8 hr phase delays, clear delaying transients in both activity onset and end were observed. Only a few rats showed advancing transients in activity after phase advances of food access. In response to 6 hr and 8 hr phase advances, 3 different responses occurred: (a) activity re-entrained to food access by the 2nd or 3rd day without clear intervening transients, (b) activity phase shifted by means of distinct delaying transients and (c) delaying transients occurred in one component of activity while a second component of activity appeared at the new phase position by the second or third day. These results provide further evidence that anticipation of food access is mediated by a circadian mechanism which is functionally independent of the SCN and illustrate some similarities as well as considerable differences between circadian rhythms entrained by feeding and those entrained by light-dark cycles.     

Circadian rhythms of somatostatin-immunoreactivity in the suprachiasmatic nucleus of the rat.

Twenty-four hour patterns in somatostatin (SS)-like immunoreactivity (LI) within the suprachiasmatic nucleus (SCN) were determined by enzyme immunoassay in rats blinded by bilateral orbital enucleation or kept sighted under light-dark conditions. A remarkable circadian rhythm was found in the concentration of SS-LI in the SCN under blinded conditions. The peak time appeared at about circadian time (CT) 4 in the early subjective day and the trough at around CT 16 or 20 in the subjective night. Light-dark cycles did not alter the circadian patterns of SS-LI observed in the blinded rat SCN. These results indicate the presence of an endogenous circadian rhythm in SS-LI in the rat SCN, independent of environmental lightning cycles.     

Period length of the light-dark cycle influences the growth rate and food intake in mice

The adaptation of the endogenous rhythm of an organism to external cycles may be critical for the development of physiological processes in which energy is expended. We sought to determine whether growth rate depends on the degree of tuning between the external cycle and the manifestation of the circadian rhythms. To do so, we studied the growth rate and the food intake of mice (seven groups of 20 animals each) kept under symmetric LD cycles with different periods (T) of 21, 22, 23, 24, 25, 26, and 27 h, respectively, for 80 days. The mice were then kept in constant darkness for a further 80 days. Throughout the experiment, motor activity was recorded every 15 min for each mouse by means of an actimeter that used crossed infrared beams. Several variables related to the circadian motor activity rhythm were calculated, and correlated with body weight, food intake, and the efficiency of food for growth (food efficiency) calculated as: 100 x body weight increase/ amount of food intake. Results show that these three variables seem to be influenced by the number of circadian cycles that the animal has experienced, but also, and more significantly, by the degree to which the alpha phase of the individual rhythm and the dark phase of the external cycle coincide. Therefore, circadian rhythms would seem to affect the physiological processes that regulate growth and energy expenditure.     

Effects of feeding a single daily meal and of changes in lighting schedule on the circadian rhythms of oxidoreductases in the rat gastric mucosa.

The present paper investigated the effect of restricted feeding (11.00 to 13.00 h) by a single daily meal upon the activity of various oxidoreductases of the rat gastric mucosa (SDH, alpha-GPDH, LDH, NADHTR), which at ad libitum feeding under normal lighting conditions with a dark night were shown to have distinct circadian activity variations related to the rat's nocturnal food intake preference (Zaviacic and Brozman 1978a). 1st part of the animals received food in 2-h-period by natural daylight (natural lighting conditions), the 2nd part at the same period of time but in the dark (lighting conditions reversed to natural). Checking the consumption of food, we found the animals to become adapted to the new time of food intake beginning with the 6th experimental day. The circadian rhythm of enzymes was examined on days 69, 83, 97, and 104 of limited feeding under the defined lighting schedule, at 06.00 h, 12.00 h, 18.00 h, and 24.00 h in groups of 5 animals. Synchronization of the highest dehydrogenases activities (particularly of SDH) with the time of restricted feeding was seen to develop in the gastric mucosa of the rat. The synchronization effect was more pronounced in the animals which received their food in the dark (and here even more in male than in female). The effect of light during food intake was found to be rather interfering with the development of synchronization of dehydrogenase activities with the time of food intake, and the influence was again more marked in male than in female. The time of food intake was at the feeding schedule restricted to daytime intake the main synchronizer for the circadian rhythm of oxidoreductases of the gastric mucosa of the rat, with the highest daily activities recorded around the feeding time and the lowest activities at night, which is the direct opposite of the circadian rhythm of the same enzymes determined in rats fed ad libitum under normal lighting conditions with a dark night.     

Rhythms in behaviors, body temperature and plasma corticosterone in SCN lesioned rats given methamphetamine

In aperiodic rats with lesions in the suprachiasmatic nuclei (SCN), rhythms with a circadian period in spontaneous locomotion, wheel-running, feeding, drinking, body temperature and plasma corticosterone were restored by chronic administration of methamphetamine. These rhythms were not entrained by a light-dark cycle. Wheel-running, feeding and drinking rhythms in individual rats were in phase in terms of ultradian bout as well as circadian fluctuation. Rhythms of the intraperitoneal temperature appeared accompanying the spontaneous locomotor rhythm. The phase relation between the two rhythms was similar to that of SCN dependent rhythms. Plasma corticosterone also fluctuated in a circadian fashion. The corticosterone peak preceded the activity onset of locomotor rhythm by a few hours, which was similar to the phase relation observed in the SCN intact animals. It is concluded that the oscillatory mechanism underlying the spontaneous locomotor rhythm in SCN lesioned and methamphetamine treated rats drives also other physiological rhythms. The phase-relations among them were similar to those of rhythms driven by the circadian pacemaker in the SCN.     

Daily rhythms of feeding in the genetically obese and lean Zucker rats

Feeding patterns were examined in obese (fa/fa) and lean (Fa/-) adult Zucker rats over the light-dark cycle during 14 days. Obese rats eat more than lean rats especially during the dark phase. Light and dark feeding expressed as percentage of 24 hr intake showed no significant differences between the lean and obese groups. The higher food intake in obese rats is mainly caused by larger meals since obese rats ate fewer meals than lean rats. Only for the obese group differences were observed between mean meal size in light and dark phase. There is some indication that the circadian controlled temporal distribution of meals is different in obese rats compared to lean rats since obese rats eat fewer but larger meals during the first half of the dark phase. During this phase meal size increases gradually in the obese rats, suggesting that the circadian influence on feeding motivation is increased.     

The role of period and phase in interactions between feeding- and light-entrainable circadian rhythms

Sixteen blind male rats were maintained on ad lib food and water for 115 days to obtain stable free-running rhythms. Fifteen rats were then exposed to restricted feeding (RF, 4 hr/cycle) for 52 days and the period of food access (T) differed from the period of the free-running rhythm (tau) by 0.05 to 0.30 hr. Among 15 animals exposed to RF, deceleration of the free-running rhythm was observed in 11 rats, small accelerations occurred in 2 rats, and tau remained unchanged in 2 rats exposed to RF and one ad lib rat. The free-running rhythm assumed the period of RF in 3 rats where T-tau was less than 0.1 hr and the change in tau persisted for 42 days after RF. However, other rats failed to synchronize their free-running rhythm despite small period differences. Although these results show that the two underlying circadian pacemaking systems are not functionally independent, they appear to be only weakly coupled.     

Diurnal patterns of food intake and plasma corticosterone levels in lactating rats

The diurnal patterns of food intake and plasma corticosterone levels were determined in lactating Wistar-Imamichi rats maintained in a light (14 L: 10 D, lights on 0500 hr) and temperature (24±2°C) controlled animal room. Lactating mothers with four or more than eight pups showed a characteristic diurnal pattern of food intake with high rates of intake around the time of lights off. The diurnal rhythmicity of food intake seemed to disappear in late lactation in mothers with more than eight pups. The plasma corticosterone concentration on day 9 of lactation displayed a diurnal rhythm with high values at 1700 hr and 2100 hr. The rhythmicity of the corticosterone levels was abolished on day 16 of lactation and a high level was maintained throughout a 24 hr period. Since the diurnal rhythm of the corticosterone level was shifted in animals fed during the restricted period (0900–1700 hr) from days 2 to 9 of lactation, the appearance of diurnal rhythm of corticoid secretion seemed to depend on the diurnal feeding rhythm in lactation as well as in the estrous cycle.     

Influences of feeding and drinking on circadian rhythms of opioid peptides in plasma, hypothalamus and pituitary gland in rats

Changes of plasma, hypothalamic and pituitary immunoreactive beta-endorphin (IR-beta-end), methionine-enkephalin (IR-Met-enk) and ACTH (IR-ACTH) were studied under various conditions of feeding and watering in rats. When rats were fed from 17:00 to 09:00 hr and water was given ad lib, plasma IR-beta-end and IR-ACTH had parallel circadian rhythms with a peak before feeding and drinking. In the hypothalamus, IR-beta-end and IR-Met-enk showed parallel circadian rhythms with a decrease before these behaviors. When rats were fed from 09:00 to 17:00 hr, the peaks of plasma IR-beta-end and IR-ACTH shifted to one hour before the onset of feeding and drinking. When feeding and watering were restricted to 17:00-09:00 hr and 09:00-12:00 hr respectively, plasma IR-beta-end and IR-ACTH exhibited parallel circadian rhythms with two separate peaks at one hour before drinking and feeding, respectively. In the hypothalamus, IR-beta-end, IR-Met-enk and IR-ACTH showed parallel circadian rhythms with a decrease before feeding but not before drinking. When rats were fed from 17:00 to 20:00 hr, plasma IR-beta-end increased and neurohypophysial IR-beta-end and IR-Met-enk decreased at 16:00 hr, one hour before feeding. It was observed that locomotor activities increased at the time of transition from light to dark and at one hour before the onset of feeding and drinking. The present results suggest that endogenous opioid peptides may have some physiological roles in feeding and drinking behaviors.     

A study on aspects of feeding and food utilization of the Indian musk shrew, Suncus murinus viridescens (Blyth).

Studies on feeding in musk shrews revealed that the mean intake of beef was 36.34% and 47.25% of their own body weight by males and females, respectively, whereas these values were 49.20% and 63.18%, respectively, on a cockroach diet. The amount of food intake per gram body weight was higher in female shrews than was that of males. Shrews exhibit a definite preference for protein rich materials. A feeding rhythm with a peak at predawn hours and a minimum during the afternoon was observed in both sexes. The endogenous nature of the original feeding rhythm persisted in shrews experimentally subjected to a reversed photoperiod. The caloric utilization of male and female shrews fed on beef was 0.484/g body wt/24 hr, and 0.579/g body wt/24 hr, respectively, whereas these values were 0.655 and 0.973, respectively, for shrews maintained on cockroaches.     

Feeding patterns of theophyllinized rats and effects of dextrose on their food intake.

Chronically theophylline administered rats did not show normal increase in food intake during dark periods, while the total amount of intake per 24 hr was not affected. These ingestive results were consistent with changes in arterial-venous blood glucose differences: i.e., those in the control group were markedly dependent on a light-dark feeding cycle, but not those in the theophylline group. Food containing relatively high concentrations of dextrose was found to facilitate food consumption of theophyllinized rats, an effect opposite to that on the controls. These observed changes in the feeding behavior of theophyllinized rats may reflect impaired feeding motivation and circadian desynchronization of feeding.     

Circadian changes in arginine vasopressin level in the suprachiasmatic nuclei in the rat

Arginine vasopressin (AVP) neurons were preferentially localized in the dorsomedial part of the suprachiasmatic nucleus (SCN). To know the role of AVP neurons in the SCN, male rats were kept under a normal light-dark cycle (L-D), or under constant darkness (D-D) for 20 days. In L-D condition, AVP levels in the SCN showed the circadian change. In D-D condition, the patterns in AVP levels showed a free-running rhythm, and an about 12-h shift per 20 days. This result suggests that the activity of AVP neurons may be closely associated with the endogenous circadian rhythm of the SCN.     

Feeding pattern and light-dark variations in water intake and renal excretion after suprachiasmatic nuclei lesions in rats

Bilateral destruction of the suprachiasmatic nuclei (SCN) eliminated light-dark (L/D) variations in water intake and urine output in albino rats. The lesions abolished also the circadian rhythm of food intake, without changing significantly the 24 hour number of meals, total meal duration and 24 hour food intake. Only the L/D distribution of the number of meals was changed from $\text{5.6}\text{16.9}$ in control period to $\text{12.7}\text{12.9}$ after lesions. In contrast, the L/D distribution of sodium, potassium and chlorides excretions demonstrated attenuated but persistent nocturnal type. These data imply that SCN play a role of driving oscillator for the circadian rhythm of food intake, but probably are not the main synchronizer for the rhythms of electrolyte excretions.     

Coupling between feeding- and light-entrainable circadian pacemakers in the rat

Activity of the rat can be entrained to LD cycles (light-entrainable rhythm = LER) and to periodic food access (feeding-entrainable rhythm = FER) and these responses appear to be mediated by separate circadian pacemaking systems. The purpose of this study was to explore interactions between these systems. In Experiment I, after entrainment of activity to a LD cycle and to restricted feeding, the LD cycle was phase delayed by 4 hr and rats were food deprived for 3 days. Delaying transients were observed in both the LER and FER although food was no longer a Zeitgeber. In Experiment II, food was scheduled at 3 different phases of the LD cycle. Food access was then phase delayed by 8 hr and rats were placed in DD. When the new food access fell into the subjective day, the phase of the LER was not affected but transients in the FER persisted for up to 18 days, 3 to 5 times longer than reported for rats with suprachiasmatic nucleus lesions. When the new food access fell into the early subjective night, the "free-running" LER was phase advanced by over 3 hr but no delaying transients in the FER were observed. When the new food access fell into the late subjective night, the LER was not phase advanced but its period remained close to 24 hr and no delaying transients in the FER were observed. In Experiment III, food was presented at two phases of the LD cycle and restricted feeding was continued in DD without phase shifts.(ABSTRACT TRUNCATED AT 250 WORDS)