Interbout Interval Research Articles

Fluoxetine-Maintained Obese Humans: Effect on Food Intake and Body Weight

WARD A. S., S. D. COMER, M. HANEY, M. W. FISCHMAN AND R. W. FOLTIN. Fluoxetine-maintained obese humans: Effect on food intake and body weight. PHYSIOL BEHAV 66(5) 815–821, 1999.—The effects of fluoxetine on food intake, body weight, and mood of obese individuals was examined in a 16-week inpatient/outpatient study. Six male and eight female obese volunteers began the study (four male and five females completed all phases of the study). They lived in a residential laboratory during three one-week inpatient periods separated by a 5-week and an 8-week outpatient period. Following an initial 4-day placebo baseline, participants were maintained on fluoxetine (60 mg/day) for the remainder of the study. Food intake parameters (total daily energy intake, macronutrient intake, mean number of eating bouts, interbout interval), body weight, subjective effects, and task performance were measured several times during the day during inpatient periods; food intake questionnaires were completed daily during the outpatient periods. Fluoxetine significantly reduced daily energy intake derived from fat, carbohydrate, and protein by decreasing the mean number of eating bouts per day throughout the study. No other food intake parameter was affected. Body weight was significantly reduced after 7 weeks, but not after 16 weeks of daily fluoxetine administration. These results indicate that fluoxetine reduced food intake for at least 16 weeks in nondepressed obese individuals without specifically affecting carbohydrate intake. Weight that was lost during the first few weeks of daily fluoxetine administration was subsequently regained even though food intake remained reduced. Therefore, fluoxetine maintenance does not appear promising as a sole long-term therapy for obesity.

Genetic and non-genetic factors influencing ingestive behavior of sheep under stall-feeding conditions

Ingestive activities of 100 stall-fed sheep (48 Muzaffarnagari and 52 1/4 Suffolk × 1/4 Dorset × 1/2 Muzaffarnagari) belonging to different age and class categories viz. lamb (<3 months), young (5–6 months), hogget (9–12 months), pregnant, lactating and adult sheep, were recorded each minute under personal surveillance for 24 consecutive hours on three occasions. The experimental sheep were confined in a paddock (15.2 × 9.1 m) where ad.lib green fodder (lucerne/maize) and water were available to the animals all the time. Bout duration of eating, ruminating and drinking activity were recorded along with the inter-bout duration (the time interval between two consecutive bouts of a particular activity). The sheep spent 7 h day −1 eating, 2 h day −1 lying ruminating, 1 h day −1 standing ruminating and 5 min day −1 drinking. Time spent eating and drinking were more ( p < 0.01) during daylight (0601–1800 hours), especially after sunrise and before sunset, than night time (1801–0600 hours), whereas the trend reversed for rumination activity in which peak activity was noticed after midnight. Genotype and sex had no effect on the time spent on the ingestive activities but category of sheep varied significantly ( p < 0.01). The mean duration of eating lasted 12 min while mean inter-bout interval among eating lasted 26 min. These intervals were almost similar among all the sheep >6 months of age. Rumination bout in lying and standing posture lasted for 14 and 9 min, respectively and their recurrences occurred every 2–3 h. Rumination bout and inter-bout differed significantly ( p < 0.05) between the categories of sheep and diurnally. Young, hogget and lactating sheep took significantly ( p < 0.01) more drinking time than the other sheep. Each drinking bout lasted about 1 min and it recurred every 2 h throughout a 24 h period. The study suggests the practice of offering feed to stall-fed sheep at least three times a day (around 0600, 1300 and 1900 hours) to facilitate higher feed intake. In the night, the sheep are to be provided with adequate space to ruminate in lying posture.

On the quantification of suckling intensity in primates.

The inhibitory effect that suckling has on the reproductive function of primate mothers varies as a function of the intensity with which they are suckled. Here we present an easily computed index of one parameter of suckling intensity, namely the temporal patterning of suckling bouts. High intensity suckling is characterized by frequent nursing bouts demarcated by short interbout intervals. Therefore, our suckling index is based on the brevity of observed interbout intervals, more specifically the proportion of such intervals that fail to exceed a criterion length. The index is an appropriate means of making interspecific comparisons of the development of infant suckling and is well suited for application to field data that include interbout intervals that were not observed in their entirety. To demonstrate its utility, we apply the index to field data collected on the suckling behavior of free-ranging rhesus monkey (Macaca mulatta) infants in India. In this context, we demonstrate that, in rhesus, between-infant differences in suckling intensity manifest themselves early in the postpartum period and contribute to between-female differences in the timing of first mating postpartum.

Ethanol consumption in rats when dose size is under subject control.

Rats orally self-administered ethanol when they could control dose size as follows: A lever press initiated a trial; a press on 1 lever increased the previous trial duration by 30% whereas a press on a 2nd lever decreased the previous trial duration by 30%. During a trial, rats could drink either water, 8%, or 16% (wt/vol) ethanol (ETOH) from a lick-sensitive fountain. Mean per session intake of 8% and 16% ETOH was 0.8 g/kg and 1.3 g/kg, respectively. Water intake was negligible. Rats did not show a tendency to maintain a particular trial duration, nor did they adjust intertrial intervals to previous dose size (number of licks). When trials were collected into bouts, a positive relationship was found between bout size and interbout interval; this relationship was statistically significant for the 8% but not the 16% ETOH condition.

Prolactin response to suckling and maintenance of postpartum amenorrhea among intensively breastfeeding Nepali women.

The aim of the study was to determine the association between PRL responses to suckling and maintenance of postpartum amenorrhea among breastfeeding mothers. Three blood spot samples (5, 30, and 50 min following a timed nursing bout) were collected from 71 intensively breastfeeding Nepali women for PRL determination. Maternal age, BMI (weight/height2), menstrual status, caste, infant age, nursing bout length, and duration of supplementation were recorded at time of sample collection. Independent and paired t tests, linear regression analyses, and general linear models were used to evaluate differences between cycling (n = 36) and amenorrheic (n = 35) women and associations among variables. Logistic regression analyses were used to relate PRL measures to the odds of maintaining lactational amenorrhea. Amenorrheic breastfeeding mothers had higher (P < .001) PRL levels at all 3 collection times than cycling breastfeeding mothers, and PRL levels declined with time since birth (P < 0.05). The odds (OR) of having ceased lactational amenorrhea was significantly higher (OR = 5.0, 95% Cl = 1.3-19.9) among mothers with lower PRL levels (< or = 10 ng/mL) at 50 min post-sucking, and PRL at 50 min showed a significant dose response relationship with menstrual status. The association between 50 min PRL levels and lactational amenorrhea appears to be independent of time postpartum, maternal age, BMI, nursing bout length, and duration of supplementation. Among intensively nursing women, maintenance of elevated PRL levels across the interbout interval increases the odds of maintaining lactational amenorrhea.

An event recorder for infant feeding research

An Event Recorder program was developed for the HP 48 calculator to record the durational events associated with breastfeeding behavior. The Event Recorder menu structure is flexible and allows for the recording of response variables such as menstrual history and fertility symptoms. A Windows ™ program was written in Visual C++ to give a graphical representation of the time-series data and to extract useful measures of breastfeeding activity from the raw data for each 24-h day postpartum. These time varying covariates include the mean and median bout length, median interbout interval, breastfeeding frequency and total 24-h suckling duration. The HP 48 calculator has proven to be a robust instrument for the self-recording of breastfeeding data collected as part of a prospective study on the factors that maintain postpartum amenorrhea. We have found also that the behavioral data collected are easily transferred electronically each month when our field workers make home visits.

Slow extinction of conditioned responding following exposure to two bouts of massed shock

Extinction of rats’ conditioned defensive freezing responses in a context associated with two bouts of massed shock (3 sec) separated by a long unreinforced interbout interval was slower than that in a context associated with distributed shock (60 sec). Resistance to extinction following two bouts of massed shock depended on the rats’ remaining undisturbed in the conditioning context during the long unreinforced interbout interval. Slow extinction of freezing was attributed to either the summation of temporal conditioning at the early and late session times or the formation of an association between the early and late bouts of shock. Importantly, the effects of the two bouts of massed shock could not be explained by what is known about the reinforcing effectiveness of massed shock.

Proximal control of fetal rat behavior

We examined the influence of the amniotic sac on spontaneous movement in late gestation fetal rats. Using techniques for in vivo observation of fetal behavior, Day 21 rat fetuses were exteriorized from the uterus, with umbilical connections to the dam intact, and videotaped for 15 min either: (a) through the intact amniotic membranes, or (b) following removal of the membranes. Analysis of fetal behavior categories replicated the findings of previous investigators: Movements of the head, forelimbs, and rearlimbs were significantly increased by sac removal, as was the total frequency of behavior categories and the simultaneous occurrence of different behavior categories. Frame-by-frame analysis of videotaped behavior revealed that amniotic sac removal increased the frequency of movement bouts without altering the overall amount of time that fetuses spent moving. Movement bout durations ranged from 50 msec to 70 s. The average duration of movement bouts was significantly reduced for fetuses lacking the amniotic sac as compared to fetuses within the sac, as was the overall distribution of movement bout durations. Frequency distributions of movement bout durations and interbout interval (IBIs) revealed that sac removal significantly increased the occurrence of short (1-2 s) movement bouts and reduced the frequency of protracted movement bouts and interbout intervals (> 10-s duration). Taken together, these findings indicate that the quantitative dimensions of fetal rat movements are influenced by proximal features of the uterine environment. During prenatal life, the amniotic sac appears to sustain movement, possibly by providing proprioceptive feedback or physical support to the fetus, or by regulating the chemical milieu.

Suckling behavior of ewes in early lactation

Previous studies have described the basic suckling behavior of ewe/lamb pairs during daylight hours, but no information is available for the hours of darkness. In this study, the natural pattern of suckling was recorded over a 24-h period once a week for the first 7 weeks of lactation in 7 free-ranging Merino ewes with single lambs. Both the mean suckling frequency per 24 hours and the mean duration of individual suckling bouts declined with increasing age of the lamb. Suckling frequencies fell from 36±5.5 sucks/24 h at 1–2 weeks of age to 14.3±2.78 sucks/24 h at 6–7 weeks of age. Individual suckling bout duration fell from 41.1±9.9 s at 1–2 weeks of age to 11.9±1.2 s by 6–7 weeks. Suckling frequencies per hour were significantly greater during daylight as compared to darkness ( p<0.05). We suggest that the declining frequency and duration of suckling bouts with age probably accounts for the waning influence of lactation on the reproductive state of the ewe, and that the maintenance of a critical interbout interval may first break down at night.

A microcomputer controlled data acquisition system for research on feeding and drinking behavior in rats

This paper describes an inexpensive, reliable computer controlled data collection system designed for the continuous monitoring of feeding and drinking behavior in rats. This system will be useful in areas of behavioral pharmacology research requiring a detailed analysis of food and fluid intake. The configuration described herein was developed for research on the “microstructure” of alcohol drinking behavior. Variables examined include: alcohol bout size, frequency and duration, interbout intervals as well as the temporal pattern of intake and its relationship to food and water consumption. Detailed analysis of behavior using this technique will enhance our ability to interpret the nature of changes in alcohol oriented behavior produced by pharmacological manipulations, aid in the development of specific hypotheses related to the regulation of alcohol drinking behavior and provide a means of testing these hypotheses.

A comparison of the effects of bilateral sections of the chorda tympani nerve and extirpation of the submaxillary and sublingual salivary glands on the eating and drinking patterns of the rat

The chorda tympani nerve (CT) innervates the fungiform papillae on the tip of the tongue and has been considered an important nerve for the sense of taste. The CT also contains the parasympathetic supply to the submaxillary and sublingual salivary glands. Therefore, changes in taste or feeding behavior following bilateral sections of CT are caused by both degeneration of fungiform papillae and the inevitable partial desalivation of the rat. In the present experiments we compared the effects of bilateral chorda tympani nerve sections with extirpation of submaxillary and sublingual glands on daily home cage eating and drinking patterns in the rat. Before and after surgery we analyzed the daily eating and drinking patterns, including such measures as intake, bout number, bout length, interbout interval and rate of consumption during bouts. The results of desalivation and bilateral CT sections were indistinguishable. The most profound change was that eating bout duration was increased following surgery. Since food intake did not increase, the results indicate a marked loss in eating efficiency over the daily ingestion periods. Although the eating patterns of desalivated and chorda tympani sectioned rats are quite similar, the evidence is not compelling that they have the same physiological basis. A second experiment was designed to test the hypothesis that the atypical eating patterns observed following bilateral sectioning of CT were the direct result of partial desalivation resulting from the denervation of the salivary glands. In this experiment a unilateral section was made of one CT and it was shown that the eating behavior was not affected. Then the contralateral submaxillary and sublingual salivary glands were removed. This resulted in a six-fold increase in feeding bout length. In all cases a unilateral CT section combined with extirpation of the contralateral salivary glands resulted in rats whose eating behavior was indistinguishable from the earlier data following either the bilateral CT sections or bilateral desalivations. The conclusion is drawn that the eating irregularities noted following bilateral CT sections result from this partial desalivation. CT sections were verified by taste bud counts in the fungiform papillae and histological examinations were made of salivary glands in rats receiving CT sections.

Feeding and drinking patterns in young pigs

Feeding and drinking patterns of six immature female pigs, weighing from 10 to 130 kg, operantly obtaining feed and water at a fixed ratio of 10, were determined. It was found by log survivorship analysis that 10 min was the minimum interbout interval defining separate eating bouts. As the pigs grew through this weight range, daily feed intake increased nearly threefold, while eating bout frequency fell from 14 to 7 per day; consequently both eating bout size and interbout interval increased. However, bout size was increased primarily by an increased rate of eating during bouts without any consistent increase in bout duration. Neither premeal nor postmeal intervals were correlated with meal size. Of the pigs' daily water intake, 75% was closely associated with eating bouts and over 1 3 of this (25%) was preprandial. Sixty-four percent of daily food intake and 68% of water intake was during the 12-hr light period. Nocturnal eating bouts were less frequent, but larger.

The influence of time constraints on diet choice of the great tit, Parus major

Great tits were given 30 or 60 s of access to food presented on a moving conveyor belt with interbout intervals of 120 s. Selectivity in a two-prey system (small and large fly pupae) was measured within access periods. The birds rejected a higher proportion of small prey during the longer foraging period, and also rejected fewer small prey with a reduction in time left within the access period (end-of-bout effect). The end-of-bout effect was greater for 30-s bouts. Previous work has shown that animals are less precise in estimating time intervals as interval length increases, and this may account for the differences in the end-of-bout effect between access periods. The birds subdivided each access period into shorter foraging subbouts, and selectivity appeared to decline within these sub-bouts. Individual differences in selectivity between birds correlated with the mean length of the individual foraging sub-bouts. Thus, when analysed over four different time scales (30-s versus 60-s access periods, time left within the access period, uninterrupted time allocated to the belt and time left within these sub-bouts), selectivity always declined with time left in the bout independently of the time scale over which the behaviour was analysed.

Thermal control of maternal contact bouts: The interbout interval

Cooling mother rats by means of sodium salicylate injections did not curtail the intervals between maternal contact bouts. To the contrary, the interbout intervals were prolonged, suggesting that the relief from hyperthermia is a necessary but not a sufficient condition for the reinitiation of pup contact by mother rats. The ability of sodium salicylate to suppress maternal temperature suggests that pyrogenic and lactational increases in temperature may have some common feature.

Determinants of mother-young contact in Norway rats

Rat dams choose to care for their pups in a relatively warm area, apparently because they have an elevated thermal set point for the regulation of their body temperature. Since the duration of their contact bouts with their pups is limited by an acute hyperthermia that they experience while on the pups, their choice limits the time that they can spend with their pups. When dams could choose the temperature at which they cared for their young they spent only about half the time in contact with their offspring as did dams caring for their pups at the ambient temperature of the laboratory. We conclude that rat dams do not attempt to maximize the duration of their contact bouts with their offspring. Dams also do not attempt to minimize the amount of time that they spend away from their offspring. The duration of the intervals between contact bouts was influenced by the ability of the dams to dissipiate the heat gained during the contact bout with the pups. Again, dams did not seek out a cool area in which to spend their interbout intervals, preferring to remain in relatively warm areas. Their thermal preference facilitated the retention of their body heat and prolongation of the interbout intervals. Dams may return to the nest periodically for brief bouts during which the state of the pups is monitored. Pups were found to play both passive and active roles in modulating the overall pattern of maternal contact, for dams maintained contact with pups if the pups were cool, but failure to attach to the nipples soon after contact was established frequently led to rapid bout termination, particularly with warm pups. Contact is maintained if the pups are cool or if they attach to the nipples. Finally, it was found that pups could actively curtail interbout intervals by emitting ultrasonic vocalizations.

Alterations in ingestive behavior following experimental portacaval anastomosis in rats

Following surgical construction of an end-to-side portacaval shunt (PCS), male rats exhibited exaggerated consumption of glucose, saccharin, saline, and ethanol solutions relative to sham-operated rats in 24-hr preference tests with water present. Spontaneous daily water intake was also increased, but daily food intake and body weight were decreased by PCS. The overconsumption of glucose, saccharin, and saline exhibited by rats with portacaval shunts was reduced, or eliminated, by providing a corn supplement to their diet, consistent with the view that the disturbance of amino acid balance may have contributed to this ingestive abnormality. In a series of short drinking tests, rats with portacaval shunts consumed more of both 10% glucose and 10% fructose (given in separate tests) than sham-operated rats and glucose intake was greater than fructose intake for both of these groups. However, neither surgical nor saccharide condition affected the duration of the first bout or the initial inter-bout interval, indicating that the relative satiating properties of these two monosaccharides were probably not altered by portacaval shunting.

The effect of postconditioning CS experience on recovery from radiation-induced taste aversion

Seventy-two hours after saccharin (CS) was paired with either a 100R or sham radiation exposure, rats received a 0-, 3-, 6-, 12-, 24-, or 46-hour saccharin-alone presentation followed by a 23-hour two-bottle preference test. Generally, faster recovery from the aversion was observed in animals receiving longer CS-alone presentations. The present procedure differs from previous work done with other toxins in that animals were not fluid-deprived during the postconditioning period. This enabled animals to constantly control the volume, duration, and inter-bout interval of the saccharin drinking episodes independent of any experimentally imposed drinking schedule. In addition, the two-bottle test provided a sensitive measure of the status of the saccharin aversion following the saccharin-alone presentation.

Why do meadowlarks switch song types?

Singing of eastern and western meadowlarks, Sturnella magna and S. neglecta, was monitored during 85-min experiments in which 13 1-min bouts of recorded conspecific song were broadcast at irregular intervals. Both species tended to switch song types at the onset of playback. Song bouts of magna were shortened in playback periods, with multiple switches occurring; bouts of neglecta during playback were of normal length. Overall, bouts of magna were shorter than those of neglecta. When playback began, long bouts were more likely to end in a switch than shorter ones. Survivorship curves of completed bouts for both species followed a log-linear function; beyond a minimum length switching was independent of previous bout length. Lengths of successive bouts were positively associated in birds with short bouts (mainly magna) but not in birds with longer bouts (mainly neglecta). Switching was associated with long interbout intervals and with movements, although most switches occurred in short intervals without movements. These results are mainly consistent with the hypothesis that delivery of repertoires reduces habituation of listeners. This antihabituation mechanism is distinguished from other explanations for repertoires. A derivative explanation, that song variety serves as a graded signal of readiness to interact (inter- or intra-sexually), is suggested and predictions are discussed.

Short-term regulation of food intake by the brown honeyeater, Lichmera indistincta

1. 1. Regardless of nectar concentration, there are strong positive correlations between the durations of feeding bouts by Lichmera indistincta and subsequent inter-bout intervals, and energy intake during feeding bouts and energy expenditure during subsequent inter-bout intervals. 2. 2. Energy utilization by L. indistincta conforms to an accumulation-depletion model, with a portion of the energy acquired during each feeding bout contributing to the gradual diurnal storage of energy that is subsequently used for maintenance during non-foraging periods. 3. 3. L. indistincta compensates for a decrease in nectar concentration by increasing the frequency of feeding bouts and decreasing the duration of inter-bout intervals. 4. 4. Changes in the duration of inter-bout intervals caused by alterations to the calorific value of nectar drunk can be explained in terms of the rate at which the stomach empties.

Nursing frequency, gonadal function, and birth spacing among !Kung hunter-gatherers.

Mothers among !Kung hunter-gatherers nurse briefly and frequently, with brief intervals between nursing bouts (mean +/- standard error, 13.19 +/- 1.28 minutes). The low levels of 17 beta-estradiol and progesterone in the serum of the mother are correlated with infant's age and with interbout interval, but not with total nursing time. Maternal gonadal function is apparently suppressed by a timing-dependent, prolactin-mediated effect of breast stimulation. Interbout interval may be a key variable in lactation infertility. If so, it solves the puzzle of !Kung birth spacing.