Cora Lee Wetherington

Schedule control of eating by fixed-time schedules of water presentation

Eating was measured in water-deprived rats when water was presented at regular intervals ranging from 30 to 240 sec. The temporal patterning of eating resembled that of schedule-induced behavior in that the probability of eating was high early in the interval and declined in the end of the interval. Additionally, (a) the number of pellets consumed was controlled by relative time in the interwater interval, (b) the pellets consumed per water presentation was inversely related to water rate, and (c) food-ingestion rate was directly related to water rate. These relationships parallel those found with behavior regarded as schedule induced.

Schedule-Induced Running and Chamber Size

Running-wheel behavior was examined as a function of the floor area of the experimental chamber in three food-deprived rats when a food pellet was delivered each minute and when it was omitted. Running-wheel behavior when food was omitted was unsystematically related to the floor area. When food was scheduled, three measures of running-wheel behavior were found to be decreasing functions of floor area: percentage of the session time spent in the wheel, percentage of the interfood intervals with a wheel entry, and the mean stay time per interfood interval with a wheel entry. Wheel revolutions per session varied unsystematically, and the local rate of running was an increasing function of floor area when food was scheduled. These results explicate some inconsistent findings in the literature, and provide support for the notion that wheel-running is not a schedule-induced behavior.

The effects of variations in the interpellet interval on wheel running in the rat

Three rats were given access to a running wheel during spaced food deliveries. As the interpellet interval increased, the overall amount of running increased, the rate of running neither systematically increased nor decreased, and the locus of maximal running occurred later in the interpellet interval. Both the overall amount and the temporal distribution of running exhibited considerable within-schedule changes during successive exposures to the different schedules. These data are discussed in terms of Staddon’s (1977) assignment of behavior into different functional classes, that is, schedule-induced and facultative.

The differential effects of naloxone hydrochloride on the acquisition and maintenance of schedule-induced polydipsia

Rats injected with the opiate antagonist, naloxone hydrochloride (10 mg/kg), 15 min prior to sessions in which they were given free food on a fixed time 75-sec schedule, displayed retarded acquisition of schedule-induced polydipsia relative to vehicle-injected subjects. Rats injected with naloxone after schedule-induced polydipsia had been acquired were unaffected, i.e., they continued to drink at control levels. Given that schedule-induced polydipsia has been considered non-opioid in nature, because of previous reports of its insensitivity to naloxone, the present report of differential effects of naloxone on the acquisition and maintenance of schedule-induced polydipsia suggests that some modification of this conclusion is necessary. Possible alternative mechanisms for these differential effects are discussed.

Schedule-induced polydipsia: Interactions with wheel running

The effect of wheel running on the level and temporal distribution of schedule-induced polydipsia was examined in 12 food-deprived rats given one food pellet per minute for 1 h. For all rats, wheel running decreased the level of Polydipsie intake. It also decreased licking in all six of the 10-sec postpellet intervals except the first. The degree of reduction in licking was a U-shaped function of the 10-sec postpellet intervals and was generally inversely related to the temporal distribution of running. The temporal distribution data are partially consistent with a temporal competition view of the interactions between schedule-induced polydipsia and wheel running

Diminution of schedule-induced polydipsia after a long rest period

Schedule-induced polydipsia was established in four food-deprived rats given daily hourly sessions in which a food pellet was presented once each min. Sessions were then discontinued for approximately six months. After this rest period, the daily sessions were resumed. Relative to the water intake during the last five sessions prior to the rest period, water intake during the first five sessions after the rest period exhibited a 55.5%, 10.3%, 32.0% and 29.6% decrement for the four rats, respectively. These results are discussed in terms of a sensitization view of schedule-induced polydipsia.

Differences in food consumption under intermittent and continuous reinforcement schedules of water delivery: Some implications for schedule-induced behavior

Consumption of food pellets was examined in four water-deprived rats during 1-h sessions in which water was presented once every 30, 60, or 120 sec independently of the rats’ behavior according to three fixed-time (FT) schedules. Correlated with each FT condition was a continuous reinforcement (CRF) control condition in which the rats received, at the start of the session, the number of dipper presentations that were programmed to occur during the corresponding FT condition. During both the FT and CRF conditions, pellets per dipper presentation decreased and food intake rate increased with rate of water presentation, and there was a direct linear relation between log food intake and log water intake. For each of these three measures there was less eating under the FT condition than under the CRF condition, but the difference between the FT and CRF functions decreased at shorter FT values. These data are discussed in terms of the effects of amount of water on food consumption and the principle of temporal summation.

A software package for the microcomputer control and analysis of research on schedule-induced polydipsia.

This manuscript describes a software package called POLY which offers a range of routines designed to allow the user to set up, run and analyze data for research on schedule-induced polydipsia. The three major routines described are SETUP, RUN and ANALYSIS. The routines are flexible and give the user efficient control over the parameters of the research and the collection and analysis of the data. Although designed for research on schedule-induced polydipsia, the software can be used for other research purposes, requiring only changes in the support hardware.

Schedule-induced polydipsia and size of water dipper

Schedule-induced polydipsia as a function of six water dipper sizes was examined in four food-deprived rats under Fixed Time 1- and 2-minute schedules. Increasing dipper size increased session water intake but did not affect the number of intervals containing at least one barpress (i.e., number of bouts), nor the number of barpresses per bout, nor the temporal distribution of barpressing within the interfood interval. Previous research showing polydipsic intake to be impervious to other types of restrictions on water availability have suggested the notion of a volume constancy mechanism. The present research raises questions about the operation of the volume constancy mechanism, questions about how to conceptualize the dipper size manipulation, and questions about variables which affect the temporal locus of drinking.