Biomedical subjects

D W Schaal

Publications and source records attributed to D W Schaal.

24 records · Page 2Linked to original sources

PubMed1992

Effects of neuropeptide Y on food-reinforced behavior in satiated rats.

The effect of NPY on behavior and food intake of food-satiated rats was examined under three different food availability conditions. Food was available during times when rats normally do not eat under either a fixed-ratio or fixed-interval reinforcement schedule, or it was freely available in the bottom of the cage (FF). Forty responses were required for each 45-mg food pellet under the ratio schedule (FR 40) and for the first response to occur 15 s after the previous reinforcement under the interval schedule (FI 15"). NPY (5 micrograms) significantly increased food intake under all conditions and increased food-reinforced responses under the FR and FI schedules. NPY's effect on food intake was greatest when food was freely available and least for rats working under the schedule requiring the most effort (FR 40). Food intake peaked after 3 days under repeated daily administration of NPY. Under free food access and under the fixed-interval schedule, eating and/or responding occurred almost immediately following the onset of the initial 4-h session under NPY. However, during the first session following NPY administration under the FR, rats emitted few responses during the first 2 h of the session. The onset of robust responding under the FR schedule began earlier with each successive daily administration of NPY. These data show NPY substantially increases food-maintained behavior and is a potent inducer of food intake even under conditions where considerable effort is required to obtain food. Further, the conditions under which food is made available can dramatically alter NPY's effect on the temporal pattern of food-maintained responding, feeding, and latency to eat.

Animals↗

PubMed1992

Key pecking of pigeons under variable-interval schedules of briefly signaled delayed reinforcement: effects of variable-interval value.

Key pecking of 4 pigeons was maintained under a multiple variable-interval 20-s variable-interval 120-s schedule of food reinforcement. When rates of key pecking were stable, a 5-s unsignaled, nonresetting delay to reinforcement separated the first peck after an interval elapsed from reinforcement in both components. Rates of pecking decreased substantially in both components. When rates were stable, the situation was changed such that the peck that began the 5-s delay also changed the color of the keylight for 0.5 s (i.e., the delay was briefly signaled). Rates increased to near-immediate reinforcement levels. In subsequent conditions, delays of 10 and 20 s, still briefly signaled, were tested. Although rates of key pecking during the component with the variable-interval 120-s schedule did not change appreciably across conditions, rates during the variable-interval 20-s component decreased greatly in 1 pigeon at the 10-s delay and decreased in all pigeons at the 20-s delay. In a control condition, the variable-interval 20-s schedule with 20-s delays was changed to a variable-interval 35-s schedule with 5-s delays, thus equating nominal rates of reinforcement. Rates of pecking increased to baseline levels. Rates of pecking, then, depended on the value of the briefly signaled delay relative to the programmed interfood times, rather than on the absolute delay value. These results are discussed in terms of similar findings in the literature on conditioned reinforcement, delayed matching to sample, and classical conditioning.

Animals↗

PubMed1991

The discriminative stimulus effects of neuropeptide Y.

Neuropeptide Y (NPY), an endogenous peptide which strongly induces food intake, is demonstrated to have discriminative stimulus properties when administered intracerebroventricularly. Rats rapidly learned to press the appropriate lever during training. NPY discrimination was dose-dependent. NPY's discriminative stimulus properties were compared to those of two doses of Peptide YY (PYY) and 24 and 48 h of food deprivation, conditions which also increase feeding. Both doses of PYY generalized to NPY, supporting previous findings that PYY has effects similar to NPY. Although food deprivation increases feeding in a manner similar to NPY, food deprivation did not result in NPY-appropriate responding.

Animals↗

PubMed1990

Responding of pigeons under variable-interval schedules of signaled-delayed reinforcement: effects of delay-signal duration.

Two experiments with pigeons examined the relation of the duration of a signal for delay ("delay signal") to rates of key pecking. The first employed a multiple schedule comprised of two components with equal variable-interval 60-s schedules of 27-s delayed food reinforcement. In one component, a short (0.5-s) delay signal, presented immediately following the key peck that began the delay, was increased in duration across phases; in the second component the delay signal initially was equal to the length of the programmed delay (27 s) and was decreased across phases. Response rates prior to delays were an increasing function of delay-signal duration. As the delay signal was decreased in duration, response rates were generally higher than those obtained under identical delay-signal durations as the signal was increased in duration. In Experiment 2 a single variable-interval 60-s schedule of 27-s delayed reinforcement was used. Delay-signal durations were again increased gradually across phases. As in Experiment 1, response rates increased as the delay-signal duration was increased. Following the phase during which the signal lasted the entire delay, shorter delay-signal-duration conditions were introduced abruptly, rather than gradually as in Experiment 1, to determine whether the gradual shortening of the delay signal accounted for the differences observed in response rates under identical delay-signal conditions in Experiment 1. Response rates obtained during the second exposures to the conditions with shorter signals were higher than those observed under identical conditions as the signal duration was increased, as in Experiment 1. In both experiments, rates and patterns of responding during delays varied greatly across subjects and were not systematically related to delay-signal durations. The effects of the delay signal may be related to the signal's role as a discriminative stimulus for adventitiously reinforced intradelay behavior, or the delay signal may have served as a conditioned reinforcer by virtue of the temporal relation between it and presentation of food.

Animals↗

PubMed1988

Responding of pigeons under variable-interval schedules of unsignaled, briefly signaled, and completely signaled delays to reinforcement.

In Experiment 1, three pigeons' key pecking was maintained under a variable-interval 60-s schedule of food reinforcement. A 1-s unsignaled nonresetting delay to reinforcement was then added. Rates decreased and stabilized at values below those observed under immediate-reinforcement conditions. A brief stimulus change (key lit red for 0.5 s) was then arranged to follow immediately the peck that began the delay. Response rates quickly returned to baseline levels. Subsequently, rates near baseline levels were maintained with briefly signaled delays of 3 and 9 s. When a 27-s briefly signaled delay was instituted, response rates decreased to low levels. In Experiment 2, four pigeons' responding was first maintained under a multiple variable-interval 60-s (green key) variable-interval 60-s (red key) schedule. Response rates in both components fell to low levels when a 3-s unsignaled delay was added. In the first component delays were then briefly signaled in the same manner as Experiment 1, and in the second component they were signaled with a change in key color that remained until food was delivered. Response rates increased to near baseline levels in both components, and remained near baseline when the delays in both components were lengthened to 9 s. When delays were lengthened to 27 s, response rates fell to low levels in the briefly signaled delay component for three of four pigeons while remaining at or near baseline in the completely signaled delay component. In Experiment 3, low response rates under a 9-s unsignaled delay to reinforcement (tandem variable-interval 60 s fixed-time 9 s) increased when the delay was briefly signaled. The role of the brief stimulus as conditioned reinforcement may be a function of its temporal relation to food, and thus may be related to the eliciting function of the stimulus.

Journal Article↗

PubMed1987

Alterations in the effects of atropine on the behavior of pigeons following chronic administration.

The acute effects of atropine (0.01-1.0 mg/kg) on pigeons' key-pecking maintained under a variable-interval (VI) 60-sec schedule of food reinforcement were determined. Atropine decreased key-peck rates in a dose-dependent manner. A rate-decreasing dose of physostigmine, an acetylcholinesterase inhibitor, was studied in combination with the range of atropine doses. The rate reduction produced by physostigmine was attenuated by some doses of atropine. An atropine dose which decreased key-peck rates was then administered to the pigeons every day after their experimental sessions (chronic post-session phase). During this regimen, the dose-effect curves for atropine and the combination of atropine and physostigmine were redetermined. Atropine was then given chronically prior to experimental sessions (chronic pre-session phase), and the dose-effect curves for atropine and the combinations of atropine and physostigmine were determined again. The pigeons became tolerant to the rate-reducing effects of atropine following chronic post-session administration. Physostigmine's effect alone was unchanged following chronic atropine administration for two pigeons, and was slightly greater for a third. The rate reduction caused by physostigmine was attenuated across a wider range of atropine doses in the two pigeons for which the effect of physostigmine alone was unchanged. The atropine/physostigmine interaction curve for the third pigeon was shifted to the right following chronic post-session atropine administration. No further changes in effects of either atropine alone or in combination with physostigmine were seen following chronic pre-session atropine administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗