Noyes Pellets Research Articles

Retention of Ordinal Position Information with Limited and Extended Serial Training

To examine the possibility that position cues are temporal and therefore ineffective early in serial runway training, rats were runway trained on a three-trial series of different rewards. The series was SNP', where Sand P' refer to series trials that concluded with four sucrose or eight plain Noyes pellets, respectively. The middle trial was never rewarded (N) . Early in training, a significant pattern of running slowly on the middle trial and rapidly on the initial and terminal trials had emerged. Transfer tests to series of trials (NNN) never rewarded after this limited training (on Day 19) and later after extended training (Day 39) , each gave evidence that the rats relied upon position cues in the tests. The three-trial patterns established before the tests were retained on the three trials of the NNN series. The results suggest the prevalence of position learning, but they work against the idea that position cues are temporal and effective only with extended training.

Ordinal Position Learning and Remote Anticipation

Rats were runway trained on each of two 3-trial series of reward outcomes. The series are labeled XNY and ZNN, for which X represents a trial that was rewarded with Noyes pellets and N represents a trial that ended with no reward. Units of distinctively flavored breakfast cereals served as reward on trials labeled Y and Z. One group (Floor) had each series occur with a correlated runway floor, either smooth and black or rough and white. For a second group (Memory), the floor cue was uncorrelated with series. Animals in both groups learned to approach the goal rapidly on the 1st trials of the 2 series and slowly on the 2nd trials, but only Group Floor learned to differentiate the 3rd trials of the series. These results recommend a view of serial learning that emphasizes the role played by information about the ordinal position of series items.

Rate of reinforcement and session duration as determinants of within-session patterns of responding

Rats pressed levers for Noyes pellets or keys for sweetened condensed milk reinforcers delivered by multiple schedules. Session length and baseline rates of reinforcement were varied in two experiments. Rates of responding increased during the early part of the session and then decreased for both responses and reinforcers, as well as for all subjects and values of the independent variables. Changes in response rates across the session sometimes exceeded 500%. Respoiise rates peaked approximately 20 min after the beginning of the session, regardless of session duration, when subjects responded on a multiple variable interval 1-min variable interval 1-min schedule. The function was flatter for longer sessions than it was for shorter sessions. The function was flatter, more symmetrical, and peaked later for lower rates of reinforcement than for higher rates of reinforcement. The function appeared early in training, and further experience moved and reduced its peak. Variables related to reinforcement exerted more control over some aspects of this function than did variables related to responding. These within-session patterns of responding may have fundamental implications for experimental design and theorizing.

Numerically restricted food intake in the rat in a free-feeding situation

Rats were trained to leave an array of food after they had consumed a fixed number (three, four, or five) of food items. This discrimination remained in effect despite a shift from 45-mg Noyes pellets to larger and irregularly sized sunflower seeds. The present demonstration replicates work first reported 50 years ago by Otto Koehler and his associates (e.g., Marold, 1939; see also Koehler, 1950), who used avian subjects, and, like those studies, it involved both positive and negative social reinforcement. The present procedure provided a rare instance in which numerical control was exerted over behavior that was primarily consummatory in nature. The results are viewed in terms of the wider literature of numerical competence in animals and are discussed in terms of a numerical process known asprotocounting (Davis & P’erusse, 1988b).

Numerical and Sensory Categorization of Serial Information by Animals

Rats were trained in a straight runway on a series consisting of 4 elements, each element being defined in terms of the number of .045-gm. Noyes pellets used as reward on 4 runway trials separated by about 20 sec. The series elements were 2, 6, 12, and 0 (2-6-12-0). The animals were trained each day on 3 such series, the series themselves being separated within a day by about 12 min. for 28 days before introducing a new transfer series to assess the relevance of the order of the series elements. In previous experiments with the simpler series, 2-12-0, alterations in order of elements eliminated the animals' tendencies to run much slower to the terminal nonreward element of the series, but transfer was clearly shown here when we shifted from 2-6-12-0 to 6-12-2-0. That is, the animals continued on the transfer test to approach the terminal element slowly, a result which we interpret as supporting the view that the rats either counted the rewarded trials and used that count to predict terminal nonreward, or they behaved on the basis of cues associated with the ordinal position of the trial.

NUMERICAL AND SENSORY CATEGORIZATION OF SERIAL INFORMATION BY ANIMALS

Rats were trained in a straight runway on a series consisting of 4 elements, each element being defined in terms of the number of .045-gm. Noyes pellets used as reward on 4 runway trials separated by about 20 sec. The series elements were 2, 6, 12, and 0 (2-6-12-0). The animals were trained each day on 3 such series, the series themselves being separated within a day by about 12 min. for 28 days before introducing a new transfer series to assess the relevance of the order of the series elements. In previous experiments with the simpler series, 2-12-0, alterations in order of elements eliminated the animals' tendencies to run much slower to the terminal nonreward element of the series, but transfer was clearly shown here when we shifted from 2-6-12-0 to 6-12-2-0. That is, the animals continued on the transfer test to approach the terminal element slowly, a result which we interpret as supporting the view that the rats either counted the rewarded trials and used that count to predict terminal nonreward, or they behaved on the basis of cues associated with the ordinal position of the trial.

A test for S-S associations in a conditional counting task

Conditional numerical discriminations were established in runway-trained rats by presenting daily a pair of reward series that differed in the number of rewarded trials preceding a terminal nonrewarded trial. One kind of series contained three rewarded trials (RRRN or NRRRN), which always occurred in either a smooth, black runway or a rough, white runway (counterbalanced). The other series contained four rewarded trials (RRRRN or NRRRRN), which occurred in a runway of the other brightness and texture. The reward on each rewarded trial was 5.045-g Noyes pellets until Day 22. For Days 22-32, the series containing four Rs was altered so that the number of pellets on each respective trial was 14, 7, 3, and 1. To test whether S-S associations controlled the serial discriminations after Day 32, we rearranged the order of elements in the 14-7-3-1-0 series to 20-7-3-14-0. Rapid approach to the terminal series element on the test day would have implied the operation of S-S associations (14 pellets would have been a cue for upcoming 7, not 0), but the approach to that element remained slow, suggesting that the animals continued their counting of rewarded trials during the training with the S-S-relevant 14-7-3-1-0 series, irrespective of the order of the series elements.

LESIONS OF THE AMYGDALOID COMPLEX IMPAIR ACQUISITION OF SERIAL PATTERN LEARNING IN RATS

Normal and amygdala-lesioned rats were trained in a runway to respond to a three-element pattern ending in 2, 12, or 0 Noyes pellets (45 mg), respectively. The amygdalectomized rats' performance was inferior to that of normal controls during the early and middle stages of training, that is, amygdalectomized rats ran more slowly on rewarded trials and developed patterned running later than control rats. In the later stages of training, the lesioned rats demonstrated tracking of the series elements, reflected by differential running times similar to those of the control animals. Results are discussed in terms of some of the current theories involving the role of the amygdaloid complex in learning and reinforcement.

The effects of response contingency and reinforcement identity on response suppression by alternative reinforcement

Rats were trained on a multiple schedule in which lever pressing was reinforced in one component and nose poking was reinforced in the other. The reinforcers contingent on the two responses were always different, either corn oil or Noyes pellets. A schedule of alternative reinforcement was superimposed in each component, either presenting the same reinforcer as that contingent on the lever/key, or the alternative reinforcer. When the alternative reinforcers were freely presented on a variable time (VT) schedule, their suppressive effects were substantially larger when the free reinforcer was the same as the reinforcer contingent on the lever/key than when it was different. But when the alternative reinforcers were presented according to a variable-interval schedule for a third response (rod pressing), the differences caused by the nature of reinforcement were greatly reduced and not statistically significant. Similar effects occurred when the alternative reinforcement was presented on a VT schedule but preceded by a signal. The results suggest that the effects of alternative reinforcement cannot be explained solely in terms of relative reinforcement rate.

Some further observations on serial enumeration and categorical flexibility

Rats were runway-trained in a variety of serial discriminations that involved three different reward outcomes: Noyes pellets (R), a Kellogg’s Corn Pop (R’), and 30 sec of confinement in an unbaited goal area (N). Each of three groups experienced a series that consisted of a single non-rewarded trip down the runway, irregularly mixed with a longer series that for one group (n = 3) consisted of three trips rewarded with the pellets, followed by a terminal nonrewarded trip (RRRN/N). A second group (n = 6) had the single N series mixed with a series that included an initial trip rewarded with a Pop, and three subsequent trips rewarded with pellets, pellets, and nothing, respectively (R’RRN/N). The remaining group was trained with an RRN/N series pair. The interval between trips within a series was about 20 sec, and the interval between series was about 10 min. All rats developed strong, accurate anticipation of the terminal nonreward event of the longer series. In a 4-day transfer shift phase, a matched one-half of the rats originally trained R’RRN/N were shifted to a new series pair, RRRN/NRRRN, as were all the animals trained RRN/N. The remaining one-half of the matched rats were shifted to RRN/NRRN, as were the animals originally trained on the RRRN/N series pair. The transfer to the new series was plainly more powerful in animals initially trained with the R’RRN series than it was in either of the control groups. This shift result is taken to mean that rats classified the differing motivational events of the R’RRN series into at least three numerical categories: (1) one R’, (2) two Rs, and (3) three rewards.

Obese male mice (ob/ob) are normally sensitive to the satiating effect of CCK-8

The ob/ob mouse has a defect in short-term satiety mechanisms because ob/ob mice eat larger meals than leans and have abnormal postprandial behaviors. We suggested that this defect involved a failure to release CCK normally in response to ingested nutrients and/or decreased receptor sensitivity to CCK [7]. McLaughlin and Baile [3] reported that female obese mice were less sensitive to the satiating effect of CCK-8, a result consistent with the hypothesis of decreased receptor sensitivity. To investigate this possibility further, we determined the sensitivity to exogenous CCK-8 of obese and lean male mice. Adult male C57B1/6J ob/ob and male +/+ controls were injected with CCK-8 (1,2,4 and 8 μg/kg, IP) 15 min prior to the presentation of solid food (Noyes pellets) after 4.5 hr food deprivation in the dark. Food intake (FI) was measured at 30 min and 150 min. CCK-8 decreased FI during the first 30 min in both obese and lean mice ( p < 0.01). The threshold dose for inhibition of FI was 2 μg/kg in obese and 4 μg/kg in lean. Since obese mice weighed approximately twice as much as lean mice, their total dose of CCK-8 was equal to that of lean mice. Thus, obese male mice were at least as sensitive to the satiating effect of CCK-8 as lean male mice. These results do not confirm McLaughlin and Baile's result in female mice eating in the light and they suggest that the defect in satiety in obese male mice is not the result of decreased sensitivity of CCK receptors.

The Goal Units Dimension in Negative Contrast Failures with Sucrose

Summary To pursue the possibility that the usual failure to obtain the successive negative contrast effect (SuNCE) with sucrose rewards is an indirect consequence of the liquid medium in which sucrose is usually delivered, Experiment 1 was designed to look for the SuNCE with sucrose pellets. Food-deprived rats were trained for 20 preshift days, two trials/day in a runway for either one or 12 45-mg Noyes pellets of either sucrose or standard formula. During six postshift days, 10 trials/day, all rats were given the one-pellet reward of the same preshift type, and the SuNCE appeared in the standard but not sucrose groups. A second experiment produced single-alternation patterning in the discrete-trial lever pressing of rats given four two-trial sequences of one or 10 sucrose or standard pellets each day for 102 days. The patterning was potentiated with a change, for the remaining 28 days, from the one-pellet reward to nonreward, but in no case throughout the experiment was the strength of patterning any dif...

Preference for Predictable Small Rewards over Unpredictable Larger Rewards

Numerous prior studies have reported that rats, pigeons, and humans prefer predictable over unpredictable rewards of equal frequency and magnitude. A frustration-theory analysis of this preference suggests that it obtains because the unpredictable partial reinforcement procedure is aversive whereas the predictable discrimination procedure loses its aversiveness. The preference, on such an analysis, arises due to the tendency to avoid the unpredictable of two alternatives. Since frustration varies as a function of magnitude of reward, the avoidance tendency should increase with increases in reward magnitude in the unpredictable alternative. One group of rats in the present study showed a clear preference for seven versus five 45-mg Noyes Pellets. A second group showed the oft reported preference for five pellets predictable versus five pellets unpredictable. A third group of rats showed a preference for a five-pellet predictable reward over a seven-pellet unpredictable reward. The results of this experiment provide evidence for a frustration-theory analysis of the preference for predictable reward.

Continuous infusion of cholecystokinin and meal pattern in the rat

Purified natural cholecystokinin (CCK-33) was infused continuously for two days at a rate of 5.9 μg/hr in two rats trained to bar-press for food (Noyes pellet 45 mg) on a fixed ratio of five bar presses to obtain one pellet. The animals also received control surgery and were tested in the operant chamber for two days, one prior to and the other following the CCK-33 treatment. CCK-33 suppressed the number of meals, the total amount of food eaten, and the total duration of time spent eating. However, the size of each meal and the rate of intake were not affected. The CCK effect did not interact with the light-dark phases of diurnal cycle. It appears that a major effect of continuous systemic elevation of CCK-33 is to reduce food intake by prolonging the satiety period rather than by decreasing the individual meal size.

Sex differences in the effects of high-fat feeding on behavior and carcass composition

Male and female Sprague-Dawley rats were fed a high-fat diet (40% by weight) for 11 weeks beginning at 70–80 days of age. At the end of the 11th week, high-fat fed rats of both sexes were significantly heavier than chow-fed controls. All rats were then food deprived and were trained to bar-press in an operant chamber for Noyes pellets. Testing on fixed ratio (FR) schedules started when their body weights reached 85% of pre-deprivation levels and they pressed bar steadily. At the end of operant testing, all rats were refed their previous diet until body weights returned to pre-deprivation levels. The animals were then sacrificed. Fat pads from retroperitoneal, inguinal and gonadal regions were dissected out and cellularity determined. Carcass composition was analyzed by chemical methods. On the operant apparatus, the high-fat fed female rats (F-HF) behaved more like VMH lesioned obese rats, i.e. decreased bar pressing responses when compared with controls. No difference in operant responding was found between males fed high-fat diet and chow. Fat cell number and size were increased in retroperitoneal and inguinal fat pad for rats fed high-fat diet. In gonadal pads, only cell size was increased. Females on the high-fat diet had higher percentages of body fat than males on the high-fat diet. The behavioral difference in F-HF rats could be attributed to their higher adiposity. The results support previously reported findings on the behavior and adipose tissue cellularity of dietary obese rats.

Random and fixed two-trial sequences of reward magnitudes

Albino rats were trained in a straight runway for 110 days, two trials/day, with an inter-trial interval of 3-5 min. One trial each day ended in large reward (10 standard Noyes pellets for one group, 1 ml of 30% sucrose solution for another) and the other trial ended with small reward (1 pellet or 3% sucrose). The daily sequence of reward magnitudes, either small-large (SL) or large-small (LS), was determined by pseudorandom orders, so that a block of 8 days contained 4 SL and 4 LS days. For 20 days following this random-sequence training, all rats received fixed sequences, always SL or always LS, with the same reward type (standard pellets or sucrose solutions) as that used during random-sequence training. Differential running for different reward magnitudes (patterning) did not develop during random-sequence training with either reward type. The fixed-sequence training generated patterning on Trial 2 but not on Trial 1. The data are discussed in the light of several possible sources of the stimulus control of patterning, and implications of the data for a sequential account of the successive negative contrast effect are briefly considered.

Pancreatic glucagon administration, feeding, glycemia, and liver glycogen in Rats

Rats were trained to bar press for Noyes pellets. Once trained, subjects were food deprived at 0800, injected with pancreatic glucagon or isotonic saline (0.35 mg/kg BW, intraperitoneally in a volume of 0.1 cc per 300 g BW) at 1100, and then placed in the operant chamber at 1115 or 1415 for a duration of 3 hr. Animals placed immediately in the chamber showed a suppression of food intake accomplished by a lengthening of the interval following the first meal rather than a reduction in the size of that meal. Animals tested 3 hr post-injection showed an enhancement of feeding by increasing the size of the first meal compared to saline-injected subjects, p<0.025. The behavioral effects of glucagon upon feeding depend on the point of the sequence of responses to the hormone during which the animal is studied. Early after glucagon administration, hyperglycemia and increased glucose utilization predominate and feeding was reduced; subsequently, blood glucose may be normal while the liver remains somewhat glycogen depleted and feeding is enhanced.

Effects of response-contingent clock stimuli on behavior maintained by intravenous codeine in the rhesus monkey

Response-contingent brief presentations of clock stimuli differentially correlated with food availability altered rates of codeine-maintained lever pressing. Rhesus monkeys performed under a two lever multiple schedule: Multiple fixed interval clock 5 min variable interval 2 min. Different colored lights were presented during successive 75 sec periods of the fixed-interval clock component. Lever pressing under the FI Clock schedule was maintained by presentation of 1 g Noyes pellets, and lever pressing under the VI schedule by 0.05 mg/kg infusions of codeine PO 4. Characteristic schedule-controlled performance developed in both schedule components. When the clock stimulus from the first or the final period of the FI Clock schedule was presented contigent upon completion of a short fixed ratio of responses during the variable-interval schedule component, the first clock stimulus decreased and the final clock stimulus increased rates of codeine-maintained lever pressing. Neither the first nor the final clock stimulus altered the frequency of codeine injection. The effect of each clock stimulus was accentuated by increasing the duration of stimulus presentation and by decreasing the response requirement for stimulus illumination. These rate-altering effects of the clock stimuli were most pronounced when different reinforcers were presented in the two components of the multiple schedule when either food or intravenous codeine injection was available under both components of the multiple schedule, response-contingent clock stimulus presentation did not alter response rates under the VI schedule.

Failure to demonstrate schedule-induced polydipsia in the degu (Octodon degus).

When rats are food-deprived and placed on an intermittent focd reinforcement schedule, they develop a post-pellet pattern of drinking which is excessive in amount. This excessive drinking is called schedule-induced polydipsia ( 1 ) . One characteristic is the generalicy to a large number of different species (1, 2 ) . However, hamsters do not show schedule-induced polydipsia ( 4 ) . In the present study a South American rodent (found in Peru and Chile), the Degu (Octodon d e g w ) , was tested. Two male (208 and 298 gm) and two female (225 and 287 gm) Degu were fooddeprived and reduced to 80% body weight. Daily l-hr. test sessions were conducted in a srandard operant chamber with a food magazine and a water bottle (no lever was present). The operant chamber was housed in a sound-attenuated cubicle. Food pellets (45-mg Noyes Pellets) were delivered according to a fixed time 1-min. (FT l-min.) food reinforcement schedule, in which one pellet was delivered every minute independently of the animal's behavior. Test sessions were conducted for 14 days. All four animals were observed to eat the food pellets readily, with a fairly short latency after pellet delivery (never more than 10 sec.). However, none of the animals developed schedule-induced polydipsia. In fact, the animals never drank from the water bottle in the test chamber in any session. This contrasrs with the rypical patter0 for domesticated rats who usually make some contact with the water bottle during the very first session, and develop schedule-induced polydipsia within 5 ro 10 sessions ( 1 ) . The present data from the Degu and the data from hamsters ( 4 ) suggcsr that schedule-induced polydipsia may have some species limitations. Habitat variables must also be considered given that both the hamster and Degu appear to inhabit somewhat marginal, at least seasonally semi-arid biotopes ( 3 ) . Current explanations ( 1 ) must be revised to accounr for possible species limitations if future research supports these findings.

Active regulation to be lean by rats with ventromedial hypothalamic lesions.

Adult female Long-Evans rats with direct-current electrolytic or radio-frequency thermocoagulatory lesions of the ventromedial hypothalamus (VMH) lived on pellet fragments or a powdered chow containing as much as 1.2% quinine sulfate by weight or lived in Skinner boxes with 45-mg Noyes pellets delivered contingent on fixed ratios (FR) of lever pressing up to FR 128. As had been found previously for intact rats, the body weights maintained by VMH rats were determined by the percentage of quinine sulfate in or the contingency of reinforcement of the food on which they lived. Even when the rats lived on highly adulterated or response-contingent food and were lean, they ate more of that food when the ambient temperature was reduced and less of that food during several weeks of forced feeding of eggnog by gavage. Weight maintenance in the cold and caloric compensation during forced feeding were as precise for VMH rats eating highly adulterated chow or Noyes pellets contingent on high fixed ratios of lever pressing as for VMH rats eating typical laboratory chow ad lib, even though the former rats at the time maintained weights no greater than intact rats and the latter rats at the time were grossly obese. Furthermore, regulation in the cold or during forced feeding was in general only a little less precise for the rats with lesions than for intact rats. It may be as characteristic of VMH rats that they eat to become lean and remain lean as that they eat to be obese. The diets of both intact and VMH rats in some manner determine the adiposities that rats will defend against caloric challenge.