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T Sagvolden

Publications and source records attributed to T Sagvolden.

At least 37 records · Page 2Linked to original sources
PubMed1992

The hyperactive spontaneously hypertensive rat learns to sit still, but not to stop bursts of responses with short interresponse times.

The spontaneously hypertensive rat (SHR) is hyperactive and has been proposed as an animal model of attention-deficit hyperactivity disorder (ADHD). Although ADHD in most cases is treated with central stimulants, behavior therapy has also been used, but with relatively limited success. The purpose of the present study was to investigate suppression of SHR hyperactivity by differentially reinforcing immobility (DRI) using a positive reinforcer. The DRI schedule required that the rat remain immobile in a particular part of an operant chamber, the target, in order to obtain the reinforcer. The time requirement, the DRI value, of these periods was increased progressively. The results showed that time spent on the target increased by increasing DRI value in both hyperactive and control rats. However, the total number of movements, on as well as outside the target, was higher for the hyperactive rats. The behavior grouped into two independent response components. One component consisted of immobility responses with durations less than 1 s, actually bursts of active responses; the other component consisted of immobility responses with durations more or less matching the DRI requirement. The reinforcement schedule modified the long-lasting immobility component in both groups. SHR received more reinforcers than WKY as long as the schedule did not require too long periods of immobility. However, the total number of movements on target was not reduced in SHR; on the contrary, it increased somewhat as the schedule requirements increased. If the behavior of ADHD children consists of two, or more, independent components similar to the ones observed in the present study, the present results may offer an explanation of why behavior therapy has limited success in the treatment of ADHD.

Animals↗
PubMed1992

Behavior of hypertensive and hyperactive rat strains: hyperactivity is not unitarily determined.

The spontaneously hypertensive rat (SHR) is behaviorally hyperactive relative to the Wistar-Kyoto rat (WKY). By breeding SHR with WKY, followed by inbreeding, two new strains have been developed in which hypertension seems to be separated from hyperactivity to novel stimuli: the WKHT and the WKHA strains. The main purpose of the present study was to determine which behavioral characteristics of SHR have been dissociated from the hypertensive trait in the WKHA strain. Male SHR, WKY, WKHT, and WKHA were subjected to three protocols: 1) Two forced-exploration tests, where the results showed that both the SHR and the WKHA rats were hyperactive. 2) A free-exploration open field, where the SHR was more active than the other strains, showing shorter latencies to leave the home cage, spending more time in the field, ambulating and rearing more. Furthermore, the WKHT behavior was more similar to the SHR behavior than the WKHA behavior. 3) A two-component schedule of reinforcement, where one component (fixed-interval 2 min) was signaled by houselight on and the other (extinction, EXT) by houselight off. In this test, the SHR behavior was markedly different from that of the three other strains: the fixed-interval scallop, the accelerated responding towards the end of the interval, was steeper in SHR than in the other groups. The SHR emitted more responses during the extinction component of the schedule. The SHR hyperactivity was dependent upon the reinforcement value of the water deliveries and was increased even further by sensory-reinforcing respones feedback lights. Thus, the hyperactivity of the WKHA strain seems to be less pervasive than that of the SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The spontaneously hypertensive rat (SHR) as an animal model of childhood hyperactivity (ADHD): changed reactivity to reinforcers and to psychomotor stimulants.

Childhood hyperactivity (attention-deficit hyperactivity disorder, ADHD) is a behavior disorder affecting 2-6% of grade-school children. The main symptoms are attention problems and hyperkinesis. The disorder is commonly treated with psychomotor stimulants, usually methylphenidate hydrochloride (ritalin) or d-amphetamine. Neither the cause of the disorder nor the basis of the effectiveness of the drug treatment is well understood. Differences in reinforcement processes have been implicated as part of the underlying problem. The main purpose of the present research was to investigate reinforcement processes and motor characteristics with and without stimulant medication in SHR, as an animal model of ADHD, and WKY controls, its normoactive progenitor strain. SHR behavior turned out to be more sensitive to immediate reinforcement and proportionately less sensitive to delayed reinforcement when compared to the behavior of WKY, as demonstrated by systematic changes in rates of responding throughout fixed-interval schedules of reinforcement of bar-presses by water. The psychomotor stimulants weakened the control by immediate reinforcers and strengthened the control by delayed reinforcers, with the effect of the drugs being more pronounced in WKY than in SHR. The results are consistent with clinical observations that ADHD children are less willing than others to accept "delayed gratification" and that methylphenidate increases the control of delayed reward over their behavior.

Analysis of Variance↗
PubMed1991

Behavioural method to detect marginal neurotoxic effects of ivermectin in DA/Orl rats.

Ivermectin (22, 23-dihydroavermectin B 1) in subtoxic doses was administered subcutaneously to young adult DA rats. Prior to treatment the rats had been trained in a visual discrimination learning programme until their response pattern was stable. The behavioural response data were recorded during continued discrimination testing following the Ivermectin injection and compared with those of a control group. The results showed that the Ivermectin injection reduced the total number of lever presses and reinforcement collections. Further the treatment caused an increase in the total number of erroneous responses.

Animals↗
PubMed1990

The spontaneously hypertensive rat as an animal model of attention-deficit hyperactivity disorder: effects of methylphenidate on exploratory behavior.

Spontaneously hypertensive rats (SHR) show a pervasive hyperactivity in several paradigms. Thus, these rats may be used as an animal model of childhood hyperactivity also called Attention-Deficit Hyperactivity Disorder. This disorder is frequently treated with psychomotor stimulant drugs, but little is known about the effects of such drugs on behavior. The present study investigated the behavioral effects of 1-24 mg/kg methylphenidate (Ritalin) on the exploratory behavior of male SHR and Wistar-Kyoto control rats (WKY) in a two-compartment free-exploration open field. Except following very high doses. SHR spent most of the session time in the field while WKY stayed in the home cage. Low and medium doses were followed by increased activity in the field for SHR and increased activity in the cage for WKY. The response-stimulatory effects of low to medium doses of methylphenidate are less in SHR than in WKY. Starting at medium doses, activity decreased and stereotyped behavior increased progressively by increasing dose. Locomotor activity in the field decreased following lower doses than locomotor activity in the cage, and vertical activity (rearing) was reduced by lower doses than horizontal activity (crossing). The following conclusions were drawn. (i) There is no "paradoxical" inhibition of SHR hyperactivity following methylphenidate. On the contrary, SHR activity is in fact stimulated, albeit to a lesser degree than that of WKY. (ii) The stimulatory effects of low to medium doses are, in general, most pronounced for the kind of exploratory behavior most frequently used by the rat during baseline conditions. (iii) Rearing might be more susceptible to adverse effects of methylphenidate than ambulation.

Animals↗
PubMed1988

Low doses of methylphenidate (Ritalin) may alter the delay-of-reinforcement gradient.

The present study investigated effects of methylphenidate on spatio-temporal distributions of responses generated by a fixed interval 60-s schedule of reinforcement. A response panel with 20 different response locations (holes) made it possible to distinguish effects of the drug on the procedurally-correct response (correct according to the contingencies) and effects on other topographically similar responses acting as functionally-adequate responses. Detailed flow charts show how the dynamics of responding changed with dose and segment of the fixed interval. The number of holes visited was increased after low and medium doses, but decreased after high doses. The spatial differences between responses in the initial and the final parts of the fixed interval gradually disappeared after 6 mg/kg or higher doses as the functionally-adequate responses moved to earlier segments of the fixed interval. Few results could, however, be described as response rate dependent. Distributions of responses around the correct hole illustrated differences between procedurally-correct and functionally-adequate classes. The number of holes included in the latter class changed by dose in an inverted U-shaped fashion. Perseverations and stereotyped responding increased with increasing dose. Most of the effects may be described as motor stimulatory. One way of explaining the stimulatory effect is in terms of a lengthened delay-of-reinforcement gradient. The rate-dependent effect of methylphenidate on the procedurally-correct class after some doses may have been due to the combined effects of a lengthened delay gradient increasing the response rates early in the interval and interference from perseverations having their most detrimental effects on the high rates late in the interval.

Animals↗
PubMed1988

Reinforcement schedules: Retroactive and proactive effects of reinforcers inserted into fixed-interval performances.

The responding maintained by a reinforcer depends on the relation of the reinforcer not merely to the response that produces it but also to other preceding responses. Early responses in a sequence that ends in a reinforcing consequence make smaller contributions to later response rates than more recent ones, by virtue of the longer delays that separate them from the reinforcer. This study shows that the relation between a response and a later reinforcer contributes to responding only if no other reinforcers intervene; in other words, each reinforcer blocks responses that precede it from the effects of later reinforcers. Pigeons' pecks were maintained by fixed-interval (FI) schedules of food reinforcement. When FI 60-s (short) and FI 75-s (long) schedules began simultaneously within constant 150-s cycles, long FIs did not affect short-FI performances, but short FIs eliminated the first 60 s of long-FI performances. Removing either short-FI reinforcers or short-FI stimuli showed that short-FI reinforcers and not short-FI stimuli blocked the first 60 s of the long-FI performance from the retroactive effects of the long-FI reinforcer. With FI 15-s and FI 75-s schedules, the short-FI reinforcer was followed by reduced long-FI responding, but a schedule that prevented discrimination based on time since a reinforcer eliminated this proactive effect of the short-FI reinforcer. In other words, the retroactive effects were reinforcer effects whereas the proactive effects were discriminative effects. Quantitative descriptions of variable-interval performances, in which reinforcer effects may operate in the absence of temporal discriminative effects, can be derived from these relations.

Journal Article↗
PubMed1987

Open-field behavior of rats previously subjected to short-term hyperbilirubinemia with or without blood-brain barrier manipulations.

The aim of this study was to investigate (i) whether bilirubin encephalopathy with lasting sequelae could be created in a rat model, and (ii) putative differences in brain toxicity between bound and unbound bilirubin. Hyperbilirubinemia was produced by infusing bilirubin 20 mg/kg/h during 3 h into 6-week-old male Sprague-Dawley rats. In addition to the hyperbilirubinemia, different groups were created by exposing the rats to hyperosmolality, hypercarbia, and sulfisoxazole. Three weeks after the infusion the rats were studied in an open-field apparatus during 10 daily sessions of 15 min duration. A data collection program was used to study the following measures of activity: crossings in cage, peeks, rearing, latency to enter field, crossings in middle and in outer field, and time outside cage. The data were subjected to multivariate analyses of variance (MANOVA). Generally, the level of activity was higher in the bilirubin-treated rats as compared to the control animals. The difference in activity between bilirubin-treated and control rats changed systematically both between and within sessions. The data show that both unbound and albumin-bound bilirubin are neurotoxic, but they indicate a more pronounced effect of unbound bilirubin. The sequelae of bilirubin brain toxicity appear to include changes in stimulus processing. This is compatible with findings from neuropsychological tests of children who have had significant neonatal hyperbilirubinemia.

Animals↗
PubMed1986

Slower acquisition of positively reinforced behavior following medial, but not dorsolateral, septal lesions in rats.

This study was conducted to examine effects of medial and dorsolateral septal lesions on acquisition by using a modified autoshaping procedure. The results showed that following medial septal lesions, lever-pressing responses had long latencies and were fewer than following either dorsolateral septal lesions or control operations. However, during later sessions, the rats with medial septal lesions started to press. The long response latencies and low response rates shown initially by rats with medial septal lesions may have been due to delayed classical conditioning. Following medial septal lesions, the acetylcholinesterase activities of the different subdivisions of the hippocampus correlated positively with the number of lever-press responses emitted during Session 1. The group with dorsolateral septal lesions acquired the task just as fast as the control group and showed higher response rates than the other two groups during the final sessions. The latter result may be ascribed to generally increased locomotor activity.

Animals↗
PubMed1980

Preference for free choice over forced choice in pigeons.

In a six-key chamber variable-interval initial links of concurrent-chain schedules operated on two lower white keys. Terminal links operated on four upper keys; green keys were correlated with fixed-interval reinforcement and red keys with extinction. Free-choice terminal links arranged three green keys and one red key; forced-choice terminal links arranged one green key and three red keys. Thus, terminal links were equivalent in number, variety, and information value (in bits) of the keylights. Preferences (relative initial-link rates) were studied both with location of the odd key color varying over successive terminal links and with the odd color fixed at key locations that had controlled either relatively high or relatively low terminal-link response rates. Free choice was consistently preferred to forced choice. Magnitude of preference did not vary systematically with terminal-link response rate or stimulus control by green and red keys. The origins of free-choice preference could be ontogenic or phylogenic: organisms may learn that momentarily preferred alternatives are more often available in free than in forced choice, and evolutionary contingencies may favor the survival of organisms that prefer free to forced choice.

Journal Article↗