Effects of lesions to ascending noradrenergic neurones on performance of a 5-choice serial reaction task in rats; implications for theories of dorsal noradrenergic bundle function based on selective attention and arousal

Five experiments examined the effects of destruction of the dorsal noradrenergic bundle (DNAB), arising in the locus coeruleus, both on brightness and spatial visual discrimination, and selective attention. An analogue o Leonard's 5-choice serial reaction task for human subjects was used. Hungry rats were trained to detect brief (0.5 sec) flashes of light presented randomly in one of 5 locations with a fixed intertrial interval of 5 sec, paced by the rat. Correct responses were rewarded with food and incorrect responses punished by time-out (darkness + delay). Following training to high levels of accuracy (80%, with less than 20% errors of omission), rats received either 6-OHDA (4 micrograms/2 microliters) injected bilaterally into the trajectory of the dorsal bundle, or injection of vehicle (0.1% ascorbic acid in 0.9% saline). The 6-OHDA lesion was sufficient to reduce cortical NA by 84%. Performance on both the spatial discrimination and brightness (produced by graded reductions in the brightness of the stimuli) discrimination was unaffected by DNAB lesions. However, the DNAB lesion produced significant decreases in accuracy and increases in omissions when the stimuli were presented at faster, unpredictable rates. In addition, although intense white noise failed to produce differential impairments when presented simultaneously with the visual discriminanda, the DNAB lesion significantly impaired accuracy when the noise was presented immediately prior to, but not overlapping, the onset of the visual stimuli. The implications of this pattern of deficits in performance found following DNAB lesions is discussed in terms of disruptive effects of cortical NA depletion upon mechanisms of selective attention and arousal.

Effects of d-amphetamine and apomorphine upon operant behavior and schedule-induced licking in rats with 6-hydroxydopamine-induced lesions of the nucleus accumbens

After training under a fixed-interval 60 sec schedule of food presentation in the presence of a water tube (to permit schedule-induced licking), groups of rats received either 6-hydroxy-dopamine (6-OHDA)(8 micrograms base/2 microliters) or 0.2% ascorbate-0.9% saline vehicle bilaterally into the nucleus accumbens. 6-OHDA produced greater than 80% depletion of the catecholamines dopamine and norepinephrine and the dopamine metabolite dihydroxyphenylacetic acid in the nucleus accumbens and olfactory tubercle, but nonsignificant depletions in the corpus striatum. The behavior of the groups treated with 6-OHDA ("lesion") and vehicle ("sham") was assessed for up to 58 days postoperatively. In the first few days after 6-OHDA, the lesion group showed reductions in high rates of responding toward the end and in high rates of licking at the beginning of the fixed-interval. However, licking was increased during later portions of the fixed interval in the lesion group. d-Amphetamine (0.25-2.0 mg/kg) increased low rates but decreased high rates of schedule-controlled responding, while generally reducing licking. The lesion group showed attenuated rate-reducing effects of d-amphetamine. In contrast, the lesion group showed enhanced rate-reducing effects of apomorphine (0.025-0.1 mg/kg) on both schedule-controlled responding and schedule-induced licking. In a second determination of the effect of d-amphetamine (0.25-2.0 mg/kg), schedule-induced locomotor activity was recorded and the water tube was removed. The lesion group showed attenuated rate-increasing and rate-decreasing effects of d-amphetamine upon schedule-controlled responding and reductions in the drug-induced increases in locomotor activity. The results are discussed in terms of the functions of dopamine in the control of behavior and in the mediation of the response to d-amphetamine and apomorphine.

Increased response switching, perseveration and perseverative switching following d-amphetamine in the rat

Four experiments examined the effects of d-amphetamine on response switching and perseveration in apparatus allowing a choice of response location. The relative 'cost' of a switch between two response locations and repetitive responding at a single location by rats was manipulated in the various test settings to provide baseline probabilities of switching. d-Amphetamine (0.2-2.3 mg/kg) increased response switching. This effect did not depend on switching being necessary to produce reinforcement and was not explained by increases in locomotor activity, motivational change or randomisation of responding. Further evidence was provided in support of a 'probability-dependency' hypothesis, that the effect of the drug depends in part upon the baseline probability of a response. A measure of perseveration independent of response switching (extra responses made prior to the collection of food) showed that increased switching and increased perseveration occurred in the same situation at the same doses, although perseveration generally occurred at higher doses than increased switching. Therefore the effect of amphetamine on response switching or repetition depends on the dose of drug, the context of the response and its probability of occurrence under control conditions.

Dissociable effects of d-amphetamine, chlordiazepoxide and alpha-flupenthixol on choice and rate measures of reinforcement in the rat

The role of reinforcers in influencing choice was studied by use of a schedule that included a random intermixing of reinforced and explicitly non-reinforced components. The just-reinforced response had a high likelihood of being repeated (win-stay), although there was no differential reinforcement for doing so, whereas responses just followed by explicit non-reinforcement had a very low probability of repetition (lose-stay). Non-parametric indices based on the theory of signal detection were used to derive a choice measure of reinforcement which was independent of alterations in average response rate. Treatments with d-amphetamine (0.2-4.5 mg/kg), chlordiazepoxide (0.25-16 mg/kg) and alpha-flupenthixol (0.03-0.6 mg/kg) showed that changes in the choice measure could be dissociated from changes in the response rate. These findings were supported by extinction and satiation tests.

Contrasting interactions of pipradrol, d-amphetamine, cocaine, cocaine analogues, apomorphine and other drugs with conditioned reinforcement

The effects of various psychomotor stimulant drugs and drugs outside this class were examined on the efficacy of stimuli previously paired with reinforcement or reward (conditioned reinforcers, CR) in controlling responding. Pipradrol (5-45 mumol/kg), d-amphetamine (1.25-15.0 mumol/kg), and the cocaine analogues WIN 35,428 (0.1-30.0 mumol/kg) and in one of two determinations WIN 35,065-2 (0.1-29.0 mumol/kg) all generally increased responding on a lever providing CR, but did not change or decreased responding on a lever providing no CR (NCR). Cocaine (5-125 mumol/kg) and chlordiazepoxide (3.75-60.0 mumol/kg) had no significant effects. Morphine (3.2-32.0 mumol/kg) and alpha-flupenthixol (0.02-2.0 mumol/kg) generally reduced responding on both levers. Apomorphine (0.1-1.0 mumol/kg) generally increased responding on both levers. Neurochemical data showed that d-amphetamine was generally more potent than pipradrol in its effects on in vitro monoamine uptake and release.

Selective disruption of displacement behaviour by lesions of the mesolimbic dopamine system

In the wild, organisms generally allocate their time among many behavioural tendencies in response to both current and anticipated motivational requirements. However, activities that are apparently 'irrelevant' often intrude, either during conflict between these behavioural tendencies, or when a strong tendency is thwarted. These 'irrelevant' activities are called displacement behaviours and are widely documented in the ethological literature. We report here that an experimental analogue of displacement behaviour in the rat depends upon the integrity of the mesolimbic dopaminergic projection to the nucleus accumbens septi, olfactory tubercle and associated structures of the forebrain.

An observational method for quantifying the behavioural effects of dopamine agonists: contrasting effects of d-amphetamine and apomorphine

A novael means of measuring and analysing behavioural effects of dopamine agonists is described and illustrated by a comparison of the effects of d-amphetamine and apomorphine in the rat. d-Amphetamine (0--15 mg/kg IP) produced significant dose- and time-dependent changes in responses such as locomotion, rearing and sniffing, but not in licking or gnawing. In contrast, apomorphine (0--5 mg/kg SC) produced significant increases in licking and gnawing, as well as in locomotion and sniffing, but no changes in rearing. The results are discussed in comparison with those obtained by other methods, such as photocell beam interruptions or sterotypy rating scales, and may be of importance in elucidating the functions of the forebrain dopamine projections.

Effects of 6-hydroxydopamine lesions of the nucleus accumbens septi and olfactory tubercle on feeding, locomotor activity, and amphetamine anorexia in the rat

Bilateral 6-hydroxydopamine lesions of the nucleus accumbens septi (NAS) and olfactory tubercle (OT) caused enhanced intake of wet mash in 23-hr-food-deprived rats tested in photocell activity cages during restricted 30-min sessions. This mild hyperphagia was accompanied by a significant hypoactivity in the group with NAS/OT lesions. No hyperphagia was observed during a prolonged 120-min test session or in free-feeding tests conducted in the home cage. Anorexia induced by d-amphetamine (.5 and 1.5 mg/kg) was unaltered by the lesion, although the locomotor stimulant action of the drug was attenuated. A second experiment showed that the NAS/OT lesion also enhanced food intake in the photocell cages during 30-min sessions with dry food pellets but that food-associated drinking was concomitantly reduced. The results are consistent with the hypothesis that the behavioral changes caused by mesolimbic neuron destruction result in part from an inability to switch from one behavioral activity to another.

Pipradrol enhances reinforcing properties of stimuli paired with brain stimulation

The hypothesis that a psychomotor stimulant drug (pipradrol) enhances the reinforcing effects of stimuli paired with reinforcing brain stimulation was tested using a conditioned reinforcement paradigm. Rats were trained to discriminate between two stimuli (S+ and S-) to obtain ICS in the lateral hypothalamus by pushing a panel in the presence of S+. In a subsequent preference test, ICS was no longer available, but responding on one of two novel levers now produced S+, whereas responding on the other lever produced S-. Four groups of four rats received 0, 5, 10 or 15 mg/kg pipradrol. Doses of 5 and 10 mg/kg significantly enhanced the preference for S+ over S-. These doses increased responding for S+, but had no effect on responding for S-. These results support the hypothesis tested, and suggest that pipradrol potentiates the effects of conditioned reinforcement.

Are the effects of psychomotor stimulant drugs on hyperactive children really paradoxical?

The improved "attention" exhibited by hyperactive children treated with amphetamine-like compounds is postulated to be related to a normal action of these drugs in producing stereotyped behavior. Such activity can be conceptualised as an increased "focusing" of attention, which would be expected to aid performance in tasks involving sustained concentration of attention, but impair performance on tasks involving reversals in cognitive strategy. These behavioural actions of the drugs can be linked to the functioning of central dopaminergic mechanisms.

Effects of chlordiazepoxide on tail pinch-induced eating in rats

The effects of 5, 10, and 20 mg/kg chlordiazepoxide on tail pinch (TP)-induced behavior were investigated. Five mg/kg enhanced TP-induced eating in terms of both latency and duration. Twenty mg/kg had decremental effects. All doses of the drug reduced the incidence of clip-directed behavior, but increased locomotor activity during the TP trials in a dose-dependent manner. On control trials, the drug increased locomotor activity at the low dose and eating at the high dose. The results are examined in terms of the various behavioral actions of the minor tranquilizers. The implications for the behavioral and neuropharmacological mechanisms underlying TP-induced and other forms of stimulus-bound behavior are discussed.

The effects of d-amphetamine on temporal discrimination in the rat

The effects of d-amphetamine on temporal discrimination in the rat were studied. Rats were trained on a two-manipulandum task involving the discrimination between two tones differing only in duration. d-Amphetamine (0.1 - 1.6 mg/kg) disrupted performance on this task, although not in an obvious dose-related manner. Lever biases were enhanced by the drug, but inconsistenly among rats. Enhanced lever bias did not necessarily correlate with deterioration of performance. The drug lengthened both response latency and the performance of terminal components of the operant chain. However the characteristic pattern of response latencies produced by the two tones was not altered significantly by the drug. The results are discussed in terms of whether the drug disrupts discrimination performance by a direct effect on processes of temporal discrimination or indirectly, by its other effects on behavior.

Alpha-flupenthixol-induced hyperactivity by chronic dosing in rats

Socially reared and isolation-reared rats treated chronically since weaning with alpha-flupenthixol showed elevated levels of spontaneous locomotor activity compared with control treated rats. However, chronic apomorphine treatment had no effect on spontaneous locomotor activity. Chronic alpha-flupenthixol treatment enhanced stereotyped behaviour after 1.5 mg/kg d-amphetamine or 0.5 mg/kg apomorphine in the socially reared condition. 'Spontaneous stereotypies' were also observed in the chronic alpha-flupenthixol-treated animals. Chronic apomorphine treatment did not affect stereotyped responding. The results are discussed in terms of 'behavioural supersensitivity'.

The effects of psychomotor stimulants on stereotypy and locomotor activity in socially-deprived and control rats

Using measures of locomotor activity and stereotypy, dose-response curves to several psychomotor stimulant drugs were obtained on rats reared in deprived or normal environments. At both 0.5 and 1.5 mg/kg d-amphetamine, the deprived rats exhibited more intense stereotyped behavior than the control rats. At 5.0 mg/kg, both groups showed maximum response. However, there was no significant difference between the two groups in locomotor response. A similar pattern of results was found for pipradrol, cocaine, and apomorphine. The findings show that different social and environmental experience can modify the response to dopaminergic stimulating agents. The results also suggest that stereotyped behavior should not be considered on the same continuum as locomotor activity. These two behaviors may be mediated by different mechanisms.