Alternation behavior, spatial discrimination, and reversal disturbances following 6-hydroxydopamine lesions in the nucleus accumbens of the rat

The effects of dopaminergic depletion of the nucleus accumbens was tested in various behavioral tasks such as alternation, spatial discrimination, and reversal learning, and in an extinction paradigm in a T maze. Animals with lesions showed impairment of spontaneous alternation behavior, disturbances in the acquisition of spatial discrimination, and great difficulty in reversing previously learned habits. In the extinction phase, experimental animals are unable to adjust their behavior, and continue to choose the previously reinforced arm of the T maze. It is suggested that the nucleus accumbens plays an important role in the transition of motivation into action, and that dopamine has a facilitatory influence on the mediation of these processes.     

Differential effects of localized lesions of n. accumbens on morphine- and amphetamine-induced locomotor hyperactivity in the C57BL/6J mouse.

Mice of the C57BL/6J strain became hyperactive to increasing doses of morphine sulfate. This response was similar to locomotor hyperactivity induced by amphetamine. Lesions and chemical blockade of posterior n. accumbens abolished amphetamine-induced hyperactivity and reduced but did not abolish the morphine response. These experiments demonstrate that the response to the two drugs is mediated by overlapping but noncongruent neural systems.     

Effects of lesions of the amygdala, preoptic area, and hypothalamus on estradiol-induced activity in the female rat.

Lesions of the anterior hypothalamic nucleus and the medial preoptic area sharply attenuated enhancement of wheel running by estradiol benzoate in ovariectomized female rats. Lesions of the corticomedial amygdala had no effect on this behavior. The hormonal effects on activity were largely independent of any changes in body weight. Results of this first experiment indicated that the anterior hypothalamic and medial preoptic areas are critically involved in the induction of activity by estradiol. However, this experiment provided no support for suggestions that the corticomedial amygdala inhibits those structures that mediate the estrogenic induction of activity. In the second experiment, food deprivation was used to stimulate activity. Results of this experiment suggested that the reduction in the ability of estradiol to induce activity following anterior hypothalamic and medial preoptic lesions does not reflect a general inability to become more active.     

Ontogeny of spontaneous locomotor activity in rabbit, rat, and guinea pig.

Postnatal locomotor activity was investigated in rabbit, rat, and guinea pig. A peak was found in this behavior at 5 days of age in the rabbit and, in confirmation of earlier studies, at 15-20 days in the rat. Neonatal guinea pigs showed no variation in activity levels due to age. The guinea pig is born at an advanced stage of neural maturation in comparison with the rat, and the rabbit is born at an intermediate stage. This difference accounts for the observed variations in postnatal activity profiles if it is assumed that the behavioral peak coincides with the transition from a stage of primarily mesencephalic arousal system maturation to a stage of primarily diencephalic and telencephalic inhibitory system maturation.     

Central noradrenergic neurons: differential effects on body weight of electrolytic and 6-hydroxydopamine lesions in rats.

The ventral noradrenergic bundle (VB) of the rate brain has been proposed as the substrate for the hyperphagia and obesity produced by ventromedial hypothalamic lesions. To determine the relationship between body weight and damage to the VB, the effects of bilateral electrolytic and 6-hydroxy-dopamine (6-OHDA) lesions of the VB were compared. When rats were fed only a standard laboratory diet, no significant differences were found between groups. When a high-fat diet supplement was introduced, the group with electrolytic lesions became significantly heavier than the control group; however, the 6-OHDA group did not differ from the controls. Norepinephrine depletion was significantly greater following the 6-OHDA than the electrolytic lesions. Both lesions reduced telencephalic dopamine and serotonin only slightly. A second study in which both types of lesions were placed at a rostral ventromedial hypothalamic site yielded the same pattern of results. Diet-dependent increases in body weight were attributed to the destruction of a non-noradrenergic system, which was spared by the relatively selective 6-OHDA lesion but damaged by the nonselective electrolytic lesion.     

Effects of d-amphetamine, diazepam, and pentobarbital on the schedule-controlled pecking and locomotor activity of pigeons

Pigeons were trained on a variant of the autoshaping procedure devised by Matthews and Lerer (1987) in which a keylight stimulus ramp of increasing brightness signaled the passing of a 30-s interfood interval. This procedure generates two distinct behavioral components: key pecking and locomotor activity. The effects of three psychoactive drugs on these behavior classes were measured. d-Amphetamine had negligible effects on both types of behavior, whereas diazepam and pentobartital increased key pecking and decreased activity in a dose-dependent fashion. In Experiment 2, the possibility that drug effects were suppressed by excessively strong stimulus control exerted in Experiment 1 was tested by decreasing the discriminability of the stimulus ramp. The direction of the effects of diazepam and pentobarbital was the same as in Experiment 1 but the magnitude of the effects tended to be larger. The effects of d-amphetamine, however, remained quite small, suggesting that, under these conditions, locomotor activity and key pecking are less sensitive to d-amphetamine. In Experiments 3 and 4, key pecking was eliminated by removing the keylight. Reinforcers were presented at fixed intervals in Experiment 3 and at variable intervals in Experiment 4. The drug effects on activity observed in Experiments 1 and 2 disappeared in both Experiments 3 and 4. The results suggest that diazepam and pentobarbital affect activity indirectly by increasing key-pecking behavior, which, in turn, competitively decreases activity.     

Alterations in shock-induced fighting and locomotor activity following intracerebroventricular injection of hydrocortisone in the rat

Three experiments were conducted in an attempt to clarify the facilitatory influence of hydrocortisone on shock-induced fighting in rats. Results of the first experiment indicated a biphasic, dose-dependent action of intraventricularly-administered hydrocortisone. Low (25 μg) and intermediate (50 μg) doses both facilitated fighting whilst the high (100 μg) dose exerted a potent suppressant effect. Two control tests were performed to determine whether alterations in pain reactivity or locomotor activity could have accounted for the observed changes in fighting behaviour. None of the treatments altered shock thresholds (Experiment 2) but whilst neither low nor intermediate doses affected activity measures, the high dose preferentially reduced vertical activity (Experiment 3).     

Age-related changes in working and reference memory performance and locomotor activity in the Wistar rat

Wistar rats of three age groups were tested in an automated tunnel-maze system of variable geometry to investigate whether changes in spontaneous locomotor activity and in learning and memory develop differentially or in a correlated fashion as a function of age. Senescent (30 months) as well as mature-adult (17 months) rats showed an age-correlated decline of locomotor activity as compared to the mature-young (5 months) group. Both working-memory (measured as within-trial arm discrimination performance) and reference-memory (measured as avoidance of "blind alley" visits) were severely affected in the senescent group, whereas the middle-aged animals suffered only from a working-memory deficit. The findings provide evidence that locomotor deficits do not necessarily interfere in the assessment of age-related changes in cognitive performance. Furthermore the results support the hypothesis that working and reference memory have different underlying physiological correlates and that these neuronal systems are differentially affected by the aging process.     

Studies in olfactory acuity. I: Measurement of olfactory thresholds in the rat

The capacity of the rat to respond to olfactory cues has been studied in three experimental situations: (i) an elevated Y-maze, (ii) a rectangular choice apparatus in which extraneous environmental cues were present, and (iii) a circular choice apparatus from which such cues were either excluded or randomized.

No rat showed any sign of learning on the Y-maze even after extensive training and the application of electric shock as deterrent for error.

Some rats succeeded in performing an olfactory discrimination in the rectangular choice apparatus but learning was retarded, and in some cases inhibited, by the counter-influence of non-olfactory factors.

All rats readily learned an identical discrimination when shielded from such cues in the circular choice apparatus which provides a satisfactory medium both for training and for the study of olfactory acuity.

Differences in the behaviour of rats on these three types of apparatus suggest first, that the formation of learned habits based on olfaction depends on the close contiguity of stimulus and reward, and second that the sense of smell possesses weak orientating properties by comparison with those exerted by other modalities. The findings thus help to explain differences in the ease or di+culty uith which olfactory discriminations have been established by earlier workers.     

Neocortex and feeding behavior in the rat.

Consummatory behavior and weight-regulation capacity were measured in 12 normal rats and in 43 rats that survived complete (C), sequential unilateral (U), anterolateral (A), or posterior (P) neocortical ablations. Groups C and A displayed aphagia and adipsia followed by a sequence of recovery stages gualitatively identical to, but shorter than, recovery typically seen following lateral hypothalamic lesions. After recovery, Group C displayed long-term effects of finickiness and pradial drinking. These effects as well as a measure of recovery of body-weight-regulation capacity were significantly intercorrelated with lesion size, and body-weight set point remained significantly lower than normal. Group U was relatively unaffected by the first unilateral ablation and showed, relative the second ablation but displayed the long-term effects. Group P, though significantly affected by the lesion, did not display the pattern or intensity of effects described for the other bilaterally ablated groups.     

Effects of short-term isolation on the locomotor activity of the angelfish (Pterophyllum scalare).

Two experiments were conducted to test in angelfish (Pterophyllum scalare) some implications of Gallup and Suarez's (1980) ethological model of open-field behavior and to differentiate between the initial locomotor effects of a novel environment and those of isolation per se. Juveniles placed alone in a novel environment initially showed increased locomotion compared with their previous level when kept as a group and with that of fish placed in the novel environment in groups of three and five. When placed alone in a novel tank, individuals that had already been isolated for 10 days moved about less than those that had been isolated for 4 days. During isolation, angelfish significantly reduced activity to a minimum after 3 to 4 days, and after 10 days the level was still lower than in the group situation. The results suggest that, in addition to birds and rodents, Gallup and Suarez's model is applicable to fish and may account for the effects of longer exposure to a novel environment.