Impairment of two-way active avoidance after pedunculopontine tegmental nucleus lesions: effects of conditioned stimulus duration.

It was investigated whether the disruptive effects of bilateral lesions of the pedunculopontine tegmental nucleus on two-way active avoidance might vary depending on variations of task demand. The animals were either subjected to bilateral electrolytic lesions of the pedunculopontine tegmental nucleus (Lesion groups) or were sham-operated (Control groups). All the rats were subjected to two 30-trial sessions of two-way active avoidance (separated by ten days), using either a 10-s conditioned stimulus (low task demand) or a 3-s conditioned stimulus (high task demand). The lesions induced a significant disruption of two-way active avoidance in the two conditions tested, but, in both lesioned and control rats, the number of avoidance responses was higher when the 10-s conditioned stimulus was used. In lesioned animals, the condition of high task demand was associated with a significant increase of escape failures. Lesions did not affect locomotor activity during the period of adaptation to the conditioning apparatus, but induced training-specific motor deficits (a decrease of intertrial crossings and an enhancement of escape latencies) regardless of the specific training conditions used. The results are discussed in terms of the influences of the pedunculopontine tegmental nucleus in thalamocortical and striatal systems.

Posttraining epinephrine and memory consolidation in rats with different basic learning capacities. The role of the stria terminalis.

Rats received bilateral stria terminalis (ST) lesions or were sham-operated. Five days later, the animals were trained in a two-way active avoidance task (one session, 30 trials) and, immediately after the training session, received 0.01 mg/kg i.p. epinephrine or distilled water. Retention was tested 20 days after the acquisition session. In sham-operated groups, epinephrine improved retention in rats that were poor learners and impaired it in rats that were good learners. In poor learners with posttraining epinephrine, lesions of the ST not only blocked the facilitatory effect of epinephrine but also disrupted performance throughout the retention session. In good learners, ST lesions attenuated the disruptive effect of epinephrine. Lesions per se did not affect either acquisition or retention. We conclude that ST is involved in the modulatory effect of posttraining epinephrine on memory consolidation. In addition and considering the results observed in rats that were poor learners, we suggest that emotional factors and/or other amygdaloid pathways different from the ST could participate in the effects of posttraining epinephrine, along with the ST.

Long-term memory modulation by posttraining epinephrine in rats: differential effects depending on the basic learning capacity.

Effects of posttraining epinephrine on retention of a massed (1 session, 30 trials) 2-way active avoidance task were studied in rats. Immediately after the training session rats received an injection of 0.05 or 0.01 mg/kg ip epinephrine, or distilled water. Retention was tested 11, 20, or 45 days after training, in independent groups of rats. The 20- and 45-day retention was improved in poor-learning rats and disrupted in good-learning rats. It was concluded that the effect (facilitatory or disruptive) of posttraining epinephrine on memory consolidation depends on the basic learning capacity of rats for this task and needs a long time to be expressed.

Effects of pretraining paradoxical sleep deprivation upon two-way active avoidance.

In order to study whether paradoxical sleep (PS) is necessary to prepare subjects for the subsequent learning of a distributed two-way active avoidance conditioning, 10 rats were subjected to 5 h of paradoxical sleep deprivation (PSD group) by means of the platform method immediately before each of 5 acquisition sessions (one daily), as well as before a long-term retention (LTR) session (14 days). Another group of rats (PSD control group; n = 10) were placed on large platforms as a control for the side effects induced by PSD platforms. Rats in the dry control group (n = 10) did not receive any treatment. The number of avoidances of the PSD group was significantly lower on the 1st, 2nd and 3rd acquisition sessions compared to the PSD control group, and on the 2nd and 3rd sessions compared to the dry control group. PSD rats made significantly less intertrial crossings than dry controls on the 2nd and 3rd acquisition sessions, but no significant correlations were found between this variable and the number of avoidances. Therefore, our results are not fully in contradiction with the hypothesis that PS previous to the training sessions might prepare the animal for subsequent learning, although the influence of locomotor changes upon the performance of PSD subjects cannot be fully rejected.

Long-term memory facilitation in rats by posttraining epinephrine.

Effects of posttraining epinephrine (EPI) on retention of a massed (1 session, 30 trials) 2-way active avoidance task in rats were studied. The rats received an injection (ip) of 0.05 mg/kg EPI, 0.01 mg/kg EPI, or distilled water immediately after the training session. EPI did not improve retention 24 hr after the training session (Experiment 1) but enhanced retention 20 days after the training session (Experiment 2). The group receiving the smaller dose of EPI had better retention than the group receiving the larger dose, indicating dose dependency. The authors suggest that the process of consolidation of massed 2-way active avoidance conditioning is long and elaborative. Posttraining EPI would facilitate this active process of consolidation, improving performance as consolidation goes on. This facilitation needs, at least under certain conditions, more than 24 hr to be expressed as a higher level of performance on the retention test.

Facilitation of a distributed shuttlebox conditioning with post-training epinephrine in rats.

Forty-two male Wistar rats were trained in a two-way active avoidance task during 5 consecutive days (10 trails/session). Immediately after each training session animals were given an injection, ip, of 0.1 mg/kg (EPI 0.1 group) or 0.05 mg/kg (EPI 0.05 group) of epinephrine, or vehicle (Vehicle group). Long-term retention was tested 20 days after the last acquisition session. Our results showed that the lower dose of epinephrine (0.05 mg/kg) led to a significant improvement of acquisition, compared with both the Vehicle and the EPI 0.1 group. On the long-term retention session the level of avoidances in both EPI 0.05 and Vehicle groups was similar to that achieved on the last acquisition session, although differences between groups failed to reach statistical significance. Concerning the EPI 0.1 group, a significant increase in the number of avoidances was observed between the last acquisition session and the long-term retention session. This later result might suggest that the higher dose of epinephrine would need a longer period to manifest its effectiveness. We conclude that the facilitatory effects of epinephrine are dose-dependent, and that under a distributed paradigm epinephrine modulates memory consolidation processes leading to an improvement of the magnitude of learning rather than merely speeding up learning.

Facilitation of shuttle-box avoidance by the platform method: effects of conditioned stimulus duration.

To evaluate whether the duration of the conditioned stimulus (CS) influences the facilitatory effect of posttraining platform treatment upon the acquisition and long-term retention (LTR) of a shuttle-box conditioning, rats were assigned to one of the four following treatments: P-3 group rats were subjected to a 5-h treatment on 16 cm diameter platforms immediately after each of 5 training sessions (10 trials each separated by 24-h intervals) in which the CS consisted of a tone lasting 3 s; control-3 rats were trained the same way but were not subjected to the platform treatment; P-10 rats did also receive the immediate 5-h treatment on platforms, but the CS was a tone lasting 10 s; finally, control-10 rats did not receive any treatment and were also trained with a 10-s tone. Ten days after training, all rats were also tested for LTR (1 session of 10 trials). When the CS duration was 3 s, the platform treatment improved both the acquisition and LTR of the task, compared to control subjects, but the same treatment had no effect when the CS lasted 10 s. With the use of a 10-s CS, the level of learning achieved by both treated and untreated subjects was similar to the final level of acquisition reached by treated subjects trained with a 3-s CS. We conclude that the facilitatory effects of the platform method treatment upon the acquisition and LTR of a distributed shuttle-box avoidance depend on the difficulty of the task.

Improvement of shuttle-box avoidance with post-training intracranial self-stimulation, in rats: a parametric study.

Rats were trained in a two-way active avoidance task followed immediately by a lateral hypothalamic intracranial self-stimulation (ICSS) treatment, during 5 consecutive days. The effects of the number of ICSS trains allowed (0, 500, 2500 or 4500) were studied upon acquisition and long-term retention (LTR, 10 and 30 days). The number of ICSS trains administered and the number of avoidances at the last acquisition session (5th) showed a positive lineal relation, that is, the more number of ICSS trains, the more number of avoidances. The level of learning achieved during the 5th session was maintained after the LTR periods in all experimental groups. It is concluded that the number of ICSS trains could be a critical parameter in the facilitatory effect of lateral hypothalamic ICSS upon learning, and it is suggested that the facilitatory effect of post-training lateral hypothalamic ICSS might be due to the activation of general activatory neural systems.

Correlations between paradoxical sleep and shuttle-box conditioning in rats.

Eighteen male Wistar rats were given one daily two-way active avoidance conditioning session followed immediately by 5 hr of sleep recording, for 5 consecutive days. The group of rats that achieved 80% or greater avoidance in some of the 5 training sessions showed significant linear increases of paradoxical sleep (PS), compared with baseline levels, throughout the successive conditioning sessions. Furthermore, (a) the group of rats showing PS increases (more than 1 SD above baseline) after some of the training sessions achieved a significantly higher final number of avoidances than the remaining animals: (b) a high and positive correlation was observed between avoidance increases in the 3rd conditioning session and previous PS; and (c) maximum increases in correct performance often occurred following high PS increases. It is concluded that PS increases facilitate the consolidation of learning.

Improvement of shuttle-box avoidance following post-training treatment in paradoxical sleep deprivation platforms in rats.

The effects of post-training paradoxical sleep deprivation (PSD), via the platform method, on acquisition and long-term retention (LTR) of shuttle-box avoidance were studied in Wistar rats. Animals had a daily training session for 5 days (acquisition), following which each rat was placed for 5 hr either on a small platform (7 cm) surrounded by water (PSD group) or on a large platform (16 cm) surrounded by water (Yoked control group), or was given no treatment (Dry control group). Another identical training session (LTR test) was also given to every subject 14 days after the last acquisition session. The treatment on the large platform (Yoked animals) improved learning in successive training sessions. A similar but not statistically significant improvement was also observed in the PSD group. In the LTR test, the PSD animals tended to decrease performance as compared with the conditioning level achieved in the previous acquisition session. Locomotor and emotional changes produced by PSD and PSD procedures are ruled out as the cause for these findings. We suggest that arousal produced by both PSD and PSD procedures could have improved the acquisition of the conditioning, whereas PSD per se could have been detrimental for LTR of the learned response.

Intracranial self-stimulation after paradoxical sleep deprivation induced by the platform method in rats.

Lateral hypothalamic intracranial self-stimulation was studied before and after paradoxical sleep deprivation (PSD) induced by the platform method. Rats were assigned to two counterbalanced groups where the sequence order of experimental (small platform) and control (large platform) treatments was permuted. In contrast with previous findings significant changes in the response rates for intracranial self-stimulation were not observed after PSD. Ineffectiveness and nonspecific effects of the treatment are ruled out as the cause for our findings. An hypothesis is suggested that the effect of PSD upon intracranial self-stimulation could be dependent of the brain electrode location.