Biomedical subjects

I Morgado-Bernal

Publications and source records attributed to I Morgado-Bernal.

At least 19 recordsLinked to original sources

PubMed2001

Nucleus basalis magnocellularis electrical stimulation facilitates two-way active avoidance retention, in rats.

We studied the effects of post-training intracranial electrical stimulation of the nucleus basalis magnocellularis on two-way active avoidance retention. After the acquisition, rats were stimulated for 20 min, and they were tested again after 24 h or 11 days. The treatment improved memory consolidation, especially in animals with a low initial learning ability. These facilitative effects could be attributed to an enhancement of cortical and/or amygdala activation, leading to an improvement in associative processes and/or cortical plasticity.

Animals↗

PubMed2001

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.

Analysis of Variance↗

PubMed2000

Differential effects of parafascicular electrical stimulation on active avoidance depending on the retention time, in rats.

To evaluate whether electrical stimulation of the parafascicular nucleus of the thalamus can improve short-term (24 h) and/or long-term (11 days) retention of two-way active avoidance, rats were implanted with an electrode at this nucleus (experimental groups with stimulation in the parafascicular, and control groups without stimulation) or above it (other control groups without stimulation). After a single 30-trial acquisition session, experimental groups were submitted to a 20-min session of electrical stimulation. Results showed that parafascicular stimulation improved the 24-h retention of the task (number of avoidances made), increasing also the percentage of subjects that achieved a learning criterion and reducing the number of trials needed to reach it. In contrast, no differences among groups were found on the 11-day retention test. The present results agree with previous data showing a short-term effect of parafascicular stimulation on retention, and confirm its involvement in learning and memory modulation. These data are discussed in the context of the acceleration and strengthening of the memory by activation of arousal systems, and/or specific cortical-striatal systems.

Analysis of Variance↗

PubMed1999

The parafascicular nucleus and two-way active avoidance: effects of electrical stimulation and electrode implantation.

To evaluate whether electrical stimulation of the parafascicular nucleus (PF) can improve short-term (24 h) and/or long-term (21 days) retention of two-way active avoidance, rats were implanted with an electrode at this nucleus (experimental groups) or above it (control groups). After a single 30-trial acquisition session, experimental groups were submitted to a 10-min session of electrical stimulation. Results showed that the simple implantation of an electrode at the posterior PF enhanced by itself the acquisition of two-way active avoidance, in such a way that the subsequent stimulation of this region may have been unable to further improve the performance of the rats. On the other hand, parafascicular stimulation improved the 24-h retention of the task in a site-specific way, since this effect was mainly seen after stimulation of the central PF region. The facilitative effect on 24-h retention could also depend on the level of performance achieved during the acquisition session, because this improvement was only evidenced in poorly learning animals. No effects were found on 21-day retention. The present results confirm the involvement of the PF in learning and memory and the functional heterogeneity of this nucleus.

Analysis of Variance↗

PubMed1998

Involvement of the parafascicular nucleus in the facilitative effect of intracranial self-stimulation on active avoidance in rats.

To evaluate whether parafascicular nucleus (PF) is involved in the facilitative effect of lateral hypothalamic intracranial self-stimulation (LH-ICSS) on two-way active avoidance acquisition (5 sessions, 10 trials each, one daily) and long-term retention (10 days), rats were lesioned bilaterally at the PF and implanted with an electrode aimed at the LH to obtain ICSS behavior. After each acquisition session rats were allowed to self-administer 2500 trains of LH-ICSS. The main results were: (1) LH-ICSS facilitated the acquisition and retention of conditioning; (2) PF lesions impaired both acquisition and retention of two-way active avoidance; (3) there was a positive relationship between PF lesions size and learning disruption, and (4) LH-ICSS failed to facilitate learning when PF was lesioned. We concluded that the lesion size is a critical variable to evaluate the effects of PF lesions on learning and memory, and that LH-ICSS treatment may exert their effects through the PF nucleus or, at least, the integrity of PF is required for LH-ICSS to improve clearly the task.

Animals↗

PubMed1998

Facilitatory effects of thalamic reticular nucleus lesions on two-way active avoidance in rats.

Two experiments were performed in order to study the effects of lesions of the rostral thalamic reticular nucleus (Rt) on two-way active avoidance. Male Wistar rats were subjected to either a bilateral electrolytical lesion of the rostral Rt or to control procedures. After recovery, all rats were trained in either a distributed (five training sessions, ten trials each; experiment I) or a massed (a single 30-trials session; experiment II) two-way, active-avoidance task. The level of long-term retention of the task was assessed 10 days later. Lesioned rats showed an overall higher performance than control rats both in experiment I (with lesions affecting the rostral Rt and small portions of some adjacent nuclei) and in experiment II (with lesions almost restricted to the rostral Rt). In contrast, detrimental effects on other tasks have been reported in the literature. Although it cannot be ruled out that those differences might be due to methodological factors, they also might be indicative of an action of rostral Rt lesions on certain mechanisms (either indirectly or directly related to information processing) that could be differentially required depending on the kind of learning task. The latter possibility is discussed in terms of the role played by this nucleus as a modulator of thalamocortical transmission, attentional mechanisms and cortical arousal.

Animals↗

PubMed1998

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.

Amygdala↗

PubMed1998

Differential site-specific effects of parafascicular stimulation on active avoidance in rats.

To study the effects of parafascicular intracranial electrical stimulation (PF ICS) on two-way active avoidance acquisition (five training sessions of ten trials each, one session per day) and long-term retention (one session of ten trials), two experiments were carried out. Experiment I tested if posttraining PF ICS can differentially affect the conditioning, depending on the stimulated region of the nucleus. Results indicated that rats stimulated at the posterior region of the parafascicular nucleus (PF) showed a better acquisition than those stimulated at the central one. Experiment II evaluated the effects of the stimulation at the medial, lateral and posterior parts of the PF area on the same task. Results showed that medial and lateral PF ICS disrupted two-way active avoidance, and that posterior PF ICS enhanced the long-term retention of the conditioning. These results suggest a possible role of the PF in modulatory processes of learning and memory, confirming that this nucleus is functionally heterogeneous. Potential facilitative effects are discussed in terms of the relations of the PF to the arousal system and the subparafascicular thalamic nucleus. Disruptive effects are discussed based on the relations of the PF with the 'motor' and 'associative-limbic' basal ganglia circuits.

Animals↗

PubMed1997

Facilitation of a distributed shuttle-box conditioning with posttraining intracranial self-stimulation in old rats.

Old Wistar rats (16-17 months) were trained in a two-way active avoidance task for 5 consecutive days (10 trials/day). Immediately after each training session a lateral hypothalamic intracranial self-stimulation session (ICSS group) or a sham-treatment session (Control group) was given to the animals. Long-term retention was tested 7 days after the last acquisition session. ICSS treatment led to a significant improvement in acquisition. In the long-term retention session the level of avoidance in both groups was similar to that achieved in the last acquisition session, although differences among groups failed to reach statistical significance. These results are compared with those obtained in previous experiments with young adult rats. While ICSS facilitated the process of acquisition in both young and old rats (however, it was much more powerful in young animals), further experiments are needed to elucidate whether this effect is long-lasting in old rats, as occurs in young adult subjects.

Animals↗

PubMed1997

Effects of habenular lesions upon two-way active avoidance conditioning in rats.

To evaluate if habenular nuclei lesions improve, impair, or have no effects on two-way active avoidance acquisition and/or retention, rats in a Lesion group were subjected to bilateral electrolytical lesions of this complex, while control rats were sham-operated (Sham group). Once recovered from the stereotaxic procedures, rats were submitted to 5 training sessions (10 trials each, one session per day) of two-way active avoidance conditioning. Ten days after the last training session, another session was administered in order to test the long-term retention of the task. Results indicated that habenular lesions did not affect the overall performance of the rats during either the acquisition sessions or the retention session of two-way active avoidance. We suggest that habenular lesions can affect the acquisition of several learning tasks, probably through their role in modulating stress responses and/or arousal states. The nature of these effects (whether facilitative, detrimental, or neutral) might depend on the interaction between several factors such as the kind of task, the specific conditioning procedures (which may generate different stress levels), and the specific area destroyed by the lesion.

Animals↗

PubMed1997

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.

Animals↗

PubMed1996

Tuberomammillary nucleus lesion facilitates two-way active avoidance retention in rats.

To evaluate whether the tuberomammillary nucleus might be involved in the acquisition and/or retention of a two-way active avoidance conditioning, rats were given a unilateral lesion of the tuberomammillary nucleus (E2 region) 24 h prior to the first conditioning session. Four learning sessions were performed: one acquisition and 3 retention sessions (short-term, 24 h; and long-term, 8 and 18 days). Results showed that the lesion facilitated the long-term retention of conditioning, but no effects were observed on acquisition and short-term retention. Since rewarding intracranial electrical stimulation seems to be a consistent way to facilitate learning and memory processes, and tuberomammillary lesion has been shown to improve intracranial self-stimulation behavior (ICSS), we suggest that lesions in the present experiment could have facilitated two-way active avoidance retention by enhancing the function of brain reward mechanisms.

Animals↗

PubMed1996

Shuttle-box memory facilitation by posttraining intracranial self-stimulation: differential effects in rats with high and low basic conditioning levels.

The effects of intracranial self-stimulation (ICSS) on retention (after 24 hr, 7, 15, or 60 days) of a massed 2-way active avoidance task were studied in independent groups of rats. All groups showed a higher performance on the retention session than on the acquisition one. In the control subjects, the higher retention performances were observed in the 7- and 15-day groups. However, the ICSS treatment facilitated the 24-hr retention compared with its control group, allowing the treated subjects to achieve the same level of performance on the 24-hr retention session than that achieved by the control rats at the 7-day retention test. In the 24-hr groups, the facilitatory ICSS effect was stronger in the subjects with a low level of conditioning and weaker in those with a high level. Results suggest that posttraining ICSS accelerates memory consolidation and equalizes the performance of poor and good learners.

Animals↗

PubMed1995

Effects of parafascicular electrical stimulation and lesion upon two-way active avoidance in rats.

To evaluate a possible role of the parafascicular nucleus (PF) in modulating distributed two-way active avoidance acquisition and long-term retention (LTR), we designed two experiments. Experiment I was aimed at checking whether posttraining PF intracranial electrical stimulation (PF ICS) can improve the acquisition and/or the LTR of the task. All subjects (Ss, male Wistar rats) were implanted with an electrode at the PF. After each learning session two groups of Ss were stimulated for 10 (ICS-10 group) and 5 (ICS-5 group) min, respectively. A Control group never received PF ICS, while Ss in an ICS-Control group received PF ICS only during a previous search for a nonconvulsive current intensity. Unexpectedly, the ICS-Control group showed poor performance of the task compared to the remaining groups. Since the histological analyses showed that the pretraining ICS treatment produced some PF tissue lesion, Experiment II was aimed at evaluating the effects upon the same task of (1) pretraining PF electrolytical lesions (PF-Lesion group) and (2) posttraining PF ICS treatment (ICS group) at a lower current intensity and without a previous search for nonconvulsive current intensity. PF pretraining lesion decreased conditioning, while posttraining PF ICS did not affect it. We concluded that PF could have a modulatory role in acquisition, and might also contribute to posttraining consolidation, of a distributed two-way active avoidance.

Animals↗

PubMed1995

Facilitatory and detrimental effects of parafascicular electrical stimulation upon two-way active avoidance conditioning in rats.

To evaluate whether post-training parafascicular intracranial electrical stimulation (PF ICS) can improve acquisition (five sessions, one daily, 10 trials each) and long-term retention (LTR) (one session, 10 trials) of two-way active avoidance conditioning in rats, experimental subjects (Ss) were implanted with an electrode at the parafascicular nucleus (PF). Control Ss were sham operated without implanted electrodes. Immediately after each acquisition session Ss in the experimental groups were stimulated in the PF during 2- or 10-min periods. After histological analyses Ss were grouped according to the antero-posterior PF stereotaxic coordinates for the electrode tip locations. Ss stimulated at the posterior PF area improved acquisition and the central PF area showed detrimental effects upon conditioning. Electrical stimulation of the anterior PF area did not affect conditioning performance. We conclude that PF appears to have differential modulatory roles in acquisition and retention of two-way active avoidance depending on the PF area involved.

Animals↗

PubMed1994

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.

Animals↗

PubMed1993

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.

Animals↗

PubMed1993

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.

Animals↗