Intracranial self stimulation upregulates the expression of synaptic plasticity related genes and Arc protein expression in rat hippocampus.

Post-training lateral hypothalamus (LH) intracranial self stimulation (ICSS) has a reliable enhancing effect on explicit memory formation evaluated in hippocampus-dependent tasks such as the Morris water maze. In this study, the effects of ICSS on gene expression in the hippocampus are examined 4.5 h post treatment by using oligonucleotide microarray and real-time PCR, and by measuring Arc protein levels in the different layers of hippocampal subfields through immunofluorescence. The microarray data analysis resulted in 65 significantly regulated genes in rat ICSS hippocampi compared to sham, including cAMP-mediated signaling as one of the most significantly enriched Database for Annotation, Visualization and Integrated Discovery (DAVID) functional categories. In particular, expression of CREB-dependent synaptic plasticity related genes (c-Fos, Arc, Bdnf, Ptgs-2 and Crem and Icer) was regulated in a time-dependent manner following treatment administration. Immunofluorescence results showed that ICSS treatment induced a significant increase in Arc protein expression in CA1 and DG hippocampal subfields. This empirical evidence supports our hypothesis that the effect of ICSS on improved or restored memory functions might be mediated by increased hippocampal expression of activity-dependent synaptic plasticity related genes, including Arc protein expression, as neural mechanisms related to memory consolidation.

Intracranial self-stimulation induces expression of learning and memory-related genes in rat amygdala.

Intracranial self-stimulation (ICSS) in the lateral hypothalamus improves memory when administered immediately after a training session. In our laboratory, ICSS has been shown as a very reliable way to increase two-way active avoidance (TWAA) conditioning, an amygdala-dependent task. The aim of this work was to study, in the rat amygdala, anatomical and molecular aspects of ICSS, using the same parameters facilitating TWAA. First, we examined the activation of ipsilateral and contralateral lateral (LA) and basolateral (BLA) amygdala, the main amygdalar regions involved in the TWAA, by the immunohistochemical determination of c-Fos protein expression. Second, we tested the effects of the ICSS treatment on the expression of 14 genes related to learning and memory processes using real-time polymerase chain reaction. Results showed a bilateral increase in c-Fos protein expression in LA and BLA nuclei after ICSS treatment. We also found that Fos, brain-derived nerve growth factor (BDNF), Arc, inducible cAMP early repressor (ICER), COX-2, Dnajb1, FKpb5 and Ret genes were upregulated in the amygdala 90 min and 4.5 h post ICSS. From this set of genes, BDNF, Arc and ICER are functionally associated with the cAMP-responsive element-mediated gene transcription molecular pathway that plays a pivotal role in memory, whereas Dnajb1 and Ret are associated with protein folding required for plasticity or neuroprotection. Our results suggest that ICSS induces expression of genes related with synaptic plasticity and protein folding functions in the rat amygdaloid area, which may be involved in the molecular mechanisms by which ICSS may improve or restore memory functions related to this brain structure.

Intracranial self-stimulation to the lateral hypothalamus, a memory improving treatment, results in hippocampal changes in gene expression.

Intracranial self-stimulation (ICSS) within the medial forebrain bundle of the lateral hypothalamus (LH) facilitates consolidation of implicit and explicit memories for a variety of learning paradigms in rats. However, the neural and molecular mechanisms involved in memory facilitation by ICSS are not known. Here, we investigated the influence of ICSS treatment on hippocampal gene expression in order to identify potential signaling pathways and cellular processes involved in ICSS-mediated cognitive improvements. Immunohistochemistry studies demonstrated that ICSS caused a rapid induction of c-Fos expression in hippocampal cornu ammonis (CA) 3 and dentatus gyrus areas. Moreover, using microarray or quantitative real-time polymerase chain reaction (PCR) analysis, we showed that ICSS modulates the expression of 62 hippocampal genes shortly after training. Most of the proteins encoded by these genes, such as calmodulin-dependent-phosphodiesterase 1 A (Pde1a), are part of signal transduction machineries or are related to anti-apoptosis, as heat shock 70 kDa protein 1A (Hspa1a). Importantly, 10 of the regulated genes have been previously related with learning and memory or neural plasticity, including the cocaine and amphetamine-regulated transcript (Cart), adenylate cyclase activating polypeptide 1 (Adcyap1), serum/glucocorticoid regulated kinase (Sgk), Ret proto-oncogene (Ret), and Fos. The fact that the Fos gene was differentially expressed in our microarray experiments validated our findings from our immunohistochemical studies mentioned above. In addition, using quantitative real-time PCR, we confirmed the observed expression changes for several of the genes identified by our microarray analyses. Our results suggest that ICSS may facilitate learning and memory by regulation of multiple signaling pathways in the hippocampus that may promote neuroplasticity.

Intracranial self-stimulation facilitates a spatial learning and memory task in the Morris water maze.

Learning and memory improvement by post-training intracranial self-stimulation has been observed mostly in implicit tasks, such as active avoidance, which are acquired with multiple trials and originate rigid behavioral responses, in rats. Here we wanted to know whether post-training self-stimulation is also able to facilitate a spatial task which requires a flexible behavioral response in the Morris water maze. Three experiments were run with Wistar rats. In each of them subjects were given at least five acquisition sessions, one daily, consisting of 2-min trials. Starting from a random variable position, rats had to swim in a pool until they located a hidden platform with a cue located on its opposite site. Each daily session was followed by an immediate treatment of intracranial self-stimulation. Control subjects did not receive the self-stimulation treatment but were instead placed in the self-stimulation box for 45 min after each training session. In the three successive experiments, independent groups of rats were given five, three and one trial per session, respectively. Temporal latencies and trajectories to locate the platform were measured for each subject. Three days after the last acquisition session, the animals were placed again in the pool for 60 s but without the platform and the time spent in each quadrant and the swim trajectories were registered for each subject. A strong and consistent improvement of performance was observed in the self-stimulated rats when they were given only one trial per session, i.e. when learning was more difficult. These findings agree with our previous data showing the capacity of post-training self-stimulation to improve memory especially in rats with little training or low conditioning levels, and clearly prove that post-training self-stimulation can also improve spatial learning and memory.

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.

Presumed 'prefrontal cortex' lesions in pigeons: effects on visual discrimination performance.

The posterodorsolateral neostriatum (PDLNS) in pigeons may be an equivalent of the prefrontal cortex (PFC) in mammals. Here we report that lesions of this brain region in pigeons have a detrimental effect on various learned visual discriminations. Pigeons with lesions of the overlying area corticoidea dorsolateralis (CDL) served as controls. Both the postoperative re-learning to criterion of a preoperatively learned simultaneous double visual mirror pattern discrimination and the learning of a simple successive go, no-go discrimination were impaired by the PDLNS lesions. The PDLNS and CDL groups did not differ significantly in the postoperative learning of a reversal of the simultaneous discrimination. The results are discussed in relation to the presumed equivalence between the avian PDNLS and the mammalian PFC.

Intracranial self-stimulation in the parafascicular nucleus of the rat.

A behavioral analysis of intracranial self-stimulation was provided for parafascicular nucleus. To evaluate whether intracranial self-stimulation in this nucleus could be site-specific and to determine if the positive sites are the same parafascicular areas that facilitate learning when stimulated, rats were tested via monopolar electrodes situated throughout the parafascicular nucleus. Animals were trained to self-stimulate by pressing a lever in a conventional Skinner box (1-5 sessions). Twenty-two of the 42 animals included in the study, had the electrode at the parafascicular nucleus. Only two of them showed intracranial self-stimulation. Histological analyses indicated that the latter rats had the electrode implanted at the anterior area of the medial parafascicular. Other two animals also showed intracranial self-stimulation but they had the electrode in a more posterior brain region, between the Dark-schewitsch nucleus and the red nucleus. The animals implanted at the parafascicular showed higher response rates than the other two rats. These results confirm that: (a) the anterior region of the medial parafascicular is a positive site for stable and regular intracranial self-stimulation behavior, and (b) these positive sites do not coincide with the parafascicular regions related to learning improvement.

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.

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.

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.

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.

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.