Facilitación de la memoria por autoestimulación eléctrica intracraneal en ratas normales y con lesión cerebral
Intracranial self-stimulation (SS) of the lateral hypothalamus (LH), in the medial forebrain bundle (MFB), facilitates learning and memory processes in a wide variety of paradigms in both young and aged rats. Some data support the idea that the LH-SS facilitative effect seems related to the arousing properties of the MFB reward system.
Memory is an active and complex process that covers different stages such as acquisition, consolidation or retrieval. Acquisition of information through the senses is necessarily the first step, which is followed by consolidation, an active process for storing the information just acquired. The retrieval could reactive these stored memories which then can be used to guide behavior. It has been demonstrated that the facilitative effects of several activatory treatments on different learning and memory stages depend on the time of administration with regard to training. To evaluate possible differential effects of lateral hypothalamic SS on memory consolidation and retrieval, independent groups of Wistar rats were trained in a single session of two-way active avoidance task acquisition session) and tested 24 h later (retention session). The post-ICSS groups received an ICSS treatment immediately after the acquisition session, and the pre-ICSS groups received the same treatment immediately before the retention session. Because the ICSS effects on memory seem to be dependent on the initial performance level shown by the subjects, the possible influence of initial training (number of trials) on ICSS effects was also studied. Therefore, we used different control and experimental groups, which received either 30 or 50 trials in the acquisition session. Post-training ICSS facilitated the 24-h retention in both training conditions (30 and 50 trials). In contrast, pre-retention ICSS treatment did not facilitate performance in the retention test. We also observed that post-training ICSS was more effective for improving the 24-h retention than increasing the initial training from 30 to 50 trials. These findings confirm that ICSS treatment improves memory consolidation and suggest that it might not affect memory retrieval mechanisms.
The activatory effects of brain reward systems could affect to multiple arousal systems. Despite the fact that each neurochemical arousal system could play a specific role in brain activation and information processing, several data indicate that the presence of multiple activating structures may compensate for the loss of certain components. So, it is plausible that the functional lack of one of the arousal systems could be functionally compensated by the activation of other systems. Since MFB activation enhances memory and modulates brain arousal, the LH-SS could be a way to compensate memory-deficits generated by the hypofunctionality of some of the arousal systems, i.e. induced by parafascicular nucleus (PF) damage. In fact, some experiments have shown that it is possible to induce a functional recovery of PF-lesion-induced effects after administration of amphetamine or ACTH(4-9) analogs. To evaluate whether SS ameliorates conditioning deficits induced by PF damage in young and aged rats, 142 animals received a daily single session of two-way active avoidance until to achieve a fixed criterion. Four experimental groups were established in both young and aged rats: 1) SS treatment after every conditioning session (SS groups), 2) Pre-training PF lesions (Lesion groups), 3) PF lesions and SS treatment (L+SS groups) and 4) Control groups. SS treatment not only canceled the detrimental effects of PF lesions, but improved conditioning in lesioned animals (L+SS groups). This effect was more powerful in aged rats. SS treatment could compensate memory deficits generated by hypofunctionality of some arousal systems, as the one involving PF.
Advisor:Segura Torres, Pilar; Morgado Bernal, Ignacio
School:Universitat Autónoma de Barcelona
Source Type:Master's Thesis
Keywords:452 departament de psicobiologia i metodologia les ciencies la salut
Date of Publication:04/03/2003