62ª Reunião Anual da SBPC

C. Ciências Biológicas - 12. Neurociências e Comportamento - 1. Neurociências e Comportamento

EXTENDING POSSIBLE APPLICATIONS OF AN EPISODIC-LIKE MEMORY TASK IN RATS

Flávio Freitas Barbosa 1 Isabella Maria de Oliveira Pontes 1 Alessandra Mussi Ribeiro 1 Regina Helena da Silva 1

1. Departamento de Fisiologia, Universidade Federal do Rio Grande do Norte

INTRODUÇÃO:

Human episodic memory refers to the capability of recollecting what, when and where a specific event occurred. It also involves mental time travelling and requires "autonoetic" consciousness. The behavioural criterion is based on the 'what-where-when' content of a certain memory, which was designated as episodic-like memory. Dere et al. have developed a new three-trial object exploration task in rodents that simultaneously access all these components. This new task involves a spontaneous behaviour; thereby it does not require various sets of training. However, the retention delay used in this new task is about 1 h, which can be a constraint in the methodological applications of the protocol. The purpose of this study was to determine if this new three-trial episodic-like memory task can persist after a 24 h delay. The effect of a classical amnestic agent (scopolamine) on episodic-like memory consolidation in this task was also investigated.

METODOLOGIA:

Four-month-old male Wistar rats were housed under conditions of controlled temperature under a 12 h light/12 h dark. All procedures were approved by the local ethical committee. The task was carried out in a circular open-field made of wood and painted in black. Three sets of objects, with four copies each, were used. In experiment I, one 10-min habituation session was performed 24 h before the procedure. The task consisted of two sample trials and one test trial. In the first sample trial, the rat was placed in the open-field with four copies of object "A" for 5min. After 1 h (second sample trial) four copies of object "B" were presented in a different spatial configuration. The test trial was performed 24 h later. In this phase, two copies of the objects introduced in each trial were presented. One object from the first trial was in a different spatial location. The other objects were in the same positions of the sample trials. In experiment II, the protocol used was identical to the previous experiment, except that a group of animals (n = 8) received scopolamine diluted in distilled water; (1mg/kg, i.p.) immediately after training and another group (n = 10) received saline (0.9% NaCl, i.p.).

RESULTADOS:

The rats had an increased "old" objects exploration ratio when compared to "recent" object exploration ratio (t(14)=4.75; p<0.001). In addition, there was no difference between the old displaced and the old stationary object exploration ratios (t(14)=0.90; p=0.38). ANOVA with repeated measures revealed a significant time effect when the old displaced object exploration ratio was analysed [F(4,56)=4.57; p=0.008]. Post hoc analyses showed a significant decrease in the exploration ratio between the first and third minutes (p = 0.001).The rats spent more time exploring the old displaced object than the old stationary object (t(14)=2.39; p=0.03). In experiment II, one-way ANOVA with repeated measures performed to saline rats showed significant effect of the object exploration ratios [F(3,27) = 4.68; p=0.009]. Saline rats spent more time exploring "old" objects when compared to "recent" objects (t(9)=2,54; p=0.03). Saline rats spent more time exploring old displaced object when compared to old stationary object (t(9)=2.5; p=0.03) in the first minute. On the other hand, scopolamine-treated rats did not discriminate either temporally or spatially the objects when both the whole test session and the first minute of the test were considered for analysis.

CONCLUSÃO:

In conclusion, the present study shows that the episodic-like memory evaluated in the object recognition task that accomplishes what, where and when components can persist at least for 24 h. Further, when an amnestic drug (i.e. scopolamine) was administered immediately post-training, animals did not present spatiotemporal discrimination of the objects, contributing to the validation of the paradigm. The important implication of this finding is that pharmacological approaches and other methods can be used to study the neurobiology of acquisition, consolidation, retrieval and extinction of episodic-like memory separately in this protocol, which is an important tool in the study of the neural mechanisms of episodic memory.

Instituição de Fomento: Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq; CAPES

Palavras-chave: Memória episódica, Ratos, Escopolamina.