Abstract
Learning is known to be accompanied by induction of c-Fos expression in cortical neurons. However, not all neurons are involved in this process. What the c-Fos expression pattern depends on is still unknown. In the present work we studied whether and to what degree previous animal experience about Task 1 (the first phase of an instrumental learning) influenced neuronal c-Fos expression in the retrosplenial cortex during acquisition of Task 2 (the second phase of an instrumental learning). Animals were progressively shaped across days to bar-press for food at the left side of the experimental chamber (Task 1). This appetitive bar-pressing behavior was shaped by nine stages (“9 stages” group), five stages (“5 stages” group) or one intermediate stage (“1 stage” group). After all animals acquired the first skill and practiced it for five days, the bar and feeder on the left, familiar side of the chamber were inactivated, and the animals were allowed to learn a similar instrumental task at the opposite side of the chamber using another pair of a bar and a feeder (Task 2). The highest number of c-Fos positive neurons was found in the retrosplenial cortex of “1 stage” animals as compared to the other groups. The number of c-Fos positive neurons in “5 stages” group animals was significantly lower than in “1 stage” animals and significantly higher than in “9 stages” animals. The number of c-Fos positive neurons in the cortex of “9 stages” animals was significantly higher than in home caged control animals. At the same time, there were no significant differences between groups in such behavioral variables as the number of entrees into the feeder or bar zones during Task 2 learning. Our results suggest that c-Fos expression in the retrosplenial cortex during Task 2 acquisition was influenced by the previous learning history.
Highlights
It has been widely shown that learning situations induce immediate early gene (IEG) expression in brain neurons of various species (Kaczmarek and Chaudhuri, 1997; Herdegen and Leah, 1998; Tischmeyer and Grimm, 1999; Clayton, 2000; Miyashita et al, 2008)
Previous studies using neuronal recording methods indicated that many neurons of the retrosplenial cortex were activated during bar-pressing appetitive task (Aleksandrov et al, 1997; Svarnik et al, 2005)
Such specific activities are probably acquired during task learning through the mechanism of IEG activation in those neurons
Summary
It has been widely shown that learning situations induce immediate early gene (IEG) expression in brain neurons of various species (Kaczmarek and Chaudhuri, 1997; Herdegen and Leah, 1998; Tischmeyer and Grimm, 1999; Clayton, 2000; Miyashita et al, 2008). One IEG, c- fos gene, might be used as a cellular marker of learning-related neuronal plasticity (Anokhin and Rose, 1991; Rylski and Kaczmarek, 2004; Lyons and West, 2011). Animals’ brains in the absence of learning situations (in home caged controls or in animals executing an over-trained skill) are characterized by a low number of c-Fos positive neurons (Anokhin et al, 2001; Svarnik et al, 2005). Some structures show an elevated number of c-Fos positive neurons after learning. Distribution of c-Fos positive neurons among brain structures seems to depend on the learning paradigm. A novelty recognition task in mice activated c-Fos expression in the basolateral amygdala, the paraventricular hypothalamic nucleus, the suprapyramidal blade of the dentate gyrus and the medial prefrontal cortex (Castilla-Ortega et al, 2012)
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