Behavioral effects of corpus callosum transection and environmental enrichment in adult rats

A common assumption about the corpus callosum transection (CCX) is that it only affects behaviors heavily relying on interhemispheric communication. However, cerebral laterality is ubiquitous across motor and perceptual, cognitive and emotional domains, and the corpus callosum is important for its establishment. Several recent studies showed that the partial denervation of the sensorimotor isocortex through CCX derepressed neural growth processes that were sensitive to motor demand (experience-dependent neural plasticity). We investigated whether the facilitatory effects of CCX on cortical neural plasticity, shaped by differential housing, extended beyond the motor domain. Adult rats were housed in enriched (EE), standard (SE) or impoverished environments (IE) for 10 weeks, that is, 2 weeks before they underwent CCX or sham surgery, and, then, 8 weeks throughout the experiments. After they recovered from surgery, the behavioral performance of rats was tested using open-field, spontaneous alternation in the T-maze, paw preference, Morris water maze, and tone fear conditioning. The results indicated that the effects of CCX and housing on open-field behavior were independent, with CCX increasing the time spent in the center of the field at the beginning of the observation (i.e., emotionality), and EE and IE increasing rearing (emotionality) and reducing teeth-chattering (habituation), respectively. CCX reduced the frequency of spontaneous alternation, denoting spatial working memory deficits, while housing did not influence this performance. Neither CCX, nor housing significantly affected paw preference lateralization, although CCX was associated with a leftward bias in paw preference. In the Morris water maze, housing had effects on spatial acquisition, while CCX reduced activity, without interfering with spatial memory. CCX did not influence tone fear conditioning, but context fear conditioning seemed to benefit from EE. We conclude that CCX in adult rats has subtle, but specific behavioral effects pertaining to emotionality, spatial working memory, and, possibly, aversively motivated exploration, and these effects are either independent or only peripherally interact with the effects of housing. (c) 2006 Elsevier B.V. All rights reserved.