Effects of intergeniculate leaflet lesions on circadian rhythms in the mouse

We investigated effects of bilateral electrolytic intergeniculate leaflet (IGL) lesions (IGLX) on circadian rhythms of the wheel-running activity in mice kept under constant darkness conditions (DD). As a result of complete bilateral IGL lesions, the period of a free-running rhythm was lengthened by ca. 45 min in comparison with a pre-operational one. The present findings confirm results obtained previously with other animals. However, for the first time locomotor activity levels were precisely assessed in mice (the number of wheel revolutions/day) before and after IGL lesions. A computer analysis of data showed a considerable decrease in that activity (by 68% on an average) in mice with complete bilateral IGL lesions in comparison with IGL-non-lesioned individuals. The obtained results show that also in mice IGL constitutes an anatomically important element of the mechanism of a circadian time-keeping system, which mediates the transfer of non-photic information to the suprachiasmatic nuclei (SCN) by modulating their activity.