Intergeniculate leaflets lesion delays but does not prevent the integration of photoperiodic change by the suprachiasmatic nuclei

The duration of the photosensitive phase of the suprachiasmatic nuclei (SCN ), as revealed by light-induced Fos protein expression, depends on the phot operiod and is tied to the length of the night. We show here in Syrian hams ters that after a transfer from long to short photoperiod, lengthening of t he photosensitive phase of the SCN is significantly delayed but not abolish ed when the intergeniculate leaflets (IGL) are lesioned. Thus IGL modulate the integration by the SCN of a photoperiodic change. (C) 2001 Elsevier Sci ence B.V. All rights reserved.