CIRCADIAN ORGANIZATION IN THE RUIN LIZARD PODARCIS-SICULA - THE ROLE OF THE SUPRACHIASMATIC NUCLEI OF THE HYPOTHALAMUS

The effects of electrolytic lesions to the suprachiasmatic nuclei of t he hypothalamus (SCN) on circadian rhythms of locomotor activity were examined in ruin lizards Podarcis sicula maintained in constant darkne ss and constant temperature (29 degrees C). All lizards (N=15) in whic h the lesion damaged 80% or more of the SCN became behaviorally arrhyt hmic. On the contrary, locomotor rhythms persisted in all cases (N=11) when the SCN remained intact and lesions were confined to neighbourin g regions of the preoptic area. Taken together with previous work whic h demonstrates that the pineal and the retinae are not essential for t he persistence of circadian locomotor rhythmicity in Podarcis sicula a nd with recent evidence showing the homology between the SCN of lizard s and those of mammals the present results strongly support the view t hat the SCN of Podarcis sicula contain the primary pacemaker(s) for lo comotor rhythms.