VARIATIONS OF RAT-BRAIN CALMODULIN CONTENT IN DARK AND LIGHT PHASES -EFFECT OF PENTYLENETETRAZOL-INDUCED KINDLING

Calmodulin (CaM) through activation of CaM-kinase II may be involved i n the molecular mechanisms underlying the epileptogenic processes. Som e evidence suggests that kindling responses change across the day-nigh t cycle. In order to test if kindling stimulation modifies CaM content , we measured CaM concentrations in amygdala, hippocampus and hypothal amus obtained from control and kindled rats during light and darkness. Male Wistar rats (250-300 g), were injected i.p. with Pentylenetetraz ol (PTZ) (35 mg/kg/24 h). Once chemical kindling was established, rats were sacrificed by decapitation at 10:30 a.m. and 01:30 a.m. The brai ns were obtained, and the amygdala, hippocampus and hypothalamus disse cted. CaM content was measured in the cytosol and membrane fractions b y radioimmunoassay. We found a significant increase in CaM content in cytosol and membrane fractions of both control and kindled rats during the dark phase. No significant differences in CaM concentrations were observed between control and experimental rats, whether during the li ght or the dark phase. The data suggest a well defined photoperiodic v ariation in CaM concentrations in limbic structures, despite the neuro nal excitability produced by kindling. In addition, the observed CaM i ncreases during the dark time may be related to a protective mechanism against enhanced sensitivity to seizures observed during the night.