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 in the molecular mechanisms underlying the epileptogenic processes. Some evidence suggests that kindling responses change across the day-night cycle. In order to test if kindling stimulation modifies CaM content, we measured CaM concentrations in amygdala, hippocampus and hypothalamus obtained from control and kindled rats during light and darkness. Male Wistar rats (250-300 g), were injected i.p. with Pentylenetetrazol (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 brains were obtained, and the amygdala, hippocampus and hypothalamus dissected. CaM content was measured in the cytosol and membrane fractions by 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 light or the dark phase. The data suggest a well defined photoperiodic variation in CaM concentrations in limbic structures, despite the neuronal excitability produced by kindling. In addition, the observed CaM increases during the dark time may be related to a protective mechanism against enhanced sensitivity to seizures observed during the night.