PERIODICITY OF THALAMIC SYNCHRONIZED OSCILLATIONS - THE ROLE OF CA2-MEDIATED UP-REGULATION OF I-H()

Thalamocortical networks can generate both normal and abnormal pattern s of synchronized network activity, such as spindle waves and spike-an d-wave seizures. These periods of synchronized discharge are often sep arated by a silent, refractory phase of between 5 and 20 s. In vitro i nvestigations have demonstrated that this refractory period is due in large part to the persistent activation of the hyperpolarization-activ ated cation current I-h in thalamocortical cells. Here, we show that i ncreases in [Ca2+](i) due to rebound Ca2+ bursts result in persistent activation of I-h resulting from a positive shift in the activation cu rve of this current. The dynamical upregulation and persistent activat ion of I-h is the critical determinant of the time course of the refra ctory period. These findings demonstrate that periodicity in neural ne twork oscillations may be generated through an interaction between the electrophysiological properties and intracellular signaling pathways of the constituent neurons.