BRAIN THYROTROPIN-RELEASING-HORMONE CONTENT VARIES THROUGH AMYGDALOIDKINDLING DEVELOPMENT ACCORDING TO AFTERDISCHARGE FREQUENCY AND PROPAGATION

Purpose: Thyrotropin-releasing hormone (TRH), present in extra hypotha lamic brain areas, has been proposed to have neuromodulatory functions and to be susceptible to change by electrical stimulation paradigms. We measured TRH concentrations of several brain areas during kindling development before its establishment and determined whether the change s detected in TRH levels were related to the behavioral stages of kind ling, the number of stimulations required to reach these stages and, w ith the electrophysiological parameters characteristic of this paradig m (amygdaloid afterdischarge (AD) frequency, duration, and propagation ). Methods: Male Wistar rats were implanted stereotaxically with indwe lling bipolar electrodes in the basolateral nucleus of the amygdala an d with two stainless-steel electrodes epidurally in frontal cortex. Am ygdaloid kindling was induced by daily electrical stimulation; AD freq uency and duration were recorded and analyzed throughout the developme nt of kindling. TRH was extracted from several regions and quantified by radioimmunoassay (RIA). Results: Modifications in TRH concentration s were detected, depending on the region assayed, from stage II of kin dling. A positive correlation was noted between the levels of TRH and the frequency and propagation of AD, but not with the number of stimul ations. The rate of change in TRH concentration in relation to AD freq uency or duration was highest in frontal cortex followed by hippocampu s and amygdala. Conclusions: A graded response was noted in the increa se in TRH concentration dependent on the increase of AD frequency and propagation. The rate of response correlated with the region's epilept ogenic susceptibility.