P. Degortari et al., BRAIN THYROTROPIN-RELEASING-HORMONE CONTENT VARIES THROUGH AMYGDALOIDKINDLING DEVELOPMENT ACCORDING TO AFTERDISCHARGE FREQUENCY AND PROPAGATION, Epilepsia, 39(8), 1998, pp. 897-903
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.