Ps. Buckmaster et al., ELECTROPHYSIOLOGICAL CORRELATES OF SEIZURE SENSITIVITY IN THE DENTATEGYRUS OF EPILEPTIC JUVENILE AND ADULT GERBILS, Journal of neurophysiology, 76(4), 1996, pp. 2169-2180
1. Naturally occurring inherited epilepsy is common among Mongolian ge
rbils, providing an opportunity to identify neurological factors that
correlate with seizure behavior. In the present study we examine the o
ntogeny of seizure behavior and compare the electrophysiology and anat
omy of the dentate gyrus in epileptic and nonepileptic gerbils. 2. Beh
avioral seizure testing revealed that young gerbils do not begin havin
g seizures until they are 2 mo of age, at which time seizure incidence
across animals is at its highest level. Most seizure-positive juvenil
e gerbils became epileptic adults, but 30% outgrew their epileptic con
dition. 3. The number of somatostatin- and parvalbumin-immunoreactive
neurons in the dentate gyrus and Ammon's horn was counted, with the us
e of quantitative stereological techniques, in juvenile and adult gerb
ils. No significant differences were detected between epileptic and no
nepileptic groups. 4. In dentate gyrus field potential responses to pe
rforant path stimulation, adult epileptic gerbils showed enhanced pair
ed-pulse inhibition at short (30 ms) interstimulus intervals and enhan
ced facilitation at intermediate (70 ms) intervals compared with nonep
ileptic controls. These differences were most pronounced when stimuli
were delivered at faster (1.0 Hz) rather than slower (0.1 Hz) rates. 5
. Compared with seizure-negative juveniles, seizure-positive juveniles
showed the same pattern of paired-pulse response abnormalities as epi
leptic adults. However, seizure-positive juveniles had a lower thresho
ld for maximal dentate activation than epileptic adults. 6. These resu
lts demonstrate similar functional abnormalities in the dentate gyri o
f epileptic adult gerbils and in juvenile gerbils before they experien
ce multiple seizures. Such findings suggest that abnormalities in func
tional inhibition of the dentate gyrus network precede and therefore m
ight contribute to overt seizure activity.