Journal of Neurophysiology, Vol 70, Issue 2 857-862, Copyright © 1993 by APS
Increased propensity for nonsynaptic epileptiform activity in immature rat hippocampus and dentate gyrus
S. N. Roper, A. Obenaus and F. E. Dudek
Division of Neurosurgery, UCLA School of Medicine 90024.
1. Low-[Ca2+] bursting was studied in hippocampal slices from immature and
adult rats to test the hypothesis that the increased seizure susceptibility
of the immature brain involves nonsynaptic mechanisms. Extracellular
recordings were obtained from area CA1 of the hippocampus and from the
dentate gyrus in slices from rats 6-9 days old (1 wk), 11-15 days old (2
wk), 19-23 days old (3 wk), and > 60 days old (adult). These slices were
exposed to a low-[Ca2+] solution that included the calcium chelator,
ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid
(EGTA), and the excitatory amino acid antagonists,
6,7-dinitroquinoxaline-2,3-dione (DNQX) and DL-2-amino-5-phosphonopentanoic
acid (AP-5). They were also exposed to a hyposmolar low-[Ca2+] solution
(diluted with 20% H2O by volume), which induced or intensified the
bursting. The propensity for nonsynaptic bursting and the characteristics
of the bursts were compared between age groups. 2. The 1-wk group showed no
bursting activity under any treatment condition in either CA1 or the
dentate gyrus. Bursting occurred more frequently in the 2- and 3-wk groups
than in the adult group in both CA1 and the dentate gyrus. 3. In CA1 the
duration of the bursts was longer in the 2- and 3-wk groups as compared
with the adult group. The number of population spikes per burst was also
higher in slices from immature rats in dilute low-[Ca2+] solution. These
findings demonstrate that nonsynaptic bursting in area CA1 is more robust
in tissue from immature rats than adults.(ABSTRACT TRUNCATED AT 250 WORDS)
