Abstracts

Rationale: Hypoxic encephalopathy is the most common cause of neonatal seizures and often leads to the development of epilepsy and cognitive impairment. We have reported changes in NMDAR(NR) function after P10 hypoxic seizures(HS), with NR redox sites reduction leading to enhanced NR eEPSC amplitude (Sanchez et al., J. Neurosci 2000), as well as a reduction in ifenprodil sensitivity in slices removed at 48 hours post HS at P10(Dai and Jensen, AES abstract 1.007, 2004). In this study we hypothesized that early HS at P10 might alter other functional NR eEPSC attributes. Methods: HS were induced in P10 rat pups by global hypoxia (15 minutes at 4-7% O2). Hippocampal slices were prepared at 1, 24, 48, 96 hrs and 1 week after HS in vivo. NR evoked(e) EPSCs were recorded in CA1 pyramidal neurons at 40. ACSF contained 60 M picrotoxin and 10 M NBQX. Ifenprodil (5 M) or cis-PPDA (2 or 0.8 M) was used to examine the NR2B or NR2C/D subunit component of NRs. 100 M DL-AP5 was used to block eEPSCs to confirm their NR identity. NR eEPSC IV curves were fitted with a Woodhull equation to obtain Mg2 Kd(mM). Results: Consistent with our prior results, slices removed following HS in vivo showed difference in the ifenprodil blockade. In slices removed at 24 and 48 hrs post HS, there was less effect of ifenprodil(24 hrs, 10.35 4.1%, n=4; 48 hrs, 21.30 6.78%, n=4) compared to controls (24 hrs, 58.2 8.0%, n=4, p<0.05; 48 hrs, 71.35 8.1%, n=4, p<0.05). In slices removed at 96 hrs or 1 week there was no difference in the ifenprodil blockade (15.54 7.8%, n=5 at 96; 15.97 8.93%, n=5 at 1 week) compared to controls (26.98 6.43%, n=5 at 96, p>0.05; 29.47 14.93%, n=4, p>0.05 at 1 week). We also examined NR eEPSCs regarding their sensitivity to cis-PPDA. At 48, 96 hrs and 1 week, NR eEPSCs showed differences in the percentage blockade (controls 48 hrs, 32.9 10.3%, n=3; 96 hrs, 48.4 12.3%, n=3; 1 week 72.3 8.43%, n=3). This suggests that NRs at these ages expressed NR2C/D subunits. However, there was no significant cis-PPDA blockade difference between HS and controls (post HS 48 hrs, 37%, n=2; 96 hrs, 44.6 8.83%, n=4, p>0.05; 1 week, 70.64 5.76%, n=4, p>0.05), implying HS may not influence NR2C/D subunit expression. In contrast, we observed significant difference in Mg2 -sensitivity at 96 hrs post HS, not at 1 week. With Woodhull equation to fit NR eEPSC IV curves, post HS at 96 hrs had larger Mg2 Kd at 0 mV (12.43 3.45 mM, n=6, p<0.05) in comparison to control (6.32 2.41mM, n=5). Conclusions: Our data suggest that early life HS at P10 cause multiple NR alterations, including decreased NR2B specific antagonist ifenprodil sensitivity, suggestive of a decrease in NR2B levels. In addition, there appears to be a developmental increase in NR2C/D antagonist cis-PPDA sensitivity, but seizures did not alter this maturational phase. Finally, HS decrease Mg2 -sensitivity, mediated specifically by an increased NR3A subunits, given the lack of change in NR2C/D function. In summary, these data justify further evaluation of NMDA subunit expression in the acute period following early HS. DP1 0D003347, RO1 NS31718, HD007466-12(T32),IDDRC P30 HD 18655