Deficit of Long-Term Potentiation Induction, but Not Maintenance, in the Juvenile Hippocampus after Neonatal...

CA3-CA1 long-term potentiation (LTP) in the hippocampal slices from juvenile Wistar rats was studied to reveal factors potentially contributing to different sensitivity to neonatal proinflammatory stress (NPS). NPS was induced by intra-peritoneal injections of bacterial lipopolysaccharide (LPS) to neonatal rats (two injections of LPS, or saline in the control group, consecutively on postnatal days 3 and 5 [PND3 and PND5]). In females, a significant effect of NPS on hippocampus development was associated with modifications of long-term synaptic plasticity, the synapses becoming more resistant to LTP induction. LTP deficit in the slices of the NPS group was not associated with a decrease in LTP maintenance, since late LTP generally corresponded to early LTP magnitude, similar in all groups. Moreover, partial correlation revealed significantly higher residual LTP 1 h after high-frequency stimulation in the NPS groups compared to the corresponding value of early LTP in the control groups, suggesting improved consolidation. Both effects were evident in NPS females. A number of males responded to NPS similarly to females, while others were relatively resistant to NPS exposure, a significant increase in variability of LTP magnitude being revealed in NPS males compared to respective females and the control groups. We suggest that postnatal development of long-term plasticity after NPS is similar in animals of both sexes; however, additional specific factor(s) may promote a relative resistance of the male brain.