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Developmental changes in long-term potentiation in CA1 of rat hippocampal slices
1Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Insights
Long-term potentiation (LTP) is impaired in young and aged rats, with significant EPSP-PS dissociation observed in juvenile rats. This dissociation appears to stem from changes in somatic excitability.
Area of Science:
- Neuroscience
- Neurophysiology
Background:
- Long-term potentiation (LTP) is a crucial mechanism for learning and memory.
- The developmental trajectory of LTP induction and its underlying mechanisms in the rat hippocampus are not fully understood.
Purpose of the Study:
- To investigate the age-dependent changes in LTP induction in the CA1 region of rat hippocampal slices.
- To elucidate the role of excitatory postsynaptic potential (EPSP)-population spike (PS) dissociation (ES-dissociation) in LTP across different postnatal ages.
Main Methods:
- Electrophysiological recordings were performed in rat hippocampal slices from postnatal day 9 (P9) to P300.
- LTP was induced using a single high-frequency tetanus (100 Hz x 1 sec).
- Population spike amplitudes and dendritic/somatic excitatory postsynaptic potentials were measured.
Main Results:
- LTP induction failed at P9 and was difficult to induce in slices from rats aged P90 and older.
- Similar degrees of LTP were observed at P15, P30, and P60.
- At P15, ES-dissociation significantly contributed to LTP, with somatic excitability changes playing a major role.
- At P30, PS amplitudes were accurately predicted by dendritic EPSP changes, indicating minimal ES-dissociation.
Conclusions:
- LTP induction is age-dependent, with impaired potentiation in very young (P9) and aged (≥P90) rats.
- ES-dissociation, driven by somatic excitability, is a significant factor in hippocampal LTP at P15.
- These findings highlight critical developmental periods and age-related alterations in synaptic plasticity mechanisms.
Abstract:
Long-term potentiation (LTP) was examined in the CA1 region of rat hippocampal slices at postnatal day 9 (P9), P15, P30, P60, P90, P120, and P300. A single 100 Hz x 1 sec tetanus failed to induce LTP in P9 slices, while similar degrees of LTP were observed at P15, P30, and P60. At P30, changes in population spike (PS) amplitudes were accurately predicted by changes in dendritic excitatory postsynaptic potentials (EPSPs). However, at P15, the predicted increase in PS calculated from corresponding changes in dendritic EPSPs was significantly less than the observed increase, suggesting that EPSP-PS dissociation (ES-dissociation) plays a substantial role in LTP at P15. Additionally, the corresponding changes in somatic EPSP height measured in the CA1 cell layer did not predict the E-S dissociation at P15, suggesting that the E-S dissociation arises largely from changes in the excitability of the soma. Using a single 100 Hz x 1 sec tetanus, LTP proved difficult to induce in slices from rats > or = P90, with slices showing initial enhancement that faded over 60 min of monitoring.