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Long-term depression in the developing hippocampus: low induction threshold and synapse nonspecificity
Pontus Wasling1, Eric Hanse, Bengt Gustafsson
1Institute of Physiology and Pharmacology, Göteborg University, SE-405 30 Göteborg, Sweden. pontus.wasling@physiol.gu.se
Summary
Neonatal rats exhibit heightened synaptic plasticity, readily undergoing long-term depression (LTD) with minimal stimulation. This synaptic depression is calcium-dependent and sensitive to NMDA receptor activity.
Area of Science:
- Neuroscience
- Synaptic Plasticity
- Developmental Neurobiology
Background:
- Synaptic plasticity, the ability of synapses to strengthen or weaken over time, is crucial for learning and memory.
- The neonatal period is a critical window for neural development, characterized by dynamic changes in synaptic function.
Purpose of the Study:
- To investigate the sensitivity of synaptic plasticity to low-frequency stimulation in the neonatal rat hippocampus.
- To elucidate the mechanisms underlying synaptic depression induced by paired-pulse stimulation in young rats.
Main Methods:
- Paired-pulse afferent stimulation at very low frequencies (0.1-0.02 Hz) was applied to the hippocampal CA1 area in young (1-2 week) and older rats.
- Electrophysiological recordings were used to measure synaptic activity and assess long-term depression (LTD) and long-term potentiation (LTP).
- The roles of NMDA receptor channels and T-type voltage-dependent calcium channels in initiating synaptic depression were examined.
Main Results:
- Very low-frequency stimulation induced long-term depression (LTD) in the hippocampal CA1 area of young rats, but not older ones.
- LTD was initiated by activation of NMDA receptor channels and/or T-type voltage-dependent calcium channels, requiring fewer than 10 stimuli.
- NMDA receptor-dependent potentiation preceded depression when stimulation exceeded the threshold for postsynaptic spike activation.
- Paired-pulse stimulation also induced depression in neighboring synapses, indicating high sensitivity during the neonatal period.
Conclusions:
- Neonatal rats display a significantly higher sensitivity for inducing synaptic depression compared to older rats.
- A brief rise in postsynaptic calcium can induce either LTP or LTD, with larger rises favoring LTP, while prolonged modest increases selectively induce LTD.
- These findings highlight the unique plasticity mechanisms present during early development and their dependence on calcium influx.