Developmental changes in synaptic properties in hippocampus of neonatal rats
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1Center for the Neurobiology of Learning and Memory, University of California, Irvine 92717.
Insights
Synaptic responses in rat hippocampus develop significantly between 7-9 and 12-15 days. Despite developmental changes, younger rats’ synaptic properties do not fully explain the absence of long-term potentiation (LTP).
Area of Science:
- Neuroscience
- Developmental Biology
- Synaptic Plasticity
Background:
- Long-term potentiation (LTP) is a key mechanism for learning and memory.
- Hippocampal synaptic properties undergo significant changes during early development.
Purpose of the Study:
- To investigate developmental changes in hippocampal CA1 synaptic properties.
- To determine if observed synaptic differences explain the lack of LTP in young neonates.
Main Methods:
- Electrophysiological analysis of hippocampal CA1 slices from 7-9 and 12-15 day old rats.
- Assessment of synaptic responses, paired-pulse facilitation, calcium sensitivity, and N-methyl-D-aspartate (NMDA) receptor activity.
- High-frequency stimulation protocols to induce and analyze synaptic potentiation.
Main Results:
- Long-term potentiation (LTP) was consistently observed only in 12-15 day old rats.
- Inhibitory responses were absent in 7-9 day old rats but present in older neonates.
- Paired-pulse facilitation and postsynaptic calcium sensitivity were reduced in younger rats.
- The N-methyl-D-aspartate (NMDA) component of responses was larger in 7-9 day old rats.
Conclusions:
- Synaptic properties, including NMDA receptor activity, change considerably during early postnatal development.
- The observed developmental differences in synaptic function do not fully account for the absence of LTP in 7-9 day old rats.
- Further investigation is needed to understand the mechanisms underlying the lack of LTP in early development.
Abstract:
The properties of synaptic responses in area CA1 of hippocampus were analyzed in slices prepared from 7-9 and 12-15 day old neonate rats. As expected from earlier work, only slices of two-week-old animals showed a consistent degree of long-term potentiation (LTP) in response to patterned high frequency stimulation. Several other synaptic properties were found to change during this developmental period. Inhibitory responses were absent in 7-9 day old but not in 12-15 day old neonates. Paired-pulse facilitation and the calcium sensitivity of postsynaptic responses were considerably reduced in 7-9 as compared to 12-15 day old rats. However, phorbol esters and 4-aminopyridine treatment still produced a strong facilitation of field potentials. The N-methyl-D-aspartate (NMDA) component of responses to single pulse stimulation in low magnesium medium was found to be larger in slices of 7-9 than 12-15 day old or adult animals. At the two time periods examined, trains of high frequency stimulation applied in the presence of regular magnesium elicited an NMDA dependent response. It is concluded that the differences in synaptic properties observed between 7-9 and 12-15 day old neonates may not account for the absence of LTP in the younger animals.