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Developmental changes in calcium channel types mediating synaptic transmission in rat auditory brainstem
1Department of Neurophysiology, University of Tokyo Faculty of Medicine, Tokyo 113-0033, Japan.
The Journal of Physiology
|May 12, 1998
Summary
Calcium channel blockers reveal a developmental switch in neurotransmitter release. Early in development, P/Q-type and N-type channels dominate, shifting to primarily P/Q-type channels in older rats.
Area of Science:
- Neuroscience
- Developmental Biology
- Molecular Pharmacology
Background:
- The calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB) is crucial for auditory processing.
- Presynaptic calcium (Ca2+) influx is essential for neurotransmitter release at this synapse.
- Understanding the developmental changes in Ca2+ channel function is key to comprehending synapse maturation.
Purpose of the Study:
- To investigate the developmental changes in presynaptic calcium channel subtypes mediating excitatory postsynaptic currents (EPSCs) at the calyx of Held-MNTB synapse.
- To determine how the contribution of different Ca2+ channel types to neurotransmitter release evolves during early postnatal development.
Main Methods:
- Electrophysiological recordings of EPSCs were performed on brainstem slices from rats aged postnatal day 4-14.
- Pharmacological blockade of specific Ca2+ channel subtypes using omega-agatoxin-IVA (P/Q-type), omega-conotoxin GVIA (N-type), and nicardipine (L-type).
- Assessment of Ca2+ channel contribution by observing changes in EPSC amplitude and kinetics following toxin application and in the presence of cadmium (Cd2+).
Main Results:
- At early postnatal ages (P4-9), EPSCs were primarily mediated by P/Q-type and N-type Ca2+ channels.
- A small, toxin-resistant component of EPSCs, abolished by Cd2+, was also observed.
- With development (after P7 and P10), the N-type Ca2+ channel contribution diminished, while the P/Q-type Ca2+ channel contribution became dominant.
- L-type Ca2+ channels did not significantly contribute to EPSCs throughout the studied period.
Conclusions:
- Presynaptic Ca2+ channel types involved in triggering transmitter release at the calyx of Held synapse undergo a significant developmental switch.
- This switch involves a transition from reliance on both P/Q-type and N-type channels to a predominant role of P/Q-type channels.
- These findings highlight the dynamic nature of synaptic transmission during early postnatal development.