CaM kinase II in long-term potentiation

Area of Science:

• Neuroscience
• Molecular Biology
• Cellular Signaling

Background:

• Autophosphorylation of CaM kinase II converts it to a Ca(2+)-independent form.
• This Ca(2+)-independent form is hypothesized to encode synaptic usage frequency and serve as a molecular basis for memory.
• CaM kinase II plays a crucial role in synaptic plasticity, including long-term potentiation (LTP).

Purpose of the Study:

• To investigate the role of CaM kinase II autophosphorylation in hippocampal LTP.
• To determine if CaM kinase II activity changes correlate with synaptic stimulation frequency.
• To identify CaM kinase II substrates involved in LTP induction in both pre- and postsynaptic regions.

Main Methods:

• Cultured rat hippocampal neurons treated with glutamate and NMDA receptor antagonist (AP5).
• High-frequency stimulation of CA1 afferents in rat hippocampus, with and without AP5 or calmidazolium.
• Analysis of CaM kinase II activity, autophosphorylation, and substrate phosphorylation (synapsin I, MAP2) in hippocampal slices.
• In vitro phosphorylation assays and electrophysiological recordings in hippocampal neurons.

Main Results:

• Glutamate increased CaM kinase II Ca(2+)-independent activity via autophosphorylation, blocked by AP5.
• High-frequency stimulation induced LTP and increased CaM kinase II activity and autophosphorylation.
• Phosphorylation of synapsin I and MAP2 increased post-LTP induction, prevented by AP5 or calmidazolium.
• CaM kinase II directly phosphorylates AMPA receptors, and its constitutive activation enhances kainate responses.

Conclusions:

• CaM kinase II autophosphorylation contributes to the induction of hippocampal LTP.
• CaM kinase II acts in both presynaptic and postsynaptic sites by phosphorylating targets like AMPA receptors, synapsin I, and MAP2.
• These findings support CaM kinase II's role in synaptic plasticity and potentially memory formation.