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L-Type Ca(2+) channels are essential for glutamate-mediated CREB phosphorylation and c-fos gene expression in
A Rajadhyaksha1, A Barczak, W Macías
1Molecular and Developmental Neuroscience Laboratory and Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Abstract:
The second messenger pathways linking receptor activation at the membrane to changes in the nucleus are just beginning to be unraveled in neurons. The work presented here attempts to identify in striatal neurons the pathways that mediate cAMP response element-binding protein (CREB) phosphorylation and gene expression in response to NMDA receptor activation. We investigated the phosphorylation of the transcription factor CREB, the expression of the immediate early gene c-fos, and the induction of a transfected reporter gene under the transcriptional control of CREB after stimulation of ionotropic glutamate receptors. We found that neither AMPA/kainate receptors nor NMDA receptors were able to stimulate independently a second messenger pathway that led to CREB phosphorylation or c-fos gene expression. Instead, we saw a consecutive pathway from AMPA/kainate receptors to NMDA receptors and from NMDA receptors to L-type Ca(2+) channels. AMPA/kainate receptors were involved in relieving the Mg(2+) block of NMDA receptors, and NMDA receptors triggered the opening of L-type Ca(2+) channels. The second messenger pathway that activates CREB phosphorylation and c-fos gene expression is likely activated by Ca(2+) entry through L-type Ca(2+) channels. We conclude that in primary striatal neurons glutamate-mediated signal transduction is dependent on functional L-type Ca(2+) channels.
Insights
Glutamate receptor activation in striatal neurons requires a sequential pathway involving AMPA/kainate and NMDA receptors to trigger calcium influx via L-type channels, ultimately activating CREB phosphorylation and gene expression.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Signaling
Background:
- Second messenger pathways linking neuronal receptor activation to nuclear events are complex.
- Understanding these pathways is crucial for deciphering neuronal function and dysfunction.
Purpose of the Study:
- To identify signaling pathways mediating cAMP response element-binding protein (CREB) phosphorylation and gene expression in striatal neurons following NMDA receptor activation.
- To investigate the roles of AMPA/kainate and NMDA receptors in this signaling cascade.
Main Methods:
- Stimulation of ionotropic glutamate receptors in primary striatal neurons.
- Measurement of CREB phosphorylation, c-fos gene expression, and reporter gene induction.
- Analysis of sequential receptor activation and calcium channel involvement.
Main Results:
- Neither AMPA/kainate nor NMDA receptors alone initiated CREB phosphorylation or c-fos expression.
- A sequential pathway was identified: AMPA/kainate receptors relieved Mg(2+) block of NMDA receptors, which then activated L-type Ca(2+) channels.
- Calcium influx through L-type Ca(2+) channels was essential for activating CREB phosphorylation and c-fos gene expression.
Conclusions:
- Glutamate-mediated signal transduction in striatal neurons is dependent on a sequential activation pathway involving AMPA/kainate and NMDA receptors.
- L-type Ca(2+) channels are critical mediators of downstream gene expression, including CREB phosphorylation, in response to glutamate stimulation.