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GABAA mediated afterdepolarization in pyramidal neurons from rat neocortex
1Veterans Affairs Puget Sound Health Care System, Seattle 98108, Washington, USA.
Journal of Neurophysiology
|February 1, 1997
Summary
Researchers discovered a novel slow afterdepolarization (sADP) in rat cortical neurons when exposed to gamma-aminobutyric acid (GABA). This GABA-induced sADP enhances neuronal excitability, particularly in dendrites, following intense neural activity.
Area of Science:
- Neuroscience
- Cellular Electrophysiology
Background:
- Layer V pyramidal neurons in the somatosensory cortex typically exhibit a slow afterhyperpolarization (sAHP) after intense firing.
- Gamma-aminobutyric acid (GABA) is a primary inhibitory neurotransmitter in the central nervous system.
Purpose of the Study:
- To investigate the effect of gamma-aminobutyric acid (GABA) on neuronal excitability in rat somatosensory cortex.
- To characterize a novel slow afterdepolarization (sADP) observed in layer V pyramidal neurons under specific experimental conditions.
Main Methods:
- Whole-cell recordings were performed on visually identified layer V pyramidal neurons in rat somatosensory cortex slices.
- Neurons were perfused with gamma-aminobutyric acid (GABA) and subjected to high-frequency stimulation to evoke action potentials.
- Experiments involved manipulating calcium levels and surgically altering dendritic structures to test hypotheses about the sADP's origin and mechanisms.
Main Results:
- Perfusion with 1 mM GABA replaced the typical sAHP with a novel sADP, averaging 18 mV in amplitude and lasting 26 seconds.
- The sADP's amplitude and duration were graded with the number of action potentials and showed time- and voltage-dependent properties.
- The sADP was independent of calcium influx and was predominantly generated in the apical dendrites, as evidenced by experiments with dendritic amputation.
- The sADP was mediated by GABAA receptors, confirmed by agonist (muscimol) and antagonist (bicuculline, picrotoxin) studies.
Conclusions:
- Intense neuronal activity in the presence of GABA induces a long-lasting enhancement of excitability in the apical dendrites of layer V pyramidal neurons.
- This GABA-mediated dendritic excitability enhancement could potentially amplify distal excitatory synaptic potentials, influencing overall neuronal computation.