Dendritic calcium encodes striatal neuron output during up-states

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Computational Neuroscience

Background:

• Striatal spiny projection neurons are critical for basal ganglia function, mediating outputs to the globus pallidus and substantia nigra.
• Activity bursts in these neurons are essential for normal basal ganglia function and implicated in dysfunction.
• Corticostriatal inputs drive these bursts by depolarizing neurons from a resting down-state to an up-state.

Purpose of the Study:

• To investigate how dendritic calcium signals encode action potential bursts in striatal spiny projection neurons during different cellular states.
• To elucidate the role of active dendritic signal propagation in shaping calcium transients during burst firing.

Main Methods:

• Utilized organotypic cortex-striatum-substantia nigra cultures (5-6 weeks in vitro).
• Employed somatic whole-cell patch-clamp recordings combined with Fura-2 imaging to measure intracellular calcium concentration ([Ca2+]i).
• Applied somatic current pulses and voltage commands to evoke action potentials and bursts.

Main Results:

• Dendritic [Ca2+]i transients during up-state bursts strongly correlated with burst strength.
• Action potentials evoked during down-states also produced dendritic [Ca2+]i transients correlated with burst strength.
• Up-state bursts induced supralinear increases (>200%) in dendritic [Ca2+]i compared to down-state activity.
• Tetrodotoxin blocked burst-evoked dendritic [Ca2+]i transients, indicating reliance on active action potential propagation.

Conclusions:

• Dendritic calcium transients in spiny projection neurons encode somatic bursts supralinearly during up-states via active action potential propagation.
• This mechanism allows for precise encoding of neuronal output contributing to basal ganglia function.
• Findings suggest a feedback mechanism where dendritic activity informs corticostriatal synapses about neuronal output.