Inhibitory control of excitable dendrites in neocortex

Area of Science:

• Neuroscience
• Computational Neuroscience
• Cellular Neuroscience

Background:

• Pyramidal cell dendrites in the mature neocortex possess active sodium (Na+) and calcium (Ca2+) conductances.
• Dendrites are frequently targeted by inhibitory synapses, suggesting a critical role for inhibition in regulating dendritic activity.

Purpose of the Study:

• To investigate the interplay between intrinsic dendritic excitability and synaptic inhibition in layer 5 pyramidal cells.
• To characterize how inhibitory postsynaptic potentials (IPSPs) affect different types of dendritic firing patterns.

Main Methods:

• Whole-cell recordings were performed on apical dendrites of layer 5 pyramidal cells in mature rat somatosensory cortex slices.
• Experiments utilized glutamate receptor antagonists and controlled temperatures (32-36°C).
• Intradendritic current injection and cortical layer 2/3 stimulation were used to evoke and record dendritic firing and IPSPs.

Main Results:

• Two distinct dendritic firing patterns (Type I and Type II) were observed upon current injection.
• IPSPs exhibited bimodal reversal potentials (-53 mV and -85 mV), correlating with dendritic spiking types.
• IPSPs effectively modulated dendritic spiking by delaying, blocking, or selectively inhibiting Ca2+-dependent components, and could phase advance or delay repetitive firing.

Conclusions:

• Synaptic inhibition plays a crucial role in shaping dendritic excitability and spike generation in neocortical pyramidal neurons.
• The impact of inhibition on dendritic activity is dependent on the timing of IPSPs relative to intrinsic dendritic events.
• IPSPs can selectively target and control specific components of dendritic calcium-based spiking.