Target-cell-specific facilitation and depression in neocortical circuits.

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Systems Neuroscience

Background:

• Neurons in the neocortex generate postsynaptic potentials (PSPs) that either facilitate or depress during repetitive activity.
• Understanding the mechanisms behind these differing synaptic responses is crucial for comprehending neural circuit function.

Purpose of the Study:

• To investigate the basis for facilitation and depression of excitatory postsynaptic potentials (EPSPs) in different classes of GABAergic interneurons in cortical layer 2/3.
• To explore how these distinct synaptic behaviors influence recurrent inhibitory pathways in the neocortex.

Main Methods:

• Simultaneous recordings from three classes of neurons in cortical layer 2/3.
• Induction of repetitive action potentials in pyramidal cells.
• Recording of evoked unitary excitatory (E)PSPs and inhibitory (I)PSPs in GABAergic neurons.
• Immunohistochemical analysis for somatostatin and parvalbumin expression.

Main Results:

• EPSPs showed facilitation in bitufted GABAergic interneurons (often somatostatin-positive).
• EPSPs exhibited depression in multipolar GABAergic interneurons (some parvalbumin-positive).
• Unitary IPSPs also displayed frequency-dependent differences between the two interneuron types.

Conclusions:

• Facilitation and depression of synaptic responses are mediated by presynaptic mechanisms.
• Retrograde signals from distinct target neurons likely induce molecular differences in presynaptic terminals, leading to varied synaptic behaviors.
• The balance of activation in recurrent inhibitory pathways is dependent on the firing frequency of pyramidal cells.