Optogenetic Mapping of Intracortical Circuits Originating from Semilunar Cells in the Piriform Cortex

Area of Science:

• Neuroscience
• Olfactory System Research
• Mammalian Brain Circuits

Background:

• The mammalian primary olfactory cortex (piriform cortex) performs complex sensory processing.
• This processing relies heavily on intracortical excitatory circuits.

Purpose of the Study:

• To investigate the connectivity of associational circuits originating from semilunar (SL) cells in layer 2a of the anterior piriform cortex (aPC).
• To determine the specific neuronal targets of SL cells within the aPC.

Main Methods:

• Utilized a novel transgenic mouse model (48L) for selective channelrhodopsin-2 (ChR) expression in SL cells.
• Employed optogenetics to measure light-evoked excitatory postsynaptic currents (EPSCs) in various aPC neurons.
• Differentiated connectivity patterns by testing responses in pyramidal cells, SL cells, and GABAergic interneurons.

Main Results:

• SL cells monosynaptically excite superficial and deep pyramidal cells in the aPC.
• SL cells do not appear to excite other SL cells.
• Specific classes of GABAergic interneurons in layer 3 of the aPC also receive direct excitation from SL cells.

Conclusions:

• SL cells are specialized for delivering feedforward excitation to distinct neuronal populations within the aPC.
• These findings confirm the role of SL cells as a functionally unique input layer in the olfactory cortex.