Horizontal synaptic connections in monkey prefrontal cortex: an in vitro electrophysiological study

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Systems Neuroscience

Background:

• The monkey dorsolateral prefrontal cortex (PFC) features long-distance, horizontal axon collaterals connecting supragranular pyramidal neuron clusters.
• Understanding the electrophysiological properties of these long-range intrinsic connections is crucial for deciphering PFC circuitry.

Purpose of the Study:

• To investigate the electrophysiological responses mediated by long-distance intrinsic projections in the monkey PFC.
• To characterize the nature and strength of synaptic communication via these horizontal connections in layer 3.

Main Methods:

• Utilized an in vitro slice preparation of monkey PFC for whole-cell patch clamp recordings from layer 3 pyramidal neurons.
• Employed low-intensity electrical extracellular stimulation at multiple sites to evoke postsynaptic currents.
• Applied tracer injections in vivo to confirm the preservation of long-distance projections in coronal slices.

Main Results:

• Long-distance monosynaptic connections were identified, characterized by a slow conduction velocity (0.14 m/s).
• Excitatory postsynaptic currents (EPSCs) from long-distance connections showed similar kinetics but comparable or larger amplitudes than short-distance connections.
• A significant majority (77%) of layer 3 neurons were monosynaptic targets of these long-distance connections, indicating robust excitatory input.

Conclusions:

• Long-distance excitatory connections represent a substantial intrinsic pathway for synaptic communication within layer 3 of the monkey PFC.
• The findings suggest that these connections effectively transmit information across significant distances within the cortical microcircuit.
• The observed peak amplitudes correlate with anatomically identified neuron clusters, supporting a structured network organization.