Callosal terminals in the rat prefrontal cortex: synaptic targets and association with GABA-immunoreactive structures

Area of Science:

• Neuroscience
• Neuroanatomy
• Cerebral Cortex Research

Background:

• Callosal projections are crucial for interhemispheric functional integration.
• Previous studies focused on sensory/motor regions; limbic association areas remain less understood.

Purpose of the Study:

• To investigate synaptic targets of callosal terminals in the rat prefrontal cortex (PFC).
• To explore the relationship between callosal afferents and GABA local circuit neurons in the PFC.

Main Methods:

• Anterograde transport of Phaseolus vulgaris leucoagglutinin (PHAL) for labeling callosal terminals.
• Electrolytic lesions of the contralateral PFC to induce anterograde degeneration.
• Electron microscopy and GABA immunolabeling to identify synaptic connections.

Main Results:

• Callosal terminals predominantly form asymmetric axo-spinous synapses (~95%) on PFC neurons.
• Some callosal terminals synapse onto dendrites of GABA-labeled local circuit neurons.
• Evidence of convergence between callosal afferents and GABA terminals on common postsynaptic targets.

Conclusions:

• Callosal terminals in the PFC primarily synapse onto pyramidal neuron spines, similar to sensory/motor cortices.
• Callosal afferents interact with GABA local circuit neurons, potentially modulating PFC activity.
• GABA terminals may regulate excitation from callosal inputs to PFC pyramidal neurons.