Pyramidal cells make specific connections onto smooth (GABAergic) neurons in mouse visual cortex

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Neocortical circuits feature recurrent excitation from pyramidal neurons balanced by inhibition from smooth GABAergic neurons.
• Previous studies in cats and monkeys indicated pyramidal cells target smooth dendrites in proportion to their neuropil presence (5-19%).

Purpose of the Study:

• To investigate the discrepancy in smooth neuron targeting by pyramidal cells in mouse visual cortex compared to previous findings in higher mammals.
• To determine if observed differences are due to neuropil composition or specific synaptic targeting by pyramidal cells.

Main Methods:

• Biocytin-filled cells were examined in the superficial layers of the primary visual cortex (V1) in five mice.
• Ultrastructural analysis was used to quantify synaptic connections between pyramidal cells and smooth dendrites.

Main Results:

• The overall neuropil composition in mouse V1 was similar to that of cats and monkeys.
• Superficial layer pyramidal cells in mice formed proportionately more synapses with smooth dendrites than observed in cats and monkeys.
• This suggests specific targeting of smooth neurons by pyramidal cells in rodents.

Conclusions:

• Mouse V1 pyramidal cells exhibit a distinct synaptic targeting preference for smooth GABAergic neurons compared to cats and monkeys.
• These differences in neuronal connectivity may underlie functional architectural variations in the visual cortex between rodents and higher mammals.