Neuronal composition and development in lamina 4C of monkey striate cortex

Area of Science:

• Neuroscience
• Visual Cortex Development
• Synaptic Plasticity

Background:

• Lamina 4C of the monkey visual striate cortex is a primary recipient of lateral geniculate nucleus (LGN) axons.
• Synaptic maturation in lamina 4C involves competitive interactions between thalamic axons, influenced by afferent activity.

Purpose of the Study:

• To define adult neuron populations in subdivisions 4C alpha and 4C beta of the monkey visual cortex.
• To understand the normal process of synapse maturation in lamina 4C by examining neuron and synapse populations.

Main Methods:

• Golgi staining was used to identify and describe spine-bearing and smooth dendritic neuron populations.
• Electron microscopy of normal and Golgi-impregnated tissue was employed to analyze synapse populations on these neurons.

Main Results:

• Three groups of spine-bearing neurons and four groups of smooth dendritic neurons were identified in lamina 4C.
• Smooth and spiny neurons maintained constant proportions (5% smooth, 95% spiny) from embryonic day 159 through adulthood.
• Type 1 synapses (on spines) shifted from dendritic shafts to spine tips during maturation, while type 2 synapses originated from smooth dendritic neurons and increased on spiny cell somata postnatally before decreasing.

Conclusions:

• Changes in spine populations during maturation reflect changes in type 1 synapse populations.
• Type 2 synapses are generated by smooth dendritic neurons and their numbers change during postnatal development.