A quantitative electron microscopic study on synapse formation in dissociated fetal rat cerebral cortex in vitro

Area of Science:

• Neuroscience
• Developmental Biology
• Cell Biology

Background:

• Dissociated fetal rat occipital cortex neurons were cultured in vitro for 2-5 weeks.
• Neurons rapidly formed dense networks, with degeneration observed after 3 weeks.
• Synapse development was tracked using electron microscopy.

Purpose of the Study:

• To investigate the role of bioelectrical activity in the formation of functional synaptic networks.
• To determine if xylocaine, a bioelectrical activity blocker, affects synaptic development in vitro.
• To analyze the ultrastructure and numerical development of different synapse categories.

Main Methods:

• Dissociation and in vitro culture of fetal rat occipital cortex neurons.
• Supplementation with horse serum and Eagle's MEM.
• Chronic exposure to xylocaine (50 µg/ml) to block bioelectrical activity.
• Electron microscopy for synapse quantification and ultrastructural analysis.
• Extracellular recordings to assess bioelectrical activity.

Main Results:

• Axo-dendritic synapses showed a sigmoid growth curve over the first 3 weeks, followed by a decline.
• Xylocaine (50 µg/ml) did not prevent the formation of functional synaptic networks with normal ultrastructure.
• Dose-dependent xylocaine effects suggested growth retardation was likely due to cytotoxicity, not bioelectrical suppression.

Conclusions:

• Bioelectrical activity is not a prerequisite for the formation of apparently normal, functional synaptic networks in dissociated cortex cultures.
• Xylocaine's effects on neurite outgrowth and synapse formation were likely cytotoxic rather than specific to bioelectrical activity.
• The study supports previous findings on fetal cerebral explants regarding synaptic development independent of bioelectricity.