Synaptic organization of the human striatum: a postmortem ultrastructural study

Area of Science:

• Neuroscience
• Electron Microscopy
• Human Brain Anatomy

Background:

• The striatum is crucial for motor control and reward processing.
• Understanding its synaptic organization is key for comparative neuroanatomy and disease research.
• Previous studies focused on animal models, leaving human striatal synaptic architecture undercharacterized.

Purpose of the Study:

• To quantitatively characterize the synaptic organization of the normal adult human striatum.
• To enable comparisons with other species and diseased human striata.
• To establish a baseline for synaptic plasticity research in humans.

Main Methods:

• Electron microscopic analysis of postmortem human striatal tissue (caudate nucleus and putamen).
• Tissue samples obtained with short postmortem intervals (<4 hours) from the Maryland Brain Collection.
• Quantitative assessment of synaptic subtype proportions, lengths, and axon terminal areas.

Main Results:

• Human striatal synaptic organization is broadly similar to non-human primates and rodents.
• Key proportions of axospinous (83.5%) and asymmetric (77.5%) synapses were quantified.
• Humans exhibit a significantly higher proportion of perforated postsynaptic densities (23%) compared to rats (5-8%), suggesting greater synaptic plasticity.
• Asymmetric synapses were longer and had larger terminal areas than symmetric synapses, consistent with other mammals.
• Axospinous and axodendritic synapses showed comparable lengths and terminal areas.

Conclusions:

• The human striatum shares fundamental synaptic organizational principles with other mammals.
• A notable difference is the higher prevalence of perforated synapses in humans, indicating enhanced synaptic plasticity.
• This quantitative data provides a critical reference for future comparative and clinical neuroscience studies of the human striatum.