NMDA antagonists in the superior colliculus prevent developmental plasticity but not visual transmission or map...

Area of Science:

• Neuroscience
• Developmental Biology
• Visual System Plasticity

Background:

• Partial ablation of the superior colliculus (SC) in hamsters compresses the retinocollicular map.
• The mechanism by which SC neurons maintain receptive field properties despite map compression is unknown.
• N-methyl-D-aspartate (NMDA) receptors are investigated for their role in retinocollicular convergence.

Purpose of the Study:

• To examine the role of NMDA receptors in controlling retinocollicular convergence.
• To understand how SC neurons compensate for induced brain damage.
• To investigate the necessity of NMDA receptors for map refinement and receptive field construction.

Main Methods:

• Chronic blockade of NMDA receptors using 2-amino-5-phosphonovaleric acid (APV) from birth in normal and partially ablated hamsters.
• Measurement of receptive field sizes of single SC neurons.
• Assessment of visual map completeness and visual responsiveness in the SC.

Main Results:

• APV blockade resulted in enlarged single-unit receptive fields in SC neurons.
• Receptive field enlargement was more pronounced in lesioned animals with compressed maps, linearly related to lesion size.
• A complete visual map and normal visual responsiveness were maintained in APV-treated animals, despite altered receptive field sizes.

Conclusions:

• NMDA receptors are essential for controlling afferent/target convergence in the normal SC and for compensating for excess retinal afferents in lesioned animals.
• NMDA receptors play a crucial role in map refinement and receptive field construction, but not overall map compression.
• NMDA receptors likely function as coincidence detectors, enabling neurons to calculate visual space representation through firing patterns, a mechanism important for nervous system development.