Volume reduction without neuronal loss in the primate pulvinar complex following striate cortex lesions

Area of Science:

• Neuroscience
• Visual System Research
• Primate Brain Studies

Background:

• Lesions in the primary visual cortex (V1) cause significant retrograde degeneration in the lateral geniculate nucleus.
• The impact of V1 lesions on other subcortical visual centers, particularly the pulvinar nuclei, remains largely uncharacterized.

Purpose of the Study:

• To investigate neuronal loss and volume changes in the inferior (IPul) and lateral (LPul) pulvinar nuclei following unilateral V1 lesions in marmosets.
• To compare the effects of V1 lesions on pulvinar nuclei with the medial pulvinar nucleus (MPul), which lacks V1 connections.

Main Methods:

• Stereological analysis techniques were applied to NeuN-stained marmoset brain sections.
• Unilateral long-term V1 lesions were induced either early postnatally or in adulthood.
• Volume and neuronal number estimations were performed on LPul, IPul, and MPul.

Main Results:

• Significant LPul volume loss was observed in animals with V1 lesions, regardless of lesion age (postnatal or adult).
• No significant neuronal degeneration was detected in the LPul following V1 lesions.
• Neuronal density in the lesioned LPul was comparable to the non-lesioned hemisphere, suggesting volume loss is not due to cell death.

Conclusions:

• The pulvinar pathway, including LPul, shows remarkable resilience to long-term V1 lesions, contrasting with the geniculocortical pathway.
• Divergent pulvinar connectivity, including strong extrastriate connections, may explain its resistance to V1 damage.
• Volume reduction in brain structures should be interpreted cautiously as it may not always indicate neuronal degeneration.