Rapid dendritic atrophy following deafferentation: an EM morphometric analysis

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Cell Biology

Background:

• The nucleus laminaris (NL) is a crucial auditory brainstem nucleus in birds.
• It receives input from the nucleus magnocellularis (NM) via ipsilateral and contralateral pathways.
• The crossed dorsal cochlear tract (CTrX) specifically targets the ventral dendrites of NL neurons.

Purpose of the Study:

• To investigate the rapid cytological effects of deafferentation on NL neurons.
• To determine the influence of presynaptic terminals on dendritic integrity.

Main Methods:

• Transection of the CTrX in young chickens.
• Sham operation as a control.
• Morphometric analysis of electron micrographs of NL tissue 96 hours post-lesion.

Main Results:

• Axon terminals from the contralateral NM were localized to the ventral NL neuropil.
• Significant reduction (85%) in ventral NL dendritic volume density after CTrX transection.
• Marked decrease (81%) in primary dendrite frequency in the ventral NL neuropil.
• Observed reduction in rough endoplasmic reticulum, Golgi apparatus, and cytoplasmic granularity in deafferented NL neurons.

Conclusions:

• Dendritic processes are rapidly and profoundly compromised by the removal of afferent input.
• Presynaptic terminals appear to exert a tonic influence on the cytological integrity of postsynaptic dendrites.