Modeling Vestibular Compensation: Neural Plasticity Upon Thalamic Lesion.

Area of Science:

• Neuroscience
• Neurophysiology
• Neuroanatomy

Background:

• The vestibular system is crucial for balance and spatial orientation.
• Understanding how the brain adapts to vestibular dysfunction is vital for treating balance disorders.
• The laterodorsal thalamic nucleus is a key relay for vestibular information to the cortex.

Purpose of the Study:

• To identify brain regions affected by vestibular transmission interruption.
• To explore functional connections within vestibular processing pathways.
• To investigate neurotransmitter systems involved in thalamo-cortical vestibular signaling.

Main Methods:

• Positron emission tomography (PET) to measure regional cerebral glucose metabolism (rCGM) in rats.
• Experimental lesion of the left laterodorsal thalamic nucleus.
• Galvanic vestibular stimulation (GVS) before and after lesion.
• Neuronal tracer injections into cortical and subcortical vestibular regions.
• Immunohistochemistry to identify neurotransmitter systems.

Main Results:

• Lesioning the laterodorsal thalamic nucleus altered GVS-induced rCGM, with increased activation in the contralateral cerebellum and superior colliculus.
• Diminished GVS-induced rCGM was observed in ipsilateral visual, entorhinal, and somatosensory cortices, suggesting compensatory mechanisms.
• Neuronal tracing revealed connections between thalamic nuclei and cortical areas (ACC, S1, insular cortex, hippocampus, amygdala).
• Traced terminal fields contacted μ-opioid receptor-expressing cortical neurons, indicating opioidergic transmission.

Conclusions:

• Brain plasticity mechanisms, including sensory substitution, underlie vestibular compensation after thalamic nucleus damage.
• The findings provide evidence for opioidergic neurotransmission in thalamo-cortical pathways processing vestibular and somatosensory information.
• These results may inform therapeutic strategies for vestibular disorders and related neurological conditions.