Ian Díaz-Nieves, Solymar-Rolon Martinez, and Maria N. Geffen,Ph.D.
University of Puerto Rico, Río Piedras Campus, and University of Pennsylvania
Interactions between inhibitory and excitatory neurons shape how acoustic information is processed in the brain. The thalamic reticular nucleus (TRN) is a major source of inhibition to the thalamus. It is responsible for modulating interactions between the medial geniculate body (MGB) or auditory thalamus and the auditory cortex (AC). The MGB is subdivided into three regions: ventral, dorsal, and medial. Meanwhile, the TRN is comprised of two main subtypes of inhibitory neurons, parvalbumin (PV) and somatostatin (SOM). These neuron subtypes have been shown to modulate frequency-dependent responses and to differentially control adaptation in the AC, but it’s still unknown if they possess a similar role differentiation in the TRN through its projections to MGB sub-regions. We hypothesize that PV and SOM neurons differentially project to distinct subregions of the MGB. We injected a Cre-dependent Adeno-associated virus directly into the TRN of transgenic PV-Cre and SOM-Cre mice. After transfection of the viral tracer, mice brains were collected and imaged with fluorescence microscopy.
We found that PV neurons had synaptic targets mainly in the ventral area of the MGB; in addition, SOM neuronal subtypes were identified to project mostly to the medial and dorsal divisions. Our results show evidence for the existence of a novel anatomical structure of thalamic inhibitory neuron types and give strength to the idea that PV and SOM neurons play functionally distinct roles in orchestrating inhibition in the TRN.