Communication between the cortex and thalamus is imperative for performing cognitive processes. This communication can be modulated at the level of the thalamus through a strategically positioned inhibitory nucleus called the thalamic reticular nucleus (TRN). The TRN’s ability to modify thalamocortical communication through a distinctly inhibitory action has implicated it in the sleep-wake cycle and in selective attention, where its effects are so profound that is has commonly been coined the attentional searchlight of the brain. While the TRN projects to the thalamus only, it receives input from both cortical and thalamic projections which organize topographically into sectors within the TRN. These projections can either be categorized as core or matrix, which refer to first-order sensory or high-order association, respectively. The topographic organization of these two projection types into sectors within the TRN creates functional diversity, as well as complexity. Neuroscientists have begun to consider the importance of core-matrix fibers as their integration is central to the brain’s ability to perform complex and dynamic functions. However, little is known about the organizational aspects underlying their divergent sensory and association functions which is central to further classifying the broad functions of thalamocortical communication. Additionally, disruptions in circuitry at the level of the TRN can act as a precursor to numerous neurological deficits and disease, which further stresses a need for a morphological understanding of these functionally distinct regions. To address this gap in knowledge, we examined functionally distinct regions on the basis of their core-matrix distributions and compared their morphological features through the use of electron microscopy (EM) and brightfield microscopy (BF). We hypothesize that there will be cellular and dendritic architectural differences in regions with core and matrix distinctions, confirming that TRN sectors are heterogenous not just on a functional basis but also on an anatomic basis. In regions predominated with matrix projections, synaptic density was shown to be preserved across dendritic order while bouton diameters decreased across all orders of dendrites. Meanwhile, for regions populated with core fibers, synaptic density decreased between some orders of dendrites, and bouton diameter was mostly preserved across all orders of dendrites. Furthermore, across the TRN as a whole, the vast majority of boutons were deemed to be excitatory. The relative proportions of boutons arising from other brain afferents such as the amygdala, superior colliculus, and basal ganglia were different among the sectors predominated with core and matrix fibers, suggesting a specific balance of excitation and inhibition is required for TRN function. As such, heterogeneity was confirmed in the TRN on a morphological basis. / 2025-07-05T00:00:00Z
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/46422 |
| Date | 05 July 2023 |
| Creators | Johnson, Rebecca |
| Contributors | Zikopoulos, Vasileios, Liu, Xuefeng |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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