Development of the thalamus: From early patterning to regulation of cortical functions

Abstract

The thalamus is a brain structure of the vertebrate diencephalon that plays a central role in regulating diverse functions of the cerebral cortex. In traditional view of vertebrate neuroanatomy, the thalamus includes three regions, dorsal thalamus, ventral thalamus, and epithalamus. Recent molecular embryological studies have redefined the thalamus and the associated axial nomenclature of the diencephalon in the context of forebrain patterning. This new view has provided a useful conceptual framework for studies on molecular mechanisms of patterning, neurogenesis and fate specification in the thalamus as well as the guidance mechanisms for thalamocortical axons. Additionally, the availability of genetic tools in mice has led to important findings on how thalamic development is linked to the development of other brain regions, particularly the cerebral cortex. This article will give an overview of the organization of the embryonic thalamus and how progenitor cells in the thalamus generate neurons that are organized into discrete nuclei. I will then discuss how thalamic development is orchestrated with the development of the cerebral cortex and other brain regions. This article is categorized under: Nervous System Development > Vertebrates: Regional Development Nervous System Development > Vertebrates: General Principles

Early Development of the GABAergic System and the Associated Risks of Neonatal Anesthesia

“…Thalamic interneurons for the most part have an early midbrain ontogeny [ 119 ]. While the majority of neurogenesis and differentiation in the thalamus occurs during gestation [ 120 , 121 ], thalamocortical connectivity continues to develop during infancy, the saliency of which has been correlated to visual working memory performance and measures of learning ability [ 122 ]. It has been generally thought that there are local GABAergic connections between TRN neurons, however, recent evidence suggests that these connections exist only for the first two weeks in mice [ 123 ].…”

Extrinsic Regulators of mRNA Translation in Developing Brain: Story of WNTs

“…One major developmental event is the ingrowth of thalamic axons at mid-neurogenesis [62]. The thalamus, a brain structure in the vertebrate diencephalon, plays a central role in regulating diverse functions of the cerebral cortex with guidance mechanisms for thalamocortical axons (TCAs) [63]. When the mouse thalamus undergoes embryonic neurogenesis, several Wnt ligands, such as WNT3, WNT3A, and WNT7B, are expressed [48,64] and involved in the development and control of TCA projection in thalamic glutamatergic neurons [65].…”

Thalamocortical axons regulate neurogenesis and laminar fates in early sensory cortex

“…These mechanisms influence region-specific regulation of neurogenesis and subsequent specification of neuronal types, which will eventually control the formation of area-specific cytoarchitecture and functional specialization of the neocortex. In contrast, topographic and area-specific projections of thalamocortical axons (TCAs) provide a major extrinsic influence on neocortical cytoarchitecture (Rakic, 1988;O'Leary, 1989;López-Bendito, 2018;Cadwell et al, 2019;Nakagawa, 2019). For example, ablation of principal sensory thalamic nuclei or blocking transmitter release from TCA terminals during the postnatal period disrupts anatomical and molecular hallmarks of the primary sensory cortex (Wise and Jones, 1978;Narboux-Nême et al, 2012;Chou et al, 2013;Li et al, 2013;Pouchelon et al, 2014).…”