| Summary: | 碩士 === 國立清華大學 === 分子醫學研究所 === 96 === The corticothalamic (CT) neurons, residing in the neocortex and sending axons to the thalamus, are important components for cortical processing and other brain functions. The morphology of DiI-back-labeled CT neurons in perinatal rat cortices was studied. The CT neurons are early-generated pyramidal cells in the neocortex. The CT neurons develop from cells having an oval cell body, no basilar dendrites and an apical dendrite with few branches in the marginal zone (MZ) into cells displaying a pyramidal-shaped cell body, 2-3 basilar dendrites and an apical dendrite with more complex branching in the MZ between embryonic day 18 (E18) and the day of birth (P0). The cellular organization of the MZ also indicates significant changes from a three-lamina pattern to a single-lamina one during the same period. The apical dendrites of the CT neurons can be found forming contacts with Cajal-Retzius (CR) and other cells in the MZ at E18. Synaptophysin-positive clusters mainly locate on the apical dendrites of E18, E20 and P0 CT neurons, while also are found on the cell bodies and proximal dendrites of P0 CT neurons. GABAergic and glutamatergic synapses are already formed on the apical dendrites of CT neurons as early as E18, when the cortical projection has reached their thalamic targets. Thus, it is likely that the cortex and thalamus in rat brains are linked to each other by functional connections in a two-way fashion at least three days before birth.
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