Abstract
The thalamic reticular nucleus (TRN) is the main source of inhibition to the somatosensory thalamus (ventrobasal nucleus, VB) in mice. However, the functional topography and development of these projections with respect to the VB barreloids has been largely unexplored. In this respect, to assist in the study of these projections, we have utilized a vesicular gamma-aminobutryic acid (GABA) transporter (VGAT)-Venus transgenic mouse line to develop a brain slice preparation that enables the rapid identification of inhibitory neurons and projections. We demonstrate the utility of our in vitro brain slice preparation for physiologically mapping inhibitory reticulothalamic (RT) topography, using laser-scanning photostimulation via glutamate uncaging. Furthermore, we utilized this slice preparation to compare the development of excitatory and inhibitory projections to VB. We found that excitatory projections to the barreloids, created by ascending projections from the brain stem, develop by postnatal day 2–3 (P2–P3). By contrast, inhibitory projections to the barreloids lag ~5 days behind excitatory projections to the barreloids, developing by P7–P8. We probed this lag in inhibitory projection development through early postnatal whisker lesions. We found that in whisker-lesioned animals, the development of inhibitory projections to the barreloids closed by P4, in register with that of the excitatory projections to the barreloids. Our findings demonstrate both developmental and topographic organizational features of the RT projection to the VB barreloids, whose mechanisms can now be further examined utilizing the VGAT-Venus mouse slice preparation that we have characterized.
Highlights
The thalamus represents an ideal structure to assess aspects of developmental plasticity of both excitatory and inhibitory projection systems
The structure of thalamic barreloids in a fixed slice is unambiguously delineated by Venus labeled RT projections from the thalamic reticular nucleus (TRN), since there are practically no intrinsic local inhibitory neurons in the rodent somatosensory thalamus (Cox et al, 1996; Guillery and Harting, 2003; Figure 3A)
Similar to that previously reported for projections from the TRN and somatosensory thalamus (Lam and Sherman, 2005, 2011; Lam et al, 2006), we found a topographic organization between inhibitory input field (IIF) centers in the TRN and recording locations in thalamic barreloids (Figures 3E,F)
Summary
The thalamus represents an ideal structure to assess aspects of developmental plasticity of both excitatory and inhibitory projection systems. Similar structural plasticity of inhibitory neural projections in the thalamus has not been intensively investigated, in part due to the lack of amenable preparations for investigating such changes. We take advantage of a vesicular gamma-aminobutryic acid (GABA) transporter (VGAT)-Venus transgenic mouse line to examine the developmental organization of inhibitory projections from the TRN to the barreloid field in the somatosensory thalamus (the VB nucleus). We demonstrate the development and structural plasticity of inhibitory projections to the barreloids using this preparation. We demonstrate a new preparation for studying the organization, development and structural plasticity of inhibitory projections to the barreloid region of the somatosensory thalamus
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