Govindaiah, G. | bioRxiv Science

bioRxiv2022

Synaptic and circuit mechanisms prevent detrimentally precise correlation in developing visual system

During development, retinal axons create broad and imprecise connections in the thalamus. This topology, very different from adults, supplies developing thalamic neurons with locally homogeneous synaptic currents and should cause spike correlation between thalamocortical neurons on a millisecond timescale. Such correlations have not been observed in vivo, at these ages, and would likely be maladaptive. Here, we use a biophysical model of the visual thalamus with the membrane and synaptic properties of 7-10 day-old mice to show that the developmentally appropriate dominance of NMDA-receptor currents and absence of strong recurrent inhibitory and excitatory connections prevents precise correlation and preserves topographic information in thalamic spikes. We illustrate possible reasons for this desynchronization using a phenomenological cortical model, which shows impaired network diversity when driven with precisely correlated inputs. Our results suggest that developing synapses and circuits evolved mechanisms to compensate for detrimental, "parasitic" correlation arising from the unrefined and immature circuit.

neuroscience↗

bioRxiv2020

Diverse GABAergic neurons organize into subtype-specific sublaminae in the ventral lateral geniculate nucleus

In the visual system, retinal axons convey visual information from the outside world to dozens of distinct retinorecipient brain regions and organize that information at several levels, including either at the level of retinal afferents, cytoarchitecture of intrinsic retinorecipient neurons, or a combination of the two. Two major retinorecipient nuclei which are densely innervated by retinal axons are the dorsal lateral geniculate nucleus (dLGN), which is important for classical image-forming vision, and ventral LGN (vLGN), which is associated with non-image-forming vision. The neurochemistry, cytoarchitecture, and retinothalamic connectivity in vLGN remain unresolved, raising fundamental questions of how it receives and processes visual information. To shed light on these important questions, we labeled neurons in vLGN with canonical and novel cell type-specific markers and studied their spatial distribution and morphoelectric properties. Not only did we find a high percentage of cells in vLGN to be GABAergic, we discovered transcriptomically distinct GABAergic cell types reside in the two major laminae of vLGN, the retinorecipient, external vLGN (vLGNe) and the non-retinorecipient, internal vLGN (vLGNi). Within vLGNe, we identified transcriptionally distinct subtypes of GABAergic cells that are distributed into four adjacent sublaminae. Using trans-synaptic viral tracing and in vitro electrophysiology, we found cells in each these vLGNe sublaminae receive monosynaptic inputs from the retina. These results not only identify novel subtypes of GABAergic cells in vLGN, they suggest the subtype-specific laminar distribution of retinorecipient cells in vLGNe may be important for receiving, processing, and transmitting light-derived signals in parallel channels of the subcortical visual system. Graphical abstract. The vLGN is organized into subtype-specific sublaminae which receive visual inputThe ventral lateral geniculate nucleus (vLGN) is part of the visual thalamus. It can broadly be separated into two structural domains or laminae, the external vLGNe (which receives retinal input) and the internal vLGNi (receives no retinal input). In this study, we describe subtypes of transcriptomically distinct GABAergic neurons that populate the vLGN and organize into discrete, adjacent sublaminae in the vLGNe. Taken together, our results show four subtype-specific sublaminae of retinorecipient neurons in vLGNe. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/073197v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@1739b12org.highwire.dtl.DTLVardef@c9e9a6org.highwire.dtl.DTLVardef@a92b8org.highwire.dtl.DTLVardef@267956_HPS_FORMAT_FIGEXP M_FIG C_FIG

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