Dataset Information

Opposing Effects of Maternal Hypo- and Hyperthyroidism on the Stability of Thalamocortical Synapses in the Visual Cortex of Adult Offspring.

ABSTRACT: Insufficient or excessive thyroid hormone (TH) levels during fetal development can cause long-term neurological and cognitive problems. Studies in animal models of perinatal hypo- and hyperthyroidism suggest that these problems may be a consequence of the formation of maladaptive circuitry in the cerebral cortex, which can persist into adulthood. Here we used mouse models of maternal hypo- and hyperthyroidism to investigate the long-term effects of altering thyroxine (T4) levels during pregnancy (corresponding to embryonic days 6.5-18.5) on thalamocortical (TC) axon dynamics in adult offspring. Because perinatal hypothyroidism has been linked to visual processing deficits in humans, we performed chronic two-photon imaging of TC axons and boutons in primary visual cortex (V1). We found that a decrease or increase in maternal serum T4 levels was associated with atypical steady-state dynamics of TC axons and boutons in V1 of adult offspring. Hypothyroid offspring exhibited axonal branch and bouton dynamics indicative of an abnormal increase in TC connectivity, whereas changes in hyperthyroid offspring were indicative of an abnormal decrease in TC connectivity. Collectively, our data suggest that alterations to prenatal T4 levels can cause long-term synaptic instability in TC circuits, which could impair early stages of visual processing.

SUBMITTER: Strobl MJ

PROVIDER: S-EPMC6059113 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Publications

Opposing Effects of Maternal Hypo- and Hyperthyroidism on the Stability of Thalamocortical Synapses in the Visual Cortex of Adult Offspring.

Strobl Marie-Therese J MJ Freeman Daniel D Patel Jenica J Poulsen Ryan R Wendler Christopher C CC Rivkees Scott A SA Coleman Jason E JE

Cerebral cortex (New York, N.Y. : 1991) 20170501 5

Insufficient or excessive thyroid hormone (TH) levels during fetal development can cause long-term neurological and cognitive problems. Studies in animal models of perinatal hypo- and hyperthyroidism suggest that these problems may be a consequence of the formation of maladaptive circuitry in the cerebral cortex, which can persist into adulthood. Here we used mouse models of maternal hypo- and hyperthyroidism to investigate the long-term effects of altering thyroxine (T4) levels during pregnancy ...[more]

PMID: 27235101

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Project description:Unified visual perception relies on the integration of bottom-up and top-down inputs in the primary visual cortex (V1), with top-down inputs known to provide behavior-related modulation on visual processing. However, the organization of top-down inputs in V1 remains unclear. Here, using optogenetics-assisted circuit mapping, we characterized how multiple top-down inputs from higher-order cortical and thalamic areas engage excitatory and inhibitory neurons in V1. Systematic layer- and cell-type-specific profiling of the innervation properties of top-down inputs ultimately revealed that each top-down input employs a unique laminar profile when innervating V1. These profiles partially overlap in superficial layers, bypass layer 4 (L4), and clearly segregate upon reaching deep layers. Specifically, inputs from the medial secondary visual cortex (V2M) and anterior cingulate cortex (ACA) preferentially activate L6 neurons, while inputs from the ventrolateral orbitofrontal cortex (ORBvl) and lateral posterior thalamic nucleus (LP) activate L5 neurons. Having defined the inputs, we conducted independent optogenetic activation studies and discovered that ORBvl and LP inputs selectively activate two types of pyramidal neurons (Pyrs) in L5: Pyr <-- ORBvl and Pyr <-- LP neurons, each with specific electrophysiological properties and gene expression profiles. Retrograde mapping subsequently revealed that Pyr <-- ORBvl neurons preferentially innervate subcortical areas and Pyr <-- LP neurons innervate cortical areas, indicating parallel processing of ORBvl and LP inputs in Pyr-type-specific subnetworks. Further, we found mutual inhibition between these two subnetworks, as LP inputs indirectly inhibit Pyr <-- ORBvl neurons and ORBvl inputs inhibit Pyr <-- LP neurons through local inhibitory neurons. Our study thus deepens understanding of the neuronal mechanisms involved in top-down modulation of visual processing by providing a valuable resource characterizing the layer- and cell-type-specific organization of top-down inputs in V1 and by revealing that L5 Pyr-type-specific subnetworks engage in parallel processing of corticocortical and thalamocortical top-down inputs.

Dataset Information

Opposing Effects of Maternal Hypo- and Hyperthyroidism on the Stability of Thalamocortical Synapses in the Visual Cortex of Adult Offspring.

Publications

Opposing Effects of Maternal Hypo- and Hyperthyroidism on the Stability of Thalamocortical Synapses in the Visual Cortex of Adult Offspring.

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