Locomotor Deficiencies and Aberrant Development of Subtype-Specific GABAergic Interneurons Caused by an Unliganded Thyroid Hormone Receptor α1

Abstract

Thyroid hormone (TH) deficiency during development causes severe and permanent neuronal damage, but the primary insult at the tissue level has remained unsolved. We have defined locomotor deficiencies in mice caused by a mutant thyroid hormone receptor ␣1 (TR␣1) with potent aporeceptor activity attributable to reduced affinity to TH. This allowed identification of distinct functions that required either maternal supply of TH during early embryonic development or sufficient innate levels of hormone during late fetal development. In both instances, continued exposure to high levels of TH after birth and throughout life was needed. The hormonal dependencies correlated with severely delayed appearance of parvalbumin-immunoreactive GABAergic interneurons and increased numbers of calretinin-immunoreactive cells in the neocortex. This resulted in reduced numbers of fast spiking interneurons and defects in cortical network activity. The identification of locomotor deficiencies caused by insufficient supply of TH during fetal/perinatal development and their correlation with subtype-specific interneurons suggest a previously unknown basis for the neuronal consequences of endemic cretinism and untreated congenital hypothyroidism, and specifies TR␣1 as the receptor isoform mediating these effects.

Thyroid hormone is required for hypothalamic neurons regulating cardiovascular functions

“…Cells expressing other calcium-binding marker proteins, such as calretinin and calbindin, were unaffected (Supplemental Figure 1, A and B) as well as a more distant nucleus of pv + cells in the lateral hypothalamic area (Supplemental Figure 1B) described recently (16). Similar to pv + neurons in the cortex (17), the AHA pv + cells also appeared between postnatal days 7 and 14 (Supplemental Figure 1C).…”

“…Immunohistochemistry was performed as described previously (17). The primary antibodies used were anti-pv (pv-25, Swant; 1:8,000), anti-calretinin (7699/4, Swant; 1:5,000), anti-calbindin (CB-38a, Swant; 1:5,000), anti-NeuN (MAB377, Millipore; 1:500), and antiorexin (sc8070, Santa Cruz Biotechnology Inc.; 1:4,000) with species-specific biotinylated secondary antibodies (Vector Laboratories, Immunkemi; 1:250).…”

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

“…However, other regions including the cerebral cortex, basal ganglia, cerebellum, and hippocampus have also been studied using standard histological approaches. These techniques have also been adapted to study the spinal cord and dorsal and ventral nerve roots (478). For example, the Purkinje cell neurons and their spatial organization are central to the function of the cerebellum.…”

“…IHC is suitable for quantitative approaches only if the detection system is kept unsaturated; quantification of secreted proteins and peptides by this method is not recommended. Studies can be performed on free-floating cryostat sections of specific brain regions (478). The approach was used to study the effects of congenital hypothyroidism on microtubule-associated protein-2 expression in the cerebellum of the rat (495) and the expression of thyroid hormone transporters in the cochlea (496).…”

“…Detailed analysis of neuronal function requires specialist techniques best performed in collaboration with established neuroscience laboratories. For example, patch-clamp analysis of whole neurons in tissue slices or microelectrode recording from tissue slices have been used to study the effects of thyroid hormones on neuron function (478). Whole-cell patch-clamp recordings of individual neurons can be performed using specialist instruments on 300 lm parasagittal brain slices obtained from mice.…”