Thyroid hormone insufficiency during brain development reduces parvalbumin immunoreactivity and inhibitory function in the hippocampus.
Thyroid hormones are necessary for brain development. gamma-Amino-butyric acid (GABA)ergic interneurons comprise the bulk of local inhibitory circuitry in brain, many of which contain the calcium binding protein, parvalbumin (PV). A previous report indicated that severe postnatal hypothyroidism reduces PV immunoreactivity (IR) in rat neocortex. We examined PV-IR and GABA-mediated synaptic inhibition in the hippocampus of rats deprived of thyroid hormone from gestational d 6 until weaning on postnatal d 30. Pregnant dams were exposed to propylthiouracil (0, 3, 10 ppm) via the drinking water, which decreased maternal serum T(4) by approximately 50-75% and increased TSH. At weaning, T(4) was reduced by approximately 70% in offspring in the low-dose group and fell below detectable levels in high-dose animals. PV-IR was diminished in the hippocampus and neocortex of offspring killed on postnatal d 21, an effect that could be reversed by postnatal administration of T(4). Dose-dependent decreases in the density of PV-IR neurons were observed in neocortex and hippocampus, with the dentate gyrus showing the most severe reductions (50-75% below control counts). Altered staining persisted to adulthood despite the return of thyroid hormones to control levels. Developmental cross-fostering and adult-onset deprivation studies revealed that early postnatal hormone insufficiency was required for an alteration in PV-IR. Synaptic inhibition of the perforant path-dentate gyrus synapse evaluated in adult offspring, in vivo, revealed dose-dependent reductions in paired pulse depression indicative of a suppression of GABA-mediated inhibition. These data demonstrate that moderate degrees of thyroid hormone insufficiency during the early postnatal period permanently alters interneuron expression of PV and compromises inhibitory function in the hippocampus.
Gilbert
M E
ME
Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA. gilbert.mary@epa.gov
Sui
L
L
Walker
M J
MJ
Anderson
W
W
Thomas
S
S
Smoller
S N
SN
Schon
J P
JP
Phani
S
S
Goodman
J H
JH
D000367:Age Factors; D000818:Animals; D013956:Antithyroid Agents / Q000494:pharmacology; D018891:Dentate Gyrus / Q000196:embryology* / Q000378:metabolism*; D005260:Female; D007037:Hypothyroidism / Q000139:chemically induced / Q000378:metabolism*; D007150:Immunohistochemistry; D007395:Interneurons / Q000378:metabolism; D019579:Neocortex / Q000196:embryology / Q000378:metabolism; D009433:Neural Inhibition / Q000502:physiology*; D010320:Parvalbumins / Q000378:metabolism*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D011441:Propylthiouracil / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D009435:Synaptic Transmission / Q000502:physiology; D013963:Thyroid Hormones / Q000172:deficiency* / Q000494:pharmacology
D013956:Antithyroid Agents; D010320:Parvalbumins; D013963:Thyroid Hormones; D011441:Propylthiouracil