Neonatal thyroxine treatment: changes in the number of corticotropin-releasing-factor (CRF) and neuropeptide Y (NPY) containing neurons and density of tyrosine hydroxylase positive fibers (TH) in the amygdala correlate with anxiety-related behavior of wistar rats
Section snippets
Animals and drug treatment
Pregnant Wistar rats were delivered from Harlan/Winkelmann (Borchen, Germany). During the first 12 days after birth, the pups were daily injected s.c. with 7.5 μg l-thyroxine (T4) in 0.05 ml of a buffered 0.9% NaCl solution (T4 sodium salt; purity approximately 98% [HPLC]; Fluka Chemie AG, Buchs, CH-9471). Control pups were injected with an identical volume of buffered carrier solution only. At the age of 4 weeks, the young animals were separated from their mothers. All animals were
General observations
The T4-treated rats showed an accelerated development including opening of eyes and snout elongation as typical signs of hyperthyroidism (Rastogi and Singhal, 1976), and a lower body (F1,41=139.62; P<0.001) and brain weight (F1,42=91.76; P<0.001) at adulthood.
Motility test
The two-way ANOVA (treatment×sex) revealed that T4-treated animals had a higher locomotor and vertical activity in the motility test during the total test period of 20 min (and the 5 min blocks). If not mentioned explicitly, there were no
Discussion
The results of the present study can be summarized as follows: First, neonatally T4-treated animals demonstrated a reduced anxiety in the motility test and EPM, and a higher locomotor activity. Second, there was a differential effect of T4-treatment on amygdala morphology: the number of CRF-containing neurons was reduced in the central nucleus of T4-treated animals, but the number of NPY-ir neurons and the density of TH-ir fibers were increased in the basolateral complex despite a reduction in
Acknowledgements
The authors thank Mr. T. Weber and Mrs. Mengert for the computerized photographic aid. We thank Prof. B. Sabel (Medical Psychology, Magdeburg) for the use of the motility apparatus, Prof. Dr. A. K. Braun (Leibniz-Institute of Neurobiology, Magdeburg) for the NIH image-analysis system, Mrs. B. Ketzler, Mrs. A. Kröber and Mrs. S. Schneider for the expert technical assistance for the in situ hybridization, and Dipl. Ing. C. Kurtz for the custom-made software used for the elevated plus-maze
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