Specific and Non-Specific Thalamocortical Afferents to the Whisker–Related Sensory Cortical Region in Rats with Congenital Hypothyroidism

Background & Aims: Thyroid hormones are of great importance in the development of the central nervous system. Congenital hypothyroidism may affect the reorganization of specific and non-specific thalamocortical afferents to whisker–related sensory (wS1) corticol region in rats. Methods: Congenital hypothyroidism was induced by adding propylthiouracil (PTU) (25 ppm) to the rats’ drinking water from embryonic day 16 to postnatal day 60. Pregnant rats were divided into normal and congenital hypothyroidism groups. Wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into wS1 cortical area as tracer. Results: Following tracer injection, retrogradely labeled neurons were observed in the thalamic specific relay nuclus including ventral posterior medial (VPM), and in the nonspecific thalamic nuclei including centrolatral (CL), centromedial (CM), ventromedial (VM), posteromedial (PO), and reunion (Re). The number of VPM and PO labeled neurons significantly reduced in the congenital hypothyroidim group compared to the normal group (P < 0.01 and P < 0.05, recpectively). No significant difference was observed between the hypothyroidism group and control group in terms of the number of labeled projection neurons in CL, CM, VM, and Re nuclei. Conclusion: The present study showed that congenital hypothyroidism alters the thalamocortical projection pattern from VPM and PO thalamic nuclei to barrel cortex