The pattern of thalamocortical and brain stem projections to the vibrissae-related sensory and motor cortices in de-whiskered congenital hypothyroid rats.

Abstract

The present study is designed to investigate the plastic organization of the thalamo-cortical (TC) and brain stem afferents of whisker primary sensory (wS1) and motor (wM1) cortical areas in congenital hypothyroid (CH) pups following whisker deprivation (WD) from neonatal to adolescence period. Maternal hypothyroidism was induced by adding propylthiouracil (PTU) to the drinking water from early embryonic day 16 to postnatal day (PND) 60. Pregnant rats were divided into intact and CH groups (n=8). In each group, the total whiskers of pups (4 of 8) were trimmed continuously from PND 1 to PND 60. Retrograde tracing technique with WGA-HRP was performed in the present study. Retrogradely labeled neurons were observed in the specific thalamic nuclei (VPM and VL) following separately WGA-HRP injections into wS1/M1 cortical areas. The number of labeled cells in the VPM, VL, VM and PO nuclei of the thalamus significantly decreased in CH offsprings rats (P<0.05). Neonatal WD did not show any significant effects on the number of VPM, VL, VM and PO labeled projection neurons to wS1 and wM1 cortical areas. In addition, retrogradely labeled neurons in dorsal raphe (DR) and locus coeruleus (LC) nuclei were observed in all experimental groups. The number of DR and LC labeled neurons were higher in the CH and whisker deprived groups compared to their matching controls (P<0.05). Upon our results, CH and WD had no synergic or additive effects on the TC and brain stem afferent patterns of barrel sensory and motor cortices.