FUNCTIONAL-DEVELOPMENT OF THE VIBRISSAE SOMATOSENSORY SYSTEM OF THE RAT - (C-14) 2-DEOXYGLUCOSE METABOLIC MAPPING STUDY

Functional development of the rat whisker somatosensory system was stu died by using the (C-14) 2-deoxyglucose (2DG) metabolic mapping techni que. Restrained rat pups had their left mystacial vibrissae stroked fo r 30 minutes and their brains harvested, sectioned, and autoradiograph ed from the level of the lower medulla to the frontal cortex. Subjects were tested at postnatal days (PNDs) 0-9 and 21. At birth, all subjec ts exhibited a significant increase of 2DG uptake in the left spinal t rigeminal nuclei, the principal trigeminal sensory nucleus, and a port ion of the right ventral posteromedial thalamic nucleus. The primary s omatosensory cortex exhibited significant 2DG uptake contralateral to stimulation by PND 6, followed by the secondary somatosensory cortex a t PND 7. The pattern of 2DG uptake in the somatosensory cortices becam e more intense and well defined by PND 9. Given that the somatosensory system develops in an orderly fashion from the periphery to higher br ain structures, the present results show that brain structures mediati ng whisker sensory input are not metabolically active until projection s from lower somatosensory centers are established. Neurons become res ponsive to whisker stimulation in the subcortical structures at birth and in the somatosensory cortex a few days later. This cortical activi ty follows the organization of the upper tier of thalamocortical fiber s into a ''barrelfield. Moreover, there is a gradual enhancement in fu nctional activity of the vibrissa neurons at different somatosensory n uclei as rats mature. The present study elucidates the time course of functional development in the rat somatosensory system. (C) 1997 Wiley -Liss, Inc.