2-Deoxyglucose uptake in the central nervous system during systemic hypercapnia in the peripherally chemodenervated rat

Changes in 2-deoxyglucose (2-DG) uptake in the central nervous system during systemic hypercapnia were determined by the [3H]2-DG autoradiographic method in peripherally chemodenervated rats. Autoradiographs were made from serial transverse sections of the brain and analyzed by a computer-based interactive image processing system for areas having increases or decreases in metabolic activity compared with control animals. The most pronounced change shown by autoradiographs of the hypercapnic animals was a generalized decrease in the metabolism of the gray matter throughout the central nervous system with respect to the normocapnic controls. However, several central structures showed evidence of either no change or an increased metabolism in the hypercapnic animals. In the brain stem these areas were localized to the ventrolateral region of the nucleus of the solitary tract rostral to the obex, around the region of the nucleus retroambiguus, in a region of the ventrolateral medullary reticular formation extending rostrally from the obex to the level of the intramedullary rootlets of the facial nerve, in the region of the ventral nucleus raphe pallidus, and in the region of the lateral parabrachial nucleus. In the diencephalon these regions included the supraoptic nucleus and the dorsal hypothalamic area, extending into the caudal portion of the paraventricular nucleus. The thoracolumbar cord showed activation of the lateral aspects of the dorsal horns, the region of lamina X and the region of the intermediolateral nucleus. These data may be interpreted as a functional map of the central structures activated in hypercapnia in the peripheral chemodenervated rat. It appears likely that these structures are involved in mediating the cardiorespiratory responses associated with the activation of central chemoreceptors by the increased carbon dioxide concentrations.