Connections of the rostral ventral respiratory neuronal cell group: An anterograde and retrograde tracing study in the rat

The connections of the rostral ventral respiratory cell group (VRG) were re trogradely and anterogradely determined after discrete injections of a mixt ure of the fluorescent tracers Fast Blue (FB) and Fluoro Ruby (FR) into the physiologically identified rostral inspiratory cell group. Retrogradely FB -labeled neurons and/or anterogradely FR-labeled fibers and terminal fields were located bilaterally in a variety of brain areas, Both retrograde and anterograde labelings were mainly found in: 1) the deep cerebellar nuclei; 2) the lateral lemniscus and paralemniscal nuclei, deep gray, and white int ermediate layers of the superior colliculus, tegmental (laterodorsal and mi crocellular) nuclei, and central gray; and 3) the septohypothalamic nucleus , and lateral and posterior hypothalamic areas. The FR-labeled terminal-lik e elements were found in: 1) Crus 2 of the ansiform lobule, acid the simple , 2, and 3 cerebellar lobules; 2) the subcoeruleus, deep mesencephalic, and Edinger-Westphal nuclei; and 3) the premammiliary, lateral, and medial mam millary nuclei, retrochiasmatic part of the supraoptic nucleus, and the zon a incerta. The FB-labeled neurons were found in: 1)the parapedunculopontine tegmental and cuneiform nuclei, caudal linear nucleus of the raphe, and ad jacent area of the cerebral peduncle; 2) the thalamic posterior nuclear gro up and subparafascicular, parafascicular, and gelatinosus thalamic nuclei; 3) the parastrial amygdaloid and subthalamic nuclei; and 4) the olfactory t ubercle, granular, and agranular insular cortex, parietal and lateral orbit al cortices. The connections of the rostral VRG with several cerebellar, mi dbrain, diencephalic, and telencephalic regions could provide an anatomical substrate for a role of these regions in the control of respiratory-relate d functions. (C) 1999 Elsevier Science Inc.