Specificity of spinal projections from hypothalamic and brainstem areas which innervate sympathetic preganglionic neurons.

The specificity and topographic organization of afferent projections to the intermediolateral column (IML) were examined using retrograde transport of fluorescent tracers injected into pairs of thoracic spinal segments. Neurons within the hypothalamus (parvocellular paraventricular nucleus, dorsomedial nucleus and lateral hypothalamus), pons (Kolliker-Fuse and A5 nuclei) and medulla (ventrolateral nucleus of the solitary tract and rostral ventrolateral medulla) each appeared to innervate only a single spinal segment. Neurons in each cell group projecting to different spinal segments were intermixed and showed no evidence of topographic organization. These results provide a potential anatomical substrate for organ-specific autonomic responses to physiological and psychological stimuli.