Single CNS neurons link both central motor and cardiosympathetic systems: a double-virus tracing study

Two anatomical experiments were performed to test the hypothesis that single CNS neurons link the central areas that regulate the somatomotor and sympathetic systems. First, the retrograde neuronal tracer cholera toxin beta-subunit was injected into the lateral parafascicular thalamic nucleus, a region that projects to both the motor cortex and striatum. Several days later, a second injection of the retrograde transneuronal tracer, pseudorabies virus (PRV), was made in the same rats in the stellate ganglion, which provides the main sympathetic supply to the heart. Using immunohistochemical methods, we demonstrate that the cholinergic neurons of the pedunculopontine tegmental nucleus (PPN) are connected to both systems. The second experiment used two isogenic strains of Bartha PRV as double transneuronal tracers. One virus contained the unique gene for green fluorescent protein (GFP) and the other had the unique gene for beta-galactosidase (beta-gal). GFP-PRV was injected in the stellate ganglion and beta-gal-PRV was injected into the primary motor cortex. Double-labeled neurons were found in the lateral hypothalamic area (50% contained orexin) and PPN (approximately 95% were cholinergic). Other double-labeled neurons were identified in the deep temporal lobe (viz., amygdalohippocampal zone and lateral entorhinal cortex), posterior hypothalamus, ventral tuberomammillary nucleus, locus coeruleus, laterodorsal tegmental nucleus, periaqueductal gray matter, dorsal raphe nucleus, and nucleus tractus solitarius. These results suggest these putative command neurons integrate the somatomotor and cardiosympathetic functions and may affect different behaviors (viz., arousal, sleep, and/or locomotion).