Rostral Elements of Sympatho-motor Circuitry: A Virally Mediated Transsynaptic Tracing Study

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Abstract
Numerous physiological and emotionally motivated behaviors, including locomotion, exercise, escape, and attack behaviors as well as passive coping responses, require concomitant activation of motor and sympathetic efferents. Such functional heterogeneity suggests the existence of dual function neurons that can simultaneously coordinate motor and sympathetic output. Because previous physiological investigations have implicated a number of mesencephalic and telencephalic regions in mediating these behaviors, we hypothesized the presence of dual function sympatho-motor neurons in these neural structures. To test this hypothesis, we used recombinant strains of the pseudorabies virus (PRV) for transsynaptic tract-tracing. PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized gastrocnemius muscle, whereas PRV-BaBlu, which expresses β-galactosidase, was injected into the adrenal gland in the same animals. Although coinfected neurons were detected in a number of mesencephalic and telencephalic regions, >50% of such neurons were located within specific subdivisions of two general areas: the hypothalamus and periaqueductal gray. These subdivisions included the ventrolateral periaqueductal gray, dorsomedial hypothalamus, dorsolateral lateral hypothalamus, and ventral portion of the medial parvocellular subdivision of the paraventricular nucleus of the hypothalamus (PVN). A subset of the sympatho-motor neurons within the PVN also contained either arginine vasopressin or oxytocin. This sympatho-motor circuitry likely plays an important role in mediating different aspects of stress responses and emotionally motivated behaviors.

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