CNS location of uterine-related neurons revealed by trans-synaptic tracing with pseudorabies virus and their relation to estrogen receptor-immunoreactive neurons.

Retrograde, transneuronal tracing with Bartha's strain of pseudorabies virus was used in rats to identify spinal cord, brainstem and hypothalamic loci of uterine-related neurons that could function in the regulation of uterine activity. Based on the premise that estrogen might influence such uterine-related neurons, the existence of estrogen receptors in neurons in these same loci was examined. Viral injections were made into the uterine cervix, body and cervical end of the uterine horns, and the rats allowed to survive for four to six days. After four days, mainly the spinal cord, medulla and pons contained virus-infected neurons. After longer survival times, progressively higher levels of the neuraxis contained viral-labeled neurons, so that by six days hypothalamic uterine-related neurons were identified. First-order virus-infected neurons were visualized by immunohistochemistry in the pelvic paracervical parasympathetic ganglia and in inferior mesenteric sympathetic ganglia. Preganglionic and putative interneurons were labeled in the lumbosacral spinal cord and thoracic spinal cord mainly in the lateral horn area (sacral parasympathetic nucleus and intermediolateral nucleus), lateral aspect of the dorsal horn, intermediate gray, lamina X and dorsal gray commissural area. In the brainstem, labeling was most evident and consistent in the nucleus tractus solitarius, ventrolateral medulla, raphe magnus and pallidus nuclei, parapyramidal area, A5 cell group, Barrington's nucleus of the pons and periaqueductal gray of the midbrain. In the hypothalamus, virus-infected neurons were most marked in the paraventricular nucleus, with fewer in the medial preoptic area and ventromedial hypothalamic nucleus. Estrogen receptor-immunoreactive neurons were most often present among the virus-labeled uterine-related neurons of the spinal cord, nucleus tractus solitarius, ventrolateral medulla, periaqueductal gray, medial preoptic area and ventromedial hypothalamic nucleus. These results identify a multisynaptic pathway of neurons whose eventual output is involved in uterine functions, whose distribution is similar to that revealed by pseudorabies virus tracing from other visceral organs, and which are often mixed among estrogen-responsive neurons.