Vagal afferents from the uterus and cervix provide direct connections to the brainstem

Previous anatomical studies demonstrated vagal innervation to the ovary and distal colon and suggested the vagus nerve has uterine inputs. Recent beha vioral and physiological evidence indicated that the vagus nerves conduct s ensory information from the uterus to the brainstem. The present study was undertaken to identify vagal sensory connections to the uterus. Retrograde tracers, Fluorogold and pseudorabies virus were injected into the uterus an d cervix. DiI, an anterograde tracer, was injected into the nodose ganglia. Neurectomies involving the pelvic, hypogastric, ovarian and abdominal vagu s nerves were performed, and then uterine whole-mounts examined for sensory nerves containing calcitonin gene-related peptide. Nodose ganglia and caud al brainstem sections were examined for the presence of estrogen receptor-c ontaining neurons in "vagal locales." Labeling of uterine-related neurons i n the nodose ganglia (Fluorogold and pseudorabies virus) and in the brainst em nuclei (pseudorabies virus) was obtained. DiI-labeled nerve fibers occur red near uterine horn and uterine cervical blood vessels, in the myometrium , and in paracervical ganglia. Rats with vagal, pelvic, hypogastric and ova rian neurectomies exhibited a marked decrease in calcitonin gene-related pe ptide-immunoreactive nerves in the uterus relative to rats with pelvic, hyp ogastric, and ovarian neurectomies with intact vagus nerves. Neurons in the nodose ganglia and nucleus tractus solitarius were immunoreactive for estr ogen receptors. These results demonstrated: (1) the vagus nerves serve as c onnections between the uterus and CNS, (2) the nodose ganglia contain uteri ne-related vagal afferent neuron cell bodies, and (3) neurons in vagal loca les contain estrogen receptors.