Enkephalin-immunoreactive neurons in the nucleus tractus solitarius project to the parabrachial nucleus of the cat.

Enkephalin immunoreactive neurons within the nucleus tractus solitarius (NTS) were found to project to the parabrachial nucleus of the cat with the use of a combination of immunohistochemistry and retrograde transport of horseradish peroxidase. Double labelled neurons were located in the medial, parvocellular and commissural subdivisions of the NTS and were present predominantly ipsilateral to the injection site within the parabrachial nucleus. Only a few double labelled neurons were found in the contralateral NTS. The presence of neurons containing enkephalin immunoreactivity suggests that the role of enkephalin in the regulation of autonomic functions may be, in part, by circuits between the NTS and the parabrachial nucleus.