IDENTIFICATION OF CARDIOVASCULAR PATHWAYS IN THE SYMPATHETIC NERVOUS-SYSTEM

1. Sympathetic autonomic neurons show distinct patterns of expression of a range of neurochemicals that can be detected immunohistochemicall y. Often, functionally homologous neurons in the autonomic nervous sys tem express identical combinations of substances that serve as a chemi cal code that allows them to be identified among other autonomic neuro ns. 2. In the rat stellate ganglion, where many neurons express either immunoreactivity (IR) to neuropeptide Y (NPY) or the calcium-binding protein calbindin, a population of large post-ganglionic neurons found along the medial border of the stellate ganglion, around the origin o f the cardiac nerves, expressed intense IR to both substances at all a ges examined, from early postnatal to adult.3. In the heart, in the fi rst few postnatal weeks, many nerve terminals were IR for both NPY and calbindin, but, with increasing age, calbindin-IR was progressively l ost from NPY-IR terminals. Nerve terminals IR for both calbindin and N PY were not seen around pulmonary blood vessels or in the trachea or t he thymus. 4. Nerve terminals IR for calretinin, another calcium-bindi ng protein, were present in dense pericellular baskets around neurons in the stellate IR for both calbindin and NPY, The terminals also cont ained nitric oxide synthase (NOS)-IR. 5. It is suggested that the calb indin- and NPY-IR neurons in the stellate ganglion are the post-gangli onic neurons that innervate the heart and that the nerve terminal cont aining calretinin and NOS-IR that surround them are the cardiac pregan glionic terminals. It thus appears possible, in the rat, to identify t he sympathetic cardiac pathway arising in the spinal cord and controll ing the heart purely on the basis of chemical coding.