Immunohistochemical and electron microscopic demonstration of vascular innervation in the mammalian brainstem.

Ultrastructural morphological relationship between microvessels and neural elements containing serotonin-like immunoreactivity, substance P and methionine-enkephalin like immunoreactivity were studied in the monkey and cat brain. A close relationship between serotonin-like immunoreactive dendritic processes, enkephalin-like immunoreactive profiles and capillary basement membrane was observed; they were usually separated by a double layer of glial membrane. More importantly, serotonin and substance P-like immunoreactive dendritic profiles are reported in close approximation with capillary basement membrane with no glial limitans at the site of contact. These intimate morphological associations may be the basis for neural regulation of tonicity, permeability and chemosensor function in the brain microvasculature.