NEUROPEPTIDE-Y IN THE HUMAN THYROID-GLAND

Autonomic nerve fibers immunoreactive to Neuropeptide Y (ir-NPY) were counted in tissue samples from human thyroid glands. Samples were take n from the non-pathological parts of gland material removed surgically from nine female patients suffering from struma nodosa or solitary ad enoma. The ir-NPY fiber population was subdivided into fibers associat ed with blood vessels (perivascular innervation) and fibers either att ached to the wall epithelium of the follicles or coursing within the g land's connective tissue (extravascular innervation). Most perivascula r fibers were found in arterioles (20-40 mu m diam.). Capillaries (< 1 0 mu m diam.) were not innervated. These fibers surrounded the vessels . They formed a characteristic reticular or coil-like pattern close to the tunica adventitia. Sometimes a second, smaller fiber layer was fo und between the tunica adventitia and media. Ir-NPY fibers were unmyel inated and less than 2 mu m in diameter. Based on counts of the gland' s arterial supply, it was calculated that about 23% of all arterial ve ssels (< 80 mu m diameter) were innervated. On average, one innervated arteriole was found per 0.2 mm(2) of thyroid tissue. Extravascular fi bers were less frequent. In ca. 3 mm(2) of thyroid tissue at least two ir-NPY fibers were found outside the vessels close to the follicular epithelium or within the connective tissue. No follicles with a dense ir-NPY innervation were found. Extravascular fibers were less arborize d. They appear to be either smaller or less intensively stained than p erivascular fibers, although some extravascular fibers were collateral s of the perivascular fibers.