S. Vanhatalo et S. Soinila, PITUITARY-GLAND RECEIVES BOTH CENTRAL AND PERIPHERAL NEUROPEPTIDE-Y INNERVATION, Brain research, 740(1-2), 1996, pp. 253-260
Neuropeptide Y (NPY)-containing neural projections to the rat pituitar
y gland were studied by combining NPY immunohistochemistry with retrog
rade tracing with Fluorogold as well as central and peripheral denerva
tions. Numerous pituitary-projecting, i.e. Fluorogold-labelled, neuron
s in the superior cervical ganglion, as well as in the hypothalamic ma
gnocellular nuclei were NPY-immunoreactive (NPY-IR). In contrast, no o
ther hypothalamic NPY-IR neurons, e.g, in the arcuate nucleus or the p
reoptic area, were observed to be projecting into the pituitary. Withi
n the posterior lobe of the pituitary gland two morphologically distin
ct NPY-LR fiber populations were discovered, namely thinner parenchyma
l terminals, distinct from the neurosecretory terminals, and thicker,
perivascular fibers. Neurosecretory nerve terminals, in contrast, were
devoid of NPY-IR, being consistent with the previous reports on their
sensitivity to osmotic stimulation. On the other hand, the anterior a
nd intermediate lobes contained no NPY-IR fibers. Bilateral extirpatio
n of the superior cervical ganglion resulted in disappearance of the p
erivascular NPY-lR fibers leaving the parenchymal NPY-IR fibers unaffe
cted, while transection of the pituitary stalk abolished all of the pa
renchymal NPY-IR neurons, leaving the perivascular fibers unaffected.
These findings together with the observed colocalization of tyrosine h
ydroxylase and NPY in the posterior lobe perivascular fibers indicated
that they are sympathetic nerve endings. The thin parenchymal termina
ls, instead, are suggested to stem from central sources other than hyp
othalamus. Our findings indicate that the pituitary gland receives NPY
-containing innervation from at least three distinct sources, and NPY
may thus affect pituitary functions in various ways, such as blood flo
w and vasopressin release.