S. Vanhatalo et al., COLOCALIZATION OF DOPAMINE AND SEROTONIN IN THE RAT PITUITARY-GLAND AND IN THE NUCLEI INNERVATING IT, Brain research, 669(2), 1995, pp. 275-284
The nerve terminals in the intermediate and posterior lobes of the rat
pituitary gland are reported to show colocalization of serotonin and
tyrosine hydroxylase. This study examined the extent of this colocaliz
ation in the pituitary gland and in the nuclei considered to project t
o the pituitary. In the intermediate lobe, two types of nerve fibers w
ere encountered, one containing serotonin (5-HT-IR) and tyrosine hydro
xylase (TH-IR) immunoreactivities and the other showing 5-HT-IR only.
Instead, there was no colocalization in the posterior lobe. In the hyp
othalamus, colchicine treatment with L-tryptophan and pargyline inject
ions resulted in 5-HT-IR in some neurons in the dorsomedial, periventr
icular and arcuate nuclei, some of which in the arcuate and periventri
cular nuclei were also TH-IR. In the raphe nuclei no colocalization of
5-HT-IR and TH-IR was observed. Catecholamine neurotoxin, 6-hydroxydo
pamine, abolished the 5-HT-IR and dramatically reduced the TH-IR in th
e intermediate lobe nerve fibers. Both effects were prevented by cocai
ne, a monoamine uptake inhibitor, but not by fluoxetine, a specific se
rotonin uptake inhibitor. Serotonin neurotoxin p-chloroamphetamine (PC
A) had no effect on intermediate lobe fibers, although it caused compl
ete disappearance of 5-HT-IR from the posterior lobe nerve fibers. Thi
s effect was prevented by fluoxetine. Our results indicate, that coloc
alization of serotonin and TH observed in the intermediate lobe occurs
both in the nerve terminals within the lobe and in some nuclei that i
nnervate it. Furthermore, drug treatments suggest that serotonin in th
e intermediate lobe is localized in catecholaminergic fibers, which do
not posses a specific serotonin uptake mechanism.