To. Mundinger et al., GALANIN IS LOCALIZED IN SYMPATHETIC NEURONS OF THE DOG LIVER, American journal of physiology: endocrinology and metabolism, 36(6), 1997, pp. 1194-1202
Stimulation of canine hepatic nerves releases the neuropeptide galanin
from the liver; therefore, galanin may be a sympathetic neurotransmit
ter in the dog liver. To test this hypothesis, we used immunocytochemi
stry to determine if galanin is localized in hepatic sympathetic nerve
s and we used hepatic sympathetic denervation to verify such localizat
ion. Liver sections from dogs were immunostained for both galanin and
the sympathetic enzyme marker tyrosine hydroxylase (TH). Galanin-like
immunoreactivity (GALIR) was colocalized with TH in many axons of nerv
e trunks as well as individual nerve fibers located both in the stroma
of hepatic blood vessels and in the liver parenchyma. Neither galanin
- nor TH-positive cell bodies were observed. Intraportal 6-hydroxydopa
mine (6-OHDA) infusion, a treatment that selectively destroys hepatic
adrenergic nerve terminals, abolished the GALIR staining in parenchyma
l neurons but only moderately diminished the GALIR staining in the ner
ve fibers around blood vessels. To confirm that 6-OHDA pretreatment pr
oportionally depleted galanin and norepinephrine in the liver, pre mea
sured both the liver content and the hepatic nerve-stimulated spillove
r of galanin and norepinephrine from the liver Pretreatment with 6-OHD
A reduced the content and spillover of both galanin and norepinephrine
by >90%. Together, these results indicate that galanin in dog liver i
s primarily colocalized with norepinephrine in sympathetic nerves and
may therefore function as a hepatic sympathetic neurotransmitter.