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Neurotensin terminals form synapses primarily with neurons lacking detectable tyrosine hydroxylase immunoreactivity in the rat substantia nigra and ventral tegmental area
Author(s) -
Woulfe John,
Beaudet Alain
Publication year - 1992
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903210114
Subject(s) - ventral tegmental area , substantia nigra , pars compacta , neurotensin , tyrosine hydroxylase , biology , axon , neuroscience , midbrain , neurotensin receptor , dopaminergic , tegmentum , dopamine , anatomy , neuropeptide , central nervous system , receptor , biochemistry
A light and electron microscopic double antigen localization technique was employed to examine the fine structural relationship between neurotensin‐containing axon terminals and dopaminergic neurons in the substantia nigra and ventral tegmental area of the rat. At the light microscopic level, neurotensin‐immunoreactive terminals were densely distributed throughout the substantia nigra pars compacta and ventral tegmental area in close proximity to tyrosine hydroxylase‐immunoreactive somata and dendrites. On electron microscopic examination, direct synaptic connections were identified between neurotensin‐immunoreactive axon terminals and tyrosine hydroxylase‐immunopositive perikarya and dendrites. However, only 8.2% and 8.8% of the neurotensin‐immunoreactive axonal profiles detected in the substantia nigra and ventral tegmental area, respectively, were found in direct apposition with tyrosine hydroxylase‐immunostained elements. In turn, only 9.3% and 10.0% of tyrosine hydroxylase immunoreactive dendrites sampled from the substantia nigra and ventral tegmental area, respectively, were seen in contact with neurotensin immunopositive axon terminals. However, neurotensin‐immunoreactive and tyrosine hydroxylase‐immunolabelled elements were frequently identified in close anatomical proximity (<5 μm) to one another. These results are interpreted in light of the selective association of neurotensin receptors with dopaminergic neurons in the substantia nigra and ventral tegmental area to suggest a predominantly parasynaptic mechanism of action for neurotensin in the ventral midbrain.