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      Ultrastructural localization of tyrosine hydroxylase in the rat ventral tegmental area: relationship between immunolabeling density and neuronal associations

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      The Journal of Neuroscience
      Society for Neuroscience

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          Abstract

          Dopaminergic neurons of the A 10 cell group in the rat ventral tegmental area (VTA) exhibit electrical and dye coupling. Also, the activity of these neurons at least partially reflects their content of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. We examined the ultrastructural localization of TH to determine the morphological features of dopaminergic neurons in the VTA and the relationships between their TH immunoreactivity content and afferent input. Antiserum against the trypsin-treated form of TH was localized using peroxidase-antiperoxidase (PAP) and immunoautoradiographic methods. Immunoreactivity was detected in perikarya, dendrites, and terminals. The perikarya contained the usual organelles, as well as cilia, lamellar bodies, and subsurface cisterns. Qualitative evaluation of peroxidase reaction product and quantitative analysis of the number of silver grains/unit area revealed varying amounts of TH immunoreactivity in nuclei and cytoplasm. Lightly or intensely labeled nuclei were not necessarily associated with corresponding cytoplasmic labeling density. However, cytoplasmic labeling directly corresponded to the relative frequencies of neuronal appositions and synaptic input. Those neurons with less dense cytoplasmic PAP product received fewer synaptic contacts and were less frequently in apposition to other TH-labeled soma and dendrites than neurons displaying relatively more dense cytoplasmic PAP product. Analysis of single sections revealed that 67% (n = 71) of all TH- labeled somata and 15% (n = 2431) of all TH-labeled dendrites were in apposition to other TH-labeled soma or dendrites. TH-labeled terminals were rarely detected and contained relatively low levels of immunoreactivity. The majority of labeled terminals (n = 29/46) formed synapses with labeled soma and dendrites. Unlabeled terminals (n = 2424) in contact with TH-labeled dendrites appeared to form predominantly symmetric synapses. Ten percent (n = 248) of the unlabeled terminals dually synapsed onto adjacent immunoreactive dendrites, perikarya, or dendrite and perikaryon. We conclude that in the rat VTA, (1) detected TH immunoreactivity in cytoplasm, but not nucleus, corresponds to the level of feedback principally from nondopaminergic afferents; (2) dendrodendritic as well as axodendritic synapses between TH-immunoreactive neurons may mediate dopaminergic autoinhibition; and (3) gap junction-like appositions between neurons and convergent inputs from unlabeled terminals onto TH-immunoreactive profiles provide an anatomical substrate whereby cellular activities might be coordinated under certain conditions.

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          Author and article information

          Journal
          J Neurosci
          J. Neurosci
          jneuro
          The Journal of Neuroscience
          Society for Neuroscience
          0270-6474
          1529-2401
          1 September 1990
          : 10
          : 9
          : 2996-3013
          Affiliations
          Department of Neurology and Neurosciences, Cornell University Medical College, New York, New York 10021.
          Article
          PMC6570237 PMC6570237 6570237 jneuro;10/9/2996
          10.1523/JNEUROSCI.10-09-02996.1990
          6570237
          1975839
          a3d82805-8173-41a9-9d9f-bf36b393066f
          © 1990 by Society for Neuroscience
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          10/9/2996
          2996

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