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An ultrastructural double‐label immunohistochemical study of the enkephalinergic input to dopaminergic neurons of the substantia nigra in pigeons
Author(s) -
Medina Loreta,
Keith D. Anderson,
Ellen J. Karle,
Keiner Anton
Publication year - 1995
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.903570307
Subject(s) - substantia nigra , dopaminergic , enkephalin , basal ganglia , biology , neuroscience , dopamine , tyrosine hydroxylase , immunogold labelling , nigrostriatal pathway , postsynaptic potential , neuron , anatomy , ultrastructure , central nervous system , biochemistry , receptor , opioid
Electron microscopic immunohistochemical double‐label studies were carried out in pigeons to characterize the ultrastructural organization and postsynaptic targets of enkephalinergic (ENK+) striatonigral projection. ENK+ terminals in the substantia nigra were labeled with antileucineenkephalin antiserum by using peroxidase‐antiperoxidase methods, and dopaminergic neurons were labeled with anti‐tyrosine hydroxylase antiserum by using silver‐intensified immunogold methods. ENK+ terminals on dopaminergic neurons were equal in abundance to ENK+ terminals on nondopaminergic neurons, although the former were typically somewhat smaller than the latter (mean size: 0.50 vs. 0.75 pm, respectively). ENK+ terminals were evenly distributed on the cell bodies and dendrites of dopaminergic neurons, and they were evenly distributed on dendrites but rare on perikarya of nondopaminergic neurons. Transection of the basal telencephalic output revealed that 75% of the nigral ENK+ terminals were of basal telencephalic origin. These telencephalic ENK+ terminals included over 80% of those smaller than 0.80 pm on dopaminergic neurons and smaller than 1.0 pm on nondopaminergic neurons, and none greater than this in size. Both telencephalic and the nontelencephalic ENK+ nigral terminals made predominantly symmetric synapses on nigral neurons. Although the basal telencephalic ENK+ terminals uniformly targeted dendrites and perikarya, nontelencephalic ENK+ terminals seemed to avoid perikarya. The results indicate that ENK+ striatonigral neurons in birds may directly influence both dopaminergic and nondopaminergic neurons of the substantia nigra. Based on similar data for substance Pcontaining striatonigral terminals, the roles of enkephalin and substance P in influencing nigral dopaminergic neurons may differ slightly, as they appear to target preferentially different portions of dopaminergic neurons. The overall results in pigeons are similar to those for ENK+ terminals in the ventral tegmental area in rats, suggesting that the synaptic organization of the ENK+ input to the tegmental dopaminergic cell fields is similar in mammals and birds. © 1995 Wiley‐Liss, Inc.