The Journal of Neuroscience, June 1, 1999, 19(11):4682-4694
Electrophysiological and Morphological Evidence for a GABAergic
Nigrostriatal Pathway
Manuel
Rodríguez1 and
Tomás
González-Hernández2
Departments of 1 Physiology and 2 Anatomy,
Faculty of Medicine, University of La Laguna, La Laguna, Tenerife,
Canary Islands, Spain
The electrophysiological and neurochemical characteristics of the
nondopaminergic nigrostriatal (NO-DA) cells and their functional response to the degeneration of dopaminergic nigrostriatal (DA) cells
were studied. Three different criteria were used to identify NO-DA
cells: (1) antidromic response to striatal stimulation with an
electrophysiological behavior (firing rate, interspike interval variability, and conduction velocity) different from that of DA cells;
(2) retrograde labeling after striatal injection of HRP but showing
immunonegativity for DA cell markers (tyrosine hydroxylase, calretinin,
calbindin-D28k, and cholecystokinin); and (3) resistance to
neurotoxic effect of 6-hydroxydomine (6-OHDA). Our results showed that
under normal conditions, 5-8% of nigrostriatal neurons are
immunoreactive for GABA, glutamic acid decarboxylase, and parvalbumin, markers of GABAergic neurons, a percentage that reached 81-84% after 6-OHDA injection. Electrophysiologically, NO-DA cells showed a behavior similar to that found in other nigral GABAergic (nigrothalamic) cells. In addition, the 6-OHDA degeneration of DA cells
induced a modification of their electrophysiological pattern similar to
that found in GABAergic nigrothalamic neurons. Taken together, the
present data indicate the existence of a small GABAergic nigrostriatal
pathway and suggest their involvement in the pathophysiology of
Parkinson's disease.
Key words:
nigrostriatal pathway; dopaminergic cells; GABAergic
cells; GABA; glutamic acid decarboxylase; parvalbumin; calretinin; calbindin-D28k; cholecystokinin; Parkinson's disease
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