Morphologically distinct subpopulations of neurotensin-immunoreactive striatal neurons observed in rat following dopamine depletions and D-2 receptor blockade project to the globus pallidus

It has been reported in previous studies that perikaryal neurotensin immunoreactivity is largely absent in the rat striatum except following striatal dopamine depletion or blockade of dopamine D-2 receptors, after which, however, neurotensin immunoreactivity is elicited in at least two distinct subpopulations of striatal neurons [Zahm D. S. (1992) Neuroscience 46, 335-350]. One subpopulation of such cells (type I), prominent following D-2 receptor blockade, is located mainly in the matrix compartment in the rostral, dorsomedial and ventrolateral parts of the striatum, and comprises neurons at the large end of the medium-sized spectrum that exhibit intense neurotensin immunoreactivity in perikarya and proximal dendrites, but rarely display Fos immunoreactivity [Senger B. er al. (1993) Neuroscience 57, 649-660]. A second subpopulation (type IT) resides predominantly in the patch (striosome) and matrix compartments in the dorsolateral quadrant of the striatum, and is prominent following administration of reserpine. These neurons are at the small end of the medium size range and exhibit very light neurotensin immunoreactivity, with little staining of dendrites. Fos immunoreactivity is frequently co-localized in striatal neurons that exhibit a type II striatal neurotensin response [Brog J. S. and Zahm D. S. (1995) Neuroscience 65, 71-86]. In the current study, neurotensin immunoreactivity was elicited in striatal neurons by ventral mesencephalic 6-hydroxydopamine lesions or administration of reserpine or haloperidol. Irrespective of which drug was given, retrogradely transported Fluoro-Gold was prominently co-localized with neurotensin-like immunofluorescence in the perikarya of striatal neurons following injections of the retrograde tracer into the globus pallidus. Few double-labeled neurons were observed following administration of any of these drugs and injections of Fluoro-Gold into the substantia nigra. it is concluded that two supopulations of neurotensin-immunoreactive striatal neurons project predominantly to the globus pallidus and minimally to the substantia nigra. Copyright (C) 1996 IBRO.