Subsets of neurotensin-immunoreactive neurons in the rat striatal complex following antagonism of the dopamine D2 receptor: an immunohistochemical double-labeling study using antibodies against Fos.

A study was done to determine if the Fos and neurotensin immunoreactivities elicited in the rat striatal complex by the selective dopamine D2 receptor antagonist, S(-)-eticlopride hydrochloride are co-localized in the same neurons. Following injections of eticlopride, Fos and neurotensin immunoreactivity were both non-uniformly distributed among the striatal compartments and subterritories. Fos was co-localized in a significant number of small, lightly neurotensin-immunoreactive neurons, but not in a larger subset of neurons with significantly greater median diameter that exhibited intense neurotensin immunoreactivity extending well into the dendritic arbor. It is proposed that neurotensin-immunoreactive neurons lacking Fos immunoreactivity are prominent following selective blockade of the dopamine D2 receptor and represent a subset of striatal neurotensin-immunoreactive neurons. Neurotensin-immunoreactive cells containing Fos nuclei represent a distinct subset, possibly the one that is dominant following administration of reserpine [Zahm (1992) Neuroscience 46, 335-350]. Insofar as Fos expression has been reported to accompany activation of striatonigral and striatopallidal neurons, the absence of Fos in the subset of neurotensin neurons displayed following D2 receptor blockade may be at odds with activation and perhaps is more consistent with inactivation and accompanying decreased release of neurotensin [see Frey et al. (1988) Neurochem. Int. 12, 33-38, and Bean et al. (1989) J. Neurosci. 9, 4430-4438] as a mechanism underlying the accumulation of neurotensin in that subset of striatal neurons.