DISTRIBUTION OF DOPAMINE BETA-HYDROXYLASE-LIKE IMMUNOREACTIVE FIBERS WITHIN THE SHELL SUBREGION OF THE NUCLEUS-ACCUMBENS

The nucleus accumbens (Acb) can be divided into distinct subfields, de lineated on the basis of histochemical markers as well as by afferent and efferent projection patterns. The shell subregion has reciprocal r elationships with a variety of limbic areas and brainstem autonomic st ructures, and has been suggested to participate in motivation-related processes, including reward, stress, and arousal. The locus coeruleus (LC)-noradrenergic system has similarly been implicated in the modulat ion of behavioral state and stress-related processes, and previous stu dies have demonstrated reciprocal projections between the locus coerul eus and Acb shell. To better understand the anatomical substrate throu gh which LC could influence activity within Acb shell, immunohistochem ical methods were used to visualize the extent and the distribution of noradrenergic axons within this structure. Coronal sections of rat br ain were processed to visualize immunoreactivity for the norepinephrin e synthetic enzyme dopamine P-hydroxylase (DBH), a specific marker for noradrenergic processes. In some cases, alternate sections were proce ssed for immunohistochemical localization of substance P, in order to delineate core, shell, and pallidal compartments. Moderate-to-dense DB H-like immunoreactivity (DBHir) was found in approximately the caudal half of the shell subregion, particularly in caudalmost (septal pole) and ventral zones. The innervation of the septal pole was contiguous w ith a dense innervation of the bed nucleus of the stria terminalis. Fe w immunoreactive fibers were observed in the caudate-putamen, Acb core , or rostral Acb shell. Many DBHir fibers within the shell region were highly arborized with numerous varicosities, features indicative of t erminal fields. These observations suggest noradrenergic systems might modulate certain processes associated with stress, behavioral state, or reinforcement via actions within the Acb shell. (C) 1997 Wiley-Liss , Inc.