Relationships of the Dendritic Arborizations of Ventral Striatomesencephalic Projection Neurons With Boundaries of Striatal Compartments. An In Vitro Intracellular Labelling Study in the Rat

Abstract

We studied the relationships of the dendrites of ventral striatomesencephalic projection neurons with the compartmental structure of the ventral striatum, as revealed by enkephalin immunohistochemistry. Lightly fixed slices were employed in which Lucifer yellow was intracellularly injected into neurons that were retrogradely labelled following Fast Blue injections in the ventral tegmental area. Double immunohistochemical staining was carried out using antisera to Lucifer yellow and Leu-enkephalin. Most of the 226 injected cells were located in the core region of the nucleus accumbens. All these neurons were of the small- to medium-sized spiny type. The dendritic arborizations of over 90% of the cells remained within the compartment in which the parent cell bodies resided. The dendrites of most of these neurons abutted the border of the compartment, whereas a smaller number of neurons had dendrites that were distant from any compartmental boundary. The dendrites of fewer than 10% of the neurons crossed the borders of compartments. Only a few cells were injected in the shell region of the nucleus accumbens. None of these neurons extended its dendrites into the core region of the nucleus or into the territory of the clusters of small cells which characterize the shell. The present results demonstrate that the dendrites of the great majority of ventral striatomesencephalic neurons comply with the boundaries of ventral striatal enkephalin compartments. Together with the results of previous studies showing that such compartments are selectively innervated by thalamic and cortical afferents, and have outputs to different areas in the ventral mesencephalon, the present data suggest the existence of discrete channels through the ventral striatum.