E. Lyndbalta et Sn. Haber, THE ORGANIZATION OF MIDBRAIN PROJECTIONS TO THE STRIATUM IN THE PRIMATE - SENSORIMOTOR-RELATED STRIATUM VERSUS VENTRAL STRIATUM, Neuroscience, 59(3), 1994, pp. 625-640
In order to examine the organization of nigrostriatal projections in t
he primate, the retrograde tracers Lucifer Yellow conjugated to dextra
n amines and horseradish peroxidase conjugated to wheatgerm agglutinin
were injected into different regions of the dorsolateral and ventral
striatum. Based on the topography of cortical inputs to the striatum,
the dorsalateral striatum is associated with the motor system, and the
ventral striatum is related to the limbic system. Our results indicat
e that although midbrain neurons projecting to the ventral and dorsola
teral striatum are mostly separate, there are neurons projecting to th
ese different striatal territories that overlap in the medial substant
ia nigra. The dopaminergic neurons of the ventral mesencephalon can be
subdivided into dorsal and Ventral tiers that include the cells of th
e ventral tegmental area, the substantia nigra pars compacta, and the
retrorubral area. Neurons projecting to the ventral striatum are found
in both the dorsal and ventral tiers. A large number of neurons occup
ying the medial densocellular zone of the ventral tier are labeled fol
lowing injections into different regions of the ventral striatum. Neur
on Neurons projecting to the sensorimotor-related striatum are derived
almost exclusively from the ventral tier. Many of these neurons are l
ocated very ventrally in the substantia nigra, where clusters of neuro
ns invade the pars reticulata. In addition, labeled neurons are found
throughout the mediolateral extent of the densocellular zone of the pa
rs compacta. Notably, neurons are labeled in the medial densocellular
zone following injections into the dorsolateral and ventral striatum.
Mesencephalic neurons projecting to different striatal territories are
distinct in that dorsal tier neurons mainly innervate the ventral str
iatum, whereas the ventral columns of neurons in the ventral tier inne
rvate the sensorimotor-related striatum. Thus, the dopaminergic regula
tion of the sensorimotor-related striatum and the ventral striatum may
be different. However, a subgroup of dopaminergic neurons in the medi
al densocellular zone projects to both striatal territories. Such dive
rgent projections may allow the substantia nigra to serve as a link, c
onnecting different striatal territories, via their connections with t
he substantia nigra.