Cholecystokinergic innervation of nucleus accumbens subregions

Behavioral and pharmacological evidence has shown a different and opposite role of the neuropeptide cholecystokinin (CCK) on the dopamine (DA) function in the caudal versus rostral part of the nucleus accumbens. Previous reports have speculated that the caudal region of the nucleus accumbens would receive CCKergic innervation from dopaminergic neurons of the mesencephalic ventral tegmental area, whereas the CCKergic input to the rostral accumbens would originate in non-dopaminergic neurons from extra-mesencephalic areas of the brain. In the present study, this issue was addressed using retrograde tracing techniques in conjunction with immunocytochemistry. Retrograde tracers were injected in the three compartments of the accumbens (i.e., rostral pole, core and septal shell). In summary, our results demonstrate that 1) the main CCKergic input of the accumbens originates in the ventral mesencephalon; 2) the rostral pole is equally innervated by CCK neurons projecting from both substantia nigra pars compacta and ventral tegmental area; 3) the primary source of CCK innervation of the accumbal core is the substantia nigra pars compacta; and 4) whereas the CCKergic input to the septal shell originates primarily in the ventral tegmental area. Additionally, our results also showed that most of the CCKergic neurons projecting to any of the accumbal compartments also produce dopamine. These data constitute the first neuroanatomical evidence for the differential effects of CCK on dopamine actions in the different regions of the nucleus accumbens.