1. ¹Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, NY, USA
2. ²Department of Radiology, Columbia University College of Physicians and Surgeons, New York, NY, USA
3. ³Department of Pharmacology and Physiology, University of Rochester School of Medicine, Rochester, NY, USA

Correspondence: Dr SN Haber, ^*Department of Pharmacology and Physiology, University of Rochester School of Medicine, 601 Elmwood Ave., Rochester, NY 14642, USA. Tel: +1 716 275 4538; Fax: +1 716 273 2652; E-mail: Suzanne_Haber@urmc.rochester.edu

Received 2 March 2005; Revised 19 October 2005; Accepted 24 October 2005; Published online 4 January 2006.

Abstract

Frontal cortical efferent fibers are thought to have important regulatory influence on cortico-basal ganglia (BG) circuits. The cortico-midbrain (substantia nigra/ventral tegmental area, SN/VTA) pathway has received particular attention in psychiatric diseases, most notably schizophrenia. Work in rodents demonstrates that the prefrontal cortico (PFC)-midbrain pathway plays a central role in regulating the firing pattern of dopamine (DA) neurons. These findings have led to some important hypotheses concerning PFC/BG interaction in schizophrenia. Descending PFC projections to the SN/VTA have been primarily documented in the rodent. The aim of this study was to determine the degree and organization of PFC afferents to these areas in the Macaque monkey. Anterograde tracer injections were made into discrete orbital, cingulate, and dorsolateral prefrontal areas. Projections were charted to the SN and VTA. Overall, there were very few fibers in the ventral midbrain following injections confined to specific areas of the PFC. To determine the relationship of the descending fibers to the midbrain DA neurons, sections were double stained for the tracer molecules and for tyrosine hydroxylase. In all cases, the prefrontal projections and the TH-positive cells did not appear to be in close juxtaposition. The results show a very limited projection from the PFC to the midbrain DA neurons in primates, terminating both within the SN proper as well as in the VTA. They arise from a broad region of the PFC, including the DLPF, cingulate, and orbital cortices. However, despite the relative lack of cortical input to the midbrain cells, these neurons are rich in glutamate receptors in primates. Thus, while, based on these anatomical studies, direct cortical control of DA neurons remains debatable in primates; the cortex may directly impact other sources of glutamatergic control.