Orbitomedial prefrontal cortical projections to hypothalamus in the rat

A previous study in the rat revealed that distinct orbital and medial prefr ontal cortical (OMPFC) areas projected to specific columns of the midbrain periaqueductal gray region (PAG). This study used anterograde tracing techn iques to define projections to the hypothalamus arising from the same OMPFC regions. In addition, injections of anterograde and retrograde tracers wer e made into different PAG columns to examine connections between hypothalam ic regions and PAG columns projected upon by the same OMPFC regions. The mo st extensive patterns of hypothalamic termination were seen after injection of anterograde tracer in prelimbic and infralimbic (PL/IL) and the ventral and medial orbital (VO/MO) cortices. Projections from rostral PL/IL and VO /MO targeted the rostrocaudal extent of the lateral hypothalamus, as well a s lateral perifornical, and dorsal and posterior hypothalamic areas. Projec tions arising from caudal PL/IL terminated within the dorsal hypothalamus, including the dorsomedial nucleus and dorsal and posterior hypothalamic are as. There were also projections to medial perifornical and lateral hypothal amic areas. In contrast, it was found that anterior cingulate (AC), dorsola teral orbital (DLO), and agranular insular (AId) cortices projected to dist inct and restricted hypothalamic regions. Projections arising from AC termi nated within dorsal and posterior hypothalamic areas, whereas DLO and AId p rojected to the lateral hypothalamus. The same OMPFC regions also projected indirectly, by means of specific PAG columns, to many of the same hypothal amic fields. In the context of our previous findings, these data indicate t hat, in both rat and macaque, parallel but distinct circuits interconnect O MPFC areas with specific hypothalamic regions, as well as PAG columns. (C) 2001 Wiley-Liss, Inc.