Morphological heterogeneity within the cingulate cortex in rat: a horseradish peroxidase transport study.

We compared the connections of two areas within rat cingulate cortex, the Cg1/Cg2 area vs the Cg3 area, by iontophoresing small quantities of wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) into either of these two divisions and identifying afferent and efferent connections. Cortical projections were more widespread for the cingulate cortex (Cg3) area than for the Cg1/Cg2 area and included the dysgranular and agranular insular cortex, and perirhinal cortex. The Cg3 area received input from the CA1 layer of the hippocampus while the Cg1/Cg2 area was interconnected primarily with retrosplenial cortex. In the brainstem, both received input from Barrington's nucleus however, many of the subcortical connections of the two areas differed and supported the hypothesis that the Cg3 area is part of the limbic and visceral motor system while the Cg1/Cg2 area is more closely allied with somatic motor control. The Cg3 area received input from the basolateral nucleus of the amygdala, the supramammillary hypothalamic nucleus, the laterodorsal tegmental nucleus, and the lateral parabrachial nucleus. The Cg1/Cg2 area received input from the substantia nigra and targeted deep layers of the superior colliculus. Thus, rat cingulate cortex is a heterogeneous area that can be further subdivided into separate limbic/autonomic (Cg3) and somatic motor areas (Cg1/Cg2).