Afferents to anterior cingulate areas 24a and 24b and midcingulate areas 24a' and 24b' in the mouse.

Areas 24a and 24b of the anterior cingulate cortex (ACC) play a major role in cognition, emotion and pain. While their connectivity has been studied in primate and in rat, a complete mapping was still missing in the mouse. Here, we analyzed the afferents to the mouse ACC by injecting retrograde tracers in the ventral and dorsal areas of the ACC (areas 24a/b) and of the midcingulate cortex (MCC; areas 24a'/b'). Our results reveal inputs from five principal groups of structures: (1) cortical areas, mainly the orbital, medial prefrontal, retrosplenial, parietal associative, primary and secondary sensory areas and the hippocampus, (2) basal forebrain, mainly the basolateral amygdaloid nucleus, the claustrum and the horizontal limb of the diagonal band of Broca, (3) the thalamus, mainly the anteromedial, lateral mediodorsal, ventromedial, centrolateral, central medial and reuniens/rhomboid nuclei, (4) the hypothalamus, mainly the lateral and retromammillary areas, and (5) the brainstem, mainly the monoaminergic centers. The neurochemical nature of inputs from the diagonal band of Broca and brainstem centers was also investigated by double-labeling, showing that only a part of these afferents were cholinergic or monoaminergic. Comparisons between the areas indicate that areas 24a and 24b receive qualitatively similar inputs, but with different densities. These differences are more pronounced when comparing the inputs to ACC's areas 24a/24b to the inputs to MCC's areas 24a'/24b'. These results provide a complete analysis of the afferents to the mouse areas 24a/24b and 24a'/24b', which shows important similarity with the connectivity of homologous areas in rats, and brings the anatomical basis necessary to address the roles of cingulate areas in mice.