Cytoarchitecture and neurocytology of rabbit cingulate cortex

The rabbit cingulate cortex is highly differentiated in contrast to rodents and numerous recent advances suggest the rabbit area map needs revision. Immunohistochemistry was used to assess cytoarchitecture with neuron-specific nuclear binding protein (NeuN) and neurocytology with intermediate neurofilament proteins, parvalbumin and glutamic acid decarboxylase. Key findings include: (1) Anterior cingulate cortex (ACC) area 32 has dorsal and ventral divisions. (2) Area 33 is part of ACC. (3) Midcingulate cortex (MCC) has anterior and posterior divisions and this was verified with extensive quantitative analysis and a horizontal series of sections. (4) NeuN, also known as Fox-3, is not limited to somata and formed nodules, granular clusters and striations in the apical dendrites of pyramidal neurons. (5) Area 30 forms a complex of anterior and posterior parts with further medial and lateral divisions. (6) Area 29b has two divisions and occupies substantially more volume than in rat. (7) Area 29a begins with a subsplenial component and extends relatively further caudal than in rat. As similar areal designations are often used among species, direct comparisons were made of rabbit areas with those in rat and monkey. The dichotomy of MCC is of particular interest to studies of pain as anterior MCC is most frequently activated in human acute pain studies and the rabbit can be used to study this subregion. Finally, the area 30 complex is not primarily dysgranular as in rat and is more differentiated than in any other mammal including human. The large and highly differentiated rabbit cingulate cortex provides a unique model for assessing cingulate cortex, pain processing and RNA splicing functions.