The limbic zone of the rabbit and rat claustrum: a study of the claustrocingulate connections based on the retrograde axonal transport of fluorescenttracers

The claustrum is a subcortical structure lying under the insular and pirifo rm cortices, whose function is still not clear. Although data exist on conn ections of the claustrum and the limbic cortex, the topography of the limbi c zone in the rabbit and rat claustrum has not been studied extensively. Th e study was performed On 17 adult Wistar rats and 12 New Zealand rabbits. T wo percent water solutions of fluorescent retrograde tracers fast blue and nuclear yellow were injected into the various regions of the limbic cortex. The limbic zone is localized throughout the whole rostrocaudal extent of t he claustrum, mainly in its ventromedial portion lying close to the externa l capsule. Although this zone of the claustrum is localized similarly in bo th rat and rabbit, some differences between these two species exist. In the rat, neurons projecting to all limbic areas are localized mainly in the an terior and central parts of the claustrum, whereas in the rabbit, the major ity of the neurons projecting to the cingulate cortex are present in the an terior and central parts of this structure, while neurons sending axons to the retrosplenial cortex are localized in the central and posterior parts. In both species, double-labeling study showed that neurons projecting to va rious limbic regions are intermingled and that neurons sending axons into t wo different limbic regions are seen only occasionally. Our findings give s upport to the role of the claustrum in integrating information between diff erent areas of the cerebral cortex and the limbic system.