Organisation of cingulum bundle fibres connecting the anteriorthalamic nuclei with the rodent anterior cingulate and retrosplenialcortices

摘要

Despite considerable interest in the properties of the cingulum bundle,descriptions of the composition of this major pathway in the rodent brain havenot kept pace with advances in tract tracing. Using complementary approaches inrats and mice, this study examined the dense, reciprocal connections theanterior thalamic nuclei have with the cingulate and retrosplenial cortices,connections thought to be major contributors to the rodent cingulum bundle. Therat data came from a mixture of fluorescent and viral tracers, some injecteddirectly into the bundle. The mouse data were collated from the Allen MouseBrain Atlas. The projections from the three major anterior thalamic nucleioccupied much of the external medullary stratum of the cingulum bundle, wherethey were concentrated in its more medial portions. These anterior thalamicprojections formed a rostral-reaching basket of efferents prior to joining thecingulum bundle, with anteromedial efferents taking the most rostral routes,often reaching the genu of the corpus callosum, while anterodorsal efferentstook the least rostral route. In contrast, the return cortico-anterior thalamicprojections frequently crossed directly through the bundle or briefly joined theinternal stratum of the cingulum bundle, often entering the internal capsulebefore reaching the anterior thalamus. These analyses confirm that anteriorthalamic connections comprise an important component of the rodent cingulumbundle, while also demonstrating the very different routes used bythalamo-cortical and cortico-thalamic projections. This information reveals howthe composition of the cingulum bundle alters along its length.