title: The nucleus "k" of Meessen and Olszewski efferents to the cerebellar paramedian lobule: a retrograde tracing histochemical (HRP) study in the rabbit and the cat.
abstract: The group "k" of Meessen and Olszewski (1949) was identified in the brain stems of normal rabbits and cats. In the rabbit, a topographical subdivision of the group "k" into the well defined cell aggregations k1, k2 and k3 was found. In the cat, the nucleus corporis pontobulbaris was subdivised into a posterodorsal and a anteroventral part. The former was located ventrally to the motor and principal sensory trigeminal nuclei, the latter was wedgeshaped and situated more anteriorly at the lateroventral margin of the pons. In 9 rabbits and 7 cats the neurons of origin for cerebellar paramedian lobule afferents were identified with retrograde transport of horseradish peroxidase within the nucleus "k" and nucleus corporis pontobulbaris, respectively. In both species, most projections to the paramedian lobule were seen as originating ipsilaterally with only a small contralateral component. The study suggests that there are certain segregated projections of the nucleus "k" or the nucleus corporis pontobulbaris to the cortex of the anterior and posterior parts of the paramedian lobule, with some valid species differences. In the cat, the whole projection was found to originate in the more anterior and ventral parts of the nucleus "k" (nucleus corporis pontobulbaris). The posterior part of the paramedian lobule in the rabbit receives afferents from the homolateral subdivisions k3 and, to a minor degree, from k2; while in the cat, afferents are bilateral with an ipsilateral preponderance and originate from the posterior cellular group of the nucleus corporis pontobulbaris dispersed among and medially to the exiting motor root of the trigeminal nerve. The anterior part of the paramedian lobule afferents in the rabbit originates bilaterally within subdivision k1, to a minor degree ipsilaterally in the dorsal region of subdivision k3, and occasionally in subdivision k2, whereas in the cat afferents originate from the anterior and posterior levels of the corpus pontobulbaris. Additionally, some afferents for the rabbit anterior paramedian lobule originate within the homolateral nucleus "n". No evidence for a longitudinal zonal pattern of the projection onto the paramedian lobule was found. The study is discussed in the light of present information on the connections of the nucleus "k" (nucleus corporis pontobulbaris).
mesh_terms: D000344:Afferent Pathways / Q000033:anatomy & histology; D000818:Animals; D001933:Brain Stem / Q000033:anatomy & histology*; D002415:Cats; D002525:Cerebellar Cortex / Q000033:anatomy & histology*; D004525:Efferent Pathways / Q000033:anatomy & histology; D006735:Horseradish Peroxidase; D009412:Nerve Fibers / Q000648:ultrastructure; D009474:Neurons / Q000145:classification / Q000648:ultrastructure; D011149:Pons / Q000033:anatomy & histology; D011817:Rabbits; D014278:Trigeminal Nuclei / Q000033:anatomy & histology
chemical_list: D006735:Horseradish Peroxidase