TOPOGRAPHY OF PURKINJE-CELL COMPARTMENTS AND MOSSY FIBER TERMINAL FIELDS IN LOBULE-II AND LOBULE-III OF THE RAT CEREBELLAR CORTEX - SPINOCEREBELLAR AND CUNEOCEREBELLAR PROJECTIONS

The cerebellar cortex is histologically uniform by conventional staini ng techniques, but contains an elaborate topography. Tn particular, on the efferent side the cerebellar cortex can be subdivided into multip le parasagittal compartments based upon the selective expression by Pu rkinje cell subsets of various molecules, for example the polypeptide antigens zebrin I and II, and on the afferent side many messy fibers t erminate as parasagittal bands of terminals. The relationships between messy fiber terminal fields and Purkinje cell compartments are import ant for a full understanding of cerebellar structure and function. In this study the locations of spino- and cuneocerebellar messy fiber ter minal fields in lobules II and III of the rat cerebellum are compared to the compartmentation of the Purkinje cells as revealed by using zeb rin II immunocytochemistry. Wheat germ agglutinin-horseradish peroxida se was injected at three different levels in the spinal cord and in th e external cuneate nucleus, and the terminal field distributions in lo bules II and III of the cerebellar cortex were compared with the Purki nje cell compartmentation. In the anterior lobe, zebrin II immunocytoc hemistry reveals three prominent, narrow immunoreactive bands of Purki nje cells, P1(+) at the midline and P2(+) laterally at each side. Thes e are separated and flanked by wide zebrin(-) compartments (P1(-) and P2(-)). There are also less strongly stained P3(+) and P4(+) bands mor e laterally. The spinocerebellar terminals in the granular layer ace d istributed as parasagittally oriented bands. Projections from the lumb ar region of the spinal cord terminate in five bands, one at the midli ne (L1), a second with its medial border midway across P1(-) and its l ateral border at the P2(+)/P2(-) interface (L2), and a third extending laterally from midway across P2(-). The lateral edge of L3 may align with the P3(+)/P3(-) border. The terminal fields labeled by a tracer i njection into the thoracic region give a very similar distribution (T1 , T2 and T3). The only systematic difference is in T2, which statistic al analysis suggests may be broader than L2. In contrast, anterograde tracer injections into the cervical region label synaptic glomeruli sc attered throughout the lobule with much weaker or no evidence of bandi ng. The terminal fields of the cuneocerebellar projection have a compl ementary distribution to those of thoracic and lumbar spinocerebellar terminals. There are two lateral bands, Cu2 and Cu3. Cu2 lies within t he Purkinje cell P1-compartment, abutting L1/T1 medially and L2/T2 lat erally. Cu3 lies between L2 and L3 within the P2(-) Purkinje cell comp artment. The medial edge of Cu3 is tightly aligned with the P2(+)/P2(- ) border. In addition, there may be a weak, narrow Cu1 band at the mid line that either overlaps with L1 and T1 or splits them into two. This highly ordered topography is the anatomical substrate of the elaborat e receptive field map of the cerebellum.