EXPERIMENTALNEUROLOGY 188,121-138(1988) Morphology of Dendrite Bundles in the Cervical Spinal Cord of the Rat: A Light Microscopic Study WILLIAM J. ANDERSON,* DENISE L. BELLINGER,~ AND DIANNE LORTON#? *Indiana University School of Medicine, Terre Haute Centerfor Medical Education, Indiana State University, Terre Haute, Indiana 47809; tDepartment ofNeurobiology anddnatomy, University of Rochester School of Medicine and Dentistry, 601 Elmwood Ave. Box 603, Rochester, New York 14642; and #Department ofNeurology, Duke University Medical Center, Durham VA Hospital, 508 Fulton Street, Durham, North Carolina 27705 Received October 28, 1986; revision received October 26, I987 Histological staining techniques and Golgi-Cox impregnation revealed three dis- crete dendrite bundles in the ventral horn of the rat cervical spinal cord. A midline dendrite bundle (MDB) traversed the ventromedial gray matter (C3-6) a central den- drite bundle (CDB) coursed the medial aspect ofthe ventral horn (C3-5) and a lateral dendrite bundle (LDB) traveled in the ventrolateral gray matter (C2-4). At the light microscopic level, the three dendrite bundles were composed of longitudinally ori- ented intertwined dendrites that coursed in close apposition among motoneuron peri- karya, neuroglia, and capillaries. A gradient of packing density of dendrites in the bundles existed, the MDB displaying the greatest packing density and the LDB form- ing the most loosely interwoven dendritic plexus. Dendrites contributing to the bun- dles originated from several different motoneuron pools. Smaller transverse dendrite bundles radiated from the longitudinal dendrite bundles at right angles and appeared to interconnect the MDB, CDB, and LDB. Transverse dendrite bundles also exited the MDB and LDB to course into the anterior and lateral funiculi, respectively. The presence of dendrite bundles among fields of motoneurons suggeststhat dendrite bun- dles may provide an anatomical substrate for the synchronization of neuronal activity for coordination of muscle groups involved in particular movements. Dendrite bun- dles also would provide a means whereby functionally similar motoneurons can re- ceive and integrate similar synaptic inputs, and thus allow these inputs to modulate and coordinate groups of neurons that act as a functional unit. The presence of trans- verse dendrite bundles interconnecting the longitudinal bundles may permit the fine Abbreviations: EM-electron microscopic; H&E-hematoxylin and eosin; i.p.-intraperito- neal, MDB, CDB, LDB-midline, central, lateral dendrite bundle. ’ The authors thank Dr. William Brett, Chairman of the Indiana State Life Sciences Depart- ment, for his support and the use of his facilities. 121 00 I4-4886/88 $3.00 Copyright 0 1988 by Academic Press, Inc. All rights of reproduction in any form reserved.