Anatomical organization of long ascending propriospinal neurons in the cat spinal cord.

Retrograde transport of lectin-HRP conjugate (WGA-HRP) was used to examine the anatomical organization of long ascending propriospinal neurons (LAPNs) projecting to the cervical enlargement (C5-T1) and to the upper part of the cervical cord (C3-4) in cats. Small injections (0.05-1.0 microliter) of dilute (1-4%) WGA-HRP were made into the C5-T1 or C3-4 regions. The field potential evoked from stimulation of the superficial radial nerve served to position the micropipette delivering injections. Small and localized populations of labelled LAPNs were found in the dorsal horn (laminae IV-V), the intermediate zone (dorsal and medial lamina VII), and the ventral horn (ventral lamina VII, laminae VIII and IX). Ventral horn LAPNs projecting to the C5-T1 region were preferentially located in rostral lumbar regions. Ventral LAPNs projecting to the C3-4 region were more caudally situated. No regional differences in distribution of dorsal horn and intermediate zone LAPNs were noted in comparing the results of C3-4 with C5-T1 injection protocols. It is concluded that the caudally located ventral LAPNs may exert their influence on cervical motor output through C3-4 propriospinal interneurons. Other LAPNs are considered to exert their effect more directly, either at the C5-T1 or the C3-4 levels.