ALTERNATIVE DEVELOPMENT OF NOCICEPTIVE AND PROPRIOCEPTIVE AFFERENT FIBERS IN THE MOUSE SPINAL CORD / 神经解剖学杂志

ABSTRACT

The present study was designed to examine the developmental changes in projection and termination of nociceptive and proprioceptive afferent fibers in the spinal cord by labeling those two fibers with calcitonion gene-related peptide (CGRP) and parvalbumin (PV)separately in mouse embryos and neonatal pups aged embryonic day 15 to posanatal day 3 (E15 -P3). CGRP-like immunoreactive (LI)nociceptive fibers first appeared in the superficial dorsal horn (DH) at E16. The afferent projections extended laterally to the DH and entered into the deep portions of the DH at E17 and E18. After birth, the projection pattern of CGRP-LI fibers remained unchanged but the intensity of afferent terminals increased in the superficial laminae and their branching patterns became more complicated. In addition,CGRP-LI collaterals that projected into the contralateral DH were also examined after E16. Around birth, the contralateral projections were also found originated from the lateral part of the DH. PV-LI proprioceptive afferents were first observed entering the gray matter at E15 and reached the intermediate gray matter (IG) and the ventral horn (VH) more obviously on E16. The number and intensity of PV-LI fibers increased in the the VH with age and reached a maximum during earlier postnatal period ( P0-P3 ). The proprioceptive terminals seemed to form close relationship with motoneurons in the VH from E17. Our results indicate that the somatotopic organization of nociceptive and proprioceptive afferents in the spinal cord both are established during the late embryonic and early postnatal stages. These results help to understand the development of the sensory transmission in more details.