DEVELOPMENTAL EXPRESSION OF PARVALBUMIN BY RAT LOWER CERVICAL SPINAL-CORD NEURONS AND THE EFFECT OF EARLY LESIONS TO THE MOTOR CORTEX

Expression of calcium binding proteins (CaBPs), increasing neuronal ac tivity and phases of synapse elimination are widely believed to be lin ked during development. We have employed immunocytochemistry to study the expression of the CaBP parvalbumin (PV) during the postnatal devel opment of the lower cervical spinal cord and investigated how early le sions to the motor cortex, at the onset of corticospinal synaptogenesi s, perturb the normal pattern of PV expression. This study confirms pr evious observations that in normal rats PV-like immunoreactivity is co nfined to large sensory afferents for at least 10 days postnatally (P1 0) and that the adult pattern of expression emerges from about P18 and involves mainly dorsal horn neurones. However, the study has also dem onstrated a transient wave of expression in ventral horn neurones whic h reaches a maximum between P14-18 and declines thereafter. Unilateral lesions made at P7 to the forelimb motor cortex, which sends an almos t completely crossed projection to the spinal cord, resulted in reduce d neuronal expression of PV in the lower cervical spinal cord contrala terally at a range of ages (P14-31). The median ratio of PV positive n eurones contralateral/ipsilateral to the lesion in spinal cord segment s C7 and C8 was significantly lower (p < 0.01) at 56.0% (34.5-76.8 95% confidence limits, n = 14) than in sham operated controls (99.7%, ran ge 93.7-113.6, n = 5). The lesion affected the transient wave of expre ssion seen in ventral horn neurones during the third postnatal week as well as dorsal horn expression at older ages. We conclude that there is considerable plasticity in PV immunoreactivity during spinal cord d evelopment. PV is transiently expressed by ventral horn neurones at an age when movement control is functionally maturing. Early cortical le sions disrupt this transient phase of expression but also alter mature patterns of PV localisation. This suggests a critical role for cortic ospinal pathways in guiding maturation of segmental spinal cord circui try. (C) 1997 Elsevier Science B.V.