JOURNAL OF NEUROTRAUMA Volume 23, Number 2, 2006 © Mary Ann Liebert, Inc. Pp. 181–192 Progesterone Increases the Expression of Myelin Basic Protein and the Number of Cells Showing NG 2 Immunostaining in the Lesioned Spinal Cord FLORENCIA LABOMBARDA, 1 SUSANA GONZALEZ, 1 MARIA CLAUDIA GONZALEZ DENISELLE, 1 LAURA GARAY, 1 RACHIDA GUENNOUN, 2 MICHAEL SCHUMACHER, 2 and ALEJANDRO F. DE NICOLA 1 ABSTRACT It is now widely accepted that progesterone (PROG) brings neuroprotection in lesions of the pe- ripheral and central nervous system. Spinal cord trauma leads to neuronal degeneration, astrogliosis, demyelination, and proliferation of oligodendrocyte-precursor cells (OPCs). In this work, we stud- ied the effects of PROG on myelin-related parameters in rats with complete spinal cord transection (TRX). To this end, sham-operated controls and rats with TRX at thoracic level T10 received ve- hicle or PROG (4 mg/kg/day) during 3 days. Three variables were measured in the lumbar L4 re- gion below the lesion: (1) expression of myelin basic protein (MBP) at the protein and mRNA lev- els; (2) density of NG 2 -immunopositive cells as markers for OPCs; and (3) number of cells immunopositive for RIP, an antibody staining mature oligodendrocytes. TRX decreased MBP im- munostaining in the corticospinal tract (CST) and dorsal ascending tract (DAT) but not the ventral funiculus (VF). NG 2  cells, which were detected in low number in controls, increased after TRX in the gray and white matter. RIP-positive cell number, however, remained unchanged. PROG treat- ment of rats with TRX enhanced the expression of MBP protein and mRNA in CST and DAT, but not VF and highly stimulated the number of cells showing NG 2 immunostaining over untreated le- sioned rats. Instead, density of RIP positive cells was similar in the PROG-treated and untreated lesioned groups. We propose that PROG effects on expression of MBP and the number of NG 2 im- munopositive cells may contribute to neuroprotection, as they go in parallel with previous results showing enhanced biochemical and morphological parameters of motoneurons of animals with TRX receiving PROG treatment. Key words: myelin basic protein; neuroprotection; NG 2 + cells; oligodendrocytes; progesterone; spinal cord injury 181 1 Laboratory of Neuroendocrine Biochemistry, Institute of Experimental Biology and Medicine, and Department of Human Bio- chemistry, Faculty of Medicine, University of Buenos Aires, Buenos Aires, Argentina. 2 INSERM U488, Hopital de Bicetre, Kremlin-Bicetre, France.