EXPRESSION OF NADPH-DIAPHORASE AND NITRIC-OXIDE SYNTHASE IN LUMBOSACRAL MOTONEURONS AFTER KNEE-JOINT IMMOBILIZATION IN THE GUINEA-PIG

The expression of nicotinamide adenine dinucleotide phosphate-diaphora se (NADPH-d) and nitric oxide synthase (NOS) in spinal ventral horn ne urons was studied in the guinea pig after right knee joint immobilisat ion (RKJI). At 1 wk after RKJI, neurons in the ipsilateral ventral hor n from L4 to S1 segments showed a moderate reactivity for NADPH-d stai ning. At 2 wk, NADPH-d labelled neurons were also observed in the cont ralateral ventral horn. Ipsilateral NOS immunoreactive cells were not detectable until wk 2. The intensity of NADPH-d and NOS labelled neuro ns in the bilateral ventral horns was sustained, peaking at the 4th wk after RKJI. In guinea pigs subjected to 4 wk of RKJI and subsequently released from the immobilisation for 2 and 4 wk, NADPH-d and NOS reac tivity in ventral horn neurons diminished. The expression of NADPH-d p ositive neurons differed from that of NOS labelled neurons in terms of time interval, cell number and staining intensity, the latter being l ater, fewer and weaker. It is suggested that the induction and upregul ation of NADPH-d and NOS are attributable to reduced activity of muscl es acting on the knee joint after RKJI; the changes are reversible. It is speculated that increased levels of NO production are involved in protective mechanisms against possible neuronal degeneration as a cons equence of target dysfunction.