AMYOTROPHIC LATERAL SCLEROSIS (ALS) is a devastating fatal form of motor neuron disease seen with similar frequencies in developed and developing countries (Gourie Devi et al., 1987; Kurtske, 1982). ALS is defined essentially by a weakness and wasting of skeletal muscles attributed to degeneration of lower motor neurons. The presence of spasticity and hyperreflexia in ALS may be due to the loss of upper motor neurons as the disease progresses (Mulder, 1982). The cause for this gradual neuronal loss is not yet understood. An altered phosphorylation of NF in ventral horn cells of patients with ALS has been reported (Manetto et al., 1988). Neurofilaments (NF) are the major cytoskeletal proteins of neurons, made up of three subunits of molecular weights 200 kDa (NF-H), 150 kDa (NF-M) and 70 kDa (NF-L) (Hoffmann & Lasek, 1975). The C terminal tail regions of NF-H and NF-M are rich in KSP [K(S/T) PXK] sequences characterized by two penta- peptide motifs, KSPXK and KSPXX (Napolitano et al., 1987). The interaction of NF with other compo- nents of cytoskeletal system is thought to be influ- enced by the phosphorylation of C terminal domains of NF-H and NF-M (Carden et al., 1987). Serum and CSF from patients with ALS has been shown to be toxic to neurons in vitro and the presence of an antineuronal factor has been suggested (Couratier et al., 1993; Roisen et al., 1982; Wolfgram & Myers, 1973). We previously reported an aberrant neurofilament phosphorylation in cultured chick spinal cord neurons exposed to CSF, but not to serum, from ALS patients (Nagaraja et al., 1994). However, the effect of CSF of ALS patients on spinal neurons in vivo has not been studied. We also wanted to explore 397 NEURODEGENERATION, Vol. 4, pp 397–401 (1995) Neurofilament Phosphorylation is Increased in Ventral Horn Neurons of Neonatal Rat Spinal Cord Exposed to Cerebrospinal Fluid from patients with Amyotrophic Lateral Sclerosis Muddanna S. Rao, 1 M. Gourie Devi, 2 A. Nalini, 2 Neelam Shahani 1 and T.R. Raju 1 Departments of 1 Neurophysiology and 2 Neurology National Institute of Mental Health and Neuro Sciences Bangalore 560 029, India Aberrant neurofilament (NF) phosphorylation in the soma of the ventral horn neurons of neo- natal rat spinal cord is observed following exposure to cerebrospinal fluid (CSF) of patients suf- fering from Amyotrophic Lateral Sclerosis (ALS). CSF samples from ALS and non-ALS neuro- logical patients were injected into the spinal subarachnoid space of 3 day old rat pups. After 48 h, sections of spinal cords were stained for the presence of phosphorylated NF epitopes with SMI- 31 antibody. The number of neuronal soma staining with this antibody in the ventral and dorsal horns sides of the spinal cord was counted. There was a significant 3-fold increase in the number of soma stained with SMI-31 antibody in the ventral horns of rat spinal cords exposed to CSF of patients with ALS compared to cords from rats exposed to CSF of non-ALS patients and those which were not exposed to any CSF samples. Such an increase in staining of neuronal soma was not observed in the dorsal horns. Hyperphosphorylation of neuronal soma suggests an initial stage of degenerative changes occurring in the motor (ventral horn) neurons following exposure to circulating factor(s) in the CSF of patients with ALS. © 1995 Academic Press Limited Key words: amyotrophic lateral sclerosis, neurofilament phosphorylation, cerebrospinal fluid, motor neurons Correspondence to: Dr T.R. Raju, Dept. of Neurophysiology, National Institute of Mental Health and Neuro Sciences, Post Box No. 2900, Bangalore 560 029, India Received 9 February 1995; revised and accepted for publication 9 June 1995 © 1995 Academic Press Limited 1055-8330/95/040397 + 5 $12.00/0