Ubiquitin immunoreactivity in presumed spinal interneurones in motor neurone disease

Previous studies have demonstrated the presence of ubiquitin-immunoreactivi ty (Ub-IR) as inclusions and skeins in motor neurones of both the familial and sporadic forms of motor neurone disease (MND). There is evidence that i nterneurones also degenerate in MND, but Ub-IR in ventral horn spinal inter neurones has not been studied previously. Here, Ub-IR was investigated in 1 445 presumed interneurones and 1086 presumed motor neurones counted in thre e random 20-mum sections of the ventral horn of the third lumbar segment of the spinal cord of each of seven controls and seven patients with MND. The ventral horn was divided into four quadrants; the dorsomedial quadrant con tains almost exclusively interneurones and the ventrolateral quadrant large ly motor neurones. The neurones were also classified by morphological and s ize criteria into presumed interneurones (<25 <mu>m) and presumed motor neu rones (greater than or equal to 25 mum). Ub-IR was classified as inclusions , skeins and dispersed cytoplasmic and nuclear staining. Ub-IR inclusions o r skeins were not observed in the controls but 6.6% of neurones (motor neur ones and interneurones) showed the presence of dispersed cytoplasm staining and nuclear staining. The incidence of Ub-IR cytoplasmic and nuclear stain ing was significantly greater in both motor neurones and interneurones of M ND patients than controls. Ub-IR was less frequent in MND cases in which a great loss of neurones was observed. Ub-IR was significantly more frequent in motor neurones than interneurones, both in patients and controls. Ub-IR inclusions and skeins were only observed in motor neurones from MND patient s. Ub-IR inclusions were not observed in presumed spinal interneurones, whi le skeins were only seen in three out of 565 of these cells (two of them in the dorsomedial quadrant) in two out of seven patients. Thus, although pre sumed spinal interneurones occasionally revealed Ub-IR features similar to motor neurones, the rare staining of Ub-IR skeins and the lack of Ub-IR inc lusions in interneurones in MND suggests that these neurones only occasiona lly form ubiquitin-protein conjugates. Neuronal size, rather than type, may be important in determining whether ubiquitin-protein conjugates form in t he ventral horn neurones in MND.