REDUCTION IN ENKEPHALIN AND SUBSTANCE-P MESSENGER-RNA IN THE STRIATUMOF EARLY GRADE HUNTINGTONS-DISEASE - A DETAILED CELLULAR IN-SITU HYBRIDIZATION STUDY

The expression of enkephalin and substance P messenger RNAs was examin ed in the caudate-putamen of human post mortem tissue from control and Huntington's disease tissue using in situ hybridization techniques an d human specific enkephalin and substance P [S-35]oligonucleotides. Ma croscopic and microscopic quantification of enkephalin and substance P gene expression was carried out using computer-assisted image analysi s. Tissue was collected from six control cases with no sign of neurolo gical disease and six Huntington's disease cases ranging from grades 0 to 3 as determined by neuropathological evaluation. The clinical and pathological diagnosis of Huntington's disease was confirmed unequivoc ally by genetic analysis of the CAG repeat length in both copies of IT 15, the Huntington's disease gene. A marked reduction in both enkephal in and substance P messenger RNAs was detected in all regions of the c audate nucleus and putamen in Huntington's disease grades 2/3 when com pared to controls; in the dorsal caudate few enkephalin or substance P messenger RNA-positive cells were detected. For the early grade (0/1) Huntington's disease cases, a heterogeneous reduction in both enkepha lin and substance P messenger RNAs was noted; for enkephalin messenger RNA the striatal autoradiograms displayed a conspicuous patchy appear ance. Detailed cellular analysis of the dorsal caudate revealed a stri king reduction in the number of enkephalin and substance P messenger R NA-positive cells detected and in the intensity of hybridization signa l/cell. These data suggest that both the ''indirect'' GABA/enkephalin and ''direct'' GABA/substance P pathways are perturbed very early in t he course of the disease and that these early changes in chemical sign alling may possibly underlie the onset of clinical symptoms.