Brain vasopressin levels in Down syndrome and Alzheimer's disease

Performing gene hunting in Down Syndrome fetal brain we detected an overexpressed sequence highly homologous to the human vasopressin gene. As this neuropeptide may be involved in the pathogenetic mechanism and, moreover, was described to play a role in memory and learning, we decided to study the brain gene product level in Down Syndrome (DS), controls and patients with Alzheimer's disease (AD). Subtractive hybridization was used to study the differential expression between steady state mRNA levels in fetal brain of DS and controls at the 23rd week of gestation. A radioimmunological method was used to determine vasopressin (AVP) in five brain regions of each 9 aged DS brains, 9 brains with AD and 9 control individuals, obtained from brain bank. An overexpressed nucleic acid sequence with 91% homology to the vasopressin gene was detected in both fetal brains with DS. AVP levels in controls were of the order cerebellum>occipital>frontal>parietal>temporal lobe and were significantly higher in temporal lobe and lower in cerebellum of patients with DS. AVP levels in brain of AD patients were also significantly increased in temporal lobe but were not reduced in cerebellum. The biological meaning of increased AVP remain unclear but may be linked to the neurodegenerative processes, proposed to be similar in both disorders. Data from gene hunting in fetal DS brain along with our data on aged DS and AD patients suggest the early involvement of AVP in the pathomechanism accompanying cholinergic, monoaminergic and neuropeptidergic deficits described in DS and AD.