<prompt> In which of the following disease decrease in levels of single neurotransmitter was first identified?Alzheimers diseaseParkinsons diseaseHuntingtons diseaseSchizophrenia  <response>: Ans. b. Parkinsons disease The systematic biochemical investigation of the brains of patients with Alzheimers disease began in the late 1960s and early 1970s. The hope was that a clearly defined neurochemical abnormality would be identified, providing the basis for the development of rational therapeutic interventions analogous to levodopa treatment of Parkinsons disease. - http: aiclesPMC1736202pdfv066p00137.pdf Schizophrenia is due to dysregulated serotonin, dopamine and noradrenaline, but a predominant role of a single neurotransmitter has not been described yet Disease Related NeurotransmitterPathology Schizophrenia Dopamine, Serotonin and Norepinephrine are Ted Huntingtons disease CAG trinucleotide expansiondeg on a gene called Huntingtin localized on chromosome 4Q. Caused by triple repeat expansion mutationQ Parkinsons disease Degeneration of dopaminergic neurons in the substantia nigra pars compacta SNc,reduced striatal dopamine, and intracytoplasmic proteinaceous inclusions known as Lewy bodies Alzheimers disease Biochemically, AD is associated with a decrease in the coical levels of several proteins and neurotransmitters, especially acetylcholine, its synthetic enzyme choline acetyltransferase, and nicotinic cholinergic receptors. 