Keywords: AD; Alzheimer's disease; CSF; cerebrospinal fluid; HDC; histidine decarboxylase; HRs; histamine receptors; HMT; histamine-methyltransferase; 6-OHDA; 6-hydroxydopamine; LBs; Lewy bodies; LNs; Lewy neuritis; MT; melatonin receptor; PD; Parkinson's disease;