Changes in cerebral neurotransmitters and metabolites induced by acute donepezil and memantine administrations: A microdialysis study

• Published in: Brain research bulletin Vol. 69; no. 2; pp. 204 - 213
• Main Authors: Shearman, E., Rossi, S., Szasz, B., Juranyi, Z., Fallon, S., Pomara, N., Sershen, H., Lajtha, A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 31-03-2006
• Subjects: Acetylcholine - metabolism; Animals; Cerebral Cortex - drug effects; Cerebral Cortex - metabolism; Cholinesterase Inhibitors - pharmacology; Donepezil; Dopamine - metabolism; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists - pharmacology; Extracellular Fluid - drug effects; Extracellular Fluid - metabolism; Hippocampus - drug effects; Hippocampus - metabolism; Indans - pharmacology; Male; Memantine - pharmacology; Memantine effects; Microdialysis; Neurotransmitter Agents - metabolism; Neurotransmitter Agents - secretion; Neurotransmitter release; Norepinephrine - metabolism; Nucleus Accumbens - drug effects; Nucleus Accumbens - metabolism; Piperidines - pharmacology; Prefrontal Cortex - drug effects; Prefrontal Cortex - metabolism; Presynaptic Terminals - drug effects; Presynaptic Terminals - metabolism; Presynaptic Terminals - secretion; Rats; Rats, Sprague-Dawley; Regional heterogeneity of drug effects; Serotonin - metabolism; Temporal Lobe - drug effects; Temporal Lobe - metabolism; Ventral Tegmental Area - drug effects; Ventral Tegmental Area - metabolism; Neurotransmitter release; Regional heterogeneity of drug effects; Donepezil; Memantine effects
• ISSN: 0361-9230; 1873-2747
• DOI: 10.1016/j.brainresbull.2005.12.001

Cholinesterase inhibitors including donepezil, rivastigmine, and galantamine and the
N-methyl-
d-aspartate (NMDA) antagonist, memantine are the medications currently approved for the treatment of Alzheimer's disease (AD). In addition to their beneficial effects on cognitive and functional domains typically disrupted in AD, these agents have also been shown to slow down the emergence of behavioral and psychotic symptoms associated with this disease. However, the underlying mechanisms for these therapeutic effects remain poorly understood and could involve effects of these medications on non-cholinergic or non-glutamatergic neurotransmitter systems respectively. These considerations prompted us to initiate a series of investigations to examine the acute and chronic effects of donepezil (Aricept (±)-2,3-dihydro-5,6-dimethoxy-2-[[1-(phenylmethyl)-4-piperidinyl]methyl]-1
H-inden-1-1 hydrochloride and memantine (1-amino-3,5-dimethyladamantane hydrochloride C
12H
21N·HCl)). The present study focuses on the acute effects of donepezil and memantine on brain extracellular levels of acetylcholine, dopamine, serotonin, norepinephrine and their metabolites. We assayed changes in the ventral and dorsal hippocampus and the prefrontal and medial temporal cortex by microdialysis. Memantine resulted in significant increases in extracellular dopamine (DA), norepinephrine (NE), and their metabolites, in the cortical regions, and in a reduction of DA in the hippocampus. Donepezil produced an increase in extracellular DA in the cortex and in the dorsal hippocampus. Norepinephrine increased in the cortex; with donepezil it increased in the dorsal hippocampus and the medial temporal cortex, and decreased in the ventral hippocampus. Interestingly both compounds decreased extracellular serotonin (5HT) levels. The metabolites of the neurotransmitters were increased in most areas. We also found an increase in extracellular acetylcholine (ACh) by memantine in the nucleus accumbens and the ventral tegmental area. Our results suggest both region and drug specific neurotransmitter effects of these agents as well as some similarities. We conclude that drugs influencing cognitive mechanisms induce changes in a number of neurotransmitters with the changes being both region and drug specific. Release and metabolism are altered and extracellular neurotransmitter levels can be increased or decreased by the drugs. Other studies are in progress to determine the pharmacological effects associated with chronic treatment with these compounds, which may be more pertinent to the clinical situation in which patients take these medications for months or years.