Donepezil induces a cholinergic sprouting in basocortical degeneration Laure Ginestet, Juan E. Ferrario, Rita Raisman-Vozari, Etienne C. Hirsch and Thomas Debeir INSERM, UMR-679, Neurology and Experimental Therapeutics, Ho ˆpital de la Salpe ˆtrie `re; and Universite ´ Pierre et Marie Curie-Paris 6, Paris, France Abstract One of the few currently approved therapies for Alzheimer’s disease (AD) consists in the administration of acetylcholine- sterase inhibitors, which enhances the lifetime of the neuro- transmitter acetylcholine. Despite numerous studies on the symptomatic effect of acetylcholinesterase inhibitors, there is as yet no direct morphological evidence to indicate that they have a neurorestorative action. We investigated the effect of the acetylcholinesterase inhibitor donepezil administered subcutaneously in a rat model of partial unilateral cortical devascularization that induces a loss of the cortical cholinergic terminal network and a retrograde degeneration of the cho- linergic projections that originate in the nucleus basalis. For 6 weeks, lesioned and sham-operated rats received a sub- cutaneous infusion of donepezil (2 mg/kg/day) or vehicle, delivered by osmotic minipumps implanted 2 weeks before the cortical devascularization. In lesioned rats, donepezil treatment increased the number and the size of vesicular acetylcholine transporter immunoreactive boutons in com- parison to vehicle treatment. Donepezil had no observable effect on any of these parameters in sham-operated animals. These results show that donepezil mitigates cholinergic neuronal degeneration in vivo. This suggests a neuroplastic activity of this drug and provides evidence for a potential use of donepezil as a disease modifier in neurodegenerative dis- eases such as AD. Keywords: vesicular acetylcholine transporter, somatosen- sory cortex, plasticity, acetylcholinesterase, Alzheimer’s dis- ease. J. Neurochem. (2007) 102, 434–440. Alzheimer’s disease (AD) is characterized pathologically by the presence of senile plaques and neurofibrillary tangles in various brain regions. Moreover, biochemical changes involving cholinergic neurotransmission have also been reported in the brain of patients with AD. Consistent with this, a decrease in choline acetyltransferase enzyme (ChAT) activity has been described in the cerebral cortex as well as in other cholinergic brain areas (Rossor et al. 1982). Further- more, a correlation between the degree of reduction of ChAT activity in the cerebral cortex and the severity of dementia has also been reported, suggesting an involvement of the cholinergic deficit in the development of dementia (Ruberg et al. 1990). In particular, we and others have reported a loss of cholinergic neurons in the nucleus basalis of Meynert (NbM) (Whitehouse et al. 1981; Lehericy et al. 1993). Furthermore, the expression of choline acetyltransferase mRNA was found to be down-regulated in the surviving cholinergic neurons in the NbM of patients with AD (Strada et al. 1992), while mRNA for trkA and p75 NTR are also decreased early in the disease process (Chu et al. 2001; Ginsberg et al. 2006). This raises the possibility of functional restoration by stimulating the synthesis of acetyl- choline, by extending its half-life in the synaptic cleft or by stimulating the re-growth of cholinergic terminals. This concept has provided a rationale for the first symptomatic treatment of AD by mimicking or maintaining the function of the forebrain cholinergic system. Various strategies have been developed to enhance the synthesis and the release of acetylcholine (ACh), to inhibit its breakdown or to mimic its effects at the level of post-synaptic receptors Received October 3, 2006; revised manuscript received January 16, 2007; accepted January 26, 2007. Address correspondence and reprint requests to Etienne Hirsch, INSERM UMR-679, Neurology and Experimental Therapeutics, Ho ˆpital de la Salpe ˆtrie `re, 47 boulevard de l’Ho ˆpital, Paris 75013, France. E-mail: hirsch@ccr.jussieu.fr Abbreviations used: ACh, acetylcholine; AChE, acetylcholinesterase; AD, Alzheimer’s disease; ANOVA, analysis of variance; ChAT, choline acetyltransferase; DAB, 3,3¢-diaminobenzidine tetrahydrochloride; NbM, nucleus basalis of Meynert; NGF, nerve growth factor; VAChT, vesicular acetylcholine transporter. Journal of Neurochemistry , 2007, 102, 434–440 doi:10.1111/j.1471-4159.2007.04497.x 434 Journal Compilation Ó 2007 International Society for Neurochemistry, J. Neurochem. (2007) 102, 434–440 Ó 2007 The Authors