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High levels of amyloid-β peptide (Aβ) have been related to Alzheimer's disease pathogenesis. However, in the healthy brain, low physiologically relevant concentrations of Aβ are necessary for long-term potentiation (LTP) and memory. Because cGMP plays a key role in these processes, here we investigated whether the cyclic nucleotide cGMP influences Aβ levels and function during LTP and memory. We demonstrate that the increase of cGMP levels by the phosphodiesterase-5 inhibitors sildenafil and vardenafil induces a parallel release of Aβ due to a change in the approximation of amyloid precursor protein (APP) and the β-site APP cleaving enzyme 1. Moreover, electrophysiological and behavioral studies performed on animals of both sexes showed that blocking Aβ function, by using anti-murine Aβ antibodies or APP knock-out mice, prevents the cGMP-dependent enhancement of LTP and memory. Our data suggest that cGMP positively regulates Aβ levels in the healthy brain which, in turn, boosts synaptic plasticity and memory. [ABSTRACT FROM AUTHOR]

Reduced activity of the mitochondrial respiratory chain and in particular of complex I is implicated not only in the etiology of Parkinson's disease but also in other forms of parkinsonism in which striatal neurodegeneration occurs, such as progressive supranuclear palsy. The pesticide rotenone inhibits mitochondrial complex I and reproduces features of these basal ganglia neurological disorders in animal models. We have characterized the electrophysiological effects of rotenone in the striatum as well as potential neuroprotective strategies to counteract the detrimental effects of this neurotoxin. We found that rotenone causes a dose-dependent and irreversible loss of the corticostriatal field potential amplitude, which was related to the development of a membrane depolarization/inward current in striatal spiny neurons, coupled to an increased release of both excitatory amino acids and dopamine (DA). In particular, we have investigated whether glutamate, DA, and GABA systems might represent possible targets for neuroprotection against rotenone-induced striatal neuronal dysfunction. Interestingly, whereas modulation of glutamatergic transmission was not neuroprotective, blockade of D2-like but not D1-like DA receptors significantly reduced the rotenone-induced effects via a GABA-mediated mechanism. In addition, because antiepileptic drugs (AEDs) modulate multiple transmitter systems, we have analyzed the possible neuroprotective effects of some AEDs against rotenone. We found that carbamazepine, unlike other tested AEDs, exerts a potent neuroprotective action against rotenone-induced striatal neuronal dysfunction. This neuroprotection was observed at therapeutically relevant concentrations requiring endogenous GABA. Differential targeting of GABAergic transmission may represent a possible therapeutic strategy against basal ganglia neurodegenerative disorders involving mitochondrial complex I dysfunction. [ABSTRACT FROM AUTHOR]