Excitatory-inhibitory imbalance in Alzheimer's disease and therapeutic significance.

The interplay between excitatory and inhibitory circuits underlies the brain's processes and their dysregulation has been linked to cognitive decline, psychiatric disorders and epilepsy. In patients with Alzheimer's disease (AD), an elevated occurrence of seizures has been observed in both sporadic and familial forms of the condition. Although seizure activity in AD has been mainly viewed as a result of neuronal cell loss and considered to occur in later stages, it is now becoming increasingly clear that aberrant neuronal activity may be more common in patients at earlier stages than previously thought and may trigger and contribute significantly to cognitive defects. Here, we review alterations of inhibitory and excitatory circuits that may lead to overexcitability and early dysregulation of neuronal networks in the context of AD and therapeutic outcomes of restoring excitatory/inhibitory balance.

Increase in c-Fos and Arc protein in retrosplenial cortex after memory-improving lateral hypothalamic electrical stimulation treatment.

Post-training Intracranial self-stimulation (ICSS) of the lateral hypothalamus (LH), a kind of rewarding deep-brain stimulation, potentiates learning and memory and increases c-Fos protein expression in specific memory-related brain regions. In a previous study, Aldavert-Vera et al. (2013) reported that post-acquisition LH-ICSS improved 48 h retention of a delay two-way active avoidance conditioning (TWAA) and induced c-Fos expression increase in CA3 at 90 min after administration. Nevertheless, this c-Fos induction was only observed after the acquisition session and not after the retention test at 48 h, when the ICSS improving effect was observed on memory. This current study aims to examine the hypothesis that post-training ICSS treatment may stimulate c-Fos expression at the time of the TWAA retention test in retrosplenial cortex (RSC), a hippocampus-related brain region more closely related with long-lasting memory storage. Effects of ICSS on Arc protein, a marker of memory-associated synaptic plasticity, were also measured by immunohistochemistry in granular and agranular RSC. The most innovative results are that the ICSS treatment potentiates the c-Fos induction across TWAA conditions (no conditioning, acquisition and retention), specifically in layer V of the granular RSC, along with increases of Arc protein levels in the granular but not in agranular areas of RSC ipsilaterally few hours after ICSS. This leads us to suggest that plasticity-related protein activation in the granular RSC could be involved in the positive modulatory effects of ICSS on TWAA memory consolidation, opening a new approach for future research in ICSS memory facilitation.