d-Cycloserine reverses scopolamine-induced object and place memory deficits in a spontaneous recognition paradigm in rats

Fosgonimeton, a Novel Positive Modulator of the HGF/MET System, Promotes Neurotrophic and Procognitive Effects in Models of Dementia

All types of dementia, including Alzheimer's disease, are debilitating neurodegenerative conditions marked by compromised cognitive function for which there are few effective treatments. Positive modulation of hepatocyte growth factor (HGF)/MET, a critical neurotrophic signaling system, may promote neuronal health and function, thereby addressing neurodegeneration in dementia. Here, we evaluate a series of novel small molecules for their ability to (1) positively modulate HGF/MET activity, (2) induce neurotrophic changes and protect against neurotoxic insults in primary neuron culture, (3) promote anti-inflammatory effects in vitro and in vivo, and (4) reverse cognitive deficits in animal models of dementia. Through screening studies, the compound now known as fosgonimeton-active metabolite (fosgo-AM) was identified by use of immunocytochemistry to be the most potent positive modulator of HGF/MET and was selected for further testing. Primary hippocampal neurons treated with fosgo-AM showed enhanced synaptogenesis and neurite outgrowth, supporting the neurotrophic effects of positive modulators of HGF/MET. Additionally, fosgo-AM protected against neurotoxic insults in primary cortical neuron cultures. In vivo, treatment with fosgo-AM rescued cognitive deficits in the rat scopolamine amnesia model of dementia. Although fosgo-AM demonstrated several procognitive effects in vitro and in vivo, a prodrug strategy was used to enhance the pharmacological properties of fosgo-AM, resulting in the development of fosgonimeton (ATH-1017). The effect of fosgonimeton on cognition was confirmed in a lipopolysaccharide (LPS)-induced neuroinflammatory mouse model of dementia. Together, the results of these studies support the potential of positive modulators of HGF/MET to be used as novel therapeutics and suggest the drug candidate fosgonimeton might protect against neurodegeneration and be therapeutic in the management of Alzheimer's disease and other types of dementia.

D-cycloserine rescues scopolamine-induced deficits in cognitive flexibility in rats measured by the attentional set-shifting task

Cognitive flexibility facilitates adaptions to a changing environment in humans and animals and can be assessed with the attentional set shifting task (ASST). In various learning paradigms for laboratory rodents, the partial NMDA receptor agonist D-cycloserine has been found to have pro-cognitive effects. However, D-cycloserine has not yet been investigated for its effects on cognitive flexibility. The aim of the present study was to determine whether D-cycloserine is able to improve cognitive flexibility measured by the ASST in rats. Rats were first pre-treated with the muscarinic antagonist scopolamine (0.5 mg/kg) before the D-cycloserine administrations (20 mg/kg) to induce deficits in ASST performance. Our findings showed impaired ASST performance after scopolamine administration with significant effects on reversal phases and extra-dimensional shift. D-cycloserine treatment selectively improved the performance in the extra-dimensional shift and the last reversal phase, where scopolamine effects were most pronounced. These findings suggest that D-cycloserine can rescue deficits in cognitive flexibility.

Protective Effects of Inosine on Memory Consolidation in a Rat Model of Scopolamine-Induced Cognitive Impairment: Involvement of Cholinergic Signaling, Redox Status, and Ion Pump Activities

This study investigated the effects of inosine on memory acquisition and consolidation, cholinesterases activities, redox status and Na⁺, K⁺-ATPase activity in a rat model of scopolamine-induced cognitive impairment. Adult male rats were divided into four groups: control (saline), scopolamine (1 mg/kg), scopolamine plus inosine (50 mg/kg), and scopolamine plus inosine (100 mg/kg). Inosine was pre-administered for 7 days, intraperitoneally. On day 8, scopolamine was administered pre (memory acquisition protocol) or post training (memory consolidation protocol) on inhibitory avoidance tasks. The animals were subjected to the step-down inhibitory avoidance task 24 hours after the training. Scopolamine induced impairment in the acquisition and consolidation phases; however, inosine was able to prevent only the impairment in memory consolidation. Also, scopolamine increased the activity of acetylcholinesterase and reduced the activity of Na⁺, K⁺-ATPase and the treatment with inosine protected against these alterations in consolidation protocol. In the animals treated with scopolamine, inosine improved the redox status by reducing the levels of reactive oxygen species and thiobarbituric acid reactive substances and restoring the activity of the antioxidant enzymes, superoxide dismutase and catalase. Our findings suggest that inosine may offer protection against scopolamine-induced memory consolidation impairment by modulating brain redox status, cholinergic signaling and ion pump activity. This compound may provide an interesting approach in pharmacotherapy and as a prophylactic against neurodegenerative mechanisms involved in Alzheimer's disease.

A Study of the Participation of NMDA Glutamate Receptors in the Mechanisms of Specific Anterograde Amnesia Reversion

We studied the involvement of NMDA glutamate receptors in the mechanisms of anterograde amnesia. It was found that repeated training of amnestic animals treated with D-cycloserine, a potent agonist of the glycine site of NMDA receptors, did not lead to consolidation of long-term memory, while expression of short-term memory was more pronounced in comparison with control animals that received saline before repeated training. It was shown that D-cycloserine in amnestic snails did not affect the food reactions caused by the presentation of a conditioned stimulus during the reminder (without combination with the unconditioned stimulus). It is assumed that NMDA glutamate receptors in amnestic animals are involved in the neural plasticity mechanisms that underlie short-term memory, but their activation does not influence the anterograde amnesia processes and does not lead to the formation or recovery of long-term memory.