Non-canonical interplay between glutamatergic NMDA and dopamine receptors shapes synaptogenesis

Esketamine-mediated alleviation of electroconvulsive shock-induced memory impairment is associated with the regulation of mGluR5 in depressive-like rats

Electroconvulsive therapy (ECT) is recognized as one of the most efficacious interventions for depression. However, it is associated with impairments in learning and memory functions. Ketamine has demonstrated potential in mitigating cognitive deficits. Notably, the metabotropic glutamate system is hypothesized to play a pivotal role in cognitive process regulation. Nevertheless, the involvement of the metabotropic glutamate system in esketamine-mediated alleviation of electroconvulsive shock (ECS, an animal analogue of ECT)-induced memory impairment remains to be elucidated. In this study, a depressive rat model was established using chronic unpredictable mild stress. The depressive-like behavior and cognitive performance of the rats were evaluated using the sucrose preference test, the open field test, and the Morris water maze test, respectively. The expression levels of type-5 metabotropic glutamate receptor (mGluR5) and N-methyl-d-aspartate receptor 1 (NMDAR1) were quantified through immunofluorescence and real-time PCR techniques. Long-term potentiation (LTP) of hippocampal Schaffer collateral (SC)-CA1 synapses was observed in electrophysiological experiments. The results of this investigation revealed that a low dose of esketamine administration upregulated the expression of mGluR5 and NMDAR1 in the hippocampus of stressed rats, alleviated ECS-induced cognitive impairment, and ameliorated depressive-like behavior. Conversely, the mGluR5 antagonist MTEP effectively reversed esketamine-mediated changes in the rat hippocampus and counteracted its protective effect on learning and memory functions following ECS. In conclusion, the findings of this study support the hypothesis that esketamine upregulates mGluR5 and NMDAR1 expression, thereby enhancing NMDAR activation in the hippocampus. This mechanism may be responsible for the protective effects on spatial learning and memory function observed in depressed rats subjected to ECS.

Aerobic exercise improves motor dysfunction in Parkinson's model mice via differential regulation of striatal medium spiny neuron

The striatum plays a crucial role in providing input to the basal ganglia circuit and is implicated in the pathological process of Parkinson's disease (PD). Disruption of the dynamic equilibrium in the basal ganglia loop can be attributed to the abnormal functioning of the medium spiny neurons (MSNs) within the striatum, potentially acting as a trigger for PD. Exercise has been shown to mitigate striatal neuronal dysfunction through neuroprotective and neurorestorative effects and to improve behavioral deficits in PD model mice. In addition, this effect is offset by the activation of MSNs expressing dopamine D2 receptors (D2-MSNs). In the current study, we investigated the underlying neurobiological mechanisms of this effect. Our findings indicated that exercise reduces the power spectral density of the beta-band in the striatum and decreases the overall firing frequency of MSNs, particularly in the case of striatal D2-MSNs. These observations were consistent with the results of molecular biology experiments, which revealed that aerobic training specifically enhanced the expression of striatal dopamine D2 receptors (D2R). Taken together, our results suggest that aerobic training aimed at upregulating striatal D2R expression to inhibit the functional activity of D2-MSNs represents a potential therapeutic strategy for the amelioration of motor dysfunction in PD.

A molecular perspective on mGluR5 regulation in the antidepressant effect of ketamine

Ketamine, a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist, has received much attention for its rapid antidepressant effects. A single administration of ketamine elicits rapid and sustained antidepressant effects in both humans and animals. Current efforts are focused on uncovering molecular mechanisms responsible for ketamine's antidepressant activity. Ketamine primarily acts via the glutamatergic pathway, and increasing evidence suggests that ketamine induces synaptic and structural plasticity through increased translation and release of neurotrophic factors, activation of mammalian target of rapamycin (mTOR), and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR)-mediated synaptic potentiation. However, the initial events triggering activation of intracellular signaling cascades and the mechanisms responsible for the sustained antidepressant effects of ketamine remain poorly understood. Over the last few years, it has become apparent that in addition to the fast actions of the ligand-gated AMPARs and NMDARs, metabotropic glutamate receptors (mGluRs), and particularly mGluR5, may also play a role in the antidepressant action of ketamine. Although research on mGluR5 in relation to the beneficial actions of ketamine is still in its infancy, a careful evaluation of the existing literature can identify converging trends and provide new interpretations. Here, we review the current literature on mGluR5 regulation in response to ketamine from a molecular perspective and propose a possible mechanism linking NMDAR inhibition to mGluR5 modulation.