Glutamate is the main excitatory neurotransmitter in the brain wherein it controls cognitive functional domains and mood. Indeed, brain areas involved in memory formation and consolidation as well as in fear and emotional processing, such as the hippocampus, prefrontal cortex, and amygdala, are predominantly glutamatergic. To ensure the physiological activity of the brain, glutamatergic transmission is finely tuned at synaptic sites. Disruption of the mechanisms responsible for glutamate homeostasis may result in the accumulation of excessive glutamate levels, which in turn leads to increased calcium levels, mitochondrial abnormalities, oxidative stress, and eventually cell atrophy and death. This condition is known as glutamate-induced excitotoxicity and is considered as a pathogenic mechanism in several diseases of the central nervous system, including neurodevelopmental, substance abuse, and psychiatric disorders. On the other hand, these disorders share neuroplasticity impairments in glutamatergic brain areas, which are accompanied by structural remodeling of glutamatergic neurons. In the current narrative review, we will summarize the role of glutamate-induced excitotoxicity in both the pathophysiology and therapeutic interventions of neurodevelopmental and adult mental diseases with a focus on autism spectrum disorders, substance abuse, and psychiatric disorders. Indeed, glutamatergic drugs are under preclinical and clinical development for the treatment of different mental diseases that share glutamatergic neuroplasticity dysfunctions. Although clinical evidence is still limited and more studies are required, the regulation of glutamate homeostasis is attracting attention as a potential crucial target for the control of brain diseases.

Ketamine may be a novel pharmacologic approach to enhance resilience and protect against stress-related disorders, but the molecular targets underlying this response remain to be fully characterized. The multifunctional protein p11 is crucial in the pathophysiology of depression and antidepressant responses. However, it is still unclear whether p11 plays a role in the pro-resilience effects induced by ketamine. Here, we demonstrated that prophylactic administration of ketamine buffers passive stress-induced maladaptive phenotypes induced by chronic stress exposure. Spatial neurotransmitter and metabolite analysis revealed that prophylactic ketamine was also effective in blunting stress-induced disturbances of tryptophan metabolism in dorsal raphe nuclei (DRN). Additionally, we demonstrated that ketamine prevented chronic restraint stress-induced p11 reduction in DRN, a highly p11-enriched region. Furthermore, we provide novel evidence indicating that p11 deficiency regulates susceptibility to stress-induced depression-related phenotypes, and these behavioral maladaptations are dependent, at least in part, on p11 function in serotonergic neurons. Spatial neurotransmitter and metabolite analysis also showed a reduction of tryptophan and dopamine metabolism in DRN of serotonergic p11-deficient mice. Viral-mediated downregulation of p11 within DRN induced a stress-susceptible phenotype. Finally, our results also unveiled that the ability of ketamine to elicit a pro-resilience response against stress-induced maladaptive phenotypes was occluded when p11 was selectively deleted in serotonergic neurons. Altogether, we showed a previously unexplored role of the DRN circuit in regulating stress susceptibility and resilience-enhancing actions of ketamine.

Behavioral stress is a recognized triggering factor for systemic diseases, including psychiatric disorders. The stress response is subjected to circadian regulation and many factors shape the susceptibility to its maladaptive consequences, including the biological sex. Accordingly, circadian dysregulation of the stress response, often occurring in a sexually dimorphic manner, is typically associated with psychiatric disorders. However, the interaction between stress, sex, circadian phases, and behavior is still largely unknown. Here, we used the chronic restraint stress (CRS) model in male and female mice to assess the impact of sex and circadian phases on the behavioral consequences of chronic stress. Animals were stressed either in the light or dark phase, and anxious-/depressive-/anhedonic-like behaviors were assessed. Associated transcriptional changes in clock genes were measured in the prefrontal cortex. A significant interaction of stress, sex, and circadian phase was found in most of the parameters evaluated, with no behavioral response to stress in males stressed in the dark phase, and an exaggerated response in females stressed in the dark phase compared to the light phase. We also found some molecular changes in corticosterone serum levels and expression of clock genes in the prefrontal cortex.