Identification of Molecular Markers of Clozapine Action in Ketamine-Induced Cognitive Impairment: A GPCR Signaling PathwayFinder Study

Impaired synaptic plasticity and decreased excitability of hippocampal glutamatergic neurons mediated by BDNF downregulation contribute to cognitive dysfunction in mice induced by repeated neonatal exposure to ketamine

AIM

Repeated exposure to ketamine during the neonatal period in mice leads to cognitive impairments in adulthood. These impairments are likely caused by synaptic plasticity and excitability damage. We investigated the precise role of brain-derived neurotrophic factor (BDNF) in the cognitive impairments induced by repeated ketamine exposure during the neonatal period.

METHODS

We evaluated the cognitive function of mice using the Morris water maze test and novel object recognition test. Western blotting and immunofluorescence were used to detect the protein levels of BDNF. Western blotting, Golgi-Cox staining, transmission electron microscopy, and long-term potentiation (LTP) recordings were used to assess synaptic plasticity in the hippocampus. The excitability of neurons was evaluated using c-Fos. In the intervention experiment, pAdeno-CaMKIIα-BDNF-mNeuronGreen was injected into the hippocampal CA1 region of mice to increase the level of BDNF. The excitability of neurons was enhanced using a chemogenetic approach.

RESULTS

Our findings suggest that cognitive impairments in mice repeatedly exposed to ketamine during the neonatal period are associated with downregulated BDNF protein level, synaptic plasticity damage, and decreased excitability of glutamatergic neurons in the hippocampal CA1 region. Furthermore, the specific upregulation of BDNF in glutamatergic neurons of the hippocampal CA1 region and the enhancement of excitability can improve impaired synaptic plasticity and cognitive function in mice.

CONCLUSION

BDNF downregulation mediates synaptic plasticity and excitability damage, leading to cognitive impairments in adulthood following repeated ketamine exposure during the neonatal period.

Dopamine Dynamics and Neurobiology of Non-Response to Antipsychotics, Relevance for Treatment Resistant Schizophrenia: A Systematic Review and Critical Appraisal

Treatment resistant schizophrenia (TRS) is characterized by a lack of, or suboptimal response to, antipsychotic agents. The biological underpinnings of this clinical condition are still scarcely understood. Since all antipsychotics block dopamine D2 receptors (D2R), dopamine-related mechanisms should be considered the main candidates in the neurobiology of antipsychotic non-response, although other neurotransmitter systems play a role. The aims of this review are: (i) to recapitulate and critically appraise the relevant literature on dopamine-related mechanisms of TRS; (ii) to discuss the methodological limitations of the studies so far conducted and delineate a theoretical framework on dopamine mechanisms of TRS; and (iii) to highlight future perspectives of research and unmet needs. Dopamine-related neurobiological mechanisms of TRS may be multiple and putatively subdivided into three biological points: (1) D2R-related, including increased D2R levels; increased density of D2Rs in the high-affinity state; aberrant D2R dimer or heteromer formation; imbalance between D2R short and long variants; extrastriatal D2Rs; (2) presynaptic dopamine, including low or normal dopamine synthesis and/or release compared to responder patients; and (3) exaggerated postsynaptic D2R-mediated neurotransmission. Future points to be addressed are: (i) a more neurobiologically-oriented phenotypic categorization of TRS; (ii) implementation of neurobiological studies by directly comparing treatment resistant vs. treatment responder patients; (iii) development of a reliable animal model of non-response to antipsychotics.