Ginsenoside Rg1 Prevents Chronic Stress-Induced Depression-Like Behaviors and Neuronal Structural Plasticity in Rats.

BACKGROUND/AIMS: Ginsenoside Rg1 has been demonstrated to exhibit neuroprotective effects in various studies. This study aimed to investigate the neuronal mechanisms underlying the neuroprotective and antidepressant-like effects of ginsenoside Rg1 in a rat model of depression. METHODS: Chronic unpredictable mild stress was used to induce depression-like behaviors in rats. Transmission electron microscopy was used to observe neuronal synapses within the basolateral amygdala (BLA). The expression of microRNA (miR)-134 in the BLA was verified by real-time quantitative PCR. Finally, the synaptic plasticity-associated proteins CAMP-response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF) were detected by immunoblotting. RESULTS: Results showed that chronic stress effectively induced depression-like behaviors in rats, which were associated with significant ultrastructural changes within BLA neurons. Moreover, chronic stress decreased the expression of miR-134 in the BLA, which was accompanied by decreased phosphorylation of CREB and decreased expression of BDNF. Remarkably, chronic administration of ginsenoside Rg1 (40 mg/kg, i.p., 5 weeks) significantly ameliorated the neuronal structural abnormalities and biochemical changes induced by chronic stress, as well as preventing depression-like behaviors in these rats. CONCLUSION: Results suggested that ginsenoside Rg1 may exhibit neuroprotection and antidepressant-like effects by activating the CREB-BDNF system within the BLA in this rat model of depression. Amelioration of depression-like behaviors by ginsenoside Rg1 appears to involve modulation of the synapse-associated factor miR-134 within the BLA. Therefore, these findings demonstrate some of the neuronal mechanisms associated with depression and the therapeutic potential of ginsenoside Rg1 for use in the treatment of depression in clinical trials.

Chronic Ketamine Exposure Causes White Matter Microstructural Abnormalities in Adolescent Cynomolgus Monkeys.

Acute and repeated exposures to ketamine mimic aspects of positive, negative, and cognitive symptoms of schizophrenia in humans. Recent studies by our group and others have shown that chronicity of ketamine use may be a key element for establishing a more valid model of cognitive symptoms of schizophrenia. However, current understanding on the long-term consequences of ketamine exposure on brain circuits has remained incomplete, particularly with regard to microstructural changes of white matter tracts that underpin the neuropathology of schizophrenia. Thus, the present study aimed to expand on previous investigations by examining causal effects of repeated ketamine exposure on white matter integrity in a non-human primate model. Ketamine or saline (control) was administered intravenously for 3 months to male adolescent cynomolgus monkeys (n = 5/group). Diffusion tensor imaging (DTI) experiments were performed and tract-based spatial statistics (TBSS) was used for data analysis. Fractional anisotropy (FA) was quantified across the whole brain. Profoundly reduced FA on the right side of sagittal striatum, posterior thalamic radiation (PTR), retrolenticular limb of the internal capsule (RLIC) and superior longitudinal fasciculus (SLF), and on the left side of PTR, middle temporal gyrus and inferior frontal gyrus were observed in the ketamine group compared to controls. Diminished white matter integrity found in either fronto-thalamo-temporal or striato-thalamic connections with tracts including the SLF, PTR, and RLIC lends support to similar findings from DTI studies on schizophrenia in humans. This study suggests that chronic ketamine exposure is a useful pharmacological paradigm that might provide translational insights into the pathophysiology and treatment of schizophrenia.

Mapping the central effects of chronic ketamine administration in an adolescent primate model by functional magnetic resonance imaging (fMRI).

Ketamine, a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, is capable of triggering excessive glutamate release and subsequent cortical excitation which may induce psychosis-like behavior and cognitive anomalies. Growing evidence suggests that acute ketamine administration can provoke dose-dependent positive and negative schizophrenia-like symptoms. While the acute effects of ketamine are primarily linked to aberrant activation of the prefrontal cortex and limbic structures with elevated glutamate and dopamine levels, the long-term effects of ketamine on brain functions and neurochemical homeostasis remain incompletely understood. In recent years, reports of ketamine abuse, especially among young individuals, have surged rapidly, with profound socioeconomic and health impacts. We herein investigated the chronic effects of ketamine on brain function integrity in an animal model of adolescent cynomolgus monkeys (Macaca fascicularis) by functional magnetic resonance imaging (fMRI). Immunohistochemical study was also conducted to examine neurochemical changes in the dopaminergic and cholinergic systems in the prefrontal cortex following chronic ketamine administration. Our results suggest that repeated exposure to ketamine markedly reduced neural activities in the ventral tegmental area, substantia nigra in midbrain, posterior cingulate cortex, and visual cortex in ketamine-challenged monkeys. In contrast, hyperfunction was observed in the striatum and entorhinal cortex. In terms of neurochemical and locomotive changes, chronically ketamine-challenged animals were found to have reduced tyrosine hydroxylase (TH) but not choline acetyltransferase (ChAT) levels in the prefrontal cortex, which was accompanied by diminished total movement compared with the controls. Importantly, the mesolimbic, mesocortical and entorhinal-striatal systems were found to be functionally vulnerable to ketamine's chronic effects. Dysfunctions of these neural circuits have been implicated in several neuropsychiatric disorders including depression, schizophrenia and attention deficit disorder (ADD). Collectively, our results support the proposition that repeated ketamine exposure can be exploited as a pharmacological paradigm for studying the central effects of ketamine relevant to neuropsychiatric disorders.

HSP70 expression in the hippocampal CA3 subfield in different chronic stress models.

This study examined the heat shock protein 70 (HSP70) expression in hippocampal CA3 subfield of rats in different chronic stress models. The chronic restraint stress (CRS) and the chronic mild stress (CMS) models were used in this study. Observation of exploratory behavior in an open field test indicated stress level. The expression of HSP70 in hippocampal CA3 subfield was measured by immunohistochemical methods. The results showed that the number of quadrant crossing in both CRS and CMS groups decreased more than that of the control (P < 0.01). CRS group crossing decreased more than CMS group. Damage in the hippocampus of the CMS group occurred later and to a less extent than that of the CRS group. Compared with CMS group, the expression of HSP70 was greater in the CRS group. Moreover, increased stress duration enhanced these effects. These results show that the CRS model affects both exploratory behavior and HSP70 expression in the hippocampus more dramatically than the CMS model.