Cajanine Reduces Anxiety and Fear Extinction Deficits in Female Mice

Addressing the Neuroinflammatory Burden of Post-Traumatic Stress

Clinicians managing post-traumatic stress disorder face significant challenges due to the limited efficacy of current pharmacological interventions and the complex, heterogeneous nature of the condition [1]. Emerging evidence suggests that chronic neuroinflammation and dysregulated ion homeostasis play critical roles in the progression of neuropsychiatric disorders and cellular apoptosis (programmed cell death) [2]. While the physiological underpinnings of stress-related pathology are increasingly understood, there remains a pressing need for therapies that can specifically modulate the inflammatory cascade within the central nervous system [1]. Furthermore, the distinct biological responses to trauma observed between sexes suggest that a one-size-fits-all approach to treatment may be insufficient [1]. A new study now offers fresh insights into a potential biochemical target that may address these persistent clinical gaps.

Modeling PTSD Through Multi-Modal Stress Exposure

Because post-traumatic stress disorder currently lacks effective treatment strategies, researchers are increasingly focusing on compounds that target the underlying biological drivers of the condition, such as chronic neuroinflammation. Cajanine, a natural compound, has previously demonstrated the ability to ameliorate neuroinflammation-related diseases through various neuroprotective pathways, suggesting it may have therapeutic utility in the context of trauma-induced brain dysfunction. To evaluate this potential, the study utilized a single prolonged stress (SPS) model, a validated laboratory method designed to mimic the complex psychological and physiological triggers of post-traumatic stress disorder. This model subjects mice to a sequence of psychological, physiological, and chemical stressors to replicate the persistent behavioral and biochemical alterations seen in clinical populations, providing a more robust analog for human trauma than single-stressor protocols.

The experimental protocol involved the administration of cajanine to the mice via oral gavage (a method of direct gastric delivery using a feeding tube), ensuring precise systemic dosing. The researchers tested two specific dosages, 20 mg/kg and 60 mg/kg, to determine if the compound exerted a dose-dependent effect on the neuroinflammatory markers and behavioral deficits induced by the single prolonged stress protocol. By comparing these dosages, the study sought to identify the minimum effective concentration required to modulate the estrogen receptor beta (ERβ) and nuclear factor kappa B (NF-κB) pathway, a signaling cascade that serves as a primary regulator of the inflammatory response. This methodological approach allows for a rigorous assessment of how specific pharmacological interventions might translate to the management of stress-related neuroinflammation in a clinical setting, particularly in brain regions such as the hippocampus, frontal cortex, and amygdala.

Quantifying Behavioral and Molecular Stress Markers

To evaluate the functional impact of the single prolonged stress model, the researchers employed a comprehensive battery of behavioral assessments designed to quantify anxiety and cognitive flexibility. These included the marble-burying test (MBT), which serves as a measure of repetitive, anxiety-like behavior; the elevated plus maze test (EPMT), a standard clinical analog for assessing avoidance and anxiety levels; and the fear memory extinction test (FMET), which evaluates the ability of a subject to unlearn a fear response. The study found that the induction of single prolonged stress successfully produced anxiety-like behaviors and fear memory extinction deficits in both male and female mice. These behavioral phenotypes are clinically relevant because they mirror the core symptoms of post-traumatic stress disorder, particularly the persistent inability to suppress fear responses even when a threat is no longer present, a hallmark of clinical treatment resistance.

Following behavioral testing, the researchers conducted a detailed molecular analysis of brain regions central to emotional regulation and memory, specifically the hippocampus, frontal cortex, and amygdala. Using enzyme-linked immunosorbent assay (ELISA), a technique that uses antibodies to detect and measure specific proteins, and other biochemical assays, they quantified the expressions of estrogen receptors and various inflammatory factors. The results indicated that single prolonged stress triggered a significant inflammatory response across both sexes. Specifically, the researchers observed increased expression of nuclear factor kappa B (NF-κB), a protein complex that controls cytokine production, along with elevated levels of pro-inflammatory cytokines including interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in the hippocampus, frontal cortex, and amygdala of both male and female mice. These molecular changes suggest that the observed behavioral deficits are closely linked to a heightened neuroinflammatory state within the limbic system and cortical structures, providing a clear biological target for intervention.

Sex-Specific Modulation of the Estrogen Receptor Beta Pathway

The study identified a distinct biological divergence in how male and female mice responded to the single prolonged stress model at the molecular level. While both sexes exhibited neuroinflammation, the researchers found that single prolonged stress triggered a reduction in estrogen receptor beta (ERβ) expression specifically in the hippocampus, frontal cortex, and amygdala of female mice. This finding is clinically significant as it suggests a sex-specific vulnerability in the hormonal regulation of brain regions responsible for memory and emotional processing. Estrogen receptor beta is a nuclear receptor that mediates the effects of estrogen in the central nervous system, often exerting protective effects against stress and inflammation. The absence of this receptor reduction in male mice highlights a potential mechanism for the sex-based differences often observed in the clinical presentation and prevalence of post-traumatic stress disorder.

Treatment with cajanine demonstrated a clear dose-dependent and sex-specific efficacy. The researchers observed that cajanine at a dose of 60 mg/kg alleviated behavioral abnormalities in female single prolonged stress mice, including the anxiety-like behaviors and fear memory deficits previously identified. This therapeutic effect was accompanied by significant molecular changes; cajanine at 60 mg/kg normalized the overexpression of neuroinflammatory factors in the hippocampus, frontal cortex, and amygdala of female mice. Furthermore, the compound normalized the reduced ERβ levels in these same brain regions. Notably, these therapeutic effects of cajanine were observed only in female single prolonged stress mice, with no comparable benefit seen in the male cohorts. This suggests that the compound's mechanism of action is intrinsically linked to female-specific hormonal pathways rather than a generalized anti-inflammatory effect, highlighting the importance of sex-stratified research in neuropsychiatry.

To confirm the necessity of the estrogen receptor in this process, the researchers utilized an antagonist (a substance that binds to a receptor and blocks its biological response) to inhibit the receptor's activity. They found that the coadministration of cajanine with an ERβ antagonist reversed the beneficial effects of the compound, effectively negating the improvements in both behavior and inflammatory markers. This evidence confirms that cajanine alleviates single prolonged stress-induced behavioral deficits by exerting anti-neuroinflammation effects via the ERβ/NF-κB pathway in the hippocampus, cerebral cortex, and amygdala. By modulating the nuclear factor kappa B (NF-κB) pathway through the activation of estrogen receptor beta, cajanine addresses the underlying neuroinflammatory drivers of the disorder. For clinicians, these findings point toward the potential for targeted therapies that leverage specific hormonal pathways to treat neuroinflammatory conditions in female patients, potentially offering a more precise alternative to current broad-spectrum treatments.

References

1. Jiang L, Zhang Y, Yan Q, Song Y. Cajanine alleviates anxiety and fear extinction deficits in female mice exposed to single prolonged stress via the ERβ/NF-κB pathway.. Brain research. 2026. doi:10.1016/j.brainres.2026.150331

2. Bachmann M, Li W, Edwards MJ, et al. Voltage-Gated Potassium Channels as Regulators of Cell Death. Frontiers in Cell and Developmental Biology. 2020. doi:10.3389/fcell.2020.611853