Ketamine For Post-Traumatic Stress Disorders And Its Possible Therapeutic Mechanism

Post-traumatic stress disorder (PTSD) is described as a debilitating psychiatric condition that can follow exposure to life‑threatening events. Epidemiological estimates reported in the paper place lifetime PTSD at about 8% in the general population, with markedly higher rates following severe trauma (up to 23% in combat veterans, 50% in rape victims and 80% in Holocaust survivors). Current first‑line pharmacotherapies are selective serotonin reuptake inhibitors (SSRIs), but these have a slow onset, limited remission rates (cited as around 30%) and tolerability problems that limit adherence, leaving many patients without adequate benefit from existing drug or psychological treatments. Asim and colleagues set out to review preclinical and clinical evidence on ketamine as a potential treatment for PTSD and to synthesise hypotheses about its molecular and circuit mechanisms. The review aims to bring together animal and human findings on efficacy, dose‑ and timing‑dependent effects, implicated glutamatergic and neurotrophic signalling pathways (including NMDA, AMPA, BDNF and mTOR), and other candidate mediators such as metabotropic glutamate receptors and cholecystokinin, with a view to identifying gaps and directions for future research.

The authors first outline animal models relevant to PTSD, emphasising fear conditioning, fear generalisation, extinction and reconsolidation. Fear generalisation (spread of a conditioned fear response to neutral cues) and impaired extinction are highlighted as core features modelled in rodents. Neuroanatomically, chronic stress and trauma‑related paradigms produce reduced synaptic connectivity in the prefrontal cortex (PFC) and hippocampus and increased connectivity in the basolateral amygdala (BLA) and nucleus accumbens (NAc). Alterations in brain‑derived neurotrophic factor (BDNF) expression and polymorphisms (Val66Met) are discussed as modifiers of amygdala and prefrontal responses during conditioning and extinction. The glutamatergic system, and NMDA receptors in particular, are framed as central to synaptic plasticity underlying fear learning and extinction; prior trials of the NMDA partial agonist D‑cycloserine produced mixed results for augmenting extinction. Ketamine is presented as a rapid‑acting intervention with accumulating preclinical and clinical evidence for effects on PTSD symptoms. Mechanistically, ketamine is an NMDA receptor antagonist that, at sub‑anesthetic doses, has been shown to stimulate neurogenesis, cell proliferation and synaptogenesis in limbic circuits implicated in mood and fear. Clinical findings summarised include a recent randomised controlled trial reporting symptom reduction after repeated intravenous ketamine infusions at 0.5 mg/kg in chronic PTSD, and double‑blind crossover studies in which a single sub‑anesthetic IV dose produced rapid reductions in core PTSD and comorbid depressive symptoms relative to midazolam or placebo. The review also notes mixed peri‑trauma findings: an early report suggested lower PTSD incidence among combat patients who received ketamine during surgery, but a later study failed to replicate that benefit, and an observational study of 50 injured patients linked ketamine given within 3 days of admission to an increased risk of acute stress disorder and PTSD. Preclinical data indicate a dose‑dependent and timing‑dependent profile. Examples reported include prophylactic ketamine at 30 mg/kg attenuating depressive‑like behaviour in mice whereas 10 mg/kg or 90 mg/kg did not; 15–30 mg/kg administered 22 hours after conditioning suppressed fear generalisation while 7.5 mg/kg did not; 10 mg/kg produced antidepressant‑like effects when given 1 hour before forced swim test in some studies; and chronic daily exposure (20–30 mg/kg for 28 days) reduced hippocampal expression of NMDAR and AMPAR subunits and decreased dendritic spine density with associated memory impairment. Behavioural side effects such as hyperlocomotion, psychotomimetic effects and long‑lasting social avoidance are noted as dose dependent, and some reports associated anaesthetic or sedative ketamine doses with worsened PTSD‑like outcomes. At the molecular and circuit level, the review focuses on several proposed mechanisms. Ketamine’s blockade of NMDA receptors, especially on GABAergic interneurons, is described as producing cortical disinhibition and a glutamate surge that leads to downstream activation of AMPA receptors, increased BDNF signalling and mechanistic target of rapamycin (mTOR) pathway engagement, with consequent upregulation of synaptic signalling proteins and rapid synaptogenesis in PFC. Evidence linking GluN2B subunits to fear consolidation and to ketamine’s effect on fear generalisation is discussed. The lateral habenula (LHb) is highlighted as another target: ketamine blocks NMDAR‑dependent burst firing in LHb slices and produces acute antidepressant effects in vivo, but whether LHb blockade underlies long‑lasting benefit is unresolved. The authors also review roles for metabotropic glutamate receptors (mGluRs) and cholecystokinin (CCK). Ketamine interactions with mGluR2 and mGlu5 (the latter via Homer1 induction) are described, though the net functional consequences remain inconsistent across studies and may depend on pre‑ versus postsynaptic localisation. CCK is presented as an abundant neuropeptide implicated in LTP and associative memory; CCK‑related signalling has been linked to panic and PTSD phenotypes, genetic variability (rs1799923) and trauma‑related flashbacks. Preclinical work cited by the authors suggests that NMDAR activation triggers CCK release that contributes to LTP, and that clinically relevant ketamine doses reduce LTP in a dose‑dependent manner without altering paired‑pulse facilitation, offering a potential pathway by which ketamine might disrupt trauma memory reconsolidation or associative strengthening.

Asim and colleagues conclude that ketamine shows promise as a novel treatment approach for PTSD but that critical uncertainties remain concerning mechanism, optimal dosing, timing relative to trauma and potential adverse effects. They emphasise that the literature contains inconsistent findings, which the authors attribute to heterogeneity in experimental approaches, animal models, behavioural assays and translational relevance. To address these gaps, the review calls for systematic, dose‑ and time‑dependent investigations of ketamine across defined memory stages (acquisition, consolidation, retention and particularly reconsolidation) and across models with varying translational validity. Specific priorities highlighted include clarifying the relationship between NMDAR blockade, CCK release and LTP formation, defining the long‑term consequences of peri‑trauma versus delayed administration, and delineating mechanistic pathways (GluN2B/GluN2D, BDNF, mTOR, mGluR) that could be targeted to maximise therapeutic benefit while limiting harms. The authors caution that ketamine administered near the time of trauma, or at anaesthetic doses, may in some contexts promote rather than prevent PTSD‑like outcomes, underscoring the need for careful dose‑ and timing‑specific research to inform preventive and therapeutic strategies.