Animal Models of Treatment-Resistant Depression

Animal models of treatment-resistant depression (TRD) serve as vital platforms for unravelling the neurobiological mechanisms underlying persistent depressive syndromes and for screening novel therapies for cases unresponsive to standard antidepressants. These models aim to replicate key hallmarks of TRD, including refractoriness to monoaminergic drugs, enduring behavioural deficits and dysregulation of neural circuits governing mood and motivation. Common paradigms encompass the chronic mild stress (CMS) protocol, in which rodents undergo weeks of unpredictable mild stressors; genetic strains such as the Wistar-Kyoto rat, characterised by innate resistance to antidepressant interventions; and pharmacological induction of resistance through repeated treatment challenges. Each model is appraised according to construct validity (shared aetiological or pathophysiological mechanisms), face validity (parallel behavioural or physiological outcomes such as anhedonia and behavioural despair) and predictive validity (responsiveness to treatments effective in humans). Recent advances have refined these models by incorporating imaging modalities, electrophysiology and molecular assays to align animal phenotypes more closely with clinical observations. The integration of stress-based, genetic and pharmacological approaches has deepened insights into mechanisms of persistent depression and facilitated exploration of innovative strategies—including neuromodulation, rapid-acting agents and multi-target pharmacotherapies—with the ultimate goal of overcoming therapeutic resistance.

Research from Nature Portfolio

Recent work has validated solitary housing of Wistar-Kyoto rats as an enhanced depression model exhibiting treatment-resistant characteristics. Voxel-based morphometry identified atrophy in regions homologous to those affected in human TRD, including the ventral hippocampus, caudate putamen and lateral septum. Behavioural assessments revealed sustained anhedonic responses that did not normalise after habituation, reinforcing the model’s translational fidelity and underscoring its utility for probing persistent depressive phenotypes and testing next-generation interventions.

Animal Models of Treatment-Resistant Depression publication trend

The graph below shows the total number of articles in animal models of treatment-resistant depression across all publications each year (not limited to Nature Index journals).

Technical terms

Treatment-resistant depression: failure to achieve remission after at least two adequate antidepressant trials.

Chronic mild stress: exposure to a sequence of mild, unpredictable stressors to induce depression-like states in rodents.

Wistar-Kyoto rat: inbred strain exhibiting endogenous depressive-like traits and reduced responsiveness to antidepressants.

Anhedonia: diminished capacity to experience pleasure, commonly measured by reduced sucrose or palatable fluid intake.

Predictive validity: extent to which an animal model accurately forecasts clinical efficacy of therapeutic interventions.

References

1. Evaluation of New Approaches to Depression Treatment Using an Animal Model of Pharmacoresistant Depression. International Journal of Molecular Sciences (2024).
2. Validation of Wistar-Kyoto rats kept in solitary housing as an animal model for depression using voxel-based morphometry. Scientific Reports (2024).
3. Preclinical models of treatment-resistant depression: challenges and perspectives. Pharmacological Reports (2023).
4. Ketamine and its metabolite, (2R,6R)-HNK, restore hippocampal LTP and long-term spatial memory in the Wistar-Kyoto rat model of depression. Molecular Brain (2020).