Screening of Antidepressant Drugs

Introduction & the central problem of modelling depression

• Definition — Antidepressant screening is the experimental in-vitro + in-vivo evaluation of candidate compounds for antidepressant-like activity in laboratory animals before clinical development — depression itself being a heterogeneous affective disorder attributed to an imbalance of central cholinergic and adrenergic tone.
• Monoamine hypothesis frames the target — Most classical screens are built on the biogenic-amine (monoamine) hypothesis — depression as reduced 5-HT/DA/GABA with dysregulated NE — exploiting the empirical link between clinical antidepressant efficacy and effects on monoamine systems.
• Core problem — no true disease model — There is no animal model that fully resembles human depressive illness and is selectively sensitive to effective treatment; most assays are empirical/predictive (they detect a compound 'behaving like a known antidepressant') rather than aetiological.
• Classical screens miss novel drugs — Classical methods are largely inadequate for non-monoaminergic (novel) antidepressants and were historically insensitive to SSRIs until modified — a recurring theme driving the field's methodological evolution.
• Battery, not one test — Screening relies on a battery: a rapid primary behavioural screen (FST/TST) with a concurrent locomotor control → a mechanism-based potentiation/reversal test → a chronic construct-valid model → genetic confirmation.