The neuropeptide substance P and its receptor, the neurokinin 1 receptor (NK(1)R) have been proposed as possible targets for new antidepressant therapies. The present study investigated the effect of the NK(1)R antagonist L-760,735 and the tricyclic antidepressant clomipramine in the chronic psychosocial stress paradigm of adult male tree shrews. Animals were subjected to a 7-day period of psychosocial stress before the onset of daily oral administration of L-760,735 (10 mg kg(-1) day(-1)) or clomipramine (50 mg kg(-1) day(-1)). The psychosocial stress continued throughout the treatment period of 28 days. Brain metabolite concentrations were determined in vivo by proton magnetic resonance spectroscopy. Cell proliferation in the dentate gyrus and hippocampal volume were measured post mortem. Stress significantly decreased in vivo concentrations of N-acetyl-aspartate (-14%), creatine and phosphocreatine (-15%) and choline-containing compounds (-15%). The proliferation rate of the granule precursor cells in the dentate gyrus was reduced (-45%), and hippocampal volume was decreased (-14%). The stress-induced changes of brain metabolites, hippocampal volume and dentate cytogenesis rate were prevented by concomitant drug administration. Elevated myo-inositol concentrations after both treatments hint to an astrocytic enhancement. These results suggest that-despite a different pharmacological profile-the NK(1)R antagonist L-760,735, a member of a novel class of antidepressant drugs, has comparable neurobiological efficacy to tricyclic antidepressants such as clomipramine.