Developing translational animal models for symptoms of schizophrenia or bipolar mania

Animal models have long been used to explore hypotheses regarding the neurobiological substrates of and treatments for psychiatric disorders. Early attempts to develop models that mimic the entirety of the diagnostic syndromes in psychiatry have evolved into more appropriate efforts to model specific symptoms. Such an approach reflects the facts that even in patients, clinical symptoms transcend diagnostic categories, and the specific etiologies of psychiatric disorders are unknown. An animal model can only be identified adequately by specifying both the manipulation (drug, lesion, strain) used to induce abnormalities and the measure(s) used to characterize them. A wide range of pharmacological, lesion, and developmental manipulations have been combined with various measures of information processing to develop useful animal models that parallel human tests. Prepulse inhibition of startle, event-related potential (ERP) measures of auditory gating, and Cambridge neuropsychological test automated battery (CANTAB) measures of cognition are examples of measures that can be used in both rodents and humans and that are robustly altered in both psychiatric disorders and animals manipulated with appropriate drugs or lesions. The further development of cross-species models is critically important, given the new opportunities for the development and registration of specific treatments for the cognitive disorders of schizophrenia that are not ameliorated by available drugs. In moving beyond the focus on psychotic symptoms to the cognitive symptoms of schizophrenia, animal models that do not involve manipulations of dopamine D-2 receptors but that do utilize information processing measures that are correlated with cognitive disturbances are receiving increased attention. Here, selected examples of how cross-species measures of psychiatric disorders are developed and validated are discussed. Specific animal paradigms that parallel the specific domains of cognition that are altered in schizophrenia provide one focus of the review. Another focus includes efforts to develop new human models of psychiatric symptoms that are designed to parallel existing tests used in rodents.