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A multitude of factors, that either singly, interactively, or sequentially influence the gene-environment interplay in affective and dementia states, include several phases of neurodevelopmental liability in both humans and laboratory animals. Genetic vulnerability for both affective disorders and dementia describes a scenario distinguished by progressive need for concern, particularly in view of the interplay between these areas of ill-health. The contribution of emotional and cognitive expression to personal outcomes, e.g., as a function of affective personality type, a state-dependent analysis of personality characteristics, appears to pervade both the individual's experience of social and physical environments and the performance of cognitive tasks. The role of the endocannabinoids in mental health may offer insights for the psychopharmacology of both cognition and affect. Maladaptive emotional reactions and a defective cognitive ability will contribution to unsatisfactory/maladaptive coping strategies, in turn, leading to further complications of an affective and dysfunctional nature, eventually with a clinical psychopathological outcome. These considerations impinge upon critical issues concerning predisposition and vulnerability. Classical eye-blink conditioning provides a highly established procedure for assessment of defective physiology in models of Alzheimer's dementia. In order to develop a consideration of the array of situations presenting the variation of outcome due to type of affective personality, the role of fear and anxiety and stress in affective states influencing cognition are examined and the critical role of brain circuits mediating emotions influencing cognitive outcomes is discussed.

Genetic studies have sought to identify subtypes or endophenotypes of schizophrenia in an effort to improve the reliability of findings. A number of chromosomal regions or genes have now been shown to have had replicated linkage to schizophrenia susceptibility. Molecules involved in neurodevelopment or neurotransmitter function are coded by many of the genes that have been implicated in schizophrenia. Studies of neurotransmitter function have identified, among others, a possible role for GABA, glutamate and dopamine in animal models of schizophrenia. GABA neurons that co-express the calcium binding protein parvalbumin have been implicated as have glutamatergic metabotropic receptors and dopamine D3 receptors. Stress influences glutamate and dopamine providing another environmental factor that may interact with the influence of genes on neurotransmitter function. Neurotransmitter interactions include influences on signaling molecules and these too have been implicated in forms of learning thought to be affected in schizophrenia. Results continue to unravel the interplay of genes and environment in the etiology of schizophrenia and other psychotic disorders.

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