Patients suffering from schizophrenia benefit from medication. Discovering the brain mechanisms whereby the medications work is most important. Action of many important drugs have been established in experimental animals. This is a difficult task for anti-schizophrenia drugs because it is difficult to establish what animals are thinking or feeling, and it is doubtful whether animals ever suffer from schizophrenia. Thus it would be very advantageous to discover a physiological response, measurable in, for example, rats, that can serve as a marker of the animal's emotional responses to situations that would normally prove anxiety-provoking. The present grant is based on the discovery, in my laboratory, that stressful stimuli cause sudden falls in blood flow to the tail in rats. My laboratory is the first in the world to measure pulsatile blood flow to the tail in conscious rats, and this is why we made our discovery. My laboratory also discovered that clozapine, a drug of major theoretical and practical importance for the treatment of schizophrenia inhibits fright-induced constriction of the tail artery. Clozapine interacts with many potential neurotransmitters in the brain. Some very complex combinations of these interactions are presumably responsible for the drug's unique psychotherapeutic action in schizophrenia. Our discovery that clozapine inhibits fright-induced constriction of the tail artery means that we will be able to investigate clozapine's mechanisms of action. Results of our findings are genuinely likely to increase our understanding of how clozapine works in schizophrenia. This information should also provide clues as to the nature of the presently mysterious brain malfunctions that result in schizophrenia.