Influence of Oxytocin on the Startle Reflex and on Its Modulation

Oxytocin (OXT) is currently regarded as a crucial neuropeptide in the mediation of various human social behaviors, e.g. social affiliation, social recognition, and the modulation of anxiety, mood, and aggression. An impairment of social behavior, emotional regulation as well as increased stress reactions are characteristic of several psychiatric conditions, including schizophrenia, social anxiety and PTSD, in which there is also some evidence for OXT dysfunction. The startle reflex is a basic defensive reaction that can be modulated by emotional stimuli. The investigation of the startle reflex and of its modulation is a well-validated method to test stress reactions and emotional regulation. These processes are impaired in the same psychiatric diseases, in which OXT dysfunction was evidenced. Although previous animal studies showed that the dysfunction of brain OXT systems might be implicated in startle reflex and in its modulation, no study has been performed yet in human that investigated the influence of OXT administration on the startle response and on its affective modulation. A first aim of this study is to investigate the influence of OXT on stress reactivity and emotional modulation in healthy humans. A second aim is to develop a method for the investigation of anxiety disorders. Fifty male healthy participants will be tested using a randomized double-blind placebo-controlled cross-over design in two occasions; once with administration of 24 IU OXT, and once with placebo using nasal sprays while performing a computer-based experiment, in which emotional pictures and auditory startle probes are presented. We will measure the subject's subjective ratings of the pictures as well as the facial EMG activation, heart rate and electrodermal activation throughout the study. This project offers a unique opportunity to study the relationship between the OXT system and basic motivational and emotional behaviors. The investigation of these mechanisms is in turn greatly worthwhile, not only for understanding of the neurochemical and physiological processes involved in emotional regulation, but also for the comprehension of the neuroendocrine and neurophysiological mechanismsunderlying anxiety disorders. In the long term, it could open the possibilities of OXT as a psychobiological therapeutics of psychiatric disorders.