This study aims to dissociate direct from indirectly mediated effects of intranasal oxytocin administration by using treatment with or without prior intranasal administration of a vasoconstrictor to reduce peripheral increases in peptide concentrations. Primary outcomes of the randomized placebo-controlled double-blind experiment are blood oxytocin concentration and oxytocin-associated responses in central and peripheral systems.

Intranasal application of the neuropeptide oxytocin has been reported to produce a number of neural, physiological and behavior effects which may be of potential therapeutic relevance, but it is unclear the extent to which they are mediated directly via the peptide entering the brain or indirectly as a result of increased peripheral concentrations. In the current placebo-controlled, double blind experiment on healthy adult male subjects the investigators will measure the effects of a single dose of intranasal oxytocin (24IU) on brain activity (using electroencephaolography - EEG) as well as on cardiac (heart-rate and heart-rate variablility) and gastric (electrogastrogram - EGG) activity and physiological arousal (skin conductance response - SCR). The pattern of functional effects observed will be compared with subjects receiving intranasal pretreatment with a vasoconstrictor prior to oxytocin in order to reduce the amount of oxytocin entering the peripheral circulation. The investigators hypothesize that prior administration of the vasoconstrictor will greatly reduce blood oxytocin concentrations following intranasal oxytocin treatment. Where neural/physiological effects are also affected, this will indicate an indirectly mediated action of intranasally administered oxytocin whereas if they are not this will indicate a directly mediated action.

Inclusion Criteria:

• Healthy subjects without past or current psychiatric or neurological disorders

Exclusion Criteria:

• history of head injury
• medical or psychiatric illness.