Oxytocin delivered nasally or intraperitoneally reaches the brain and plasma of normal and oxytocin knockout mice

Intranasal delivery of oxytocin (Oxt) has been identified as a potential therapeutic to target human conditions characterized by social deficits, yet the ability of this administrative route to deliver to the brain is unconfirmed. Oxt knockout (Oxt KO) and wildtype C57BL/6 J male mice received Oxt (12 mu g total amount) either by nasal or intraperitoneal administration. Oxt concentrations were monitored for 2 h after administration in circulation via a jugular vein catheter and in the brain by two intracerebral microdialysis probes. Group sizes varied from 4 to 7 mice (n = 22 total). We document for the first time that Oxt applied to the nasal mucosa after nasal administration is delivered to the extracellular fluid in the brain. After nasal application, Oxt concentrations in circulation and in the extracellular fluid of the amygdala and, to an extent, the dorsal hippocampus, rose within the first 30 min and remained elevated for the subsequent hour. These findings were confirmed in an Oxt KO mouse line, establishing that the circulating and brain Oxt elevations derive from the administered dose. Interestingly, the pharmacokinetics of Oxt were slightly biased to the brain after nasal administration and to the periphery following intraperitoneal injection. No change in vasopressin levels was detected. These findings have stimulating implications for the interpretation of various behavioral and physiological effects described in animal and human studies after nasal administration of Oxt and provide the pharmacokinetics necessary to develop this drug delivery route for therapeutic purposes.