|BODY WEIGHT:||160 lb|
It does cross the bbb, just a small amount thoSo oxytocin doesn't cross the blood brain barrier, but it still acts on peripheral receptors. iirc there was a bit of a scandal around this some papers published 10-15yrs ago showing pro-social effects after it was administered intranasally without any discussion of this.
I had a chance to ask Dr. Gul Dolen (the MDMA and octopuses researcher) about this and she explained the likely mechanism behind those results. Unfortunately, I have a crap memory. I know that she confirmed that oxytocin wasn't acting centrally, but that the effects were explicable through their peripheral activity. I just don't remember exactly how to my enduring frustration.
Also interesting: you might expect some sex differentiation in the role of oxytocin in the brain. The social learning window that oxytocin opens in female mice is instead regulated by vasopressin in male mice iirc, something Dr. Dolen's lab was actually researching last year.