Oxytocin (OT) is a neuropeptide that mediates a variety of complex social behaviors in animals and humans. Intranasal OT has been used as an experimental therapeutic for human conditions characterized by deficits in social functioning, especially autism spectrum disorder and schizophrenia. However, it is currently under intense debate whether intranasal delivery of OT reaches the central nervous system. In this study, four female rhesus macaques were implanted with chronic intrathecal catheters and used to investigate the pharmacokinetic profile of OT in the central nervous system and the peripheral vasculature following intravenous (IV) and intranasal (IN) administration of OT. In a randomized, crossover design, OT was given to four awake monkeys at three different doses based on body weight (0.1 IU/kg; 1 IU/kg; 5 IU/kg). A time course of concurrent cerebrospinal fluid (CSF) and plasma samples were taken following administration. We found a dose-dependent effect of IV OT treatment on plasma OT levels, which peaked at 5 min post-dose and gradually returned to baseline by 120 min. In contrast, a change in CSF OT was only observed at the highest IV dose (5 IU/kg) at 15 min post-dose and gradually returned to baseline by 120 min. After IN administration, there was no significant change in plasma OT at any of the three doses. However, at the highest dose level, we found a significant increase in CSF OT at 15-30 min post- dose. The results of this study in light of recent, similar publications highlight the importance of methodological consistency across studies. This study also establishes a non-human primate model that can provide a stable platform for carrying out serial sampling from the central nervous system and peripheral vasculature concurrently.

Here we evaluated the utility of MRI to monitor intrathecal infusions in nonhuman primates. Adeno-associated virus (AAV) spiked with gadoteridol, a gadolinium-based MRI contrast agent, enabled real-time visualization of infusions delivered either via cerebromedullary cistern, lumbar, cerebromedullary and lumbar, or intracerebroventricular infusion. The kinetics of vector clearance from the cerebrospinal fluid (CSF) were analyzed. Our results highlight the value of MRI in optimizing the delivery of infusate into CSF. In particular, MRI revealed differential patterns of infusate distribution depending on the route of delivery. Gadoteridol coverage analysis showed that cerebellomedullary cistern delivery was a reliable and effective route of injection, achieving broad infusate distribution in the brain and spinal cord, and was even greater when combined with lumbar injection. In contrast, intracerebroventricular injection resulted in strong cortical coverage but little spinal distribution. Lumbar injection alone led to the distribution of MRI contrast agent mainly in the spinal cord with little cortical coverage, but this delivery route was unreliable. Similarly, vector clearance analysis showed differences between different routes of delivery. Overall, our data support the value of monitoring CSF injections to dissect different patterns of gadoteridol distribution based on the route of intrathecal administration.