Evolutionary Origins of Transventricular Transmission of Hypothalamic Hormones and Neuromodulatory Substances

Liquor-contacting cells, immunoreactive to oxytocin, vasopressin, monoamines (dopamine, serotonin) and calbindin, were found in hypothalamic neurosecretory nuclei of turtles (Testudo horsfieldi and Emys orbicularis). They are considered as sources of the nonsynaptic transventricular pathway responsible for the delivery of a broad variety of hormones and neuromodulators to different hypothalamic and extrahypothalamic brain structures. This phylogenetically ancient tract is inherent to all vertebrates, including humans, and contributes to the organization of different forms of social behavior.