A thalamo-hypothalamic pathway that activates oxytocin neurons in social contexts in female rats.

Oxytocin is released from neurons in the paraventricular hypothalamic nucleus (PVN) in mothers upon suckling and during adult social interactions. However, neuronal pathways that activate oxytocin neurons in social contexts are not established yet. Neurons in the posterior intralaminar complex of the thalamus (PIL), which contain tuberoinfundibular peptide 39 (TIP39) and are activated by pup exposure in lactating mothers provide a candidate projection. Innervation of oxytocin neurons by TIP39 neurons was examined by double labeling in combination with electron microscopy and retrograde tract-tracing. Potential classical neurotransmitters in TIP39 neurons were investigated by in situ hybridization histochemistry. Neurons activated after encounter with a familiar conspecific female in familiar environment were mapped with the c-fos technique. PVN and the supraoptic nucleus oxytocin neurons were closely apposed by an average of 2.0 and 0.4 TIP39 terminals, respectively. Asymmetric (presumed excitatory) synap...