Enhanced neurotransmitter release at glutamatergic synapses on oxytocin neurones during lactation in the rat

1. The increased release of oxytocin during lactation has been shown to be dependent upon glutamatergic transmission and is associated with an increas ed synaptic innervation of the supraoptic nucleus (SON). 2. To determine whether the glutamatergic synaptic properties of oxytocin n eurones are changed during lactation, we recorded excitatory postsynaptic c urrents (EPSCs) from identified oxytocin neurones in the SON of slices take n from adult virgin and lactating rats. 3. The frequency of AMPA-mediated miniature EPSCs (mEPSCs) more than double d during lactation. In addition, the decay time constant, but not the ampli tude of the mEPSCs was significantly increased in both vasopressin and oxyt ocin neurones. 4. Paired-pulse facilitation (PPF) was significantly reduced in oxytocin ne urones during lactation, whereas no change was observed in vasopressin neur ones. Elevating Ca2+ reduced PPP in oxytocin neurones in virgin rats but di d not alter PPF in oxytocin neurones from lactating rats. 5. Collectively, our results suggest that excitatory glutamatergic transmis sion is strengthened in oxytocin neurones during lactation, probably by a c ombination of an increased number of terminals, slower decay kinetics, and an increase in the probability of release.