Neuronal-glial and synaptic plasticity in the adult rat paraventricular nucleus.

Using quantitative ultrastructural analysis on cells identified by immunogold postembedding immunocytochemistry, we show that magnocellular oxytocinergic neurons in the adult rat paraventricular nucleus (PVN) undergo significant neuronal-glial and synaptic changes upon stimulation. Thus, during lactation, the surface membranes of most PVN oxytocinergic somata and dendrites were directly juxtaposed; many were also contacted synaptically by the same axonal terminal ('shared' synapses). Non-oxytocinergic profiles showed few plasmalemma juxtapositions and 'shared' synapses. These ultrastructural changes are similar to those that modify oxytocin neurons in the supraoptic nucleus under the same conditions, and indicate that the whole oxytocinergic system in the hypothalamus is capable of neuronal-glial and synaptic plasticity when stimulated to release its neurohormone.