Synapse formation and disappearance in adult rat supraoptic nucleus during different hydration states.

Activation of the adult rat supraoptic nucleus by a chronic stimulus (10 days of drinking 2% NaCl instead of tap water) brought about the appearance of newly formed specialized synapses onto the magnocellular neurosecretory cells. The increase in these synapses was reversed when the animals were allowed to rehydrate by drinking tap water. The apparent retraction and reinsertion of the thin glial processes from between the neurosecretory cell somata, which results in significant changes in soma-somatic direct membrane appositions, is most likely involved in the formation and elimination of these synapses.