Quantification of hippocampal noradrenaline and zinc changes after selective cell destruction.

Deafferentation of septo-hippocampal projections results in sprouting of sympathetic noradrenergic (NA) fibers into the hippocampus. To determine whether dentate granule cells are necessary for the initiation and/or direction of this sprouting, both NA intensity and zinc density were microspectrophotometrically quantified at 10 or 30 days after selective neurotoxin lesions of either granule cells or CA3 pyramidal cells, and electrolytic lesions of medial septum. Groups with elevated zinc density at 10 days also had significantly higher NA levels at 30 days. Destruction of granule cells eliminated the rise in zinc and prevented the NA increase. The zinc increase may be related to a nerve growth factor-like protein responsible for the initiation of sympathetic sprouting.