Oxytocin induces long-term depression on the rat dentate gyrus: possible ATPase and ectoprotein kinase mediation.

We studied the effects of the neuropeptide oxytocin (OT) on the long-term potentiation (LTP) paradigm in the dentate gyrus (DG) of urethane anesthetized rats. Intracerebroventricular injection of 1 microg of the hormone in 1 microl of physiological solution 2min before tetanization produced a significant decrease in both components of the perforant path evoked potentials (EP) in the DG. The effects appeared right after the tetanization stimuli and were more pronounced in the excitatory postsynaptic components of the EPs. The decrements lasted for the 2h of recording time. We concluded that OT induced and maintained long-term depression on the DG. In contrast, injection of OT in the absence of tetanic stimulation did not significantly affect perforant path EP in the DG. The results are discussed taking particular consideration of the inhibitory effects the OT has on (Ca(2+)+Mg(2+)) ATPase at membrane levels and the potential interference that this action may have with phosphorylation processes via an ectoprotein kinase isolated from membranes of hippocampal pyramidal neurons. Blocking of this ectoprotein kinase in vitro significantly impairs establishment and maintenance of LTP.