Hippocampal vasopressin release evoked by N-methyl D-aspartate (NMDA) microdialysis.

Hippocampus is a brain structure containing vasopressin (AVP) fibers and specific binding sites for this peptide. There is growing evidence that AVP and its metabolites participate in glutamate-mediated plasticity of the hippocampus. The aim of the present study was to evaluate the influence of NMDA on AVP release in the rabbit hippocampus. Caudate nucleus was chosen as the reference structure. The mentioned brain structures were simultaneously microdialyzed with 0.9 % NaCl solution. AVP was determined in the outflowing fluid by radioimmunoassay. The mean basal AVP content in the fluid outflowing from the hippocampus was significantly greater than that from the caudate nucleus. The addition of K(+) into the fluid perfusing the probes implanted into the hippocampus and caudate nucleus significantly increased AVP release into the extracellular fluid of both brain structures. NMDA applied into the mentioned brain structures increased AVP release only from the hippocampus but not from the caudate nucleus. Our findings indicate a role which NMDA receptors play in AVP release into the extracellular fluid of the hippocampus.