Long-lasting potentiation produced by a phorbol ester in the hippocampus of the anaesthetized rat is not associated with a persistent enhanced release of excitatory amino acids.

The relationship between the long-lasting enhancement of synaptic transmission produced by a phorbol ester and the release of endogenous excitatory amino acids has been investigated in the CA1 hippocampal region of the anaesthetized rat. Using the push-pull technique, the concentration of glutamate and aspartate was assayed in the perfusate by high-pressure liquid chromatography. Application of phorbol 12-13 diacetate produced a long lasting enhancement of the field excitatory postsynaptic potential (EPSP) (over 2 h). This was associated with a brief (10 min) significant increase in the release of glutamate and aspartate. However, subsequently the levels of the amino acids in the perfusate were not different from the pre-drug (control) levels although the field EPSP was still enhanced. It is concluded that the long-lasting enhancement produced by phorbol ester is not due to a persistent increase in the release of excitatory amino acids.