Keele Research Repository

The entorhinal cortex serves as the interface region between allocortical input and the hippocampus, with current theories suggesting that the region is involved in memory encoding, with dopamine serving as a “motivational currency” provided to memories of higher importance to the organism’s survival. This study aims to analyse the effects of dopamine on the ability to induce and maintain activity-dependent synaptic plasticity in the lateral entorhinal cortex. Here field recordings of excitatory post-synaptic potentials within rat lateral entorhinal cortex as well as bath application of drugs, including dopamine, were used to analyse their effects following stimulation of layers I and II of the lateral entorhinal cortex. The results indicate that the application of dopamine during paired-pulse low frequency stimulation causes a block of LTD. It was also found that the metaplastic effect of multiple dopamine applications of the same concentration remains in a slice which had been previously depressed by LTD. Results of LTP experiments were inconclusive, with a failure to induce LTP with either a high frequency stimulation or theta burst stimulation protocol. However, switching to a high calcium (10mM) ACSF during HFS improved the success rate of inducing LTP to 44%, with potentiation of the response remaining until the end of the 120-minute experiment. In conclusion, the results surrounding LTD provide further evidence to the theory that dopamine acts as a modulator of synaptic plasticity in the lateral entorhinal cortex (LEC). The LTP data requires further exploration, with use of a wider range of protocols to successfully induce LTP, at which point application of dopamine could be used to examine its effects.