UC San Diego

Recently, there have been studies on the projection from the entopeduncular nucleus (EP) to the lateral habenula (LHb) and its relationship to the reward and disappointment systems. Specifically, the projection from the EP to the LHb have been found to be excitatory and behaviorally aversive in rats. However, the response to pain in the projection from the EP to the LHb has not yet been studied or identified. Here, we find that many neurons are initially excited, then inhibited in both the EP and LHb, but only the EP has a large proportion of cells that are only inhibited after the shock. We also found that the majority of inhibited EP cells had high baseline firing rates, whereas the majority of LHb neurons with high baseline firing rates were excited by tailshock. These results suggest that there at least two populations of cells in the EP that project to the LHb and are activated by shock. One population sends excitatory projections to the LHb and is excited initially, then inhibited by shock. The other population sends inhibitory projections to the LHb and is only inhibited by shock