Effect of Ih Current Blockers on Learning and Memory in Honey Bees
Rivera Rodríguez, Emmanuel José
Giray, Tugrul (Consejero)
In nature, honey bees are exposed to both aversive and appetitive stimuli, such as odors and colors when they arrive to a flower, or the shape of a spider web after they escape from it. Bees need to learn from these experiences in order to appropriately respond to its environment. With a relatively simple brain with only 960,000 neurons, and a complex learning capacity, comparable to that of vertebrate organisms, honey bees represent a great model to study the molecular mechanisms of learning and memory. Many of the molecular components of learning have been studied in honey bees, however the role of HCN channels and Ih currents has not been examined. The hyperpolarization-‐activated cyclic nucleotide gated channels (HCN), responsible for the Ih currents production, are molecular components that have been associated with learning and memory in vertebrates (Nolan et al., 2003). The present work examines the following hypothesis: If HCN channels and Ih currents play a role in honey bee learning and memory, then treatment with an Ih blocker will affect both their aversive and appetitive learning. In order to test this hypothesis we fed honey bees two Ih blockers ZD7288 and DK-‐AH269 (Cilobradine) and followed two lines of inquiry: Determine Ih blocker effect on 1) honey bee aversive learning and memory by using the electric shock avoidance (ESA) assay 2) honey bee appetitive learning and memory by using the proboscis extension response conditioning (PER) assay. By using the ESA assay, we found that feeding honey bees the Ih blocker ZD7288 does not have a significant effect on the aversive learning Acquisition Phase. Even though no significant effect of treatment with ZD7288 on ESA was found on the aversive learning Acquisition Phase, a tendency was observed, in which individuals treated with ZD7288 presented a higher ESA performance than individuals from the control group. Following this tendency, I found that treatment with the Ih blocker Cilobradine (1.0, 2.0mM) caused a statistically significant effect on the learning Acquisition Phase, enhancing the ESA performance. Treatment with ZD7288 caused a significantly detrimental effect on honey bee aversive learning Reinforcement Phase, while on the contrary, treatment with Cilobradine (2.0mM) caused an enhancing effect on aversive learning Reinforcement Phase. On the other hand, for aversive STM, ZD7288 has a significant negative effect but Cilobradine has no effect. I examined appetitive learning by using the PER assay and found that feeding honey bees the Ih blocker ZD7288 significantly enhances appetitive learning acquisition, while it does not affect appetitive short term memory. Taken together these results suggest an important role of HCN channels and Ih currents on honey bee learning modulation. Given that HCN channels and Ih currents have been associated with Dopamine modulation in various organisms, I suggest that the observed effects of treatment with the Ih blockers ZD7288 and Cilobradine on aversive and appetitive learning and memory, could be explained by changes in dopamine levels. Even though further experiments, such as pharmacological experiments using dopamine agonist and antagonists are needed in order to prove this inference.