Three types of opioid receptors mu, delta, and kappa are expressed in high levels in the hippocampus and are associated with the processes of learning and memory and prevention of seizures. The mechanisms of opioid action in the hippocampus are unknown and elucidation will increase understanding of these processes. Previous studies from Dr. Chavkin's laboratory suggest that opioid receptors produce presynaptic inhibition by activation of dendrotoxin-sensitive, delayed rectifying (Kv1-type) potassium channels resulting in decreased neurotransmitter release. A series of whole cell voltage clamp recording experiments are proposed to further define the mechanisms by which mu selective agonist modulate the delayed rectifier conductance in mouse hippocampal slices. First, post-synaptic neurons that demonstrate inhibitory post-synaptic current (IPSCs) that are modulated presynaptically by mu opioids will be identified. It will then be determined if the opioid sensitive channels demonstrate pharmacology characteristic of Kv1 channels. Following this, the Kv1 subtype will be characterized using selective toxins and Kv1.1 and 1.2 null mice. Subsequently, molecular mechanisms of opioid activation of Kv1-type conductances will be determined pharmacologically to identify the potential mechanisms underlying kinases and arachidonic acid signal transduction pathways. Finally, because it is not possible to record events directly at the nerve terminal, somatic whole cell voltage clamp recordings will be performed to further characterize the channel and molecular mechanisms involved in the presynaptic ion channel modulation by opioids. Whole cell recordings using infrared microscopy techniques will enable further identification of the subpopulation of cells demonstrating opioid activation of presynaptic Kv1-type conductances. By comparing the results of synaptic and somatic IPSCs recordings, greater understanding of the mechanisms responsible for the opioid effect will emerge.
