All ETDs from UAB

Advisory Committee Chair

John J Hablitz

Advisory Committee Members

Asim K Bej

Farah Lubin

Anne B Theibert

Document Type

Thesis

Date of Award

2014

Degree Name by School

Master of Science (MS) College of Arts and Sciences

Abstract

Our laboratory has taken a recent interest in understanding the role Ih plays in epilepsy. Ih is an inward rectifying current which is activated at hyperpolarized membrane potentials. Our lab found that in the freeze lesion epilepsy model, Ih is reduced, EPSP summation is increased, and membrane excitability is increased. In the present study, we used whole cell patch clamp technique to examine the role of Ih in the 4-AP hyperexcitability model. We first wanted to establish the effects of 4-AP on layer 5 (L5) pyramidal neurons. Treatment of L5 pyramidal cells with 4-AP resulted in changes in the intrinsic properties of the cell, but did increase the network excitability signified by the generation of evocable epileptiform discharges. Next, we examined the effects of Ih inhibition on the intrinsic membrane excitability and network excitability in L5 pyramidal cells. Using somatic current-clamp recordings, we found that inhibition of Ih with ZD7288 resulted in increased excitability of L5 pyramidal cells. Inhibition of Ih increased the durations of evoked epileptiform discharges and increased the duration of inhibition. Voltage clamp analysis revealed that inhibition of Ih resulted in changes in the early excitatory current as well as increase in the duration of epileptiform discharges. Ih inhibition resulted in depolarizing shift in the reversal potential of the early excitatory current of the epileptiform discharge as well as a decrease in membrane conductance. This study also examined the effects enhancing Ih would have on intrinsic excitability and network activity in the 4-AP model. Once again using somatic current-clamp recordings, it was shown that enhancing Ih with lamotrigine lead to a decrease in the intrinsic excitability of L5 pyramidal cells. Enhancement of Ih caused decreases in the duration of inhibition as well as decreases in maximum amplitude and duration of epileptiform events. Voltage clamp analysis revealed decreases in the duration and maximum amplitude of the epileptiform discharges following the enhancement of Ih. Enhancement of Ih also caused a decrease in the early excitatory conductance, but to alterations in the reversal potential. Taken together, these experiments reveal that in a 4-AP induced hyperexcitable cortical network, alterations in Ih results in changes in both intrinsic and network excitably. The epileptiform discharges observed in this study were GABA mediated and influenced by Ih. Thus, the resultant Ih mediated changes in network excitability were in part due to its effects on synaptic GABAergic signaling. Overall, alterations in Ih affected both network and intrinsic excitability of L5 pyramidal cells in the 4-AP hyperexcitability model.

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