Membrane mechanism of progesterone actions on the rat brain
P exerts modulatory effects in a variety of physiological functions in discrete brain areas of mammals. It is generally held that actions of stroids in the CNS are mediated via genomic mechanisms. However, there are at least three lines of evidence indicating that a nongenomic mechanism of P's action is also involved. First, P exerts effects on tissue preparations without genomic apparatus. Second, P's effects are insensitive to protein biosynthesis inhibitors. Finally, responses of P's actions on the CNS are more rapid than most documented genomic responses of steroids. There are several advantages of using the P-BSA complex instead of P itself to study the nongenomic action mechanism of P. First, P-BSA is less likely to diffuse freely through the plasma membrane into cytoplasm due to its large size and hydrophilic properties compared to P. Second, the required functional structure of P can be examined by using P-BSA complexes which have BSA conjugated at different positions of the P moiety. Third, radioactive iodide can be introduced in the BSA molecule of the P-BSA complex which can then serve as a probe for membrane binding studies. This thesis research focused in the use of P-BSA instead of free P for studying the membrane mechanism of P's actions in the rat brain. The first part of this thesis demonstrates that BSA conjugated at the position 3 of the P molecule (P-3-BSA) has the same biological activity as P in stimulating LHRH release from hypothalami of female rats in vitro. The second part of this thesis describes a radioligand binding assay for P-BSA which can be used to examine the interaction between P-BSA and its binding sites on plasma membrane of brain cells. The third part of this thesis characterizes further the interaction between P-3-BSA and its binding molecules in an attempt to gain more insights into the membrane mechanism of P action. Finally, the fourth part of this thesis tests the hypothesis that the possible membrane mechanism of P action in the brain is mediated by voltage sensitive calcium channels.
Biology, Neuroscience, Biology, Animal Physiology
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign