Abstract
Mouse genetics has revolutionized the way biomedical research is conducted today. Forward and reverse genetics in the mouse have enabled us to link genes with function by analyzing spontaneously occurring mouse mutants and through manipulation of the mouse genome. In the central nervous system (CNS) the investigation of genes and their roles have proven particularly difficult due to the many vital functions controlled by the CNS. Frequently, gene over‐expression or deletions result in lethal genotypes or compensatory gene expression patterns, hampering phenotyping. To overcome these limitations, more sophisticated manipulations of the mouse genome have been developed which aim at gene alterations with high spatial and/or temporal precision. In this thesis, two projects aim at introducing such subtle manipulations into the mouse genome, which should allow addressing gene function with minimal confounding factors. The first project took advantage of RNA interference (RNAi) to knock down serine racemase. Serine racemase is an enzyme that generates D‐serine, an atypical neurotransmitter involved in modulating the gating properties of the NMDA receptor. Robust silencing of serine racemase was obtained by introducing a transgene featuring RNAi capability through lentiviral gene transfer. Furthermore, this gene silencing was made temporarily inducible and cell specific by taking advantage of the Cre‐loxP system, which allowed specific down‐regulation of serine racemase in astrocytes or forebrain neurons. The second project aims at addressing the role of spinal NMDA receptor‐dependent long‐term potentiation (LTP) of excitatory glutamatergic synapses as a possible synaptic mechanism leading to chronic pain. The goal of this project was to generate a mouse that cannot express LTP at spinal excitatory synapses and to investigate the consequences of lost spinal LTP for chronic inflammatory or neuropathic pain states. At many CNS synapses expression of LTP requires phosphorylation of GluRA which is contained in most glutamat receptors. Mutation of these phosphorylation sites abolishes LTP but does not interfere with baseline synaptic transmission. An inducible phospho‐mutated GluRA knockin construct was therefore generated and introduced into mouse ES cells. Clones that had undergone the desired homologous recombination were used to generate transgenic mice. In the last project the contribution of the prostaglandin E receptor subtype 1 (EP1) to inflammatory pain was investigated. The EP1 receptor is one of four receptors of the pro‐inflammatory prostaglandin E2 (PGE2), which is a major contributor to pain sensitization during inflammation. By binding the EP1 receptor PGE2 promotes peripheral heat sensitization. EP1 has also been suggested to play a role in mechanical pain through central mechanisms. These studies have all relied on a pharmacologic antagonist of the EP1 receptor, however, the specificity of this antagonist might not have been sufficient to exclude effects on other receptors of the EP family. In this project it was possible to show that the EP1 receptor is not involved in the previously suggested CNS‐dependent mechanical sensitization to PGE2. Rather, this project points to an involvement of EP1 only in heat sensitization during inflammation.
Johansson, L T T