[show abstract][hide abstract] ABSTRACT: Prostaglandin E(2) (PGE(2)) is a key mediator of exaggerated pain sensation during inflammation. Drugs targeting the PGE(2) pathway by global inhibition of cyclooxygenases are well established in the treatment of inflammatory pain, but also cause significant unwanted effects. Enzymes downstream of the cyclooxygenases, or prostaglandin receptors are candidate targets possibly enabling therapeutic intervention with potentially fewer side effects. Among the PGE(2) receptors, the EP1 subtype has repeatedly been proposed as a promising target for treatment of inflammatory hyperalgesia. However its involvement in sensitization at specific (peripheral or central) sites has not been thoroughly investigated. Here, we have used mice deficient in the EP1 receptor (EP1(-/-)) to address this issue. EP1(-/-) mice showed normal mechanical and heat sensitivity during baseline conditions. Local subcutaneous PGE(2) injection into one hindpaw, caused thermal and mechanical sensitization in wild-type mice and EP1(-/-) mice. Thermal sensitization in EP1(-/-) mice was less than in wild-type mice while no significant difference was seen for mechanical sensitization. Injection of PGE(2) into the subarachnoid space of the lumbar spinal cord, resulted in a similar mechanical sensitization in EP1(-/-) mice and in wild-type mice, while a tendency towards reduced reaction to noxious heat stimulation was observed in EP1(-/-) mice. These results support a major contribution of EP1 receptors to peripheral heat sensitization, but only a minor role in mechanical sensitization and in spinal heat sensitization by PGE(2). After local subcutaneous zymosan A injection, EP1(-/-) mice showed indistinguishable mechanical and heat sensitization compared with wild-type mice. Taken together, these results suggest that peripheral EP1 receptors contribute significantly to inflammation induced heat pain sensitization while evidence for a contribution to central sensitization was not obtained.
[show abstract][hide abstract] ABSTRACT: The spinal cord is the first site of temporal and spatial integration of nociceptive signals in the pain pathway. Neuroplastic changes occurring at this site contribute critically to various chronic pain syndromes. Gene targeting in mice has generated important insights into these processes. However, the analysis of constitutive (global) gene-deficient mice is often hampered by confounding effects arising from supraspinal sites. Here, we describe a novel Cre mouse line that expresses the Cre recombinase under the transcriptional control of the Hoxb8 gene. Within the neural axis of these mice, Hoxb8-Cre expression is found in spinal cord neurons and glial cells, and in virtually all neurons of the dorsal root ganglia, but spares the brain apart from a few cells in the spinal trigeminal nucleus. The Hoxb8-Cre mouse line should be a valuable new tool for the in vivo analysis of peripheral and spinal gene functions in pain pathways.
[show abstract][hide abstract] ABSTRACT: Transgenic mice are highly valuable tools for biological research as they allow cell type-specific expression of functionally instrumental genes. In this protocol, the generation of bacterial artificial chromosome (BAC) transgenic constructs is described. We give an overview of different transgenic inserts, such as fluorescent proteins (alone or in combination with Cre variants), diphtheria toxin receptor, lacZ, and light-activated ion channels. The most reliable and versatile approach to express these genes is by using BACs, which allow "highjacking" of the expression pattern of a gene without characterizing its transcriptional control elements. Here, we describe the necessary cloning techniques compared with conventional transgenesis. With the provided "toolbox" of already available transgene constructs, the generation of the BAC transgenes is made easy and rapid. We provide a comprehensive outline how to insert the different transgenes into a chosen BAC by either ET cloning or recombineering. We also describe in detail the methods to identify the correct insertion and the integrity of the final BAC construct, and finally, the preparation of the BAC DNA for oocyte injection is described.
[show abstract][hide abstract] ABSTRACT: The gate-control-theory of pain attributes a pivotal role in nociceptive processing to inhibitory interneurons in the superficial
dorsal horn of the spinal cord. Loss of synaptic inhibition is a contributing factor to the generation and maintenance of
chronic pain. Different signaling pathways involved in inflammatory and neuropathic pain converge onto diminished synaptic
inhibition in the spinal dorsal horn. Accordingly, restoring inhibition through drugs that facilitate GABAergic or glycinergic
neurotransmission should reverse exaggerated pain sensitivity. Indeed, subtype-selective GABAA receptor ligands and inhibitors of glycine transporters might constitute new treatments for chronic pain.