The first reaction to a minor wound or sprain is to apply ice. Cold's analgesic effects are a profound and under appreciated phenomenon. The nerve providing the sensation we know as cold acts to inhibit the "pain pathway." This wonderful nervous pathway is called TRPM8.
This study indicates that the ion channel called "transient receptor potential melastatin 8", or TRPM8, is a primary component of cold sensation. Cultured nerve fibers devoid of this ion channel have considerably less response to the sub-ambient temperatures and cold-simulating chemicals that these nerves normally respond to fervently. Mice that have been genetically deprived of the TRPM8 channel also display a noticeable decrease in non-noxious cold sensitivity. Essentially without this component of the nerve, mice don’t notice mild cold, and actually have no particular preference to warmth. This appears to be true only for non-noxious temperatures (roughly above 12C in this case). Below that threshhold, it is thought that cold is perceived by thermal nociceptors as pain due to the extreme and potentially harmful aspects of severe cold.
The analysis of this ion channel was observed on both the cellular and behavioral perspectives in an attempt to identify the biochemical properties and characteristics of the channel and the ramifications thereof in a model organism.
Methods: Gene Deletion
Gene Deletion: The researchers deleted a significant portion of the TRPM8 gene. This was done through PCR, digestion, and ligation, effectively stopping the production of TRPM8 ion channel. PCR or polymerase chain reaction is a process which uses enzymes and primers to amplify or modify a DNA sequence. Deletion is accomplished by creating primers without the sequence intended to be deleted. Then, digestion via restriction enzymes is used to cut the the now dysfunctional gene and insert the gene into a vector. Finally the dysfunctional TRPM8 gene was inserted into the vector through ligation, which is the process that is used to join two ends of DNA. This stopped production of TRPM8.
The researchers then used homologous recombination to insert the dysfunctional TRPM8 along with a linked color coat gene into embryotic stem cells. The embryonic stem cells were injected into a blastocyst, which was injected into a female mouse, which gave birth to litter of mice. The chimera mice in the litter were mated to produce heterozygous offspring for the TRPM8 deletion. The heterozygotes were then mated and the homozygous offspring for the TRPM8 deletion were selected.Since the dysfunctional TRPM8 gene was linked to coat color, the researchers knew that the mice displaying the coat color also posessed the dysfunctional TRPM8.
Verification of Deletion: The researchers performed a Southern Blot to confirm the deletion of the TRPM8 gene. This was done by using restriction enzymes to cut out the TRPM8 gene sequence and using a probe to detect the presence of...