Use of the tetracycline-regulated transactivator system to study the role played by galanin in sensory neuron survival

Galanin is a small protein that is widely expressed in the pain-sensing nerves (DRG) of the body. The levels of galanin in these nerves increase by a least 100 fold after an injury or cut to the nervous system. To find out more about the galanin protein we have used the techniques of genetic engineering to generate mice in which galanin has been deleted in the pain sensing nerves. This causes a complete reversal of neuropathic pain in a number of different animal models. We have now shown that galanin is necessary for the survival of some pain sensing neurons and in its absence they die shortly after birth.

This application is a direct continuation of our previous MRC-funded studies and we will use the latest techniques in genetic engineering to separate and further study the roles played by galanin and its receptor subtypes in the pain sensing nerves during development and in the adult, with specific reference to neuropathic pain behaviour.

One of the most potent changes observed in the dorsal root ganglion (DRG) following injury, is the 120-fold increase in the levels of the neuropeptide galanin. Work undertaken during my MRC Clinician Scientist Fellowship, Career Establishment Grant and Programme Grant has demonstrated that knockout of the neuropeptide galanin or its receptor GalR2 causes the developmental loss of a subset of pain sensing neurons (nociceptors) in the early postnatal period. This neuronal loss underlies the complete absence of neuropathic pain (NP) observed in both KO mice.

We have used the tetracycline-regulated transactivator system to inducibly rescue the existing GalKO allowing us to separate and independently study the developmental survival and adult trophic roles played by galanin. We will use these novel transgenic lines to address the following aims:-

(1) Identify the time course and mechanisms by which galanin and GalR2 play a developmental survival role to a subset of nociceptors and how the neuropeptide interacts with other known neurotrophic factors.
(2) Define the phenotype of the nociceptors that are lost in the early post-natal period.
(3) Study how the presence or absence of developmental deficits modifies NP, without the confounding effects of the absence of galanin in the adult.
(4) Identify and then functionally characterise the genes whose expression is altered in the DRG of adult Gal-KO and GalR2-KO animals by the developmental loss of a subset of nociceptors.