Pain arises when a stimulus activates a pain-specific nerve fibre by opening an ion channel, causing a depolarisation (positive change in membrane potential) and triggering action potentials that propagate to the central nervous system to elicit a sensation of pain. The rate of depolarisation between action potentials determines their frequency, and thus the pain intensity. An important modulator of this rate is the hyperpolarisation-activated inward current, Ih. Ih ion channels are made up from combinations of four different subunits, HCN1-4. We have shown that the fast HCN1 subunits are expressed in large neurones sensing light touch, and the slower HCN2 in small pain-sensitive neurones. We aim to find out more about which subunits are expressed in which types of sensory neurones, and how their behaviour is modulated by inflammatory mediators. Neuropathic pain, an anomalous pain state characterised by ongoing pain and hypersensitivity, is not well understood and causes a substantial reduction in quality of life for those who suffer from it. There is evidence that Ih is involved in neuropathic pain, but which subunit is important and how it enhances neuropathic pain is unknown. We will tackle these and other questions by the use of mice in which each HCN subunit has been genetically deleted. We will record electrical responses from neurones in cell culture, where their behaviour can more readily be investigated. We will study the response of wild-type and HCN knockout mice to a mild painful stimulus. These studies will advance our understanding of the role of HCN subunits in pain, and if particular subunits have crucial roles in some aspects of pain (e.g. in neuropathic pain) the work will act as a stimulus to the development of novel drugs aimed at specifically blocking those subunits.
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