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The cellular basis of magnetic sensation

Reference	BB/C006208/1
Principal Investigator / Supervisor	Professor Peter Anthony McNaughton
Co-Investigators / Co-Supervisors
Institution	University of Cambridge
Department	Pharmacology
Funding type	Research
Value (£)	241,477
Status	Completed
Type	Research Grant
Start date	16/01/2005
End date	15/01/2008
Duration	36 months

Abstract

It is now established beyond doubt that many species, and most particularly those which need to navigate over long distances, are able to detect the earth¿s magnetic field. Two components are of interest in establishing a magnetic map the direction of the magnetic field vector (ie. both its compass direction and its declination, which gives clues to latitude) and its intensity, which varies slowly with latitude and more rapidly around magnetic anomalies, or landmarks. What are the neural detectors (the magetoreceptors) which undertake this task? They must contain a sensitive detector of magnetic fields, for which a strong candidate is the highly magnetic substance magnetite (Fe304). Magnetite has been identified in a number of species, from bacteria to birds and fish. Recently magnetite-containing receptors have been identified in birds and fish, and electrophysiological recording show them to respond to small magnetic field changes, with a sensitivity of the order required to detect small changes in the earth¿s magnetic field. However, there has been no work to date on the biophysics of the transduction process in isolated magnetoreceptors, and it is this gap that the proposed work aims to fill. Much of the pioneering work on magnetoreceptors has been carried out by the group of Professor Michael Walker in Auckland, New Zealand, with whom we propose to collaborate. Walker has identified magnetoreceptor cells in the olfactory epithelium of rainbow trout. These cells contain chains of magnetite, have a distinctive morphology, and can be isolated intact. Recordings from the afferent nerve projecting to these receptors show sensitivity to changes intensity, but interestingly not to changes in direction, of the applied magnetic field. The first step will be to establish a method for isolating and identifying magnetoreceptors. Isolating cells from the olfactory epithelium will, we anticipate, be relatively straightforward, but magnetoreceptor cells appear to be rare. Wewill investigate a number of methods for identifying them, including using reflectance mode confocal microscopy to visualise magnetite, tagging them with magnetic beads, looking for changes in intracellular calcium in response to magnetic field changes, and marking them with the dye FM1-43, which permeates through open transducer channels. When magnetoreceptors can be reliably identified we will use both calcium imaging and patch-clamp electrophysiological recordings to establish a number of fundamental features of their response to magnetic fields. How sensitive are they, and do they respond preferentially to changes in direction or magnitude of the magnetic field? Are there two distinct populations of receptors detecting changes in direction and magnitude of the field? What are the characteristics of the ion channel activated by magnetic field changes? What are the temporal characteristics of the response, how quickly do the cells respond, and do they adapt to maintained stimulation? Finally, we will investigate the electrical properties of identified magnetoreceptors. Do they express the ion currents characteristic of neurons? Is calcium released from internal stores in response to magnetic stimulation? Are there any relevant physiological stimuli (eg. odours or light) which modulate the response to magnetic fields?

Summary

unavailable

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	X – not assigned to a current Research Topic
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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