Not just a stroke of luck

Grooming and stroke activity, within species, is a fascinating topic for animal behaviourists; helping to unravel intricate patterns of group politics and hierarchy.

However, beneath the social implication lies the complex question of how this behaviour is determined at a genetic and molecular level. A recent collaboration between California Institute of Technology, University of Louisville and University of Pittsburgh, has addressed this question with a study published in Nature (Anderson et al, 2013).

Scientifica's customer, Dr Kristofer Rau, was involved in the study that revealed a subpopulation of unmyelinated fibres that respond to "massage-like stroking of hairy skin in vivo". A previous study revealed the existence of these rare, sensory neurons that expressed the G-Protein-coupled receptor MRGPRB4; this study expanded on these findings to characterise their response to different stimuli and determine whether stimulation created a positive behavioural valence.

The study used two-photon imaging of calcium transients (within the spinal projections of these neurons), to analyse the response of MRGPRB4+ neurons, to stroking versus pinch stimuli. They confirmed that mimicked-stroking elicited response of the MRGPRB4+ neurons, whereas pinch stimulation did not. This was contrasted with the response of MRGPRD fibres (a different subpopulation of fibres) which were conversely stimulated by pinch stimuli but not by stroking.

This study was the first in vivo, application of calcium imaging to record the functional activity of neurons in response to mechanical, skin stimulation. The study also demonstrated that stimulation of the MRGPRB4+ neurons (using a pharmacological agent) evoked a behavioural preference for the location in which the stimulation occurred.

This study offers remarkable insight into the function of MRGPRB4 neurons during natural, social behaviour. It also offers a model for future studies linking molecular identity to stimulus-selective, sensory neurons.

Nature 493,669–673(31 January 2013) doi:10.1038/nature11810

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