Responses of Rat Trigeminal Ganglion Neurons to Longitudinal Whisker Stimulation

• Published in: Journal of neurophysiology 2008-10, Vol.100 (4), p.1879-1884
• Main Authors: Stuttgen, Maik C, Kullmann, Stephanie, Schwarz, Cornelius
• Format: Article
• Language: English
• Subjects: Animals; Biomechanical Phenomena; Electric Stimulation; Electrodes, Implanted; Excitatory Postsynaptic Potentials - physiology; Female; Neurons - physiology; Physical Stimulation; Rats; Rats, Sprague-Dawley; Trigeminal Ganglion - cytology; Trigeminal Ganglion - physiology; Vibrissae - innervation; Vibrissae - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.90511.2008

1 Abteilung für Kognitive Neurologie, Hertie-Institut für Klinische Hirnforschung and 2 Graduate School for Neural and Behavioural Sciences, Universität Tübingen, Tübingen, Germany Submitted 28 April 2008; accepted in final form 31 July 2008 Responses of rat trigeminal ganglion neurons to longitudinal whisker stimulation. Rats use their mobile set of whiskers to actively explore their environment. Parameters that play a role to generate movement dynamics of the whisker shaft within the follicle, thus activating primary afferents, are manifold: among them are mechanical properties of the whiskers (curvature, elasticity and taper), active movements (head, body, and whiskers), and finally, object characteristics (surface, geometry, position, and orientation). Hence the whisker system is confronted with forces along all three axes in space. Movements along the two latitudinal axes of the whisker (horizontal and vertical) have been well studied. Here we focus on movement along the whisker's longitudinal axis that has been neglected so far. We employed ramp-and-hold movements that pushed the whisker shaft toward the skin and quantified the resulting activity in trigeminal first-order afferents in anesthetized rats. Virtually all recorded neurons were highly sensitive to longitudinal movement. Neurons could be perfectly segregated into two groups according to their modulation by stimulus amplitude and velocity, respectively. This classification regimen correlated perfectly with the presence or absence of slowly adapting responses in longitudinal stimulation but agreed with classification derived from latitudinal stimulation only if the whisker was engaged in its optimal direction and set point. We conclude that longitudinal stimulation is an extremely effective means to activate the tactile pathway and thus is highly likely to play an important role in tactile coding on the ascending somatosensory pathway. In addition, compared with latitudinal stimulation, it provides a reliable and easy to use method to classify trigeminal first-order afferents. Address for reprint requests and other correspondence: C. Schwarz, Hertie Institut für Klinische Hirnforschung, Universität Tübingen, Abteilung für Kognitive Neurologie, Otfried Müller Str. 27, 72076 Tübingen, Germany (E-mail: cornelius.schwarz{at}uni-tuebingen.de )