Primary Afferent Neurons Innervating Guinea Pig Dura.
Bove, Geoffrey M., Michael A. Moskowitz.
Department of Neurosurgery, Massachusetts General Hospital and Department
of Neurology, Harvard Medical School, 149 13 th St., CNY 6403, Charlestown, MA
APStracts 3:0232N, 1996.
We made recordings from filaments of guinea pig nasociliary nerve to study
response properties of afferent axons innervating the anterior superior
sagittal sinus and surrounding dura mater. Thirty eight units in 14
experiments were analyzed. Units were initially located using mechanical
stimuli, and were then characterized by their conduction velocity and
sensitivities to mechanical, thermal, and chemical stimuli. Single unit
recordings revealed innervation of dura and superior sagital sinus by slowly
conducting axons, mostly in the unmyelinated range. The receptive fields were
1-30 mm 2 , and typically had 1-3 punctate spots of highest sensitivity. All
units tested responded to topical application of chemical agents. Ninety seven
percent of units responded to 10 -5 M capsaicin, 79% responded to a mixture of
inflammatory mediators, and 37% responded to an acidic buffer (pH 5). These
data underline the importance of chemical sensitivity in intracranial
sensation. Heat and cold stimuli evoked responses in 56% and 41% of units
tested, respectively. Though the response patterns during heating were typical
of polymodal nociceptors innervating other tissues, the thresholds were lower
than for other tissues (32.3 - 42 C ). Cooling led to a phasic discharge, with
thresholds between 25 and 32 C . Though units had different combinations of
responses to mechanical, chemical, and thermal stimuli, when grouped by their
sensitivities the groups did not differ regarding mechanical thresholds or
presence of ongoing activity. This suggests that meningeal primary afferents
are relatively homogeneous. Sensitivities of these units are in general
consistent with nociceptors, though the thermal thresholds differ. These data
provide the first detailed report of response properties of intracranial
primary afferent units, likely to be involved in transmission of nociception
and possibly mediation of intracranial pain.
Received 26 July 1996; accepted in final form 27 September 1996.
APS Manuscript Number J595-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996