Journal of Neurophysiology, Vol 57, Issue 6 1813-1836, Copyright © 1987 by APS
Mechanoreceptor response to mechanical and thermal stimuli in the glans penis of the dog
R. D. Johnson and R. L. Kitchell
In the dog, we isolated 126 mechanoreceptive afferent fibers of the A-delta
myelinated fiber class from the dorsal nerve of the penis using
microdissection and extracellular electrophysiological techniques.
Receptive fields on the glans penis were stimulated with a
computer-controlled mechanostimulator and Peltier effect thermostimulator.
The great majority of units were categorized as either rapidly adapting
(RA) or slowly adapting (SA) and were located primarily proximally and
distally, respectively, on the glans. In comparison to values from other
glabrous skin regions in other species, mean displacement and force
thresholds of penile mechanoreceptors were high, whereas the mean velocity
thresholds were low. SA units, generally poor encoders of static
displacement, were distinguishable into two types based on static response
firing pattern but were not homologous to either the SA I or SA II
mechanoreceptors found in other skin regions. Fifty-five units were given
simultaneous mechanical and thermal stimulation. Very few units responded
to pure thermal stimulation or increased their discharge frequency to skin
cooling. Warm receptive-field temperatures between 35 and 43 degrees C
increased mechanical sensitivity, measured by displacement and velocity
coding functions, in almost all units tested. We conclude that canine
penile mechanoreceptors, capable of encoding a variety of skin movements
when the penis is warm, provide the spinal cord with the sensory input
necessary to drive the spinal sexual reflexes. However, many appear to be
at least physiologically different from mechanoreceptors native to other
skin areas.
