Journal of Neurophysiology, Vol 38, Issue 3 601-612, Copyright © 1975 by APS
Afferent new fiber activity responding to temperature changes of scrotal skin of the rat
F-K. Pierau, P. Torrey and D. O. Carpenter
The discharge patterns of single afferent fibers from rat pudendal nerve
were studied as a function in temperature of the scrotal skin, an area
known to function in temperature regulation. In a number of respects the
population of temperature-sensitive afferents here differ from most
previously described; 75% of temperature-sensitive afferents were also
sensitive to mechanical stimulation. Of the 25% nonmechanosensitive units,
half showed dynamic and static responses to cooling, while most of the
remaining fibers gave only static discharges to warming. The most frequent
thermal reaction of the mechanosensitive units was a dynamic-static cold
response or a pure static warm response. However, fibers were also present
with only dynamic or only static cold responses. Of the bimodal units, 20%
had a dynamic cold response, but showed a minimal static discharge at
intermediate temperatures (about 35 degrees C) and an increased discharge
on both warming and cooling from that temperature. One unit had static and
dynamic warm responses. Whereas a bursting discharge in the cold has
previously been considered to be a distinguishing characteristic of
specific cold receptors, in the pudendal afferents a bursting discharge on
cooling or at low temperatures is common both in mechanosensitive and
specific cold fibers. This observation and the identical discharge patterns
and mechanisms underlying the thermosensitivity argue for the view that the
mechanosensitive afferents participate in thermal sensation and/or
regulation along with the specific temperature receptors. Hellon and Misra
(7) have concluded that there is processing of thermal information from the
scrotal skin at the level of the first synapse in the cord. However, in
this study, we have found peripheral afferents which have most of the
discharge properties that led Hellon and Misra to conclude that processing
had occurred. The unusual characteristics of thermosensitive afferents of
the pudendal nerve suggest that there is probably organ specificity of
neuronal discharge properties.
