Acupuncture-evoked responses of subnucleus reticularis dorsalis neurons
in the rat medulla.
by
Bing Z; Villanueva L; Le Bars D
Address:
INSERM U. 161, France.
Recordings were made from neurons in subnucleus reticularis dorsalis of
the rat. Two populations of neurons could be distinguished: those with
total nociceptive convergence which were driven by activating A delta-
and C-fibers from any part of the body and those with partial
nociceptive convergence which were driven by activating A delta-fibers
from any part of the body or C-fibers from some, mainly contralateral,
regions. The effects on subnucleus reticularis dorsalis neurons of
manual acupuncture, performed by a traditional Chinese acupuncturist at
the "Renzhong", "Sousanli", "Changqiang", and "Zusanli" acupoints and
at a non-acupoint next to "Zusanli", were studied. Acupuncture
stimulation for 30 s at the acupoints or the non-acupoint strongly
excited all the total nociceptive convergence neurons tested; these
neurons responded with a discharge of rapid onset which was often
followed by after-discharges lasting for approximately 30-60 s. The
majority but not all of the partial nociceptive convergence neurons
responded to 30 s of acupuncture stimulation at the acupoints or the
non-acupoint. This was especially the case when the stimulus was
applied to contralateral or midline parts of the body. The potency of
acupuncture as a means of activating subnucleus reticularis dorsalis
neurons varied significantly with the area of the body being stimulated
such that: contralateral greater than midline greater than ipsilateral
areas. The levels of induced activity were of similar magnitude to
those evoked by noxious mechanical stimuli applied under identical
experimental conditions. No differences were found between the
capacities to activate subnucleus reticularis dorsalis neurons of the
"Zusanli" point and the adjacent non-acupoint, no matter whether these
were stimulated ipsi- or contralaterally; this suggests a lack of
topographical specificity in the activation of these neurons. Since
subnucleus reticularis dorsalis neurons are activated exclusively or
preferentially by noxious inputs, it is concluded that the signals
elicited by manual acupuncture travel through pathways responsible for
the transmission of nociceptive information. Since acupuncture, a
manoeuvre which is known to elicit widespread extrasegmental
antinociceptive effects, activates subnucleus reticularis dorsalis
neurons which, anatomically, send dense projections to the dorsal horn
at all levels of the spinal cord, we would suggest that this structure
may be involved not only in signalling pain but also in modulating pain
by means of spino-reticulo-spinal feed-back mechanisms.