1 The localization of brain sites where bradykinin (BK) induces its antinoc
iceptive effect in rats, was studied using as index the threshold for the j
aw-opening reflex elicited by the dental pulp electrical stimulation test (
DPEST).
2 The microinjection of BK into the lateral or fourth cerebral ventricles i
nduced an antinociceptive effect, with Index of Antinociception (IA) of 0.5
1+/-0.03 and 0.68+/-0.05, respectively. However, microinjections of the pep
tide into the third ventricle induced a less marked antinociception (IA = 0
.28 +/- 0.08).
3 The brain sites where the microinjection of BK caused an antinociceptive
effect were: locus coeruleus, principal nucleus, oral part of the spinal se
nsorial trigeminal nucleus, and the sensory root of the trigeminal nerve.
4 The antinociceptive effect was more intense when BK (4-16 nmol) was injec
ted into the locus coeruleus. Microinjection of BK (4 nmol) into the fourth
ventricle, but not into the locus coeruleus, induced an increase in blood
pressure. The microinjection of the peptide into the nucleus tractus solita
rius, a site that is also involved in the presser effect of BK, did not ind
uce an antinociceptive effect. These results indicate that the antinocicept
ive effect of BK is not related to blood pressure changes.
5 The microinjection of BK into some of the sites involved in the mechanism
s of analgaesia, including the periaquenductal gray matter (dorsal, lateral
and ventrolateral) and the dorsal raphe nucleus did not induce an antinoci
ceptive effect.
6 The results suggest that the most likely brain sites involved in the anti
nociceptive effect of BK are the locus coeruleus and the principal sensory
trigeminal nucleus. The present results did not exclude the involvement of
other brain sites surrounding the lateral and the third ventricles.