Pre- Versus Postformalin Effects of Ketamine or Large-Dose Alfentanil in the Rat

Role of the vestibular nuclei in endothelin-1-induced barrel rotation in rats

The fourth or lateral ventricular injection of endothelin-1 resulted in a dose-dependent increase in the barrel rotation and produced marked induction of c-Fos-positive cells in the vestibular nuclei. The doses of the former injection were lower and had shorter mean latent periods compared with the later injection. c-Fos expression after endothelin-1 injection was prevented by the pretreatment with the endothelin ET(A) receptor antagonist, cyclo(D-alpha-aspartyl-L-propyl-D-valyl-L-leucyl-D-tryptophyl) (BQ-123), the glutamate NMDA receptor antagonist, dizocilpine maleate (MK-801), or the L-type Ca(2+) channel antagonist, verapamil, in addition to the incidence of the rotational behavior. There was a significant difference in c-Fos expression between the right and left medial vestibular nuclei, and the number of c-Fos-labeled neurons in the medial vestibular nucleus was markedly increased on the opposite side of the rotational direction. These results suggest that the elicitation of the barrel rotation may be mediated by endothelin ET(A) receptors, glutamate NMDA receptors, and L-type Ca(2+) channels. The changes in the receptor and channel systems induced by endothelin-1 injections appeared to exert crucial influences on the vestibular nuclei and then on the maintenance of equilibrium. The direction of the barrel rotation has a deep connection with the imbalance of neuronal activity in the left and right medial vestibular nuclei.

Inhibitory effect of intrathecally administered nociceptin on the expression of Fos-like immunoreactivity in the rat formalin test

Nociceptin, an opioid receptor-like 1 receptor agonist, has been reported to produce an analgesic effect in the rat formalin test. The authors examined the effect of 17 nmol of nociceptin on the expression of Fos-like immunoreactivity (Fos-LI) in the spinal dorsal horn induced by paw formalin injection and compared the effect of 17 nmol of nociceptin with that of equiantinociceptive dose (3 nmol) of morphine. Nociceptin and morphine were administered intrathecally 10 min before the formalin injection and the expression of Fos-LI was examined 2.5 h after the formalin injection. Both 17 nmol of nociceptin and 3 nmol of morphine suppressed the expression of Fos-LI in laminae I-II, but not in laminae III-V, to the same extent. These data suggest that intratheally administered nociceptin and morphine suppress the nociceptive input into the laminae I-II and produce antinociceptive effect.