behaviors have already been demonstrated. Systemic morphine inhibited both the early and late phases of the formalin-induced licking responses, and this action was naloxone-sensitive (Dubuisson & Dennis, 1977; Oluyomi, Hart, & Smith, 1992) as well. It has been shown that wide variety of brain regions including the frontal lobe, anterior cingulate cortex, insula, amygdala, hypothalamus, periaque...

BACKGROUND Recent studies have revealed that N2O exerts its antinociceptive effect by inducing opioid peptide release in the brain stem, thereby activating the descending noradrenergic inhibitory neurons, which modulate pain processing in the spinal cord. However, the precise neuronal pathways that mediate these events remain to be determined. METHODS Using immunohistochemical and behavioral ...