Involvement of supraspinal and spinal histamine receptors in immobilization stress-induced antinociception in the mouse

We have previously reported that supraspinally and spinally located histami ne receptors are involved in modulating opioids-induced antinociception. Im mobilization stress produces an antinociception and opioid receptors are in volved in immobilization stress induced antinociception. The present study was then designed to determine if supraspinal or spinal histamine receptors were involved in the modulation of immobilization stress-induced antinocic eption. The antinociception measurement was assessed by the tail-flick test . Various doses of cyproheptadine (H-1 receptor antagonist] or ranitidine ( H-2 receptor antagonist) injected intracerebroventricularly (i.c.v.) or int rathecally (i.t.) alone did not show any antinociceptive effect. The i.c.v. pretreatment with cyproheptadine (1 to 20 mu g), but not ranitidine (1 to 20 mu g), dose dependently attenuated the immobilization stress-induced inh ibition of the tail-flick response. On the other hand, i.t. pretreatment wi th ranitidine (1 to 20 mu g), but not cyproheptadine (1 to 20 mu g), dose d ependently attenuated the immobilization stress-induced inhibition of the t ail-flick. Our results suggest that, at the supraspinal level, H-1-receptor s may be involved in modulating the immobilization stress-induced antinocic eption, while at the spinal cord level, H-2-receptors appear to be involved in modulating the immobilization stress-induced antinociception.