DA receptor subtypes modified LLS of nociceptive responses induced by HFS. A. Pre: A typical case with sulpiride injection is shown. Nociceptive responses were normally evoked by mechanical stimulation delivered to the rat tail after microinjection of sulpiride (upper trace). At 30 min after HFS, a D2 receptor antagonist completely blocked LLS of nociceptive responses induced by HFS to the BLA (lower trace). B. D2 and D4 receptor antagonists suppressed the induction of LLS of nociceptive responses by HFS. Error bars represent S.E. n = 19. The control figure is same as figure 3 B, C. *p < 0.05, **p < 0.001, versus the pre-HFS control value.