“…Opioid type receptors or sensitivity Kream et al, 1980Greenberg and Price, 1983Fiorito, 1986Stefano and Scharrer, 1981Greenberg and Price, 1983Nunez et al, 1983Zabala et al, 1984Fiorito, 1986 Responses modified by analgesics Dyakonova, 2001 Zabala and Gomez, 1991 Dyakonova, 2001Gritsai et al, 2004Maldonado and Miralto., 1982Lozda et al, 1988Bergamo et al, 1992Dyakonova, 2001Agnisola et al, (1996 Response to noxious stimulus persists Balaban and Maksimova, 1993Walters et al, 2001Kawai et al, 2004Robertson et al, 1995 Associates neutral with noxious stimuli Gelperin, 1975Sahley et al, 1981Carew and Sahley., 1986Yamada et al, 1992Balaban., 1993Krasne and Glanzman, 1995Horridge, 1962Carew and Sahley, 1986Krasne and Glanzman, 1995Robertson et al, 1995 * Information is equivocal 2.5. Fetal and embryonic animals which might be protected 2.5.1.…”