66 



After saline substitution the rats were restebilized under the FR 

 1 sche-jule of iv nicotine infusion (32 ug/kg per infusion) and ^ rats 

 were given presession injections of saline followed 24 h later by a 

 presess'ion injection of siecamyl amine (0.75, 1.5, 3.0 irg/kg/sc) . These 

 sane 4 rats were also treated it a later time with hexsirethoniLiir (l.£ 

 and 3.0 mg/kc/sc). The doses of rrecary'anine used in this study were 

 chosen on the basis of previous findings that 1.0 - 3.0 mg/kg of meca- 

 irylair-lne can block fie behavioral effect of r.icotire (Screcter and 

 Posecrans 1972; CeNcble et al. 1982a; Spealn-an and Goldberg 1982) with- 

 out altering baseline responding. The hexeiret^oniuir dcses *ere chosen 

 on the basis that it does not readily peretrate the central nervous sys- 

 tetr tot is effective at bloct'-ng the periphe'-al effects of nicotine 

 (Mclssac 1962). The regaining four rjts were giver presession saline 

 injections followed 2^ h later by presession injections of na'oxone 

 (0.75. 1.5, 3.0 mg'kg/ip) . These coses of pa^cxore were crcsen since 

 doses be'ow l.C trg/kg are r_ receptor artaconist wi-ereas above l.C 

 Tig/kg ralovone antagonizes ether opio-c receptors (Pcirer et al . 1981; 

 Leander et al. 1982). All injections were given in descending order 

 and separated by 5 days. 



