Preferential increase of extracellular dopamine in the rat nucleus accumbens shell as compared to that in the core during acquisition and maintenance of intravenous nicotine self-administration.
BACKGROUND
It has been reported that passive administration of nicotine increases preferentially extracellular dopamine (DA) release in the shell as compared to that in the core of the nucleus accumbens (NAc). To date, no information is available if this also applies to active, response-contingent nicotine administration.


OBJECTIVE
This study was aimed to monitor the changes of extracellular DA in the NAc shell and core during active intravenous nicotine self-administration (SA).


METHODS
Rats were bilaterally implanted with chronic cannulae and were trained to self-administer nicotine (0.03 mg/kg, i.v.) in single daily 1-h session for 6 weeks, with an initial fixed ratio (FR) 1 schedule increased to FR 2. Dialysate DA from the NAc shell and core was monitored before and for 90 min after the start of SA.


RESULTS
Significant increases of active nose-pokes over inactive ones were found starting from the 16th SA session. No differences were found in basal extracellular DA in the NAc subdivisions. Data analysis showed (1) significant increases over basal of dialysate DA in the NAc subdivisions during nicotine SA, starting from the first week in the shell and from the second week in the core, (2) preferential increase of extracellular DA during nicotine SA in the shell (24-43%) compared to that in the core (10-23%) and (3) no change in dialysate DA in NAc subdivisions during extinction.


CONCLUSIONS
Response-contingent nicotine SA preferentially increases the DA output in the NAc shell as compared to that in the core, independently from the duration of the nicotine exposure. Increase in NAc DA is strictly related to nicotine action since is not observed during extinction in spite of active responding.
Lecca
Daniele
D
Department of Toxicology, University of Cagliari, Via Ospedale 72, 09124 Cagliari, Italy.
Cacciapaglia
Fabio
F
Valentini
Valentina
V
Gronli
Janne
J
Spiga
Saturnino
S
Di Chiara
Gaetano
G
D000818:Animals; D001931:Brain Mapping; D004195:Disease Models, Animal; D004298:Dopamine / Q000378:metabolism*; D005108:Extinction, Psychological / Q000502:physiology; D045604:Extracellular Fluid / Q000187:drug effects* / Q000378:metabolism; D007262:Infusions, Intravenous; D008297:Male; D009538:Nicotine / Q000008:administration & dosage*; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D012646:Self Administration; D014029:Tobacco Use Disorder / Q000503:physiopathology*
D009538:Nicotine; D004298:Dopamine