Effects of withdrawal from an escalating dose of amphetamine on conditioned fear and dopamine response in the medial prefrontal cortex.
Neurochemical studies have shown that mesocortical dopamine projections are particularly responsive in aversive situations such as fear conditioning. The present study assessed behavioural and medial prefrontal cortex (mPFC) dopamine responses utilizing in vivo microdialysis during acquisition and expression of a conditioned fear response. In two independent experiments, rats were presented with either two or nine tone-shock pairings during formation of a conditioned fear response. In the second experiment, rats were pre-treated with repeated injections of either amphetamine or saline over a 6-day period and tested during withdrawal. Amphetamine pre-treatment as well as the conditioning procedure itself potentiated an increase in dopamine levels during formation, but not expression of a conditioned fear response. Locomotor activity induced by an amphetamine challenge (1mg/kg) was also enhanced in pre-treated amphetamine compared to saline pre-treated animals (experiment two). However, mPFC dopamine response to amphetamine challenge did not differ between treatment groups. We conclude that while the exact role of mPFC dopamine in behavioural sensitization is yet to be determined, mPFC dopamine release may underlie the increased fear response during acquisition but not expression of fear response.
Peleg-Raibstein
D
D
Laboratory of Behavioural Neurobiology, Swiss Federal Institute of Technology (ETH Zurich), Schorenstrasse 16, CH-8603 Schwerzenbach, Switzerland.
Feldon
J
J
D000661:Amphetamine / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001245:Association Learning / Q000187:drug effects / Q000502:physiology; D003214:Conditioning, Classical / Q000187:drug effects* / Q000502:physiology; D004298:Dopamine / Q000378:metabolism*; D015259:Dopamine Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005239:Fear / Q000187:drug effects / Q000502:physiology; D008297:Male; D017551:Microdialysis; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018709:Statistics, Nonparametric; D013375:Substance Withdrawal Syndrome / Q000378:metabolism*
D015259:Dopamine Agents; D000661:Amphetamine; D004298:Dopamine