Margaret Della Vecchia 2 and Anthony S. Rauhut 1,2, Department of Psychology 1 and Neuroscience Program 2, Dickinson College, Carlisle, PA References Discussion Abstract Hypothesis Introduction Objective Methods Procedure Results This research was supported by a National Institutes of Health grant (DA019866), awarded to A. S. Rauhut, and “matching funds” provided by Dickinson College. Acclimation (Handling) 7 Days Drug Day 4 Acknowledgements Test Day 1: Conditioning Test 1 Day - Day 9 30 minute session in activity chamber s following vehicle (saline) injection for all mice Conditioning: Drug days 4 Days — Days 1, 3, 5, 7 Drug Days: Injection (IP) of vehicle (dH 2 0) or prazosin (0.5, 1.0, or 2.0 mg/kg, IP) followed 30 minutes later by an injection (SC) of vehicle (saline; Unpaired) or methamphetamine (1.0 mg/kg; Paired). Then, all mice were placed in the activity chambers for a 30-minute session. Prazosin Attenuates the Unconditioned and Conditioned Hyperactive Effects of Methamphetamine Conditioning: Non-drug days 4 Days — Days 2, 4, 6, 8 Non-drug Days: Injection (SC) of either vehicle (saline) or methamphetamine (1.0 mg/kg, SC) for paired and unpaired animals, respectively, in their home cages. Test Day 2: Methamphetamine challenge 1 Day - Day minute session in activity chamber following methamphetamine (1.0 mg/kg) injection for all mice Drug Day 1 Test Day 2: Methamphetamine Challenge 24 h The present experiment determined the ability of the α 1 -noradrenergic receptor antagonist, prazosin, to attenuate the unconditioned and conditioned hyperactive effects in male Swiss-Webster mice. After the initial acclimation period (7 days), the experiment lasted 10 days and consisted of 2 phases (Conditioning and Tests). The Conditioning Phase lasted 8 days and consisted of 4 alternating Drug and Non-drug days. During Drug Days, mice were injected (IP) with vehicle (dH 2 O) or prazosin (0.5, 1.0, or 2.0 mg/kg) followed 30 minutes later by an injection (SC) of either vehicle (saline; Unpaired mice) or methamphetamine (1.0 mg/kg; Paired mice) before entering the activity chamber for a 30-minute session. On Non-drug Days, mice remained in their home cages and received an injection (SC) of vehicle (physiological saline; Paired) or methamphetamine (1.0 mg/kg; Unpaired). The tests for conditioned hyperactivity (Test Day 1) and methamphetamine sensitization (Test Day 2) occurred 48 and 72 hours following the last drug days, respectively. On Test Days 1 and 2, all mice were injected with vehicle or methamphetamine (1.0 mg/kg), respectively. Prazosin dose-dependently attenuated with unconditioned and conditioned hyperactive effects of methamphetamine. These results suggest the α 1 receptor contributes to the development of the unconditioned (i.e., pharmacological) and conditioned hyperactive (i.e., learned) effects of methamphetamine.  The role of the mesolimbic dopamine system in mediating the unconditioned and conditioned hyperactive effects of psychostimulants has been well established (Beninger and Hahn, 1983; Mazurski and Beninger, 1991)  Recent research has suggested that the noradrenergic system, particularly the α 1 receptor system, interacts with the dopaminergic system and contributes to the unconditioned and conditioned hyperactive effects of psychostimulants (see Weinshaker and Schoeder, 2007, for a review).  Support for this view comes from a number of studies o Prazosin, an α 1 receptor antagonist, blocks the locomotor-activating effects of amphetamine in rats (Darraq et al., 1998; Drouin et al., 2002 Snoddy & Tessel, 1985). o Depletion of norepinephrine from the medial prefrontal cortex abolishes amphetamine-produced conditioned place preference in mice (Ventura et al., 2003).  Little research, however, has examined the contribution of the noradrenergic, α 1 receptor system, in mediating the unconditioned and conditioned hyperactive effects of methamphetamine in mice. The present experiment examined the ability of the α 1 receptor antagonist, prazosin, to attenuate the unconditioned and conditioned hyperactive effects of methamphetamine. Because the α 1 receptor system has been shown to be involved in mediating the unconditioned and conditioned effects of other psychostimulants (e.g., amphetamine; see Weinshaker and Schoeder, 2007, for a review), it was predicted that prazosin, a selective α 1 noradrenergic receptor antagonist (Duteil et al. 1990), should dose-dependently attenuate the unconditioned and conditioned hyperactive effects of methamphetamine.  Prazosin dose dependently attenuated the hyperactive effects of methamphetamine following acute (Day 1) and repeated (Day 4) administrations. The 1.0 mg/kg prazosin dose attenuated the hyperactive effect of methamphetamine without disrupting activity in unpaired control mice. These results are consistent with previous studies that have reported that prazosin dose dependently attenuates the hyperactive effects of amphetamine (Snoddy & Tessel, 1985; Darraq et al., 1998; Drouin et al., 2002).  On Days 1 and 4, the high prazosin dose (2.0 mg/kg) did decrease behavior in Unpaired mice, suggesting that this dose non-specifically decreased locomotor activity.  However, On Test Day 1 (Conditioning Test), paired mice pretreated with the moderate (1.0 mg/kg) and high (2.0 mg/kg) prazosin doses during conditioning did not differ from their unpaired counterparts, suggesting that these doses attenuated the conditioned hyperactive response. Moreover, the 2.0 mg/kg prazosin dose did not decrease behavior in unpaired mice on Test Day 1, suggesting that attenuated conditioned hyperactive response was not due to drug-induced disruptions in behavior.  Collectively, these results suggest that the α 1 receptor system contributes to the unconditioned and conditioned hyperactive effects of methamphetamine and further supports the role of the noradrenergic α 1 receptor system in mediating the unconditioned and conditioned effects of psychostimulants. 1.Beninger, R.J., & Hahn, B. L. (1983). Pimozide blocks establishment but not the expression of amphetamine-produced environment-specific conditioning. Science, 220: Darraq, L., Blanc, G., Glowinski, J., & Tassin, J-P. (1998). Importance of the noradrenalin- dopamine coupling in the locomotor-activating effects of d-amphetamine. Journal of Neuroscience, 18: Drouin, C., Darraq, L., Trovero, F., Blanc, G., Glowinski, J., Cotecchia, S., Tassin, J-P. (2002). Journal of Neuroscience, 22: Duteil, J., Rambert, F.A., Pessonnier, J., Hermant, J-F., Gombert, R., & Assous, E. (1990). Central α-1 adrenergic stimulation in relation to the behavior stimulating effect of modafinil; studies with experimental animals. European Journal of Pharmacology, 180: Mazurski, E. J., & Beninger, R. J. (1991). Effects of selective drugs for dopaminergic D1 and D2 receptors on conditioned locomotion in rats. Psychopharmacology, 105: Snoddy, A.M. & Tessel (1985). Prazosin: effect of psychomotor-stimulant cues and locomotor activity in mice. European Journal of Pharmacology, 116: Weinshenker, D. & Schroeder, J.P. (2007). There and back again: a tale of norepinephrine and drug addiction. Neuropsychopharmacology, 32: h Paired mice pretreated with the moderate (1.0 mg/kg) and high (2.0 mg/kg) prazosin doses showed significantly less locomotor activity compared to veh-meth paired control mice (left and middle panels). The low (0.5 mg/kg) and high (2.0 mg/kg) prazosin doses decreased locomotor activity in the unpaired mice compared to their respective veh-veh control group during the first 5 minute of the session (right panel). * = difference of 1.0 mg/kg prazosin relative to their respective vehicle control group, p < # = difference of 2.0 mg/kg prazosin relative to their respective vehicle control group, p < $ = difference of 0.5 mg/kg prazosin relative to their respective vehicle control group, p < 0.05 Paired mice pretreated with moderate (1.0 mg/kg) and high (2.0 mg/kg) prazosin showed significantly less locomotor activity compared to their veh-meth paired control mice (left and middle panels). However, these prazosin doses also produced a decrease in locomotor activity in unpaired mice relative to their veh-veh unpaired control group (left and right panels). * = difference of 1.0 mg/kg prazosin relative to respective vehicle group, p < # = difference of 2.0 mg/kg prazosin relative to respective vehicle control group, p < $ = difference of 0.5 mg/kg prazosin relative to respective vehicle control group, p < Paired mice pretreated with the moderate (1.0 mg/kg) or the high (2.0 mg/kg) prazosin doses during conditioning did not differ from their unpaired counterparts (left panel). Paired mice pretreated the high prazosin dose (2.0 mg/kg) during conditioning did not differ from methamphetamine paired control mice. # = difference of 2.0 mg/kg prazosin relative to their respective control group, p < Only paired mice that were pretreated with veh-meth during conditioning differed from their unpaired counterparts (veh-veh; left panel), suggesting that all prazosin doses attenuated the challenge with methamphetamine. Paired mice that were pretreated with the high prazosin dose (2.0 mg/kg) differed from their veh-meth paired control mice (middle panel). Group differences were not detected in unpaired mice (right panel). # = difference of 2.0 mg/kg prazosin relative to respective control group, p < Introduction Locomotor Activity Chamber Test Day 1: Conditioning Test