NEUROBIOLOGY OF LEARNING AND MEMORY 68, 51–59 (1997) ARTICLE NO. NL973776 Posttraining Intraamygdala Infusions of Oxotremorine and Propranolol Modulate Storage of Memory for Reductions in Reward Magnitude Juan A. Salinas,* Ines B. Introini-Collison,† Carla Dalmaz,‡ and James L. McGaugh† , § ,1,2 *Department of Psychology, University of Virginia, 102 Gilmer Hall, Charlottesville, Virginia 22903; †Center for the Neurobiology of Learning and Memory and §Department of Psychobiology, University of California, Irvine, Irvine, California 92717-3800; and ‡Centro de Memoria, Departamento de Bioquimica, Instituto de Biociencias, Universidade Federal do Rio Grande do Sul, 90049 Porto Alegre, RS Brazil days of shifted training. The findings indicate that the muscarinic cholinergic and b-noradrenergic systems These experiments examined the effects of posttraining intraamygdala administration of the muscarinic agonist, within the amygdala interact in regulating memory and support the view that noradrenergic influences are medi- oxotremorine, and the b-noradrenergic antagonist, pro- pranolol, on memory for reduction in reward magnitude. ated through cholinergic activation.  1997 Academic Press Male Sprague–Dawley rats (175–200 g) implanted with bilateral intraamygdala cannulae were food deprived (maintained at 80% of body weight) and trained to run a INTRODUCTION straight alley (six trials/day) for either ten 45-mg food pel- lets (high reward) or one 45-mg food pellet (low reward) A well-established body of evidence strongly sug- for 10 days. In Experiment One, the animals in the high- gests that changes in b-noradrenergic activity in the reward group were then shifted to a one-pellet reward and amygdala mediate the influence of many drug and immediately given intraamygdala infusions (0.5 ml/side) hormone treatments which enhance or impair mem- of either oxotremorine (10 ng) or phosphate buffer. Shifted ory retention (Introini-Collison, Ford, & McGaugh, training continued for 4 more days and no further injec- 1995; Introini-Collison, Miyazaki, & McGaugh, 1991; tions were given. Shifted animals given the buffer solution displayed an increase in runway latencies but returned to Introini-Collison, Nagahara, & McGaugh, 1989; Li- preshift latencies by the fifth day of shifted training. In ang, Juler, & McGaugh, 1986; McGaugh, Cahill, Par- contrast, animals given oxotremorine exhibited increased ent, Mesches, Coleman-Mesches, & Salinas, 1995; latencies through the fifth day. In Experiment Two, rats McGaugh, Introini-Collison, Cahill, Castellano, Dal- were trained as in Experiment One but immediately fol- maz, Parent, & Williams, 1993; McGaugh, Introini- lowing the shift received intraamygdala infusions of oxo- Collison, Cahill, Kim, & Liang, 1992; McGaugh, In- tremorine (10 ng), propranolol (0.3 mg), both, or phosphate troini-Collison, & Nagahara, 1988). The evidence buffer. Shifted vehicle-injected rats returned to preshift also suggests that the effects of amygdala b-norad- performance by the fifth day of shifted training. Shifted renergic activation are, in turn, mediated by subse- propranolol rats returned to preshift latencies by the third quent muscarinic cholinergic activation within the day of shifted training. In contrast, the shifted oxotremo- amygdala (Dalmaz, Introini-Collison, & McGaugh, rine and the shifted oxotremorine/propranolol rats dis- played longer latencies than unshifted controls through 5 1993; Introini-Collison, Dalmaz, & McGaugh, 1996). Most of the research investigating the role of the amygdala in memory storage is based on tasks using 1 This research was supported by American Psychological Asso- ciation Minority Research Fellowship 2 T32 MH 18882 (J.A.S.), footshock punishment. We have also examined the CAPES/Brasil fellowship (C.D.), and USPHS Grant MH12526 involvement of the amygdala in modulating memory from NIMH and NIDA (J.L.M.). storage for changes in reward magnitude (Salinas, 2 Address correspondence and reprint requests to Juan Salinas, Packard, and McGaugh, 1993; Salinas and McGaugh, Department of Psychology, University of Virginia, 102 Gilmer 1996). It is well established that reducing reward Hall, Charlottesville, VA 22903. Fax: (804) 982-4785. E-mail: jas7t@virginia.edu. magnitude results in a transient performance decre- 51 1074-7427/97 $25.00 Copyright  1997 by Academic Press All rights of reproduction in any form reserved.