Pharmacology Biochemistry& Behavior, Vol. 40, pp. 173-176. ©Pergamon Press plc, 1991. Printed in the U.S.A. 0091-3057/91 $3.00 + .00 RAPID COMMUNICATION Forebrain Noradrenaline Concentration Following Weakly Reinforced Training SIMON F. CROWE, KIM T. NG AND MARIE E. GIBBS La Trobe University, Bundoora, Victoria, Australia, 3083 Received 14 June 1991 CROWE, S. F., K. T. NG AND M. E. GIBBS. Forebrain noradrenaline concentrationfollowing weakly reinforced training. PHARMACOL BIOCHEM BEHAV 40(1) 173-176, 1991.--Day-old chicks trained on a single-trial discriminated passive avoid- ance task using a concentrated taste aversant, methyl anthranilate, have been shown to exhibit three stages of memory processing; short-, intermediate-, and long-term memory. If the aversant is diluted to 20% v/v methyl anthranilate in absolute ethanol, only the short-term and some of the intermediate stage are observed, in this study we investigated the whole forebrain levels of nor- adrenaline in response to differing intensities of the training experience. The results show a profound difference in the level of whole forebrain NA at all training-sacrifice intervals for the trained as compared to the untrained controls, except at 15- and 20-minute posttraining, when a substantial reduction in the level of NA was achieved under all training conditions. Furthermore, subjects which received treatments which resulted in the emergence of behavioural evidence of long-term memory tended to have higher levels of whole-forebrain NA at 30 minutes after initial training. This is the time when we have postulated that triggering of protein synthesis associated with long-term memory formation takes place. Day-old chicks Long-term memory Triggering Noradrenaline Training stimulus intensity THE dependence of learning on reinforcement and attentional mechanisms is well established at the behavioural level and there is an obvious adaptive advantage to an organism which retains in long memory only those experiences which are necessary for survival (15,18). These suggestions have prompted a number of investigations in our laboratory into the processing of weakly re- inforced training experiences. Our results indicate that day-old chicks trained on a single-trial passive discrimination avoidance task using a concentrated aversant substance exhibit three stages of memory processing; short-, intermediate- and long-term mem- ory (10). Futhermore, the intermediate stage is shown to have two phases, a phase A [ITM(A)] sensitive to inhibition by dini- trophenol (DNP) and a non-DNP sensitive phase B [ITM(B)]. In a variant of the task where the aversant has been diluted to a 20% v/v concentration in absolute ethanol the training leads to short- and intermediate-term memory, but not long-term mem- ory (5). The intermediate stage appears to only contain phase A. It was possible to induce long-term memory formation in chicks which had been trained initially with the weakly reinforced training experience by two means: giving the chicks a second training trial with the same aversant stimulus (6) or applying the neurohormonai effects of a strong training experience closely contiguous to the weakly reinforced learning trial (7). In each instance when long-term memory was produced in the initially weakly trained subject the emergence of long-term memory was invariably associated with the alteration of the in- termediate-memory stage by the emergence of the non-DNP sensitive ITM(B) phase (6-7). We have previously argued that the initiation of a protein synthesis associated with long-term memory formation may occur at the transition from the ITM(A) to the ITM(B) phase of the intermediate memory stage (8,11). The facilitatory effect of noradrenaline on weak training re- gimes has been numerously reported in the literature over the last twenty years (15, 18-19). We have shown that the [3-nor- adrenergic blocker propranolol inhibits ITM(B) and subsequent LTM formation, when LTM is induced by either strong training or weak training coupled with the neurohormonal peptide ACTH 1-24 (8). Similar results have been observed with another [3-blocker, sotalol, following strong learning (21). A number of laboratories have reported a correlation between posttraining release of whole brain noradrenaline (NA) and later retention performance (9, 12-13, 16--17). Gold and his col- leagues have observed that in the rat, there is a transient de- crease in NA levels maximal at 10 minutes after initial training. In weakly trained subjects, brain NA levels did not seem to show such a decrease and later retention performance was weak. In subjects which were initially weakly trained and given the neurohormonal consequences of strong reinforcement, a similar decrement in NA levels 10 minutes after training was observed (12,14). More recent experiments indicate that the observed decrement in NA levels is widespread throughout the brain and does not appear to be delimited to particular brain areas (17). The aim in this study was to determine the levels of NA in the whole forebrain of day-old chicks at various times following learning, under five training regimes: no training, a single 20% aversant training experience, a single 100% aversant training ex- perience, a single 20% aversant training trial followed by a 50 p,g/chick dose of ACTH 1-24, and an initial 20% aversant 173