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Posttrial administration of corticosterone was previously shown to enhance consummatory successive negative contrast (cSNC) in rats. The present series of experiments provides additional information that helps determine the boundaries of this effect. Posttrial corticosterone administration (1) enhances cSNC when rats experience a large downshift (32% to 4% sucrose), but not after a small downshift (8% to 4% sucrose; Experiment 1); (2) has no effect in an anticipatory negative contrast situation in which 4% sucrose precedes 32% sucrose in daily trials (Experiment 2); (3) does not support the development of a conditioned taste aversion to 4% sucrose, in the absence of an incentive downshift (Experiment 3); and (4) facilitates the extinction of consummatory behavior (Experiment 4). These results suggest that corticosterone facilitates the encoding of an egocentric aversive memory of the incentive downshift experience. Fil: Ruetti, Eliana Martha. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Justel, Nadia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Mustaca, Alba Elisabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Papini, Mauricio Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina

The anterior cinculate cortex (ACC) is known to be implicated in pain-fear and reward expectations. Animals were given electrolytic lesions of the ACC and then trained in the consummatory successive negative contrast (cSNC) situation. In cSNC, animals exposed to an incentive downshift from 32% to 4% sucrose exhibit less consummatory behavior than animals always exposed to 4% sucrose. The ACC lesion had no measurable effects on the consummatory performance of animals before the downshift (i.e., the lesion did not affect consumption of 32% vs. 4% sucrose); on the performance of unshifted, 4% sucrose animals; and on the first downshift trial. However, ACC animals exhibited a significant retardation of recovery from cSNC relative to downshifted shams. Within-trial analysis of consummatory behavior indicated that ACC lesions facilitated cSNC during both the initial and last 100 s of postshift trials after the first downshift experience, relative to sham controls. These results suggest that the ACC is part of the neural circuit normally involved in coping with the emotional response induced by the incentive downshift event by inducing learning of the new incentive conditions.

Rats given access to a 32% sucrose solution and then downshifted to a 4% solution exhibit less contact with the sipper tube than unshifted controls always given access to 4% solution. This phenomenon, called consummatory successive negative contrast, was facilitated in Experiment 1 by a post-trial injection of corticosterone (3 mg/kg) administered immediately after the first downshift trial. Experiment 2 demonstrated that this facilitatory effect of post-trial corticosterone does not occur when administered 3 hr after the first downshift trial. These results support the hypothesis that corticosterone strengthens an aversive emotional component elicited by the surprising downshift in reward magnitude during the initial downshift trial. Fil: Bentosela, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Universidad de Buenos Aires. Facultad de Psicología; Argentina Fil: Muzio, Ruben Nestor. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Psicología; Argentina Fil: Ruetti, Eliana Martha. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Psicología; Argentina Fil: Mustaca, Alba Elisabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Universidad de Buenos Aires. Facultad de Psicología; Argentina Fil: Papini, Mauricio Roberto. Texas Christian University; Estados Unidos

Two experiments explored the role of the opioid system in a situation involving a surprising reduction in reward magnitude: consummatory successive negative contrast. Rats received access to 32% sucrose solution (preshift Trials 1-10) followed by 4% solution (postshift Trials 11-15). Independent groups received an injection of either the vehicle or the delta-receptor agonist [D-Ala2-,N-Me-Phe4,Gly-ol] enkephalin (DPDPE; 24 microg/kg). DPDPE attenuated the contrast effect when injected before Trial 11 but not when injected before Trial 12. An additional experiment showed that the attenuating effect of partial reinforcement on the recovery from contrast was reduced by DPDPE injections administered before nonreinforced preshift trials.

Two experiments on the nature of avoidance behavior in the goldfish are reported. In the first experiment, a master/yoked design was used to determine the degree to which Pavlovian conditioning would generate acquisition of a shuttle response by goldfish. Results indicated that the mere sequence of signal-shock pairings experienced by the avoidance animals is not in this situation sufficient to explain the development of the instrumental avoidance responding. The second experiment was conducted to study the effects of three variables on the retention and extinction of the avoidance response. First, unilateral lesions of the telencephalon produced a transient deficit from which the subjects recovered to normal levels. Retention of the avoidance response after bilateral telencephalon ablation was impaired and never fully recovered with additional training. Second, this deficit was reduced under higher intensities of electric shock. Third, overtraining on the task before the ablation had only a nonsignificant enhancing effect on retention levels. Extinction was always poorer following ablation, independent of the type of ablation, intensity of shock, degree of overtraining, and terminal retention level of performance. The results are discussed in terms of various theories of telencephalic function in fish.

Simultaneous bilateral ablation of the teleost telencephalon was confirmed to dramatically impair the retention, extinction, and "reversal learning" of a preoperatively learned instrumental avoidance response in a shuttle box. The focus of the experiment was on whether two-stage serial unilateral ablations of the teleost telencephalon would ameliorate the effects seen following one-stage bilateral ablation and whether such amelioration would be a function of the fish's experiences between the staged ablations. The degree of retention, relearning, and extinction of the avoidance response was not modulated by the serial ablation procedure whether or not there was interoperation retraining experience. However, reversal learning, in which the previous warning signal became the safety signal and the previous safety signal became the new warning signal, was less impaired following serial ablations than following single-stage bilateral ablation. These results are contrasted with those from experiments with mammalian subjects.