The distribution of ceroid in human atherosclerosis.

It has been suggested that macrophages in atherosclerotic plaques oxidize the lipid they contain, leading to necrosis in the plaque. Over 200 human aortic and coronary atherosclerotic plaques from 102 human necropsy subjects aged between 5 and 88 were, therefore, examined histologically for the presence of insoluble lipid (ceroid), thought to be a product of lipid oxidation. Ceroid was present in all the plaques but not in areas of diffuse intimal thickening. In early lesions the insoluble lipid was within membrane-bound vesicles in macrophage-like cells, many showing characteristic ring structures suggesting that membrane-associated oxidative systems might be responsible for rendering the lipid insoluble. Staining was increased by an oxidizing agent and abolished by a reducing agent. It is suggested that this distribution supports the concept of lipid oxidation by macrophages within the plaque.

Effects of paleocerebellar lesions on DRL performance in the albino rat.

Normal rats and rats with paleocerebellar lesions were trained to bar press for food on continuous reinforcement (CRF) and differential reinforcement of low response rates (DRL) schedules. The animals with lesions showed normal acquisition of the CRF schedule, but they exhibited a marked deficit on the DRL task. This deficit was related to overresponding which appeared to result from an inability to inhibit the response, rather than from a dysfunction in timing ability or motor capacity. The DRL deficit, however, was overcome by the introduction of a salient stimulus object (wood block) into the operant situation. Although no explicit reinforcement contingencies were placed on interaction with the stimulus object, it appeared that the wood block facilitated the development of "collateral" behaviors that served to mediate the DRL interval. These results are consistent with the suggestion that the cerebellum may contribute to the sequential organization of complex behaviors.

Response suppression in normal and septal rats.

After 11 days of lever press training on a variable interval 30 sec schedule, separate groups of septal and normal rats were exposed for 10 days to one of two response-suppression procedures: extinction or differential reinforcement of other behaviors. Both procedures were effective in suppressing responding, with the septal rats taking longer to reach the suppression asymptote than did the normals. All rats then received 5 days of non-contingent food presentation. Under these conditions responding recovered to a much greater degree in rats previously given extinction than in those given DRO. Further, septal rats given extinction showed more recovery than did normals given extinction.

Operant conditioning in redwinged blackbirds.

An operant conditioning technique for use with passerine birds is described. Two redwinged blackbirds were successfully conditioned to perch-hop for food reinforcement. Continuous reinforcement and fixed-ratio schedules involving substantial ratio requirements were used to maintain this response. The behavior of the two redwinged blackbirds was comparable to that of more conventional organisms working on similar schedules of reinforcement.