Elemental and configural learning and the perception of odorant mixtures by the spiny lobster Panulirus argus.

The present study used a conditioning assay to investigate if the type of learning task that spiny lobsters (Panulirus argus) were required to perform influenced the way that they perceived odorant mixtures. Mixtures were composed of 2 food-related compounds (adenosine-5'-monophosphate, betaine, or L-glutamate) at concentrations that produced the same duration of searching behavior in unconditioned animals. Aversive conditioning of search behavior coupled with generalization testing was used to evaluate perceptual similarity between related mixtures. When animals were conditioned to stop searching to a binary mixture AX, they did not generalize significantly from this mixture to either of its components (A or X), or to a binary mixture containing one novel component (AY). However, when lobsters were conditioned to avoid AX but to continue responding to AY, they generalized between AX and X and between AY and Y. The results support the hypothesis that altering the salience of a mixture's components by giving them different reinforcement contingencies changed the way that the mixtures were perceived. As a result of such conditioning, animals perceived the mixture's components as separate elements, rather than as a configuration, and, as a consequence, animals generalized between binary mixtures and their most salient or predictive components.

Generalization among related complex odorant mixtures and their components: analysis of olfactory perception in the spiny lobster.

We investigated the processing of odorant mixtures containing two to seven components by the spiny lobster Panulirus argus. The chemicals tested were food-related compounds that are attractive to spiny lobsters, and include adenosine-5'-monophosphate, betaine, L-cysteine, L-glutamate, DL-succinate, taurine, and ammonium. Components were tested at concentrations that produced search behavioral responses of equal magnitude in unconditioned animals. Responses of unconditioned animals to mixtures and their components reveal hypoadditivity, in which the response to a mixture is less than the sum of the responses to that mixture's components. Aversive conditioning coupled with generalization testing was used to evaluate generalization and hence perceptual similarity between related mixtures. Animals were conditioned to either an individual odorant, a four-compound mixture, or a seven-compound mixture, followed by generalization testing with submixtures or larger mixtures containing the conditioned stimulus. Animals tended not to generalize, but significant generalization between a more simple conditioned stimulus and more complex mixtures containing that conditioned stimulus occurred in 2 of 11 cases, and significant generalization between a conditioned mixture and its submixtures was observed in 4 of 9 cases. Both the number and chemical identity of components of mixtures may contribute to the degree of generalization between mixtures. Overshadowing, in which the ability to learn about a chemical is affected by simultaneous presentation of other chemicals, occurred in two of three cases. We discuss implications of these findings with respect to elemental and configural processing of odorant mixtures in the spiny lobster, possible neural mechanisms responsible for these results, and the potential utility of generalization and overshadowing to the spiny lobster's natural behavior.

Bone histomorphometry in vitamin D-deficient rats infused with calcium and phosphorus.

Defective mineralization of bone and cartilage is the classical histological finding in vitamin D deficiency. Whether this represents a direct effect on mineral deposition or is a consequence of the decreased calcium and phosphorus levels that result from impaired intestinal absorption is not clear. A method has been developed in which vitamin D-deficient rats have plasma calcium and phosphorus levels maintained in the normal range by continuous infusion. Histomorphometric analysis of undecalcified tibiae from these animals was compared with that of rats given vitamin D. Epiphyseal growth plate thickness, trabecular osteoid volume, and mean osteoid seam width were not increased. Moreover, the administration of two time-spaced courses of tetracycline revealed that the mineralization rate and the time interval between apposition and subsequent mineralization of osteoid (mineralization lag time) were identical to those in rats treated with vitamin D. Trabecular bone volume was increased (osteosclerosis) in the vitamin D-deficient rats. In vitamin D-deficient controls without infusions, the osteosclerosis was mostly osteoid, whereas the excess bone was well mineralized in the vitamin D-deficient rats infused with calcium and phosphorus. Osteosclerosis in vitamin D-deficient animals may result from both decreased bone resorption and increased osteoid apposition. This study provides firm evidence that vitamin D is not essential for mineralization in young growing rats. Decreased availability of calcium and phosphorus thus may be the sole basis of the mineralization defect seen in vitamin D deficiency.