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G S Wasserman

Publications and source records attributed to G S Wasserman.

77 records · Page 5Linked to original sources
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Categorical and prolonged potentials are evoked when brief, intermediate-intensity flashes stimulate horseshoe crab lateral eye photoreceptors during octopamine neuromodulation.

Octopamine, a major efferent neurotransmitter in the lateral eye of the horseshoe crab (Limulus polyphemus), has previously been shown to modulate photoreceptor responses evoked by long flashes. Quantification of these data indicates that this modulation produced a genuine increase in sensitivity to light which cannot be entirely due to an increase in optical efficiency consequent on an anatomical alteration. Other previous studies demonstrated that extrinsic current can modulate Limulus lateral eye photoreceptor cells by inducing a bistable membrane potential with two distinct states. The present study was therefore undertaken to find out if octopamine could modulate visual responses by inducing prolonged and bistable polarization shifts similar to those demonstrated in several other neural systems. Intracellular microelectrodes were used to execute an electrophysiological study of the receptor potentials evoked in the lateral eye of Limulus when brief (20-ms) flashes were delivered while 50 microM octopamine perfused dark-adapted photoreceptors. The combined chemical and optical stimuli prolonged photoreceptor responses to light to the degree that they often exceeded the duration of the brief stimulus by hundreds of milliseconds. Moreover, these prolonged potentials were clearly bistable because they were categorical--either a prolongation was perceptually clear-cut and present or it was not, with no intermediate patterns being observed. During seawater control perfusions, such prolongations were absent. This appears to be the first demonstration of such categorical and prolonged potentials in a photoreceptor neuron. This finding particularly suggests that efferent-driven neuromodulation can enable the development of a persisting short-term representation of a brief stimulus, with this representation being retained at the most distal possible neural site.

Animals↗
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Electroretinographic measures of vision in horseshoe crabs with uniform versus variegated carapaces.

The carapace characteristics of horseshoe crabs (Limulus polyphemus) have been correlated by others with male mating performance and it has also been suggested that such mating differences might depend on visual differences. The effect of carapace character on horseshoe crab vision was therefore noninvasively investigated using the electroretinogram (ERG) of the lateral compound eye as a measure. Male Limulus were dichotomized on three carapace dimensions: clear versus dark eyes, light versus dark carapaces, and presence versus absence of barnacles. All dichotomizations gave similar results: No crab was ERG-blind. Analyses based on ERG magnitude yielded trivial sensitivity differences between these groups. However, analyses based on ERG latency indicated that response speeds exhibited reliably different trends between groups: Although responses to dim flashes were similar for all animals, increasing flash intensity produced significantly greater changes in the latencies of the ERGs in uniform males than in variegated males. This interactive dependence of ERG speed differences on flash energy cannot be the result of greater light absorption by the variegated specimens' darkened corneas. The visual capacities of variegated specimens are therefore somewhat altered, but certainly not absent. Equalizing animal size between groups did not measurably affect these results, implying that age was not a factor. The previously reported correlation of an individual male's appearance with its performance in mating competitions is extended by these data to include its sensory functioning as well.

Animals↗
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Isomorphism, task dependence, and the multiple meaning theory of neural coding.

The neural coding problem is defined and several possible answers to it are reviewed. A widely accepted answer descends from early suggestions that neural activity, in general, is isomorphic with sensation and that the biological signals resident in the axons of neurons, in particular, are given by their frequency of firing. More recent data are reviewed which indicate that the pattern of neural responses may also be informative. Such data led to the formulation of the multiple meaning theory which suggests the neural pattern may encode different information features in single responses. After a period in which attention turned elsewhere, the multiple meaning theory has quite recently been revived and has stimulated novel and careful experimental investigations. A corollary theory, the task dependence hypothesis, suggests that these information-bearing multiple response features are accessed differentially in different behavioral tasks. These theories place stringent temporal requirements on the generation and analysis of neural responses. Recent data are examined indicating that both requirements may indeed be satisfied by the nervous system. Finally, several methods of experimentally testing such coding theories are described; they involve manipulating the biological signals of neurons and observing the effect of these manipulations on behavior.

Animals↗
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Loxoscelism and necrotic arachnidism.

The Brown recluse spider has emerged into a potent venomous creature. Loxoscelism and necrotic arachnidism is not an infrequent medical problem. Spiders other than L. reclusa are capable of inflicting painful and persisting necrotic wounds, however, management of the local cutaneous lesions are similar. Systemic complications of loxoscelism appear to be characteristic for spiders of the genus loxosceles. The authors review an indepth discussion of the spider, venom, diagnosis, clinical presentation, laboratory findings, treatment, and prevention. The literature on loxoscelism is contradictory because of the individuality of the reaction. Experience with many patients is the only guide to management of these cases.

Adrenal Cortex Hormones↗