Dr. Peter Daniel: Research Interests

biopcd@hofstra.edu

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Click here for my isot 2000 poster (You need Acrobat Reader to view, 548 kB)

 

 


               My research considers the mechanisms of chemosensory processing, from stimulus recognition to activation of behavior. Thus far I have relied mostly on the  Florida spiny lobster, Panulirus argus, as a model organism because 1) its behavioral responses to relevant chemicals is easy to discern and is reproducible in the laboratory, 2) its olfactory organs are easy to record from with electrophysiological techniques, and 3) a large body of information concerning diverse aspects of chemical sensing in this organism has accumulated. I have concentrated on two basic research problems: 1) How do lobsters process information on mixtures of chemicals representing odorant stimuli? 2) How are complex stereotypical behaviors driven by chemosensory input? I am also involved in applying some of my research results, namely the development of artificial bait for American lobsters. These projects are described in more detail below.   

Chemosensory Processing of Mixtures of Chemical Stimuli

            Over the past nine years, I have concentrated on how the olfactory system encodes information on mixtures of chemicals that represent prey odorants lobsters may encounter in their natural environment. My research, as well as others, has shown that olfactory receptor neurons (ORNs) are tuned narrowly to specific chemicals (e.g., Daniel, Fine, Derby & Girardot 1994). Cross-adaptation studies of these cells show evidence for two transduction pathways: one activated exclusively by the best chemical for a cell and a second pathway activated by a broader spectrum of chemicals (Daniel, Fine, Derby & Girardot 1994). We have discovered that it is the pattern of response across neurons (= across neuron pattern (ANP)) of the ORNs that encodes information about complex mixtures of up to 41 chemicals mimicking natural odorants (e.g., Derby, Daniel, Fine-Levy, & Girardot 1990). Different complex mixtures evoke different ANPs. Associative and non-associative conditioning studies have demonstrated that lobsters can discriminate behaviorally between these same complex mixtures (e.g., Daniel and Derby 1988, Fine-Levy, Girardot, Derby & Daniel. 1989).

            When lobsters are presented with a mixture of two chemicals, the behavioral response of the lobster to these chemicals is often less than predicted based on responses of the same chemicals presented singly (Daniel & Derby 1991a & b), a phenomenon known as a mixture interaction and observed in many animals including humans. This effect has some of its basis in peripheral mechanisms: ORNs also exhibit suppression for many binary mixtures (Derby, Girardot, & Daniel 1991a). We have some evidence, based on a limited subset of ORNs, that mixture suppression can alter the ANP towards a binary mixture enough that it is represented as a unique quality rather than a blend of the qualities of its component chemicals (Derby, Girardot, & Daniel 1991b). Recently, we were able to refute this hypothesis. A more representative data set of responses of ORNs indicates that we can predict ANPs for mixtures based on ANPs for components (Daniel, Burgess, & Derby, 1996). We have also demonstrated that the response intensities of a population of ORNs toward binary mixtures can be predicted fairly well if information on binding inhibition between chemicals (derived from ligand-binding studies by my collaborators at Georgia State University) is incorporated into predictive mixture models.


 

Chemosensory Mechanisms for Release of a Stereotypical Behavior: Antennule Grooming

            Others and I have described several behaviors activated by water-borne chemical stimuli. One of these, antennule grooming behavior (AGB), is a stereotypical activity that involves the wiping of the first pair of antennules, the olfactory organs of the lobster, through the third maxillipeds, feeding appendages located near the mouth. This is followed by the rubbing of the maxillipeds together, a behavior called auto-grooming. One of my undergraduate research students, John Barbato, discovered that this behavior, unlike other behaviors stimulated by odorants, appeared to be activated by only one of the chemicals, l-glutamate, found typically in food-associated odorants. This is a markedly different result than what has been observed for other chemosensory-driven behaviors in the lobster such as search and antennular flick. Both of these behaviors can be elicited toward a considerable number of chemicals found in extracts of food. It is likely that chemosensory input eliciting AGB is processed in a manner fundamentally different than processing of chemosensory input eliciting search and flick behaviors. Hence, the current research direction of my laboratory. John Barbato, as a graduate student, was able to confirm the specific nature of the stimulus: of 27 chemicals found in extracts of food, l-glutamate was by far the most excitatory (click here to see these results). Only a few other chemicals presented at very high concentrations induced moderate levels of AGB. Even d-glutamate is only weakly excitatory and N-methyl-D-aspartate, an agonist of glutamate receptors, elicited no response. Based on these results we have proposed that chemosensory elicitation of AGB requires input from a specific class of sensory neurons tuned narrowly to l-glutamate (Barbato and Daniel 1997). Barbara Schmaltz, an undergraduate, is testing this hypothesis. She is using a cross-linker, BS3, which can bind irreversibly a ligand to its receptor site. After cross-linking glutamate to its receptor, she tests responses of lobsters to glutamate and other chemicals which can elicit AGB. If the hypothesis is correct than responses to glutamate and all other chemical stimuli will be greatly attenuated.

John has also examined the responses of lobsters towards complex mixtures and found that the magnitude of AGB toward glutamate was less than expected in the presence of other chemicals in the mixture (Barbato, Kalina, & Daniel 1996). In addition the magnitude of search behavior toward the search mixture was attenuated. Joanna Wroblewska, as an undergraduate, showed that one of the suppressant chemicals is probably taurine, a common constituent of food odorants (Wroblewska & Daniel, 1997). Reciprocal inhibition of search behavior and AGB may occur via inhibitory connections between "command centers" activating these behaviors. In this way glutamate may activate the AGB command center and inhibit the search command center while other chemicals in the mixture may inhibit the AGB command center and activate the search command center.

I am very much interested in determining which chemosensory organs and receptors are providing input. Michael Kalina, a graduate student, performed experiments that indicated that the antennules and the third maxillipeds were the probable sites (Barbato, Kalina, & Daniel 1996). In fact, our most recent results indicate that a specific region of the antennules is instrumental in providing chemosensory input. This region contains all the olfactory sensilla, called aesthetascs. Olfactory receptors in the sensilla project to the olfactory lobe of the brain. Thus, it is likely that the behavior is partially olfactory-driven. The maxillipeds on the other hand, probably contain non-olfactory chemoreceptors, which project to other undetermined regions of the central nervous system. Thus, AGB may be driven by two types of chemosensory input processed initially by different regions of the brain before integration to command a motor output. Sean Whalley, an undergraduate, is conducting experiments that will show conclusively whether other setae in the same region of the antennules as the aesthetascs might provide chemosensory input driving AGB. Joanna Wroblewska, now a Master’s student, is investigating if third maxillipeds provide chemosensory input driving AGB and will determine through electrophysiological recording techniques the tuning characteristics of chemosensory neurons located on these appendages.

I am also interested in the function of this behavior. It is clear from earlier research on other crustacean species that antennular grooming serves to remove fouling material from the antennules. Without this behavior the antennules degrade structurally. But why would chemosensory activation occur? And why would the behavior be tuned towards one chemical? My current hypothesis is that l-glutamate is the best and most sensitive cue of the potential for fouling following contact with food. Specifically, this is because 1) it is a common constituent of food, 2) its charge characteristics at the pH of the ambient environment favors adherence to crustacean cuticle more than most other compounds found in food, and 3) lobsters have receptors specialized to detect it. This hypothesis will be tested through biochemical binding studies using radiolabelled ligands.

Finally, AGB can serve as a model for comparative studies among crustaceans. All crustaceans appear to display this behavior. There is considerable variation in the structure of their antennules which is correlated with variation in motor patterns. One other species of spiny lobster, Panulirus interruptus, has been shown to display AGB via chemosensory activation, although to a much wider variety of chemicals found in their food. Presumably, AGB in other crustaceans may also be elicited by food stimuli. Therefore, AGB may serve as an important model of the evolution of sensory/motor processing of a specific behavior in a major animal group.   

Artificial Baits for American Lobsters

While a graduate student at the University of Maine I developed an artificial bait for catching lobsters. In laboratory studies it appeared to be very promising (Daniel and Bayer 1989) but was never tested in field trials. Matthew French, an undergraduate, tested the bait in lobster pots fished in Long Island waters. The results were very promising: he caught as many lobsters with the artificial bait as with baits currently used by lobstermen. Furthermore, the incidental catch of spider crabs and other species that are not marketable was much lower for pots with artificial bait. In the future I will test the bait on a larger scale and also determine if it is marketable. 
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