We are interested in understanding the neural basis of aggressive behavior and the establishment of dominance hierarchies, and the manner in which the underlying mechanisms may be modulated. We use as an experimental animal model the freshwater prawn Macrobrachium rosenbergii. Besides providing the well known benefits of other invertebrate model systems (e.g., simpler nervous systems, large identifiable neurons, stereotyped behaviors, etc.), this prawn has the added advantage of establishing dominance hierarchies on the basis of claw morphotype, a fixed characteristic, rather than only the basis of body size. Adult prawns progress through three claw morphotypes (small, yellow and blue) each corresponding to a higher level of dominance within a group.

Our research project integrates a variety of experimental approaches, including immunohistochemistry, confocal microscopy, in situ hybridization, western blot analysis, electrophysiology, video recorded behavioral observation, proteomics and molecular biology (cloning, RT-PCR, expression). Rotating students can become involved in any of the ongoing projects and get exposed to any or all of these techniques.

We have characterized the location and distribution of various neurotransmitters/modulators (e.g., serotonin, octapamine, dopamine, GABA, glutamate, FMRF, proctolin, etc.) in the central nervous systems (CNS) of all three male and female morphotypes, as well as colocalizations and other forms of interactions among neurotransmitters systems, within each morphotype (e.g., dopamine and serotonin colocalization in single neurons, interactions between serotonin and dopamine neurons and octopamine and FMRF neurons, etc.).

We have used behavioral observation experiments to characterize interactive behaviors amongst morphotypes and have shown that the typical behavior of a morphotype can be manipulated to change into those of another morphotypes through systemic injections of neurotransmitters or agonists and antagonist of specific receptors.

Molecular biology techniques have been used to clone the fist crustacean aminergic receptors (two serotonergic and one octopaminergic). Antibodies and molecular probes have been raised against these cloned receptors and used to map their location and distribution in the prawn’s CNS, using immunohistochemistry, confocal microscopy and in situ hybridization techniques. Quantitative Western blot analysis and real-time RT-PCR techniques are being used to measure levels of expression of these receptors in different regions of the CNS of the three morphotypes of the prawn.

Other lines of experiments presently in progress include the expression and characterization of the cloned aminergic receptors, the cloning of other crustacean transmitter and neuropeptide receptors, the use of techniques of differential expression to isolate other target molecules that may be present in higher or lower amounts in each morphotype, and the isolation and identification of water-borne messenger molecules that communicate information on dominance status to animals with a group.

A new project being developed in the lab concerns studying the impact of anthropogenic changes in Puerto Rico urban rivers on behavior and underlying neural circuitry of fish and crustacean species. This project compares the effects of urbanization on Puerto Rican rivers and its aquatic fauna. To do this, we first analyze three representative rivers in which we identify and quantify extraneous chemicals. Four animal models, zebrafish, mosquitofish, and two types of prawn, will be exposed to pollutants found in the three rivers followed by monitoring of their fast-start escape response and associated behaviors and assessment of the integrity of the underlying neural networks. Thus, this project will accomplish three objectives: 1) assess the levels of heavy metals and storm sewer runoff contaminants on acutely and chronically contaminated urban rivers in comparison with those of undeveloped areas; 2) monitor the effect of heavy metals and storm sewer runoff contaminants on the fast-start escape response and associated interactive behaviors in fish and freshwater prawn; and finally 3) we will determine the effect of heavy metals and storm sewer runoff contaminants on survival and integrity of the neural networks involved in the fast-start escape response and associated interactive behaviors in fish and freshwater prawn.