Rhythmic activities in the nervous system of invertebrates.

Our research focuses on the neuronal circuits that govern behavior. We use several marine invertebrate animal models, due to the advantageous properties of their simple nervous systems. In the blue crab, Callinectes sapidus, we are investigating how the central system regulates the heartbeat, and specifically how neuromodulators achieve such modulation via coordinated central and peripheral actions. In the marine mollusk, Aplysia californica, we have identified key interneurons that regulate feeding behavior using two classical neurotransmitters, GABA and dopamine. These studies increase our understanding of the neural control of behavior in all animals, including humans. They should also provide insight into fundamental neuronal mechanism that underlines maladaptive brain activities. Techniques included in the laboratory include intracellular and extracellular recording, dye injection of neurons, nerve backfills, immunohistochemistry and confocal microscopy.

A new project in the lab uses a parasite-host as a model system for studying neuronal circuits governing behavior. The digenetic trematode Schistosoma mansoni that causes the form of schistosomiasis found in the Western Hemisphere requires the freshwater snail Biomphalaria glabrata as its primary intermediate host. It has been proposed that the transition from the free-living S. mansoni miracidium to parasitic mother sporocyst depends upon uptake of biogenic amines, e.g. serotonin, from the snail host. However, little is known about potential sources of serotonin in B. glabrata tissues. This investigation examines the localization of serotonin-like immunoreactivity (5HTli) in the central nervous system (CNS) and peripheral tissues of B. glabrata. Emphasis is placed upon the cephalic and anterior pedal regions that are commonly the sites of S. mansoni miracidium penetration. The anterior foot and body wall are densely innervated by 5HTli fibers but no peripheral immunoreactive neuronal somata have been detected. Within the CNS, clusters of 5HTli neurons are observed in the cerebral, pedal, left parietal, and visceral ganglia, suggesting that the peripheral serotonergic fibers originate from the CNS. Double-labeling experiments (biocytin backfill x serotonin immunoreactivity) of the tentacular nerve and the three major pedal nerves (Pd n. 10, Pd n. 11, and Pd n. 12) have disclosed central neurons that project to the cephalopedal periphery. Overall, the central distribution of 5HTli neurons suggests that, as in other gastropods, serotonin regulates the locomotion, reproductive, and feeding systems of Biomphalaria. The projections to the foot and body wall indicate that serotonin may also participate in defensive, nociceptive, or inflammation responses. These observations identify potential sources of host-derived serotonin in this parasite-host.

Another project in the lab is titled “Estuary systems: Consequences of estuary contamination on crab heart and neurosecretory systems”. These studies focus on a ubiquitous crustacean inhabitant of the San Juan Bay Estuary, the blue crab Callinectes sapidus, as an experimental model for assessing effects of anthropogenic factors on nervous system function.  This species is native to waters of the western Atlantic, ranging from northern Argentina to as far north as Nova Scotia and supports one of the largest fisheries industries in the United States, estimated at more than 100 million dollars in 2005.  However, alarming decreases in its populations have been documented in recent years. The central hypothesis of this project posits that pollutants can exert significant sub-lethal effects on nervous system structure and function. This project is comprised of three objectives that will explore this hypothesis: 1) develop bioprobes to monitor levels of contaminants in sediments, water and crab tissue samples in the SJBE; 2) assess the impact of contaminants and oxygen levels on the cardiac system of crabs obtained from distinct environmental condition; and finally, 3) assess the impact of contaminants and oxygen levels on the sinus gland neurosecretory system of crabs obtained from distinct environmental conditions.