About Dr. Murphy's Research

Research interests in my laboratory include: Neuronal mechanisms underlying rhythmic behaviors; Sensori-motor integration and modulation of neuronal circuitry involved in multiple behaviors; comparative neurobiology of Molluscan feeding and development and evolution of defined neural circuits and behaviors.

Rhythmic behaviors such as feeding, locomotion and respiration are critical for sustaining life in multicellular animals. Motor patterns mediating these behaviors are typically generated by neuronal circuits called central pattern generators (CPGs). The motor output of multifunctional CPGs is modulated as a function of environmental stimuli and internal behavioral states so that an appropriate behavior is produced at any given time. Feeding and regurgitation behaviors in gastropod molluscs have rhythmic components mediated by a multifunctional CPG in the buccal ganglia. Changes in motor patterns mediated by the buccal CPG can be effected by application of particular neurotransmitters or by stimulation of specific identified neurons.

Modifications of identified neurons and their synaptic interactions has also occurred over evolutionary time scales. The modulation of neuronal circuitry can be examined phylogenetically by comparing homologous identified neurons and their interactions in different species of gastropod molluscs. Opportunities are particularly ripe to examine the evolution of functional neuronal circuits since many distantly related molluscs have quite similar feeding mechanisms, whereas some very closely related gastropods have diverged significantly in structural and behavioral components of feeding. Comparative studies have recently become an important component of research in the Murphy laboratory. These studies are designed to test the universality of the Helisoma model of the buccal CPG and to determine similarities and differences in putatively homologous identified neurons and their interconnections in diverse gastropods.

Techniques and experimental approaches range from videomicroscopy of freely behaving intact animals through electrophysiological and pharmacological analyses of neural circuitry, and determination of mechanisms of action of specific neurotransmitters. Immunocytochemistry and a number of neuronal staining techniques are used to determine the morphology of physiologically characterized identifiable neurons. A new project in the lab will look at the effects of changing the concentrations of neuromodulators (such as dopamine and serotonin, which are known to affect neurite outgrowth differentially in regenerating neurites) in the milieu of developing embryos. This project will examine the effects of embryonic manipulation on defined neural circuitry assayed in adults.

Representative Publications

Murphy AD (2001) The neuronal basis of feeding in the snail, Helisoma, with comparisons to selected gastropods. Progress in Neurobiology. 383-408.

Quinlan EM, Arnett BC and Murphy AD (1997) Feeding stimulants activate an identified dopaminergic interneuron that induces the feeding motor program in Helisoma. J Neurophysiol 78:812-824.

Quinlan EM and Murphy AD (1996) Plasticity in the multifunctional buccal central pattern generator of Helisoma illuminated by the identification of phase 3 interneurons. J Neurophysiol 75:561-574.

Quinlan EM, Gregory K and Murphy AD (1995) An identified glutamatergic interneuron patterns feeding motor activity via both excitation and inhibition. J. Neurophysiol. 73:945-956.