PoKay Ma

Biological background

I earned a BS degree in Biology from the University of Oregon. I stayed on in Oregon as a research technician studying the development of the visual system in amphibians, before moving on to obtain my Ph.D. degree in neuroscience at Washington University in Saint Louis. My dissertation was an examination of the vibrissal (whisker) system in the brains of mice, rats and guinea pigs. Vibrissae are important sense organs used by rodents to explore the environment. In their brains, the vibrissae are represented by a highly specialized cellular organization. My study described the architecture, development and plasticity of this central vibrissal representation. For post-doctoral studies, I moved to Harvard Medical School in Boston and shifted my focus to neurohormonal control of posture and locomotion in lobsters and crayfish. Taking advantage of the simpler and relatively more accessible nervous system of these decapods, I uncovered some electrophysiological mechanisms by which serotonin modulates central motor output. These studies were continued at the Marine Science Center at Northeastern University in Boston, where I was appointed senior research scientist. While at the Marine Science Center, I initiated several projects aiming at investigating how the nervous system controls behavior in fishes.

Research interests:

The main focus in our laboratory is to understand how the nervous system controls behavior using two fish model systems. (i) The agonistic display of the Siamese fighting fish. The Siamese fighting fish is one of the most aggressive animals known; it will engage in agonistic display and fight with conspecifics under almost any circumstances. The most salient feature of the agonistic behavior is the frontal display, which is characterized by tonic abduction of the gill opercula. The display is subject to modifications such as habituation, sensitization, conditioning, hormonal states and social experience, suggesting that it is mediated by a plastic network in the brain. It is therefore a useful model for studying many aspects of the neural control of behavior. Currently, we are using neuroanatomical tract-tracing methods and focal brain lesion to identify the display neural circuits. Changes in the dynamics of display under various experimental conditions are studied using computer-assisted video analysis. Central motor output programs are studied by electromyographic recording. In the near future, we plan to perform in vitro electrophysiological recording of display motoneurons to examine some of their cellular properties. We are also planning a developmental study to correlate behavioral changes with the ontogeny of neural and neuromuscular elements. (ii) The locus coeruleus of the zebrafish. The vertebrate nervous system contains a large number of nerve cells, which often creates difficulties in exploring its functional organization. We have discovered recently that the locus coeruleus-a noradrenergic brainstem nucleus-contains only 5 to 8 neurons in the zebrafish. The number of neurons appears to be determined by both genetic and epigenetic factors. Since these neurons are relatively large and easy to identify, they may serve as a useful model for studying the functional organization of an entire nucleus. We are currently conducting experiments to elucidate the projection pattern, targets and electrophysiological properties of all neurons in this nucleus.

Selected Publications:

Ma, P. M. (1995) On the agonistic display of the Siamese fighting fish. I. The frontal display apparatus. Brain Behav. Evol. 45:301-313.

Ma, P. M. (1995) On the agonistic display of the Siamese fighting fish. II. The distribution, number and morphology of opercular display motoneurons. Brain Behav. Evol. 45:314-326.

Ma, P. M. (1994) Catecholaminergic systems in the zebrafish. I. Number, morphology and histochemical characteristics of neurons in the locus coeruleus. J. Comp. Neurol. 344:242-255.

Ma, P. M. (1994) Catecholaminergic systems in the zebrafish. II. Projection pathways and pattern of termination of the locus coeruleus. J. Comp. Neurol. 344:256-269.

Ma, P. M. (1997) Catecholaminergic systems in the zebrafish. III. Organization and projection pattern of medullary dopaminergic and noradrenergic neurons. J. Comp. Neurol. 380:411-427.

List of Publications from PubMed