Peter D. Brodfuehrer, Ph.D. - US grants

My long-term research goal is to understand the cellular mechanisms by which neural networks control animal behaviors. It is also becoming clear in many systems that the final motor response of an animal to a given sensory stimulus is significantly influenced by not only excitatory interactions in the nervous system, but also by inhibitory interactions. In several invertebrates it has been suggested that the initiation of a specific rhythmic behavior may not only depend on neurons that excite the appropriate neural network, but also requires disinhibition of inhibitory inputs to the neural network. Even higher order behaviors, such as behavioral choice, involve the inhibitory interactions between central neural networks. Thus to fully understand how an animal determines the appropriate motor response to a given sensory stimulus it is essential to investigate how the nervous system integrates both excitatory and inhibitory inputs at the neural network level. I propose to identify swim inhibitory neurons (SINs) in the head ganglion. To facilitate searching for SINs, I will use an ionic manipulations technique which is based on the fact that an increase in the extracellular K4+ concentration depolarizes neurons and an increase in the extracellular Cl- concentration hyperpolarizes neurons. Each SIN identified will be physiologically characterized by their input and output connections to the segmental swim generating network. In addition, I plan to examine the role SINs play in determining whether stimulation of cell Trl triggers swimming behavior. Variations in the activity levels of SINs will be compared in swimming and non-swimming trials to establish whether SIN activity is predictive of Trl induced swimming behavior. This research thus will directly examine how the leech nervous system integrates excitatory and inhibitory inputs to regulate swimming behavior. Similar integrative properties of the nervous system are likely used by other animals to control their behavioral responses to environment signals.

9514617 Brodfuehrer It is commonly observed that an animal when presented with the same stimulus on successive trials will often perform different behaviors. This means that an animal decides, often very rapidly, which behavior is appropriate for the circumstances at that moment. The concept of `motivation' is often used to explain this type of short-term behavioral variability observed under conditions where sensory input is constant. The underlying neuronal mechanism of motivation, however, has yet to be defined. Since an animal's survival depends upon it continually making the appropriate behavioral response to ever changing environmental conditions, understanding how an animal decides upon an appropriate motor response is integral to our understanding of animal behavior. In the medicinal leech, research on the neuronal basis of swimming has progressed to the point where the initiation of swimming following body wall stimulation can be traced from the sensory neurons that perceive the stimulus to the motor neurons that produce the swimming movements. However, stimulation of this pathway does not always elicit swimming. The probability that swimming occurs following a given stimulus trial is quite variable. The role that a pair of identified interneurons in the leech head ganglion plays in biasing the behavioral response of a leech toward swimming following a given sensory input will be addressed in this proposal. The results generated from this study will provide additional insights into the principles governing behavioral variability in the leech with respect to the initiation of swimming, and further enhance our understanding of the types of neuronal networks and mechanisms that can influence the motivational state of animals.

Six faculty members and their students in the Biology Departments at Bryn Mawr and Haverford Colleges will use a Nikon laser scanning confocal microscope for studies in cell and molecular biology. This system includes a Nikon Eclipse E800 Upright Research Microscope, a Nikon PCM-2000ML scanning confocal with two multi-lines lasers, an argon ion laser (457 nm, 488 nm and 514 nm) and a HeNe green laser (543 nm), a transmitted light detector, and a quantitative 2D/3D software package. The Nikon scanning confocal microscope will greatly facilitate and broaden the scope of research performed by the Biology faculty at Bryn Mawr and Haverford Colleges by providing a state-of-the-art system for detailed image acquisition and analysis.

Each investigator will incorporate the scanning laser confocal microscope into their independent research programs. These programs address a variety of molecular, cellular and developmental questions, including calcium imaging of plateau potentials in leech neurons; assembly of synaptic proteins in developing rat sympathetic neurons; cell proliferation in chick embryonic neuromeres; control of meiosis in C. elegans; molecular basis of programmed cell death in T lymphocytes, and biogenesis and regulation of microtubule containing structures in Chlamydomonas.

The acquisition of the Nikon scanning confocal microscope will also enrich the research experience of undergraduate biology majors at Bryn Mawr and Haverford Colleges, which is a major component of science education at both institutions. It will also benefit the graduate program in Biology at Bryn Mawr College by providing a high quality research tool for developing investigative skills.

Many of the recent successes in behavioral neuroscience in both invertebrate and vertebrate systems have been attained by identifying individual neurons and assessing the role of each neuron in behavior by physiologically manipulating its activity level. There are, however, aspects of behavior that have not been adequately explained by this approach. In the case of the medicinal leech, the neuronal network controlling the initiation of swimming is well-understood at several levels, but this understanding does not account for the unpredictability with which stimulation of this pathway leads to swimming. Two possible reasons for this inadequacy will be addressed in this proposal: (1) neuronal networks provide static descriptions of the system and do not accurately reflect their dynamics, and (2) even simple behaviors are a function of large populations of neurons distributed throughout the nervous system.
Because of the inherent complexity in the firing patterns of large populations of neurons, computational approaches are necessary for deciphering how the nervous system encodes behavior. This project will use linear statistical and spectral techniques and nonlinear techniques, in conjunction with discrete wavelet transforms, to test: (1) whether the 'state' or pattern of ongoing activity in the leech nerve cord prior to stimulation determines the likelihood that swimming will be elicited by a specific input, and (2) whether the neuronal control of swim initiation is a distributed property of the entire ventral nerve cord or is localizable to neuronal activity from specific regions of the leech nervous system. This project will provide research experiences for 10 undergraduate students from a primarily undergraduate women's college.

Animals initiate movements either in response to specific stimuli (such as touch, sound
or light signals), or as a result of an internal change in state (such as hunger). One
important aspect of such voluntary animal movements that has received relatively little
attention is their episodic nature, with distinct beginnings and endings. Much is already
known about the networks of nerve cells that control rhythmic movements like flying and
swimming, but the nervous system components that control the initiation and
termination of rhythmic behavior are largely unknown. The experiments funded by this
grant are designed to significantly advance the understanding of how nervous systems
process information generated by brief sensory stimuli and how they thereby produce
episodic locomotion.
Experiments will be conducted on isolated central nervous systems of the medicinal
leech using two different approaches. One approach is electrophysiological, with
experiments to investigate connections among nerve cells that control the initiation and
maintenance of swimming movements. The second approach is pharmacological, with
studies on the neurohormone serotonin and on other messenger molecules to learn
how these substances are involved in converting the quiescent motor system into one
that is functionally active. Because there is significant functional similarity between
swimming and related locomotory movements in all animals and because the
transformation of a system from quiescence to activity and back to quiescence is a
feature of all episodic animal movements, insights gained from this research will have a
major impact on our understanding of how the nervous system controls animal
movements generally.
The activities funded by this grant have a broader impact on science by increasing the
opportunities for undergraduates, primarily women, to conduct scientific research at
Bryn Mawr and at the University of Virginia. Also, experiments conducted in the
research laboratory are subsequently incorporated into laboratory exercises for
advanced neurobiology courses at both institutions. Finally, training is provided to
graduate students in modern electrophysiological recording techniques, data
acquisition, and analysis. Results from these experiments are widely disseminated
through posters at scientific meetings, including student presentations at local science
fairs and scientific meetings; publication in scientific journals; lectures open to the
public; and demonstrations on animal behavior at K-12 schools.

Bryn Mawr College and Haverford College are collaborating to prepare STEM teachers for high need school districts. An objective is to determine whether purposefully integrating a broad range of existing campus student-support and civic engagement structures together with a strong scholarship program and an ambitious publicity/recruitment campaign will increase the number of students who become precollege STEM teachers. Additional new initiatives designed to enhance teacher success include professional development and induction components. The program is developing a model for STEM teacher education that is compatible with the goals and structure of a liberal arts education: students complete a rigorous disciplinary major during their four years of undergraduate study and then complete their education requirements during a fifth year. Bryn Mawr and Haverford Colleges are collaborating with three local, secondary schools, and with the Math Science Partnership of Greater Philadelphia/21st Century Partnership Network. Nine Noyce Scholars are receiving two-year scholarships during the senior and fifth year. The program also is providing post-certification mentoring and professional development support during their first two years of teaching. The project's merit involves investigating the program's impact on encouraging STEM majors in a liberal arts setting to pursue careers in teaching. The project has the potential to serve as a model for the development of STEM teachers within the context of a highly selective liberal arts college.