Research Group of Professor Hadley Wilson Horch, Bowdoin College, Maine

Research Group of Professor Hadley Wilson Horch, Bowdoin College, Maine

From left to right Jackie Brosnan, Hadley Wilson Horch, Sarah McCarthy,Claire Cutting and James Harris

Professor Hadley Wilson Horch is the Assistant Professor of Biology and Neuroscience at Bowdoin College in Brunswick, Maine.

Hadley’s research group focuses on the understanding of the molecular control of dendritic growth and plasticity. Neuronal injuries induce profound changes in axons, dendrites, and synapses that usually lead to a devastating loss of function. While a large amount of research has broadened our understanding of axonal regeneration, very little is known about the ability of dendrites to regenerate after injury or denervation. Obviously, any successful clinical strategy will eventually need to consider the regeneration of dendrites and synapses if the full complexity of neuronal circuitry is to be restored. Thus, it is of great importance to understand how dendritic regeneration proceeds and to identify factors that may be involved.

Professor Horch obtained her PhD with Dr. Larry Katz at Duke University (2001) examining the role of the neurotrophin BDNF on the development of pyramidal cells in the visual cortex. She then spent a year studying with Dr. Ron Hoy at Cornell. Twenty years ago, Dr. Hoy had described the unusual regeneration of auditory interneuron dendrites after denervation in the cricket auditory system and began to apply more modern techniques to this anatomical study.

In 2002, Hadley went on to become an Assistant Professor at Bowdoin College in Brunswick, Maine. At Bowdoin Professor Horch teaches neuroscience and biology classes and manages a small, federally funded research program involving undergraduates.

Specifically, work in Hadley’s lab examines the compensatory regeneration of auditory interneurons in the cricket. Past research has demonstrated that unilateral removal of the ear in crickets induces denervated interneuron dendrites to grow across the midline, a boundary they usually observe, and form functional synaptic connections with the auditory afferents from the opposite ear (Hoy et al., 1985; Schildberger et al., 1986). This reinnervation is remarkably precise, reinstating interneuron-specific threshold and intensity responses.

The central hypothesis of Hadley’s research is that the compensatory regeneration and synapse formation of auditory dendrites in the cricket is guided by a recapitulation of the expression of developmental molecules. The team is using dye backfills, confocal microscopy, and Volocity software to analyze changes in the morphology of these denervated neurons. They are interested in understanding the morphological consequences of this regeneration. Is the novel growth across the midline at the expense of dendrites elsewhere in the cell’s arbor? Is the total amount of membrane in the cell essentially conserved? With increased post-synaptic demand (two cells instead of one), how does the pre-synaptic terminal compensate? What changes are seen in pre-synaptic axon number or pre-synaptic boutons?

Hadley says “The user friendly interface of Volocity allows me to easily obtain the essential measurements of surface area and volume in these complex dendritic arbours.” Hadley adds “ It has sometimes been a challenge to figure out the best classifier strategy, and working with the technical support has been extremely helpful. ”

Hadleys’ team also employs molecular techniques such as cloning, subtractive hybridization, and differential display to identify candidate genes that are differentially regulated. Hadley hopes that an investigation of this invertebrate regeneration phenomenon will advance our fundamental understanding of the plasticity of dendrites, and reveal principles governing dendritic regeneration that may be applicable to all neuronal systems, including mammals.

Regenerated auditory neuron

For more information about Professor Horch’s research please visit her website.