Most retinal amacrine cells do not appear to "spike."
(That is, they do not appear to fire the traveling
"action potentials" typical of most nerve cells).
However, certain types of amacrine cells have long axon-like
processes which spread laterally over long distances
(several millimeters) in the
inner plexiform layer of the retina.
These "wide-field" amacrine cells (and perhaps a few other types
of amacrine cells) do appear to fire action potentials.
It has long been known that retinal ganglion cells receive information
about visual stimulation over these distances, and we wondered
whether wide-field amacrines were responsible.
We used tetrodotoxin to
block action potentials in an intact
in vitro retina, and intracellularly recorded the
activity of ganglion cells which receive inputs from
these spiking amacrine cells. Two important results are
(1) Action potentials are necessary to
transmit visual information to ganglion cells over
long distances (more than a millimeter),
implicating the spiking wide-field
(2) A few minutes after all action potentials in the retina
were blocked, ganglion cell responses
to visual stimulation increased.
Thus, the over-all sensitivity of the retina to visual
stimulation is controlled, to some extent, by the continual
activity of spontaneously spiking cells. I plan to continue these studies
into the functional circuitry of amacrine cells and the role they play
in encoding visual information.
Investigation of possible neuronal function for Probstís bundles
Agenesis of the corpus callosum (ACC) is a congenital defect. In some human and
animal types, neuronal fibers which ordinarily would cross the midline during fetal
development instead run in a rostral-to-caudal direction and terminate in the
ipsilateral cortex, forming Probstís bundles (PB). Despite its potential clinical
importance, no study to date has established the physiological or behavioral
significance of these fibers. We will use the electrophysiology rig to study tissue
slices from PBs from a mouse strain which consistently exhibits ACC. We will
investigate if the PB axons conduct action potentials, if the fibers become functional
GABAergic neurons, and if they result in inhibitory or excitatory post-synaptic
potentials on their targets. (This work is currently being done in collaboration with
Prof. Paul Moes of Calvin College's Psychology Department.)
Poster on first results results.
Caveat: Results on these posters have been presented to colleagues and at conferences,
but have not yet been published in a peer-reviewed journal.
My curriculum vitae.
e-mail for more information
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(Last updated 2010 June 9)