For example, Allison Quaglino is studying how the neurotrophin
family of growth factors regulates neuron survival in RA,
the cortical brain region that controls motor production
of vocal behavior. Past work in the lab has shown that pre-synaptic
axons from lMAN are necessary to support the survival of
RA neurons in 20-day old birds at the onset of song learning.
Allison’s thesis project will test how pre-synaptic lMAN inputs to RA regulate growth factors such as BDNF and
NT-3 to prevent the death of RA neurons. Read
more...
Haruhusa Okawa is studying the effects of the neurotrophin
family of growth factors on the neurophysiology of song-control
neurons. He is following up on work done in mammalian brain
showing that BDNF can elicit extremely rapid depolarization
of neurons – that is BDNF can act as a potent excitatory
neurotransmitter. His initial work has shown that applying
BDNF to lMAN in brain slices causes neurons to fire a train
of action potentials. One idea is that BDNF is released
at synapses to cause a strong depolarization. Read
more...
Michael Grammer is studying developmental changes in NMDA
receptors during vocal learning. In order to be activated,
NMDA receptors require both a ligand-binding signal (provided
by release of glutamate from pre-synaptic axons), and also
require that the post-synaptic cell be de-polarized (caused
by correlated activity of many pre-synaptic inputs, for
example). He has found that many synapses on lMAN neurons
have synapses that contain only NMDA receptors. We believe
such synapses may act as a selective filter that gate through
only highly correlated patterns of information, such as
auditory and motor feedback that match the tutor song that
the bird is learning to copy. Read
more...
Brie Altenau is testing structure-function relationships
of brain regions involved in vocal learning. Past work in
the lab has shown that lMAN is composed of two different
sub-divisions: a core of mostly large neurons and a surrounding
shell of large and small neurons. The axonal connections
of the core and shell sub-divisions form independent neural
pathways that traverse the forebrain in parallel. Brie is
lesioning the shell pathway and then studying the resultant
disruption in song behavior. We think the shell pathway
may be important during early stages of song learning for
evaluating the degree of error between the vocal sounds
the bird actually produces with the tutor song sounds he
is trying to produce. Read
more...
Another project in the lab focuses on the morphology of
individual axon terminals and how axonal connections between
different brain regions achieve the specificity required
to encode a specific song pattern during development. For
example, Soumya Iyengar showed that the projection from
lMAN to RA was exuberant at the onset of the sensitive period
for vocal learning in 20-day old birds, and that these axons
regressed substantially by 35 days to create the adult pattern
of organizational specificity in this pathway. Thus, it
is interesting that lMAN inputs to RA are greatest in number
at the onset of song learning, when RA neurons are dependent
on these inputs for survival. By 40 days, lMAN axons have
regressed, and RA neurons no longer require pre-synaptic
contact from these axons to survive. Future experiments
will study how growth factors influence neuron survival,
axon re-modeling, and the development of learned vocal behavior.
Read more...
For more information on projects in the lab, read the additional
descriptions of Past
Lab Members.
