Title: Zebra Finch : The machine behind the mouth (or beak)
1Zebra Finch The machine behind the mouth (or
beak)
- General facts about Zebra Finches
- The common and widespread in Australia
(particularly drier areas), Timor and the Lesser
Sunda Islands. - Live year round in social flocks of up to 100 or
more birds. - Feed on grass seed and insects.
- One of the most common caged birds selectively
bread for a number of traits. - Considered to be one of the best model systems
for basic biomedical research of learning and
memory. - Also used as a model system to study many other
things (i.e. olfaction).
2Zebra Finch Song Unique because of its harmonic
characteristics and complexity
- The song of the zebra finch as of other birds can
be broken down into 3 hierarchical levels - Syllables Consist of the basic elements of song
for a species. They develop and crystallize
during song learning Some types of syllables - harmonic stacks
- frequency sweeps
- high-pitch notes
- broadband sounds
- Motifs Consist of a number of introductory notes
followed by sequences of syllables these
sequences are crystallized - Bouts Consist of a sequence of motifs that is
not necessarily stereotyped even in the adult - In adult birdsong, syllables may also be
demarcated by intervals of relative silence or
sharp frequency modulation changes
3Zebra Finches female
4Nuclei of the avian song learning and production
pathways
Blue (production/output pathway)
Red Anterior forebrain pathway (learning
pathway)
5Lateralization of birdsong production
Hypoglossal dominance
- White crown sparrows chaffinches and canaries are
left dominant - Severing the left hypoglossal nerve (XII cranial
nerve) has a more profound effect on song
production than severing of the right. - Zebra finches are right dominant.
- Swamp sparrows show no lateralization
6Lateralization of birdsong production
Hemispheric dominance
- Lesion experiments of HVc High Vocal Center
(Hyperstriatum Ventralis pars caudalis) in
canaries - Left HVc lesions produce profound disruption of
song production - Right HVc lesions have modest effects on song
production - Lesioning effects on either side were largely
reversible (recuperation takes months) - Requires auditory feedback.
- Bilateral lesions of HVc produce permanent and
profound loss of song production.
7Hormones control brain structure size controls
acquisition/singing behavior
Learning and production systems also change size,
complexity or protein profiles with changing
hormonal levels. There is evidence that song
production and learning are hormone-dependent.
Cells in the LMAN Area X RA nXIIts
accumulate testosterone or testosterone
metabolites these chemicals can directly
influence cell proliferation (neurogenesis) and
nuclei size
Male produced estrogen and melatonin are
necessary for normal development of HVC--RA
pathway.
- Known environmental mediators of hormone levels
- Social interactions territorial battles, sex,
child bearing, love (pair bonding) - Stress, diet parasite load
- Season light/dark cycles, temperature
- Weather barometric pressure, temperature
8Hormone levels mediate sexually related
differences in size of song production nuclei
Comparative analysis establishes that dimorphic
singing is related to relative brain dimorphism
9Hormones and neurogenesis The development of new
neurons
- One limitation of most central nervous system
neurons Once development is complete,
neurogenesis ends. - Notable exceptions in vertebrates
- bird song system which seasonally expand based on
neurogenesis. - olfactory receptor cells which regularly turn
over - GNRH cells in some fishes
- Testosterone flux in songbirds appears to
rekindle neurogenesis - Can result in as much as a doubling in structure
size/cell count - True in males and females
- Males either seasonally or by injections
- Greatest effect in juvenile vs. adult males
- Results in male song production out of season
- Females by injection (but to a lesser extent than
in males). - Injection of testosterone alone in females
affects song production in some species but not
others. - Thus in both males and females there is a direct
correlation between - Increased testosterone
- Increased cell proliferation in LMAN, Area X, RA
and nXIIts - Overall size of these areas
- Increased number of syllables produced
10Hormones and neurogenesis The development of new
neurons
- Estrogen
- Developing male gonads produce estrogen
- Blockade of estrogen during development in males
results in loss of song production as adults. - Is not reversible with testosterone injections as
adults - In females, estrogen injection during development
followed by testosterone injection as adults
results in song production. - Generally more effective than testosterone
injections alone - This tells us that estrogen mediates the
development of normal bird song centers in adults
and testosterone regulates the expression of song
in normal adults
11Its not just neurogenesis Gene expression in
song in the zebra finch learning pathway
Experiment Hypothesis learning is mediated in
the caudal part of the neostriatum (NCM) and of
the hyperstriatum ventrale (cHV).
- Procedures
- Zebra finch males were reared without their
father/song and exposed to a tape-recorded song
during the sensory period for song learning. - Placed in sound isolation cages for sensory motor
period. As sound production began recordings were
made of the juvenile song to confirm learning
from tutor. - At the start of the crystallization period, they
were re-exposed to the tutor song but in the dark
so that they would not sing. - Matched control experiments also used canary
song. - Other controls received the same treatment but
were not re-exposed to tutor song. - Measured expression of the protein products of
the immediate early genes egr-1 (ZENK) and c-fos
these are indicators of neural activity
12- Results
- Only males exposed to within species tutor song
showed increased staining for immediate early
genes egr-1 (ZENK) and c-fos in the cell bodies
of - NCM
- cHV
- Males did not show increased ZENK or c-fos in any
other conventional "song-production/learning
nuclei. - Subsequent studies show that even playback of
different species song will not induce ZENK or
c-fos
Photomicrographs of the zebra finch brain at the
level of the NCM, showing egr-1 (ZENK)-like
immunostaining. The sections are from a bird in
the control (a) and of a bird in the experimental
group (b) that both showed a high degree of song
learning. V, ventricle Hp, hippocampus.
13Counts of stained cells reveal relative
differences in ZENK c-fos between experimental
and controls
14Furthermore Strength of ZENK and c-fos staining
in NCM and cHV correlates to the number of song
elements that the birds had copied from the tutor
song
Stained nuclei per sq mm
ZENK
C-fos
Fraction shared song elements
Exp
Exp
Cont.
Cont.
Conclusion These results show localized neural
activation in response to tutor song exposure
that correlates with the strength of song
learning. This suggests that the memory for tutor
song is stored in NCM and cHV