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Zebra Finch : The machine behind the mouth (or beak)

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The song of the zebra finch as of other birds can be broken down into 3 hierarchical levels: ... Zebra finch males were reared without their father/song and ... – PowerPoint PPT presentation

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Title: Zebra Finch : The machine behind the mouth (or beak)


1
Zebra 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).

2
Zebra 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

3
Zebra Finches female
4
Nuclei of the avian song learning and production
pathways
Blue (production/output pathway)
Red Anterior forebrain pathway (learning
pathway)
5
Lateralization 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

6
Lateralization 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.

7
Hormones 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

8
Hormone levels mediate sexually related
differences in size of song production nuclei
Comparative analysis establishes that dimorphic
singing is related to relative brain dimorphism
9
Hormones 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

10
Hormones 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

11
Its 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.
13
Counts of stained cells reveal relative
differences in ZENK c-fos between experimental
and controls
14
Furthermore 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
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