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).

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: 1. 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

2. Motifs: Consist of a number of introductory notes followed by sequences of syllables: these sequences are crystallized

3. 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

Zebra Finches female

Blue: (production/output pathway) Red: Anterior forebrain pathway (learning pathway)

DLM: Dorso-Lateral division of the Medial thalamus

X: Area X of the paraolfactory lobe

LMAN: Lateral Magnocellular nucleus of the Anterior Neostriatum

MMAN: Medial nucleus Magnocelularis of the Anterior Neostriatum

NIf: interfacial nucleus of the neostriatum

cHV: Hyperstriatum Ventrale

HVc: High Vocal Center (Hyperstriatum Ventralis pars caudalis)

NCM: Neostriatum Caudo-Medial nucleus

NCM

RA: Robust nucleus of the Archistriatum

nXII: nucleus of the 12th cranial nerve

VL medulla: VentroLateral medulla Uva: nucleus Uvaeformis of the thalamusDM: Dorso-Medial subdivision of the intercollicular nucleus

AVT: Area Ventralis of Tsai

Nuclei of the avian song learning and production pathways

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

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.

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.

Hormones control brain structure size… controls acquisition/singing behavior

Cells in the… LMAN Area XRA 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

Hormone levels mediate sexually related differences in size of song production nuclei

Comparative analysis establishes that dimorphic singing is related to relative brain dimorphism

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

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

Hormones and neurogenesis: The development of new neurons

Its not just neurogenesis: Gene expression in song in the zebra finch learning pathway

Procedures:1. Zebra finch males were reared without their father/song and exposed to a tape-recorded

song during the sensory period for song learning. 2. 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.3. 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.1. Matched control experiments also used canary song.

4. Other controls received the same treatment but were not re-exposed to tutor song.5. Measured expression of the protein products of the immediate early genes egr-1 (ZENK)

and c-fos: these are indicators of neural activity

Experiment:Hypothesis: learning is mediated in the caudal part of the neostriatum (NCM) and of the hyperstriatum

ventrale (cHV).

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:1. NCM2. cHVMales 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.

Counts of stained cells reveal relative differences in ZENK & c-fos between experimental and controls

c-Fos ZENK

experimental

control

c-Fos ZENK

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

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

Sta

ine

d n

ucl

ei p

er

sq m

m

Fraction shared song elements

ZENKC-fos

Exp

Cont.

Exp

Cont.