the Cowbird Hippocampus Using Substance P to define the ...
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Neural Adaptations for Brood Parasitism
Using Substance P to define the borders ofthe Cowbird Hippocampus
?
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Brood Parasites are Brainy Birds
Brood Parasitism
A form of breeding in which the parasite lays its eggs in thenests of another species, the host.
Special Demands on Spatial Memory
� patrol the home range, identify nests and remember thelocation and status of each potential site.
Do these spatial memory demands give rise to specificadaptations in the brains of brood parasites ?
� update this information after each egg is laid - book-keeping.
Parasites
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6 species inhabit the American continent
5 species are OBLIGATE BROOD PARASITES
The Bay-winged Cowbird non-parasitic
The Screaming Cowbird specialist
single host: the Bay-winged Cowbirdboth males and females target host nests
The Shiny Cowbirdgeneralist
over 200 different host speciesSexually dimorphic
Females alone perform the parasitic behaviour
The Cowbirds
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coronal section
� a brain structure involved in the processing of spatialmemory.
� lesions disrupt the learning of locations and landmarks.
avian brain - dorsal view
hippocampal region
The Avian Hippocampus
� essential for tasks such as spatial navigation and food-hoarding.
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� the parasitic cowbirds have larger hippocampal formationsthan the non-parasitic species.
Seasonal hippocampal enlargement in parasites
* in collaboration with JC Reboreda and NS Clayton
Our neuroanatomical studies* comparing hippocampal volumesin the three cowbird species show that:
During the Breeding Season
� in the dimorphic species where only the female performs the parasitic behaviour only the female has the larger hippocampus .
These differences are not seen outside the breeding season
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The Cresyl Violet stain gives only an approximatedemarcation for the lateral boundary of the hippocampus
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Substance P (SP)
� a neuropeptide found in the central nervous system of manyvertebrates (mammals, reptiles, fish,birds)
SP is thought to play a role in promoting and facilitatingmemory and learning processes in vivo:
� administration of SP has been shown to affect memory andlearning in mammals and fish :
• within 5 hours post-trial SP promotes memory consolidationand longer retention of learning.
• during conditioning trials SP acts as a reinforcer.
� chronic SP administration reverses age-related memorydeficits in rats
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Gould et al. (2001) investigated the distribution of SP in 4species of song bird:
A food-hoarder (Black-capped chickadee) was compared tothree non-storers (blue tit, great tit, dark eyed junco).
The relative volume of Spm was larger in the storer than in thethree other species.
SP-rich regions in the Songbird hippocampal region
SP and the hippocampus in food-storing birds
Hippocampus
“Lateral SP field”
“Medial SP field”
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“Medial SP field”
“Lateral SP field”
Hippocampus
SP areas around the Cowbird hippocampus
Is the medial SP field larger in brood parasites?
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A Substance P-rich region forms a defined lateral boundary forthe avian hippocampus
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What are these punctate particleswithin this novel, well-defined regionof the cowbird hippocampus?
cells? fibres? terminals?
A population of SP+ particles in the cowbird hippocampus
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Illustrating the outline of neurones within the hippocampus
Nomarski differential interference microscopy
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The SP rich terminals densely encapsulate neuronal cell bodies
SP +ve pre-synaptic boutons contacting neurones
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Synaptic Boutons
Synapses• the electro-chemical connections between neurones
• plasticity- a mechanism for encodinginformation in memory and learningprocesses?
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A qualitative difference in the density and size of SPterminals
Brain Observations
16
74 r
92 r
68 v
70 v
64 v
95 r
69 r
91 r
terminals are faint and small
Medium intensity of signal
terminals are faint and small
terminals are darkly stained and large
terminals are darkly stained and large
terminals are darkly stained and large
terminals are faint and small
terminals are small and widespread
terminals are faint and small
Are these differences related to Brood Parasitism?
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Conclusions and Future Work
• Description of a novel regional subdivision within the avianhippocampus.
• Differences in density and size of Substance P terminals couldbe related to specific adaptations for Brood Parasitism.
• What is the significance of Substance P circuits within theavian hippocampus in the context of learning and memory?
Bridging the gap between ecological, behavioural andneuro-anatomical approaches to memory and learning.
• Future work: Immunohistochemistry, Golgi Staining andElectron Microscopy to investigate the structure of neuronalconnections and neural circuits within the cowbird hippocampus.
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AcknowledgementsThanks to:
Juan Carlos Reboreda (University of Buenos Aires) Jon Erichsen (Cardiff University)
Jenny Corrigan (Oxford).
Funding: The Wellcome Trust and Magdalen College Oxford