Neural Distribution of Nonapeptide Receptors in Two Species of Songbird Open Access
Leung, Cary Hoi-Wah (2009)
Published
Abstract
Abstract
Neural Distribution of Nonapeptide Receptors in Two Species of
Songbird
By
Cary H. Leung
Vasotocin (VT) and its mammalian homologue, vasopressin, modulate
many social
behaviors across vertebrate groups. In songbirds, the effects of
centrally administered VT
vary according to species, which may reflect species-specific
distributions of VT binding
sites. Using two model songbird species, the white-throated sparrow
( Zonotrichia
albicollis) and zebra finch ( Taeniopygia guttata), I
labeled putative VT receptors using
two radioligands, an iodinated vasotocin analog ([125I]OVTA) and a
V1a receptor
antagonist ([125I]LVA). [125I]OVTA labeled receptors throughout the
telencephalon,
diencephalon, midbrain and brainstem, with a similar distribution
in both species. In
contrast, the binding of [125I]LVA was restricted to the septal
area, dorsal arcopallium,
and the optic tectum in sparrow, and was essentially non-detectable
in zebra finch.
Competitive binding assays in the lateral septum showed that both
ligands were
effectively displaced by both VT and a related nonapeptide,
mesotocin (MT), showing
that these radioligands, which were developed to label mammalian
nonapeptide receptors,
label at least one population of related receptors in songbirds.
Because multiple receptor
subtypes are expressed in the avian brain, I developed and used
species-specific
riboprobes to show the neural distribution of three VT receptor
subtypes, VT1, VT3 and
VT4 in white-throated sparrow and zebra finch. I found that there
were similarities in
distribution between species, and that the expression of each
receptor subtype overlapped
with one another in several brain regions. In sparrow, VT3 and VT4
were widely
distributed in the brain, whereas VT1 distribution was more
limited. In zebra finch, all
three receptors were widely distributed in the brain. Based on the
predicted amino acid
sequences for these receptors, VT1 and VT4 likely bind with greater
affinity to VT than
MT, and VT3 likely binds with greater affinity to MT than VT.
Because testosterone (T)
is known to have a modulatory effect on the VT system, I tested for
an effect of T on VT
receptor expression in white-throated sparrow. There was no effect
of T on VT receptor
expression although plasma T was elevated in T treated birds and T
treated birds sang
more than control birds. No relationship between behavior and
receptor expression,
however, was detected. Furthermore, sex differences in VT receptor
expression were not
detected in either white-throated sparrow or zebra finch.
Table of Contents
Table of Contents
General Introduction
1
Literature Cited
10
Figure Legends
18
Chapter One: Neural Distribution of Nonapeptide Receptors in
Two
21
Species of Songbird
Abstract
22
Introduction
23
Materials and Methods
26
Results
30
Discussion
35
Literature Cited
42
Tables
51
Figure Legends
54
Chapter Two: Neural Distribution of Nonapeptide Receptor mRNA in
Two
62
Species of Songbird
Abstract
63
Introduction
64
Materials and Methods
66
Results
74
Discussion
81
Literature Cited
89
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