Where do hormones exert their effects? Many of the neurons in the auditory pathway accumulate gonadal steroids and express steroid receptors in
birds, frogs, and rodents (Arnold et al. 1976; Kelley et al. 1978; Kelley 1980;
Simerly et al. 1990; Balthazardt et al. 1992). For example, in Xenopus laevis,
neurons in the ventral striatum and anterior preoptic area that are considered to be auditory concentrate estrogen, whereas the TS contains receptors for both estrogens and androgens (Kelley 1980, 1981).
5.3. Beyond Acoustic Perception: Downstream
Effects of Signal Perception
Subsequent to perceiving acoustic signals, animals often show a variety of
physiological changes, including endocrine responses. For example, female
canaries lay more eggs when exposed to complex male songs than when
exposed to simpler songs (Kroodsma 1976).
Where do acoustic stimuli gain access to the neuroendocrine system that
controls sebsequent steroid secretion? Anatomical projections from the TS
to the ventral hypothalamus (VH) and APOA (the two anuran GnRH
centers) have been described in several frogs (Neary and Wilczynski 1986;
Allison and Wilczynski 1991). Auditory activity in VH and APOA varies
with the circannual mating cycle (Allison 1992). This kind of anatomical
pathway—from an auditory brain nucleus to one controlling GnRH
release—could provide a means for acoustic stimulation to influence
endocrine state. Endocrine state may then feed back on these same auditory regions.
6. Conclusion
It is clear that hormones play a critical role in triggering vocal production
as well as in the development of neural and muscular substrates for vocal
production. The acoustic perception of vocalizations is also likely to be
influenced by hormones, although more research in this area is needed. The
study of the neuroendocrine basis of acoustic communication provides an
excellent opportunity to understand the effect of neuromodulation on the
expression of discrete behavior. The future challenges that we face are
twofold. First, extensive catalogs of pairwise parameters (hormone as independent variable and behavior and physiological phenomena as dependent
variable) need to be integrated to make better sense of how hormonal
changes at physiological levels lead to the expression of behavior. Comparative approaches as well as bottom-up approaches—by focusing on
lower-order neurons with identified function—are expected to yield fruitful results. Second, we must recognize that the hormone–behavior relation
is not unidirectional; hormones not only regulate vocal production and perception of acoustic signals, but the very act of vocalizing and/or perceiving
vocalizations can modify the hormonal state. The endocrine basis of
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A. Yamaguchi and D.B. Kelley
birds, frogs, and rodents (Arnold et al. 1976; Kelley et al. 1978; Kelley 1980;
Simerly et al. 1990; Balthazardt et al. 1992). For example, in Xenopus laevis,
neurons in the ventral striatum and anterior preoptic area that are considered to be auditory concentrate estrogen, whereas the TS contains receptors for both estrogens and androgens (Kelley 1980, 1981).
5.3. Beyond Acoustic Perception: Downstream
Effects of Signal Perception
Subsequent to perceiving acoustic signals, animals often show a variety of
physiological changes, including endocrine responses. For example, female
canaries lay more eggs when exposed to complex male songs than when
exposed to simpler songs (Kroodsma 1976).
Where do acoustic stimuli gain access to the neuroendocrine system that
controls sebsequent steroid secretion? Anatomical projections from the TS
to the ventral hypothalamus (VH) and APOA (the two anuran GnRH
centers) have been described in several frogs (Neary and Wilczynski 1986;
Allison and Wilczynski 1991). Auditory activity in VH and APOA varies
with the circannual mating cycle (Allison 1992). This kind of anatomical
pathway—from an auditory brain nucleus to one controlling GnRH
release—could provide a means for acoustic stimulation to influence
endocrine state. Endocrine state may then feed back on these same auditory regions.
6. Conclusion
It is clear that hormones play a critical role in triggering vocal production
as well as in the development of neural and muscular substrates for vocal
production. The acoustic perception of vocalizations is also likely to be
influenced by hormones, although more research in this area is needed. The
study of the neuroendocrine basis of acoustic communication provides an
excellent opportunity to understand the effect of neuromodulation on the
expression of discrete behavior. The future challenges that we face are
twofold. First, extensive catalogs of pairwise parameters (hormone as independent variable and behavior and physiological phenomena as dependent
variable) need to be integrated to make better sense of how hormonal
changes at physiological levels lead to the expression of behavior. Comparative approaches as well as bottom-up approaches—by focusing on
lower-order neurons with identified function—are expected to yield fruitful results. Second, we must recognize that the hormone–behavior relation
is not unidirectional; hormones not only regulate vocal production and perception of acoustic signals, but the very act of vocalizing and/or perceiving
vocalizations can modify the hormonal state. The endocrine basis of
310
A. Yamaguchi and D.B. Kelley