dependent variables (i.e., molecular, cellular, or systemic properties) that
can change in response to changes in hormone levels. Determining which
of these physiological changes is critically responsible for behavioral change
is a steep challenge. Problems include identification of all of the neural and
somatic cells involved in vocal production and perception and the difficulty
of relating hormonally induced changes at one level of biological organization to another, higher level of organization (e.g., cellular to systems,
systems to behavioral levels). Some vocal communication systems, those of
frogs for example, appear less complex in this regard, especially in terms of
vocal production. In this chapter, we will first review the cellular changes
induced by different types of hormones and then extend our study to the
endocrine basis of behavior. Abbreviations used throughout the text are
listed in Table 6.1.
2. The Biological Effect of Hormones
2.1. Source of Hormones
Hormones are chemical messengers released from cells in a variety of secretory glands and the central nervous system. The types of hormones
discussed in this chapter are restricted to gonadal steroids and a few neurohypophysial hormones released from the pituitary gland (Fig. 6.1).
Gonadal steroids such as androgens and estrogens are primarily released
from the male testis and female ovary, respectively (Fig. 6.1A). The synthesis and release of these gonadal steroids are regulated by the plasma
levels of luetenizing hormone (LH) released from the adenohypophysis
(anterior pituitary; Fig. 6.1B). LH synthesis and secretion, in turn, are regulated by gonadotrophin-releasing hormones (GnRH) released from the
hypothalamus. Thus, the neuronal activity of GnRH-synthesizing neurons
in the hypothalamus determines the levels of LH released from the pituitary and eventually controls plasma levels of gonadal steroids.
Neuropeptides such as arginine vasopressin (AVP) or its nonmammalian
homolog, arginine vasotocin (AVT in birds, reptiles, amphibians, and fishes),
and oxytocin (OXT) are released from the neurohypophysis of the pituitary gland (posterior pituitary; Fig. 6.1C). These hormones are synthesized
by neurons whose cell bodies lie in two hypothalamic nuclei—the supraoptic and the paraventricular—and released from the axon terminals of
these cells in the neurohypophysis (Fig. 6.1C). The primary function of systemic AVT/AVP is to regulate osmolarity and blood pressure, and that of
OXT is to regulate milk release and uterine contraction. Recent studies
reveal that OXT- and AVT/AVP-synthesizing neurons project to a variety
of brain regions aside from the pituitary. Neurohormones secreted directly
in the brain may affect neuronal function to modify behavior in addition to
their more classical, systemic effects.
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A. Yamaguchi and D.B. Kelley
can change in response to changes in hormone levels. Determining which
of these physiological changes is critically responsible for behavioral change
is a steep challenge. Problems include identification of all of the neural and
somatic cells involved in vocal production and perception and the difficulty
of relating hormonally induced changes at one level of biological organization to another, higher level of organization (e.g., cellular to systems,
systems to behavioral levels). Some vocal communication systems, those of
frogs for example, appear less complex in this regard, especially in terms of
vocal production. In this chapter, we will first review the cellular changes
induced by different types of hormones and then extend our study to the
endocrine basis of behavior. Abbreviations used throughout the text are
listed in Table 6.1.
2. The Biological Effect of Hormones
2.1. Source of Hormones
Hormones are chemical messengers released from cells in a variety of secretory glands and the central nervous system. The types of hormones
discussed in this chapter are restricted to gonadal steroids and a few neurohypophysial hormones released from the pituitary gland (Fig. 6.1).
Gonadal steroids such as androgens and estrogens are primarily released
from the male testis and female ovary, respectively (Fig. 6.1A). The synthesis and release of these gonadal steroids are regulated by the plasma
levels of luetenizing hormone (LH) released from the adenohypophysis
(anterior pituitary; Fig. 6.1B). LH synthesis and secretion, in turn, are regulated by gonadotrophin-releasing hormones (GnRH) released from the
hypothalamus. Thus, the neuronal activity of GnRH-synthesizing neurons
in the hypothalamus determines the levels of LH released from the pituitary and eventually controls plasma levels of gonadal steroids.
Neuropeptides such as arginine vasopressin (AVP) or its nonmammalian
homolog, arginine vasotocin (AVT in birds, reptiles, amphibians, and fishes),
and oxytocin (OXT) are released from the neurohypophysis of the pituitary gland (posterior pituitary; Fig. 6.1C). These hormones are synthesized
by neurons whose cell bodies lie in two hypothalamic nuclei—the supraoptic and the paraventricular—and released from the axon terminals of
these cells in the neurohypophysis (Fig. 6.1C). The primary function of systemic AVT/AVP is to regulate osmolarity and blood pressure, and that of
OXT is to regulate milk release and uterine contraction. Recent studies
reveal that OXT- and AVT/AVP-synthesizing neurons project to a variety
of brain regions aside from the pituitary. Neurohormones secreted directly
in the brain may affect neuronal function to modify behavior in addition to
their more classical, systemic effects.
276
A. Yamaguchi and D.B. Kelley