preoptic area, MPOA. An intact MPOA is necessary for the expression of
sexual behavior in rodents, including ultrasonic vocalizations (reviewed by
Hart and Leedy 1985).
The MPOA serves as a direct target for gonadal steroid hormones;
neurons in the MPOA express receptors for gonadal steroids and their
metabolizing enzymes. Intracellular androgen and estrogen receptors are
concentrated in the MPOA in many species (rats: Handa et al. 1986;
McGinnis and Dreifuss 1989; Roselli et al. 1989; Simerly et al. 1990; Lauber
et al. 1991; gerbils: Commins and Yahr 1985; hamsters: Li et al. 1993; Woods
and Newman 1993), and aromatase is also concentrated in the nucleus as
measured by aromatase mRNA expression (Roselli et al. 1998). Thus, the
MPOA may act as a direct link between hormones and courtship vocal
behavior in rodents. Direct application of appropriate steroid hormones to
the MPOA, but not to other regions of the brain, restores vocal activity in
castrated males (Holman et al. 1991; Nyby et al. 1992; Matochik et al. 1994).
Moreover, OXT application to the MPOA results in rapid induction of
vocalizations in female hamsters (Floody et al. 1998). Thus, it is likely that
activating hormones, such as steroids and OXT, directly change the function of neurons in the MPOA to induce changes in vocal production.
What are the intracellular responses that follow hormone binding?
Recent studies reveal a causal relation between protein synthesis in the
MPOA and vocal production. By directly applying the protein synthesis
inhibitor anisomycin to the MPOA, McGinnis and Kahn (1997) demonstrated that T fails to increase vocal behavior in castrated males when
protein synthesis is inhibited in the MPOA. Determining which proteins are
synthesized in response to binding of T to its receptor, and how these proteins modulate neuronal function and morphology, will greatly enhance our
understanding of hormonal mediation of behavioral activation.
What subsequent changes in the MPOA are observed? Similar to findings obtained in songbirds, some structural modification of the MPOA is
observed in response to vocal activating hormones. For example, one
nucleus included in the MPOA, the sexually dimorphic area (SDA), shows
androgen-dependent changes in its volume in gerbils (Ulibarri and Yahr
1993). Interestingly, the size of SDA is lateralized in this species, and the
volume and the number of cells in the left nucleus, but not the right nucleus,
correlates well with rates of vocalization (Holman and Hutchison 1993;
Holman and Janus 1998). However, as we discussed in Section 3.1.1.3,
how these hormone-dependent anatomical modifications bring about the
expression of vocal behavior is not clear.
3.1.4. Fish
Some species of teleost fishes produce courtship vocalizations underwater.
Male weakfish, Cynoscion regalis, for example, produce a drumming sound
to attract gravid females (Connaughton and Taylor 1996). The expression
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A. Yamaguchi and D.B. Kelley
sexual behavior in rodents, including ultrasonic vocalizations (reviewed by
Hart and Leedy 1985).
The MPOA serves as a direct target for gonadal steroid hormones;
neurons in the MPOA express receptors for gonadal steroids and their
metabolizing enzymes. Intracellular androgen and estrogen receptors are
concentrated in the MPOA in many species (rats: Handa et al. 1986;
McGinnis and Dreifuss 1989; Roselli et al. 1989; Simerly et al. 1990; Lauber
et al. 1991; gerbils: Commins and Yahr 1985; hamsters: Li et al. 1993; Woods
and Newman 1993), and aromatase is also concentrated in the nucleus as
measured by aromatase mRNA expression (Roselli et al. 1998). Thus, the
MPOA may act as a direct link between hormones and courtship vocal
behavior in rodents. Direct application of appropriate steroid hormones to
the MPOA, but not to other regions of the brain, restores vocal activity in
castrated males (Holman et al. 1991; Nyby et al. 1992; Matochik et al. 1994).
Moreover, OXT application to the MPOA results in rapid induction of
vocalizations in female hamsters (Floody et al. 1998). Thus, it is likely that
activating hormones, such as steroids and OXT, directly change the function of neurons in the MPOA to induce changes in vocal production.
What are the intracellular responses that follow hormone binding?
Recent studies reveal a causal relation between protein synthesis in the
MPOA and vocal production. By directly applying the protein synthesis
inhibitor anisomycin to the MPOA, McGinnis and Kahn (1997) demonstrated that T fails to increase vocal behavior in castrated males when
protein synthesis is inhibited in the MPOA. Determining which proteins are
synthesized in response to binding of T to its receptor, and how these proteins modulate neuronal function and morphology, will greatly enhance our
understanding of hormonal mediation of behavioral activation.
What subsequent changes in the MPOA are observed? Similar to findings obtained in songbirds, some structural modification of the MPOA is
observed in response to vocal activating hormones. For example, one
nucleus included in the MPOA, the sexually dimorphic area (SDA), shows
androgen-dependent changes in its volume in gerbils (Ulibarri and Yahr
1993). Interestingly, the size of SDA is lateralized in this species, and the
volume and the number of cells in the left nucleus, but not the right nucleus,
correlates well with rates of vocalization (Holman and Hutchison 1993;
Holman and Janus 1998). However, as we discussed in Section 3.1.1.3,
how these hormone-dependent anatomical modifications bring about the
expression of vocal behavior is not clear.
3.1.4. Fish
Some species of teleost fishes produce courtship vocalizations underwater.
Male weakfish, Cynoscion regalis, for example, produce a drumming sound
to attract gravid females (Connaughton and Taylor 1996). The expression
296
A. Yamaguchi and D.B. Kelley