Japanese quail as a model system for studying the neuroendocrine control of reproductive and social behaviors

Abstract

Japanese quail (Coturnix japonica; referred to simply as quail in this article) readily exhibit sexual behavior and related social behaviors in captive conditions and have therefore proven valuable for studies of how early social experience can shape adult mate preference and sexual behavior. Quail have also been used in sexual conditioning studies illustrating that natural stimuli predict successful reproduction via Pavlovian processes. In addition, they have proven to be a good model to study how variation in photoperiod regulates reproduction and how variation in gonadal steroid hormones controls sexual behavior. For example, studies have shown that testosterone activates male-typical behaviors after being metabolized into estrogenic and androgenic metabolites. A critical site of action for these metabolites is the medial preoptic nucleus (POM), which is larger in males than in females. The enzyme aromatase converts testosterone to estradiol and is enriched in the POM in a male-biased fashion. Quail studies were the first to show that this enzyme is regulated both relatively slowly via genomic actions of steroids and more quickly via phosphorylation. With this base of knowledge and the recent cloning of the entire genome of the closely related chicken, quail will be valuable for future studies connecting gene expression to sexual and social behaviors.

Figure 1

Schematic representation of the two-compartment cage used to observe and measure the learned social proximity response, a form of appetitive sexual behavior, in male Japanese quail (Coturnix japonica). The experimental male is introduced into the larger compartment (90 × 90 cm) that is separated by a sliding door from an adjacent smaller cage (20 × 26 cm) containing the stimulus female. A small vertical “window” (1 × 15 cm) that can be closed by an opaque swinging panel (not shown) is located in the middle of the sliding door and provides the male with a limited visual access to the female. When the window is open, the male can see the female through the window only if he stands in the test area in front of the window. Modified from Balthazart et al. (2004).

Figure 2

Acquisition and expression of the learned social proximity response in castrated male Japanese quail (Coturnix japonica) that were treated either with testosterone in silastic capsules (T) or testosterone in association with the aromatase inhibitor R76713 (T + R76713). In the first phase of the experiment (left panel), birds underwent eight training tests during which they were treated with T and learned the social proximity response indicative of appetitive sexual behavior (i.e., they spent increasing amounts of time in front of the window). During the second phase of the experiment (right panel), access to the female was provided to males only on the 5^th and 10^th test (E and J) and therefore cloacal contact movement (CCM) could be recorded only during these tests (results represented by bar graphs). The 8 pretests and 10 tests were performed over a period of 10 days each. The aromatase inhibitor, injected only during the second phase of the experiments, produced a significant decrease in both appetitive and consummatory aspects of male sexual behavior, supporting the claim that estrogenic metabolites of T are necessary to activate and maintain both aspects of male-typical sexual behavior (redrawn from data in Balthazart et al. 1997). SEM, standard error of the mean

Figure 3

Schematic view of the neural circuit controlling male sexual behavior in Japanese quail (Coturnix japonica). The aromatase-rich (black filling) medial preoptic nucleus (POM) and medial part of the bed nucleus of the stria terminalis (BSTM) are bidirectionally connected and critical to the activation of sexual behavior. Both receive inputs from the nucleus taeniae of the amygdala (TnA) that contains a small number of aromatase-expressing neurons (gray filling) and may relay olfactory information. We do not know how visual and auditory inputs that reach the telencephalon influence the POM but some visual information may reach the POM from the dorsal thalamus. The POM also receives dopaminergic inputs (thick lines) from dopaminergic cells (nuclei surrounded by a thick line) in the ventral tegmental area (VTA), the hypothalamus (Hyp.DA), and, to a lesser extent, the periaqueductal gray (PAG) and substantia nigra (SN). Outputs from POM that may contribute to the control of reproductive behaviors include a projection to the mesencephalic nucleus intercollicularis (ICo) and a projection specifically from the aromatase-positive neurons that reaches the PAG. In mammals the PAG projects to the nucleus paragigantocellularis (nPGi), which in turn projects to spinal motoneurons; this projection has not been identified in quail but motoneurons located in synsacral segments 7 to 9 (SS7-9) project directly to the muscles of the cloacal gland (Seiwert and Adkins-Regan 1998). Based on data from Absil et al. 2001a; Balthazart et al. 1994; Balthazart and Absil 1997; Carere et al. 2007; for more detail, Ball and Balthazart 2004.

Figure 4

Testosterone (T) increases the aromatase messenger RNA (ARO mRNA) concentrations, the number of aromatase-immunoreactive (ARO-ir) cells, and the aromatase activity in the preoptic area of castrate (CX) male Japanese quail (Coturnix japonica). These effects of T have approximately the same magnitude for the three dependent variables even if the effect increases slightly from the transcriptional level (mRNA; +372%) to the protein (ARO-ir cells; +497%) and to the enzymatic activity (+645%). One implication of these data is that aromatase activity may be regulated by mechanisms acting at the post-transcriptional level in addition to the major effect of the steroid on the transcription of the corresponding gene. Redrawn from data in Balthazart and Foidart (1993).

Figure 5

Rapid changes in aromatase activity (AA) in preoptic-hypothalamic explants of Japanese quail (Coturnix japonica) in which the cumulative enzymatic activity is measured every 5 minutes based on the release of tritiated water from tritiated androstenedione. Enzymatic activity was measured in paired hypothalamic explants incubated in vitro in which one explant was exposed for 10 minutes (between 20 [up arrow] and 30 [down arrow] min) (A) to thapsigargin, a lactone that mobilizes intracellular calcium ion (Ca²⁺) stores, (B) to kainate, or (C) to kainate associated or not with a preincubation with the non-NMDA glutamate antagonist NBQX. All data are expressed in percentage of basal release, defined as the activity during the period preceding the experimental manipulation (15–20 min). All data are means ± standard error of the mean (SEM). Redrawn from data in Balthazart et al. (2001, 2006).