The ventromedial hypothalamic nucleus in the zebra finch (: Afferent and efferent projections in relation to the control of reproductive behaviorTaeniopygia guttata: Afferent and efferent projections in relation to the control of reproductive behavior): Afferent and efferent projections in relation to the control of reproductive behavior
The ventromedial hypothalamic nucleus (VMH) plays a key role in mammalian feeding and female reproductive behaviors. However, in comparison to our knowledge of the structure, hodology, and function of this nucleus in both mammals and reptiles (e.g., Bruce & Neary, 1995a; Canteras, Simerly, & Swanson, 1994; Flanagan‐Cato, 2011; Holder et al., 2010; Johnson, Corini, Ball, & McKewan, 1989; Krieger, Conrad, & Pfaff, 1979; Lanuza, Font, Martinez‐Marcos, & Martinez‐Garcia, 1997; Luiten & Room, 1980; Rubin & Barfield, 1980; Saper, Swanson, & Cowan, 1976), our knowledge of the comparable VMH nucleus in birds (also known as the posteromedial hypothalamic nucleus (PMH) (Karten & Hodos, 1967; Kuenzel & Van Tienhoven, 1982; Shen, Schlinger, Campagnoni, & Arnold, 1995) is meager. As in mammals, an involvement in satiety was originally suggested by the effects of VMH lesions in a songbird (Kuenzel, 1974) and in geese (Felix, Bereziat, & Auffray, 1981), and an involvement in female reproductive behavior was shown in ring doves by the effects of VMH implants of estradiol, which elicited the copulation solicitation display (CSD) (Gibson & Cheng, 1979). The avian CSD is analogous to lordosis in rodents, for which the VMH in female rats is considered necessary for its evocation (Kow & Pfaff, 1998; Pfaff & Sakuma, 1979). Thus, as in mammals, VMH in birds has been implicated in both feeding (but see Kuenzel, 2015) and reproductive functions. Further support for the latter has been supplied for doves (Cheng & Zuo, 1994; Durand, Tepper, & Cheng, 1992) and Bengalese finches (Zeng, Zhang, Peng, & Zuo, 2004), in which there is a projection to VMH from periovoidal nuclei (the Ov shell). In turn, the periovoidal nuclei receive an auditory input from the interface of the midbrain intercollicular nucleus (ICo) and nucleus mesencephalicus lateralis, pars dorsalis (MLd), the avian equivalent of the central nucleus of the mammalian inferior colliculus, which projects specifically to nucleus ovoidalis (Ov; Akesson, De Lanerolle, & Cheng, 1987; Durand et al., 1992; Karten, 1967). VMH then projects back upon ICo (Berk & Butler, 1981; Cheng, Akesson, & de Lanerolle, 1987) to complete a loop that in female doves has been suggested to mediate auditory self‐stimulation important for the neuroendocrine control of ovulation (Cheng & Durand, 2004; Cheng & Zuo, 1994).
In addition, in doves and starlings VMH receives a distinct projection from nucleus taeniae of the amygdala (TnA) (Cheng, Chaiken, Zuo, & Miller, 1999) via the hypothalamic component of the occipito‐mesencephalic tract (HOM; Zeier & Karten, 1971). TnA is a medial arcopallial nucleus considered on connectional, steroid accumulation, and sexual behavioral grounds to be comparable to the medial nucleus of the amygdala of mammals (Absil, Baquenier, Balthazart, & Ball, 2002; Ikebuchi, Hasegawa, & Bischof, 2009; Martinez‐Vargas, Stumpf, & Sar, 1976; Patzke, Manns, & Güntürkün, 2011; Reiner et al., 2004; Thompson, Goodson, Ruscio, & Adkins‐Regan, 1998; Yamamoto, Sun, Wang, & Reiner, 2005). However, TnA is only one nucleus within the medial arcopallium of birds, but injections of anterograde tracers into other medial components of the arcopallium in chicks, ducks, and pigeons have either not resulted in a terminal field within the medial hypothalamus (Davies, Csillag, Szekely, & Kabai, 1997; Dubbeldam, den Boer‐Visser, & Bout, 1997), or have produced such a terminal field, but which has not been confirmed retrogradely (Atoji & Wild, 2009). Thus, in the pigeon, the exact location and distribution of medial arcopallial neurons projecting to the medial hypothalamus in general and PMH in particular is unknown. In the present study we used a combination of aromatase immunohistochemistry—which previously has defined “VMH” in the zebra finch (Balthazart et al., 1996; Saldanha et al.