Claustrum of the short‐tailed fruit bat, : Alignment of cellular orientation and functional connectivityCarollia perspicillata: Alignment of cellular orientation and functional connectivity

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Carollia perspicillata belongs to the New World fruit bats also known as microbats. Mistakenly, bats are often thought of as rodents. In fact, the Russian (летучая мышь) and German (Fledermaus) words for bat translate as “flying mouse.” However, bats are more closely related to horses, dolphins, and cows (O'Leary et al., 2013; Welker et al., 2015).
Carollia weighs on average about 18 g. As all microbats, it orients primarily by echolocation (Hartley and Suthers, 1987; Esser and Eiermann, 1999; Koay et al., 2003; Heffner et al., 2007; Brinklov et al., 2011), generating sonar pulses in the larynx. Carollia also has excellent vision (Heffner et al., 2007; Butz et al., 2015) and olfaction (Parolin et al., 2015).
Carollia is native to the warm climates of Central and South America. Our colony derives from wild‐caught animals from Trinidad. It is exclusively frugivorous, with opportunistic nectar feeding. It does not hibernate, but is capable of torpor (Audet and Thomas, 1997), specifically in response to food shortage. Carollia can live in captivity for more than a decade (Rasweiler and Badwaik, 1996, 1997), making it an interesting model for aging studies. Among other valuable features, Carollia has a full menstrual cycle (Rasweiler et al., 2010, 2011), unlike the estrus cycles of rats and mice.
While not related to the mouse, the brain of Carollia is similar in size to the mouse brain (Scalia et al., 2013). Several key neuroanatomical features stand out. The hippocampus runs in a dorsoventral axis in Carollia, as opposed to a principal rostrocaudal axis in rats and mice. Carollia's striatum has a distinct caudate nucleus and putamen separated from each other by the internal capsule and bounded laterally by an obvious external capsule. In primate brains, the claustrum is a slender subcortical region located between the external and extreme capsules, and, in lower mammalian brains, the claustrum is located superficial to the external capsule, just beneath the neocortex (Kowianski et al., 1999) (for reviews: Sherk, 1986; Edelstein and Denaro, 2004; Baizer et al., 2014; Mathur, 2014; Smythies et al., 2014; Deutch and Mathur, 2015; Goll et al., 2015). Perhaps most striking are the very large relative sizes of the bat amygdala and claustrum when compared with rats and mice on the basis of available brain atlases. In Carollia, the claustrum, along its short axis, is about ½ of the thickness of the overlying neocortex (Scalia et al., 2013). By contrast, the claustrum's short axis is ⅓ to ¼ of the thickness of the overlying neocortex in rat (Paxinos and Watson, 2007) and mouse (Paxinos and Franklin, 2004).
We sought to define the claustrum of Carollia using latexin immunohistochemistry as we have done in the rat (Orman, 2009; 2015). Arimatsu and colleagues showed in the 1990s (Arimatsu, 1994; Hatanaka et al., 1994; Arimatsu et al., 1999a, 2009), that latexin, an endogenous inhibitor of metallocarboxypeptidases (Pallares et al., 2005; Jin et al., 2006), is a distinctive marker for several brain regions, including cells of the lateral neocortex and claustrum. In the rat, we used latexin immunohistochemistry to define the boundaries of the claustrum, where a densely stained, “egg”‐shaped principal region (Orman, 2009, 2015) overlaps with a region that is universally accepted to constitute the claustrum on the basis of several other markers (reviewed in Mathur, 2014; Deutch and Mathur, 2015).
Bats have been shown to differ from rodents in the activity of specific brain regions and circuits. Studies of place, head‐direction, and grid cells in navigational behavior have shown clear coding of three dimensions in bats (Yartsev and Ulanovsky, 2013), but only variations of two‐dimensional coding in rodents (Stackman et al., 2000; Hayman et al.
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