Complex brains and behaviors have occurred repeatedly within vertebrate classes throughout evolution. What adaptive pressures drive such changes? Both environmental and social features have been implicated in the expansion of select brain structures, particularly the telencephalon. East African cichlid fishes provide a superb opportunity to analyze the social and ecological correlates of neural phenotypes and their evolution. As a result of rapid, recent, and repeated radiations, there are hundreds of closely-related species available for study, with an astonishing diversity in habitat preferences and social behaviors. In this study, we present quantitative ecological, social, and neuroanatomical data for closely-related species from the (monophyletic) Ectodini clade of Lake Tanganyikan cichlid fish. The species differed either in habitat preference or social organization. After accounting for phylogeny with independent contrasts, we find that environmental and social factors differentially affect the brain, with environmental factors showing a broader effect on a range of brain structures compared to social factors. Five out of seven of the brain measures show a relationship with habitat measures. Brain size and cerebellar size are positively correlated with species number (which is correlated with habitat complexity); the medulla and olfactory bulb are negatively correlated with habitat measures. The telencephalon shows a trend toward a positive correlation with rock size. In contrast, only two brain structures, the telencephalon and hypothalamus, are correlated with social factors. Telencephalic size is larger in monogamous species compared to polygamous species, as well as with increased numbers of individuals; monogamy is also associated with smaller hypothalamic size. Our results suggest that selection or drift can act independently on different brain regions as the species diverge into different habitats and social systems.

Increased intraocular pressure (IOP) leads, by an unknown mechanism, to apoptotic retinal ganglion cell (RGC) death in glaucoma. We now report cleavage of the autoinhibitory domain of the protein phosphatase calcineurin (CaN) in two rodent models of increased IOP. Cleaved CaN was not detected in rat or mouse eyes with normal IOP. In in vitro systems, this constitutively active cleaved form of CaN has been reported to lead to apoptosis via dephosphorylation of the proapoptotic Bcl-2 family member, Bad. In a rat model of glaucoma, we similarly detect increased Bad dephosphorylation, increased cytoplasmic cytochrome c (cyt c), and RGC death. Oral treatment of rats with increased IOP with the CaN inhibitor FK506 led to a reduction in Bad dephosphorylation and cyt c release. In accord with these biochemical results, we observed a marked increase in both RGC survival and optic nerve preservation. These data are consistent with a CaN-mediated mechanism of increased IOP toxicity. CaN cleavage was not observed at any time after optic nerve crush, suggesting that axon damage alone is insufficient to trigger cleavage. These findings implicate this mechanism of CaN activation in a chronic neurodegenerative disease. These data demonstrate that increased IOP leads to the initiation of a CaN-mediated mitochondrial apoptotic pathway in glaucoma and support neuroprotective strategies for this blinding disease.retina ͉ optic nerve ͉ apoptosis

In glaucoma, retinal ganglion cells (RGCs) die by apoptosis, generally attributed to an elevated intraocular pressure (IOP). We now describe the impact of elevated IOP in the rat on expression of caspase 8 and caspase 9, initiators of the extrinsic and intrinsic caspase cascades, respectively. Activation of both caspases was demonstrated by the presence of cleaved forms of the caspases and the detection of cleaved Bid and PARP, downstream consequences of caspase activation. Surprisingly, the absolute level of procaspase 9 was also elevated after 10 days of increased IOP. To examine the cause of increased levels of the procaspase, we used laser capture microdissection to capture Fluorogold back-labeled RGCs and real-time polymerase chain reaction to measure mRNA changes of initiating caspases. The mRNA levels of both caspase 8 and caspase 9 were increased specifically in RGCs. These data suggest that elevated IOP activates a transcriptional up-regulation and activation of initiating caspases in RGCs and triggers apoptosis through both extrinsic and intrinsic caspase cascades. The pathological hallmark of glaucoma is atrophy of the optic nerve associated with retinal ganglion cell (RGC) death, leading to vision loss and blindness throughout decades. The major risk factor for developing glaucoma is increased intraocular pressure (IOP). RGCs have been shown to die by apoptosis in both human 1,2 and animal models 3-5 although the exact mechanism(s) by which RGC apoptosis occurs in response to increased IOP is unknown. Two distinct pathways of upstream, initiating caspases can each begin a cascade that leads to activation of downstream effector caspases resulting in apoptosis. 6 Caspase 8 is the initial caspase activated by cleavage of procaspase 8 to the active form in response to extrinsic cell signaling, such as binding of receptors with death domains that interact with Fas-associated death domains (FADD). 7 The mitochondrial stress pathway on the other hand, begins with the release of cytochrome c from mitochondria, which then interacts with Apaf-1, causing cleavage and activation of caspase 9. 8 The extrinsic pathway (through the death receptors) and the intrinsic pathway (through the mitochondria) for apoptosis are capable of operating independently leading to the activation of downstream effector caspases, caspase 3, 6, and 7. Poly (ADP-ribose) polymerase (PARP) is a 116-kd nuclear protein that is involved in the repair of DNA and in differentiation and in chromatin structure formation. During the late stages of apoptosis, downstream caspases, such as caspase 3, cleave PARP to yield 85-kd and 25-kd fragments. 9 It is unclear which of the specific upstream molecular events occur in the retina under conditions of elevated IOP. In one report, caspase 8 was shown by immunohistochemistry to be activated in RGCs in experimental glaucoma in the rat. 10 In another report, we showed that caspase 9 is activated by immunohistochemistry in RGCs and by Western blot analysis under conditions of elevated IOP also in the rat. ...