Browsing by Subject "Optic tectum"
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Item An intrinsic CRF signaling pathway in the optic tectum(2012-08) Zhang, Sherry; Carr, James A.; Strauss, Richard E.; Held, Lewis I.; Gollahon, LaurenCorticotropin-releasing factor (CRF) is a 41 amino acid peptide that is best known as the principle hypophysiotropic hormone regulating the pituitary-adrenal axis during stress. CRF also regulates many stressors and anxiety related behaviors including food intake, and over-expression of CRF is thought to be the main causative agent in anxiety related eating disorders such as anorexia nervosa. Recent data collected in our laboratory using amphibian models indicate that, in addition to affecting appetite, CRF may modulate visual sensory pathways involved in detecting and responding to food. Here we examined the hypothesis that CRF directly modulates sensorimotor processing in the optic tectum of the African clawed frog, Xenopus laevis, the major site for integration of visually guided behavior in the non-mammalian brain. Previous studies in X. laevis using RT-PCR revealed that cells in the optic tectum express mRNA for CRF and the CRF R1 receptor but not the CRF R2 receptor. Furthermore, immunohistochemical studies by our laboratory indicate that CRF producing neurons are located strategically in tectal layers 6-8 to intercept retinal information. While these studies suggest that may be released by neurons in the tectum to act locally on CRF R1 receptors, whether or not CRF is actually released by tectal neurons and the existence of cognate CRF R1 receptors in the tectum has never been shown. In the current work, in vitro CRF-release studies revealed that both basal and depolarization-induced release of CRF, determined using a homologous radioimmunoassay, was greater from the optic tectum relative to the telencephalon, hypothalamus/midbrain or brainstem. These findings most likely reflected regional differences in the inhibitory regulation of CRF, as tectal content of CRF was actually lower than that of the hypothalamus in the two anuran species that have been studied to date. Depolarization-induced release of CRF from the optic tectum was calcium dependent. Radioligand binding studies indicated that specific binding of [125I-Tyr]-oCRF to tectal cell membranes could be displaced by the CRF R1 selective antagonists antalarmin or NBI 27914. CRF enhanced cAMP content in tectal slices in vitro, but the differences were not statistically significant. In order to figure out whether the control of CRF neurons is controlled by chemically defined pathways innervating the tectum we conducted in vitro studies with glutamate, the primary excitatory neurotransmitter in the tectum, neuropeptide Y (NPY) and the cholinergic agonist carbachol. The results showed that glutamate significantly inhibited basal and depolarization-induced CRF release from optic tectum. We conclude that the optic tectum possesses a CRF signaling system that may be involved in modulating communication between sensory and motor pathways involved in food intake.Item Characterization of CRF immunoreactive neurons in the anuran optic tectum(2008-12) Lustgarten, Jacob; Carr, James A.; Patino, Reynaldo; Collie, Nathan L.In amphibians, it has been determined that CRF has an affect on subcortical visual pathways that regulate prey capturing ability. The pathways targeted by CRF effects on visually guided feeding are unknown, but CRF-ir fibers have been reported in the superficial layers of the amphibian optic tectum that collect retinal innervation. These findings have led to the hypothesis that CRF may originate from retinal afferents that innervate the superficial layers of the tectum. A series of experiments were carried out in the cane toad (Bufo marinus) and the African clawed frog (Xenopus laevis) to examine an alternate hypothesis that CRF neurons intrinsic to the optic tectum may contribute to the CRF content innervation of this visual center in the amphibian brain. In both species, CRF-immunoreactive neurons were observed in tectal layers 6 and 7 with axons directed toward the more superficial layers of the tectum. To confirm the identity of CRF neurons in the tectum, I examined the expression of CRF and CRF related genes in the tectum by reverse transcriptase PCR using primers generated against sequences in the Xenopus genes for CRF, urocortin-1 (UCN-1), the CRF receptors CRF R1, CRF R2, CRF binding protein and the ribosomal protein, rpL8, as a housekeeping gene. RT-PCR showed the relative expression of CRF, CRF R1, CRF-R2, UCN-1, CRF-BP and rpL8 mRNA in four different brain regions of X. laevis. Results showed the forebrain to contain CRF, CRF R1 and R2, and rpL8. The hypothalamus and brain stem contained all 6 mRNA’s, and the absence of CRF R2 and CRF BP was shown in the optic tectum. Finally, we used a radioimmunoassay to investigate CRF peptide content in differential brain regions of the toad and the effects of unilateral eye ablation on CRF content in the tectum to discern the relative contribution of retinal CRF to tectal CRF content. There were no significant differences in CRF content between right and left optic tectum after unilateral eye ablation, suggesting that the majority of CRF in the tectum arises from intrinsic tectal CRF neurons. Therefore, we conclude that CRF in the optic tectum does not arise from retinal afferents that innervate the superficial layers of the tectum.