Browsing by Author "Shekhar, Anantha, 1957-"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Elucidating mechanisms that lead to persistent anxiety-like behavior in rats following repeated activation of corticotropin-releasing factor receptors in the basolateral amygdala
    (2012-03-16) Gaskins, Denise; Shekhar, Anantha, 1957-; Harris, Robert A. (Robert Allison), 1939-; Hingtgen, Cynthia M., 1966-; Truitt, William A.
    Anxiety disorders are estimated to impact 1 in 4 individuals within their lifetime. For some individuals, repeated episodes of the stress response leads to pathological anxiety and depression. The stress response is linked to increased levels of corticotropin-releasing factor (CRF) in the basolateral nucleus of the amygdala (BLA), a putative site for regulating anxiety and associative processes related to aversive emotional memories, and activation of CRF receptors in the BLA of rats produces anxiety-like behavior. Mimicking repeated episodes of the stress response, sub-anxiogenic doses of urocortin 1 (Ucn1), a CRF receptor agonist, are microinjected into the BLA of rats for five consecutive days, a procedure called priming. This results in 1) behavioral sensitization, such that a previously non-efficacious dose of Ucn1 will elicit anxiety-like response after the 3rd injection and 2) the development of a persistent anxiety-like phenotype that lasts at least five weeks after the last injection without any further treatment. Therefore, the purpose of this thesis was to identify mechanisms involved in the Ucn1-priming-induced anxiogenesis. The first a set of experiments revealed that the anxiety-like behavior was not due to aversive conditioning to the context or partner cues of the testing environment. Next, Ucn1-priming-induced gene expression changes in the BLA were identified: mRNA expression for Sst2, Sst4, Chrna4, Chrma4, and Gabrr1 was significantly reduced in Ucn1-primed compared to Vehicle-primed rats. Of these, Sst2 emerged as the primary receptor of interest. Subsequent studies found that antagonizing the Sstr2 resulted in anxiety-like behavior and activation of Sstr2 blocked acute Ucn1-induced anxiety-like responses. Furthermore, pretreatment with a Sstr2 agonist delayed the behavioral sensitization observed in Ucn1-induced priming but did not stop the development of persistent anxiety-like behavior or the Ucn1-priming-induced decrease in the Sstr2 mRNA. These results suggest that the decrease in Sstr2 mRNA is associated with the expression of persistent anxiety-like behavior but dissociated from the mechanisms causing the behavioral sensitization. Pharmacological studies confirmed that a reduced Sstr2 mediated effect in the BLA is likely to play a role in persistent anxiety and should be investigated further.
  • Thumbnail Image
    Item
    Nf1-DEFICIENT MICE DISPLAY SOCIAL LEARNING DEFICITS THAT ARE RESCUED BY THE DELETION OF PAK1 GENE
    (2011-03-16) Spence, John Paul; Shekhar, Anantha, 1957-; Clapp, D. Wade; Johnson, Philip L.; Yang, Feng-Chun
    Neurofibromatosis type 1 (NF1) is a neurocutaneous disorder that affects roughly 1 in 3500 individuals. In addition to physical features (e.g., neurofibromas), developmental disorders are also common that can affect cognition, learning, attention and social function. The NF1 gene encodes neurofibromin, a GTPase activating protein (GAP)-like protein that negatively regulates Ras GTPase activation. Mutation at the NF1 locus increases the output of MAPK and PI3K signal transduction from the cellular membrane to the nucleus. Similar to humans, Nf1+/- mice show spatial learning abnormalities that are potentially correlated with increases in GABA-mediated inhibition and deficits in long-term potentiation in the hippocampus. Here, we demonstrate for the first time that Nf1+/- mice exhibit a selective loss of long-term social learning / memory and increased GABAergic inhibition in the basolateral amygdala, a critical brain region for regulating social behaviors. Next, utilizing a genetic intercross, we show that the co-deletion of p21-activated kinase type 1 (Pak1-/-), which positively regulates MAPK activation, restores Nf1+/--dependent MAPK hyperactivation in neurons cultured from the frontal cortex. We found that the co-deletion of Pak1 in Nf1+/- mice (Nf1+/- / Pak1-/-) also restores the deficits in long-term social learning / memory seen in Nf1+/- mice and normalizes the increases in GABA-mediated inhibition in the BLA, as compared to Nf1+/- mice. Together, these findings establish a role for Nf1 and Pak1 genes in the regulation of social learning in Nf1-deficient mice. Furthermore, proteomic studies identify dysregulation of F-actin and microtubule dynamics in the prefrontal cortex, and implicate proteins associated with vesicular release as well as neurite formation and outgrowth (e.g., LSAMP, STXBP1, DREB). In the BLA, disintegrin and metalloproteinase domain-containing protein 22 (ADAM22) was identified, and ADAM22 may play a role in the regulation of AMPA receptors. Finally, due to the increased co-occurrence of NF1 and autism, these findings may also have important implications for the pathology and treatment of NF1-related social deficits and some forms of autism.