Rainbow trout () exposed to acid-base challenges activate branchial mechanisms for the excretion of acid-base equivalents. Current models of branchial acid-base excretion in freshwater rainbow trout propose two main ionocyte types: the peanut lectin agglutinin-positive (PNA) mitochondrion-rich cell or ionocyte is believed to secrete HCO in exchange for Cl, whereas H secretion is thought to occur across PNA ionocytes in exchange for Na Both HCO and H are supplied by intracellular hydration of CO catalysed by cytosolic carbonic anhydrase (CAc). Immunohistochemical approaches revealed that under control conditions, CAc was detectable in 92.3±1.0% (=11) of PNA ionocytes, and the abundance of PNA ionocytes increased in response to systemic acidosis elicited by 72 h exposure to water of low pH (nominally pH 4.5), hypercapnia (1% CO, nominally 7.6 Torr) or hyperoxia (achieved by gassing water with pure O), as did the abundance of PNA ionocytes that exhibited immunofluorescence for CAc. However, just 4.3±0.6% (=11) of PNA ionocytes expressed detectable CAc under control conditions. Marked increases in the abundance of CAc-positive PNA ionocytes were detected following exposure of trout to a base load via recovery from hypercapnia or base infusion (72 h infusion with 140 mmol l NaHCO). The percentage of CAc-positive PNA ionocytes also was increased in trout treated with cortisol (10 mg kg hydrocortisone 21-hemisuccinate daily for 7 days). These results suggest that regulation of CA within PNA ionocytes and/or the abundance of CAc-positive PNA ionocytes plays a role in activating base secretion in response to systemic alkalosis.

Internet social networking devices like Twitter have increased in popularity between 2005 and 2010. Twitter is unique because of the brevity in which users interact with other users; Twitter messages, or tweets, are limited to 140 characters. Often in those messages are hyperlinks to other Web sites. Even when people are connected to Twitter, they feel compelled to click the hyperlink and navigate to another page. This thesis employs an experiment to determine what motivates Twitter users to click the hyperlinks in tweets. The research conducted for this study looked at motivation, the uses and gratifications theory, and the matching theory of functionalism. All three areas were tied to the Internet and social networks.