Carbonic Anhydrase Activation in the Extinction of Fear Conditioning in Rats

Abstract

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyse the interconversion between CO2 and bicarbonate as well as other hydrolytic reactions. At least 16 different alpha-CA isoforms were isolated in mammals, where these enzymes play crucial physiological roles such as pH regulation, CO2 and HCO3 transport, bone resorption, gluconeogenesis, ureagenesis and lipogenesis. In addition some studies suggest CAs can also influence the formation of fear memory. Importantly, autonomic fear responses such as freezing behavior, increased heart rate and respiration, can be reduced by presentation of the conditioned stimulus in the absence of the unconditioned stimulus, a process termed extinction. In this work, we expect the memory extinguishing process be more robust and last longer in animals treated with D-Phenylalanine, a carbonic anhydrase activator. For this, will be used male Wistar rats weighing 180-200g maintained in a thermoregulated environment. The animals will receive a intraperitoneal injection of saline or D-Phenylalanine and, 90 seconds later, they will be placed in a conditioning chamber with foot shock three times with 30 seconds of rest between them. Twenty-four hours after fear-conditioning, the rats will be placed on conditioning chamber for 30 minutes without shock and returned to the housing box to evaluate the extinction. Twenty-four hours after, the rats will be placed on conditioning chamber for 3 minutes without shock and returned to the housing box to evaluate retention. Seven and fifteen days after procedure, the animals will be placed again on conditioning chamber for 3 minutes without shock to measure the duration of behavior extinction. The duration of the freezing will be measured at each stage. Statistical analysis included the homogeneity test and multi-factor analysis of variance (ANOVA) followed by Duncan's Multiple Range test. The level of significance will be set at P < 0.05.