Nitric oxide may underlie learned fear in the elevated T-maze

• Published in: Brain research bulletin 2001-05, Vol.55 (1), p.37-42
• Main Authors: Calixto, Ana Valquı́ria, Vandresen, Nadine, de Nucci, Gilberto, Moreno, Heitor, Faria, Moacir Serralvo
• Format: Article
• Language: English
• Subjects: Animals; Anti-Anxiety Agents - pharmacology; Anxiety; Avoidance Learning - drug effects; Avoidance Learning - physiology; Behavior, Animal - drug effects; Behavior, Animal - physiology; Behavioral psychophysiology; Biological and medical sciences; Blood Pressure - drug effects; Blood Pressure - physiology; Brain - metabolism; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Fear - drug effects; Fear - physiology; Fundamental and applied biological sciences. Psychology; Hypertension; L-Arginine; L-NAME; Learning; Male; Maze Learning - drug effects; Maze Learning - physiology; Midazolam - pharmacology; Miscellaneous; N(G)-nitro-D-Arginine methyl ester; N(G)-nitro-L-Arginine methyl ester; N@uG-nitro-D-Arginine methyl ester; N@uG-nitro-L-Arginine methyl ester; NG-Nitroarginine Methyl Ester - pharmacology; Nitric Oxide - antagonists & inhibitors; Nitric Oxide - metabolism; Nitric Oxide Synthase - antagonists & inhibitors; Nitric Oxide Synthase - metabolism; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rats; Rats, Wistar
• ISSN: 0361-9230; 1873-2747
• DOI: 10.1016/S0361-9230(01)00480-4

The present study evaluated the role of nitric oxide (NO) in learned and innate fear in rats submitted to the elevated T-maze (ETM). Learned and innate fear were evaluated through the inhibitory avoidance and escape behaviour from the open arms, respectively. Rats treated with the inhibitor of NO synthesis N ω-nitro-L-Arginine methyl ester (L-NAME; 5, 10, and 50 mg · kg −1) were able to learn the inhibitory avoidance. However, L-NAME (50 mg · kg −1), but not its inert isomer N ω-nitro-D-arginine methyl ester (D-NAME, 50 mg · kg −1), impaired the inhibitory avoidance 2 with no change in the baseline values, thus suggesting an anxiolytic-like effect without locomotor impairment. All treatments with L-NAME were able to induce increased mean arterial pressure (MAP), measured indirectly through the animal’s tail. The treatment with L-NAME (5 and 10 mg · kg −1) failed to induce anxiolysis but significantly increased the MAP of the animals, which indicates that hypertension per se, did not underlie anxiolysis induced by L-NAME. L-Arginine, the precursor molecule for NO synthesis, facilitated the inhibitory avoidance and counteracted the L-NAME (50 mg · kg −1)-induced anxiolysis. Neither previous treatment was able to change the escape behaviour. The results indicate that NO may underlie learned, but not innate, fear in the ETM.