Nitric oxide may underlie learned fear in the elevated T-maze.
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(omega)-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(omega)-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.
Calixto
A V
AV
Department of Physiological Sciences, Centre of Biological Sciences, Federal University of Santa Catarina, Santa Catarina, Brazil.
Vandresen
N
N
de Nucci
G
G
Moreno
H
H
Faria
M S
MS
D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology*; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology*; D008874:Midazolam / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D014151:Anti-Anxiety Agents; D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D008874:Midazolam; D019331:NG-Nitroarginine Methyl Ester