The inactivation of the basolateral nucleus of the rat amygdala has an anxiolytic effect in the elevated T-maze and light/dark transition tests.
Pharmacological evidence indicates that the basolateral nucleus of the amygdala (BLA) is involved in the mediation of inhibitory avoidance but not of escape behavior in the elevated T-maze test. These defensive responses have been associated with generalized anxiety disorder (GAD) and panic disorder, respectively. In the present study, we determined whether the BLA plays a differential role in the control of inhibitory avoidance and escape responses in the elevated T-maze. Male Wistar rats (250-280 g, N = 9-10 in each treatment group) were pre-exposed to one of the open arms of the maze for 30 min and 24 h later tested in the model after inactivation of the BLA by a local injection of the GABA A receptor agonist muscimol (8 nmol in 0.2 microL). It has been shown that a prior forced exposure to one of the open arms of the maze, by shortening latencies to withdrawal from the open arm during the test, improves the escape task as a behavioral index of panic. The effects of muscimol in the elevated T-maze were compared to those caused by this GABA agonist in the avoidance reaction generated in the light/dark transition test. This defensive behavior has also been associated with GAD. In the elevated T-maze, intra-BLA injection of muscimol impaired inhibitory avoidance (control: 187.70 +/- 14.90 s, muscimol: 37.10 +/- 2.63 s), indicating an anxiolytic effect, without interfering with escape performance. The drug also showed an anxiolytic effect in the light/dark transition test as indicated by the increase in the time spent in the lighted compartment (control: 23.50 +/- 2.45 s, muscimol: 47.30 +/- 4.48 s). The present findings point to involvement of the BLA in the modulation of defensive responses that have been associated with GAD.
Bueno
C H
CH
Laboratório de Psicofarmacologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil.
Zangrossi
H
H
Viana
M B
MB
D000679:Amygdala / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D001008:Anxiety Disorders / Q000503:physiopathology / Q000523:psychology*; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology*; D003624:Darkness; D004924:Escape Reaction / Q000187:drug effects / Q000502:physiology*; D018755:GABA Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D008027:Light; D008297:Male; D018782:Maze Learning; D008845:Microinjections; D009118:Muscimol / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D018755:GABA Agonists; D009118:Muscimol