Use of the light/dark test for anxiety in adult and adolescent male rats

Abstract

The light/dark (LD) test is a commonly used rodent test of unconditioned anxiety-like behavior that is based on an approach/avoidance conflict between the drive to explore novel areas and an aversion to brightly lit, open spaces. We used the LD test to investigate developmental differences in behavior between adolescent (postnatal day (PN) 28-34) and adult (PN67-74) male rats. We investigated whether LD behavioral measures reflect anxiety-like behavior similarly in each age group using factor analysis and multiple regression. These analyses showed that time in the light compartment, percent distance in the light, rearing, and latency to emerge into the light compartment were measures of anxiety-like behavior in each age group, while total distance traveled and distance in the dark compartment provided indices of locomotor activity. We then used these measures to assess developmental differences in baseline LD behavior and the response to anxiogenic drugs. Adolescent rats emerged into the light compartment more quickly than adults and made fewer pokes into the light compartment. These age differences could reflect greater risk taking and less risk assessment in adolescent rats than adults. Adolescent rats were less sensitive than adults to the anxiogenic effects of the benzodiazepine inverse agonist N-methyl-β-carboline-3-carboxamide (FG-7142) and the α₂ adrenergic antagonist yohimbine on anxiety-like behaviors validated by factor analysis, but locomotor variables were similarly affected. These data support the results of the factor analysis and indicate that GABAergic and noradrenergic modulation of LD anxiety-like behavior may be immature during adolescence.

Keywords: Adolescence; Anxiety; FG-7142; Factor analysis; Light/dark test; Yohimbine.

Fig. 1

Regression of total distance with (A) latency to emerge into the light compartment, (B) pokes into the light compartment, (C) time in the light compartment, and (D) percent of total distance traveled in the light compartment. The r value is listed for each regression. *Significant regression, p < 0.05.

Fig. 2

Behavior of control adults (n = 88) and adolescent (n = 93) animals in the LD test. (A) time spent in the light compartment, (B) percent of total distance traveled in the light compartment, (C) latency to emerge into the light compartment, (D) rearing across both compartments, (E) total distance traveled, (F) distance traveled in the dark compartment, (G) entries into the light compartment, (H) pokes into the light compartment. *Significant age difference, p < 0.05.

Fig. 3

The effects of treatment with FG-7142 on: (A) time spent in the light compartment, (B) percent of total distance traveled in the light compartment, (C) latency to emerge into the light compartment, (D) rearing across both compartments, (E) total distance traveled, (F) distance traveled in the dark compartment, (G) entries into the light compartment, (H) pokes into the light compartment. *Significantly different from age-matched vehicle, p < 0.05. ^#Significantly different from adolescents treated with same dose, p < 0.05. Vehicle, n = 20 per age group, 2.5 mg/kg, n = 8 per age group, 7.5 mg/kg, n = 8 per age group, 10 mg/kg, n = 12 adolescents, 11 adults.

Fig. 4

The effects of treatment with yohimbine on: (A) time spent in the light compartment, (B) percent of total distance traveled in the light compartment, (C) latency to emerge into the light compartment, (D) rearing across both compartments, (E) total distance traveled, (F) distance traveled in the dark compartment, (G) entries into the light compartment, (H) pokes into the light compartment. *Significantly different from age-matched vehicle, p < 0.05. ^#Significantly different from adolescents treated with same dose, p < 0.05. Vehicle, n = 15 adolescents, 14 adults, 1 mg/kg, n = 8 per age group, 2.5 mg/kg, n = 8 per age group, 5 mg/kg n = 9 adolescents, 8 adults.