Objective: Determine whether lesions of areas projected to by the central amygdaloid nucleus disrupt classical conditioning of autonomic and/or behavioral emotional responses, specifically testing lateral hypothalamus involvement in conditioned fear responses
Materials & Equipment Checklist
7 items
Gather these items before starting the experiment. Check off items as you prepare.
Equipment4
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Protocol Steps
View Abstract
The purpose of the present study was to determine whether lesions of areas projected to by the central amygdaloid nucleus (ACE) would disrupt the classical conditioning of autonomic and/or behavioral emotional responses. The areas studied included 3 projection targets of the ACE: the lateral hypothalamic area (LH), midbrain central gray (CG) region, and bed nucleus of the stria terminalis (BNST). Lesions were made either electrolytically or by microinjection of ibotenic acid, which destroys local neurons without interrupting fibers of passage. Two weeks later, the animals were classically conditioned by pairing an acoustic stimulus with footshock. The next day, conditioned changes in autonomic activity (increases in arterial pressure) and emotional behavior (“freezing,” or the arrest of somatomotor activity) evoked by the acoustic conditioned stimulus (CS) were measured during extinction trials. Electrolytic and ibotenic acid lesions of the LH interfered with the conditioned arterial pressure response, but did not affect conditioned freezing. Electrolytic lesions of the rostral CG disrupted conditioned freezing but not conditioned changes in arterial pressure. Ibotenic acid injected into the rostral CG reduced neither the arterial pressure nor the freezing response. Injection of ibotenic acid in the caudal CG, like electrolytic lesions of the rostral CG, disrupted the freezing, but not the arterial pressure response. Injection of ibotenic acid into the BNST had no effect on either response. These data demonstrate that neurons in the LH are involved in the autonomic, but not the behavioral, conditioned response pathway, whereas neurons in the caudal CG are involved in the behavioral, but not the autonomic, pathway. Different efferent projections of the central amygdala thus appear to mediate the behavioral and autonomic concomitants of conditioned fear.
1
Create lesions in target brain regions
Lesions were made in three projection targets of the central amygdaloid nucleus: lateral hypothalamic area (LH), midbrain central gray (CG) region, and bed nucleus of the stria terminalis (BNST). Lesions were created either electrolytically or by microinjection of ibotenic acid.
Not specifiedNot specified
Note: Ibotenic acid destroys local neurons without interrupting fibers of passage, allowing distinction between neuronal involvement and fiber passage effects
View evidence from paper
“Lesions were made either electrolytically or by microinjection of ibotenic acid, which destroys local neurons without interrupting fibers of passage”
2
Recovery period
Allow animals to recover from lesion surgery before behavioral testing
Two weeksNot specified
Note: Two-week interval between lesion creation and conditioning
View evidence from paper
“Two weeks later, the animals were classically conditioned by pairing an acoustic stimulus with footshock”
3
Classical conditioning
Pair acoustic stimulus (conditioned stimulus) with footshock (unconditioned stimulus) to establish conditioned fear response
Not specifiedNot specified
Note: Single conditioning session mentioned; specific parameters not detailed
View evidence from paper
“the animals were classically conditioned by pairing an acoustic stimulus with footshock”
4
Measure conditioned responses
The next day after conditioning, measure both autonomic and behavioral conditioned responses during extinction trials. Record increases in arterial pressure (autonomic response) and freezing behavior (behavioral response) evoked by the acoustic conditioned stimulus.
Not specifiedNot specified
Note: Measurements taken during extinction trials; both autonomic and behavioral measures recorded simultaneously
View evidence from paper
“The next day, conditioned changes in autonomic activity (increases in arterial pressure) and emotional behavior ('freezing,' or the arrest of somatomotor activity) evoked by the acoustic conditioned stimulus were measured during extinction trials”