Amygdala Inactivation Blocks Expression of Conditioned Memory Modulation and the Promotion of Avoidance and Freezing.

Abstract

Rats were exposed to shock-paired cues immediately after training on an appetitive preference task. Elevated levels of freezing in and active avoidance of the shock-paired compartment were observed, and memory for the appetitive task was improved when tested 24 hr later. Intra-amygdala muscimol injected before the posttraining exposure eliminated freezing, avoidance, and memory modulation. The blockade of both freezing and active avoidance, which involve competing behavioral tendencies, makes it unlikely that the amygdala itself generates either behavior. The elimination of conditioned memory modulation suggests that conditioned neurohormonal responses were blocked. These conditioned internal responses may comprise the intervening variable of "conditioned fear" and may promote observable behaviors, the form of which is determined by the environment in which they occur.

Intra-Amygdala Muscimol Injections Impair Freezing and Place Avoidance in Aversive Contextual Conditioning

“…Although their crossover rates were higher than those for the saline control rats, there is no conclusive evidence that activity levels affect conditioned avoidance (Holahan and White 2003) and clear evidence that activity levels do not affect the expression of conditioned preferences (Hiroi and White 1991;White and McDonald 1993).…”

“…First, the fact that there was no difference in I/F between groups test-mus and con-sal during the closed-door test is inconsistent with the existence of such an effect. Second, we have previously reported (Holahan and White 2001) that nonshocked rats injected with muscimol or saline have similar activity levels (muscimol: 2.99 ‫ע‬ 0.30 crossovers/sec; saline: 2.49 ‫ע‬ 0.33; t[8] = 1.0, P = 0.35) and latencies to exit their "paired" compartment (muscimol 3.65 ‫ע‬ 0.83 sec; saline: 5.73 ‫ע‬ 1.51; t[8] = 1.5, P = 0.26) in the same apparatus as was used in the present experiments. Third, others have reported that amygdala lesions do not produce elevations in activity levels during exposure to aversive cues (Goldstein 1968;Decker et al 1995;Maren 1998;Fanselow and Gale 2003).…”

“…Lesions restricted to specific amygdala regions have produced less consistent results. Lesions of the LA or BLA blocked active avoidance of a tone-paired shock (Killcross, et al 1997;Amorapanth et al 2000) while neither electrolytic (Holahan and White 2002), quinolinic (Selden et al 1991), ibotenic (Jellestad and Cabrera 1986;Ambrogi Lorenzini et al 1991), nor NMDA (Vazdarjanova and McGaugh 1998) lesions of the BLA disrupted place avoidance. Electrolytic lesions of the CeA impaired active avoidance of shock-conditioned cues in some reports (Poremba and Gabriel 1997;Smith et al 2001;Holahan and White 2002) but not others (Killcross et al 1997;Amorapanth et al 2000).…”

“…In this case, rats that have been shocked while confined in a compartment and subsequently allowed to move freely (with no shock) between that compartment and a neutral one, spend less time in the shocked than in the neutral compartment (Miller 1948;Goldstein 1960;Campbell and Campbell 1962;McAllister and McAllister 1962;Blanchard 1968, 1970a,b;Kumar 1970;Selden et al 1991;Vazdarjanova and McGaugh 1998;Antoniadis and McDonald 1999;Holahan and White 2002).…”

“…Pretraining electrolytic lesions of the amygdala complex attenuate elevated freezing during exposure to a shock-paired compartment (Phillips and LeDoux 1992), as do lesions restricted to the medial (MeA; Blanchard and Blanchard 1972;Holahan and White 2002), the central (CeA), or basolateral (BLA) amygdala regions (Kim et al 1993;Amorapanth et al 2000;Nader et al 2001;Holahan and White 2002). Pretraining (Maren, 1998(Maren, , 1999Vazdarjanova and McGaugh, 1998;Cahill et al 2000) or posttraining (Lee et al 1996;Maren et al 1996a;Maren 1998) NMDA lesions of the BLA as well as pretraining NMDA lesions of the lateral amygdala (LA) or CeA (Goosens and Maren 2001) also block freezing during exposure to a contextual CS.…”