The role of the amygdala and dorsal raphe nucleus in mediating the behavioral consequences of inescapable shock.

Abstract

It has been argued that exposure to inescapable shock produces later behavioral changes such as poor shuttle box escape learning because it leads to the conditioning of intense fear, which later transfers to the shuttle box test situation and interferes with escape. Both fear, as assessed by freezing, and escape were measured in Sprague-Dawley rats 24 hr after exposure to inescapable shock. Lesions of the basolateral region and central nucleus of the amygdala eliminated the fear that transfers to the shuttle box after inescapable shock, as well as the fear conditioned in the shuttle box by the shuttle box shocks. However, the amygdala lesions did not reduce the escape learning deficit produced by inescapable shock. In contrast, dorsal raphe nucleus lesions did not reduce the fear that transfers to the shuttle box after inescapable shock, but eliminated the enhanced fear conditioning in the shuttle box as well as the escape deficit. The implications of these results for the role of fear and anxiety in mediating inescapable shock effects are discussed.

Freewheel Running Prevents Learned Helplessness/Behavioral Depression: Role of Dorsal Raphe Serotonergic Neurons

“…Consistent with previous reports (Maier et al, 1993), exposure to uncontrollable tail shock led to poor escape performance and exaggerated fear conditioning in sedentary rats. Six weeks of voluntary access to running wheels before stressor exposure, however, caused a significant reduction in LH behaviors compared with sedentary, stressed counterparts.…”

“…Shocks terminated automatically after 30 sec if escape had not occurred, and a 30 sec latency was assigned. Previous uncontrollable stress does not alter FR-1 shuttle box escape latencies (Maier et al, 1993); therefore, stressed and control animals were exposed to shocks of equal duration in this phase.…”

“…Both shuttle box escape learning and conditioned fear were tested 24 hr after stress or control treatment, as described previously (Maier et al, 1993). Freezing was measured for the first 5 min after placement in the shuttle box (46 ϫ 20.7 ϫ 20 cm), during which time each rat (n ϭ 8 per group) was scored every 8 sec as either freezing or not freezing.…”

Estrogen-mediated effects on depression and memory formation in females

“…In the model, it was proposed that exposure to uncontrollable and stressful life events led to a feeling of 'loss of control' which ultimately led to depression. Adding to its usefulness as an animal model of depression, treatment with standard antidepressants such as the SSRIs and lesions to the serotonergic system ameliorated some if not all of the performance deficits (Maier et al, 1993). Although compelling, there is concern that some of these effects of stress on learning are attributable to nonspecific effects on performance (Maier and Jackson, 1979;Weiss and Glazer, 1975).…”

Learned helplessness is independent of levels of brain-derived neurotrophic factor in the hippocampus

“…The behavioral testing procedure was performed as previously described (Maier et al, 1993. A single test session lasted approximately 50 min and was performed by an observer blind to treatment condition of the animals.…”