The basolateral amygdala can mediate the effects of fear memory on sleep independently of fear behavior and the peripheral stress response

- Outbred rats can show either fear-induced increases or decreases in REM.
- Basolateral amygdala (BLA) mediates effects of fear memory on REM sleep.
- Inactivation of BLA blocks fear-induced reductions in REM.
- Reductions in REM can be blocked without altering freezing.
- Fear-induced alterations in REM are independent of stress-induced hyperthermia.

Fear conditioning associated with inescapable shock training (ST) and fearful context re-exposure (CR) alone can produce significant behavioral fear, a stress response and alterations in subsequent REM sleep. These alterations may vary among animals and are mediated by the basolateral nucleus of the amygdala (BLA). Here, we used the GABAA agonist, muscimol (Mus), to inactivate BLA prior to CR and examined the effects on sleep, freezing and stress-induced hyperthermia (SIH). Wistar rats (n = 28) were implanted with electrodes for recording sleep, data loggers for recording core body temperature, and with cannulae aimed bilaterally into BLA. After recovery, the animals were habituated to the injection procedure and baseline sleep was recorded. On experimental day 1, rats received ST (20 footshocks, 0.8 mA, 0.5 s duration, 60 s interstimulus interval). On experimental day 7, the rats received microinjections (0.5 μl) into BLA of either Mus (1.0 μM; n = 13) or vehicle (Veh; n = 15) prior to CR (CR1). On experimental day 21, the animals experienced a second CR (CR2) without Mus. For analysis, the rats were separated into 4 groups: (Veh-vulnerable (Veh-Vul; n = 8), Veh-resilient (Veh-Res; n = 7), Mus-vulnerable (Mus-Vul; n = 7), and Mus-resilient (Mus-Res; n = 6)) based on whether or not REM was decreased, compared to baseline, during the first 4 h following ST. Pre-CR1 inactivation of BLA did not alter freezing or SIH, but did block the reduction in REM in the Mus-Vul group compared to the Veh-Vul group. These data indicate that BLA is an important region for mediating the effects of fearful memories on sleep.