Figure 1.
Xenon- (Xe) and oxygen (O2) gas concentration time course averaged across all exposures in this study.
Percent Xe reflects exposure chamber atmospheric Xe concentration along with oxygen (maintained at 20.9%) and balanced with nitrogen. The rate of Xe delivery was approximately 2.5 liters per minute (supplied as 100% Xe from an external tank) and continuously mixed with chamber atmosphere by circulating fans to reach a maximum preset concentration of 25%. Data included in the figure are from 14 total Xe exposures (Fig. 2B &C, n = 3 runs; Fig. 2D & E, n = 3 runs; Fig. 2F & G, n = 2 runs; Fig. 3 B & C, n = 3 runs after Reactivation test and 3 runs after PR-LTM1). Data are shown as mean ± s.e.m.
Figure 2.
Xenon exposure impairs reconsolidation and reduces conditioned freezing in a reactivation- and time-dependent manner.
(A) Schematic of the experimental design. Twenty-four h after fear conditioning, fear memories either were or were not reactivated and rats were exposed either to Xe (25%) or Air for 1 h beginning either immediately or after a 2 h delay. An additional control group housed in the regular main rat vivarium (Normal exposure) also was included in some studies to control for any potential effects of housing in the exposure chambers. Post-reactivation long-term memory (PR-LTM) was subsequently probed 48 h (PR-LTM1) and 96 h (PR-LTM2) later. A subset of rats (n = 6–7/group) were further tested for spontaneous recovery of freezing by testing 18 d after Reactivation (PR-LTM3). (B & C) Percent freezing to context alone and context + tone (respectively) in animals exposed to Xe (25%) or Air immediately after Reactivation. **P<0.005; *P<0.05 compared to Air exposure. Normal exposure, n = 8; Air exposure, n = 11; Xe exposure, n = 11. (D & E) Percent freezing to context alone and context + tone in rats not receiving a Reactivation test. Normal exposure, n = 8; Air exposure, n = 11; Xe exposure, n = 11. (F & G) Percent freezing to context alone and context + tone in rats exposed either to Xe (25%) or Air beginning 2 h after Reactivation. Air exposure, n = 7; Xe exposure, n = 8. Data are shown as mean ± s.e.m.
Figure 3.
Multiple Xe exposures after fear memory reactivations do not enhance amnestic effects on conditioned freezing.
(A) Schematic of the experimental design for multiple Xe-exposure treatment. In addition to administering Xe (25%) or Air for 1 h after Reactivation, animals were exposed a second time to Xe (25%) or Air for 1 h immediately after PR-LTM1 and freezing was again probed 48 h later, (PR-LTM2). (B & C) Percent freezing to context alone and context + tone (respectively) in animals exposed to Xe (25%) or Air for 1 hr immediately after Reactivation and PR-LTM1. (D & E) Normalized freezing data to context and tone. Data are expressed as % differences from the first Reactivation test day in order to compare the effects of multiple Xe exposures. A second Xe exposure did not alter freezing either to context alone or context + tone at PR-LTM2 compared to PR-LTM1. ***P<0.0005; **P<0.005; *P<0.05; Air–1 exposure, n = 11; Air–2 exposures, n = 9; Xe–1 exposure, n = 11; Xe–2 exposures, n = 10. Data are shown as mean ± s.e.m.