Background/Objectives: The glymphatic system plays a crucial role in clearing brain metabolic waste, and its dysfunction has been correlated to various neurological disorders. The Diffusion Tensor Imaging Analysis Along the Perivascular Space (DTI-ALPS) index has been proposed as a non-invasive marker of glymphatic function by measuring diffusivity along perivascular spaces; however, its sensitivity to sleep-related changes in glymphatic activity has not yet been validated. This study aimed to evaluate the feasibility of using the DTI-ALPS index as a quantitative marker of dynamic glymphatic activity during sleep. Methods: Diffusion tensor imaging (DTI) data were obtained from 12 healthy male participants (age = 24.44 ± 2.5 years; Pittsburgh Sleep Quality Index (PSQI) < 5), once while awake and 16 times during sleep, following 24 h sleep deprivation and administration of 10 mg zolpidem. Simultaneous MR-compatible electroencephalography was used to determine whether the subject was asleep or awake. DTI preprocessing included eddy current correction and tensor fitting. The DTI-ALPS index was calculated from nine regions of interest in projection and association areas aligned to standard space. The final analysis included nine participants (age = 24.56 ± 2.74 years; PSQI < 5) who maintained a continuous sleep state for 1 h without awakening. Results: Among nine ROI pairs, three showed significant increases in the DTI-ALPS index during sleep compared to wakefulness (Friedman test; p = 0.027, 0.029, 0.034). These ROIs showed changes at 14, 19, and 25 min after sleep induction, with FDR-corrected p-values of 0.024, 0.018, and 0.018, respectively. Conclusions: This study demonstrated a statistically significant increase in the DTI-ALPS index within 30 min after sleep induction through time-series DTI analysis during wakefulness and sleep, supporting its potential as a biomarker reflecting glymphatic activity.

Glutamate (Glu) is a major excitatory neurotransmitter and an essential component of cerebral energy metabolism, both of which may be influenced by stress and anesthesia. This study investigated the temporal profile of hippocampal Glu in control mice and mice exposed to acute restraint stress during continuous anesthesia and after intervening periods of awake recovery. Twenty‐four mice were assigned to control and stress groups ( n = 12 per group), and hippocampal Glu was measured longitudinally using in vivo proton magnetic resonance spectroscopy at 0.33, 0.67, 1, 1.33, 1.67, 2, 4, 6, and 24 h. The first six measurements were obtained under uninterrupted isoflurane anesthesia, whereas measurements at 4, 6, and 24 h were obtained after intervening periods of awake recovery. Glu was designated a priori as the primary metabolite, and the continuous‐anesthesia and recovery phases were analyzed separately using two‐way mixed‐design repeated‐measures analyses of variance. During continuous anesthesia, Glu decreased significantly over time ( p < 0.001), whereas neither the overall group effect ( p = 0.733) nor the group‐by‐time interaction ( p = 0.711) was significant. During the recovery phase, Glu was lower overall in the stress group than in the control group ( p = 0.011), although the group‐by‐time interaction did not reach statistical significance ( p = 0.059). Between‐group differences observed at 4 and 24 h before multiplicity correction were no longer significant after Holm adjustment (adjusted p = 0.062 for both). In an exploratory analysis using the 2‐h measurement as a post hoc reference, Glu increased from 2 to 4 h in the control group but decreased slightly in the stress group, resulting in a significant difference in change between the groups (Holm‐adjusted p = 0.033). No group differences were detected for the 2⟶6‐ or 2 ⟶ 24‐h changes. These findings indicate that hippocampal Glu varies substantially during prolonged anesthesia and suggest a possible stress‐related alteration during the early postanesthetic period. Because the 2‐h reference and subsequent change contrasts were not prespecified, however, the early difference should be considered exploratory and requires prospective confirmation in an independent, adequately powered study.