Sex Differences in Brainstem Astrocytic and Glutamatergic Protein Rhythmicity in Circadian Misalignment

Approximately 16% of employees in the US are shift workers, i.e., their work hours fall outside a standard daytime schedule. Shift work induces a misalignment between the endogenous circadian system and the sleep/wake cycle, known as circadian misalignment (CM), a risk factor for cardiovascular disease. The nucleus of the solitary tract (nTS) is the central regulator that integrates peripheral afferents and reflexes using glutamate as the main neurotransmitter. In the nTS, baroreceptor afferents release glutamate that binds to ionotropic glutamatergic receptors (AMPA and NMDA) to regulate excitatory transmission and control blood pressure. Astrocytes engage in bidirectional communications with neurons, influencing synaptic transmission and plasticity in the nTS. They uptake glutamate via excitatory amino acid transporters (EAATs). We and others have shown that glutamatergic activity follows a circadian rhythm in the nTS of male rats; however, little is known about whether CM affects the expression of glutamatergic receptors and astrocytic proteins in the nTS. We hypothesize that there is a rhythmic glutamatergic signaling in the nTS that is disrupted in CM. To test this, we used male and female Sprague-Dawley rats (7–13 weeks old). Rats were assigned to either a control (CTL; 12:12 light-dark, LD) or placed in Actimetrics circadian chambers for the circadian-misalignment (CM) protocol. The protocol consisted of a 6-h advance of the LD cycle every two days, for a total of 10 shifts over 22 days. 24/7 telemetry was used to measure blood pressure in CTL and CM animals. Animals were euthanized at ZT3 (9 am), ZT9 (3 pm), ZT15 (9 pm), or ZT21 (3 am) on day 22 for analyses. First, we found that in males, CM increases systolic and mean arterial pressure. Our data indicate a main effect of sex for GluA1 expression, with females expressing less GluA1 expression (p=0.01). Post hoc analysis revealed an increase in GluA1 expression, peaking at 9 pm, in the male control group only. In contrast, female expression remains similar over time. Female controls have significantly lower GluA1 levels at 9 pm compared to CTL males. NR1 expression remained consistent among the groups. However, there is a trend to a main effect of sex for NR1 expression (p=0.06). Although no changes were observed in the expression of the astrocyte soma marker S100b. We found a main effect of sex, CM, and interaction of time x sex and sex x CM (p< 0.05) in GFAP expression. GFAP is a key structural protein highly associated with increased branching and reactive astrocytes. We found that GFAP expression in CTL males follows a circadian rhythm, with higher expression in this group, particularly during the active period (9 pm – 3 am), compared to CM and female groups. Our data suggest that EAAT2 was not affected by time or sex, but we found a trend for the main effect of CM (p=0.08). In summary, our data indicate that females appeared less affected by circadian rhythm and sleep disturbances. While males exhibit greater rhythmicity in protein expression, circadian misalignment seems to disrupt the circadian rhythms of the proteins GluA1, GFAP, and EAAT2. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.