In our study, chronic REM sleep deprivation was associated with region-specific changes in selected neurotrophic, oxidative, and metabolic markers in the hippocampus and prefrontal cortex. In the PFC, BDNF and CREB levels were reduced in the SD group, and telmisartan treatment effectively prevented the decrease in CREB. In contrast, CREB levels in the hippocampus were not significantly affected by sleep deprivation. GSK-3β expression showed an increase following sleep deprivation in the PFC, which was attenuated by telmisartan at a dose of 3 mg/kg. In addition, MCT2 levels were elevated in both regions in the SD + Tel1 group, suggesting a potential enhancement of neuronal energy metabolism. Although LDH activity and plasma CORT levels did not differ significantly among groups, oxidative stress–related parameters showed a favorable profile in telmisartan-treated animals, as reflected by reduced MDA and increased GSH levels. Taken together, these findings indicate that telmisartan may exert neuroprotective effects under conditions of chronic REM sleep deprivation, possibly through modulation of GSK-3β-related signaling, partial normalization of CREB/BDNF pathways in the PFC, support of neuronal energy metabolism, and attenuation of oxidative stress.

Sleep is a vital homeostatic process essential for central nervous system function, energy regulation, and cognitive performance [42]. Chronic sleep deprivation disrupts these processes, leading to impairments in memory and learning, neuronal injury, oxidative stress, and systemic physiological alterations, including changes in body weight, blood glucose, blood pressure, body temperature, and brain/body weight ratio [42]. Sleep deprivation has been widely used as an experimental model to investigate the effects of impaired restorative processes on neuronal function, synaptic plasticity, and energy metabolism [43]. In the present study, we examined the neurobiological consequences of chronic REM sleep deprivation and assessed the potential neuroprotective effects of telmisartan, an angiotensin II receptor blocker with partial PPARγ agonist activity [21], on hippocampal and PFC neurobiology and cognitive function. Our findings offer additional insight into potential mechanisms associated with sleep deprivation–related cognitive impairment and suggest that telmisartan may influence neurotrophic signaling, kinase pathways, oxidative stress markers, and energy metabolism.

Consistent with previous reports [44], CSD was associated with impaired weight gain, as reflected by significantly lower body weight in the SD, SD + Tel1, and SD + Tel3 groups compared with controls. This reduction in body weight is in line with reported alterations in energy metabolism [45] during prolonged wakefulness. However, alterations in body weight observed in REM sleep deprivation models are also frequently associated with stress, hypermetabolism, and changes in feeding behavior. Telmisartan treatment did not appear to normalize body weight, suggesting that its potential neuroprotective effects are not primarily mediated through changes in systemic energy balance. Similarly, sleep-deprived animals showed reduced blood glucose levels, most notably in the SD + Tel1 group, which may be related to telmisartan’s partial PPARγ agonist activity and its known influence on carbohydrate metabolism [21]. Since a stress-control group was not included in the present study, the contribution of nonspecific stress effects to both body weight and glucose alterations cannot be fully ruled out. Accordingly, these results should be interpreted cautiously rather than being ascribed solely to REM sleep loss or telmisartan administration.

Thermoregulatory alterations were observed in sleep-deprived animals, with both SD + Tel1 and SD + Tel3 groups showing reduced body temperature compared to control groups. However, body temperature was measured only at the beginning (day 1) and at the end (week 3) of the experimental protocol, providing a limited snapshot of thermoregulatory status under prolonged REM sleep deprivation and telmisartan treatment. Given that core temperature is highly sensitive to stress exposure, circadian variability, and the effects of anesthesia used during measurement, these reductions should be interpreted cautiously. While the observed changes may suggest a directional effect, they do not allow robust conclusions regarding dynamic or circadian fluctuations. More frequent or continuous temperature monitoring would be required to fully characterize thermoregulation during chronic sleep deprivation. Similarly, blood pressure measurements showed that SD animals exhibited an increase during the first week, while the SD + Tel3 group displayed a partial attenuation of this response, suggesting a possible cardiovascular effect of telmisartan under chronic sleep deprivation [46]. However, given the variability of blood pressure changes across experimental weeks and the absence of a consistent or sustained dose-dependent pattern, these findings should be regarded as descriptive rather than definitive evidence of cardiovascular protection.

The brain-to-body weight ratio was used as a descriptive index reflecting the relationship between brain mass and systemic body weight, which can be influenced by chronic stress and metabolic challenges such as REM sleep deprivation. Therefore, the increase in this ratio observed in the SD and SD + Tel3 groups should not be interpreted as direct evidence of brain edema. Given the marked body weight loss in REM sleep–deprived animals, the elevated ratio may largely reflect reduced body mass, with relative preservation of brain tissue, rather than a true increase in brain volume or clear structural pathology.

BDNF and CREB form a key molecular axis that underlies learning and memory. CREB regulates the transcription of synaptic plasticity-related genes, including BDNF, while BDNF activates TrkB signaling pathways that enhance CREB phosphorylation. This reciprocal interaction strengthens synaptic connections and supports long-term potentiation, thereby facilitating memory consolidation. Disruption of this pathway impairs synaptic plasticity and cognitive performance, whereas interventions that enhance CREB activity or BDNF expression restore neuronal function and learning capacity [47]. These molecular insights provide a framework to understand the region-specific effects of sleep deprivation and the neuroprotective action of telmisartan observed in our study. Among the most consistent findings in the literature is the vulnerability of the hippocampus and PFC to sleep deprivation. Both regions are crucial for memory consolidation and executive function, and their impairment is strongly associated with reduced levels of BDNF and its transcriptional regulator CREB [48]. In our study, hippocampal BDNF levels were significantly elevated in the SD + Tel1 group compared to both control and SD groups, indicating a robust protective effect of telmisartan at this dose. Similarly, BDNF levels in the PFC were significantly decreased in the SD group compared to the control group, but BDNF levels normalized by telmisartan at a dose of 1 mg/kg. These results support previous reports that telmisartan at 1 mg/kg promotes hippocampal BDNF production and extend these findings to the PFC [49]. PFC CREB levels were compared across groups, a statistically significant increase was observed in the SD + Tel3 group compared with the SD group. In the present study, telmisartan treatment was associated with region- and dose-specific changes in BDNF and CREB levels. Given the well-established interplay between BDNF and CREB in synaptic plasticity, these molecular alterations may be relevant to the cognitive improvements observed following telmisartan treatment. Nevertheless, while the study was designed to examine CREB–BDNF-related signalling, the present findings do not allow definitive conclusions regarding the dynamic interactions or causal relationships within this pathway.

As BDNF–CREB activation enhances long-term potentiation and supports hippocampus-dependent memory, subsequent behavioral analyses were performed to examine the impact of sleep deprivation and telmisartan treatment on learning and memory performance. During the four-day training with a hidden platform, all groups showed a gradual decrease in escape latency compared with day one, indicating successful acquisition of the platform location. On the fifth day, memory performance was evaluated by the probe trial, which revealed that animals in the SD and SD + Tel1 groups spent significantly less time in the target quadrant than controls, demonstrating that sleep deprivation impaired memory retention. Previous studies have shown that hippocampus-dependent memory is particularly vulnerable to sleep deprivation, whereas hippocampus-independent memory remains intact [50], supporting the view that hippocampal function is especially affected. Consistent with research showing telmisartan’s positive effects on cognitive function [49], our findings demonstrated that the SD + Tel1 group exhibited a shorter escape latency on the fourth training day compared to the SD group. These findings align with earlier evidence suggesting that NREM sleep enhances synaptic plasticity and performance gains, whereas REM sleep plays a stabilizing role in memory consolidation [51]. Thus, our results support the hypothesis that REM sleep contributes to the stabilization of pre-sleep learning, and suggest that telmisartan may mitigate sleep deprivation–induced hippocampal dysfunction primarily at the level of learning acquisition rather than long-term memory retention. The improvement in learning performance observed following telmisartan treatment at the 1 mg/kg dose may be associated with preserved hippocampal BDNF levels.

Energy metabolism is a critical determinant of neuronal viability under stress conditions. MCTs, and specifically MCT2, are responsible for shuttling lactate from astrocytes to neurons, thereby providing a vital energy substrate [52]. In our study, MCT2 levels in the hippocampus and PFC were significantly increased in SD + Tel1 animals compared to the SD group. However, this increase was not observed consistently across other experimental groups, limiting the interpretation of this finding. Accordingly, the present results do not support definitive conclusions regarding a telmisartan-mediated enhancement of neuronal lactate transport, but instead indicate a dose-specific association. Previous studies have reported reduced MCT2 expression in cerebral ischemia [53] and partial restoration following telmisartan treatment, as well as similar observations in traumatic brain injury models [27]. In this context, our findings suggest a limited and condition-dependent association between angiotensin II inhibition and neuronal energy–related markers under chronic sleep deprivation.

GSK-3β, a serine/threonine kinase highly expressed in the central nervous system, regulates multiple cellular processes, including apoptosis and synaptic function [24]. Our results complement this finding by demonstrating that telmisartan. Hippocampal GSK-3β levels did not differ significantly between groups. In contrast, GSK-3β levels in the PFC were significantly reduced in SD + Tel3 animals relative to SD rats. Importantly, chronic inhibition of GSK-3β has been linked to enhanced neuronal survival, supporting the idea that telmisartan modulates kinase activity in a region-specific manner [24]. Our findings suggest that GSK-3β–related alterations in the PFC under conditions of CSD may be of potential relevance to its role in higher cognitive functions.

Glycogen, as the primary energy reserve in the brain, represents a key component of cerebral energy metabolism and is known to be depleted during prolonged wakefulness and replenished during sleep [54]. In our study, brain glycogen levels were significantly increased in the SD + Tel1 group compared with SD rats, suggesting that telmisartan at this dose is associated with improved glycogen recovery following sleep deprivation. Conversely, SD animals exhibited reduced glycogen levels relative to controls, consistent with evidence indicating that chronic wakefulness leads to cerebral glycogen depletion. Previous research has shown that GSK-3β inhibits glycogen synthase and thereby impairs glycogen synthesis [24]. Although we did not assess GSK-3β phosphorylation status, glycogen synthase activity, or regional glycogen dynamics, our findings indicate dissociable dose-dependent effects of telmisartan, with increased brain glycogen levels observed in the SD + Tel1 group, whereas significant modulation of GSK-3β expression in the prefrontal cortex was detected only in the SD + Tel3 group. These results suggest that telmisartan may influence cerebral energy regulation through mechanisms that are not directly coupled across doses under sleep deprivation. Therefore, these findings do not support a direct causal relationship but suggest that telmisartan may modulate cerebral energy metabolism, including pathways linked to glycogen regulation and GSK-3β–associated signalling, under conditions of sleep deprivation.

LDH catalyzes the reversible conversion of lactate to pyruvate and is commonly used as a general indicator of cellular damage [55]. However, when assessed in tissue homogenates, LDH lacks specificity for neuronal injury and its interpretation is inherently limited. In the present study, LDH levels in both the hippocampus and prefrontal cortex did not differ significantly between experimental groups. Although minor variations in mean values were observed following sleep deprivation and telmisartan treatment, these changes were not statistically significant and do not support conclusions regarding neuronal injury or neuroprotection. In this context, LDH was considered only as a downstream, supportive marker rather than a primary indicator of neuroprotective efficacy. Future studies incorporating region-specific analyses and more sensitive markers of neuronal injury are required to clarify these aspects.

Sleep deprivation has been shown to activate the hypothalamic–pituitary–adrenal (HPA) axis, leading to elevated corticosterone levels during acute stress conditions [56]. However, in chronic sleep deprivation paradigms, the HPA axis may undergo functional adaptation, and several studies have reported significant physiological and neurobiological alterations in the absence of sustained changes in circulating corticosterone levels [10, 57]. In particular, long-term sleep deprivation has been shown to impair synaptic plasticity and increase oxidative stress in the brain without concomitant elevations in plasma corticosterone, suggesting that central nervous system alterations can occur without detectable changes in systemic glucocorticoid output.

Consistent with these reports, we observed no significant differences in plasma corticosterone levels across experimental groups following 21 days of REM sleep deprivation induced by the modified multiple-platform method. This finding may reflect adaptive regulation of the HPA axis during prolonged sleep loss, but alternative explanations related to methodological factors—such as sampling timing, circadian variability, assay sensitivity, and the absence of a dedicated stress-control group cannot be excluded. Therefore, the CORT data should be interpreted cautiously, and no definitive conclusions regarding HPA-axis adaptation can be drawn. Importantly, these findings indicate that the protective effects observed in other outcome measures are unlikely to be mediated by changes in circulating corticosterone and may instead involve mechanisms operating independently of overt systemic glucocorticoid modulation.

Oxidative stress is recognized as an important contributor to neuronal alterations associated with sleep deprivation. MDA, a lipid peroxidation product, was assessed as an index of oxidative damage, while GSH was measured as a key component of endogenous antioxidant defense. In the present study, brain MDA levels were significantly reduced and GSH levels were significantly increased only in the SD + Tel3 group compared with the SD group, indicating a dose-dependent and condition-specific effect of telmisartan rather than a generalized antioxidant action. In the absence of additional oxidative stress markers or enzymatic activity measurements, such as superoxide dismutase or catalase activity, these findings should be interpreted cautiously. Accordingly, the observed changes in MDA and GSH are best viewed as reflecting an alteration in redox balance associated with high-dose telmisartan treatment, rather than definitive evidence of neuroprotection. Overall, the present data support a modulatory role of telmisartan on oxidative processes under REM sleep deprivation conditions, without allowing firm conclusions regarding its protective efficacy on oxidative stress–related neuronal injury.

Nitric oxide (NO) is an essential signaling molecule involved in cerebral blood flow regulation, neuronal activity, and inflammatory processes [58]. Owing to its short half-life, NO is commonly assessed via its stable metabolites, nitrate and nitrite [59]. In the present study, brain nitrate levels were significantly elevated in both the SD and SD + Tel3 groups compared with controls, and neither 1 mg/kg nor 3 mg/kg telmisartan reduced these levels. This finding indicates that REM sleep deprivation is associated with increased nitrosative stress that persists despite telmisartan treatment.

Moreover, the similar elevation of nitrate levels in both SD and SD + Tel3 groups suggests that nitrosative pathways are not uniformly suppressed by telmisartan under REM sleep deprivation conditions and may be regulated independently from other redox-related processes. In line with previous reports, these findings imply that telmisartan may have limited efficacy on nitrosative pathways when administered as monotherapy [60], underscoring the need for caution in attributing antioxidant or antinitrosative effects based solely on nitrate measurements.

While the present study provides new insights into the effects of chronic REM sleep deprivation and telmisartan treatment on cognitive, molecular, and metabolic parameters, several limitations should be acknowledged. First, biochemical and oxidative stress markers were assessed using non–region-specific brain tissue, which may have masked region-dependent alterations known to occur during REM sleep deprivation and limited direct comparison with region-specific hippocampal and prefrontal cortex analyses.

Second, the absence of a stress-matched or large-platform control group in the modified multiple-platform paradigm restricts the ability to fully dissociate REM-specific effects from nonspecific stress-related influences. Third, oxidative stress assessment relied on the thiobarbituric acid–based MDA assay, which has limited specificity for lipid peroxidation, and additional enzymatic or region-specific redox markers were not evaluated.

Fourth, body temperature was measured only at two time points, precluding assessment of temporal or circadian variability in thermoregulation. Finally, direct measures of cerebral edema, such as tissue water content or volumetric analyses, were not performed; therefore, changes in the brain-to-body weight ratio should be interpreted cautiously, as they may primarily reflect REM sleep deprivation–associated body weight loss rather than structural brain alterations.

Future studies incorporating stress-control groups, region-specific sampling, longitudinal physiological monitoring, and more selective molecular approaches will be necessary to further clarify the mechanisms underlying these findings.