Maryam Zahmatkesh

Nader Charkhgard, Anahita Torkaman-Boutorabi, Maryam Zahmatkesh, Nasim Vousooghi, Maryam Farahmandfar, Nasim Nadi Moghadam. Clin Psychopharmacol Neurosci 2026;24:166-76. https://doi.org/10.9758/cpn.25.1348

Melatonin, the pineal gland hormone, is produced in various extrapineal tissues as well, and its reduction has been reported in sporadic Alzheimer's disease (AD). The exact reason for tissue melatonin synthesis, despite the pineal source of melatonin, is not well understood, although the melatonin decline in the biological fluids of AD patients is a reasonable justification for melatonin therapy in cognitive impairment. However, the effectiveness of melatonin administration in AD patients was insignificant. Additionally, there is evidence of alterations in local melatonin synthesis in pathological situations, and little is known regarding its physiological or pathological modulators. Recently, the decline in the hippocampal enzyme of melatonin synthesis has been reported in amyloid-β neurotoxicity. It has been shown that reduced hippocampal melatonin synthesis by siRNA has been associated with cognitive decline. This review has included AD studies that noticed the impacts of melatonin prescription on memory and cognitive function in both animal research and randomized controlled trials, while also reviewing the available data regarding the alterations in brain tissue melatonin synthesis. This review highlights the role of brain (extrapineal) tissue melatonin synthesis in cognitive function in AD pathophysiology. Understanding the induction pattern of extrapineal melatonin synthesis, dosing optimization of exogenous administration, noting gender-specific differences, and clarifying microbiota-melatonin interactions point toward new approaches that may enhance the effectiveness of melatonin-based interventions for preventing or delaying AD progression.

Melatonin, the pineal gland hormone, is produced in several extra-pineal tissues. The arylalkylamine N-acetyltransferase (AANAT) enzyme activity determines the overall rate of tissue melatonin synthesis. A decline in AANAT enzyme activity during acute amyloid-β (Aβ) neurotoxicity and reduced melatonin levels in Alzheimer’s patients have been reported. These findings raise the question of whether brain melatonin synthesis is altered during cognitive decline. We investigated whether cognitive impairment induced by Aβ administration could affect the activation status of AANAT, a key hippocampal enzyme of melatonin synthesis. Male Wistar rats received intra-cerebroventricular Aβ injection. Two weeks after Aβ administration, the neuroinflammation was assessed by interleukin-1 (IL-1β) immunohistochemical staining. Hippocampal long-term potentiation (LTP) was evaluated using the technique of local field recording. The cognitive function was assessed using the Morris water maze behavioral test.The hippocampal AANAT activation status was assessed by Western blotting, and HPLC was used for melatonin level analysis. Aβ-induced spatial memory and LTP impairments were confirmed by increased escape latencies and alterations in the fEPSP slope. The Aβ provided a neuroinflammatory context, demonstrated by increased in the IL-1𝛽 staining. These alterations were accompanied by a reduction in the activation status of AANAT, as indicated by the p-AANAT/total AANAT ratio, in both the electrophysiology and behavioral experimental groups.These data suggest that the local activation status of AANAT may be contributed in the cognitive function of the hippocampus in a rodent model of cognitive decline induced by Aβ administration. Graphical abstract

Introduction: Alzheimer’s disease (AD) is a neurodegenerative disease associated with progressive impairment of cognitive function. The primary pathological features of AD include aggregation of amyloid-β (Aβ) and hyperphosphorylation of the tau protein. Histone deacetylases (HDACs) play a crucial role in the pathophysiology of neurodegenerative diseases. This study aimed to investigate the potential ...

Background: While it is established that addictive doses of methamphetamine correlate with inflammation-mediated neurotoxic pathways, the extent of toxicity resulting from subchronic administration at lower doses remains uncertain. Objectives: This study aimed to investigate the subtle effects of daily subchronic methamphetamine (MA) administration on neuroinflammatory processes, cognitive dimensions, gene expression, and hippocampal morphology. Methods: The experimental study employed a longitudinal design with three groups (G1B, G2B, G3B) receiving methamphetamine (5 mg/kg, intraperitoneally, once daily) for 1, 2, or 3 weeks, respectively. Corresponding control groups (G1A, G2A, G3A) received 0.2 mL of normal saline. Spatial learning, novel object recognition, and passive avoidance tests were conducted to assess spatial, recognition, and fear avoidance memories. Hippocampal morphology was evaluated using Nissl staining, and the expressions of NLRP3, ASC, and caspase-1 genes were measured as markers of neuroinflammation. Results: Statistical analyses, including one-way and two-way ANOVA, showed that subchronic low-dose administration of MA led to significant activation of the inflammasome (NLRP3, ASC, and caspase-1), which may have resulted in pyramidal cell death in the hippocampus. The hippocampal structure in the CA1 region was completely disrupted. Spatial memory and passive avoidance learning were impaired in the MA groups, while recognition memory remained unaffected. Conclusions: The findings suggest that prolonged administration of 5 mg/kg of methamphetamine may be associated with significant inflammasome activation, pyramidal cell death, and mild cognitive decline. Contrary to previous evidence, even lower doses of methamphetamine taken over an extended period could be neurotoxic.

Arylalkylamine N-acetyltransferase (AANAT), a rate-limiting enzyme in melatonin synthesis, is present in extra-pineal tissues such as the hippocampus. The hippocampal AANAT activity in amyloid β (Aβ) neurotoxicity has not been exactly defined. Adult male rats received bilateral intra-CA1 Aβ administration. The hippocampus tissue sampling was performed 2, 12, and 24 h after Aβ injection in the morning and night. The inflammation was monitored using tumor necrosis factor-alpha (TNF-α) immunohistochemistry. The AANAT enzyme activity and melatonin levels were measured using western blotting and high-performance liquid chromatography. The sampling in the morning vs night showed no significant differences in the AANAT activity. The Aβ increased the area of TNF-α positive staining 24 h after injection, which indicated the induction of an inflammatory context. It was accompanied by a significant reduction in AANAT activity and hippocampal melatonin. A reverse correlation was also detected between TNF-α and AANAT activity in the 24-h group. The TNF-α positive area was significantly increased in the 24-h group as compared to the 12-h group. Data showed that inflammatory processes began 12 h after the Aβ injection and augmented 24 h later. In the second experiment, the impact of Aβ injection on hippocampus AANAT activity was examined in the pinealectomized (PIN×) animals. The PIN× per se did not affect the hippocampal AANAT and melatonin levels. However, there was a significant decrease in hippocampal melatonin in the PIN×+Aβ group. The findings suggest the accompanying hippocampal inflammatory context and AANAT enzyme activity reduction in early stages after Aβ administration. Understanding the underlying mechanism of the decreased AANAT activity may suggest new treatment strategies.