INTRODUCTION: The mechanistic target of rapamycin (mTOR) is a key regulator of neuronal metabolism, growth, and synaptic plasticity. While its role is well characterized in developing neurons, its nuclear behavior and regulation under metabolic stress in mature neurons remain poorly understood.

AIM(S): This study aimed to investigate the time-dependent response of mTOR signaling in mature hippocampal neurons during nutrient deprivation and to explore the nuclear localization patterns of mTOR complex component Raptor under both metabolic and synaptic stimulation.

METHOD(S): Primary hippocampal neurons from embryonic rats were cultured until maturity and subjected to nutrient deprivation in Neurobasal (NB) medium for 2 or 6 hours. Recovery was assessed by reintroducing full medium for 20 minutes. Immunocytochemistry was used to assess the levels and localization of mTOR, phospho-mTOR (P-mTOR), and Raptor. Kainic acid (KA) stimulation was used to mimic synaptic activity.

RESULTS: Short-term (2h) nutrient deprivation followed by refeeding resulted in a marked increase in mTOR and P-mTOR levels, indicating nutrient-sensitive activation. In contrast, prolonged (6h) deprivation led to elevated mTOR and P-mTOR levels even without refeeding, suggesting a shift in regulatory mechanisms. Raptor showed distinct nuclear puncta under control conditions and became more diffusely localized after KA stimulation. Raptor co-localized with nucleolin, indicating consistent nucleolar localization

CONCLUSIONS: mTOR signaling in mature neurons exhibits duration-dependent responses to nutrient stress. Raptor shows distinct nuclear localization dynamics, suggesting spatially and functionally separate roles from mTOR, particularly in response to synaptic activation.

FINANCIAL SUPPORT: This research was supported by the Polish National Science Centre, Maestro grant no. 2020/38/A/NZ3/00447.