**2.1 Brain tissue and vitamin C**

VC is found in millimolar concentrations in neurons [2, 4, 6], hence it serves as a "micronutrient" in the central nervous system (CNS) [4, 6, 10]. VC is most abundant in the hippocampus, cerebral cortex, and amygdala [8]. Neurons are vulnerable to VC deficiency because they have higher rates of oxidative metabolism compared to glia. The antioxidant effect of VC enhances its impact on reducing ROS-mediated neurodegenerative disorders [6]. VC plays a significant role as a scavenger of ROS in brain tissue [8]. In terms of VC uptake in the CNS, it has been reported that VC is transported very slowly across the blood-brain barrier. Additionally, the ability to maintain a concentration gradient of VC from blood to neuronal cells is produced by the cerebrospinal fluid (CSF) and brain cells [4, 6]. VC distributes throughout the body and reaches the highest concentrations in brain tissue [2, 12]. VC exhibits neuroprotection and neuromodulation effects [2, 3]. It has been reported that VC plays an important role in modulating neurotransmitter synthesis and release in brain tissue. The functions of VC in brain tissue include its involvement in the conversion of dopamine to noradrenaline, where dopamine serves as a cofactor for beta-hydroxylase. It also regulates the release of catecholamines and acetylcholine from synaptic vesicles. VC has been reported to possess antioxidant properties in limiting ischemiareperfusion damage and protecting against glutamate excitotoxicity in brain tissue [4, 14]. It particularly plays a crucial role in the synthesis of catecholamines, including norepinephrine and dopamine. Additionally, it is involved in the synthesis of elastin and collagen, components of blood vessels that supply the basal lamina and neural tissue [4]. Vitamin C (VC) has multiple functions in brain tissue. It has both antioxidant and non-antioxidant functions. Its antioxidant function directly acts to remove
