Melatonin Potentiates Cells Proliferation in the Dentate Gyrus Following Ischemic Brain Injury in Adult Rats

Ischemic brain injury: New insights on the protective role of melatonin

Stroke represents one of the most common causes of brain's vulnerability for many millions of people worldwide. The plethora of physiopathological events associated with brain ischemia are regulate through multiple signaling pathways leading to the activation of oxidative stress process, Ca²⁺ dyshomeostasis, mitochondrial dysfunction, proinflammatory mediators, excitotoxicity and/or programmed neuronal cell death. Understanding this cascade of molecular events is mandatory in order to develop new therapeutic strategies for stroke. In this review article, we have highlighted the pleiotropic effects of melatonin to counteract the multiple processes of the ischemic cascade. Additionally, experimental evidence supports its actions to ameliorate ischemic long-term behavioural and neuronal deficits, preserving the functional integrity of the blood-brain barrier, inducing neurogenesis and cell proliferation through receptor-dependent mechanism, as well as improving synaptic transmission. Consequently, the synthesis of melatonin derivatives designed as new multitarget-directed products has focused a great interest in this area. This latter has been reinforced by the low cost of melatonin and its reduced toxicity. Furthermore, its spectrum of usages seems to be wide and with the potential for improving human health. Nevertheless, the molecular and cellular mechanisms underlying melatonin´s actions need to be further exploration and accordingly, new clinical studies should be conducted in human patients with ischemic brain pathologies.

The dynamics of adult neurogenesis in human hippocampus

The phenomenon of adult neurogenesis is now an accepted occurrence in mammals and also in humans. At least two discrete places house stem cells for generation of neurons in adult brain. These are olfactory system and the hippocampus. In animals, newly generated neurons have been directly or indirectly demonstrated to generate a significant amount of new neurons to have a functional role. However, the data in humans on the extent of this process is still scanty and such as difficult to comprehend its functional role in humans. This paper explores the available data on as extent of adult hippocampal neurogenesis in humans and makes comparison to animal data.

Melatonin and Nitrones As Potential Therapeutic Agents for Stroke

Stroke is a disease of aging affecting millions of people worldwide, and recombinant tissue-type plasminogen activator (r-tPA) is the only treatment approved. However, r-tPA has a low therapeutic window and secondary effects which limit its beneficial outcome, urging thus the search for new more efficient therapies. Among them, neuroprotection based on melatonin or nitrones, as free radical traps, have arisen as drug candidates due to their strong antioxidant power. In this Perspective article, an update on the specific results of the melatonin and several new nitrones are presented.

Adult neurogenesis in the African giant rat (Cricetomysgambianus, waterhouse)

African giant rats (AGR) are large nocturnal rodents with well-developed olfactory abilities uniquely linked to cognition. The post natal proliferation of neurons (adult neurogenesis), is thought to play an important role in spatial memory and learning. Eighteen brains of the African giant rats (Cricetomys gambianus, Waterhouse) belonging to three age groups (neonates n = 6, juveniles n = 6 and adults n = 6) were examined by immunohistochemistry, using antibodies for proliferating cells (Ki-67), and immature neurons (Doublecortin, DCX). Mean brain weights were 0.40 ± 0.00 g; 4.48 ± 0.43 g and 5.48 ± 0.56 g for neonate, juvenile and adult brains respectively. Our results show positive cell proliferation in the subventricular (SVZ) zone of the lateral ventricle and in the dentate gyrus (DG) of the hippocampus but at low levels in adults compared to juveniles. Estimate of the mean total proliferative Ki-67 positive cells in the SVZ and DG in the neonates was 21145 ± 8395, and 11800 ± 1230; brains from juvenile AGRs, 45530 ± 13950 and 12480 ± 7860 and from adult brains, (6880 ± 340 and 1130 ± 150) respectively. Juvenile AGR in particular, stained positively in potential sites such as the piriform and somatosensory cortices, striatum and cerebellum. This intensity of the proliferating cells within the dentate gyrus in the juvenile and adult brains could be associated with a role in the cognitive functions of landmine detection and tuberculosis diagnosis after olfactory training of the African giant rat. The juvenile rats are proposed as the most suited for experimental research and olfactory training.