Comparative Enhancement of Motor Function and BDNF Expression Following Different Brain Stimulation Approaches in an Animal Model of Ischemic Stroke

Neurotoxic and cytoprotective mechanisms in the ischemic neocortex

Neuronal damage in ischemic stroke occurs due to permanent imbalance between the metabolic needs of the brain and the ability of the blood-vascular system to maintain glucose delivery and adequate gas exchange. Oxidative stress and excitotoxicity trigger complex processes of neuroinflammation, necrosis, and apoptosis of both neurons and glial cells. This review summarizes data on the structural and chemical changes in the neocortex and main cytoprotective effects induced by focal ischemic stroke. We focus on the expression of neurotrophins (NT) and molecular and cellular changes in neurovascular units in ischemic brain. We also discuss how these factors affect the apoptosis of cortical cells. Ischemic damage involves close interaction of a wide range of signaling molecules, each acting as an efficient marker of cell state in both the ischemic core and penumbra. NTs play the main regulatory role in brain tissue recovery after ischemic injury. Heterogeneous distribution of the BDNF, NT-3, and GDNF immunoreactivity is concordant with the selective response of different types of cortical neurons and glia to ischemic injury and allows mapping the position of viable neurons. Astrocytes are the central link in neurovascular coupling in ischemic brain by providing other cells with a wide range of vasotropic factors. The NT expression coincides with the distribution of reactive astrocytes, marking the boundaries of the penumbra. The development of ischemic stroke is accompanied by a dramatic change in the distribution of GDNF reactivity. In early ischemic period, it is mainly observed in cortical neurons, while in late one, the bulk of GDNF-positive cells are various types of glia, in particular, astrocytes. The proportion of GDNF-positive astrocytes increases gradually throughout the ischemic period. Some factors that exert cytoprotective effects in early ischemic period may display neurotoxic and pro-apoptotic effects later on. The number of apoptotic cells in the ischemic brain tissue correlates with the BDNF levels, corroborating its protective effects. Cytoprotection and neuroplasticity are two lines of brain protection and recovery after ischemic stroke. NTs can be considered an important link in these processes. To develop efficient pharmacological therapy for ischemic brain injury, we have to deepen our understanding of neurochemical adaptation of brain tissue to acute stroke.

Topography of neurotrophins in the rat neocortex and their role in neuron apoptosis after experimental ischemic stroke

Neuronal loss due to apoptosis after ischemic injury depends on the trophic support of neurons and cytoprotective effects of neurotrophins (NTs). Different NTs may activate both pro- and antiapoptotic factors. Their distribution in the ischemic core (IC) and penumbra (IP) has been poorly studied. The available data on the localization of NTs in the ischemic brain are contradictory and depend to a certain degree on the pathogenetic model used. The distribution of NTs in different layers of the ischemic cortex is also largely unknown hindering our understanding of their exact effects and targets in different zones of the ischemic brain. We examined the immunolocalization of brain-derived neurotrophic factor (BDNF), neurotrophin-3, and glial cell line-derived neurotrophic factor (GDNF) in the parietal cortex using a rat model of ischemic stroke due to permanent occlusion of the middle cerebral artery. The spatial density of immunoreactive (IR) cells varied across the cortical layers and changed with time after ischemic injury. Their distribution in the IC differed considerably from that in the IP. The immunolocalization of neurotrophins in the contralateral hemisphere was similar to that in IP. We also studied the distribution of pro- and anti-apoptotic factors in IC and IP with and without intravenous BDNF administration. In the model without BDNF administration, the proportions of Bcl-2-, p53-, caspase-3-, and Mdm2-IR cells showed different dynamics during the ischemic period. In the model with BDNF administration, Mdm2 immunoreactivity was mainly observed in pyramidal cells of layers V/VI, and Bcl-2, in interneurons of layers II and III. The dynamics of p53 immunoreactivity was opposite to that of caspase-3 throughout the ischemic period. The present results suggest that after ischemic injury, 1) the number of neurotrophin-positive cells increases in the early ischemic period and decreases afterwards; 2) there is a close metabolic relationship between astrocytes and neurons contributing to their adaptation to ischemic conditions; 3) the IP borders undergo constant changes; 4) in the IP, neuronal loss occurs mainly by apoptotic pathway throughout the ischemic period; 5) BDNF may enhance considerably antiapoptotic mechanisms with a predominance of Mdm-2 activity in pyramidal neurons.