Extended neuronal protection induced after sublethal ischemia adjacent to the area with delayed neuronal death

Cellular and molecular neurobiology of brain preconditioning

The tolerant brain which is a consequence of adaptation to repeated nonlethal insults is accompanied by the upregulation of protective mechanisms and the downregulation of prodegenerative pathways. During the past 20 years, evidence has accumulated to suggest that protective mechanisms include increased production of chaperones, trophic factors, and other antiapoptotic proteins. In contrast, preconditioning can cause substantial dampening of the organism's metabolic state and decreased expression of proapoptotic proteins. Recent microarray analyses have also helped to document a role of several molecular pathways in the induction of the brain refractory state. The present review highlights some of these findings and suggests that a better understanding of these mechanisms will inform treatment of a number of neuropsychiatric disorders.

Neuronal damage in hydrocephalus and its restoration by shunt insertion in experimental hydrocephalus: a study involving the neurofilament-immunostaining method

OBJECT

The morphological and functional impairments of neurons and their connections caused by hydrocephalus, and their restoration by ventricular shunt placement were investigated in experimental hydrocephalus by the immunostaining of neurofilaments, which constitute the major component of the neuronal cytoskeleton.

METHODS

Progressive hydrocephalus was induced in 15 young mongrel dogs 1 to 2 months of age, 3 to 4 weeks after cisternal injection of kaolin. The dogs were divided into three groups of five animals each, a "preshunt," "post-shunt," and "nonshunt" group, depending on whether the hydrocephalic animals underwent a procedure to insert a ventriculoperitoneal shunt. Neurofilament, glial fibrillary acid protein (GFAP), and synaptophysin immunostaining were performed using samples of brain tissue from each hydrocephalic group and a fourth "control" group (five animals). In the cortex, morphological deformation and heterogeneous neurofilament immunoreactivity of the apical dendrites became pronounced in accordance with the progression of hydrocephalus (from the preshunt to the nonshunt group), and these changes remained after shunt insertion (postshunt group). In the periventricular white matter, swollen and fragmented axons increased in number along with hydrocephalic progression and were incompletely repaired by ventricular shunt placement. The GFAP-positive astrocytes observed around repaired axons in the postshunt group were seen more prominently than in the untreated hydrocephalic groups. In the internal capsule, fairly good recovery from axonal damage caused by the hydrocephalic condition was achieved by insertion of a ventricular shunt, compared with that seen in the periventricular white matter.

CONCLUSIONS

Cytoskeletal damage of neurons in hydrocephalus and its incomplete restoration by shunt placement were most significant in the periventricular white matter. This finding may account for the impaired cognitive function seen in children who have shunts and an apparently reconstituted cerebral mantle; therefore, neuronal protection in the early hydrocephalic state should be considered.

Ischaemic preconditioning: therapeutic implications for stroke?

Ischaemic preconditioning (IPC), also known as ischaemic tolerance (IT), is a phenomenon whereby tissue is exposed to a brief, sublethal period of ischaemia, which activates endogenous protective mechanisms, thereby reducing cellular injury that may be caused by subsequent lethal ischaemic events. The first description of this phenomenon was in the heart, which was reported by Murry and co-workers in 1986. Subsequent studies demonstrated IPC in lung, kidney and liver tissue, whereas more recent studies have concentrated on the brain. The cellular mechanisms underlying the beneficial effects of IPC remain largely unknown. This phenomenon, which has been demonstrated by using various injury paradigms in both cultured neurons and animal brain tissue, may be utilised to identify and characterise therapeutic targets for small-molecule, antibody, or protein intervention. This review will examine the experimental evidence demonstrating the phenomenon termed IPC in models of cerebral ischaemia, the cellular mechanisms that may be involved and the therapeutic implications of these findings.

Short-term ischemia usually used for ischemic preconditioning down-regulates central cannabinoid receptors in the gerbil hippocampus

Transient forebrain ischemia of 5-min duration causes delayed neuronal death (DND) of vulnerable CA1 neurons in the gerbil hippocampus, which can be prevented by "preconditioning" with a short ischemic stimulus of 2.5-min duration. While a key role of excitatory glutamate receptors for both phenomena has been widely accepted, little is known about the postischemic regulation of central cannabinoid (CB1) receptors. The present study was designed to test whether ischemic preconditioning is associated with specific alterations of protein expression and/or ligand binding of these receptors compared to ischemia severe enough to induce DND. Gerbils were subjected to either a 5-min ischemic period resulting in DND of CA1 neurons, or a 2.5-min period of ischemia usually used for preconditioning. Postischemic hippocampal CB1 receptor protein expression was investigated immunohistochemically, while postischemic ligand binding of [3H]CP 55940 to CB1 receptors was analyzed by quantitative receptor autoradiography in both experimental groups after 24, 48, and 96 h (n=4-5 per time point), respectively, and compared to sham-treated gerbils (n=10). Short-term ischemia of 2.5-min duration caused a transient reduction of hippocampal CB1 receptor protein expression, while receptor binding density was permanently decreased. In contrast, 5-min ischemia did not alter protein expression or ligand binding up to 48 h. Based on these data, postischemic down-regulation of hippocampal CB1 receptors, specifically seen after short-term ischemia usually used for preconditioning, may participate in the mechanisms of endogenous postischemic neuroprotection.

White matter damage and chemokine induction in developing rat brain after intrauterine infection

In order to investigate the neuropathological effects on the developing rat brain after intrauterine infection, identification of glail fibrillary acidic protein (GFAP), 2', 3'-cyclic nucleotide phosphodiesterase (CNPase), and neurofilament (NF) was observed. Escherichia coli (E. coli) was inoculated into uterine horn of pregnant rats when gestation was 70% complete (15 days) and the control group was inoculated with normal saline. Immunohistochemistry was used for evaluation of GFAP, CNPase, and NF expression in pup brains at postnatal day 7 (P7) and reverse transcriptase-PCR (RT-PCR) to analyze macrophage inflammatory protein-1 alpha mRNA (MIP-1 alpha mRNA), macrophage inflammatory protein-1 beta mRNA (MIP-1beta mRNA), the regulated upon activation normal T expressed and secreted chemokine mRNA (RANTES mRNA) and Eotaxin mRNA expression in pup brains at P1, P3 and P7. The numbers of GFAP-positive cells of the E. coli-treated group pups were marked increased in periventricular white matter and hippocampus at P7 compared with the control group but no significant different levels of GFAP expression in corpus callosum were found between two groups. The integrate density (ID) of CNPase-positive staining of the Escherichia coli-treated group pups were marked decreased in periventricular white matter and corpus callosum at P7 compared with the control group. The ID of NF-positive staining of the Escherichia coli-treated group pups were marked decreased in periventricular white matter at P7 compared with the control group and no significant different levels of NF expression in corpus callosum were found between two groups. The expression of MIP-1 alpha mRNA and MIP-1 beta mRNA in brain of the E. coli-treated pup rat were higher than the control at P1, but the expression of MIP-1 alpha mRNA and MIP-1 beta mRNA in brain of the pup rat at P3 and P7 had no significant difference between two groups. The alteration of expression of GFAP, CNPase, and NF in the brain of neonatal rats after intrauterine infection suggested that intrauterine infection could cause neonatal white matter damage. Moreover, the transient increase in expression of chemokine such as MIP-1 alpha, MIP-1 beta in neonatal brain after intrauterine infection indicated that MIP-1 alpha, MIP-1 beta may be a mechanism mediating between the neonatal white matter damage and the intrauterine infection.

Expression of glial fibrillary acidic protein in developing rat brain after intrauterine infection

In order to investigate the neuropathological effects on the developing rat brain after intrauterine infection, identification of GFAP was observed. Escherichia coli (E. coli) was inoculated into uterine horn of pregnant rats when gestation was 70% complete (15 days) and the control group was inoculated with normal saline. Immunohistochemistry was used for evaluation of GFAP expression in pup brains at postnatal day 1 (P1), P3, P7, P14 and P21, and RT-PCR was used to analyze GFAP mRNA, interleukin-1beta, mRNA (IL-1beta mRNA) and tumor necrosis factor-alpha mRNA (TNF-alpha mRNA) expression in pup brains at P1, P3 and P7. At P1 and P3, GFAP was expressed very scarcely in periventricular white matter but not in other brain regions between the two groups. Compared with the control group, at P7 GFAP expression of the E. coli-treated pups was remarkably increased in periventricular white matter and hippocampus. The E. coli-treated pups at P14 showed a marked increase of GFAP expression in periventricular white matter, corpus callosum and cortex. However, no significant difference in levels of GFAP expression in any brain regions were found at P21 between the two groups. GFAP mRNA expression of the E. coli-treated pups was higher than the control at P1 and P3, but there was no significant difference between the two groups at P7. IL-1beta mRNA and TNF-alpha mRNA expressions of the E. coli-treated pups were higher than the control at P1 but there was no significant difference between the two groups at P3 and P7. These present results suggest that intrauterine infection could increase GFAP expression in the pup brain and indicate that intrauterine infection might damage the developing white matter and IL-1beta, TNF-alpha might be a mechanism mediating between the two events.

Ischemic tolerance

A brief period of cerebral ischemia confers transient tolerance to a subsequent ischemic challenge in the brain. This phenomenon of ischemic tolerance has been confirmed in various animal models of forebrain ischemia and focal cerebral ischemia. Since the ischemic tolerance afforded by preceding ischemia can bring about robust protection of the brain, the mechanism of tolerance induction has been extensively studied. It has been elucidated that ischemic tolerance protects neurons, and at the same time, it preserves brain function. Further experiments have shown that metabolic and physical stresses can also induce cross-tolerance to cerebral ischemia, but the protection by cross-tolerance is relatively modest. The underlying mechanism of ischemic tolerance still is not fully understood. Potential mechanisms may be divided into two categories: (1) A cellular defense function against ischemia may be enhanced by the mechanisms inherent to neurons. They may arise by posttranslational modification of proteins or by expression of new proteins via a signal transduction system to the nucleus. These cascades of events may strengthen the influence of survival factors or may inhibit apoptosis. (2) A cellular stress response and synthesis of stress proteins may lead to an increased capacity for health maintenance inside the cell. These proteins work as cellular "chaperones" by unfolding misfolded cellular proteins and helping the cell to dispose of unneeded denatured proteins. Recent experimental data have demonstrated the importance of the processing of unfolded proteins for cell survival and cell death. The brain may be protected from ischemia by using multiple mechanisms that are available for cellular survival. If tolerance induction can be manipulated and accelerated by a drug treatment that is safe and effective enough, it could greatly improve the treatment of stroke.

[3H]muscimol binding to gamma-aminobutyric acid(A) receptors is upregulated in CA1 neurons of the gerbil hippocampus in the ischemia-tolerant state

BACKGROUND AND PURPOSE

Excitotoxic activation of glutamate receptors is currently thought to play a pivotal role in delayed neuronal death (DND) of highly vulnerable CA1 neurons in the gerbil hippocampus after transient global ischemia. Postischemic degeneration of these neurons can be prevented by "preconditioning" with a short sublethal ischemic stimulus. The present study was designed to test whether ischemic preconditioning is associated with specific alterations of ligand binding to excitatory glutamate and/or inhibitory gamma-aminobutyric acid (GABA)A receptors compared with ischemia severe enough to induce DND.

METHODS

With the use of quantitative receptor autoradiography, postischemic ligand binding of [3H]MK-801 and [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) to excitatory N-methyl-D-aspartate (NMDA) and AMPA receptors as well as [3H]muscimol to inhibitory GABA(A) receptors in hippocampal subfields CA1, CA3, and the dentate gyrus were analyzed in 2 experimental paradigms. Gerbils were subjected to (1) a 5-minute ischemic period resulting in DND of CA1 neurons and (2) a 2.5-minute period of ischemia mediating tolerance induction.

RESULTS

[3H]MK-801 and [3H]AMPA binding values to excitatory NMDA and AMPA receptors showed a delayed decrease in relatively ischemia-resistant CA3 and dentate gyrus despite maintained neuronal cell density. [3H]Muscimol binding to GABA(A) receptors in CA1 neurons was transiently but significantly increased after preconditioning but not after global ischemia with consecutive neuronal death.

CONCLUSIONS

Downregulation of ligand binding to glutamate receptors in relatively ischemia-resistant CA3 and dentate gyrus neurons destined to survive suggests marked synaptic reorganization processes despite maintained structural integrity. More importantly, upregulation of binding to inhibitory GABA(A) receptors in the hippocampus indicates a relative shift between inhibitory and excitatory neurotransmission that we suggest may participate in endogenous postischemic neuroprotection.