Site-specific effects of local pH changes in the substantia nigra pars reticulata on flurothyl-induced seizures

Brain and cancer: the protective role of erythropoietin

Erythropoietin (Epo) is a pleiotropic agent, that is to say, it can act on several cell types in different ways. An independent system Epo/Epo receptor (EpoR) was detected in brain, leading to the hypothesis that this hormone could be involved in cerebral functions. Epo/EpoR expression changes during ontogenesis, thus indicating the importance of this system in neurodevelopment. Moreover, the hypoxia-induced production of Epo in the adult brain suggests that it could exert a neurotrophic and neuroprotective effect in case of brain injury. Epo could also influence neurotransmission, inducing neurotransmitters (NT) release. Epo therapy in anemic cancer patients is still a controversial issue, because of its possible action as a growth and an angiogenic factor. In our speculative hypothesis Epo could be involved in a "two steps process" that, after a neovascularization phase, leads to its down regulation. Moreover, Epo-activated signaling pathways could be modulated as possible targets to interfere in neoplastic cells cycle. In conclusion, treatment with rHuEpo could change therapeutical perspectives in different pathological conditions, such as central nervous system (CNS) diseases, but further studies are needed to clarify its physiopathological activities in different clinical fields.

Regulation and modulation of pH in the brain

The regulation of pH is a vital homeostatic function shared by all tissues. Mechanisms that govern H+ in the intracellular and extracellular fluid are especially important in the brain, because electrical activity can elicit rapid pH changes in both compartments. These acid-base transients may in turn influence neural activity by affecting a variety of ion channels. The mechanisms responsible for the regulation of intracellular pH in brain are similar to those of other tissues and are comprised principally of forms of Na+/H+ exchange, Na+-driven Cl-/HCO3- exchange, Na+-HCO3- cotransport, and passive Cl-/HCO3- exchange. Differences in the expression or efficacy of these mechanisms have been noted among the functionally and morphologically diverse neurons and glial cells that have been studied. Molecular identification of transporter isoforms has revealed heterogeneity among brain regions and cell types. Neural activity gives rise to an assortment of extracellular and intracellular pH shifts that originate from a variety of mechanisms. Intracellular pH shifts in neurons and glia have been linked to Ca2+ transport, activation of acid extrusion systems, and the accumulation of metabolic products. Extracellular pH shifts can occur within milliseconds of neural activity, arise from an assortment of mechanisms, and are governed by the activity of extracellular carbonic anhydrase. The functional significance of these compartmental, activity-dependent pH shifts is discussed.

The pleiotropic effects of erythropoietin in the central nervous system

Erythropoietin (Epo) is a hydrophobic sialoglycoproteic hormone produced by the kidney and responsible for the proliferation, maturation, and differentiation of the precursors of the erythroid cell line. Human recombinant erythropoietin (rHuEpo) is used to treat different types of anemia, not only in uremic patients but also in newborns with anemia of prematurity, in patients with cancer-related anemia or myeloproliferative disease, thalassemias, bone marrow transplants, or those with chronic infectious diseases. The pleiotropic functions of Epo are well known. It has been shown that this hormone can modulate the inflammatory and immune response, has direct hemodynamic and vasoactive effects, could be considered a proangiogenic factor because of its interaction with vascular endothelial growth factor, and its ability to stimulate mitosis and motility of endothelial cells. The multifunctional role of Epo has further been confirmed by the discovery in the central nervous system of a specific Epo/Epo receptor (EpoR) system. Both Epo and EpoR are expressed by astrocytes and neurons and Epo is present in the cerebrospinal fluid (CSF). Therefore, novel functions of Epo, tissue-specific regulation, and the mechanisms of action have been investigated. In this review we have tried to summarize the current data on the role of Epo on brain function. We discuss the different sites of cerebral expression and mechanisms of regulation of Epo and its receptor and its role in the development and maturation of the brain. Second, we discuss the neurotrophic and neuroprotective function of Epo in different conditions of neuronal damage, such as hypoxia, cerebral ischemia, and subarachnoid hemorrhage, and the consequent possibility that rHuEpo therapy could soon be used in clinical practice to limit neuronal damage induced by these diseases.

The effects of N-methyl-D-aspartate antagonist 2-amino-7-phosphonoheptanoic acid microinfusions into the adult male rat substantia nigra pars reticulata are site-specific

We examined the effects of regional infusions of 2-amino-7-phosphonoheptanoic acid (AP7) into the substantia nigra pars reticulata (SNR) in adult male rats on flurothyl-induced clonic seizures. AP7 infusions in the SNR had dose- and region-specific effects. In the SNR(anterior), both doses of AP7 (0.1 and 5 nmol) produced an anticonvulsant effect. In the SNR(posterior), the lower dose (0.1 nmol) did not influence the seizure threshold whereas the higher dose (5 nmol) of AP7 had a proconvulsant effect. The data indicate that there are two distinct regions within the SNR which differentially respond to pharmacological manipulations of the glutamatergic system. The region-specific effects in the SNR may provide an explanation for the previous conflicting reports regarding infusions of N-methyl-D-aspartate antagonists into this structure.

Erythropoietin protects against brain ischemic injury by inhibition of nitric oxide formation

Erythropoietin prevents in vitro glutamate-induced neuronal death and could play a role in the central nervous system. We investigated the in vivo effects of recombinant human erythropoietin after intraperitoneal (i.p.; 25-100 U) or intracerebroventricular (i.c.v.; 0.25-25 U) administration on survival, brain malonildialdehyde (MDA) levels, brain edema, hippocampal neuronal death and brain nitric oxide (NO) synthesis after bilateral carotid occlusion (5 min), followed by reperfusion in the Mongolian gerbil. Peripheral posttreatment with recombinant human erythropoietin reduced postischemic MDA levels, brain edema and increased survival. Either peripheral or i.c.v. posttreatment with recombinant human erythropoietin significantly reduced hippocampal CA1 neuronal loss, observed 7 days after the ischemic event. Increase of nitrite and nitrate (as an index of NO formation) in the hippocampus, as observed after ischemia, was reduced in animals treated with recombinant human erythropoietin. These data suggest that in vivo recombinant human erythropoietin effects on brain ischemic injury could be due to inhibition of NO overproduction.

In vivo evidence that erythropoietin has a neuroprotective effect during subarachnoid hemorrhage

To ascertain in vivo whether recombinant human erythropoietin has a neuroprotective effect on the cortex during subarachnoid hemorrhage, 56 rabbits were divided into the following groups: Group 1 control sham operated plus placebo (n=14; saline solution - NaCl 0.9%); Group 2 control sham operated plus recombinant human erythropoietin (n=14); Group 3 subarachnoid hemorrhage plus placebo (n=14); Group 4 subarachnoid hemorrhage plus recombinant human erythropoietin (n=14; intraperitoneal administration of recombinant human erythropoietin immediately after inducing subarachnoid hemorrhage). In none of the Groups 1 and 2 animals was subarachnoid hemorrhage induced. In Group 3 rabbits, an increase in locomotor activity (open field apparatus) was observed 24, 48 and 72 h after surgery, and the mortality rate was 42.9% within 72 h after surgery, and, no increase in locomotor activity was observed in Group 4 rabbits, which survived for at least 72 h. Our findings suggest that recombinant human erythropoietin may be of benefit in the treatment of subarachnoid hemorrhage.

Animal models of the ketogenic diet: what have we learned, what can we learn?

Despite its clinical use as a therapy for refractory epilepsy for more than 75 years, the ketogenic diet (KD) remains a therapy in search of an explanation. The mechanism of action of the KD is unclear and the optimal indications for its clinical use are incompletely defined. Animal models could help to elucidate these questions. Surprisingly, there have been very few animal studies of the KD, and those that have been performed are difficult to compare because of wide discrepancies in experimental methods. Earlier models concentrated on the effect of the KD on acute seizure threshold in normal (i.e. nonepileptic) animals. Recent studies are beginning to examine the longer term effects of the KD and its role in epileptogenesis. Some features of clinical experience have been replicated in animal models, including the role of ketosis, elevation of seizure threshold by both classic ketogenic and medium chain triglyceride diets, better effectiveness at younger ages, and rapid reversal of the seizure protective effect when the diet is discontinued. These parallels raise hope that pertinent clinical questions can be addressed in the more controlled setting of the research laboratory. As in the clinical arena, there has been a recent resurgence of interest in pursuing basic questions related to the ketogenic diet, using techniques of modern neuroscience. Experimental approaches such as brain slice neurophysiology, genetic models, dissection of metabolic pathways, and neurohistological techniques hold much promise in the effort to understand this intriguing alternative to standard anticonvulsants.