Protective effects of glial cell line-derived neurotrophic factor on hippocampal neurons after traumatic brain injury in rats.

OBJECT: The purpose of this study was to evaluate whether glial cell line-derived neurotrophic factor (GDNF) can protect against hippocampal neuronal death after traumatic brain injury (TBI). METHODS: Male Sprague-Dawley rats were subjected to moderate TBI with a controlled cortical impact device while in a state of halothane-induced anesthesia. Then, GDNF or artificial cerebrospinal fluid ([aCSF]; vehicle) was infused into the frontal horn of the left lateral ventricle. In eight brain-injured and eight sham-operated rats, GDNF was infused continuously for 7 days (200 ng/day intracerebroventricularly at a rate of 8.35 ng/0.5 microl/hour). An equal volume of vehicle was infused at the same rate into the remaining eight brain-injured and eight sham-operated rats. Seven days post-injury, all rats were killed. Their brains were sectioned and stained with cresyl violet, and the hippocampal neuronal loss was evaluated in the CA2 and CA3 regions with the aid of microscopy. A parallel set of sections from each brain was subjected to immunoreaction with antibodies against glial fibrillary acidic protein (GFAP; astroglia marker). In the aCSF-treated group, TBI resulted in a significant neuronal loss in the CA2 (60%, p < 0.05) and CA3 regions (68%, p < 0.05) compared with the sham-operated control animals. Compared with control rats infused with aCSF, GDNF infusion significantly decreased the TBI-induced neuronal loss in both the CA2 (58%, p < 0.05) and CA3 regions (51%, p < 0.05). There was no difference in the number of GFAP-positive astroglial cells in the GDNF-infused rats in the TBI and sham-operated groups compared with the respective vehicle-treated groups. CONCLUSIONS: The authors found that GDNF treatment following TBI is neuroprotective.

Transient focal cerebral ischemia down-regulates glutamate transporters GLT-1 and EAAC1 expression in rat brain.

Transient focal cerebral ischemia leads to extensive excitotoxic neuronal damage in rat cerebral cortex. Efficient reuptake of the released glutamate is essential for preventing glutamate receptor over-stimulation and neuronal death. Present study evaluated the expression of the glial (GLT-1 and GLAST) and neuronal (EAAC1) subtypes of glutamate transporters after transient middle cerebral artery occlusion (MCAO) induced focal cerebral ischemia in rats. Between 24h to 72h of reperfusion after transient MCAO, GLT-1 and EAAC1 protein levels decreased significantly (by 36% to 56%, p < 0.05) in the ipsilateral cortex compared with the contralateral cortex or sham control. GLT-1 and EAAC1 mRNA expression also decreased in the ipsilateral cortex of ischemic rats at both 24h and 72h of reperfusion, compared with the contralateral cortex or sham control. Glutamate transporter down-regulation may disrupt the normal clearance of the synaptically-released glutamate and may contribute to the ischemic neuronal death.

Neuroprotection by memantine, a non-competitive NMDA receptor antagonist after traumatic brain injury in rats.

This study investigated whether memantine, a non-competitive NMDA receptor antagonist is neuroprotective after traumatic brain injury (TBI) induced in adult rats with a controlled cortical impact device. TBI led to significant neuronal death in the hippocampal CA2 and CA3 regions (by 50 and 59%, respectively), by 7 days after the injury. Treatment of rats with memantine (10 and 20 mg/Kg, i.p.) immediately after the injury significantly prevented the neuronal loss in both CA2 and CA3 regions. This is the first study showing the neuroprotective potential of memantine to prevent the TBI-induced neuronal damage.

Ornithine decarboxylase knockdown exacerbates transient focal cerebral ischemia-induced neuronal damage in rat brain.

Transient cerebral ischemia leads to increased expression of ornithine decarboxylase (ODC). Contradicting studies attributed neuroprotective and neurotoxic roles to ODC after ischemia. Using antisense oligonucleotides (ODNs), the current study evaluated the functional role of ODC in the process of neuronal damage after transient focal cerebral ischemia induced by middle cerebral artery occlusion (MCAO) in spontaneously hypertensive rats. Transient MCAO significantly increased the ODC immunoreactive protein levels and catalytic activity in the ipsilateral cortex, which were completely prevented by the infusion of antisense ODN specific for ODC. Transient MCAO in rats infused with ODC antisense ODN increased the infarct volume, motor deficits, and mortality compared with the sense or random ODN-infused controls. Results of the current study support a neuroprotective or recovery role, or both, for ODC after transient focal ischemia.

Up-regulation of the peripheral-type benzodiazepine receptor expression and [(3)H]PK11195 binding in gerbil hippocampus after transient forebrain ischemia.

In mammalian CNS, the peripheral-type benzodiazepine receptor (PTBR) is localized on the outer mitochondrial membrane within the astrocytes and microglia. The main function of PTBR is to transport cholesterol across the mitochondrial membrane to the site of neurosteroid biosynthesis. The present study evaluated the changes in the PTBR density, gene expression and immunoreactivity in gerbil hippocampus as a function of reperfusion time after transient forebrain ischemia. Between 3 to 7 days of reperfusion, there was a significant increase in the maximal binding site density (B(max)) of the PTBR antagonist [(3)H]PK11195 (by 94-156%; P < 0.01) and PTBR mRNA levels (by 1.8- to 2.9-fold; P < 0.01). At 7 days of reperfusion, in the hippocampal CA1 (the brain region manifesting selective neuronal death), PTBR immunoreactivity increased significantly. Increased PTBR expression after transient forebrain ischemia may lead to increased neurosteroid biosynthesis, and thus may play a role in the ischemic pathophysiology.

Antisense knockdown of the glial glutamate transporter GLT-1, but not the neuronal glutamate transporter EAAC1, exacerbates transient focal cerebral ischemia-induced neuronal damage in rat brain.

Transient focal cerebral ischemia leads to extensive neuronal damage in cerebral cortex and striatum. Normal functioning of glutamate transporters clears the synaptically released glutamate to prevent excitotoxic neuronal death. This study evaluated the functional role of the glial (GLT-1) and neuronal (EAAC1) glutamate transporters in mediating ischemic neuronal damage after transient middle cerebral artery occlusion (MCAO). Transient MCAO in rats infused with GLT-1 antisense oligodeoxynucleotides (ODNs) led to increased infarct volume (45 +/- 8%; p < 0.05), worsened neurological status, and increased mortality rate, compared with GLT-1 sense/random ODN-infused controls. Transient MCAO in rats infused with EAAC1 antisense ODNs had no significant effect on any of these parameters. This study suggests that GLT-1, but not EAAC1, knockdown exacerbates the neuronal death and thus neurological deficit after stroke.

Antisense knockdown of the glial glutamate transporter GLT-1 exacerbates hippocampal neuronal damage following traumatic injury to rat brain.

Traumatic injury to rat brain induced by controlled cortical impact (CCI) results in chronic neuronal death in the hippocampus. In the normal brain, glutamate transporters actively clear the glutamate released synaptically to prevent receptor overactivation and excitotoxicity. Glutamate transporter 1 (GLT-1) is the most abundant and active glutamate transporter, which mediates the bulk of glutamate uptake. CCI injury significantly decreased GLT-1 mRNA (by 49-66%, P < 0.05) and protein (by 29-44%, P < 0.05) levels in the ipsilateral hippocampus, compared with either the respective contralateral hippocampus or the sham-operated control, 24-72 h after the injury. CCI injury in rats infused with GLT-1 antisense oligodeoxynucleotides (ODNs) exacerbated the hippocampal neuronal death and mortality, compared with the GLT-1 sense/random ODN-infused controls. At 7 days after the injury, hippocampal neuronal numbers were significantly lower in the CA1 (reduced by 32%, P < 0.05), CA2 (by 45%, P < 0.01), CA3 (by 68%, P < 0.01) and dentate gyrus (by 31%, P < 0.05) in GLT-1 antisense ODN-infused rats, compared with the GLT-1 sense/random ODN-infused controls. This study suggested a role for GLT-1 dysfunction in promoting the hippocampal neuronal death after traumatic brain injury.

Loose ligation of the rat sciatic nerve is accompanied by changes in the subcellular content of protein kinase C beta II and gamma in the spinal dorsal horn.

This study examined whether loose ligation of the sciatic nerve was accompanied by specific changes in protein kinase C (PKC) betaII and gamma isozymes in the spinal dorsal horn. The isozyme staining pattern was visualized with immunocytochemistry. Their content in subcellular fractions was estimated from Western immunoblots. In control animals, PKC betaII immunoreactivity extended from lamina I into lamina III, while PKC gamma immunoreactivity was concentrated within laminae II and III. In ligated animals exhibiting thermal hyperalgesia, the content of both PKC betaII and gamma in the synaptosomal membrane fraction, but not crude cytosolic fraction, was significantly greater by an average of 40% from their respective controls. These data support suggestions that peripheral nerve injury engenders plastic changes in the dorsal horn to contribute to the development of persistent pain.

Glial glutamate transporter GLT-1 down-regulation precedes delayed neuronal death in gerbil hippocampus following transient global cerebral ischemia.

Glial (GLT-1 and GLAST) and neuronal (EAAC1) high-affinity transporters mediate the sodium dependent glutamate reuptake in mammalian brain. Their dysfunction leads to neuronal damage by allowing glutamate to remain in the synaptic cleft for a longer duration. The purpose of the present study is to understand their contribution to the ischemic delayed neuronal death seen in gerbil hippocampus following transient global cerebral ischemia. The protein levels of these three transporters were studied by immunoblotting as a function of reperfusion time (6 h to 7 days) following a 10 min occlusion of bilateral common carotid arteries in gerbils. In the vulnerable hippocampus, there was a significant decrease in the protein levels of GLT-1 (by 36-46%, P < 0.05; between 1 and 3 days of reperfusion) and EAAC1 (by 42-68%, P < 0.05; between 1 and 7 days of reperfusion). Histopathological evaluation showed no neuronal loss up to 2 days of reperfusion but an extensive neuronal loss (by approximately 84%, P < 0.01) at 7 days of reperfusion in the hippocampal CA1 region. The time frame of GLT-1 dysfunction (1-3 days of reperfusion) precedes the initiation of delayed neuronal death (2-3 days of reperfusion). This suggests GLT-1 dysfunction as a contributing factor for the hippocampal neuronal death following transient global cerebral ischemia. Furthermore, decreased EAAC1 levels may contribute to GABAergic dysfunction and excitatory/inhibitory imbalance following transient global ischemia.

Traumatic brain injury leads to increased expression of peripheral-type benzodiazepine receptors, neuronal death, and activation of astrocytes and microglia in rat thalamus.

In mammalian CNS, the peripheral-type benzodiazepine receptor (PTBR) is localized on the outer mitochondrial membrane within the astrocytes and microglia. PTBR transports cholesterol to the site of neurosteroid biosynthesis. Several neurodegenerative disorders were reported to be associated with increased densities of PTBR. In the present study, we evaluated the changes in the PTBR density and gene expression in the brains of rats as a function of time (6 h to 14 days) after traumatic brain injury (TBI). Sham-operated rats served as control. Between 3 and 14 days after TBI, there was a significant increased in the binding of PTBR antagonist [(3)H]PK11195 (by 106 to 185%, P < 0.01, as assessed by quantitative autoradiography and in vitro filtration binding) and PTBR mRNA expression (by 2- to 3. 4-fold, P < 0.01, as assessed by RT-PCR) in the ipsilateral thalamus. At 14 days after the injury, the neuronal number decreased significantly (by 85 to 90%, P < 0.01) in the ipsilateral thalamus. At the same time point, the ipsilateral thalamus also showed increased numbers of the glial fibrillary acidic protein positive cells (astrocytes, by approximately 3.5-fold) and the ED-1 positive cells (microglia/macrophages, by approximately 36-fold), the two cell types known to be associated with PTBR. Increased PTBR expression following TBI seems to be associated with microglia/macrophages than astrocytes as PTBR density at different periods after TBI correlated better with the number of ED-1 positive cells (r(2) = 0.95) than the GFAP positive cells (r(2) = 0.56). TBI-induced increased PTBR expression is possibly an adaptive response to cellular injury and may play a role in the pathophysiology of TBI.

Traumatic injury to rat brain upregulates neuronal nitric oxide synthase expression and L-[3H]nitroarginine binding.

Overstimulation of N-methyl-D-aspartate (NMDA) receptors is felt to precipitate the neuronal damage following traumatic brain injury (TBI). NMDA receptor-mediated, glutamate-induced excitotoxicity is thought to be mediated via nitric oxide (NO) formed by neuronal nitric oxide synthase (nNOS). The present study examined the mRNA and protein levels of nNOS in the ipsilateral and contralateral cortex of rats as a function of time (5 minutes to 1 week) after controlled cortical impact (CCI) brain injury. Sham-operated rats served as controls. TBI resulted in a significant increase in the levels of nNOS mRNA (1.5- to 2.8-fold, p < .05) between 2 and 4 hours after the injury. There was also a significant increase in the levels of nNOS protein (by 55% to 90%, p < .05) and binding densities of the nNOS-specific ligand L-[3H]nitroarginine (L-[3H]NOARG) (by 35% to 59%, p < .05) between 2 and 12 hours after the injury. Increased nNOS expression and function may contribute to the concomitant excitotoxic neuronal death after TBI.

Retrograde tracing of projections between the nucleus submedius, the ventrolateral orbital cortex, and the midbrain in the rat.

The fluorescent tracers fluoro-gold and 1,1'-dioctadecyl-3,3,3,3-tetramethyl indocarbocyanine perchlorate were used as retrograde markers to examine reciprocal connections between the rat nucleus submedius and the ventrolateral orbital cortex. In addition, midbrain projections to each of these regions were examined. In the prefrontal cortex, we found that input from the nucleus submedius terminates rostrally within the lateral and ventral areas of the ventrolateral orbital cortex. Conversely, the cortical input to the nucleus submedius originates from the medial and dorsal parts of the ventrolateral orbital cortex. Our data also demonstrated that neurons from the ventrolateral periaqueductal gray and the raphe nuclei project to the midline nuclei of the thalamus, including a small projection to the nucleus submedius. We further determined that regions within the ventrolateral periaqueductal gray and raphe nuclei project to the ventrolateral orbital cortex, and that these regions overlap with those that project to the nucleus submedius. These findings suggest that the nucleus submedius might be part of a neural circuit involved in the activation of endogenous analgesia.