Profiles of glutamate and GABA efflux in core versus peripheral zones of focal cerebral ischemia in mice

Specific stimulation of PV+ neurons at early stage ameliorates prefrontal ischemia-induced spatial working memory impairment

Prefrontal ischemia can cause impairments in learning and memory, executive functions and cognitive flexibility. However, the related cellular mechanisms at the early stage are still elusive. The present study used ischemic stroke in medial prefrontal cortex and systemically investigated the electrophysiological changes of the parvalbumin (PV⁺) interneurons 12 h post ischemia. We found that I_h and the related voltage sags in PV⁺ interneurons are downregulated post ischemia, which correlates with hyperpolarization of the membrane potentials and increased input resistance in these interneurons. Consistent with the suppression of I_h, postischemic PV⁺ interneurons exhibited a reduction in excitability and exerted a less inhibitory control over the neighboring pyramidal excitatory neurons. Moreover, we found that specifically chemogenetic activation of PV⁺ neurons at early stage ameliorated prefrontal ischemia-induced spatial working memory dysfunction in T-maze without effects on the locomotor coordination and balance. In contrast, suppression of PV⁺ neurons by blockade of I_h leaded to further aggravate the damage of spatial memory. These findings indicate that dysfunctional I_h in the PV⁺ neuron postischemia induces the imbalance of excitation and inhibition, which might represent a novel mechanism underlying the prefrontal ischemia-induced cognitive impairment.

Neurovascular Unit as a Source of Ischemic Stroke Biomarkers-Limitations of Experimental Studies and Perspectives for Clinical Application

Cerebral stroke, which is one of the most frequent causes of mortality and leading cause of disability in developed countries, often leads to devastating and irreversible brain damage. Neurological and neuroradiological diagnosis of stroke, especially in its acute phase, is frequently uncertain or inconclusive. This results in difficulties in identification of patients with poor prognosis or being at high risk for complications. It also makes difficult identification of these stroke patients who could benefit from more aggressive therapies. In contrary to the cardiovascular disease, no single biomarker is available for the ischemic stroke, addressing the abovementioned issues. This justifies the need for identifying of effective diagnostic measures characterized by high specificity and sensitivity. One of the promising avenues in this area is studies on the panels of biomarkers characteristic for processes which occur in different types and phases of ischemic stroke and represent all morphological constituents of the brains' neurovascular unit (NVU). In this review, we present the current state of knowledge concerning already-used or potentially applicable biomarkers of the ischemic stroke. We also discuss the perspectives for identification of biomarkers representative for different types and phases of the ischemic stroke, as well as for different constituents of NVU, which concentration levels correlate with extent of brain damage and patients' neurological status. Finally, a critical analysis of perspectives on further improvement of the ischemic stroke diagnosis is presented.

Role of neuronal nitric oxide synthase on cardiovascular functions in physiological and pathophysiological states

This review describes and summarizes the role of neuronal nitric oxide synthase (nNOS) on the central nervous system, particularly on brain regions such as the ventrolateral medulla (VLM) and the periaqueductal gray matter (PAG), and on blood vessels and the heart that are involved in the regulation and control of the cardiovascular system (CVS). Furthermore, we shall also review the functional aspects of nNOS during several physiological, pathophysiological, and clinical conditions such as exercise, pain, cerebral vascular accidents or stroke and hypertension. For example, during stroke, a cascade of molecular, neurochemical, and cellular changes occur that affect the nervous system as elicited by generation of free radicals and nitric oxide (NO) from vulnerable neurons, peroxide formation, superoxides, apoptosis, and the differential activation of three isoforms of nitric oxide synthases (NOSs), and can exert profound effects on the CVS. Neuronal NOS is one of the three isoforms of NOSs, the others being endothelial (eNOS) and inducible (iNOS) enzymes. Neuronal NOS is a critical homeostatic component of the CVS and plays an important role in regulation of different systems and disease process including nociception. The functional and physiological roles of NO and nNOS are described at the beginning of this review. We also elaborate the structure, gene, domain, and regulation of the nNOS protein. Both inhibitory and excitatory role of nNOS on the sympathetic autonomic nervous system (SANS) and parasympathetic autonomic nervous system (PANS) as mediated via different neurotransmitters/signal transduction processes will be explored, particularly its effects on the CVS. Because the VLM plays a crucial function in cardiovascular homeostatic mechanisms, the neuroanatomy and cardiovascular regulation of the VLM will be discussed in conjunction with the actions of nNOS. Thereafter, we shall discuss the up-to-date developments that are related to the interaction between nNOS and cardiovascular diseases such as hypertension and stroke. Finally, we shall focus on the role of nNOS, particularly within the PAG in cardiovascular regulation and neurotransmission during different types of pain stimulus. Overall, this review focuses on our current understanding of the nNOS protein, and provides further insights on how nNOS modulates, regulates, and controls cardiovascular function during both physiological activity such as exercise, and pathophysiological conditions such as stroke and hypertension.

Effect of ligustrazine on levels of amino acid neurotransmitters in rat striatum after cerebral ischemia-reperfusion injury

This study aimed to evaluate the effect of ligustrazine on levels of amino acid transmitters in the extracellular fluid of striatum following cerebral ischemia/reperfusion (I/R) in male Sprague-Dawley rats. A microdialysis cannula guide was implanted into the right striatum. After recovery, animals underwent a sham operation or middle cerebral artery occlusion (MCAO). Those that developed cerebral ischemia after MCAO were randomized to receive propylene glycol salt water and ligustrazine respectively. Striatal fluid samples were collected from all animals at 15-min intervals after treatment and were subjected to HPLC analysis of aspartic acid, glutamic acid, taurine, and γ-amino butyric acid. Upon the last sample collection, animals were sacrificed and brain tissue specimens were collected for triphenyltetrazolium chloride staining and NeuN staining. Compared with the sham operation, MCAO induced significant neurological deficits and increased striatal concentrations of the four neurotransmitters assessed in a time-dependent manner (P < 0.01). Ligustrazine effectively attenuated the detrimental effects of MCAO on the brain. These observations suggest that ligustrazine as a novel cerebral infarction-protective agent may have potential clinical implications for I/R-related brain damage.

Effects of medullary administration of a nitric oxide precursor on cardiovascular responses and neurotransmission during static exercise following ischemic stroke

We have reported that in rats with a 90 min left middle cerebral artery occlusion (MCAO) and 24 h reperfusion, pressor responses during muscle contractions were attenuated, as were glutamate concentrations in the left rostral ventrolateral medulla (RVLM) and left caudal VLM (CVLM), but gamma-aminobutyric acid (GABA) levels increased in left RVLM and CVLM. This study determined the effects of L-arginine, a nitric oxide (NO) precursor, within the RVLM and (or) CVLM on cardiovascular activity and glutamate/GABA levels during static exercise in left-sided MCAO rats. Microdialysis of L-arginine into left RVLM had a greater attenuation of cardiovascular responses, a larger decrease in glutamate, and a significant increase in GABA levels during muscle contractions in stroke rats. Administration of N(G)-monomethyl-L-arginine, an NO-synthase inhibitor, reversed the effects. In contrast, L-arginine administration into left CVLM evoked a greater potentiation of cardiovascular responses, increased glutamate, and decreased GABA levels during contractions in stroked rats. However, L-arginine administration into both left RVLM and left CVLM elicited responses similar to its infusion into the left RVLM. These results suggest that NO within the RVLM and CVLM modulates cardiovascular responses and glutamate/GABA neurotransmission during static exercise following stroke, and that a RVLM-NO mechanism has a dominant effect in the medullary regulation of cardiovascular function.

Effect of ginkgolide B on striatal extracellular amino acids in middle cerebral artery occluded rats

ETHNOPHARMACOLOGICAL RELEVANCE

Ginkgo biloba leaves are traditionally used in China for its health-promoting properties. There is substantial experimental evidence to support the view that Ginkgo biloba extracts have neuroprotective properties under conditions such as hypoxia/ischemia. Although a number of studies have investigated that ginkgolide B, a purified terpene lactone component extracted from Ginkgo biloba leaves, is available "platelet activating factor (PAF) receptors antagonist", "antioxidant" with a variety of actions, very little has been performed to explore the effect of ginkgolide B on extracellular amino acids in experimental animal of focal cerebral ischemia/reperfusion. In this study, the effect of ginkgolide B on the striatal extracellular levels of glutamate (Glu), aspartic acid (Asp), glycine (Gly) and γ-aminobutyric acid (GABA) was evaluated in rats undergone middle cerebral artery occlusion (MCAO) for 1h followed by 23 h reperfusion.

MATERIALS AND METHODS

The Sprague-Dawley (SD) rats received intraperitoneal injections of ginkgolide B dissolved at a dose of 10 mg kg(-1)d(-1), 20 mg kg(-1)d(-1), or normal saline (NS) of same volume 3d before the middle cerebral artery occlusion model establishment. Extracellular concentrations of glutamate, aspartic acid, glycine and GABA in striatum were monitored using in vivo microdialysis and analyzed using high-performance liquid chromatography. Excitotoxic index (EI) was calculated. Twenty-four hours after MCAO, the cerebral infarct volume was detected on 2,3,5-triphenyltetrazolium chloride-stained coronal sections.

RESULTS

The result showed that administration of ginkgolide B (10 or 20 mg kg(-1)) before ischemia reduced the ischemia-induced elevation of levels of glutamate, aspartic acid and glycine, increased the elevation of extracellular GABA, decreased the excitotoxic index and diminished the volume of cerebral infarction, although a clear concentration-response relationship was not found.

CONCLUSIONS

The present work provides the first evidence that ginkgolide B protects against cerebral ischemic injury by inhibiting excitotoxicity by modulating the imbalance of excitatory amino acids versus inhibitory amino acids, which may support the traditional use of Ginkgo biloba leaves for the treatment of stroke.

Effects of GABA(A) receptor blockade on regional cerebral blood flow and blood-brain barrier disruption in focal cerebral ischemia

In cerebral ischemia, transmission by the inhibitory neurotransmitter, γ-aminobutyric acid (GABA) is altered. This study was performed to determine whether blockade of GABA(A) receptor would affect regional cerebral blood flow (rCBF) and blood-brain barrier (BBB) permeability in a focal ischemic area of the brain. Rats were anesthetized with isoflurane and mechanically ventilated. Fifteen minutes after a permanent middle cerebral artery (MCA) occlusion, one half of the rats were infused with bicuculline 1mg/kg/min iv for 2 min followed by 0.1mg/kg/min iv to the end of the experiment. The other half were infused with normal saline. At one hour after MCA occlusion, rCBF was determined using ¹⁴C-iodoantipyrine and BBB permeability was determined by measuring the transfer coefficient (Ki) of ¹⁴C-α-aminoisobutyric acid. With MCA occlusion, rCBF was decreased in the ischemic cortex (IC) (-70%) in the control rats. In the bicuculline treated rats, the rCBF of the IC was lower (-48%) than the contralateral cortex but higher than the rCBF of the IC of the control rats (+55%). MCA occlusion increased Ki in the IC of the control rats (+72%) and bicuculline administration increased Ki further (+53%) in the IC. Blockade of GABA(A) receptors did not significantly affect rCBF or BBB permeability in the non-ischemic brain regions under isoflurane anesthesia. Our data demonstrated that blockade of GABA(A) receptors increased rCBF and enhanced the BBB disruption in focal cerebral ischemia. Our data suggest that GABA(A) receptors are involved, at least in part, in modulating rCBF and BBB disruption in focal cerebral ischemia.

Endothelial NOS expression within the ventrolateral medulla can affect cardiovascular function during static exercise in stroked rats

Temporary occlusion of the middle cerebral artery (MCA) causing damage to brain tissue occurs in the majority of human stroke victims. Reflex cardiovascular responses during static exercise were attenuated following transient MCA occlusion (MCAO) and reperfusion, mediated via alteration of the neuronal nitric oxide synthase (nNOS) protein isoform within the rostral (RVLM) and caudal (CVLM) ventrolateral medulla (Ally, A., Nauli, S.M., Maher, T.J. 2005. Molecular changes in nNOS protein expression within the ventrolateral medulla following transient focal ischemia affect cardiovascular functions. Brain Res. [1055, 73-82]. We hypothesized that the endothelial NOS (eNOS) isoform within the RVLM and CVLM might also play a role in integrating cardiovascular function. Thus, we compared cardiovascular responses to static muscle contraction and eNOS expression within the four quadrants, i.e., left and right sides of both RVLM and CVLM in sham operated rats and in rats with a temporary 90-minute one-sided MCAO followed by 24 hour reperfusion. Increases in arterial pressure during a muscle contraction were attenuated in MCAO rats when compared to sham rats. Left-sided MCAO significantly decreased the expression of eNOS in the ipsilateral side but not contralateral RVLM, and to both RVLM quadrants in sham-operated rats. In contrast, compared to sham rats and the right CVLM quadrant of MCAO rats, eNOS expression was significantly increased in the left ipsilateral CVLM quadrant in left-sided MCAO rats. These data suggest that attenuation of cardiovascular responses during muscle contraction in MCAO rats may be partly due to a reduction in eNOS expression within the ipsilateral RVLM and an overexpression of eNOS within the ipsilateral CVLM. Results demonstrate that the eNOS protein within the medulla may play a significant role in mediating cardiovascular responses during static exercise in pathophysiological conditions, such as stroke.

Reduced cortical inhibition in a mouse model of familial childhood absence epilepsy

Mutations in the GABA(A) receptor gamma2 subunit are associated with childhood absence epilepsy and febrile seizures. To understand better the molecular basis of absence epilepsy in man, we developed a mouse model harboring a gamma2 subunit point mutation (R43Q) found in a large Australian family. Mice heterozygous for the mutation demonstrated behavioral arrest associated with 6-to 7-Hz spike-and-wave discharges, which are blocked by ethosuximide, a first-line treatment for absence epilepsy in man. Seizures in the mouse showed an abrupt onset at around age 20 days corresponding to the childhood nature of this disease. Reduced cell surface expression of gamma2(R43Q) was seen in heterozygous mice in the absence of any change in alpha1 subunit surface expression, ruling out a dominant-negative effect. GABA(A)-mediated synaptic currents recorded from cortical pyramidal neurons revealed a small but significant reduction that was not seen in the reticular or ventrobasal thalamic nuclei. We hypothesize that a subtle reduction in cortical inhibition underlies childhood absence epilepsy seen in humans harboring the R43Q mutation.

A microdialysis study of effects of gastrodin on neurochemical changes in the ischemic/reperfused rat cerebral hippocampus

Gastrodin is a component extracted from the rhizome of Gastrodia elata, and has been shown to possess protective effects against neuron damage induced by simulated cerebral ischemia in previous studies. But its neurochemical effects on the ischemic brain had not been well studied. The present study aimed at evaluating the effects of gastrodin on the changes of transmitter amino acids in rat hippocampus during cerebral ischemia/reperfusion. Microdialysis sampling was performed during ischemia and early reperfusion periods in rats, and the glutamate and gamma-aminobutyric acid (GABA) in the dialysate were measured using high-performance liquid chromatography (HPLC). Administration of gastrodin (100 mg/kg) before ischemia significantly reduced the ischemia-induced elevation of glutamate levels during the postischemic period, increased the rise of extracellular GABA during the reperfusion periods, thus decreased the glutamate/GABA ratios during ischemia and reperfusion. These results provide insights to explain the neurochemical effects of gastrodin when applied prior to an ischemic event.

Erratum to "Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintenance of epilepsy." [Pharmacol. Ther. 105(3) (2005) 229-266]

Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury [central nervous system (CNS) insult]. (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels ([Ca(2+)](i)) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but the share a common molecular mechanism for producing brain damage--an increase in extracellular glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.

Cardiovascular responses and neurotransmitter changes during static muscle contraction following blockade of inducible nitric oxide synthase (iNOS) within the ventrolateral medulla

The enzyme nitric oxide synthase (NOS) which is necessary for the production of nitric oxide from L-arginine exists in three isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Our previous studies have demonstrated the roles of nNOS and eNOS within the rostral (RVLM) and caudal ventrolateral medulla (CVLM) in modulating cardiovascular responses during static skeletal muscle contraction via altering localized glutamate and GABA levels (Brain Res. 977 (2003) 80-89; Neuroscience Res. 52 (2005) 21-30). In this study, we investigated the role of iNOS within the RVLM and CVLM on cardiovascular responses and glutamatergic/GABAergic neurotransmission during the exercise pressor reflex. Bilateral microdialysis of a selective iNOS antagonist, aminoguanidine (AGN; 1.0 microM), for 60 min into the RVLM attenuated increases in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during a static muscle contraction. Levels of GABA within the RVLM were increased. After 120 min of discontinuation of the drug, MAP and HR responses and glutamate/GABA concentrations recovered to baseline values during a subsequent muscle contraction. In contrast, bilateral application of AGN (1.0 microM) into CVLM potentiated cardiovascular responses and glutamate concentration while attenuating levels of GABA during a static muscle contraction. All values recovered after 120 min of discontinuation of the drug. These results demonstrate that iNOS within the ventrolateral medulla plays an important role in modulating cardiovascular responses and glutamatergic/GABAergic neurotransmission that regulates the exercise pressor reflex.

Advances in stroke neuroprotection: hyperoxia and beyond

Refinements in patient selection, improved methods of drug delivery, use of more clinically relevant animal stroke models, and the use of combination therapies that target the entire neurovascular unit make stroke neuroprotection an achievable goal. This article provides an overview of the major mechanisms of neuronal injury and the status of neuroprotective drug trials and reviews emerging strategies for treatment of acute ischemic stroke. Advances in the fields of stem cell transplantation, stroke recovery, molecular neuroimaging, genomics, and proteomics will provide new therapeutic avenues in the near future. These and other developments over the past decade raise expectations that successful stroke neuroprotection is imminent.

Survival after treatment of rabies with induction of coma

We report the survival of a 15-year-old girl in whom clinical rabies developed one month after she was bitten by a bat. Treatment included induction of coma while a native immune response matured; rabies vaccine was not administered. The patient was treated with ketamine, midazolam, ribavirin, and amantadine. Probable drug-related toxic effects included hemolysis, pancreatitis, acidosis, and hepatotoxicity. Lumbar puncture after eight days showed an increased level of rabies antibody, and sedation was tapered. Paresis and sensory denervation then resolved. The patient was removed from isolation after 31 days and discharged to her home after 76 days. At nearly five months after her initial hospitalization, she was alert and communicative, but with choreoathetosis, dysarthria, and an unsteady gait.

Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintainance of epilepsy

Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury (central nervous system [CNS] insult), (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels [Ca(2+)](i) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but they share a common molecular mechanism for producing brain damage-an increase in extracellular glutamate concentration that causes increased intracellular neuronal calcium, leading to neuronal injury and/or death. Neurons that survive the injury induced by glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.

Functional validation of adult hippocampal organotypic cultures as an in vitro model of brain injury

To determine whether hippocampal pyramidal neurons retain authentic functional properties in mature organotypic culture, hippocampal slice cultures were established from young adult rats (P20-21). Cultures maintained 7 days in vitro retained tight organization of neuronal layers, as opposed to the widening restructure of pyramidal neurons often observed in perinatal slices. CA3 and CA1 pyramidal neurons fired action potentials in response to current injection and exhibited spontaneous and evoked synaptic currents, indicating intact neuronal function and normal hippocampal neural circuitry. We also tested neuronal sensitivity of slice cultures to ischemic injury. Acute ischemic paradigm resulted in selective death of pyramidal neurons in the CA1 region, which was prevented by treatment with an NMDA-antagonist, MK-801. Robust efflux of excitatory and inhibitory amino acid neurotransmitters was detected during ischemia, consistent with changes shown in acute slices. In summary, hippocampal organotypic cultures prepared from young adult rats maintained neuronal architecture and synaptic activity in vitro and can be used in parallel with an acute slice system to model mature brain tissue to examine ischemic pathophysiology and neuroprotective treatment.

Volume-Regulated Anion Channels Are the Predominant Contributors to Release of Excitatory Amino Acids in the Ischemic Cortical Penumbra

BACKGROUND AND PURPOSE

Release of excitatory amino acids (EAA) is considered a cause of neuronal damage in ischemia. We investigated the sources and mechanisms of EAA release using microdialysis in regions of incomplete ischemia where perfusion was reduced by 50% to 80%, by applying inhibitors of volume-regulated anion channels (VRACs) and the GLT-1 glutamate transporter.

METHODS

Reversible middle cerebral artery occlusion (rMCAo) was induced in anesthetized rats using the intraluminal suture technique. Microdialysate concentrations of glutamate, aspartate, and taurine were measured before, during 2 hours of rMCAo, and for 2 hours after rMCAo. Vehicle, dihydrokainate (DHK, 1 mmol/L), a GLT-1 inhibitor, or tamoxifen (50 micromol/L), a VRAC inhibitor, were administered continuously via the dialysis probes starting one hour prior to ischemia.

RESULTS

During incomplete ischemia, dialysate glutamate levels averaged 1.74+/-0.31 micromol/L (SEM) in the control group (n=8), 2.08+/-0.33 micromol/L in the DHK group (n=7), and were significantly lower at 0.88+/-0.30 micromol/L in the tamoxifen group (n=9; P<0.05). As perfusion returned toward baseline levels, EAA levels declined in the vehicle and tamoxifen-treated animals but they remained elevated in the DHK-treated animals.

CONCLUSIONS

In contrast to previous results in severely ischemic regions, DHK did not reduce EAA release in less severely ischemic brain, suggesting a diminished role for transporter reversal in these areas. These findings also support the hypothesis that in regions of incomplete ischemia, release of EAAs via VRACs may play a larger role than reversal of the GLT-1 transporter.

A review of heat shock protein induction following cerebellar injury

Exposure of cells to stressful environments such as heat shock, ischemia, trauma and disease, induces the cellular expression of heat shock proteins (Hsps). Since the discovery of heat shock proteins in the early 1960s, efforts to understand their function in both stressed and non-stressed cells have remained the focus of a vast collection of researchers. Post-injury heat shock protein induction is believed to identify regions of reversible cell injury as well as contribute to repair and protective mechanisms following stress. With the role of cerebellum expanding to include a number of cognitive processes in addition to contributing to motor coordination, research contributions that further our understanding of cerebellar repair strategies following injury are significant. Following cellular stress, heat shock protein expression was observed in both neuronal and glial cell populations in the injured cerebellum. Specifically, Hsp27 expression was localized primarily in Purkinje cells and glial cells within the injured cerebellum, whereas Hsp72 induction was more prominent in the granule cell layer of the cerebellum. Thus, there appears to be a preferential expression of different families of heat shock proteins in different cell populations in the injured cerebellum. There are also distinct post-injury time frames of induction for each family of heat shock protein, emphasizing differences in cellular functional requirements for each family of heat shock protein. Hsp27 was expressed immediately following injury and continued up to 20 days post-injury whereas Hsp72 was expressed immediately following injury and disappeared by 4 days post-injury, suggesting the latter contributes to processes involved in the initial repair of injured cells. This review discusses heat shock protein induction patterns in both in vivo and in vitro cerebellar injury models and provides suggestions as to the functional role of heat shock proteins in the injured cerebellum.

Synaptically evoked GABA transporter currents in neocortical glia

The presence, magnitude, and time course of GABA transporter currents were investigated in electrophysiologically characterized neocortical astrocytes in an in vitro slice preparation. On stimulation with a bipolar-tungsten stimulating electrode placed nearby, the majority of cells tested displayed long-lasting GABA transporter currents using both single and repetitive stimulation protocols. Using subtype-specific GABA transporter antagonists, long-lasting GABA transporter currents were identified in neocortical astrocytes that originated from at least two subtypes of GABA transporters: GAT-1 and GAT-2/3. These transporter currents displayed slow rise times and long decay times, contrasting the time course observed for glutamate transporter currents, and are indicative of a long extracellular time course of GABA as well as a role for glial GABA transporters during synaptic transmission.