The preservation of nerve cells in rat neostriatal slices maintained in vitro: a morphological study

Neuronal Death: Now You See It, Now You Don't

Fatally injured neurons may necrose and rupture immediately, or they may initiate a programmed cell death pathway and then wait for microglial phagocytosis. Biochemical and histopathologic assays of neuronal death assess the numbers of neurons awaiting phagocytosis at a particular time point after injury. This number varies with the fraction of neurons that have necrosed vs initiated programmed cell death, the time elapsed since injury, the rate of phagocytosis, and the assay's ability to detect neurons at different stages of programmed cell death. Many of these variables can be altered by putatively neurotoxic and neuroprotective interventions independent of the effects on neuronal death. This complicates analyses of neurotoxicity and neuroprotection and has likely contributed to difficulties with clinical translation of neuroprotective strategies after brain injury. Time-resolved assays of neuronal health, such as ongoing expression of transgenic fluorescent proteins, are a useful means of avoiding these problems.

Pannexin-1 opening in neuronal edema causes cell death but also leads to protection via increased microglia contacts

Neuronal swelling during cytotoxic edema is triggered by Na+ and Cl- entry and is Ca2+ independent. However, the causes of neuronal death during swelling are unknown. Here, we investigate the role of large-conductance Pannexin-1 (Panx1) channels in neuronal death during cytotoxic edema. Panx1 channel inhibitors reduce and delay neuronal death in swelling triggered by voltage-gated Na+ entry with veratridine. Neuronal swelling causes downstream production of reactive oxygen species (ROS) that opens Panx1 channels. We confirm that ROS activates Panx1 currents with whole-cell electrophysiology and find scavenging ROS is neuroprotective. Panx1 opening and subsequent ATP release attract microglial processes to contact swelling neurons. Depleting microglia using the CSF1 receptor antagonist PLX3397 or blocking P2Y12 receptors exacerbates neuronal death, suggesting that the Panx1-ATP-dependent microglia contacts are neuroprotective. We conclude that cytotoxic edema triggers oxidative stress in neurons that opens Panx1 to trigger death but also initiates neuroprotective feedback mediated by microglia contacts.

Synergism of type 1 metabotropic and ionotropic glutamate receptors in cerebellar molecular layer interneurons in vivo

Type 1 metabotropic glutamate receptors (mGluR1s) are key elements in neuronal signaling. While their function is well documented in slices, requirements for their activation in vivo are poorly understood. We examine this question in adult mice in vivo using 2-photon imaging of cerebellar molecular layer interneurons (MLIs) expressing GCaMP. In anesthetized mice, parallel fiber activation evokes beam-like Ca_i rises in postsynaptic MLIs which depend on co-activation of mGluR1s and ionotropic glutamate receptors (iGluRs). In awake mice, blocking mGluR1 decreases Ca_i rises associated with locomotion. In vitro studies and freeze-fracture electron microscopy show that the iGluR-mGluR1 interaction is synergistic and favored by close association of the two classes of receptors. Altogether our results suggest that mGluR1s, acting in synergy with iGluRs, potently contribute to processing cerebellar neuronal signaling under physiological conditions.

Isoflurane Postconditioning Upregulates Phosphorylated Connexin 43 in the Middle Cerebral Artery Occlusion Model and Is Probably Associated with the TGF-β1/Smad2/3 Signaling Pathway

Aim

Connexin 43 (Cx43) has been identified to be important for cerebral ischemia/reperfusion (I/R) injury as well as protection from it. This study was aimed at investigating the relationship between phosphorylated Cx43 (p-Cx43), transforming growth factor-β1 (TGF-β1 (TGF.

Methods

The middle cerebral artery occlusion (MCAO) model was induced in 96 male Sprague-Dawley rats, weighing 250-300 g. The rats were randomized into 12 groups, namely, sham, middle cerebral artery occlusion (MCAO)/I/R, I/R+1.5% ISPOC, I/R+LY2157299 (blocker of TGF-β1 (TGF-β1 (TGF-β1 (TGF-β1 (TGF.

Results

Neurological deficit scores, brain infarct volume, and damaged neurons in the I/R group significantly increased compared to those in the sham group (P < 0.05). However, in the ISPOC group, damage of the brain was significantly ameliorated (P < 0.05). However, in the ISPOC group, damage of the brain was significantly ameliorated (P < 0.05). However, in the ISPOC group, damage of the brain was significantly ameliorated (β1 (TGF-P < 0.05). However, in the ISPOC group, damage of the brain was significantly ameliorated (β1 (TGF-P < 0.05). However, in the ISPOC group, damage of the brain was significantly ameliorated (β1 (TGF-β1 (TGF-P < 0.05). However, in the ISPOC group, damage of the brain was significantly ameliorated (.

Conclusion

Isoflurane postconditioning (ISPOC) may alleviate cerebral I/R injury through upregulating the expression of p-Cx43, and the TGF-β1/Smad2/3 signaling pathway may be involved in the process.β1 (TGF.

Effects of activin A and its downstream ERK1/2 in oxygen and glucose deprivation after isoflurane-induced postconditioning

BACKGROUND

Isoflurane postconditioning (ISPOC) plays a neuroprotection role in the brain. Previous studies confirmed that isoflurane postconditioning can provide better protection than preconditioning in acute hypoxic-ischemic brain damage, such as acute craniocerebral trauma and ischemic stroke. Numerous studies have reported that activin A can protect rat's brain from cell injury. However, whether activin A and its downstream ERK1/2 were involved in isoflurane postconditioning-induced neuroprotection is unknown.

METHODS

A total of 80 healthy Sprague-Dawley rats weighing 50-70g were randomly divided into 10 groups of 8: normal control, oxygen and glucose deprivation (OGD), 1.5% ISPOC, 3.0% ISPOC, 4.5% ISPOC, blocker of activin A (SB431542), blocker of ERK1/2 (U0126), 3.0% ISPOC+SB431542, 3.0% ISPOC+U0126, and vehicle (dimethyl sulfoxide(DMSO)) group. Blockers (SB431542 and U0126) were used in each concentration of isoflurane before OGD. Hematoxylin-eosin staining, 2,3,5-triphenyl tetrazolium chloride staining, and propidium iodide (PI) staining were conducted to assess the reliability in the brain slices. Immunofluorescence, Western blot, and quantitative real-time PCR(Q-PCR) were performed to validate the protein expression levels of activin A, Smad2/3, P-Smad2/3, ERK1/2, and phosphorylation ERK1/2 (P-ERK1/2).

RESULTS

The number of damaged neurons and mean fluorescence intensity(MFI) of PI staining increased, but formazan generation, expression levels of activin A and P-ERK1/2 protein, and mRNA synthesis level of activin A decreased in the OGD group compared with the normal control group (p<0.05). The number of damaged neurons and MFI of PI staining decreased, but formazan production, expression levels of activin A, P-Smad2/3, and P-ERK1/2, and mRNA synthesis level of activin A increased significantly in the 1.5% ISPOC and 3.0% ISPOC groups (p<0.05) compared with the OGD group. The result in the 4.5% ISPOC group, was completely opposite to the 1.5% ISPOC and 3.0% ISPOC groups. The number of damage neuron and MFI of PI staining increased, but formazan production, expression levels of activin A, P-Smad2/3, and P-ERK1/2, and mRNA synthesis level of activin A decreased in the 4.5% ISPOC group. However, the expression levels of activin A, P-Smad2/3, and P-ERK1/2, and mRNA synthesis level of activin A in the 4.5% ISPOC group were higher than the OGD group (p<0.05). The other results were compared between the SB431542 group/the U0126 group and 3.0% ISPOC group. The MFI of PI staining increased, but the expression levels of activin A, P-Smad2/3, and P-ERK1/2 decreased (p<0.05). The expression level of ERK1/2 protein in all groups exhibited no change (p>0.05).

CONCLUSION

Results of this study showed that 3.0% concentration of isoflurane postconditioning provided better neuroprotection than 1.5% and 4.5% concentrations of isoflurane. Activin A/Smad 2/3 and activin A/ERK1/2 signaling pathway may be involved in ISPOC-induced neuroprotection.

Acute and chronic efficacy of bumetanide in an in vitro model of posttraumatic epileptogenesis

BACKGROUND

Seizures triggered by acute injuries to the developing brain respond poorly to first-line medications that target the inhibitory chloride-permeable GABAA receptor. Neuronal injury is associated with profound increases in cytoplasmic chloride ([Cl(-)]i) resulting in depolarizing GABA signaling, higher seizure propensity and limited efficacy of GABAergic anticonvulsants. The Na(+)-K(+)-2Cl(-) (NKCC1) cotransporter blocker bumetanide reduces [Cl(-)]i and causes more negative GABA equilibrium potential in injured neurons. We therefore tested both the acute and chronic efficacy of bumetanide on early posttraumatic ictal-like epileptiform discharges and epileptogenesis.

METHODS

Acute hippocampal slices were used as a model of severe traumatic brain injury and posttraumatic epileptogenesis. Hippocampal slices were then incubated for 3 weeks. After a 1-week latent period, slice cultures developed chronic spontaneous ictal-like discharges. The anticonvulsant and anti-epileptogenic efficacy of bumetanide, phenobarbital, and the combination of these drugs was studied.

RESULTS

Bumetanide reduced the frequency and power of early posttraumatic ictal-like discharges in vitro and enhanced the anticonvulsant efficacy of phenobarbital. Continuous 2-3 weeks administration of bumetanide as well as phenobarbital in combination with bumetanide failed to prevent posttraumatic ictal-like discharges and epileptogenesis.

CONCLUSIONS

Our data demonstrate a persistent contribution of NKCC1 cotransport in posttraumatic ictal-like activity, presumably as a consequence of chronic alterations in neuronal chloride homeostasis and GABA-mediated inhibition. New strategies for more effective reduction in posttraumatic and seizure-induced [Cl(-)]i accumulation could provide the basis for effective treatments for posttraumatic epileptogenesis and the resultant seizures.

Depolarizing GABA and developmental epilepsies

Early in development, GABA, which is the main inhibitory neurotransmitter in adult brain, depolarizes immature neurons and exerts dual--excitatory and shunting/inhibitory--effects in the developing neuronal networks. The present review discusses some general questions, including the properties of excitation at depolarizing GABAergic synapse and shunting inhibition by depolarizing GABA; technical issues in exploration of depolarizing GABA using various techniques and preparations, including the developmental aspects of traumatic injury and what is known (or rather unknown) on the actions of GABA in vivo; complex roles of depolarizing GABA in developmental epilepsies, including a contribution of depolarizing GABA to enhanced excitability in the immature networks, caused by repetitive seizures accumulation of intracellular chloride concentration that increases excitatory GABA power and its synchronizing proconvulsive effects, and correction of chloride homeostasis as a potential strategy to treat neonatal seizures.

Excitatory actions of GABA in the intact neonatal rodent hippocampus in vitro

The excitatory action of gamma-aminobutyric acid (GABA) is considered to be a hallmark of the developing nervous system. However, in immature brain slices, excitatory GABA actions may be secondary to neuronal injury during slice preparation. Here, we explored GABA actions in the rodent intact hippocampal preparations and at different depths of hippocampal slices during the early post-natal period [post-natal days (P) 1–7]. We found that in the intact hippocampus at P1–3: (i) GABA exerts depolarizing action as seen in cell-attached single GABA(A) channel recordings; (ii) GABA(A) receptor (GABA(A)-R) agonist isoguvacine and synaptic activation of the GABA(A)-Rs increase the frequency of multiple unit activity and the frequency of the network-driven giant depolarizing potentials (GDPs); and that (iii) Na⁺–K⁺–2Cl^- cotransporter (NKCC1) antagonist bumetanide suppresses GDPs and the excitatory actions of isoguvacine. In the hippocampal slices at P2–5, isoguvacine and synaptic activation of GABA(A)-Rs-evoked excitatory responses at all slice depths, including surface and core. Thus, GABA exerts excitatory actions in the intact hippocampus (P1–3) and at all depths of hippocampal slices (P2–5). Therefore, the excitatory actions of GABA in hippocampal slices during the first post-natal days are not due to neuronal injury during slice preparation, and the trauma-related excitatory GABA actions at the slice surface are a fundamentally different phenomenon observed during the second post-natal week.

Traumatic alterations in GABA signaling disrupt hippocampal network activity in the developing brain

Severe head trauma causes widespread neuronal shear injuries and acute seizures. Shearing of neural processes might contribute to seizures by disrupting the transmembrane ion gradients that subserve normal synaptic signaling. To test this possibility, we investigated changes in intracellular chloride concentration ([Cl(-)](i)) associated with the widespread neural shear injury induced during preparation of acute brain slices. In hippocampal slices and intact hippocampal preparations from immature CLM-1 mice, increases in [Cl(-)](i) correlated with disruption of neural processes and biomarkers of cell injury. Traumatized neurons with higher [Cl(-)](i) demonstrated excitatory GABA signaling, remained synaptically active, and facilitated network activity as assayed by the frequency of extracellular action potentials and spontaneous network-driven oscillations. These data support a more inhibitory role for GABA in the unperturbed immature brain, demonstrate the utility of the acute brain slice preparation for the study of the consequences of trauma, and provide potential mechanisms for both GABA-mediated excitatory network events in the slice preparation and early post-traumatic seizures.

Excitatory GABA: How a Correct Observation May Turn Out to be an Experimental Artifact

The concept of the excitatory action of GABA during early development is based on data obtained mainly in brain slice recordings. However, in vivo measurements as well as observations made in intact hippocampal preparations indicate that GABA is in fact inhibitory in rodents at early neonatal stages. The apparent excitatory action of GABA seems to stem from cellular injury due to the slicing procedure, which leads to accumulation of intracellular Cl⁻ in injured neurons. This procedural artifact was shown to be attenuated through various manipulations such as addition of energy substrates more relevant to the in vivo situation. These observations question the very concept of excitatory GABA in immature neuronal networks.

Effect of vasopressin on survival of Purkinje neurons in rat cerebellar slices after an in vitro simulated ischemia

BACKGROUND

Arginine vasopressin (AVP) is frequently used in patients under the risk of brain injury. It has been shown to induce brain injury after ischemia and reperfusion in in vivo animal models. We determined the effect of vasopressin on the brain injury after ischemia-reperfusion using in vitro model.

METHODS

Cerebellar brain slices were prepared from adult Sprague-Dawley rats. They were then subjected to simulated ischemia (oxygen-glucose deprivation) for 20 min in the absence (control) or presence of vasopressin (5, 10, 50, 100, 500 pg/ml). After being recovered in oxygenated artificial cerebrospinal fluid for 5 h, they were fixed for morphologic examination to determine the percentage of live Purkinje cells.

RESULTS

There were no differences in the survival rate of Purkinje cells among the control and vasopressin groups.

CONCLUSIONS

Vasopressin at concentrations studied has no direct effect on brain ischemia-reperfusion injury.

Postconditioning with isoflurane reduced ischemia-induced brain injury in rats

BACKGROUND

Preexposure of brain to isoflurane, a commonly used anesthetic, induces ischemic tolerance. This phenomenon is called isoflurane preconditioning. However, it is not known whether isoflurane application after ischemia provides neuroprotection.

METHODS

Corticostriatal slices (400 microm) freshly prepared from adult male Sprague-Dawley rats were subjected to a 15-min oxygen-glucose deprivation (OGD; to simulate ischemia in vitro). Isoflurane was applied after OGD. Brain slices were harvested 2 h after OGD for measuring 2,3,5-triphenyltetrazolium chloride (TTC) conversion to quantify cell injury. Adult male Sprague-Dawley rats were also subjected to middle cerebral arterial occlusion for 90 min and then treated with or without 2% isoflurane for 60 min started at the onset of reperfusion. The infarct volumes, neurologic deficit scores, and performance on rotarod were evaluated at 24 h after the onset of reperfusion.

RESULTS

Isoflurane applied immediately after the 15-min OGD for 30 min dose-dependently reversed the OGD-induced decrease of TTC conversion. The TTC conversion was 34 +/- 16% and 58 +/- 28% of the control, respectively, for OGD alone and OGD plus 2% isoflurane (P < 0.05, n = 12). Application of 2% isoflurane for 30 min started at 10 min after the OGD also reduced the OGD-decreased TTC conversion. The presence of 0.3 microm glibenclamide, a general adenosine 5'-triphosphate-sensitive potassium channel blocker, or 500 microm 5-hydroxydecanoic acid, a mitochondrial adenosine 5'-triphosphate-sensitive potassium channel blocker, during the application of 2% isoflurane abolished the isoflurane preservation of TTC conversion. Application of isoflurane during reperfusion also improved neurologic outcome after brain ischemia.

CONCLUSIONS

The results suggest that isoflurane administrated after OGD or brain ischemia provides neuroprotection. Mitochondrial adenosine 5'-triphosphate-sensitive potassium channels may be involved in this protection.

Hypothermic preconditioning reduces Purkinje cell death possibly by preventing the over-expression of inducible nitric oxide synthase in rat cerebellar slices after an in vitro simulated ischemia

We showed that hypothermic preconditioning (HPC) increased survival of Purkinje neurons in rat cerebellar slices after oxygen-glucose deprivation (OGD). HPC also reduced the OGD-increased expression of high mobility group I (Y) proteins, a transcription factor that can enhance inducible nitric oxide synthase (iNOS) expression. iNOS is a putatively damaging protein that contributes to ischemic brain injury. Heat shock proteins (HSPs) can be induced by various stimuli to protect cells. We hypothesize that HPC induces neuroprotection by reducing the expression of putatively damaging proteins such as iNOS and/or by increasing the expression of putatively protective proteins such as HSPs. Cerebellar slices were prepared from adult male Sprague-Dawley rats and incubated in circulating artificial cerebrospinal fluid. OGD was for 20 min at 37 degrees C and was followed by a 5-h recovery at 37 degrees C before slices were used for morphological, immunohistochemical and Western analyses. HPC was performed by incubating slices at 33 degrees C for 20 min at 1 h before the OGD. HPC and aminoguanidine, an iNOS inhibitor, prevented OGD-induced Purkinje cell death/injury. OGD increased the expression of iNOS and nitrosylated proteins. These increases were abolished by aminoguanidine and HPC. Interestingly, the expression of HSP70 was increased by OGD but not by HPC. Our results suggest that an increased iNOS expression contributes to the pathophysiology of OGD-induced Purkinje neuronal death in our model. Our results also suggest the involvement of inhibiting the expression of the putatively damaging iNOS proteins in the HPC-induced neuroprotection. HSP70 may not contribute to the HPC-induced neuroprotection.

nPKCepsilon and NMDA receptors participate in neuroprotection induced by morphine pretreatment

Morphine pretreatment induces ischemic tolerance in neurons, but it remains uncertain whether novel protein kinase C epsilon isoform (nPKCepsilon) and N-methyl-D-aspartate (NMDA) receptors are involved in this neuroprotection. The present study examined this issue. Hippocampal slices from adult BALB/C mice were incubated with morphine at 0.1-10.0 muM in the presence or absence of various antagonists for 30 minutes and then kept in morphine- and antagonist-free buffer for 30 minutes before being subjected to oxygen-glucose deprivation for 20 minutes. After recovery in oxygenated artificial fluid for 5 hours, assessment of slice injury was done by determination of the intensity of slice stain after they were incubated with 2% 2,3,5-triphenyltetrazolium chloride for 30 minutes and extracted by organic solvent for 24 hours. At designated periods, slices were preserved for immunoblot analysis to observe effects of morphine pretreatment on membrane translocation and total protein expression of nPKCepsilon and phosphorylation of NR1 subunits of NMDA receptors. The neuroprotection induced by morphine pretreatment was partially blocked by chelerythrine (a nonselective PKC blocker), epsilonv(1-2) (a selective nPKCepsilon antagonist), MK-801 (a noncompetitive NMDA receptor blocker), chelerythrine combined with MK-801, and epsilonv(1-2) with MK-801. Morphine pretreatment significantly inhibited nPKCepsilon membrane translocation and phosphorylation of NR1 subunits of NMDA receptors during reperfusion injury. However, epsilonv(1-2) blocked these effects induced by morphine pretreatment. These findings suggested that nPKCepsilon and NMDA receptors might participate in neuroprotection induced by morphine pretreatment, and NMDA receptors might be downstream targets of nPKCepsilon.

Isoflurane preconditioning decreases glutamate receptor overactivation-induced Purkinje neuronal injury in rat cerebellar slices

A brain slice model was used to test the hypothesis that preconditioning with isoflurane, a commonly used volatile anesthetic in clinical practice, reduces neuronal injury caused by overstimulation of glutamate receptors. Glutamate receptors were stimulated by various concentrations of glutamate for 20 min, N-methyl-d-aspartate (NMDA) for 15 min or alpha-amino-3-hydroxy-5-methyl-4-isoxazol propionic acid (AMPA) for 15 min. Morphology of Purkinje neurons in the cerebellar slices of adult male Sprague-Dawley rats was evaluated 5 h after the agonist stimulation. Glutamate, NMDA and AMPA induced a dose-dependent decrease in the percentage of morphologically normal Purkinje neurons. The concentration to induce the maximal neurotoxic effect was 300 microM for glutamate, 300 microM for NMDA and 30 microM for AMPA. Isoflurane preconditioning (2% isoflurane for 30 min and then a 15-min rest period before the agonist stimulation) significantly reduced the neurotoxicity induced by 300 microM glutamate, 300 microM NMDA or 30 microM AMPA. Isoflurane preconditioning-induced protection against glutamate neurotoxicity was abolished by two protein kinase C (PKC) inhibitors, calphostin C (0.5 microM) and chelerythrine (5 microM), or a nitric oxide synthase (NOS) inhibitor, l-nitro(G)-arginine methyl ester (l-NAME, 1.5 mM), but was not affected by an adenosine A1 receptor inhibitor, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 300 nM), or a Gi protein inhibitor, pertussis toxin (PTX, 200 ng/ml). Isoflurane preconditioning-induced protection against NMDA neurotoxicity was also abolished by calphostin C, chelerythrine or l-NAME. Thus, isoflurane preconditioning reduced glutamate receptor overstimulation-induced neuronal injury/death. This neuroprotection may be PKC- and NOS-dependent.

Optical assessment of motoneuron function in a “twenty-four-hour” acute spinal cord slice model from fetal rats

In acute slice preparations of most brain regions, neuronal functions are preserved for only few hours. Since the effects of growth factors or neurotoxic agents are often manifested beyond this time scale, corresponding studies are typically performed on cultured cells. However, cell cultures are generated and maintained under vastly different conditions that can grossly alter neuronal properties. For example, glutamate application to motoneuronal cultures has been reported to modulate neurite formation in some studies while in others it has been reported to kill cells. Here, we have examined whether acute spinal cord slices from rat fetuses can be used within a time window of 24 h for assessment of long-term effects of neuromodulators. In these slices, we have studied the action of glutamate on lumbar motoneurons loaded with fura-2 and rhodamine-123 to monitor intracellular Ca2+ ([Ca2+]i) and mitochondrial potential (Deltapsi), respectively. Further, loading with fura-2 or propidium iodide allowed for morphological assessment of cell viability and death, respectively. Pulses (15 s) or 1 h application of glutamate (300 microM) evoked a moderate (approximately 500 nM) [Ca2+]i rise, but no change of Deltapsi. Even after 24 h, no glutamate-induced cell death was observed and glutamate pulse-evoked [Ca2+]i transients were comparable to controls. The data demonstrate that glutamate does not deregulate [Ca2+]i homeostasis in fetal motoneurons in situ. We propose that acute spinal cord slices from perinatal rodents are a robust model that allows for analysis of neuronal properties and cell viability within a time window of at least 24 h.

Isoflurane preconditioning reduces purkinje cell death in an in vitro model of rat cerebellar ischemia

We monitored survival of Purkinje cells in rat cerebellar slices to test the hypothesis that isoflurane preconditioning reduces ischemia-induced neuronal death. Preconditioning the brain slices with isoflurane, a volatile anesthetic commonly used in clinical practice, at 1-4% for 15 min at 37 degrees C significantly decreased Purkinje cell injury and death caused by a 20-min ischemia (simulated by oxygen-glucose deprivation, OGD). The effective concentration for half of the maximal effect (EC(50)) for this isoflurane preconditioning-induced neuroprotection was 1.17+/-0.31% and the maximal protective effects were achieved at 3% or higher concentrations of isoflurane. In addition, preconditioning the cells with isoflurane for 15-30 min was needed for the preconditioning to be maximally protective. Although farnesyl protein transferase inhibitor III blocked the protective effects of OGD preconditioning (a 3-min OGD 15 min before the 20-min OGD), this inhibitor did not affect the neuroprotection induced by isoflurane preconditioning. While DL-threo-beta-hydroxyaspartic acid (THA), a specific glutamate transporter inhibitor, did not change basal OGD-induced cell death rate, THA blocked the neuroprotection induced by isoflurane preconditioning but not by OGD preconditioning. Glybenclamide, a K(ATP) channel inhibitor, did not block the neuroprotection induced by either isoflurane or OGD preconditioning. Our results suggest that isoflurane preconditioning is neuroprotective. The isoflurane concentrations and times needed for the preconditioning to be neuroprotective are clinically relevant. The mechanisms of this protection seem to involve modulation of glutamate transporter activity.

Laminar variation in neuronal viability and trophic dependence in neocortical slices

Organotypic slices are used frequently in studies of central nervous system development and function because they provide excellent experimental access with significant preservation of cellular context and relationships. Within a slice, however, a variety of factors may cause individual classes of neurons to respond differently to the culture environment. Differences in deafferentation, cellular maturation, trophic dependence and ongoing naturally occurring cell death may produce changes in the neuronal population that are transparent to the experimenter but that could affect experimental results significantly. In this study, we examined the distribution and prevalence of cell death among neurons in each cortical layer in organotypic slices. In addition, we assessed the ability of several neurotrophic factors to ameliorate neuronal death in each cortical layer. Within the first 24 hr in culture, there was striking laminar variation in the extent of neuronal death in culture, which could not be accounted for by the pattern of programmed cell death in vivo. In addition, neurons in the six layers of the neocortex differed in the degree to which they could be rescued by neurotrophic factors. These data suggest that differential neuronal death and rescue are important considerations in studies utilizing organotypic slices and may represent particularly confounding variables in studies of effects of trophic factors in such preparations.

Chemical preconditioning in mice is not mediated by upregulation of nitric oxide synthase isoforms

Ischemic preconditioning requires increased nitric oxide (NO) production. However, NO may also trigger delayed neuronal death cascades. The goal therefore was to investigate nitric oxide synthase (NOS) isoforms (neuronal NOS: nNOS; endothelial NOS: eNOS; inducible NOS: iNOS) with reverse transcriptase-polymerase chain reaction in hippocampal slices from control mice and slices prepared upon preconditioning in vivo (single intraperitoneal injection of 20 mg/kg body weight 3-nitropropionate (3NP)). One hour after preconditioning nNOS (108+/-34%, mean+/-SD), eNOS (93+/-34%), and iNOS (282+/-261%) remained at control levels. Similarly, nNos, eNOS, and iNOS stayed at control level 12, 24, and 72 h after preconditioning with 3NP. Incubation of slices, however, drastically increased iNOS (1676+/-818, P<0.01). We conclude that chemical preconditioning other than ischemic preconditioning may not increase potentially harmful nitric oxide synthase isoforms.

Confocal laser scanning microscopy used to monitor intracellular Ca2+ changes in hippocampal CA 1 neurons during energy deprivation

An increase in intracellular calcium during cerebral ischemia has been proposed as a common final pathway underlying the events leading to neuronal death. Intracellular calcium has been measured with ion selective electrodes during energy deprivation (ED) in hippocampal slices and with fluorescent techniques in neuronal cultures. In the present study, we describe a novel method to visualize and quantify changes in intracellular calcium in brain slices using Confocal Laser Scanning Microscopy (CLSM). CA 1 pyramidal neurons in hippocampal slices were filled by intracellular injection with a 1:2 mixture of the fluorescent dyes Fluo 3 and Fura Red. The neurons were then visualized using CLSM, and the ratio of the fluorescence from each probe used to quantify intracellular calcium concentrations before and during ED. The free intracellular calcium concentration was 60 nM prior to ED and increased to 24 microM during ED. These results demonstrates that CLSM and fluorescent probes can be used in functional neuronal networks in addition to cell cultures as previously described.

Neuronal thermosensitivity and survival of rat hypothalamic slices in recording chambers

Several studies have examined the activity of neurons in hypothalamic tissue slices. The present experiments studied relationships between neuronal activity (firing rate and thermosensitivity) and tissue survival as a function of time and slice thickness. Rat hypothalamic tissue slices were sectioned at different thicknesses (350, 450, and 600 microm) and maintained in an oxygenated interface chamber which was perfused with artificial cerebrospinal fluid (ACSF). Electron and light microscopy were used to examine tissue morphology at different depths from the slice surfaces, and extracellular recordings were used to measure each cell's spontaneous activity and response to changes in temperature. Tissue damage was most evident at tissue layers nearest the gas-exposed surface. At 9 h in the chamber, 350 microm thick slices showed subtle changes in morphology with little difference between the gas-exposed and ACSF-exposed surfaces. In the 450 and 600 microm thick slices, tissue degeneration became more evident with increased damage at the gas-exposed surface. This damage extended fully into the tissue of the 600 microm section. There were no differences in firing rate or thermosensitivity between 350 and 450 microm slices; but in 600 microm slices, there were fewer spontaneously active neurons, although these neurons had a higher mean thermosensitivity. Based on the incidence of spontaneous activity and morphological integrity, the results suggest that electrophysiological experiments using 350 microm slices are preferable to experiments using thicker slices.

Ultrastructural features of the isolated guinea-pig brain maintained in vitro by arterial perfusion

The morphological features of cerebral tissue in the isolated guinea-pig brain maintained in vitro by arterial perfusion are described. Light and electron microscopic analysis of the thalamus, the somatosensory cortex and the limbic cortices (hippocampus, piriform and entorhinal cortices) was performed after different periods of incubation in vitro (1, 7 and 12 h), in parallel with an electrophysiological study. The morphological analysis showed that neuronal elements retained their normal appearance at both cellular and subcellular level in the examined brain regions up to an incubation period of 12 h. Immunoreactivity for GABA was also preserved for up to 12 h of in vitro perfusion. Vasogenic edema and perivascular extracellular swelling appeared after 7 h, together with signs of progressive astrocytic deterioration. These findings show that normal electrophysiological recordings correlate with good anatomical preservation of the isolated guinea-pig brain preparation after prolonged times of arterial in vitro perfusion.

Depolarization-induced release of corticotropin-releasing factor (CRF) in primary neuronal cultures of the amygdala

The 41-amino acid neuropeptide, corticotropin-releasing factor (CRF) is distributed throughout the central nervous system and appears to play a pivotal role in stress, anxiety and depression. CRF is present in high concentrations in the limbic brain region, the amygdala, an area important in emotional and autonomic responses to stress. In this report, primary neuronal cultures of amygdala from fetal rat brains (E18-E19) were used to study depolarization-induced CRF release. Immunocytochemical analyses of the cultures revealed a bead-like distribution of CRF immunoreactivity (CRFir) in about 1% of the neurons. Time course studies showed that 56 mM KCl-evoked CRF release occurred with an initial burst during the first minute that was maintained over 30 min; basal CRF release slightly increased over a 30-min period. CRF release in response to depolarization increased with increasing cell density and with increasing days in culture. Multiple serial incubations alternating basal and depolarizing conditions caused a depletion of the releasable pool of CRF. Potassium-evoked CRF release was calcium-dependent. These data suggest that primary neuronal cultures of fetal rat amygdala are an effective model system to study CRF release in this brain region.

Overview of chemical sampling techniques

Although many of the ideas for sampling the chemical microenvironment of the brain were present, at least in nascent form, three decades ago or more, the last 10 years have witnessed a particularly spectacular surge of development, refinement, and use. We are now able to measure virtually any endogenous brain chemical in vivo at commendable levels of sensitivity, selectivity, and speed. The long-dreamt-of goal of being able to correlate neurochemical events with ongoing behavior and/or presentation of salient environmental cues and stimuli has already been largely achieved. Further refinements of existing techniques may well lead to levels of analysis inconceivable even a few years ago. The implications for theory-building and hypothesis-testing are enormous, particularly within such essentially virgin domains as behavioral neuroscience and biological psychiatry. These are truly exciting times.

Depression of glutamatergic and GABAergic synaptic responses in striatal spiny neurons by stimulation of presynaptic GABAB receptors

The influence of gamma-aminobutyric acidB (GABAB) receptor stimulation on the excitatory and inhibitory synaptic potentials and membrane properties of identified striatal spiny neurons was examined in a corticostriatal slice preparation. Stimulation of the subcortical white matter evoked a monosynaptic, excitatory postsynaptic potential (EPSP) and a polysynaptic, inhibitory postsynaptic potential (IPSP) in spiny neurons. The EPSP had two components: a large amplitude response which could be blocked by the kainate/quisqualate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM), and a small amplitude, long-duration depolarization which could be blocked by the N-methyl-D-aspartate receptor antagonist, d-(-)-2-amino-5-phosphonovaleric acid (APV, 100 microM). The IPSP was observed as a membrane depolarization when recorded from neurons at resting membrane potential. However, when neurons were injected with the Na(+)-channel blocker, QX-314, allowing cells to be depolarized above their spike thresholds, a prominent hyperpolarizing IPSP was readily observed which could be blocked by the GABAA antagonist, bicuculline (10-50 microM). This bicuculline-sensitive IPSP was responsible for the inhibition of EPSP amplitude and probability of spike discharge revealed using paired stimulation of the subcortical white matter. The amplitude of both the EPSP and the IPSP were depressed by the GABAB receptor agonist, p-chlophenyl-GABA (baclofen, 0.5-100 microM) in a concentration-dependent manner. Baclofen also blocked paired stimulus inhibition of spike discharge. These effects of baclofen persisted in slices in which the cortex was removed and were reversed by the GABAB receptor antagonist, 3-amino-3-hydroxy-2-(4-chlorophenyl)-propanesulphonic acid (saclofen, 100-500 microM). In contrast to its profound influence on synaptic input, baclofen did not alter resting membrane potential, input resistance, membrane current-voltage relationship, or spike threshold of the cells recorded, and therefore did not appear to exert direct postsynaptic effects on the striatal spiny neurons. Taken together, these data indicate that the depressant effects of baclofen on EPSPs are mediated through GABAB receptors located on the terminals of glutamatergic afferents within the striatum. Moreover, the results suggest that the actions of baclofen on IPSPs and paired stimulus inhibition are produced by activation of GABAB receptors within the striatum at a site presynaptic to spiny neurons, either on the terminals of GABAergic afferents or on an interposed non-spiny GABAergic cell. Thus, GABAB hetero- and auto-receptors have the capacity to provide a negative feedback mechanism through which the major excitatory and inhibitory inputs to striatal spiny neurons are regulated.

Morphology of CA3 neurons in hippocampal slices with nonepileptic and epileptic activity: a light and electron microscopic study

In guinea pig hippocampal slices, relations between morphology and spontaneous bioelectric activity of neurons were studied in control saline and with exposure to the epileptogenic drug pentylenetetrazole (PTZ) for 2-3 h. Light and electron microscopic structures of the CA3 region were analysed after recording the membrane potential. Neurons in slices kept in control saline exhibited spontaneous aperiodic bioelectric activities partly mixed with rhythmically occurring burst discharges. In slices exposed to PTZ, these periodic burst discharges and/or paroxysmal depolarization shifts (PDS) predominated. Light microscopic comparison focussing on tissue preservation showed no significant differences between control and PTZ-treated slices. Ultrastructural morphology revealed, on the one hand, no differences regarding spine and synaptic densities, and on the other hand, significantly more irregular electron translucent vacuoles within dendrites of PTZ-treated slices being either randomly distributed or clustered. The vacuoles are interpreted as early changes during epileptic activity.

Functionally distinct subpopulations of striatal neurons are differentially regulated by GABAergic and dopaminergic inputs--II. In vitro analysis

In the companion report [Nisenbaum and Berger (1992) Neuroscience 48, 561-578] the contrasting paired impulse responses to stimulation of the corticostriatal pathway which define the Type I and Type II subpopulations of striatal neurons were shown to reflect differential regulation by GABAergic and dopaminergic inputs. More specifically, the decreased probability of spike discharge (inhibition) to long interstimulus intervals (60-260 ms) characteristic of Type I neurons was found to be dependent on dopaminergic input via D1 receptor activation, whereas the inhibition to short interstimulus intervals (10-20 ms) distinctive of Type II neurons was found to be mediated by GABAergic input acting through GABAA receptor stimulation. The present experiments have further investigated the contribution of GABAergic and dopaminergic feedforward and/or feedback circuits to the functional identities of Type I and Type II neurons using an in vitro corticostriatal slice preparation. In this preparation, the cortical afferents to the striatum are preserved, allowing for activation of striatal cells in a manner similar to that used in vivo; however, all axons arising from midbrain and brainstem structures including the substantia nigra are transected, and intrastriatal GABAergic pathways are reduced. Consistent with the predicted effect of disrupting these two neurotransmitter pathways, the paired impulse responses of striatal neurons recorded in vitro were not similar to the responses of either Type I or Type II neurons recorded in vivo. Indeed, the paired impulse profiles of striatal neurons recorded in vitro were relatively homogeneous in that virtually all cells displayed an increased probability of spike discharge (facilitation) to the second impulse of all interstimulus intervals (10-500ms) tested. Low concentrations of allosteric agonists for the GABAA receptor, pregnanolone (5 microM) and pentobarbital (50 microM), selectively inhibited spike discharge in response to short interstimulus intervals (10-20 ms) for approximately 40% of the neurons sampled, but produced no change in facilitation to longer interstimulus intervals (30-500 ms). The agonist-induced inhibition to short interstimulus intervals was blocked by bicuculline (10-20 microM), and was not mimicked by the GABAB receptor agonist, baclofen (1-5 microM). In addition, application of dopamine (5-10 microM) or the D1 receptor agonist, SKF38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; 5 microM), inhibited spike discharge to longer interstimulus intervals (40-500 ms) for approximately 10% of striatal cells recorded. The inhibition to longer interstimulus intervals was blocked by the D1 receptor antagonist, SCH23390 [R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin+ ++-7-ol], but not the D2 antagonist, sulpiride.(ABSTRACT TRUNCATED AT 400 WORDS)

Background firing activity in guinea-pig neocortex in vitro

The background firing activity was recorded extracellularly in experiments on guinea-pig neocortical slices maintained in vitro. The following types of background firing activity were revealed: (i) high regular single spikes (48%), (ii) irregular single spikes (15%), (iii) bursts (7%), (iv) groups (7%), (v) mixed activity where single spikes alternated with bursts or groups (28%). The specific interspike interval distribution and the specific shape of autocorrelogram corresponded to each of these background firing activity types. Furie analysis of autocorrelograms showed periodic components in spike sequences with the maxima at 3, 12, and 28 Hz. When blocking synaptic transmission with 100 mM adenosine, about 70% of the background active cells "fell silent" and the remaining 30% of neurons continued to generate action potentials. The latter seem to be actual spontaneously active neurons, i.e. they were capable of autonomous spike generation. We failed to find any correlation between the type of neuronal firing and the ability of neurons to be spontaneously active. The selective blockade of inhibitory synapses with 100 mM picrotoxine did not practically change the character of background firing activity though the responses to stimulation became epileptic. An important conclusion to emerge from this study is that the background firing activity in cortical slices can include the actual spontaneous discharges related to intrinsic cell properties as well as those concerned with synaptic actions. Furthermore, a small number of spontaneously active neurons seem to be able to synaptically activate twice the number of cells. The inhibitory interneurons did not significantly influence the propagation of excitation with the absence of stimulation.

Effect of brain ischemia on protein kinase C

We examined the influence of brain ischemia on the activity and subcellular distribution of protein kinase C (PKC). Two different models of ischemic brain injury were used: postdecapitative ischemia in rat forebrain and transient (6-min) cerebral ischemia in gerbil hippocampus. In the rat forebrain model, at 5 and 15 min postdecapitation there was a steady decrease of total PKC activity to 60% of control values. This decrease occurred without changes in the proportion of the particulate to the soluble enzyme pools. Isolated rat brain membranes also exhibited a concomitant decrease of [3H]phorbol 12,13-dibutyrate ([3H]PDBu) binding with an apparent increase of the ligand affinity to the postischemic membranes. On the other hand, the ischemic gerbil hippocampus model displayed a 40% decrease of total PKC activity, which was accompanied by a relative increase of PKC activity in its membrane-bound form. This resulted in an increase in the membrane/total activity ratio, indicating a possible enzyme translocation from cytosol to the membranes after ischemia. Moreover, after 1 day of recovery, a statistically significant enhancement of membrane-bound PKC activity resulted in a further increase of its relative activity up to 162% of control values. In vitro experiments using a synaptoneurosomal particulate fraction were performed to clarify the mechanism of the rapid PKC inhibition observed in cerebral tissue after ischemia. These experiments showed a progressive, Ca(2+)-dependent, antiprotease-insensitive down-regulation of PKC during incubation. This down-regulation was significantly enhanced by prior phorbol (PDBu) treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

O2 tension in adult and neonatal brain slices under several experimental conditions

Brain tissue O2 tension (pO2) was measured in brainstem slices of adult and neonatal rats using carbon fiber polarographic microelectrodes. These studies were performed in order to examine the relation between pO2 and a variety of experimental conditions including temperature, distance from slice surface, brain region, animal age, tissue thickness and ambient O2 levels. Baseline brain tissue pO2 was inversely proportional to temperature and depth from slice surface. White matter had a much higher pO2 than gray matter. Tissue thickness and animal age had major effects on tissue pO2. In slices of 800 microns thick at 37 degrees C, for example, brain tissue pO2 in the adult dropped to 0 mm Hg at a depth of 200-300 microns, but remained above 45 mm Hg throughout neonatal (3-10 days) slices, when O2 tension in the perfusate was about 600 mm Hg. In thicker neonatal slices (1500 microns), pO2 decreased also to 0 mm Hg in deep areas. An N2 environment produced a rapid reduction in pO2 to 0 mm Hg within 15 s, and O2 levels of 21, 10 and 5% induced graded pO2 minima and graded latencies to reach each pO2 nadir. We conclude that: (1) tissue thickness has a major effect on tissue pO2 level: pO2 can reach zero if the slice is thicker than 600 microns in the adult and 1500 microns thick in the neonate; (2) pO2 level is higher in neonatal brain tissue at all ambient O2 concentrations than in the adult; and (3) graded hypoxia produces patterned and graded reductions in tissue pO2.

Profiles of percent reduction of cytochromes in guinea pig hippocampal brain slices in vitro

Percent reduction profiles of cytochromes (cyt.) aa3, b and c were investigated in bloodless guinea pig hippocampal brain slices of 400, 600 and 800 microns in thickness ranging in temperature from 22 to 37 degrees C. The extent of the percent reduction of cytochromes was compared with the generation of orthodromic potentials elicited by the stimulation of the stratum radiatum, and the cessation of the potentials was found to be correlated with the extent of the percent reduction of the cytochromes. In the case of 400 microns slices, they were found to be in normoxia both from the extent of the percent reduction levels of cytochromes and from the generation of orthodromic responses over a range in temperature. In the case of 600 microns slices, those incubated under temperatures of 22 to 32 degrees C were not in hypoxia from the levels of cytochrome reduction and the production of a field potential. However, slices at 37 degrees C were in hypoxia because of cyt. c levels approached those of cyt. b and the orthodromic response was suppressed. In 800 microns slices, those at 22-27 degrees C were in normoxia; however, slices maintained at 32-37 degrees C were in hypoxia because the levels of cyt. c reduction closely approximated those of cyt. b at 32 degrees C whereas those of cyt. aa3, b and c were almost the same as at 37 degrees C. Moreover, the orthodromic field potential was not evoked.

Glial localization of adenylate-cyclase-coupled beta-adrenoceptors in rat forebrain slices

Fluorocitrate (FC), a selective inhibitor of glial cell respiration, was used to estimate the extent to which glial cells contain adenylate cyclase-coupled beta-adrenoceptors in rat brain slices. The drug blocked 75-95% of the elevation of cyclic AMP caused by the beta-agonist, isoproterenol, in the 4 forebrain regions sampled (frontal and parietal cortex, caudate nucleus, olfactory tubercle). Intracellular recording of neurons in the treated slices confirmed that they were unaffected by FC. Treatment with the neurotoxin, kainic acid, eliminated all electrophysiological activity but did not affect the cAMP response. The results indicate that glial cells contain the preponderance of adenylate-cyclase-coupled beta-adrenoceptors in slices of the rat forebrain and may constitute an important target of the central noradrenergic system in vivo.

N-methyl-D-aspartate receptor activation and Ca2+ account for poor pyramidal cell structure in hippocampal slices

The CA1 pyramidal cells appear damaged in micrographs of guinea pig hippocampal slices incubated in normal physiological buffer at 36-37 degrees C. This is remedied if slices are incubated in modified buffers for the first 45 min. Cell morphology is improved if this buffer is devoid of added Ca2+ and much improved if it contains N-methyl-D-aspartate (NMDA) receptor antagonists or 0 mM Ca2+ and 10 mM Mg2+. The cells then appear similar to CA1 pyramidal cells in situ. These findings support the notion that NMDA receptor activation and Ca2+, acting in the period immediately after slice preparation, permanently damage CA1 pyramidal cells in vitro.

Protein synthesis as a function of depth in slices of rat hippocampus

Physiologically viable slices of rat hippocampus were incubated in radiolabeled valine, then cut into 20 microns serial sections to evaluate the profile of protein synthesis through the depth of the slice. Maximum radiolabel incorporation was observed near the center of the slice, while at the upper (gas interface) and lower (liquid interface) surfaces radiolabel incorporation per section was reduced by about 30% and 90%, respectively. The results suggest that in properly slices damage due to slicing may be less important to cell viability than are limits on oxygen diffusion into the tissue.

Preservation of neuronal ultrastructure in hippocampal slices using rapid microwave-enhanced fixation

The goal of this study was to obtain fixation as rapidly as possible and to achieve preservation of neuronal ultrastructure to a depth in hippocampal slices where electrophysiological responses are optimal. This study demonstrates that perfusion quality preservation of in vitro hippocampal slices can be achieved within seconds after removal from the incubation chamber by using microwave (MW)-enhanced immersion in mixed aldehydes. The optimal method was determined to be MW irradiation of the slice for 8-11 s, to a tissue temperature of 35-50 degrees C, during immersion in fixative containing 6% glutaraldehyde and 2% paraformaldehyde. Electron microscopy of these slices revealed ultrastructural preservation that was comparable to hippocampi from animals perfused with mixed aldehyde fixative containing 2.5% glutaraldehyde and 2% paraformaldehyde. Excellent ultrastructural preservation extended to 100-175 microns from the hippocampal slice surface after MW-enhanced fixation and therefore was much deeper than the 8-20 microns that can be obtained by rapid freezing. Hippocampal slices are routinely maintained in vitro for electrophysiological or pharmacological studies. This method of MW-enhanced fixation preserves tissue within seconds after removal from incubation, and should provide good preservation of the hippocampal anatomy that might be associated with in vitro physiology.

GABA-like activity in in vitro slices of the rat visual cortex: immunocytochemistry and electrophysiology

Using antisera raised against gamma-aminobutyric acid (GABA), GABA-like immunoreactivity was determined in in vitro slices fixed after various incubation times. Synaptic efficacy of GABAergic innervation was concurrently assessed in adjacent slices by intracellular recordings. We show that GABA-like immunoreactivity dramatically decreases already after one hour of incubation and remains low throughout the following hours. Nevertheless robust GABA-mediated synaptic potentials are recordable for more than 8 h.

Characterization of input synapses on intracellularly stained neurons in hippocampal slices: an HRP/EM study

This study describes the fine structure of input synapses on identified neurons in slices of the guinea pig hippocampus. For morphological identification, granule cells of the fascia dentata and pyramidal neurons of regio inferior of the hippocampus were impaled and intracellularly stained with horseradish peroxidase (HRP). Input synapses on the HRP-stained neurons were identified in the electron microscope by the location of the synapses in inner or outer zones of the dentate molecular layer, as in the case of the synaptic contacts on injected granule cells, or by unique fine structural characteristics, as in the case of the giant mossy fiber boutons on CA3 pyramidal cells. As in tissue fixed in situ by transcardial perfusion, a large number of terminals arising from the different afferents in inner and outer zones of the dentate molecular layer were well preserved and formed synaptic contacts with small spines, large complex spines, and dendritic shafts of the HRP-filled granule cells. Mossy fiber synapses on the stained CA3 neurons were densely filled with clear vesicles, contained a few dense-core vesicles, and formed synaptic contacts with large spines or excrescences. Occasionally electrondense degenerating boutons were also found impinging on the stained dendrites and spines. The significance of the present findings for electrophysiological and pharmacological studies on brain slices is discussed.

The in vitro slice preparation for combined morphological and electrophysiological studies of rat visual cortex

The morphological condition of slices of rat visual cortex, maintained in vitro in an interface-type recording chamber, was assessed. In addition, neurones in these slices were impaled with glass micropipettes for intracellular recording and horseradish peroxidase (HRP) injection. After fixation and embedding, slices were examined by light and electron microscopy. Slices sectioned orthogonally to the original plane of cutting showed a vertical zonation of tissue preservation. The upper zone contained dense and flattened neuronal somata, although the neuropil appeared normal. The central zone was well preserved, with the appearance of most somata, dendrites, axons and synapses comparing favourably with perfusion-fixed material. The lower zone contained many abnormal, vacuolated somata. The morphology of HRP-injected neurones was assessed by light microscopy. Dendrites could be visualised in great detail and spines were clearly visible. Local axon arbors were well represented. There was good correlation between electrophysiological and morphological criteria for the assessment of the condition of the slice. We conclude that, provided the extent of degeneration within the slice is monitored and appreciated, slices of visual cortex can provide both electrophysiological and morphological data of high quality.

Thick brain slices model the ischemic penumbra

Hypothalamic brain slices, varying in thickness from 400 mu to 1,000 mu, were assessed by studying 2-deoxyglucose (2DG) metabolism, lactate accumulation, inulin spaces, and morphology at the light and ultrastructural levels. Evidence of increased glycolytic flux due to anaerobic metabolism is found at thickness greater than 600 mu in association with a progressive increase in the inulin-exclusion space. The metabolic profiles, as a function of depth into the slices, reveal that 700-mu slices function in a manner similar to 540-mu slices at the surfaces, but with a core of increased 2DG phosphorylation at the slice center. In contrast, the 1,000-mu slices show significant reduction of 2DG and increases in 2DG6P relative to the 540-mu slices at the slice surface as well as in the slice interior, suggesting impaired transport of 2DG into cells and spread of ischemic injury from the slice interior to the slice surface. Despite these metabolic changes, only minor morphologic changes of ischemic injury were found at the center of thicker slices, and in vitro glucose utilization of 1000-mu slices remained constant for up to 15 h. These three slice thicknesses should provide a useful model for studying the neurochemistry and neuropharmacology of the ischemic penumbra.

Pitfalls in the use of brain slices

In vitro brain slices are the preparation of choice for the detailed examination of local circuit properties in mammalian brain. However it is the investigator's responsibility to verify that the circuits under investigation are indeed confined within the boundaries of the functional region of the slice used. The medium in which the slice is maintained is under the full control of the investigator. This places the burden on the investigator to ensure that: (1) the properties of the medium are fully under control; (2) the effects of the medium on the slice are known; (3) the conditions under which the slice is being maintained bear some reasonable relation to those it enjoys (or endures) in vivo. Generalizations to in vivo conditions must be made with caution. If at all possible, similar studies (perhaps less extensive, due to the greater technical difficulties) should be done in vivo to provide a basis for comparison. Investigators using drugs should be aware of, and respect, the basic pharmacological principles cited in the text. In particular, the substantial freedom the investigator has in defining the extracellular medium should not be abused.

Tissue slices in radioligand binding assays: studies in brain, pineal and muscle

The use of tissue homogenates in receptor binding assays raises serious questions as to the physiological value of a preparation which examines receptors (binding sites) in disrupted tissue. In order to usefully study the regulatory properties of neurotransmitter receptors under physiological conditions, the necessity for tissue preparations which retain some degree of cellular integrity is clear. We review here the experiments which have utilized intact tissue - largely in the form of thick slices - to perform radioligand binding assays. There are many reports which note marked differences between studies in intact versus broken cell preparations. For example, significant discrepancies in KD and Bmax values are apparent for [3H] quinuclidinyl benzilate (muscarinic) and [3H] ouabain (Na+/K+-ATP ase, sodium pump) sites in brain and muscle respectively. A further example is the well-described stimulatory effect of GABA on benzodiazepine binding sites which is not seen in tissue slices. Other examples are highlighted. For all ligands so far examined, binding to slices is reversible, stereospecific, saturable, displaceable by appropriate drugs and of high affinity (nM). The method developed in our own laboratory is inexpensive, rapid and involves a minimum of tissue preparation. The technique is so simple as to allow many workers to enter this field who would not otherwise have done so. We suggest that metabolically active tissue slices offer the simplest approach to the study of cell-surface receptor regulation in living tissue.

Dependence of liver-specific transcription on tissue organization

When the liver is disaggregated and hepatocytes are cultured as a cellular monolayer for 24 h, a sharp decline (80 to 99% decrease) in the transcription of most liver-specific mRNAs, but not common mRNAs, occurs (Clayton and Darnell, Mol. Cell. Biol. 2:1552-1561, 1983). A wide variety of culture conditions involving various hormones and substrates and cocultivation with other cells failed to sustain high rates of liver-specific mRNA synthesis in cultured hepatocytes, although they continued to synthesize common mRNAs at normal or elevated rates. In contrast, when slices of intact mouse liver tissue were placed in culture, the transcription of liver-specific genes was maintained at high levels (20 to 100% of normal liver). Furthermore, we found that cells in the liver could be disengaged and immediately reengaged in a tissue-like structure by perfusing the liver with EDTA followed by serum-containing culture medium. Slices of reengaged liver continued to transcribe tissue-specific mRNA sequences at significantly higher rates after 24 h in culture than did individual cells isolated by EDTA perfusion followed by culturing as a monolayer. Therefore we conclude that a mature tissue structure plays an important role in the maintenance of maximum tissue-specific transcription in liver cells.

pO2-dependent distribution of potassium in hippocampal slices of the guinea pig

The distribution of extracellular K+-concentration (cK+s) in 200-1000-micron thick hippocampal slices was studied with ion-selective microelectrodes. In ca. 500-micron thick slices cK+s increased from the surface to the innermost layers by ca. 2 mmol/liter if the pO2 of the bath (pBO2) ranged from 300-600 mm Hg and if the temperature was 28 degrees C. In thicker slices and lowered pO2-values further elevations of cK+s were observed. In vital slices thinner than 500 micron cK+s-values exceeded the potassium-concentration of the bath (cK+B) only when pBO2 was markedly lowered. When pBO2 was reincreased in such thin slices, cK+s rapidly declined and often decreased transiently below ck+B. Similar undershoots of cK+s were observed when cK+B was lowered from high to normal levels. The rapid decline was blocked by hypoxia, ouabain, antimycine and a temperature of 18 degrees C. A stepwise rise of cK+B also caused rapid changes of cK+s in vital thin slices. The rates of changes, however, were hardly affected e.g. by a transient hypoxia. Diffusion did not contribute significantly to these steep changes of cK+s. These rapid distribution modes were widely missing in slices thicker than 500 micron. Therefore in such preparations, the extracellular microenvironment of neurons may markedly differ from the ionic concentrations in the bath.

Effects of clonidine on the stimulation-evoked release of 3H-noradrenaline from superfused rat brain slices as a function of the biophase concentration. Temperature dependent widening of extracellular space

The influence of clonidine on the stimulation-evoked overflow of tritium was studied in brain slices preincubated with 3H-noradrenaline. The slices were prepared from parietal cortex (Cx), nucleus anterior hypothalami (nah) and nucleus tractus solitarii (nts). After preincubation, the tissues were superfused at 23 degrees C or 37 degrees C with a medium containing the noradrenaline uptake inhibitor desipramine. Electrical field stimulation was applied using stimulation frequencies of 0.3-10 Hz. At 23 degrees C/0.3 Hz, clonidine concentration-dependently inhibited the evoked overflow of tritium in all three brain regions. In contrast, at 23 degrees C/3 Hz the inhibitory effect of the drug in the Cx was abolished and a facilitation was observed in the nah and nts. When tested at increasing frequencies of stimulation in the nts at 23 degrees C, clonidine exerted a dual action, characterized by a reduction of electrically evoked responses at frequencies below 1 Hz and a facilitation at frequencies above 1 Hz. At 37 degrees C, clonidine concentration-dependently decreased the evoked overflow in all brain regions studied, this effect being more pronounced at 0.3 Hz than at 3 Hz. The apparent lack of an effect of clonidine on the stimulation-evoked overflow of tritium in the Cx at 23 degrees C/3 Hz was turned to a facilitation when noradrenaline (0.01 mumol/l) was included in the superfusion medium. Conversely, an inhibitory effect of clonidine was seen when the uptake blocker desipramine (as well as noradrenaline) was omitted from the superfusion medium.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo treatment with GM1 prevents the rapid decay of ATPase activities and mitochondrial damage in hippocampal slices

Slices from rat CA3 hippocampal area show a 30% decrement in ATPase activity after 35 min of 'in vitro' incubation. Such a drop is accompanied by an alteration of mitochondrial ultrastructure. However, if rats are treated daily with GM1 ganglioside (10 mg/kg during 3 days) both phenomena are fully prevented. These results would suggest a protective effect of gangliosides onto membrane structures under stress conditions.

Dependence of liver-specific transcription on tissue organization

When the liver is disaggregated and hepatocytes are cultured as a cellular monolayer for 24 h, a sharp decline (80 to 99% decrease) in the transcription of most liver-specific mRNAs, but not common mRNAs, occurs (Clayton and Darnell, Mol. Cell. Biol. 2:1552-1561, 1983). A wide variety of culture conditions involving various hormones and substrates and cocultivation with other cells failed to sustain high rates of liver-specific mRNA synthesis in cultured hepatocytes, although they continued to synthesize common mRNAs at normal or elevated rates. In contrast, when slices of intact mouse liver tissue were placed in culture, the transcription of liver-specific genes was maintained at high levels (20 to 100% of normal liver). Furthermore, we found that cells in the liver could be disengaged and immediately reengaged in a tissue-like structure by perfusing the liver with EDTA followed by serum-containing culture medium. Slices of reengaged liver continued to transcribe tissue-specific mRNA sequences at significantly higher rates after 24 h in culture than did individual cells isolated by EDTA perfusion followed by culturing as a monolayer. Therefore we conclude that a mature tissue structure plays an important role in the maintenance of maximum tissue-specific transcription in liver cells.

Cerebral cortex slices in sodium-free medium: depletion of synaptic vesicles

Rat cerebral cortex slices superfused for 5 min in sodium-free medium after 30-min stabilization and 25-min superfusion periods in sodium-containing medium displayed a well-preserved tissue structure and mostly intact neurons and glial cells. Electron-microscopic morphometry showed the number of presynaptic terminals containing few (less than or equal to 10) vesicles to increase 3-fold after the 5-min depletion of sodium. The 90-min sodium depletion resulted in increased swelling and an additional decrease in synaptic vesicles. The results show that from a morphological point of view the substitution of sodium by choline with brain slice techniques is an eminently suitable method for studies on synaptic neurochemistry.

Morphofunctional changes in activated neurons for different depths of narcosis in animals

Experiments on frogs showed that intensive synaptic activation of spinal cord motoneurons leads to their pycnotic corrugation. Preliminary deep narcotization prevents the appearance of these pathological changes in cell structure. It was also established that for a deeper anesthesia of intact animals the decrease in the excitability of the spinal centers and loss of the motoneurons' capacity to generate synaptic and spike potentials in response to stimulation are not attended by a change in neuron size or structure.