In vitro investigations of the effects of nonfreezing low temperatures on lesioned and uninjured mammalian spinal neurons

Cellular level cryo-neuromodulation using rapid and localized cooling device combined with microelectrode array

Cryotherapy, a rapid and effective medical treatment utilizing low temperatures, has not been widely adopted in clinical practice due to a limited understanding of its mechanisms and efficacy. This challenge stems from the absence of methods for fast, precise, and localized spatiotemporal temperature control, as well as the lack of reliable real-time quantitative techniques for measuring and analyzing the effects of cooling. To address these limitations, this study introduces a cryo-neuromodulation platform that integrates a high-speed precision cooling device with a microelectrode array (MEA) system. This platform enables the investigation of cellular-level cryo-modulation of neuronal activity and its effects on surrounding cells, providing a novel framework for advancing research in cryotherapy and neuromodulation. Experiments show that neurons recovered fully within 1 min of cooling with a fast-cooling rate (-20 °C/s at cooling) and that silenced neurons can influence distant cells via a well-organized network. Extended cooling durations (e.g., 10 min) resulted in altered neuronal dynamics, including delayed recovery and reduced burst activity, highlighting the importance of precise control over cooling parameters. This device offers reversible neural control, with potential applications in both research and clinical settings, such as anesthesia, pain management and treatment of neurological disorders like neocortical seizures.

Time Limiting Boundaries of Reversible Clinical Death in Rats Subjected to Ultra-Deep Hypothermia

BACKGROUND

It is well known that body temperature maintenance between 20 and 35°C prevents hypoxic damage. However, data regarding the ideal duration and permissible temperature boundaries for ultra-deep hypothermia below 20°C are rather fragmentary. The aim of the present study was to determine the time limits of reversible clinical death in rats subjected to ultra-deep hypothermia at 1-8°C.

RESULTS

Rat survival rates were directly dependent on the duration of clinical death. If clinical death did not exceed 35 min, animal viability could be restored. Extending the duration of clinical death longer than 45 min led to rat death, and cardiac functioning in these animals was not recovered. The rewarming rate and the lowest temperature of hypothermia experienced did not directly influence survival rates.

CONCLUSIONS

In a rat model, reversible ultra-deep hypothermia as low as 1-8°C could be achieved without the application of hypercapnia or pharmacological support. The survival of animals was dependent on the duration of clinical death, which should not exceed 35 min.

Brain temperature and its role in physiology and pathophysiology: Lessons from 20 years of thermorecording

It is well known that temperature affects the dynamics of all physicochemical processes governing neural activity. It is also known that the brain has high levels of metabolic activity, and all energy used for brain metabolism is finally transformed into heat. However, the issue of brain temperature as a factor reflecting neural activity and affecting various neural functions remains in the shadow and is usually ignored by most physiologists and neuroscientists. Data presented in this review demonstrate that brain temperature is not stable, showing relatively large fluctuations (2-4°C) within the normal physiological and behavioral continuum. I consider the mechanisms underlying these fluctuations and discuss brain thermorecording as an important tool to assess basic changes in neural activity associated with different natural (sexual, drinking, eating) and drug-induced motivated behaviors. I also consider how naturally occurring changes in brain temperature affect neural activity, various homeostatic parameters, and the structural integrity of brain cells as well as the results of neurochemical evaluations conducted in awake animals. While physiological hyperthermia appears to be adaptive, enhancing the efficiency of neural functions, under specific environmental conditions and following exposure to certain psychoactive drugs, brain temperature could exceed its upper limits, resulting in multiple brain abnormalities and life-threatening health complications.

REVIEW ■ : Physical Injury of Neurons: Important Roles for Sodium and Chloride Ions

There is growing evidence that ions other than Ca2+ play important roles in the deterioration of neuronal elements in both gray and white matter after physical injury. This review features information gathered with a tissue culture model of dendrite transection regarding the contributions of Na+ and CI- to ultrastructural damage and neuronal death. This information and the results of other in vitro investigations of physical and ischemic/excitotoxic injuries indicate that elevation of internal Na+ is an early event that may contribute significantly to neuronal injury through effects on Na+-driven transport mechanisms. Proposed deleterious consequences include cytoplasmic acidification, reduced mitochondrial energy production, and elevation of intracellular Ca2+ and extracellular excitatory amino acids to toxic levels. Prevention of Na+ entry into neurons after injury has been found to limit ultrastructural damage, prevent death, and preserve electrophysiological function. Although the role of CI- in neuronal injury is less well defined, there is also evidence that elevation of intracellular CI- contributes to structural damage, particularly to the smooth endoplasmic reticulum. In terventions that limit Na+- and CI--mediated damage to injured neurons may have utility in neurosurgery and as acute phase treatments for nervous system trauma and other pathological states. NEURO SCIENTIST 3:89-101, 1997

Enhancement of cultured adult motor neuron survival with cold pre-incubation

The aim of the study was to extend the survival of adult spinal motor neurons in serum free culture. Anterior half of the spinal cord was removed from young adult mice and dissociated. Cultured cells attempted to extend neurites within hours of incubation at 37 °C and died within 24 h. To prevent this early regenerative activity, thus to decrease the metabolic requirements of the neurons, cultures were transferred to 4 °C immediately after they were set and kept there for 3 days. Preparations were then taken to 37 °C where they lived up to 8 days. Some neurons continued to extend neurites until the day they died. To understand whether the enhancement of survival involves new protein synthesis, transcription and translation were blocked during cold pre-incubation, which shortened the half life of neurons but not changed the maximum survival period. In conclusion this study has shown that, in the serum-free cultures, the survival of adult spinal motor neurons can be significantly enhanced by cold pre-incubation whose effect seems to depend largely on a reduction in the metabolic activity and less on new protein synthesis.

Maximizing neuroprotection: where do we stand?

Brain and spinal cord traumas include blunt and penetrating trauma, disease, and required surgery. Such traumas trigger events such as inflammation, infiltration of inflammatory and other cells, oxidative stress, acidification, excitotoxicity, ischemia, and the loss of calcium homeostasis, all of which cause neurotoxicity and neuron death. To prevent trauma-induced neurological deficits and death, each of the many neurotoxic events that occur in parallel or sequentially must be minimized or prevented. Although neuroprotective techniques have been developed that block single neurotoxic events, most provide only limited neuroprotection and are only applied singly. However, because many neurotoxicity triggers arise from common events, an approach for invoking more effective neuroprotection is to apply multiple neuroprotective methods simultaneously before the many neurotoxic triggers and cascades are initiated and become irreversible. This paper first discusses some triggers of neurotoxicity and neuroprotective mechanisms that block them, including hypothermia, alkalinization, and the administration of adenosine. It then examines how the simultaneous application of these techniques provides significantly greater neuroprotection than is provided by any technique alone. The paper also stresses the importance of determining whether the neuroprotection provided by these techniques can be further enhanced by combining them with additional techniques, such as the systemic administration of glucocorticoids. Finally, the paper stresses the absolute critical importance of applying these techniques within the "golden hour" following trauma, before the many neurotoxic events and cascades are manifest and before the neurotoxic cascades become irreversible.

Hypothermia and rewarming injury in hippocampal neurons involve intracellular Ca2+ and glutamate excitotoxicity

This study examines the causes of hypothermia and rewarming injury in CA1, CA3, and dentate neurons in rat hippocampal slice cultures. Neuronal death, assessed with propidium iodide or Sytox fluorescence, Fluoro-Jade labeling, and Cresyl Violet staining, depended on the severity and duration of hypothermia. More than 6 h at temperatures less than 12 °C followed by rewarming to 37 °C (profound hypothermia and rewarming, PH/RW) caused swelling and death in large number of neurons in CA1, CA3, and dentate. During PH, [ATP] decreased and [Ca(2+)](I) and extracellular [glutamate] increased, with neuron rupture and nuclear condensation following RW. The data support the hypothesis that neuronal death from PH/RW is excitotoxic, due to ATP loss, glutamate receptor activation and Ca(2+) influx. We found that antagonism of N-methyl-D-aspartate (NMDA) receptors, but not 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl) propanoic acid or metabotropic glutamate receptors, decreased neuron death and prevented increases in [Ca(2+)](I) caused by PH/RW. Chelating extracellular Ca(2+) decreased PH/RW injury, but inhibiting L- and T-type voltage-gated Ca(2+) channels, K+ channels, Ca(2+) release from the endoplasmic reticulum, and reverse Na(+)/Ca(2+) exchange did not affect the Ca(2+) changes or cell death. We conclude that the mechanism of PH/RW neuronal injury in hippocampal slices primarily involves intracellular Ca(2+) accumulation mediated by NMDA receptors that activates necrotic, but not apoptotic processes.

Environmental conditions modulate neurotoxic effects of psychomotor stimulant drugs of abuse

Psychomotor stimulants such as methamphetamine (METH), amphetamine, and 3,4-metylenedioxymethamphetamine (MDMA or ecstasy) are potent addictive drugs. While it is known that their abuse could result in adverse health complications, including neurotoxicity, both the environmental conditions and activity states associated with their intake could strongly enhance drug toxicity, often resulting in life-threatening health complications. In this review, we analyze results of animal experiments that suggest that even moderate increases in environmental temperatures and physiological activation, the conditions typical of human raves parties, dramatically potentiate brain hyperthermic effects of METH and MDMA. We demonstrate that METH also induces breakdown of the blood-brain barrier, acute glial activation, brain edema, and structural abnormalities of various subtypes of brain cells; these effects are also strongly enhanced when the drug is used at moderately warm environmental conditions. We consider the mechanisms underlying environmental modulation of acute drug neurotoxicity and focus on the role of brain temperature, a critical homeostatic parameter that could be affected by metabolism-enhancing drugs and environmental conditions and affect neural activity and functions.

Combinatorial techniques for enhancing neuroprotection: hypothermia and alkalinization

Brain and spinal cord (CNS) trauma typically kill a number of neurons, but even more neurons are killed by secondary causes triggered by the initial trauma. Thus, a minor insult may rapidly cause the death of a vastly larger number of neurons and complete paralysis. The best mechanism for reducing the extent of neurological deficits is to minimize the number of neurons killed by post-trauma sequelae. Neuroprotection techniques take many diverse forms with a breadth too great for a short review. Therefore, this review focuses on the neuroprotection provided by hypothermia and a number of other neuroprotective techniques, when administered singly or in combination, because it is generally found that combinations of applications lead to significantly better neuroprotection than is achieved by any one alone. The combinatorial approach to neuroprotection holds great promise for enhancing the degree of neuroprotection following trauma, leading to maximum maintenance of neurological function.

Neuroprotection by hypothermia plus alkalinization of dorsal root ganglia neurons through ischemia

Brain and spinal cord (CNS) trauma typically directly kill some neurons leading to permanent neurological deficits. However, they also lead to a number of triggers which in turn frequently kill a vastly larger number of neurons than were killed by the initial insult. The best mechanism for reducing the extent of neurological deficits is to minimize the number of neurons that die immediately due to the trauma, and post-trauma sequelae. Neuroprotection techniques have taken many diverse forms with a breadth too great for a short review. Therefore, this review is focused on the roles of only a small number of neuroprotective agents, with its primary focus being on neuroprotection provided by hypothermia, alone and when combined with the other methods. Included are also recent results involving a novel neuroprotective technique, tested on adult human dorsal root ganglion neurons, comparing the influences of hypothermia and alkalinization singly, providing fourfold and eightfold increases in neuroprotection, respectively, but when combined providing a 26-fold increase in neuroprotection. This combinatorial approach to neuroprotection holds great promise for enhancing the degree of neuroprotection clinically following CNS trauma, leading to the preservation of maximal neurological functions.

Brain temperature fluctuations during physiological and pathological conditions

This review discusses brain temperature as a physiological parameter, which is determined primarily by neural metabolism, regulated by cerebral blood flow, and affected by various environmental factors and drugs. First, we consider normal fluctuations in brain temperature that are induced by salient environmental stimuli and occur during motivated behavior at stable normothermic conditions. Second, we analyze changes in brain temperature induced by various drugs that affect brain and body metabolism and heat dissipation. Third, we consider how these physiological and drug-induced changes in brain temperature are modulated by environmental conditions that diminish heat dissipation. Our focus is psychomotor stimulant drugs and brain hyperthermia as a factor inducing or potentiating neurotoxicity. Finally, we discuss how brain temperature is regulated, what changes in brain temperature reflect, and how these changes may affect neural functions under normal and pathological conditions. Although most discussed data were obtained in animals and several important aspects of brain temperature regulation in humans remain unknown, our focus is on the relevance of these data for human physiology and pathology.

Neuroprotection of adult rat dorsal root ganglion neurons by combined hypothermia and alkalinization against prolonged ischemia

Ischemia and ischemia-induced secondary events, such as acidosis and excessive activation of receptors by amino acids, trigger neuron death. The isolation and dissociation of dorsal root ganglion (DRG) involves time during which the neurons are ischemic due to being densely packed within the intact DRG and surrounded by a connective tissue coat. Thus, the longer the time between killing the host animal and when the DRG are dissociated, the longer the neurons are ischemic and exposed to ischemia-induced secondary causes of neuron death. It is well established that hypothermia and alkalinization each separately protect neurons from ischemia and ischemia-induced secondary causes of neuron death, but there are no data on the neuroprotection provided by simultaneous hypothermia and alkalinization. The present experiments were designed to determine the combination of hypothermic and alkaline conditions that yield the largest number of viable neurons dissociated from intact DRG maintained ischemic for up to 4 h. Hypothermia (20 degrees C>15 degrees C>37 degrees C) and alkalinization (pH 9.3>pH 8.3>pH 7.4) increased the yield of viable neurons compared with the yield from DRG maintained under physiological conditions. Hypothermia and alkalinization combined (20 degrees C/pH 9.3) provided the greatest neuroprotection with a yield of viable neurons after 1 h of ischemia 2.5-fold larger than that from DRG maintained under physiological conditions (37 degrees C/pH 7.6). Over 4 h of ischemia, the yield of viable neurons from DRG maintained under both hypothermic/alkaline and physiological conditions decreased in a linear manner, but those at 20 degrees C/pH 9.3 had a 4.5-fold greater yield of viable neurons than those at 37 degrees C/pH 7.6. Thus, combined hypothermia and alkalinization provide significantly greater protection against ischemia and ischemia-induced secondary causes of neuron death than either alone.

Effects of mild and moderate hypothermia on apoptosis in neuronal PC12 cells

BACKGROUND

There is still a possibility that mild hypothermic therapy may be useful as a neuroprotective tool during the intraoperative period, although the mechanism of cerebral protection by mild hypothermia is not well understood. We hypothesized that mild hypothermia may be protective against cerebral ischaemia by inhibiting post-ischaemia apoptosis. In this study, we used serum-deprived PC12 cells as the neuronal apoptotic model and examined the direct effects of mild and moderate hypothermia.

METHODS

Apoptosis was induced by depriving the cell culture medium of serum, which is one of the most representative methods to induce apoptosis, but not necrosis, in PC12 cells. Effects of mild (35 and 33 degrees C) and moderate (31 and 29 degrees C) hypothermia on apoptosis were evaluated. Cytotoxicity (lactate dehydrogenase leakage) and the percentage of apoptotic cells (calculated by flow cytometry with propidium iodide) were evaluated 4 days after induction of apoptosis. As a control, cells without induction of apoptosis were incubated under the same conditions as the apoptosis group.

RESULTS

Without induction at 37 degrees C, cytotoxicity and the percentage of apoptotic cells were over 60 and 90%, respectively. At each temperature examined below 35 degrees C, significant decreases in cytotoxicity and the percentage of apoptotic cells were observed. Mean cytotoxicity at 31 and 29 degrees C was 50.2 (SD 4.2)% and 47.9 (4.4)%, respectively. The percentage of apoptotic cells at 31 and 29 degrees C was 42.5 (7.4)% and 36.5 (7.3)%, respectively. In the control group, cytotoxicity and the percentage of apoptotic cells were significantly higher at 29 degrees C than at 37 degrees C.

CONCLUSIONS

Mild and moderate hypothermia (29-35 degrees C) inhibited apoptosis, although hypothermia below 30 degrees C may induce apoptosis in intact cells.

Effects of sodium and chloride on neuronal survival after neurite transection

An in vitro investigation was undertaken to study the roles of Na+ and Cl- in mammalian spinal cord (SC) neuron deterioration and death after injury involving physical disruption of the plasma membrane. Individual SC neurons in monolayer cultures were subjected to UV laser microbeam transection of a primary dendrite. Neurons lesioned in modified ionic environments (MIEs) where 50%-75% of the NaCl was replaced with sucrose had higher survival (65%-75%) than neurons lesioned in medium with normal (125 mM) NaCl (28%; p < 0.001). Subsequent experiments found a comparable increase in lesioned neuron survival in MIEs in which only Na+ was replaced with specific ionic substitutes; however, replacement of Cl- was not protective. Electron microscope examinations of neurons fixed <16 min after lesioning showed a dramatic decrease in vesiculation of the smooth endoplasmic reticulum and Golgi apparatus in the low NaCl or low Na+ MIEs. It is hypothesized that Na+ entry after membrane disruption may stimulate elevation of [Ca+2]i leading to ultrastructural disruption and death of injured neurons. The results of these studies suggest that a low NaCl MIE may be useful as an irrigant to limit damage spread and cell death within CNS tissues during surgery or after trauma.

Temperature dependence of membrane sealing following transection in mammalian spinal cord axons

Using an in vitro sucrose-gap recording chamber, sealing of cut axons in isolated strips of white matter from guinea pig spinal cord was measured by recording the "compound membrane potential". This functional sealing was found to correlate well with anatomical resealing, measured by a horseradish peroxidase uptake assay. Near-complete functional and anatomical recovery of the axonal membrane occurred routinely within 60 min following transection at 37 degrees C in regular Krebs' solution. The rate of membrane potential recovery is exponential, with a time-constant of 20+/-5 min. The sealing process at 31 degrees C was similar to that at 37 degrees C, and was effectively blocked at 25 degrees C, under which condition most axons continued to take up horseradish peroxidase for more than 1h, and failed to substantially recover their membrane potential. Seventy-five percent of the cords transected at 40 degrees C had similar sealing behavior to those at 37 degrees C and 31 degrees C. The balance failed to seal the cut end. Two-dimensional morphometric analysis has shown that raising the temperature from 25 degrees C to above 31 degrees C significantly decreases axonal permeabilization to horseradish peroxidase (increases the sealing of transected ends) across all areas of a transverse section of spinal cord. Moreover, this enhancement of sealing exists across all axon calibers. Since severe cooling compromises membrane resealing, caution needs to be taken when hypothermic treatment (below 25 degrees C) is applied within the first 60 min following mechanical injury. In summary, we have found that at normal temperature (37 degrees C), nerve fibers repair their damaged membrane following physical injury with an hour. This is similar at mildly lower (31 degrees C) and relatively higher (40 degrees C) temperature, although some fibers tend to collapse under this febrile temperature. Moreover, severely low temperature (25 degrees C) hindered the repair of damaged membranes. Based on our study, caution is needed in treating spinal cord injury with low temperatures.

In vitro central nervous system models of mechanically induced trauma: a review

Injury is one of the leading causes of death among all people below the age of 45 years. In the United States, traumatic brain injury (TBI) and spinal cord injury (SCI) together are responsible for an estimated 90,000 disabled persons annually. To improve treatment of the patient and thereby decrease the associated mortality, morbidity, and cost, several in vivo models of central nervous system (CNS) injury have been developed and characterized over the past two decades. To complement the ability of these in vivo models to reproduce the sequelae of human CNS injury, in vitro models of neuronal injury have also been developed. Despite the inherent simplifications of these in vitro systems, many aspects of the posttraumatic sequelae are faithfully reproduced in cultured cells, including ultrastructural changes, ionic derangements, alterations in electrophysiology, and free radical generation. This review presents a number of these in vitro systems, detailing the mechanical stimuli, the types of tissue injured, and the in vivo injury conditions most closely reproduced by the models. The data generated with these systems is then compared and contrasted with data from in vivo models of CNS injury. We believe that in vitro models of mechanical injury will continue to be a valuable tool to study the cellular consequences and evaluate the potential therapeutic strategies for the treatment of traumatic injury of the CNS.

Characterization of neuroprotection from excitotoxicity by moderate and profound hypothermia in cultured cortical neurons unmasks a temperature-insensitive component of glutamate neurotoxicity

Although profound hypothermia has been used for decades to protect the human brain from hypoxic or ischemic insults, little is known about the underlying mechanism. We therefore report the first characterization of the effects of moderate (30 degrees C) and profound hypothermia (12 degrees to 20 degrees C) on excitotoxicity in cultured cortical neurons exposed to excitatory amino acids (EAA; glutamate, N-methyl-D-aspartate [NMDA], AMPA, or kainate) at different temperatures (12 degrees to 37 degrees C). Cooling neurons to 30 degrees C and 20 degrees C was neuroprotective, but cooling to 12 degrees C was toxic. The extent of protection depended on the temperature, the EAA receptor agonist employed, and the duration of the EAA challenge. Neurons challenged briefly (5 minutes) with all EAA were protected, as were neurons challenged for 60 minutes with NMDA, AMPA, or kainate. The protective effects of hypothermia (20 degrees and 30 degrees C) persisted after rewarming to 37 degrees C, but rewarming from 12 degrees C was deleterious. Surprisingly, however, prolonged (60 minutes) exposures to glutamate unmasked a temperature-insensitive component of glutamate neurotoxicity that was not seen with the other, synthetic EAA; this component was still mediated via NMDA receptors, not by ionotropic or metabotropic non-NMDA receptors. The temperature-insensitivity of glutamate toxicity was not explained by effects of hypothermia on EAA-evoked [Ca2+]i increases measured using high- and low-affinity Ca2+ indicators, nor by effects on mitochondrial production of reactive oxygen species. This first characterization of excitotoxicity at profoundly hypothermic temperatures reveals a previously unnoticed feature of glutamate neurotoxicity unseen with the other EAA, and also suggests that hypothermia protects the brain at the level of neurons by blocking, rather than slowing, excitotoxicity.

The effects of ciliary neurotrophic factor on murine spinal cord neurons subjected to dendrite transection injury

Ciliary neurotrophic factor (CNTF) has been found to increase neuronal survival during development and after axotomy. The present study tested the effects of CNTF on lesioned and uninjured mouse spinal cord (SC) neurons grown in tissue culture. An initial toxicity study found that a 24-72 h exposure of SC cultures to concentrations of CNTF above 1000 ng/ml caused stress and death of unlesioned neurons and glia. Pre-selected SC neurons were then subjected to transection of a primary dendrite 100 microns from the edge of the perikaryon (approximately 50% average survival at 24 h). Application of CNTF at concentrations ranging from 0.5 to 1000 ng/ml immediately after lesioning had no statistically significant effects on SC neuron survival 24 h after dendrotomy. Separation of control (no CNTF) and CNTF-treated cells into groups of putative alpha-motor (multipolar with somal diameters > or = 25 microns) and non-alpha-motor neurons (< 25 microns somal diameters) also failed to reveal any significant differences in survival. The lack of protection by CNTF of lesioned SC neurons in mature (21-28 DIV) cultures may reflect a loss of sensitivity to CNTF that occurs with development. Alternatively, protection by CNTF may require co-factors or factors that are released from target or other cells after injury but that are not present in SC cultures.

The role of excitatory amino acids in hypothermic injury to mammalian spinal cord neurons

Hypothermia has been reported to be beneficial in CNS physical injury and ischemia. We previously reported that posttraumatic cooling to 17 degrees C for 2 h increased survival of mouse spinal cord (SC) neurons subjected to physical injury (dendrite transection) but that cooling below 17 degrees C caused a lethal NMDA receptor-linked stress to both lesioned and uninjured neurons. The present study tested whether cooling below 17 degrees C increases extracellular levels of excitatory amino acids (EAA). SC cultures were placed at 10 degrees C or 37 degrees C. Glutamate (Glu) and aspartate (Asp) levels were higher in the medium of the cooled cultures after 0.5 h (23 +/- 4 nM/microgram vs. 4 +/- 1 nM/microgram and 4 +/- 1 nM/microgram vs. 1 +/- 0 nM/microgram, respectively). The concentration of each EAA then declined and reached a plateau at 2-4 h that was still significantly higher than control levels (p < 0.0001, two-factor ANOVA, three cultures per group). Other amino acids (glycine, asparagine, glutamine, serine) showed an opposite pattern, with higher levels in the 37 degrees C group. Both NMDA and non-NMDA antagonists prevented the lethal cold injury. Survival of SC neurons cooled at 10 degrees C for 2 h and rewarmed for 22 h was 58% +/- 25% in the control group, 94% +/- 5% in the CNQX-treated group, 97% +/- 5% in the DAPV-treated group, and 99% +/- 2% in the group treated with both antagonists [p < 0.0006, one factor ANOVA, five cultures (> 120 neurons) per group]. These results show that death of neurons cooled to 10 degrees C is caused by elevated extracellular Glu and Asp and requires activation of both the NMDA and non-NMDA receptor subtypes.

Responsiveness to ATP with an increase in intracellular free Ca2+ is not a distinctive feature of calbindin-D28 immunoreactive neurons in myenteric ganglia

The aim of this study was to test the hypothesis that ATP elevates cytosolic free Ca2+ levels ([Ca2+]i) in myenteric neurons expressing the Ca2+ binding protein, calbindin-D28. A laser microbeam marked the location of cultured neurons on coverslips and provided unequivocal relocation of ATP-responsive neurons after immunocytochemistry. All myenteric multipolar neurons displayed ATP Ca2+ transients, and 42% also expressed calbindin-D28 reactivity. Statistical analysis of the kinetics and shape of ATP Ca2+ transients revealed no differences between calbindin and non-calbindin neurons. The identity of other responsive neurons is unknown. Less than 8% of ganglion cells with ATP Ca2+ transients were immunopositive for the glial protein S-100. We conclude that one of the actions of ATP in myenteric ganglia is to increase [Ca2+]i which may activate gKCa leading to membrane hyperpolarization in AH, Dogiel Type II neurons expressing calbindin-D28. An efficient buffering mechanism for handling large purinergic Ca2+ loads is a common feature of all types of myenteric ganglion cells.

Ultrastructural damage and neuritic beading in cold-stressed spinal neurons with comparisons to NMDA and A23187 toxicity

While exposure of cultured spinal neurons to mild hypothermia provides some protection from physical trauma (dendrotomy), profound cooling (< 17 degrees C) causes unrelated neuronal injury and death, which can be prevented by treatment with NMDA receptor antagonists. To investigate the mechanism of hypothermic neuronal injury we examined the ultrastructure of cultured spinal neurons after 2 h of cooling to 17 degrees C or 10 degrees C, with or without the presence of the NMDA receptor antagonist D-2-amino-5-phosphonovalerate, and with or without rewarming to 37 degrees C. These groups were compared to cultures exposed to NMDA or to the calcium ionophore A23187. Patterns of ultrastructural change, involving cytoskeletal disruption, mitochondrial abnormalities and vacuolization of the cytoplasm, suggest a common mechanism of injury in all treatment groups, involving an elevation of intracellular calcium. Some neurons exposed to hypothermia, NMDA or ionophore developed beaded dendrites. Microtubules were fragmented in varicosities but not in the intervening constrictions; other organelles were largely excluded from the constrictions. Varicosities may form when organelles and cytoplasm accumulate as the result of disruption of transport and membrane stabilizing proteins by proteases activated by calcium influx via NMDA mediated channels. The periodic nature of the swellings may reflect inherently discontinuous distribution of molecular subunits of the cytoskeleton.