Neurotoxic effects of methamphetamine on rat hippocampus pyramidal neurons.

Methamphetamine (MAP) is known to alter behavior and cause deficits in learning and memory. While the major site of action of MAP is on mesolimbic dopaminergic pathways, the effects on learning and memory raise the possibility of important actions in the hippocampus. We have studied electrophysiologic and morphologic effects of MAP in the CA1 region of hippocampus from young male rats chronically exposed to MAP, male rats exposed during gestation only and the effects of bath perfusion of MAP onto brain slices from control rats. Pyramidal neurons in brain slices from chronically exposed rats had reduced membrane potential and membrane resistance. Long-term potentiation (LTP) was reduced as compared to control, but when MAP was acutely perfused over control slices the amplitude of LTP was increased. LTP in young adult animals that had been gestationally exposed to MAP showed reduced LTP as compared to controls. Morphologically CA1 pyramidal neurons in chronically exposed animals showed a high prevalence of extensive blebbing of dendrites. We conclude that the NMDA receptor and the process of LTP are also targets of MAP dysfunction, at least in the hippocampus.

Electrogenic sodium pump and high specific resistance in nerve cell bodies of the squid.

An electrogenic sodium pump contributes to the membrane potential in squid nerve cell bodies, imparting a temperature dependence to the resting potential that is abolished by strophanthidin. The existence of a potential produced by the pump in the soma but not the axon is correlated with a higher membrane resistance in the soma. Thus, membranes from different parts of a neuron may have functionally significant differences in resistance.

Thermosensitivity of neurons in the sensorimotor cortex of the cat.

Extracellular action potentials were recorded from 80 neurons in the sensorimotor cortex of the cat as brain temperature was varied by 4 degrees to 8 degrees C. The discharge rate of 37 percent of the neurons studied increased with increasing brain temperature. The discharge rate varied inversely with temperature in 11 percent of the neurons.

Aspartate: distinct receptors on Aplysia neurons.

Aplysia neurons have specific aspartate receptors that are distinct from those to glutamate. In some cells, asparate selectively increases the membrane permeability to chloride, giving rise to a hyperpolarization, while on other cells it increases the permeability to sodium, causing a depolarization. There are also specific receptors for L-glutamate which mediate sodium, chloride, or potassium conductance increases, and another class of receptors activated by both glutamate and aspartate.

Phenylethanolamine: a new putative neurotransmitter in Aplysia.

Phenylethanolamine is present in the Aplysia nervous system in concentrations similar to that of octopamine. These are receptors that are very specific for phenylethanolamine, which on different neurons mediate sodium, chlorine, or potassium conductance increase responses. These observations indicate that phenylethanolamine may act as a neurotransmitter in Aplysia.

Low internal conductivity of Aplysia neuron somata.

The internal conductivity of Aplysia neuron somata was measured by passing constant current pulses across a calibrated four-electrode array. The intracellular medium is less than one-tenth as conductive as seawater. The low conductivity probably results from structured cell water since ions are present in quantity and do not appear to be bound.

Octopamine: presence in single neurons of Aplysia suggests neurotransmitter function.

Octopamine has been identified and measured in individual neurons from Aplysia californica. Neither dopamine nor norepinephrine was detected in these cells. Thus, in Aplysia there may be separate populations of catecholaminergic and monophenolaminergic cells. Octopamine may have functions of its own in the central nervous system of mollusks.

Anti-apoptotic effects of 3,5,3'-tri-iodothyronine in mouse hepatocytes.

The present study demonstrates that 3,5,3'-tri-iodothyronine (T3) in physiological dose range inhibits tumor necrosis factor alpha(TNFalpha)/Fas-induced apoptosis in mouse hepatocytes. T3 pretreatment prevented Fas-induced early stage of apoptosis signs assessed by flow cytometry analysis of the annexin V positive cell population. T3 attenuated TNFalpha/Fas-induced cleavage of caspase-8 and DNA fragmentation. We found that T3 exerted its anti-apoptotic effects by mobilization of several non-genomic mechanisms independent of transcriptional activity. Inhibition of protein kinase A (PKA), extracellular signal-regulated kinase (ERK), and Na+/H+ exchanger blocked T3-dependent anti-apoptotic effects indicating an involvement of these intracellular targets into T3-induced signaling cascade. Furthermore, physiological concentrations of T3, but not reverse T3, caused increases in intracellular cAMP content and activated PKA. T3 markedly induced phosphorylation of ERK. We also detected T3-dependent intracellular alkalinization that abolished TNFalpha-induced acidification. PKA inhibitor KT-5720 blocked T3-induced activation of ERK and intracellular alkalinization confirming the upstream position of PKA signaling. We further detected that hepatocytes from hypothyroid mice are more sensitive to TNFalpha/Fas-induced apoptosis than euthyroid animals in vivo. Together, these findings imply that T3 triggers PKA- and ERK-regulated intracellular pathways capable of driving and ensuring hepatocytes survival in the presence of death receptor ligand-induced damage under chronic inflammatory conditions.

Cross-modal innervation of primary visual cortex by auditory fibers in congenitally anophthalmic mice.

Auditory-visual cross-modal innervation was examined in control (sighted, ZRDCT-N) and congenitally anophthalmic (eyeless, ZRDCT-AN) mice using electrophysiological recording and pathway tracing with carbocyanine dyes. Electrophysiological data demonstrate that the primary visual cortex of congenitally eyeless, blind, mice receives auditory stimuli. Neuroanatomical data demonstrate a direct connection between the inferior colliculus (IC) and visual cortex. Our experiments provide new information about how the brain adapts to the loss of sight.

Temperature effects on pacemaker generation, membrane potential, and critical firing threshold in Aplysia neurons.

Temperature increases cause a regular and reproducible increase in the frequency of generation of pacemaker potentials in most Aplysia neurons specialized for this type of activity which can only be explained as a direct stimulating effect of temperature upon the ionic mechanisms responsible for pacemaker potentials. At the same time all cells in the visceral ganglion undergo a membrane potential hyperpolarization of approximately 1-2 mv/ degrees C warmed. In spite of the marked variation in resting membrane potential the critical firing threshold remains at a constant membrane potential level at all temperatures in the absence of accommodative changes. The temperature-frequency curves of all types of cells are interpreted as a result of the interaction between the effects of temperature on the pacemaker-generating mechanism and resting membrane potential. Previous observations on the effects of temperature on excitability of mammalian neurons suggest that other types of neurons may undergo similar marked shifts in resting membrane potential with temperature variation.

A contribution of an electrogenic Na+ pump to membrane potential in Aplysia neurons.

The resting membrane potential (RMP) of Aplysia neurons is very temperature-dependent, and in some cells increases with increasing temperature by as much as 2 mv/ degrees C. RMP at room temperature may significantly exceed the potassium equilibrium potential, which can be determined by measurement of the equilibrium point of the spike after potential. The hyperpolarization on warming is completely abolished by ouabain, replacement of external Na(+) by Li(+), removal of external K(+), and by prolonged exposure to high Ca(++), while it is independent of external chloride but is increased by cocaine (3 x 10(-3)M). In an identified cell that shows a marked temperature dependence of RMP, both the potassium equilibrium potential and the membrane resistance were found to be relatively independent of temperature. The hyperpolarization on warming, which may increase RMP by as much as 50%, can most reasonably be ascribed to the activity of an electrogenic Na(+) pump.

Resistivity of axoplasm. II. Internal resistivity of giant axons of squid and Myxicola.

The specific resistivity of the axoplasm of giant axons of squid and Myxicola was measured utilizing a single metal microelectrode subjected to alternating current in a circuit in which the voltage output varies with the conductivity of the thin layer of fluid at the exposed electrode tip. The average specific resistivity of stellar axons of Loligo pealei was 31 omegacm (1.55 times seawater [X SW]) while for Loligo opalescens it was 32 omegacm (1.30 X SW). Smaller giant axons had a higher average resistivity. Myxicola giant axons had a resistivity of 68 omegacm (2.7 X SW) in normal seawater, and 53 omegacm (2.1 X SW) in a hypertonic high-Mg++ seawater. The temperature dependence of squid axon resistivity does not differ from that of an equally conductive dilution of seawater.

Vitamin E enhances Ca(2+)-mediated vulnerability of immature cerebellar granule cells to ischemia.

The effects of vitamin E on lipid peroxidation, intracellular free Ca2+ concentration ([Ca2+]i), and cell death were investigated in the postischemic immature cerebellum. Deprivation of oxygen and glucose for 10-min in a suspension of freshly dissociated granule cells from the cerebellum of 9-day-old male rat pups resulted in a recovery-induced consumption of cell nonenzymatic antioxidants (ascorbic acid, glutathione, and alpha-tocopherol) and development of membrane lipid peroxidation as measured by the thiobarbituric acid method. The rate of lipid peroxidation of the postischemic cells was stimulated, not reduced, by treatment of the cells with vitamin E (5-30 microM alpha-tocopherol phosphate). In flow-cytometric studies a 10-min period of ischemia resulted in a small increase in intracellular calcium concentration, lipid peroxidation products and cell death, but in the presence of alpha-tocopherol the same treatment caused a dramatic increase in cell death, accompanied by a large increase in [Ca2+]i and lipid peroxidation products. Pretreatment of the cells with a mixture of three antioxidants (vitamin C/rutin/ubiquinol-10, 10/5/1) or nickel (Ni2+) reduced the alpha-tocopherol-induced increases in [Ca2+]i, and cell death. Hydrogen peroxide (1 mM) and the water-soluble analogue of vitamin E, trolox (50 microM), mimicked the effect of vitamin E on lipid peroxidation in the postischemic cells. Pretreatment of the cells with the intracellular Ca2+ chelator BAPTA-AM, reduced both the alpha-tocopherol-induced increase in [Ca2+]i and cell death. The effect of vitamin E on [Ca2+]i was age dependent and decreased abruptly during maturation of the cerebellum between the first and second weeks of life. Results of in vitro treatment of the immature cerebellar cells with the water-soluble form of vitamin E (alpha-tocopherol phosphate) suggest that, after consumption of cellular co-antioxidants, vitamin E may be converted to an alpha-tocopheroxyl radical, which act as a toxic prooxidant as cellular bioenergetics deteriorate.

Fine structure and organization of the infrared receptor relay, the lateral descending nucleus of the trigeminal nerve in pit vipers.

The morphology of the nucleus of the lateral descending tract of V has been studied in species of two genera of pit vipers, cottonmouth moccasin (Agkistrodon piscivorus piscivorus), and rattlesnake (Crotalus ruber and Crotalus horridus horridus). The nucleus is the site of termination of primary afferent neurons forming the infrared receptors in the facial pits. It is located on the external surface of the common descending tract of V and contains somata that range in size from 7 to 22 micrometer in A. p. piscivorus and 7 to 27 micrometer in C. ruber. Electron microscopy reveals that the lateral descending tract contains both A delta and C fibers. Degeneration experiments indicate that the A delta fibers are primary afferents. The source of the C fibers is unknown. The lateral descending nucleus in both the cottonmouth and rattlesnake is fundamentally similar in organization. Afferent terminals containing clear spherical vesicles make synaptic contact with dendritis processes within the main neuropil. These axon terminals are also postsynaptic to boutons containing pleomorphic vesicles and some large dense-core vesicles. The C fibers terminate in a neuropil at the margin of the lateral descending tract on small dendritic processes that appear to come from neurons within the nucleus. This neuropil is found external to the tract in the cottonmouth and internal to the tract in the rattlesnake. The terminals contain clear spherical vesicles and large dense-core vesicles. The singularity of input to this nucleus is apparently reflected in the morphology. This is discussed in relation to the subnucleus caudalis of the mammalian brainstem.

Protein kinase C activation is necessary but not sufficient for induction of long-term potentiation at the synapse of mossy fiber-CA3 in the rat hippocampus.

The involvement of protein kinase C in long-term potentiation was investigated in the mossy fiber-CA3 pathway in an in vitro slice preparation of rat hippocampus. Tetanic stimulation induced stable long-term potentiation in the mossy fiber-CA3 pathway which was not affected by N-methyl-D-aspartate receptor antagonists. Long-term potentiation was not induced in the presence of a protein kinase C inhibitor, sphingosine. Application of 1 microM phorbol-12, 13-diacetate, an activator of protein kinase C, potentiated the synaptic response by about 400% and this potentiation was completely reversible upon washing. Sphingosine blocked the potentiation when it was applied before protein kinase C activation by phorbol-12, 13-diacetate. However, sphingosine had no effect on the potentiation when it was applied after the synaptic response was potentiated to a plateau following phorbol-12,13-diacetate perfusion. Long-term potentiation and phorbol ester-induced potentiation were not additive when phorbol-12,13-diacetate was applied after induction of long-term potentiation, suggesting that long-term potentiation and phorbol-12, 13-diacetate activate the same protein kinase C pool. The enhanced response caused by phorbol-12,13-diacetate returned to the long-term potentiation level after wash-out of phorbol-12,13-diacetate. Thus the cellular changes underlying long-term potentiation are long-lasting or permanent, while those caused by phorbol-12,13-diacetate are not. However, if tetanic stimulation was induced during prolonged phorbol-12,13-diacetate application (1 h), a potentiation similar in amplitude to long-term potentiation was induced but the population response returned to the control pre-long-term potentiation level after 2 h of washing. The potentiation following tetanic stimulation during prolonged application of phorbol-12,13-diacetate was blocked in the presence of D-2-amino-5-phosphonovaleric acid, a N-methyl-D-aspartate receptor antagonist. Thus, in the presence of phorbol esters the N-methyl-D-aspartate-independent long-term potentiation is occluded but a transient potentiation appears, presumably due to hyperexcitability and activation of N-methyl-D-aspartate receptors in recurrent pathways of area CA3. Normal N-methyl-D-aspartate-independent long-term potentiation could be induced after the 2 h washout period and now was maintained. In conclusion, protein kinase C activation is essential but not sufficient for long-term potentiation in the mossy fiber-CA3 pathway and when stimulated by application of phorbol esters produces a large and reversible synaptic potentiation. These investigations show that long-term potentiation in CA3 is a complex event involving several steps, and that activation of protein kinase C is only one of them.

Beta-N-methylamino-L-alanine in the presence of bicarbonate is an agonist at non-N-methyl-D-aspartate-type receptors.

Beta-N-Methylamino-L-alanine, a component of the neurotoxic Cycas circinalis plant, activates an ionic current which is antagonized by extracellular Ca2+ but not by the excitatory amino acid receptor antagonists D,L-2-amino-5-phosphonovalerate (10-100 microM) or 6-cyano-7-nitroquinoxaline-2,3-dione (1-10 microM). This current was reduced by 50% in 0.5 mM extracellular Ca2+ and 92% in 3.0 mM Ca2+ when compared to those recorded in 0.1 mM Ca2+. Addition of 10 or 20 mM NaHCO3 to beta-N-methylamino-L-alanine (500 microM) potentiated the currents 224% and 578%, respectively. Addition of NaHCO3 to the extracellular Ringers (pH 7.2) shifted the pH to 7.7 (10 mM) or 8.3 (20 mM). beta-N-Methylamino-L-alanine was potentiated by NaHCO3 at pH 7.2, 7.7 and 8.3, but the potentiation with NaHCO3 (20 mM) was larger at pH 8.3 (5.7-fold) compared to pH 7.2 (3-fold). NaHCO3 (20 mM) had no effect on quisqualate-, N-methyl-D-aspartate- or kainate-activated ionic currents. The beta-N-methylamino-L-alanine-NaHCO3-activated currents were reduced 49% by 1 microM and 80% by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione suggesting an agonist action at non-N-methyl-D-aspartate-type receptors. Activity at N-methyl-D-aspartate receptors is unlikely since the beta-N-methylamino-L-alanine-NaHCO3 currents are not antagonized by D,L-2-amino-5-phosphonovalerate (10-100 microM), potentiated by addition of glycine (10 microM) or blocked by extracellular Mg2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonists of GABA responses, studied using internally perfused frog dorsal root ganglion neurons.

Responses of frog dorsal root ganglion neurons to GABA were studied under conditions of internal perfusion. Conductances to Na, Ca and K were pharmacologically blocked, C1 concentrations were maintained equal on both sides of the membrane and a small holding potential was used. Under these conditions GABA-induced C1 currents could be studied in isolation without shifts in EC1 occurring after GABA application. GABA currents were blocked by a variety of agents. The blockade by bicuculline and Zn was competitive, while that to penicillin was competitive at low concentrations (6 x 10(-5) M) and non-competitive at high concentrations (3 x 10(-4) M). Picrotoxin was non-competitive at all concentrations studied. The time course of the GABA-induced currents was changed in the presence of antagonists, including those that were competitive. These actions appear to be due to a change in the rates of receptor desensitization rather than shifts in EC1. Pretreatment with antagonists increased the degree of inhibition only for picrotoxin as compared to simultaneous application of GABA plus antagonist. The voltage dependence of the GABA response was altered by penicillin but not by other antagonists. GABA responses on frog dorsal root ganglion cell were also depressed by a variety of other metal ions (Cd, Ni, Cu, Co, Mn) and other drugs (strychnine, curare, 4-acetamide, 4'-isothiocyano-stilbene-2,2'-dilsulfonic acid disodium salt, 4,4'-diisothiocyano-stilbene-2,2'-dilsulfonic acid disodium salt trihydrate, bemegride and folic acid). In this preparation bicuculline and the heavy metal ions appear to block at or very near to the agonist binding site, while penicillin probably blocks the ion channel. The non-competitive action of picrotoxin appears not to be channel blockade, but to be due to a slowly equilibrating action at a site different from either the agonist binding site or the channel.

Failure of neuronal ion exchange, not potentiated excitation, causes excitotoxicity after inhibition of oxidative phosphorylation.

Neuronal cell death during impaired energy metabolism is often attributed to increased activity at glutamate receptors, but this increase has not been directly demonstrated. We recorded responses to glutamate and N-methyl-D-aspartate in hippocampal slice CA1 neurons and glia while inhibiting mitochondrial complex II with 3-nitropropionic acid. As the period of inhibition increased, neuronal depolarization following bath application of glutamate (5 mM) or N-methyl-D-aspartate (50 microM) increased dramatically. However, depolarization upon iontophoresis of glutamate and N-methyl-D-aspartate decreased with time. A transient hyperpolarization, reflecting electrogenic sodium pump activity, was present immediately after responses to iontophoretic glutamate agonists. In the presence of the inhibitor, this hyperpolarization decreased and eventually disappeared. Even the repolarization seen upon washing of the iontophoretic or bath application of glutamate or N-methyl-D-aspartate was incomplete. Glial depolarization upon bath application of glutamate increased during inhibition, while glial depolarization upon application of N-methyl-D-aspartate decreased. Application of the N-methyl-D-aspartate antagonists aminophosphonovaleric acid (100 microM) or MK-801 (20 microM) resulted in a delay of further depolarization when applied early during the terminal decay of membrane potential following metabolic inhibition. We conclude that during impaired oxidative phosphorylation the failure of repolarizing mechanisms, not potentiated neuronal depolarization by excitants, is the primary cause of the terminal depolarization. Large glial depolarization increases the demand for neuronal ion exchange which cannot be met in situations of reduced energy metabolism. Our results provide further evidence that acute and chronic blockade of energy metabolism have different effects.(ABSTRACT TRUNCATED AT 250 WORDS)