Isolation and characterization of halotolerant Streptomyces radiopugnans from Antarctica soil

An actinomycete wild strain PM0626271 (= MTCC 5447), producing novel antibacterial compounds, was isolated from soil collected from Antarctica. The taxonomic status of the isolate was established by polyphasic approach. Scanning electron microscopy observations and the presence of LL-Diaminopimelic acid in the cell wall hydrolysate confirmed the genus Streptomyces. Analysis of 16S rRNA gene sequence showed highest sequence similarity to Streptomyces radiopugnans (99%). The phylogenetic tree constructed using near complete 16S rRNA gene sequences of the isolate and closely related strains revealed that although the isolate fell within the S. radiopugnans gene subclade, it was allocated a different branch in the phylogenetic tree, separating it from the majority of the radiopugnans strains. Similar to type strain, S. radiopugnans R97(T) , the Antarctica isolate displayed thermo tolerance as well as resistance to (60) Co gamma radiation, up to the dose of 15 kGy. However, media and salt tolerance studies revealed that, unlike the type strain, this isolate needed higher salinity for its growth. This is the first report of S. radiopugnans isolated from the Antarctica region. The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of Streptomyces radiopugnans MTCC 5447 is JQ723477.

Chronic ethanol exposure delays the 'developmental switch' of the NMDA receptor 2A and 2B subunits in cultured cerebellar granule neurons

Chronic ethanol treatment of cultured neurons from various brain areas has been found to increase NMDA receptor function and to alter the levels of some NMDA receptor subunit proteins. Because the cultured neurons are exposed to ethanol during a period when the NMDA receptor is undergoing developmental changes in subunit expression, we wished to determine whether ethanol treatment alters this developmental pattern. We found that 3 days of treatment of cerebellar granule neurons with ethanol, which was previously reported to increase NMDA receptor function, resulted in a delay in the 'developmental switch' of the NR2A and NR2B subunits, i.e. the developmental decrease in NR2B and increase in NR2A protein expression. As a result, the level of NR2B was higher, and that of NR2A was lower, in the ethanol-treated cells than in control cells. Cross-linking experiments showed that the changes in total receptor subunit proteins levels were reflected in cell-surface expressed proteins, indicating changes in the amount of functional receptors. These results were confirmed by a higher potency of glycine at the NMDA receptor in the ethanol-treated cells, as determined by NMDA/glycine-induced increases in intracellular Ca(2+). The results suggest that the mechanism by which ethanol alters NMDA receptor expression in cultured neurons, where receptors are undergoing development, differs from the mechanism of ethanol's effect on NMDA receptors in adult brain. Changes in the proportion of NR2A and NR2B subunits may contribute to effects of ethanol on neuronal development.

Chronic ethanol exposure attenuates the anti-apoptotic effect of NMDA in cerebellar granule neurons

Ethanol, added to primary cultures of cerebellar granule neurons simultaneously with NMDA, was previously shown to inhibit the anti-apoptotic effect of NMDA. The in vitro anti-apoptotic effect of NMDA is believed to mimic in vivo protection against apoptosis afforded by innervation of developing cerebellar granule neurons by glutamatergic mossy fibers. Therefore, the results suggested that the presence of ethanol in the brain at a critical period of development would promote apoptosis. In the present studies, we examined the effect of chronic ethanol exposure on the anti-apoptotic action of NMDA in cerebellar granule neurons. The neurons were treated with ethanol in vitro for 1-3 days in the absence of NMDA. Even after ethanol was removed from the culture medium, as ascertained by gas chromatography, the protective effect of added NMDA was significantly attenuated. The decreased anti-apoptotic effect of NMDA was associated with a change in the properties of the NMDA receptor, as indicated by a decrease in ligand binding, decreased expression of NMDA receptor subunit proteins, and decreased functional responses including stimulation of increases in intracellular Ca(2+) and induction of brain-derived neurotrophic factor expression. The latter effect may directly underlie the attenuated protective effect of NMDA in these neurons. The results suggest that ethanol exposure during development can have long-lasting effects on neuronal survival. The change in the NMDA receptor caused by chronic ethanol treatment may contribute to the loss of cerebellar granule neurons that is observed in animals and humans exposed to ethanol during gestation.

Novel structure having antagonist actions at both the glycine site of the N-methyl-D-aspartate receptor and neuronal voltage-sensitive sodium channels: biochemical, electrophysiological, and behavioral characterization

A novel series of N-substituted 4-ureido-5,7-dichloro-quinolines were synthesized to contain pharmacophores directed at voltage-sensitive sodium channels (VSNaCs) and N-methyl-D-aspartate (NMDA) receptors. These compounds were shown to act in a use-dependent manner as antagonists of VSNaCs and to act as selective competitive antagonists at the strychnine-insensitive glycine recognition site of NMDA receptors. These agents had little or no effect on alpha-adrenergic receptors, other glutamate receptors, or sites other than the glycine site on the NMDA receptor, and did not block voltage-sensitive calcium channels in vitro. In vivo, the compounds were active in preventing or reducing the signs and symptoms of neurohyperexcitability and had anxiolytic properties. Unlike benzodiazepines, N-substituted 4-ureido-5, 7-dichloro-quinolines showed little interaction with the sedative effects of ethanol, but were effective in controlling ethanol withdrawal seizures. The combined actions of these compounds on VSNaCs and NMDA receptors also impart properties to these compounds that are important for preventing and reducing excitotoxic neurodegeneration, but these compounds lack the undesirable side effects of other agents used for these purposes.

Brain-derived neurotrophic factor mediates the anti-apoptotic effect of NMDA in cerebellar granule neurons: signal transduction cascades and site of ethanol action

Cerebellar granule neurons cultured in medium containing a physiological concentration of KCl (5 mM) undergo apoptosis. The cells can be rescued by the in vitro addition of NMDA. The protective effect of NMDA is thought to reflect the in vivo innervation of developing cerebellar granule neurons by glutamatergic afferents. In the current work, we investigated the mechanism of the anti-apoptotic (protective) effect of NMDA. NMDA treatment reduced caspase-3-like activity in cerebellar granule neurons, and the time course and concentration dependence of the protective effect of NMDA mirrored the ability of NMDA to induce brain-derived neurotrophic factor (BDNF) expression. Furthermore, a Trk receptor antagonist, K252a, as well as a blocking antibody to BDNF, attenuated the protective effects of both NMDA and BDNF. These results suggest that NMDA-induced BDNF expression mediates the anti-apoptotic effect of NMDA. The protective effects of NMDA and BDNF were reduced by inhibitors of the phosphatidylinositol 3'-OH kinase (PI 3-kinase) signal transduction cascade (wortmannin and LY29004) but not by a MAP kinase kinase (MEK) inhibitor (PD98059) or a protein kinase A inhibitor (Rp-cAMPS). BDNF increased phosphorylation of Akt, a target of PI 3-kinase, and NMDA also induced Akt phosphorylation, but only after an exposure that was long enough to induce BDNF expression. Furthermore, ethanol, which interferes with NMDA receptor function, inhibited the NMDA-induced increase in BDNF levels but did not block the protective effect of BDNF. These findings further support the role of BDNF in the anti-apoptotic effect of NMDA in cerebellar granule neurons and suggest that the NMDA-BDNF interaction may play a key role in in vivo cerebellar granule neuron development, as well as in the deleterious effects of ethanol on the developing cerebellum.

Ethanol sensitivity of NMDA receptor function in developing cerebellar granule neurons

The mechanism by which ethanol inhibits the function of the NMDA subtype of glutamate receptor has not been elucidated. One possibility that has been suggested is that NMDA receptor subunit composition influences the sensitivity of the receptor to ethanol. We have taken advantage of developmental changes in subunit composition of the NMDA receptor in cultured neurons to examine possible changes in the effect of ethanol. We found an increase in expression of the NR2A subunit, and a decrease in expression of the NR2B subunit of the NMDA receptor in primary cultures of cerebellar granule neurons over time in culture, with no significant change in NR1 expression. This change in NR2 subunit expression was associated with the expected changes in functional properties of the NMDA receptor (measured as the NMDA-induced increase in intracellular Ca2+), i.e., ifenprodil sensitivity and glycine potency were higher when there was a relatively greater proportion of NR2B in the cultured neurons. However, the potency of ethanol to inhibit NMDA receptor function was lower when there was a greater proportion of NR2B subunits. Previous studies showed that ethanol inhibition of NMDA receptor function in cerebellar granule neurons resulted from an ethanol-induced decrease in potency of the co-agonist, glycine, and that this effect of ethanol was blocked by inhibitors of protein kinase C. Our current results suggest that the lower potency of ethanol to inhibit the response of NMDA receptors when cerebellar granule neurons are expressing a greater proportion of NR2B subunits is a result of the higher affinity of the NMDA receptors for endogenous levels of glycine at this point in time.

Pentobarbital decreases the gamma-aminobutyric acidA receptor subunit gamma-2 long/short mRNA ratio by a mechanism distinct from receptor occupation

Treatment with pentobarbital of primary cultured cerebellar granule cells decreased the gamma-aminobutyric acid, (GABA)A receptor subunit gamma-2 long/short (gamma-2L/S) mRNA ratio. A high dose of pentobarbital (500 microM) decreased the gamma-2L/S ratio by 64%; the decrease was dose and time dependent and reversible. (-)-Hexobarbital (500 microM), the less potent stereoisomer for GABA(A) receptor activation, decreased the ratio slightly (30%) but significantly more than (+)-hexobarbital (20%). Other GABA(A) receptor activators had no (100 mM ethanol) or little (2 microM 5alpha-pregnane-3alpha-ol-20-one) effect on the gamma-2L/S ratio. Furthermore, picrotoxin (10 microM), which blocks the GABA- and pentobarbital-activated GABA(A) receptor channel, neither changed the gamma-2L/S ratio nor blocked the pentobarbital-induced changes. These data suggest that barbiturates alter the gamma-2L/S mRNA ratio by a mechanism that does not require GABA(A) receptor activation. The gamma-2L/S subunit mRNA includes an exon encoding an octapeptide that contains a protein kinase C phosphorylation consensus site. This exon-encoded peptide, occurring in the putative intracellular loop, can be phosphorylated, and in vitro, this phosphorylation has been shown to have functional consequences. This is the first report of a drug-induced alteration in receptor mRNA splicing. Furthermore, the changes in the gamma-2L/S ratio produced by pentobarbital exposure may have significant effects on the function of an important brain protein, the GABA(A) receptor.

Ethanol promotes apoptosis in cerebellar granule cells by inhibiting the trophic effect of NMDA

When primary cultures of cerebellar granule neurons are grown in a physiological concentration of KCl (5 mM) they undergo apoptosis, which can be prevented by growing the cells in the presence of N-methyl-D-aspartate (NMDA). We now show that ethanol inhibits this trophic effect of NMDA, i.e., promotes apoptosis, and also inhibits the NMDA-induced increase in intracellular Ca2+ concentration in cells grown in 5 mM KCl. Both effects of ethanol show a similar concentration dependence and are reversed by a high concentration of glycine, the co-agonist at the NMDA receptor. The data suggest that the effect of ethanol on apoptosis is mediated, at least in part, by inhibition of NMDA receptor function. This effect of ethanol to increase apoptosis could contribute to the previously described in vivo sensitivity of the developing cerebellum to ethanol-induced damage.

Mechanism of ethanol inhibition of NMDA receptor function in primary cultures of cerebral cortical cells

Ethanol is a potent inhibitor of the function of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor in various neuronal preparations. In primary cultures of cerebellar granule cells, ethanol was suggested to interact with the glycine co-agonist site of the receptor by a mechanism involving protein kinase C. In the present study, the interaction of ethanol with various sites on the NMDA receptor was examined in primary cultures of cerebral cortical cells from embryonic rats. NMDA receptor function was determined by measuring increases in intracellular Ca2+ with fura-2 fluorescence. Ethanol inhibited the function of the NMDA receptor in cerebral cortical cells, but in contrast to the results in cerebellar granule cells, phorbol ester treatment did not inhibit the NMDA response, and ethanol did not alter the effect of glycine on NMDA receptor function. Ethanol also did not affect inhibition of the NMDA response by Mg2+ or dizocilpine. The results support the hypothesis that the mechanism of ethanol inhibition of NMDA receptor function can vary in neurons from different brain regions.

Age-dependent sensitivity of cultured peripheral sympathetic neurons to 1-methyl-4-phenylpyridinium: role of glutathione

We demonstrate that 1-methyl-4-phenylpyridinium (MPP+) is toxic to chick peripheral sympathetic neurons maintained in culture in the presence of nerve growth factor (NGF). When MPP+ was added to the culture medium at the time the neurons were plated, cell loss after 3 days in culture was evident at concentrations as low as 3 nM, and near maximal at 1 microM. Toxicity was blocked by brief preincubation with the norepinephrine (NE)-reuptake blocker desipramine (DMI; 10 microM for 30 min). MPP+ blocked the uptake of [3H]NE by sympathetic neurons in a dose-dependent manner with a potency roughly equal to DMI. At concentrations up to 10 microM, MPP+ had no neurotoxic effect on the survival of sensory neurons maintained in the presence of NGF. The sensitivity of sympathetic neurons to the toxic effects of MPP+ diminished gradually with increasing lengths of time in culture. When MPP+ was added to the culture medium 48 h after plating, concentrations up to 100 microM did not cause neuronal death. This increasing resistance of sympathetic neurons to MPP+-induced cell death could not be explained by an increasing capacity for sequestration of MPP+ within synaptic vesicles. The loss of sensitivity with time in culture was, however, accompanied by a threefold increase in the levels of glutathione (GSH). Furthermore, addition of MPP+ (1 microM) to cultures previously maintained for 2 days in the presence of the GSH-synthesis inhibitor L-buthionine-[S,R]-sulfoximine (1 microM) caused the same degree of cell death as when added to freshly plated neurons. These results suggest that the observed toxicity of MPP+ in freshly plated chick sympathetic neurons may involve the formation of free radicals and that GSH plays a role in protecting sympathetic neurons in vivo from the toxicity of MPP+.

The 71 kDa glutamate-binding protein is increased in cerebellar granule cells after chronic ethanol treatment

Besides the N-methyl-D-aspartate (NMDA) receptor proteins NR1 and NR2, another complex of proteins which has been shown to contain ligand-binding sites characteristic of NMDA receptors is expressed in cerebellar granule cells. One of the proteins in the latter complex is the 71 kDa glutamate-binding protein (GBP). To determine the role of the GBP in the response to NMDA, primary cultures of cerebellar granule cells were treated with an antisense oligonucleotide complementary to mRNA for this protein. This treatment substantially reduced both mRNA and protein levels of the GBP, as well as the response of the cells to NMDA, measured as an increase in intracellular Ca2+ with fura-2 fluorescence. The antisense oligonucleotide treatment did not alter the Ca2+ responses to KC1 or kainate. Chronic ethanol exposure has previously been shown to increase NMDA receptor function and the density of binding sites for the NMDA receptor channel blocker, dizocilpine, in cerebellar granule cells. Chronic exposure of the cells to 100mM ethanol is now shown to result in significant increases in mRNA and protein levels for the GBP (45% and 100%, respectively). Ethanol treatment did not affect mRNA levels for NR1 or NR2A, caused only a small increase (20%) in protein levels for NR1, and resulted in a decrease (30%) in NR2A protein. Although a role of the NMDA receptor NR1/NR2 subunits cannot be ruled out, these results are compatible with the hypothesis of involvement of the GBP in the chronic ethanol-induced increase in NMDA receptor function in cerebellar granule cells.

Cardiac cells control transmitter release and calcium homeostasis in sympathetic neurons cultured from embryonic chick

1. The contribution of target cells in controlling the functional properties of sympathetic neurons was investigated using pure neuronal cultures and co-cultures of neurons with their physiological target cells. 2. Chick embryo sympathetic neurons cultured alone exhibited maximal elevation of cytosolic free Ca2+ ([Ca2+]i) and release of tritiated noradrenaline ([3H]NA) when given ten stimulating pulses at 1 Hz but not at 10 Hz, yielding a negative frequency-release response. Stimulation-evoked release was only slightly enhanced by the K+ channel blocker tetraethylammonium (TEA, 10 mM). 3. When sympathetic neurons were co-cultured with cardiac cells of the chick embryo, electrically stimulated transmitter release and neuronal [Ca2+]i were reduced by 3- to 5-fold. Co-cultured neurons had a positive stimulation frequency--[3H]NA release response and 5- to 7-fold facilitation of release by TEA. 4. Voltage-clamped Ca2+ current density was decreased from 0.61 +/- 0.13 pA micron-2 in neurons alone to 0.19 +/- 0.03 pA micron-2 in co-cultured neurons. 5. Neonatal rat superior cervical ganglion (SCG) neurons were also relatively insensitive to TEA when cultured alone, but [3H]NA release was greatly facilitated by TEA when tested in SCG neurons co-cultured with rat neonatal cardiac myocytes. 6. The cardiac cell-induced changes in Ca2+ handling and release properties were produced within 24 h by sympathetic neuroeffector cells, but not by skeletal muscle cells or sensory neurons, and did not occur spontaneously in neurons grown alone for up to 6 days. 7. The frequency and TEA responses of neurons grown with cardiac cells are characteristic of responses seen in sympathetic neuroeffector organs. We conclude that physiological targets play a crucial role in development of normal transmitter-release properties by controlling Ca2+ homeostasis in sympathetic neurons.

Tetraethylammonium facilitation of single-pulse mediated action potential, [Ca2+]i and transmitter release in sympathetic neurons

A single stimulus applied to sympathetic neurons co-cultured with cardiac cells produced a very small increase in the release of tritiated norepinephrine and intracellular free Ca2+ concentration ([Ca2+]i), but evoked a typical neuronal action potential. Treatment with 10 mM tetraethylammonium caused a dramatic increase in the responses to a single stimulus, and [3H]norepinephrine release remained above baseline for as long as 20 s. [Ca2+]i increased in cell bodies and neurites from basal levels of 50 to 100 nM to over 300 nM. [Ca2+]i remained elevated for 18 +/- 1 s and required 6.8 +/- 0.5 s for 50% recovery to basal levels. Action potential duration at 50% repolarization was increased from 4.5 +/- 0.3 ms to 88 +/- 20 ms and resting membrane potential decreased from -55 +/- 2 to -43 +/- 4 mV in the presence of tetraethylammonium. Repetitive firing was not observed after a single stimulus in current clamped neurons before or during tetraethylammonium exposure. These findings show a direct relation between action potential duration, Ca2+ entry and transmitter release in response to a single stimulus.

Massive exocytosis triggered by sodium-calcium exchange in sympathetic neurons is attenuated by co-culture with cardiac cells

Entry of Ca2+ through voltage-dependent Ca2+ channels is known to be linked to the exocytotic release of transmitter from sympathetic neurons. In this paper we provide evidence that transmitter release can also be stimulated by Ca2+ influx via the Na-Ca exchanger. Furthermore, the release linked to Na-Ca exchange is regulated by cardiac target cells. Cultured sympathetic neurons of the chick embryo incubated in Ca2(+)-Mg(2+)-free Krebs solution for 20 min and then switched to Ca(2+)-containing solution exhibited 15-20-fold increases in [3H]noradrenaline release over the spontaneous release. Electrophysiologic studies showed that neurons were completely depolarized in Ca(2+)-Mg(2+)-free medium. Indo-1 fluorescence revealed a large and sustained increase in intracellular free Ca2+ concentration ([Ca2+]i) after addition of Ca2+ to Ca(2+)-Mg(2+)-free medium. The increased [3H]noradrenaline release and [Ca2+]i were dependent on external Na+ and Ca2+, but were not affected by the Ca2+ channel blockers lanthanum, cadmium, verapamil or omega-conotoxin. A conventional depolarizing stimulus (125 mM K+) produced a 13-fold increase in [3H]noradrenaline release over spontaneous release. However, K(+)-induced release and rise in [Ca2+]i declined rapidly and were sensitive to the Ca2+ channel blockers. When sympathetic neurons were co-cultured with embryonic cardiac cells the release induced by change from Ca(2+)-Mg(2+)-free to Ca(2+)-Krebs solution was dramatically reduced. The change from Ca(2+)-Mg(2+)-free to Ca(2+)-Krebs solution was ineffective in evoking [3H]noradrenaline release from sympathetic neurons in situ using perfused hearts of 15-day-old chick embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

Sites of transmitter release and relation to intracellular Ca2+ in cultured sympathetic neurons

Fluorescence imaging of indo-1 loaded cells was used to monitor influx and distribution of Ca2+ in cell bodies, neurites and growth cones of sympathetic neurons cultured from embryonic chick. Similar experiments on release of tritiated noradrenaline were performed to assess the relationship between intracellular Ca2+ concentration ([Ca2+]i) and transmitter release. Effects of Ca2+ channel antagonists on electrically stimulated rise in [Ca2+]i were dependent on the neuronal region examined. Cadmium and verapamil blocked Ca2+ entry in cell bodies but were less effective in neurites and growth cones. Nifedipine partially inhibited Ca2+ entry in cell bodies and was less effective in neurites and growth cones. Combination of cadmium and nifedipine blocked [Ca2+]i rise in all neuronal regions. Omega-conotoxin was an effective Ca2+ channel blocker in all regions. Ca2+ channel blockers had effects on [3H]noradrenaline release which paralleled effects on [Ca2+]i in neurites (and growth cones) but not cell bodies. Cadmium, verapamil and nifedipine each caused a partial, reversible block of the evoked release. Combination of cadmium and nifedipine completely blocked evoked [3H]noradrenaline release. Omega-conotoxin caused complete, irreversible block of electrically evoked release. During prolonged depolarization with 125 mM K+ Krebs solution, elevation of [Ca2+]i was maintained in cell bodies but was transient in neurites and growth cones. The amplitude and time course of [3H]noradrenaline release paralleled [Ca2+]i in neurites and growth cones, but not the cell body under the above conditions. A new method is described to study localized uptake and release of [3H]noradrenaline in cell bodies versus neurites of sympathetic neurons. Incubation of these modified cultures with [3H]noradrenaline showed that cell bodies had very low [3H]noradrenaline uptake (0.23 x 10(-6) c.p.m./mg protein), whereas neurites contained approximately 20 times more radioactivity. Depolarization of neurites by excess K+ and field stimulation caused a large increase in the net release of [3H]noradrenaline. The release was unaffected by removal of cell bodies. Neurites remained functionally viable for more than 2 h after separation from their cell bodies. [3H]Noradrenaline release could be evoked repeatedly over this time. [3H]Noradrenaline release from isolated neurites was partially blocked by nifedipine and fully blocked by combination of cadmium and nifedipine or by omega-conotoxin. The uptake and release of [3H]noradrenaline by neurites alone (expressed per mg protein) accounted for the total [3H]noradrenaline in intact cultures with neurites and cell bodies. Therefore, we conclude that neurites (and growth cones) are the prominent sites of uptake, storage and release of sympathetic transmitter.(ABSTRACT TRUNCATED AT 400 WORDS)

Barium-induced exocytosis is due to internal calcium release and block of calcium efflux

The concentration of cytosolic free Ca2+ ([Ca2+]i) and the release of tritiated norepinephrine ([3H]NE) were monitored during Ba2+ stimulation of sympathetic neurons cultured from chick embryos. Ba2+ (2.5 mM in Ca(2+)-free medium) caused a rise in [Ca2+]i in all regions (cell bodies, neurites, and growth cones) of sympathetic neurons and evoked [3H]NE release in the absence of other stimuli. The increase in [Ca2+]i and release of [3H]NE were sustained for up to 30 min in the presence of Ba2+. When Ba(2+)-stimulated cells were immediately washed in Ca(2+)-free Ba(2+)-free EGTA solution, both the elevated [Ca2+]i and [3H]NE release returned to basal levels, with similar, fast, time courses. Ba2+ also blocked Ca2+ efflux from neurons loaded with 45Ca. We conclude from the parallel effects of Ba2+ on [Ca2+]i and [3H]NE release that Ba2+ stimulates exocytosis by a Ca(2+)-dependent mechanism. The Ba(2+)-induced rise in [Ca2+]i is a result of two separate actions: (i) the release of Ca2+ from intracellular sites and (ii) an effective block of Ca2+ extrusion. The ability of Ba2+ to release Ca2+ in growth cones that are insensitive to caffeine suggests that Ba2+ may displace Ca2+ from binding sites other than endoplasmic reticulum.

Activation of K+ channels by lanthanum contributes to the block of transmitter release in chick and rat sympathetic neurons

We studied the effects of lanthanum (La3+) on the release of 3H-norepinephrine (3H-NE), intracellular Ca2+ concentration, and voltage clamped Ca2+ and K+ currents in cultured sympathetic neurons. La3+ (0.1 to 10 microM) produced concentration-dependent inhibition of depolarization induced Ca2+ influx and 3H-NE release. La3+ was more potent and more efficacious in blocking 3H-NE release than the Ca(2+)-channel blockers cadmium and verapamil, which never blocked more than 70% of the release. At 3 microM, La3+ produced a complete block of the electrically stimulated rise in intracellular free Ca2+ ([Ca2+]i) in the cell body and the growth cone. The stimulation-evoked release of 3H-NE was also completely blocked by 3 microM La3+. However, 3 microM La3+ produced only a partial block of voltage clamped Ca2+ current (ICa). Following La3+ (10 microM) treatment 3H-NE release could be evoked by high K+ stimulation of neurons which were refractory to electrical stimulation. La3+ (1 microM) increased the hyperpolarization activated, 4-aminopyridine (4-AP) sensitive, transient K+ current (IA) with little effect on the late outward current elicited from depolarized holding potentials. We conclude that the effective block of electrically stimulated 3H-NE release is a result of the unique ability of La3+ to activate a stabilizing, outward K+ current at the same concentration that it blocks inward Ca2+ current.

Dissociation between intracellular Ca2+ and modulation of [3H]noradrenaline release in chick sympathetic neurons

1. We studied the relation between cyclic AMP, intracellular Ca2+ concentration and release of [3H]noradrenaline ([3H]NA) in sympathetic neurons cultured from chick embryos. 2. Forskolin (10 microM) and vasoactive intestinal polypeptide (VIP, 3 microM) increased cellular levels of cyclic AMP 8- and 3-fold, respectively, either in the absence or presence of electrical stimulation. Electrical stimulation (1 Hz for 10 s) alone had no effect on cyclic AMP levels. 3. Electrically evoked (1 Hz for 10 s) release of [3H]NA was facilitated by 10 microM-forskolin, 3 microM-VIP and by the non-hydrolysable cyclic AMP analogue, 8-bromoadenosine 3': 5'-cyclic monophosphate (8-Br-cyclic AMP). The inactive analogue of forskolin, dideoxyforskolin, had no effect on [3H]NA release. 4. The stimulation-evoked release of [3H]NA was completely inhibited by the neuronal blocking drugs guanethidine (1 microM) and bretylium (3 microM). 5. Whole-cell voltage-clamp studies showed that forskolin and VIP did not facilitate and guanethidine and bretylium did not block voltage-activated Ca2+ currents in the cell bodies of sympathetic neurons. 6. Fluorescence measurements using the Ca(2+)-sensitive dye Indo-1 revealed that forskolin and guanethidine had no effect on the electrically stimulated increase in intracellular Ca2+ concentration recorded from the cell bodies and the growth cones. 7. We conclude that release of [3H]NA can be enhanced or blocked without affecting the increase in intracellular Ca2+ concentration produced by electrical stimulation. Therefore, it is possible that pharmacological agents enhance or depress the release of [3H]NA by acting on steps of exocytosis that are down-stream from Ca2+ mobilization.

Depolarizing stimuli and neurotransmitters utilize separate pathways to activate protein kinase C in sympathetic neurons

Several types of extracellular signals affect the function of peripheral neurons. Depolarizing stimuli cause sudden increases in permeability to various ions leading to propagation of nerve impulses and release of transmitter substances. Neurons also receive external signals via neurotransmitter receptors located on the membrane. Different types of receptors present on sympathetic neurons are believed to modulate stimulation-evoked release of norepinephrine. We have investigated the effects of depolarizing stimuli and neurotransmitters on different signaling pathways in homogeneous cultures of chick sympathetic neurons. Depolarizing stimuli (35 mM KCl; electrical stimulation, 1 Hz for 5 min) and neurotransmitters (acetylcholine and 5-hydroxytrypatmine) enhanced membrane binding of protein kinase C by 2-5-fold. 35 mM KCl increased formation of 1,2-diacylglycerol and hydrolysis of [3H]phosphatidycholine without affecting [3H] phosphoinositide hydrolysis. Neurotransmitters increased [3H]inositol phosphates and 1,2-diacylglycerol without affecting the hydrolysis of [3H]phosphatidylcholine. 5-Hydroxytryptamine and acetylcholine (muscarinic component) did not increase Ca2+ concentration in the Indo-1-loaded neuronal cell body or the growth cone, but 35 mM KCl and electrical stimulation caused a marked increase in Ca2+ concentration in both regions of sympathetic neurons. We believe this to be the first demonstration of these two types of signalling mechanisms co-existing in sympathetic neurons; depolarization activate the phosphatidylcholine pathway and neurotransmitters activate the phosphatidylinositol pathway. The importance of two pathways in controlling neuronal Ca2+ concentration and the release of transmitter is discussed.

Stimulated rise in neuronal calcium is faster and greater in the nucleus than the cytosol

Calcium is an important regulator of a variety of neuronal activities including gene expression. However, it is not clear how Ca2+ influx affects intracellular Ca2+ concentration [( Ca2+]i) in the nucleus. We have taken advantage of laser photometry, the Ca2(+)-sensitive dye Indo-1 that allows ratio imaging, and confocal microscopy to eliminate the influences of unequal cell geometry and dye distribution. We show that Ca2+ influx into sympathetic neurons causes a significantly greater and faster increase in [Ca2+]i in the nucleus than in the cytosol. The differential increase in nuclear [Ca2+]i was apparent when Ca2+ entered from the extracellular medium during K+ depolarization, ionomycin or acetylcholine treatment, and brief periods of electrical stimulation. When intracellular Ca2+ was mobilized by caffeine the rise in nuclear [Ca2+]i was again greater than in any other region of the neuron. The increased nuclear Ca2+ levels were uniform throughout the nucleus and not associated with the nuclear envelope. The differential rise in nuclear Ca2+ was eliminated by acridine orange binding to nucleic acids. Nonexcitable cells (astrocytes, oligodendrocytes, and fibroblasts) did not show differential distribution of Ca2+ after ionomycin treatment. These results support the idea that activity-dependent gene regulation in sympathetic neurons may be mediated by changes in Ca2+ concentration at the level of the chromatin material.

Beta-amyloid from Alzheimer disease brains inhibits sprouting and survival of sympathetic neurons

The significance of the amyloid plaque core proteins (APCP) in Alzheimer's disease (AD) and its consequences for neuronal survival have been controversial. To address this problem we purified the APCP and beta A obtained from brains with AD, and assessed their biological effects in tissue culture. APCP and beta A caused severe toxicity to chick and rat sympathetic and sensory neurons whose survival is dependent upon NGF. This toxicity was dose dependent and reversible at low doses. APCP and beta A prevented sprouting of neurites in freshly plated neurons. In established cultures addition of these molecules caused vacuolation and fragmentation of neurites and disintegration of neuronal soma. We suggest that the deposition of APCP in AD may be partly responsible for the destruction of the neuritic arbor, thereby contributing to the formation of the neuritic plaque and to neuronal death.

Activation of muscarinic and serotonergic receptors results in phosphoinositide hydrolysis but not in mobilization of calcium in sympathetic neurons

The effects of various neurotransmitters on phosphoinositide hydrolysis, mobilization of Ca2+ and release of [3H]-norepinephrine ([3H]-NE) were studied in cultures of sympathetic neurons of chick embryos. [3H]-inositol-1,4,5-triphosphate ([3H]-IP3) was increased in sympathetic neurons by acetylcholine (ACh), muscarine and serotonin (5-HT). Dopamine and norepinephrine did not stimulate phosphoinositide hydrolysis. Intracellular concentration of free Ca2+ ([Ca2+]i) was measured in Indo-1-loaded sympathetic neurons at rest and after addition of test agents. Measurements were made in the cell body and growth cone regions since Ca2+ mobilization is known to be different in different regions of the sympathetic neurons. ACh (nicotinic component was blocked by hexamethonium) and 5-HT failed to increase the [Ca2+]i, in the cell body as well as in the growth cone. The spontaneous release of [3H]-NE was not affected by ACh and 5-HT. Caffeine increased the [Ca2+]i only in the cell body but not in the growth cone and had no effect on the release of [3H]-NE. These results suggest that an IP3-insensitive but caffeine-sensitive pool of Ca2+ is present only in the somatic region of sympathetic neurons and is not coupled to the transmitter release.

Ca2+ mobilized by caffeine from the inositol 1,4,5-trisphosphate-insensitive pool of Ca2+ in somatic regions of sympathetic neurons does not evoke [3H]norepinephrine release

The effects of electrical stimulation, muscarinic and serotonergic agonists, and caffeine on [3H]inositol 1,4,5-trisphosphate ([3H]Ins(1,4,5)P3) content, intracellular free Ca2+ concentration ([Ca2+]i), and release of [3H]norepinephrine ([3H]NE) were studied in cultured sympathetic neurons. Neuronal cell body [Ca2+]i was unaffected by muscarinic or serotonergic receptor stimulation, which significantly increased [3H]Ins(1,4,5)P3 content. Stimulation at 2 Hz and caffeine had no effect on [3H]Ins(1,4,5)P3, but caused greater than two-fold increase in [Ca2+]i. Only 2-Hz stimulation released [3H]NE. Caffeine had no effect on the release. When [Ca2+]i was measured in growth cones, only electrical stimulation produced an increase in [Ca2+]i. The other agents had no effect on Ca2+ at the terminal regions of the neurons. We conclude that Ins(1,4,5)P3-insensitive, but caffeine-sensitive Ca2+ stores in sympathetic neurons are located only in the cell body and are not coupled to [3H]NE release.

Phosphoinositide hydrolysis is not negatively regulated by protein kinase C in the peripheral tissues of rat and chick

1. Phorbol esters are known to inhibit phospholipase C-mediated hydrolysis of membrane phosphoinositide. This inhibition is attributed to participation of protein kinase C (PKC) in a negative-feedback control of phosphoinositide metabolism. We have tested this hypothesis by using different types of activators and inhibitors of PKC. 2. Phorbol-12,13-dibutyrate (PDB) inhibited the stimulatory effect of acetylcholine (ACh) on [3H]inositol monophosphate ([3H]IP) formation in cultured sympathetic neurons of the chick embryo and adrenal medulla of the rat. 3. Acetylcholine (ACh) and 5-hydroxytryptamine (5-HT) activated neuronal PKC by 3- to 8-fold. The extent of PKC activation by 100 microM-ACh was comparable to that of 100 nM-PDB. Activation of PKC by pre-incubation of sympathetic neurons with ACh (or 5-HT) did not inhibit the stimulatory effects of ACh (or 5-HT) on [3H]IP formation. 4. Pre-treatment of sympathetic neurons or adrenal medulla with a PKC inhibitor H7 (1-(5-isoquinolinyl-sulphonyl)-2-methyl-piperazine) almost completely blocked activation of the enzyme induced by PDB, ACh or 5-HT. However, blockade of PKC did not prevent the inhibitory effects of PDB on ACh-induced [3H]IP formation. 5. Vasoactive intestinal polypeptide (VIP) and muscarine induced catecholamine secretion from the perfused adrenal medulla via formation of inositol-1,4,5-tirisphosphate (IP3). Phorbol-12,13-dibutyrate decreased muscarine-induced catecholamine secretion. However, activation of PKC by VIP had no effect on muscarine-induced catecholamine secretion and vice versa. 6. These results suggest that PKC is not negatively coupled to phosphoinositide hydrolysis in sympathetic neurons and chromaffin cells. Phorbol esters must have targets other than PKC to interfere with the phosphoinositide hydrolysis.

Effects of neurotransmitters and peptides on phospholipid hydrolysis in sympathetic and sensory neurons

The effects of neurotransmitters and peptides on phosphoinositide hydrolysis were studied by measuring [3H]inositol monophosphate ([3H]IP) and protein kinase C (PKC) activity in the sympathetic and sensory neuronal cultures of the chick embryo. [3H]IP was increased in sympathetic neurons by acetylcholine (ACh), muscarine, serotonin (5-HT), and vasoactive intestinal polypeptide. ACh, muscarine, 5-HT, and bradykinin increased [3H]IP in sensory neuronal cultures. Dopamine, norepinephrine, histamine, and nerve growth factor did not stimulate [3H]IP formation in both cultures. ACh and phorbol 12,13-dibutyrate (PDB) increased the PKC activity by two- to sevenfold in the particulate fraction of both cultures. In sympathetic neurons, PKC activity was increased in the particulate fraction; activity in the cytosolic fraction was not affected. There was a 50% decline in the protein kinase C activity of the cytosolic fraction after PDB and ACh treatment of sensory cultures. The decline in PKC activity in the cytosolic fraction was attributed to the presence of nonneuronal cells in sensory cultures. To confirm this, the enzyme activity was determined in tissues that contain a heterogeneous population of cells. PDB activated PKC in the adrenal medulla and the brain of the rat. In both tissues there was a 65% decline in the PKC activity of the cytosolic fraction and about a 75% increase in the particulate fraction. We conclude that the mechanism of activation of protein kinase C in pure cultures of sympathetic neurons is different than in tissues containing a mixed population of neurons and nonneuronal cells.

Forskolin mediates the survival of nerve growth factor-dependent sympathetic neurons of chick embryo by a cyclic AMP-independent mechanism

Forskolin has become an invaluable tool for exploring the involvement of cyclic AMP in a variety of cellular functions. The diterpine directly activates the catalytic subunit of adenylate cyclase, causing a marked increase in cyclic AMP content. Because of this well-characterized action, practically all the observed effects of forskolin are commonly attributed to cyclic AMP-dependent processes. We show here that forskolin exerts a neurotrophic action that is almost identical to that of nerve growth factor (NGF) and phorbol 12,13-dibutyrate (PDB) but independent of cyclic AMP. Sympathetic neurons of the chick embryo supported in culture for 2 days by NGF, forskolin plus 3-isobutyl-1-methylxanthine (IBMX), or PDB had almost identical levels of cyclic AMP (between 9 and 12 pmol/mg protein). Neurons supported in culture for 2 days by NGF or PDB when challenged with forskolin plus IBMX showed almost a 15-fold increase in cyclic AMP, but those supported by forskolin plus IBMX and then exposed to the same combination of drugs did not show an increase in cyclic AMP, exhibiting a marked down-regulation. Exposure of neurons to forskolin for 2 h was ineffective in supporting long-term survival, suggesting that an initial increase in cyclic AMP formation is not sufficient but the continued presence of the drug is essential for survival. Effects of forskolin on the survival of these neurons could be observed even in the presence of dideoxyadenosine, and inhibitor of adenylate cyclase. Neurons supported by PDB for 2 days in culture when exposed to NGF for the first time did not show any increase in cyclic AMP, providing clear evidence that NGF does not affect this second messenger in its target cells. Similarly, neurons supported by NGF for 2 days when exposed to PDB did not show an increase in cyclic AMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Veratrine supports the in vitro survival of embryonic chick sympathetic neurons

Veratrine (VT), an alkaloid known to act on the sodium channels and cause depolarization of a cell membrane, was found to support the survival of cultured sympathetic neurons. At 30 microM it was as effective as nerve growth factor (NGF), as determined by the cell counts and [3H]norepinephrine ([3H]NE) uptake. Protein kinase C (PKC) activity of the surviving neurons was measured because of our previous finding that depolarizing concentrations of K+ support the survival and cause several fold increase in the enzyme activity. An acute treatment of NGF-supported sympathetic neurons by VT did not alter PKC activity.

Survival of chick embryonic sensory neurons in culture is supported by phorbol esters

Sensory neurons of the chick embryo are supported in culture by several neurotrophic factors, including the phorbol esters. Because phorbol esters are known to activate one of the second messengers, namely, protein kinase C, it was of interest to see if the neurotrophic action of phorbol 12,13-dibutyrate (PDB) was related to the activation of protein kinase C in sensory neurons. Sensory neurons were obtained from dorsal root ganglia of 10-day-old chick embryos and maintained in a serum-free medium for several days to quantify survival and analyze protein kinase C activity. PDB (30 nM) supported the survival of approximately 50% of the total number of neurons plated. This value was comparable to that supported by nerve growth factor (NGF; 40 ng/ml). If PDB and NGF were added together, there was no additive effect on the survival. The protein kinase C activity of the particulate and cytosolic fractions of sensory neurons supported by NGF for 3 days was 1.26 +/- 0.1 and 2.9 +/- 0.32 pmol/min/mg of protein, respectively. In contrast, neurons supported by PDB showed an approximately 500% increase in enzyme activity in their particulate fraction. The enzyme activity of the cytosolic fraction was decreased by approximately 40%. If NGF-supported neurons were treated with PDB (30 nM) for 15 min, protein kinase C activity increased greater than 400% in the particulate fraction, whereas an approximately 50% decrease was observed in the cytosolic fraction. The protein kinase C value, expressed as a ratio of the activities in the particulate to cytosol fractions, showed large increases after phorbol treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of adrenergic and dopaminergic receptors in cultured sympathetic neurons--their coupling to cAMP but not to the transmitter release process

Experiments were carried out on cultured sympathetic neurons of the chick embryo; first, to demonstrate the presence of adrenergic and dopaminergic receptors, and then to see if these receptors are involved in regulation of transmitter release. We show that alpha 2-agonists, norepinephrine, epinephrine and clonidine, had no effect on neuronal cyclic 3',5'-adenosine monophosphate content. Forskolin enhanced neuronal cyclic 3',5'-adenosine monophosphate from a control value of about 20 pmoles/mg protein to 150 pmoles/mg protein. In the presence of alpha 2-agonists and forskolin the cyclic 3,5'-adenosine monophosphate content increased between 340 and 430 pmoles/mg protein. The alpha 1-agonist, phenylephrine, had no such effect. The facilitatory effect of alpha 2-agonist on forskolin-stimulated cyclic 3',5'-adenosine monophosphate production was blocked by the alpha 2-antagonist, yohimbine, but not the alpha 1-agonist, prazosin. Dopamine did not affect neuronal cyclic 3',5'-adenosine monophosphate content, but forskolin-stimulated increase in cyclic 3',5'-adenosine monophosphate was further facilitated by dopamine, and this effect was blocked by haloperidol. Activation of neuronal alpha 2-receptors by norepinephrine, epinephrine and clonidine did not interfere with electrically induced release of tritium from [3H]-norepinephrine-loaded sympathetic neurons. However, if sympathetic neurons were co-cultured with heart cells, clonidine, norepinephrine and epinephrine markedly inhibited the stimulation-induced release. Yohimbine or phentolamine partially reversed the inhibitory effects of alpha 2-agonists. alpha 2-Agonists and -antagonists also modified stimulation-induced release of tritium from [3H]norepinephrine-loaded hearts of the chick embryo.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic properties of embryonic chick sensory neurons

Experiments were carried out to determine the cholinergic properties of sensory neurons of the chick embryo by measuring the choline acetyltransferase activity (ChAT) and [3H]choline uptake. The choline acetyltransferase activity in the dorsal root ganglia of an 8-day-old chick embryo was 24.2 +/- 2.52, which increased to 45.4 +/- 9.69 pmol ACh/mg protein/min in the ganglia of 12-day-old embryos. Sensory neurons derived from dorsal root ganglia of 10-day-old embryos and maintained in a serum-free culture medium supplemented with insulin, transferrin and nerve growth factor (NGF) also contained significant amounts of ChAT (21.9 pmol ACh/mg protein/min). Omission of NGF resulted in neuronal death, and the enzyme activity could not be measured in these cultures. A specific inhibitor of ChAT, hydroxyethyl naphthylvinyl pyridine (NVP), when added to the assay mix produced a dose-dependent inhibition of ChAT from cultured neurons. Cultured sensory neurons incubated with [3H]choline followed by repeated washouts took up and retained [3H]choline. The uptake of [3H]choline was reduced by about 45% when NaCl, in the incubation medium, was replaced by LiCl. A specific inhibitor of choline uptake, hemicholinium-3, caused about 75% inhibition of [3H]choline uptake. It is implied that sensory neurons of the chick dorsal root ganglia express cholinergic properties during development.

Excess K+ and phorbol ester activate protein kinase C and support the survival of chick sympathetic neurons in culture

The effects of phorbol esters were investigated on the survival of chick sympathetic neurons in a serum-free culture medium. The protein kinase C activator phorbol 12,13-dibutyrate (PDB) supported about 40% of the plated sympathetic neurons. This number was comparable to that supported by nerve growth factor (NGF). A combination of phorbol ester and NGF did not significantly increase the number of surviving neurons. Phorbol ester-supported sympathetic neurons possessed desipramine-sensitive [3H]-norepinephrine uptake mechanism, and therefore were noradrenegic in character. Two days after the start of cultures, if NGF was replaced by phorbol ester, or phorbol ester was replaced by NGF, the number of surviving sympathetic neurons was essentially the same in both groups, and the uptake of [3H]norepinephrine was also comparable when examined 2 days after the switchover. Interchangeability between phorbol ester and NGF in the survival of sympathetic neurons suggests that both agents act on the same subpopulation of neurons of the chick sympathetic ganglia. The protein kinase C activity of cytosol and particulate fractions of NGF-supported neurons was 0.14 and 0.09 pmol/min/mg protein, respectively. In phorbol ester-supported neurons the activity in the particulate fraction increased by about fivefold. Removal of the phorbol ester after 2 days resulted in restoration of the enzyme activity in less than 1 h, and readdition of the phorbol ester again increased the activity by fivefold. When NGF was added to these neurons (1 microgram for 15 min), there was no change in the enzyme activity. Phorbol 13-acetate was ineffective in supporting sympathetic neurons in culture, as well as in enhancing protein kinase C activity. We also compared the protein kinase C activity of sympathetic neurons supported in culture by NGF and excess potassium (35 mM K+) Neurons supported in culture by 35 mM K+ for 2 days had almost eightfold more protein kinase C activity in their particulate fraction than in cytosol fraction. In NGF-supported neurons were acutely treated with excess K+, the protein kinase C activity was increased in the particulate fraction by about sevenfold in a concentration- and time-dependent manner. Excess K+ plus phorbol ester did not produce an additive effect on protein kinase C activity. PDB and excess K+ had no effect on cyclic AMP content of sympathetic neurons. In summary, the present data suggest that the neurotrophic action of PDB and excess K+ is probably mediated through protein kinase C.

Protein kinase C of sympathetic neuronal membrane is activated by phorbol ester--correlation between transmitter release, 45Ca2+ uptake, and the enzyme activity

The effects of phorbol esters [phorbol 12,13-dibutyrate (PDB), 12-O-tetradecanoylphorbol 13-acetate (TPA), and phorbol 13-acetate] were investigated on the release of [3H]norepinephrine, 45Ca2+ accumulation, and protein kinase C activity in cultured sympathetic neurons of the chick embryo. Sympathetic neurons derived from 10-day-old chick embryo were cultured in serum-free medium supplemented with insulin, transferrin, and nerve growth factor. After 3 days, neurons were loaded with [3H]-norepinephrine and the release of [3H]norepinephrine was determined before and after electrical stimulation. Stimulation at 1 Hz for 15 s increased the release of [3H]-norepinephrine over the nonstimulation period. Stimulation-evoked release gradually declined with time during subsequent stimulation periods. Incubation of neurons in Ca2+-free Krebs solution containing 1 mM EGTA completely blocked stimulation-evoked release of [3H]-norepinephrine. Stimulation-evoked release of [3H]-norepinephrine was markedly facilitated by 3 and 10 nM PDB or TPA. The spontaneous release was also enhanced by PDB and TPA. The net accumulation of 45Ca2+ during stimulation of sympathetic neurons was increased by two- to fourfold in the presence of PDB or TPA. PDB at 1-100 nM produced a concentration-dependent increase in the activation of protein kinase C. PDB at 30 nM increased the activity of protein kinase C of the particulate fraction from 0.09 to 0.58 pmol/min/mg protein. There was no significant change in protein kinase C activity of the cytosolic fraction (0.14 pmol/min/mg versus 0.13 pmol/min/mg protein). The ratio of the particulate to cytosolic protein kinase C increased from a control value of 0.62 to 4.39 after treatment with 30 nM PDB. TPA (10 and 30 nM) also increased protein kinase C activity of the particulate fraction by six- to eightfold. Phorbol 13-acetate had no effect on protein kinase C activity, [3H]norepinephrine release, and 45Ca2+ accumulation. These results provide direct evidence that activation of protein kinase C enhances Ca2+ accumulation, which in turn leads to the facilitation of transmitter release in sympathetic neurons.

Facilitation of noradrenergic character of sympathetic neurons by co-culturing with heart cells

Noradrenergic properties of peripheral sympathetic neurons obtained from 10-12-day-old chick embryos were examined under various culture conditions. Sympathetic neurons supported by nerve growth factor in serum-free or serum-containing medium took up significant and almost equivalent amounts of [3H]norepinephrine. The uptake was markedly enhanced when neurons were co-cultured with heart cells, either in the absence or presence of nerve growth factor, for 3 days. The facilitatory effect of heart cells on the uptake was persistent only if the nerve growth factor was present. In its absence there was a gradual decrease in the uptake. Endogenous norepinephrine content was increased by several fold when sympathetic neurons were grown with either heart cells or in a medium conditioned by the heart cells. Sympathetic neurons initially selected in culture by nerve growth factor in regular medium and then exposed to a conditioned medium for 3 days exhibited a marked facilitation of [3H]norepinephrine uptake. The number of surviving neurons was almost constant when culture media were changed. Choline acetyltransferase activity of neurons grown in heart-conditioned medium plus nerve growth factor was not significantly higher than that of neurons grown in regular medium plus nerve growth factor. The overall conclusion of the study is that the noradrenergic character of sympathetic neurons can be further enhanced by heart cells or a medium conditioned by these cells.

Effects of nutritional stress on brain tyramine concentration and dopamine turnover

This is an investigation of the effect of nutritional stress at various ages on the levels of the p- and m-isomers of tyramine in the caudate nucleus of the rat. For comparison, the effects of nutritional stress on the concentration and turnover of dopamine were also studied. Nutritional stress induced in pre-weaning (3 weeks of age) or post-weaning (up to 9 weeks of age) rats resulted in a decrease in the concentration of p-tyramine and an increase in the concentration of m-tyramine in the caudate nucleus. Dopamine concentration or turnover in the caudate nucleus was not affected by pre-weaning undernutrition; in the olfactory tubercles, however, a significant decrease was observed in dopamine turnover, calculated from the decrease in homovanillic acid levels after monoamine oxidase inhibition. The results suggest the changes observed are dependent on the availability of the amino acid precursors p- and m-tyrosine and their competition towards aromatic-L-amino acid decarboxylase.