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J F Bowyer

Publications and source records attributed to J F Bowyer.

At least 19 recordsLinked to original sources
PubMed1995

Comparison of glutamine-enhanced glutamate release from slices and primary cultures of rat brain.

Increased extracellular glutamate has been associated with a wide range of effects including production of neurotoxicity. Glutamine has previously been shown to cause increased release of glutamate from a variety of preparations. Extracellular central nervous system (CNS) glutamine levels are known to increase with neurotoxin exposures, hepatic failure, renal failure, head trauma or stroke. However, the action of glutamine to enhance the release of glutamate under nondepolarizing conditions has not been well studied. Since glutamine-mediated increases in extracellular glutamate are potentially of significance in cellular damage as a result of CNS insult, further examination of this phenomenon is important. Striatal and hippocampal slices or virtually neuron-free primary striatal glial cultures were employed in studies to further elucidate the mechanism(s) of glutamine-enhanced glutamate release. Elevated extracellular glutamine caused increased glutamate release in all three preparations. In hippocampal and striatal slices elevated glutamine caused an enhancement of N-methyl-D-aspartate (NMDA) receptor-mediated [3H]catecholamine release equivalent to that produced by high concentrations (up to 100 microM) of exogenous glutamate. In both striatal slices and primary cultures kynurenate increased glutamate release in the presence of 500 microM glutamine, while kainate either had no effect or decreased glutamate levels in the presence of glutamine. Since several presynaptic modulators of release did not affect the glutamate release produced by glutamine in slices, vesicular release of glutamate from nerve terminals was probably not involved in the effects of the exogenous glutamine. The similarities between striatal slices and primary striatal cultures indicate that enzymatic conversion of glutamine to glutamate within glia may be an important factor in the glutamine-mediated elevation of extracellular glutamate levels.

Analysis of Variance↗
PubMed1995

Determination of d-amphetamine in biological samples using high-performance liquid chromatography after precolumn derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid.

An HPLC method is described for the determination of amphetamine using fluorometric detection after derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid. This procedure is more sensitive (detection limit 370 fmol in microdialysate buffer standards, 1.5 pmol in extracted plasma and tissue samples) than most of the previous methods described for the determination of amphetamine with HPLC-fluorescence detection. Due to the stability of the derivative it is also suitable for autosampling after manual derivatization. Investigators currently using o-phthaldialdehyde derivatization and fluorometric detection for amino acid determination should be able to rapidly implement this method.

3-Mercaptopropionic Acid↗
PubMed1995

Age-dependent sensitivity of rats to the long-term effects of the serotonergic neurotoxicant (+/-)-3,4-methylenedioxymethamphetamine (MDMA) correlates with the magnitude of the MDMA-induced thermal response.

The effects of developmental age on (+/-)-3,4-methylenedioxymethamphetamine (MDMA)-induced reductions in 5-hydroxytryptamine (5-HT) content and 5-HT reuptake sites were investigated in conjunction with the effects of developmental age on MDMA-induced thermoregulatory responses. MDMA was administered to rats at postnatal days (PND) 10, 40 and 70 in a range of ambient temperature environments (10 degrees C, 25 degrees C and 33 degrees C). Animals were monitored for alterations in body temperature and sacrificed 1 week after MDMA administration. MDMA administration at PND 10 did not result in persistent reductions in 5-HT content or 5-HT reuptake sites in frontal cortex, nor could a hyperthermic response be elicited. In contrast, MDMA administration at PND 40 and PND 70 resulted in a hypothermic response in cold environments (10 degrees C) and a hyperthermic response in warm environments (> or = 25 degrees C). When hypothermia was observed after MDMA (10 degrees C environment), long-term reductions in 5-HT content and 5-HT reuptake sites were significantly attenuated or abolished. Conversely, when a hyperthermic response was observed (25 degrees C and 33 degrees C environments), long-term MDMA-induced reductions in 5-HT content and 5-HT reuptake sites were significantly enhanced. Thus, thermal responses significantly correlated with MDMA-induced reductions in 5-HT content and 5-HT reuptake sites. These experiments demonstrate a role for hyperthermia in the expression of serotonergic neurotoxicity after MDMA administration.

Aging↗
PubMed1995

Amphetamine levels in brain microdialysate, caudate/putamen, substantia nigra and plasma after dosage that produces either behavioral or neurotoxic effects.

Extracellular levels of d-amphetamine (AMPH) in caudate/putamen were determined using microdialysis and HPLC quantitation after s.c. doses that produced increased motor activity (1 mg/kg), stereotypic behavior (2.5 mg/kg) or dopamine depletion in the caudate/putamen (4 x 5 mg/kg). In 6-mo-old rats exposed to neurotoxic doses of AMPH sulfate (4 x 5 mg/kg in a 23 degrees C environment), extracellular caudate/putamen AMPH rose to levels of 7.9 +/- 0.9 microM after the first dose and peaked at 15.1 +/- 2.5 microM after the third dose with no further increases after the fourth dose. After one or three doses of 5 mg/kg, peak plasma and tissue levels of AMPH were 1.7 +/- 0.2 and 2.9 +/- 0.3 microM in plasma, 36 +/- 6 and 73 +/- 10 in substantia nigra and 25 +/- 4 and 50 +/- 8 in caudate/putamen, respectively. Caudate/putamen extracellular AMPH levels were about three times higher (in either 6- or 12-mo-old rats) after 4 x 15 mg/kg in a 10 degrees C environment and tissue levels in caudate/putamen and substantia nigra were three to five times higher after three doses of AMPH. However, these higher levels did not produce dopamine depletion in the caudate/putamen, while the lower doses (4 x 5 mg/kg) given at 23 degrees C did. Estimated caudate/putamen extracellular AMPH levels of 2.5 to 5 microM after single doses (1 and 2.5 mg/kg) that caused hyperactivity and stereotypic behavior are compatible with the 2 to 10 microM AMPH concentrations reported to be necessary to produce pronounced dopamine release in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Low environmental temperatures or pharmacologic agents that produce hypothermia decrease methamphetamine neurotoxicity in mice.

Recently we have reported that methamphetamine (METH) neurotoxicity in rats depends on the environmental temperature. Here, we evaluate whether a cold environment (4 degrees C) or drugs which chloride and glutamate ion channel function block METH neurotoxicity in mice. Adult male CD mice received METH i.p. (4 x 10 mg/kg METH at 23 degrees C along with saline. 2.5 mg/kg (+)-MK-801, 40 mg/kg phenobarbital or 2.5 mg/kg diazepam and either 4 x 10 or 4 x 20 mg/kg METH at 4 degrees C). Multiple injections of METH (4 x 10 mg/kg i.p.) at room temperature (23 degrees C) produced a significant depletion of dopamine (DA) in striatum at 24, 72 h, 1 and 2 weeks. Three days post 4 x 10 mg/kg METH at 23 degrees C, an 80% decrease in striatal dopamine (DA) occurred while the same dose at 4 degrees C produced only a 20% DA decrease, and 4 x 20 mg/kg METH at 4 degrees C produced a 54% DA decrease. At 23 degrees C (+)MK-801 completely blocked while phenobarbital (40% decrease) and diazepam (65% decrease) partially blocked decreases in striatal DA produced by 4 x 10 mg/kg METH. Decreases in DOPAC and HVA were similar to the decreases in DA after METH and antagonists. Multiple injections of METH (4 x 10 mg/kg, i.p.) at room temperature also produced a significant depletion of serotonin (5-HT) in striatum at 24, 72 h, 1 and 2 weeks. This depletion of 5-HT at room temperature was blocked either by changing the environmental temperature to 4 degrees C, or by pretreatment with MK-801, diazepam and phenobarbital.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗
PubMed1994

Further studies of the role of hyperthermia in methamphetamine neurotoxicity.

The depletion of striatal dopamine (DA) that can occur after methamphetamine (METH) administration has been linked to METH-induced hyperthermia. The relationship between METH-induced hyperthermia, neurotoxicity (striatal DA depletions) and compounds that protect against METH neurotoxicity was further investigated in this study. Typically, rats exposed to METH die when their body temperatures exceed 41.3 degrees C but such hyperthermic rats can be saved by hypothermic intervention. Subsequently, rats saved by hypothermic intervention have greater depletion of striatal DA at an earlier time of onset (18 hr or less post-METH) than do METH-exposed rats that do not attain such high temperatures. Striatal damage was present 3 days post-METH in these hyperthermic rats, as assessed by silver degeneration of terminals and increases in the astrocytes that express glial fibrillary acidic protein immunoreactivity. By contrast, alterations in the number of [3H]dizoclipine (MK-801) binding sites in cortical or striatal membranes at 1, 3 or 14 days post-METH were not detected. The experiments showed that mean and maximal body temperature correlated well with striatal DA concentrations 3 days post-METH (r = -0.77, n = 58), which suggests a role for hyperthermia in METH neurotoxicity. However, hyperthermia (alone or with haloperidol present) induced by high ambient temperatures did not deplete striatal DA in the absence of METH. Haloperidol, diazepam and MK-801 all reduced METH-induced striatal DA depletion to a degree predicted by their inhibition of hyperthermia and increased ambient temperature abolished their neuroprotection. Although an interleukin-1 receptor antagonist reduced maximal body temperature enough to lower the lethality rate, it did not reduce the temperature sufficiently to block METH neurotoxicity. It was concluded that short- and long-term decreases in striatal DA levels depend on the degree of hyperthermia produced during METH exposure but cannot be produced by hyperthermia alone. In addition, several agents that block DA depletions do so by inhibiting METH-induced hyperthermia. Finally, the results suggested a role for interleukin-1 in the extreme hyperthermia and lethality produced by METH.

Animals↗
PubMed1993

Development of dopamine and N-methyl-D-aspartate systems in rat brain: the effect of prenatal phencyclidine exposure.

Phencyclidine (PCP) inhibits the uptake of the neurotransmitter dopamine (DA), and blocks N-methyl-D-aspartate (NMDA) receptor-regulated ion channels. PCP also binds to sigma receptors in vivo and in vitro in rat brain. Prolonged exposure to PCP in adults has been observed to reduce the number of PCP binding sites in brain. We designed these experiments to evaluate whether prolonged prenatal exposure to PCP produces alterations in the development of DA and NMDA systems in brain. To do so, we characterized the normal course of development of basal and stimulated DA release in striatal slices, the ontogeny of striatal DA concentrations, and the development of NMDA receptor channels and associated glutamate binding sites in frontal cortex. We compared these developmental profiles to those in rats exposed to prenatal PCP, in an attempt to characterize the effect of prenatal PCP exposure on the pattern of brain development. Pregnant CD rats were injected s.c. with either 0, 10 or 20 mg/kg PCP daily on gestational days 8 through 20. On postnatal days (PND) 8, 21, 45, or 100, rats were sacrificed and brain tissues isolated for in vitro assessment. In vitro [3H]DA release from striatal slices evoked by either 40 microM glutamate or 15 mM K+ increased over 250% from PND 8 to PND 45, and glutamate-stimulated release was still significantly below adult levels at PND 45. In contrast, D-methamphetamine (D-METH)-evoked [3H]DA release, frontal cortical glutamate binding sites and NMDA channels developed early, reaching adult levels on or before PND 21.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Effects of a cold environment or age on methamphetamine-induced dopamine release in the caudate putamen of female rats.

Extracellular levels of dopamine (DA) and metabolites as well as serotonin [5-hydroxytryptamine (5-HT)] and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the caudate putamen (CPU) of either 6- or 12-month-old female rats using microdialysis and high-performance liquid chromatography with electrochemical detection (HPLC-ED) before, during, and after four consecutive injections (given at 2-h intervals) of methamphetamine (METH). In 6-month-old rats administered 4 x 5 mg/kg METH at an environmental temperature (ET) of 23 degrees C, peak extracellular DA levels (between 50 and 150 rho g/10 microliters) were attained 30-45 min after each dose of METH while dihydroxyphenylacetic acid (DOPAC) decreased steadily after the first doses of METH until it reached a plateau at 50% of control (550-700 pg/10 microliters) levels. Increases in 5-HT levels during METH administrations paralleled DA increases while 5-HIAA decreases paralleled DOPAC decreases. The total CPU DA and 5-HT content of these rats was about 65% of control at 3 days post-METH. Reducing the ET to 4 degrees C during dosing decreased the peak and average DA levels attained during the 4 x 5 mg/kg METH administration to about 50% of that observed at a 23 degrees C ET. Increasing the dose to 4 x 10 mg/kg METH (4 degrees C ET) increased peak and average CPU DA levels to 200% that observed during 4 x 5 mg/kg METH at a 23 degrees C ET. However, no significant decreases in total CPU DA content of any rats dosed with METH at a 4 degrees C ET were observed 3 days post-METH. In 12-month-old rats dosed with 4 x 5 mg/kg METH (23 degrees C ET), the peak and average extracellular DA levels were only 30-60% that of 6-month-old rats. However, the CPU DA content of older rats was significantly decreased both 3 (30% control) and 14 (60% control) days post-METH. In summary, METH toxicity may not be predicted solely by the extracellular levels of DA attained during METH administration; age and ET also greatly influence METH neurotoxicity.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Fluoro-gold and pentamidine inhibit the in vitro and in vivo release of dopamine in the striatum of rat.

Fluoro-Gold (FG), first developed as an antifungal/antiparasitic agent, is now also used extensively as a retrograde tracer in histological studies of nervous tissue. The fact that FG is taken up by dopamine (DA) terminals before its retrograde transport to DA cell bodies implies a presynaptic interaction, though the biochemical target(s) and mechanism(s) are unknown. To further elucidate, FG and another aromatic diamidine, pentamidine, were tested on [3H]DA release and uptake in vitro from striatal slices and synaptosomes. Neither compound affected [3H]DA uptake in synaptosomes and slices, and neither inhibited DA efflux mediated through reversal of DA uptake mechanisms. NMDA-mediated glutamate-evoked DA release was completely inhibited by either FG (IC50 approximately 3 microM) or pentamidine (IC50 approximately 1 microM), and 20 mM K(+)-evoked DA release was inhibited by similar concentrations but only to 60% of control. Arginine (up to 500 microM) and spermidine (200 microM) failed to reverse 33 microM FG inhibition of either the spontaneous or the glutamate-evoked DA release, indicating that FG inhibition of release was not necessarily via blockade of either nitric oxide generation or spermidine binding to NMDA receptors. Interestingly, FG (33 microM) and pentamidine (10 microM) inhibited 1 and 5 microM D-methamphetamine (METH)-evoked [3H]DA release to approximately 50% of control, and in striatal synaptosomes, FG (33 microM) and pentamidine (10 microM) inhibited 5 microM METH- and 1.25 mM Ca(++)-evoked DA release. Additionally, in vivo brain microdialysis supported the in vitro results; 100 microM FG in the microdialysis buffer inhibited 70% of the increase in extracellular DA in the striatum produced by 2.5 mg/kg METH.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗
PubMed1992

Phosphorylation and activation of tyrosine hydroxylase in PC18 cells: a cell line derived from rat pheochromocytoma PC12 cells.

Treatment of rat pheochromocytoma PC18 cells (a variant subclone of PC12 cells) with forskolin produced increased activity and phosphorylation of tyrosine hydroxylase. In contrast, treatment of the PC18 cells with 56 mM K+, A23187, phorbol-12-myristate-13-acetate (PMA) or phorbol-12,13-dibutyrate (PDB) did not affect the activity and only slightly increased the phosphorylation of tyrosine hydroxylase. None of the treatments except forskolin increased cyclic AMP levels in PC18 cells. Furthermore, 45Ca2+ uptake into PC18 cells was not affected by 56 mM K+, PDB or forskolin; however, A23187 increased 45Ca2+ uptake 4-fold over basal uptake. Nevertheless, no activation and little increase in phosphorylation of tyrosine hydroxylase was observed in PC18 cells treated with A23187. When tyrosine hydroxylase levels in PC18 cells were elevated by treatment with dexamethasone, activation of tyrosine hydroxylase by 56 mM K+, PDB or A23187 was still not observed. Both purified Ca2+/calmodulin-dependent protein kinase and cyclic AMP-dependent protein kinase catalyzed the phosphorylation of tyrosine hydroxylase purified from PC18 cells in vitro. Furthermore, crude cell extracts from PC12 cells and PC18 cells possessed Ca2+/calmodulin-dependent protein kinase activity that catalyzed the phosphorylation of purified tyrosine hydroxylase. These results suggest that tyrosine hydroxylase activity in PC18 cells is regulated by a cyclic AMP-dependent mechanism. However, due to a number of abnormalities the Ca(2+)-dependent mechanisms do not result in the activation of tyrosine hydroxylase and only slightly increase the phosphorylation of the enzyme in PC18 cells.

Animals↗
PubMed1992

The influence of environmental temperature on the transient effects of methamphetamine on dopamine levels and dopamine release in rat striatum.

When male rats were injected four times (once every 2 hr) with 5 mg/kg methamphetamine (METH) at an environmental temperature of 23 degrees C, transient changes occurred in the levels of striatal dopamine (DA) and the regulation of striatal DA release. Striatal DA levels were minimally affected 1 day after METH treatment, but 3 days after METH treatment, striatal DA levels decreased to approximately 40% of control. DA levels returned to 70% of control 2 weeks after METH. Similarly, striatal tyrosine hydroxylase (TH) activity decreased to approximately 50% of control activity 3 days after METH treatment at 23 degrees C, but did not differ from controls at 1 or 14 days after METH treatment. No changes in striatal DA levels were observed in rats treated with four doses of 5 mg/kg METH at an environmental temperature of 4 degrees C. Striatal DA levels decreased modestly to approximately 70% of controls 3 days after treatment with four doses of 10 mg/kg METH at 4 degrees C, but DA levels returned to control levels 14 days after METH treatment. Furthermore, striatal TH activity was not affected by 10 mg/kg METH at 4 degrees C. Thus, a cold environmental temperature (4 degrees C) reduced the effects of METH on striatal DA levels and striatal TH activity. Changes in the presynaptic regulation of DA release after either 5 mg/kg (23 degrees C) or 10 mg/kg (4 degrees C) METH treatment were determined in vitro using striatal slices.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

A further evaluation of the effects of K+ depolarization on glutamate-evoked [3H]dopamine release from striatal slices.

Exogenous glutamate will evoke dopamine (DA) release from striatal slices in vitro. To further characterize glutamate-evoked DA release from striatal slices, experiments were designed to: 1) determine if sufficient endogenous glutamate can be released in vitro to presynaptically mediate [3H]DA release in the absence of Mg++ and 2) reevaluate how K+ depolarization affects glutamate-evoked [3H]DA release. Removal of Mg++ to potentiate N-methyl-D-aspartate (NMDA) receptor-mediated DA release increased 15 mM K(+)-evoked [3H]DA release to about 200% of control. The potentiation of this release was probably not mediated by NMDA receptors because it was not blocked by the glutamate receptor antagonists MK-801, 6,7-dinitroquinoxalinedione (DNQX) or kynurenate. Furthermore, the removal of Mg++ increased DA release substantially (200%) in the presence of 5 microM sulpiride and 10 microM nomifensine, indicating that DA reuptake and DA D2 autoreceptors are not primarily responsible for increased DA release. In the absence of Mg++, depolarization produced by 20 mM or greater [K+] inhibited DA released by exogenous glutamate, whereas a much higher [K+] was necessary to evoke endogenous glutamate release. In the presence of 1.5 mM Mg++, a reduction of the "Mg++ blockade" of NMDA receptors by 15 mM K+ depolarization during glutamate-evoked DA release was evaluated with and without the DA reuptake inhibitor nomifensine and the DA D2 antagonist sulpiride. DA released by K+ depolarization (Mg++ present) was markedly increased by 1 mM glutamate, but this effect was only partially reversed by kynurenate or high concentrations of either MK-801 (25 microM) or DNQX (100 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Interactions of MK-801 with glutamate-, glutamine- and methamphetamine-evoked release of [3H]dopamine from striatal slices.

The interactions of MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine], glutamate and glutamine with methamphetamine (METH)-evoked release of [3H]dopamine were assessed in vitro to determine whether MK-801 inhibition of METH neurotoxicity might be mediated presynaptically, and to evaluate the effects of glutamatergic stimulation on METH-evoked dopamine release. MK-801 inhibition of glutamate- or METH-evoked dopamine release might reduce synaptic dopamine levels during METH exposure and decrease the formation of 6-hydroxydopamine or other related neurotoxins. Without Mg++ present, 40 microM and 1 mM glutamate evoked a N-methyl-D-aspartate receptor-mediated [3H]dopamine and [3H]metabolite (tritium) release of 3 to 6 and 12 to 16% of total tritium stores, respectively, from striatal slices. With 1.50 mM Mg++ present, 10 mM glutamate alone or in combination with the dopamine uptake blocker nomifensine released only 2.1 or 4.2%, respectively, of total tritium stores, and release was only partially dependent on N-methyl-D-aspartate-type glutamate receptors. With or without 1.50 mM Mg++ present, 0.5 or 5 microM METH evoked a substantial release of tritium (5-8 or 12-21% of total stores, respectively). METH-evoked dopamine release was not affected by 5 microM MK-801 but METH-evoked release was additive with glutamate-evoked release. Without Mg++ present, 1 mM glutamine increased glutamate release and induced the release of [3H]dopamine and metabolites. Both 0.5 and 5 microM METH also increased tritium release with 1 mM glutamine present. When striatal slices were exposed to 5 microM METH this glutamine-evoked release of glutamate was increased more than 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Regulation of tyrosine hydroxylase activity in pheochromocytoma PC-12 cells by bradykinin.

Tyrosine hydroxylase is activated and phosphorylated following treatment of PC-12 cells with bradykinin. In order to determine the mechanisms by which this occurs, we have evaluated the second messenger systems that may be responsible for this activation and phosphorylation. Inositol phosphates appear to play an important role in the activation and phosphorylation of tyrosine hydroxylase because bradykinin treatment significantly increased the formation of [3H]inositol phosphates and the concentration of intracellular free calcium ([Ca2+]i) in PC-12 cells. The uptake of extracellular 45Ca2+ into PC-12 cells at 1 min was significantly increased (107%) by bradykinin treatment and this increase was blocked by La3+, an inorganic calcium channel inhibitor, but not by nifedipine, an inhibitor of voltage-dependent calcium channels. The activation of tyrosine hydroxylase in PC-12 cells following bradykinin treatment was partially inhibited by La3+. Additivity experiments were performed to evaluate whether the activation and phosphorylation of tyrosine hydroxylase in PC-12 cells following treatment with bradykinin (10 microM) was similar to the activation and phosphorylation of tyrosine hydroxylase in PC-12 cells following treatment with dibutyryl cAMP (2 mM), 4 beta-phorbol-12 beta-myristate-13 alpha-acetate (PMA) (2 microM), and high K+ (56 mM). The combination of bradykinin and PMA produced additive effects, indicating that the activation of tyrosine hydroxylase by treatment with these two compounds was through different mechanisms. Furthermore, exposure of PC-12 cells to bradykinin did not increase intracellular cAMP levels. The combination of bradykinin and PMA treatments produced only partial additivity in tyrosine hydroxylase activity and phosphorylation. No additivity was produced with bradykinin and high K-treatment. Phosphopeptide analysis was performed on tyrosine hydroxylase obtained from PC-12 cells treated with bradykinin. Bradykinin treatment produced a significant incorporation of [32P]-phosphate into two phosphopeptides of tryptically digested tyrosine hydroxylase. One of these peptides corresponds to a peptide obtained by trypsinization of purified tyrosine hydroxylase that is phosphorylated by purified calcium/calmodulin-dependent protein kinase. The other 32P-tyrosine hydroxylase-peptide obtained from PC-12 cells treated with bradykinin corresponds to the phosphorylation site obtained during PMA stimulation of PC-12 cells. These results indicate that bradykinin treatment increases intracellular inositol phosphates, calcium, and possibly diacylglycerol levels in PC-12 cells. These effects could then increase calcium/calmodulin-dependent protein kinase activity and possibly calcium/phospholipid-dependent protein (protein kinase C) activity, resulting in increased phosphorylation and activity of tyrosine hydroxylase.

Animals↗
PubMed1990

Alpha-2 adrenergic inhibition of Ca(++)-evoked [3H]norepinephrine release from synaptosomes is blocked by depolarization.

The Ca(++)-evoked release of [3H]norepinephrine was used in these studies to investigate presynaptic regulation of norepinephrine release. In hippocampal synaptosomes, previously unexposed to Ca++ during isolation and superfusion, 1.25 mM Ca++ evoked a modest (4 to 7% of total stores) release of [3H]norepinephrine with 4.5 mM [K+] present. The alpha-2 adrenergic agonist clonidine inhibited 60% of the Ca(++)-evoked [3H]norepinephrine release. The alpha-2 adrenergic antagonists idazoxan and yohimbine reversed clonidine inhibition of release whereas the alpha-1 antagonist prazosin did not. Increasing the [K+] before Ca++ exposure increased [3H]norepinephrine release, and at 20 [K+] the release increased to over 20% of total stores. However, at [K+] above 9 mM, inhibition of Ca(++)-evoked release by clonidine decreased, and by 20 mM [K+] clonidine no longer inhibited release. Release was unaffected by 5 microM idazoxan or the opiate antagonist naloxone at 15 or 20 mM [K+]. The K+ channel blockers tetraethylammonium (5 mM) and 4-aminopyridine (0.1 mM) increased Ca(++)-evoked release almost 4-fold above control (4.5 mM [K+] present). Neither clonidine nor idazoxan affected Ca(++)-evoked release with the K+ channel blockers present. Therefore, even though K+ channel blockers and 20 mM [K+] increase neurotransmitter release, it is not autoreceptor activation by released endogenous norepinephrine that is responsible for blocking alpha-2 inhibition, but the depolarization produced by these treatments. The 20 mM [K+] blockade of alpha-2 inhibition was decreased by lowering the [Ca++] in the superfusion buffer. Therefore, synaptosomal accumulation of Ca++ may partially explain the loss of alpha-2 inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗