Effects of cocaine on the electrical activity of single noradrenergic neurons from locus coeruleus

The effects of intravenous (i.v.) cocaine HCl on single identified spontaneously firing noradrenergic neurons in the nucleus locus coeruleus (LC) were studied in rats in vivo. Cocaine (0.25-1 mg/kg) produced inhibition of spontaneously firing LC neurons, which was reversed by the administration of the selective alpha 2-adrenoceptor antagonist, piperoxane (250 micrograms/kg, i.v.). Procaine, a local anesthetic that is structurally related to cocaine, did not inhibit LC neurons in doses up to 4 mg/kg, i.v. These results suggest that cocaine in low doses has significant central sympathomimetic effects at the single noradrenergic neuron level and that the inhibition of spontaneous activity may be mediated by alpha 2-adrenoceptors. Our results also indicate that cocaine in pharmacologically relevant doses, can significantly affect central alpha 2-adrenoceptor regulatory processes.     

Effects of monoamines on heterosynaptic facilitation in giant neurons of Planorbis corneus

The effects of noradrenaline and dopamine on heterosynaptic facilitation (HSF) were investigated during experiments on giant identified neurons from the cerebral ganglion of the freshwater molluskPlanorbis corneus. It was found that catecholamines, while inducing an increase in the amplitude of response obtained by iontophoretic application of acetylcholine, also sharply reduce the amplitude of EPSP occurring as a result of stimulating the cerebral nerve, although acetylcholine also acts as transmitter in this instance. Catecholamines were also found to exert a blocking action on synaptic transmission during the period of HSF. Noradrenaline washout immediately after blockade of HSF was shown to reinstate and promote continuing independent facilitation of synaptic transmission. Duration of this facilitatory after-effect frequently exceeded that of initial HSF. This would imply that if serotonin promotes development of HSF, then the secretion of noradrenaline and dopamine brought about by certain effects act as the mechanism controlling duration and intensity of HSF under naturally-occurring conditions of the mollusk and perhaps even human nervous system activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 224–232, March–April, 1989.     

Effects ofp-chlorophenylalanine on the metabolism of serotonin from 5-hydroxytryptophan

The effects ofD,L--chlorophenylalanine methyl ester (PCPA-methyl ester) and two of its metabolites, 2-(-chlorophenyl)-ethylamine (PCPEA) and -chlorophenylacetic acid (PCPAA), on the metabolism of serotonin (5-HT) fromD,L-5-hydroxytryptophan (5-HTP) ware studied in vitro and in vivo using the telencephalon and brainstem of the rat. For in vivo studies and some in vitro experiments, rats were injected with either 100 mg/kg PCPA-methyl ester or saline alone on days 1, 2, and 3, and were killed on day 15. When the in vivo metabolism of 5-HT was to be studied, the saline group and the PCPA group of animals were injected with 75 g/kg [³H]D,L-5-HTP 20 min before sacrificing. With respect to the values found for the saline-injected animals, the specific activity (S.A.; dpm/nmol) of 5-HIAA was significantly greater in the telencephanol and brainstem of the animals injected with PCPA-methyl ester. The S.A. of 5-HTP was the same in both groups; the S.A. of 5-HT was lower in the telencephalon of the PCPA group than in the saline group; in the brainstem, there was no difference. In both the saline- and PCPA-injected animals, the S.A. of 5-HIAA was greater than the S.A. of 5-HT. There was no difference between the saline- and PCPA-injected animals with regard to: (1)L-5-HTP decarboxylase activity; (2)L-5-HTP-induced release of [³H]5-HT in vitro from crude nerve ending fractions (P₂); or (3) in vitro uptake of [³H]D,L-5-HTP and its conversion to [³H]5-HT using the P₂ fraction. In vitro studies demonstrated that the PCPEA could directly cause a large increase in the release of [³H]5-HT from the P₂ fraction, whereas PCPA and PCPAA had little or no apparent effect. The data were interpreted to suggest that in the telencephalon of the animals treated with PCPA-methyl ester, there was a higher turnover of 5-HT than was found in the saline-treated group.     

Effects of adenosine analogs on rat cerebral cortical neurons

Adenosine and the adenosine 5'-phosphates (5'-AMP, 5'-ADP and 5'-ATP) depress the spontaneous firing of cerebral cortical neurons. In this study adenosine analogs, adenosine transport blockers and adenosine deaminase inhibitors have been used to gain further insight into the nature of the adenosine receptor and the likely routes of metabolism of extracellularly released adenosine. The firing rate of cortical neurons, including identified corticospinal neurons, was depressed by 2-substituted derivatives of adenosine. 2-Halogenated derivatives of adenosine were potent depressors while 2-aminoadenosine and 2-hydroxyadenosine (crotonoside) were slightly less potent than adenosine. The α,β-methylene isosteres of 5'-ADP and 5'-ATP were almost devoid of agonist activity while the β,γ-methylene analog was an active agonist. This suggests that ADP and ATP must be converted to AMP or possibly adenosine before they can activate the adenosine receptor. 2'-, 3'- and 5'- deoxyadenosine depressed spontaneous firing without antagonizing the effect of adenosine. Adenosine deaminase inhibitors, deoxycoformycin and $\text{erythro}$-9-(2-hydroxy-3-nonyl) adenine had potent, long lasting depressant actions on the spontaneous firing of cortical neurons and concurrently potentiated the actions of adenosine or 5'-AMP. Inhibitors of adenosine transport, papaverine and 2-hydroxy-5-nitrobenzylthioguanosine, prolonged the duration of action of adenosine and 5'-AMP. Intracellular recordings show that 5'-AMP hyperpolarizes cerebral cortical neurons and suppresses spontaneous and evoked excitatory postsynaptic potentials, in the absense of any pronounced alterations in membrane resistance.     

神经活性甾体别孕烯醇酮对脑皮质神经元损伤的保护作用

目的：利用N-甲基-D-天门冬氨酸（NMDA）诱发新生小鼠脑皮质神经元损伤模型,探讨神经活性甾体别孕烯醇酮对脑皮质神经元的保护作用及其机制。方法：应用RT-PCR和Western blot法检测别孕烯醇酮对β2-γ-氨基丁酸受体（β2-GABA-R）表达和对蛋白激酶B（PKB,又称为Akt）磷酸化的影响。应用Western blot和DNA-Ladder方法检测NMDA诱发的神经元凋亡及别孕烯醇酮对NMDA诱发凋亡的影响。结果：Western blot和RT-PCR分析表明0.5×10-6mol/L-5×10-6mol/L别孕烯醇酮使Akt磷酸化增加并促进β2-GABA-R mRNA的表达。1×10-6mol/L别孕烯醇酮预处理小鼠脑皮质神经元有抗凋亡作用,但5×10-6mol/L别孕烯醇酮预处理小鼠脑皮质神经元使NMDA诱发的DNA-Ladder减弱明显,并能有效抵抗NMDA诱发的活化型PRAP、Caspase-3、Caspase-9的增加。结论：别孕烯醇酮可通过促进β2-GABA-R表达和增加Akt磷酸化抵抗NMDA诱发的脑皮质神经元凋亡。     

Neurotrophic activity of honokiol on the cultures of fetal rat cortical neurons

Honokiol, a main biphenyl neolignan of the traditional crude medicine, Magnoliae cortex, was found to show neurotrophic activity on the cultures of rat cortical neurons at concentration from 0.1 to 10 microM. In the cortical neurons cultured in serum-free medium supplemented with B27, honokiol could promote neurite outgrowth. In addition, the survival and growth of neurons were significantly enhanced by adding honokiol to the primary cultures in serum-free medium supplemented with N2. Its neurotrophic activity was comparable to 40 ng mL(-1) of bFGF at concentration of 10 microM.     

Differences in monoamine oxidase activity between cultured noradrenergic and cholinergic sympathetic neurons

Two types of monoamine oxidase activity (MAO-A and MAO-B) help regulate the levels of biogenic amines such as catecholamines and serotonin. Although MAO-A has greater activity toward most catecholamines than MAO-B, no direct experiments have determined the types and levels of MAO activity that are normally expressed in noradrenergic neurons. Noradrenergic neurons from neonatal rat superior cervical ganglia were isolated and cultured under conditions that permit either continued expression of the noradrenergic phenotype or promote a transition to a predominantly cholinergic phenotype. After 14-21 days in vitro, neurons from both types of cultures were assayed for the type and amount of monoamine oxidase activity using tryptamine, a common substrate for both MAO-A and MAO-B. Neurons cultured under noradrenergic conditions expressed sevenfold greater MAO activity than neurons cultured under cholinergic conditions. Essentially all MAO activity in the noradrenergic cultures was inhibited by preincubation with 10(-8)-10(-9) M clorgyline, which indicated that this activity was primarily MAO-A. Cultures grown under cholinergic conditions exhibited 6- to 10-fold lower MAO-A activity and an 8- to 10-fold lower level of catecholamine synthesis from labeled precursors compared to neurons grown under noradrenergic conditions. These results directly demonstrate that high MAO-A activity is expressed in noradrenergic neurons in vitro. The corresponding decreases in both MAO-A specific activity and catecholamine synthesis as neurons become cholinergic in vitro suggest that the expression of the noradrenergic phenotype involves the coordinate regulation of degradative as well as synthetic enzymes involved in catecholamine metabolism.     

Network dynamics and synchronous activity in cultured cortical neurons

Neurons extracted from specific areas of the Central Nervous System (CNS), such as the hippocampus, the cortex and the spinal cord, can be cultured in vitro and coupled with a micro-electrode array (MEA) for months. After a few days, neurons connect each other with functionally active synapses, forming a random network and displaying spontaneous electrophysiological activity. In spite of their simplified level of organization, they represent an useful framework to study general information processing properties and specific basic learning mechanisms in the nervous system. These experimental preparations show patterns of collective rhythmic activity characterized by burst and spike firing. The patterns of electrophysiological activity may change as a consequence of external stimulation (i.e., chemical and/or electrical inputs) and by partly modifying the "randomness" of the network architecture (i.e., confining neuronal sub-populations in clusters with micro-machined barriers). In particular we investigated how the spontaneous rhythmic and synchronous activity can be modulated or drastically changed by focal electrical stimulation, pharmacological manipulation and network segregation. Our results show that burst firing and global synchronization can be enhanced or reduced; and that the degree of synchronous activity in the network can be characterized by simple parameters such as cross-correlation on burst events.     

Effects of simulated microgravity on the development and maturation of dissociated cortical neurons

Although a wealth of evidence supports the hypothesis that some functions of the nervous system may be altered during exposure to microgravity, the possible changes in basic neuronal physiology are not easy to assess. Indeed, few studies have examined whether microgravity affects the development of neurons in culture. In the present study, a suspension of dissociated cortical cells from rat embryos were exposed to 24 h of simulated microgravity before plating in a normal adherent culture system. Both preexposed and control cells were used after a period of 7-10 d in vitro. The vitality and the level of reactive oxygen species of cultures previously exposed did not differ from those of normal cultures. Cellular characterization by immunostaining with a specific antibody displayed normal neuronal phenotype in control cells, whereas pretreatment in simulated microgravity revealed an increase of glial fibrillary acidic protein fluorescence in the elongated stellate glial cells. Electrophysiological recording indicated that the electrical properties of neurons preexposed were comparable with those of controls. Overall, our results indicate that a short time of simulated microgravity preexposure does not affect dramatically the ability of dissociated neural cells to develop and differentiate in an adherent culture system.     

Effect of disulfiram on the interconnected activity of cortical neurons in trained cats

The action of disulfiram on interconnected activity of neurones in the visual and motor cortical areas was studied in cats with food-procuring conditioned responses to light. Multiunit activity was recorded from the areas and, by means of amplitude discrimination, separated into impulse flows. Crosscorrelation analysis of the impulse series was used to reveal the character and temporal parameters of interconnected activities of neurones firing in correlation within the limits both of the same cortical area and of the two different ones. A depressing action was shown of the disulfiram on the food-procuring reaction, accompanied by a decrease of the number of pairs of neurones from the visual and motor cortical areas mostly acting in interconnection, interactions with long time delays being mostly affected. The character of action of neighbouring neurones in the visual and motor cortical areas changed in the same direction, expressed in their firing by a "common source" type. The question is discussed of disulfiram influence on interneuronal connections of both types suggesting a decrease of alimentary motivation as well as disturbance of food-procuring conditioned motor coordination.     

Effects of Vinpocetine on mitochondrial function and neuroprotection in primary cortical neurons

Vinpocetine (ethyl apovincaminate), a synthetic derivative of the Vinca minor alkaloid vincamine, is widely used for the treatment of cerebrovascular-related diseases. One of the proposed mechanisms underlying its action is to protect against the cytotoxic effects of glutamate overexposure. Glutamate excitotoxicity leads to the disregulation of mitochondrial function and neuronal metabolism. As Vinpocetine has a binding affinity to the peripheral-type benzodiazepine receptor (PBR) involved in the mitochondrial transition pore complex, we investigated whether neuroprotection can be at least partially due to Vinpocetine’s effects on PBRs.Neuroprotective effects of PK11195 and Ro5-4864, two drugs with selective and high affinity to PBR, were compared to Vinpocetine in glutamate excitotoxicity assays on primary cortical neuronal cultures. Vinpocetine exerted a neuroprotective action in a 1–50 μM concentration range while PK11195 and Ro5-4864 were only slightly neuroprotective, especially in high (>25 μM) concentrations. Combined pretreatment of neuronal cultures with Vinpocetine and PK11195 or Ro5-4864 showed increased neuroprotection in a dose-dependent manner, indicating that the different drugs may have different targets. To test this hypothesis, mitochondrial membrane potential (MMP) of cultured neurons was measured by flow cytometry. 25 μM Vinpocetine reduced the decrease of mitochondrial inner membrane potential induced by glutamate exposure, but Ro5-4864 in itself was found to be more potent to block glutamate-evoked changes in MMP. Combination of Ro5-4864 and Vinpocetine treatment was found to be even more effective.In summary, the present results indicate that the neuroprotective action of vinpocetine in culture can not be explained by its effect on neuronal PBRs alone and that additional drug targets are involved.     

Effects of Vinpocetine on mitochondrial function and neuroprotection in primary cortical neurons

Vinpocetine (ethyl apovincaminate), a synthetic derivative of the Vinca minor alkaloid vincamine, is widely used for the treatment of cerebrovascular-related diseases. One of the proposed mechanisms underlying its action is to protect against the cytotoxic effects of glutamate overexposure. Glutamate excitotoxicity leads to the disregulation of mitochondrial function and neuronal metabolism. As Vinpocetine has a binding affinity to the peripheral-type benzodiazepine receptor (PBR) involved in the mitochondrial transition pore complex, we investigated whether neuroprotection can be at least partially due to Vinpocetine’s effects on PBRs.Neuroprotective effects of PK11195 and Ro5-4864, two drugs with selective and high affinity to PBR, were compared to Vinpocetine in glutamate excitotoxicity assays on primary cortical neuronal cultures. Vinpocetine exerted a neuroprotective action in a 1–50 μM concentration range while PK11195 and Ro5-4864 were only slightly neuroprotective, especially in high (>25 μM) concentrations. Combined pretreatment of neuronal cultures with Vinpocetine and PK11195 or Ro5-4864 showed increased neuroprotection in a dose-dependent manner, indicating that the different drugs may have different targets. To test this hypothesis, mitochondrial membrane potential (MMP) of cultured neurons was measured by flow cytometry. 25 μM Vinpocetine reduced the decrease of mitochondrial inner membrane potential induced by glutamate exposure, but Ro5-4864 in itself was found to be more potent to block glutamate-evoked changes in MMP. Combination of Ro5-4864 and Vinpocetine treatment was found to be even more effective.In summary, the present results indicate that the neuroprotective action of vinpocetine in culture can not be explained by its effect on neuronal PBRs alone and that additional drug targets are involved.     

Effect of temperature on impulse activity of cortical neurons in guinea pigs

The temperature change of incubating fluid from 37 to 24 degrees C results in significant decrease of neuronal spontaneous firing rate in parietal cortex slices. Evoked spike responses to microiontophoretic application of glutamate practically did not change.     

Differentiation of noradrenergic and dopaminergic neurons in the cardiovascular system

Dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and norepinephrine (NE) are present in the rat cardiovascular system. All of the catechols can be partially depleted by administering 6-hydroxydopamine (6-HODA). When animals are pretreated with desipramine before 6-HODA, there is a selective partial depletion of DA and DOPAC. NE can be partially depleted with minimal effects on DA and DOPAC by administering N-(2-chloroethyl)N-ethyl-2-bromobenzylamine (DSP-4). These results are consistent with the hypothesis that independent dopaminergic and noradrenergic elements are present in the rat cardiovascular system and that DA is not solely a precursor for NE. NE, DA and DOPAC were assayed in human vessels and the pattern of distribution of the catechols is consistent with the results reported for animals.