Pemoline alters dopamine modulation of synaptic responses of neostriatal neurons in vitro

Pemoline, a central stimulant, administered systemically at high doses (300 mg/kg) reliably produces self-biting behavior in rats. Pemoline-induced self-biting shares many similarities with self-injury seen in certain human disorders. Recent evidence has shown that alterations in neostriatal neurochemistry accompany the self-biting behavior seen in the rat. The present study used intracellular electrophysiological techniques to reveal changes in neostriatal cellular physiology in slices from rats which had displayed self-injury. Depolarizing postsynaptic potentials (DPSPs) were examined in neostriatal slices from rats that received pemoline and had been engaging in self-injurious behavior and from two control populations: rats that received the same concentration of pemoline and did not engage in self-biting, and rats that received vehicle alone (peanut oil). Data were acquired in standard artificial cerebral spinal fluid. DPSPs were evoked by cortical electrical stimulation in the slice. In neurons from rats that received the vehicle or that had received pemoline but had not engaged in self-injury, dopamine (DA, 20 microM) application produced a significant decrease in the size of the cortically evoked neostriatal DPSP. In contrast, DA application produced an increase in DPSP size in neurons from rats which had received pemoline and had engaged in self-injury. Bath application of a combination of D1 and D2 receptor agonists best replicated the enhancing effect of DA. Furthermore, the enhancement could be blocked by pretreatment with the competitive N-methyl-d-aspartate receptor antagonist, 2-amino-5-phosphonopentanoic acid. The results indicate that alterations in neostriatal DA-glutamate interactions accompany pemoline injections which produce self-injurious behavior.     

Optical responses recorded after local stimulation in rat neostriatal slice preparations: effects of GABA and glutamate antagonists, and dopamine agonists

Congenital syphilis has been diagnosed very seldom in ancient populations. The case that we examined comes from San Jeronimo's Church (17th and 18th centuries AD; Mexico City). Coffin 43 contained an incomplete skeleton of an approximately 2-year-old infant. The pathological lesions of this skeleton include bilateral osteochondritis, diaphyseal osteomyelitis, and osteitis and/or periostitis on the long bones. The radiographic appearance depicts symmetrical osteomyelitic foci, particularly at the proximal extremity of both tibiae (Wimberger's sign). The skull exhibits hydrocephaly and periosteal changes on the vault, and the unerupted upper incisors evince dental hypoplasia and other pathological alterations reminiscent of Hutchinson's incisors. All these features strongly suggest a case of early congenital syphilis.     

Dopaminergic modulation of NMDA-induced whole cell currents in neostriatal neurons in slices: contribution of calcium conductances

The present experiments were designed to examine dopamine (DA) modulation of whole cell currents mediated by activation of N-methyl-D-aspartate (NMDA) receptors in visualized neostriatal neurons in slices. First, we assessed the ability of DA, D1 and D2 receptor agonists to modulate membrane currents induced by activation of NMDA receptors. The results of these experiments demonstrated that DA potentiated NMDA-induced currents in medium-sized neostriatal neurons. Potentiation of NMDA currents occurred at three different holding potentials, although it was more pronounced at -30 mV. It was mediated by D1 receptors, because it was mimicked by D1 agonists and blocked by exposure to a D1 antagonist. Activation of D2 receptors produced inconsistent effects on NMDA-induced membrane currents. Either decreases, increases, or no effects on NMDA currents occurred. Second, we examined the contributions of intrinsic, voltage-dependent conductances to DA potentiation of NMDA currents. Blockade of K+ conductances did not prevent DA enhancement of NMDA currents. However, voltage-activated Ca2+ conductances provided a major contribution to DA modulation. The dihydropyridine L-type Ca2+ channel blockers, nifedipine, and methoxyverapamil (D-600), markedly reduced but did not totally eliminate the ability of DA to modulate NMDA currents. The D1 receptor agonist SKF 38393 also enhanced Ba2+ currents in neostriatal neurons. Together, these findings provide evidence for a complex interplay between DA, NMDA receptor activation and dihydropyridine-sensitive Ca2+ conductances in controlling responsiveness of neostriatal medium-sized neurons.     

On the in-vivo modulation of neostriatal dopamine release by fluoxetine and 5-hydroxy-L-tryptophan in conscious rats

To help determine the nature of serotonergic regulation of dopamine activity in the brain an in-vivo microdialysis study has been performed in conscious rats to investigate the modulation of dopamine release in the neostriatum by 5-hydroxytryptamine (5-HT). The 5-HT uptake inhibitor, fluoxetine, and the 5-HT precursor, 5-hydroxy-L-tryptophan (5-HTP), were used to produce an increase in extracellular 5-HT concentration Systemic administration of fluoxetine (10 mg kg-1, s.c.) produced a 2- to 3-fold increase in extracellular 5-HT concentration but did not change extracellular dopamine concentration in the neostriatum. Co-administration of fluoxetine and 5-HTP (40 mg kg-1, s.c.; 60-90 min after fluoxetine) caused a highly significant tenfold increase in extracellular 5-HT concentration in the neostriatum with a slight but non-significant decrease in extracellular dopamine concentration. Pergolide, a dopamine D2 agonist, given systemically caused a dramatic decrease in extracellular dopamine concentration demonstrating the responsiveness of the neurons. These results demonstrate that high concentrations of extracellular 5-HT do not modulate dopamine release in the neostriatum. The possibility that different 5-HT receptor subtypes may mediate different regulation of dopamine release remains to be explored.     

Chromogranin A inhibits dopamine release from rat striatal slices

Chromogranin A (CGA), a prohormone and a protein component of endocrine and neural secretory granules, neuritic plaques in Alzheimer's disease and Lewy bodies in Parkinson's disease, inhibited the release of dopamine (DA) from perfused rat striatal slices. Dopamine release was stimulated by a pulse of high potassium (40mM) medium introduced at 20 minutes (K1) and 55 minutes (K2) following equilibration. The ratio of K2/K1 was 0.80+/-0.04 in control tissues, but fell significantly to 0.26+/-0.08 when 100nM purified CGA was added prior to the second potassium pulse. This reduction in DA release was equivalent to that seen when calcium was excluded from the buffer (0.19+/-0.05). Pancreastatin, a centrally active peptide product of CGA, had no effect on stimulated DA release (0.77+/-0.06), although it, as well as the other treatments, did reduce basal DA release. It is likely that the parent molecule itself, CGA, or an as yet unidentified product is responsible for inhibition of K-stimulated striatal DA release.     

Multiple ionic conductances of the human dopamine transporter: the actions of dopamine and psychostimulants

Electrophysiological and pharmacological studies of a cloned human dopamine transporter (hDAT) were undertaken to investigate the mechanisms of transporter function and the actions of drugs at this target. Using two-electrode voltage-clamp techniques with hDAT-expressing Xenopus laevis oocytes, we show that hDAT can be considered electrogenic by two criteria. (1) Uptake of hDAT substrates gives rise to a pharmacologically appropriate "transport-associated" current. (2) The velocity of DA uptake measured in oocytes clamped at various membrane potentials was voltage-dependent, increasing with hyperpolarization. Concurrent measurement of transport-associated current and substrate flux in individual oocytes revealed that charge movement during substrate translocation was greater than would be expected for a transport mechanism with fixed stoichiometry of 2 Na+ and 1 Cl- per DA+ molecule. In addition to the transport-associated current, hDAT also mediates a constitutive leak current, the voltage and ionic dependencies of which differ markedly from those of the transport-associated current. Ion substitution experiments suggest that alkali cations and protons are carried by the hDAT leak conductance. In contrast to the transport-associated functions, the leak does not require Na+ or Cl-, and DAT ligands readily interact with the transporter even in the absence of these ions. The currents that hDAT mediates provide a functional assay that readily distinguishes the modes of action of amphetamine-like "DA-releasing" drugs from cocaine-like translocation blockers. In addition, the voltage dependence of DA uptake suggests a mechanism through which presynaptic DA autoreceptor activation may accelerate the termination of dopaminergic neurotransmission in vivo.     

Multiple actions of methohexital on hippocampal CA1 and cortical neurons of rat brain slices

To explore the mechanism by which methohexital (MTH) activates epileptiform activity in patients with epilepsy, we examined the effects of MTH on hippocampal CA1 and neocortical neurons via extracellular and whole-cell patch-clamp recordings in rat brain slices. Perfusion of slices with 10 to 100 microM MTH caused no significant change in glutamatergic transmission in the hippocampal CA1 region, but enhanced gamma-aminobutyric acid (GABA)A-mediated inhibitory postsynaptic currents and induced spontaneous inhibitory postsynaptic currents in neocortical and hippocampal CA1 neurons. In addition, MTH induced a tonic, bicuculline-sensitive hyperpolarization in association with increases in membrane conductance, suggesting a direct stimulation of GABAA receptors by MTH. Spontaneous epileptiform activity was not observed in the neocortex and hippocampus after exposure of slices to MTH, neither in the standard in vitro condition nor in the presence of 4-aminopyridine, which promotes rhythmic synaptic activities. We suggest that the activation of epileptiform activity in vivo by MTH may result from increased neuronal synchrony via the potentiation of GABAA-mediated synaptic inhibition.     

Protein kinase C inhibitors block amphetamine-mediated dopamine release in rat striatal slices

The stimulant drug amphetamine is postulated to enhance dopamine release through the plasmalemmal dopamine transporter by an exchange diffusion with synaptosomal dopamine. Because protein kinase C has been shown to have an effect on dopamine transporter activity, we examined the effect of protein kinase C inhibitors on endogenous dopamine release stimulated by amphetamine in perfused rat striatal slices. At concentrations of 1 microM, the selective protein kinase C inhibitors chelerythrine, Ro31-8220 and calphostin C nearly completely inhibited endogenous dopamine release elicited by 1 microM amphetamine. The inactive analog bisindoylmaleimide V had no effect. Extracellular Ca++ was not required for the effect of the inhibitors. The importance of vesicular dopamine release was examined by determining inhibitor activity in reserpine-treated rats. Dopamine release elicited by 1 microM amphetamine was not significantly altered in reserpine-treated rats compared with control animals. Ro31-8220 at 1 microM completely blocked amphetamine-induced dopamine release in reserpine-treated rats. Activation of protein kinase C with 250 nM of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate increased dopamine release, and the release was not additive with 1 microM amphetamine. Both chelerythrine and Ro31-8220 at 1 microM increased [3H]dopamine uptake by 17% and 30%, respectively, whereas a brief exposure to 12-O-tetradecanoylphorbol 13-acetate slightly inhibited [3H]dopamine uptake. Our results suggest that amphetamine-mediated dopamine release through the plasmalemmal transporter is highly dependent on protein kinase C activity.     

Effects of natriuretic peptides and dopamine on single-unit activity of dorsomedial arcuate neurons in rat brain slices

The effects of atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) on single-unit activity of dorsomedial arcuate (DM-ARC) neurons were reported. The modulatory effect of CNP on dopamine's (DA) action was also studied. ANP alone in 0.05-0.5 nmol doses induced 26% inhibition and 14% excitation of 37 DM-ARC neurons; the majority (60%) were not responsive. CNP, however, inhibited 46% and excited 4% of 74 DM-ARC neurons. Dose-dependent inhibitory effects of CNP were also observed. In 71 neurons tested with both CNP and DA, more neurons were inhibited by DA (66%) than those by CNP (46%). About one-third (34%) of them were inhibited by both. Furthermore, in 41 neurons inhibited by DA, more than half (54%) of their responses were potentiated by co-administration of CNP. In conclusion, CNP by itself exhibited a predominantly inhibitory action on DM-ARC neurons; and it also potentiated the inhibitory effect of DA on these neurons.     

Differential release of dopamine by nitric oxide in subregions of rat caudate putamen slices

Inherited susceptibility to breast cancer has been an area of intense investigation for the past 10 years. Early work focused on identifying modes of transmission, which culminated in the identification of chromosome 17q12-21 as the first human genomic region that harbored an autosomal dominant susceptibility gene for breast cancer (BRCA1) in 1990. BRCA1 was subsequently identified and was followed shortly by the identification of BRCA2. Research in the past 3 years has elucidated much about the mutation spectrum and mutation frequency of these genes in specific populations and is beginning to identify potential functions. Whereas progress in this area has been rapid and much is now known about inherited susceptibility to breast cancer, much more needs to be done to make these discoveries useful in the diagnosis, treatment, and ultimately, the prevention of breast cancer.     

Cholinergic excitation induces activity-dependent electrophysiological and transcriptional responses in hippocampal slices

To explore the correlations between short-term neurophysiological events initiated by over-activation of acetylcholine receptors, and long-lasting changes in brain function, we combined electrophysiology and PCR-based measurements in hippocampal slices or live mice subjected to stress or drug-induced cholinergic activation. Our findings reveal a common cascade of neuronal events resulting in delayed suppression of cholinergic transmission.     

Modulation of [3H]dopamine release by neuropeptide Y in rat striatal slices

Polycythemia vera (PV) is associated with a high incidence of thrombosis. The association of apparent and secondary polycythemia with thrombosis is not clear. It was suggested that activation of the coagulation system contributes to thrombus formation in PV. However, the mechanism of activation is unknown. Monocytes generate a potent tissue factor (TF) upon stimulation with various substances, which is involved in thrombus formation in various disorders. Therefore, we studied the possibility that the factor is involved in the activation of coagulation and thrombus formation also in PV. Unstimulated peripheral blood mononuclear cells (PBMC) from each of the different types of polycythemia expressed weak TF activity (2 U) and antigen (41.4 to 52.9 pg/ml), which were similar to normal controls. Following stimulation with endotoxin, PBMC from normal controls and from apparent and secondary polycythemia showed a 3.9- to 4.5-fold increase in TF, while cells from PV showed a 21-fold increase (P<0.001). Similar levels were generated by PBMC after treatment of PV and at the spent phase. TF was generated by monocytes but not by lymphocytes. Plasma prothrombin fragment1+2 (F1+2) levels, assayed at the same time, were significantly higher in PV (2.46 nm) compared to normals and apparent and secondary polycythemia (0.22 to 0.32 nm), and were in a significant correlation with monocyte TF activity and antigen levels (r = 0.77, 0.87). The high levels of F1+2 confirm that the coagulation system is activated in PV. The increased capacity of monocytes to generate TF may be responsible for the activation of the coagulation system and thrombus formation. The hypercoagulability state that is induced by this mechanism suggests that long-life oral anticoagulation should be considered once thrombosis has been developed in PV.     

The gamma-aminobutyric acid uptake inhibitor NO-711 potentiates 3-aminopropylphosphinic acid-induced actions in rat neocortical slices

In rat neocortical slices maintained in Mg2+-free Krebs medium, the GABAB receptor agonists baclofen and 3-aminopropylphosphinic acid dose-dependently reduced the frequency of spontaneous discharges, 3-aminopropylphosphinic acid being 10 times less potent than baclofen. These were sensitive to the antagonist CGP 52432 (3-[[3,4-dichloro-phenyl)methyl]-amino]propyl](-P-diethoxymethyl)- phosphinic acid) (1, 5 and 10 microM). The GABA uptake inhibitor NO-711 (1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,5,6-tetrahydro-3-+ ++pyridinecarboxylic acid) (5 and 10 microM) produced 2.9 and 9 fold increases in the potency of 3-aminopropylphosphinic acid without affecting baclofen-induced responses. In this study, the low potency of 3-aminopropylphosphinic acid when compared to baclofen, may be attributed to its uptake by NO-711-sensitive GABA transporters.     

Relationship between dopamine agonist stimulation of inositol phosphate formation and cytidine diphosphate-diacylglycerol accumulation in brain slices

Dopamine receptor-coupled stimulation of inositol phosphate formation has been characterized extensively, but little is known about the diacylglycerol arm of this dual-signaling pathway. This study examined several parameters of cytidine diphosphate-diacylglycerol (CDP-DG) accumulation as an index of agonist-stimulated DG formation. Rat brain slices pre-labeled with 5-[3H]cytidine were incubated with various test agents in the presence of LiCl and accumulated CDP-DG analyzed. Dopamine and SKF38393 significantly and dose-dependently stimulated CDP-DG accumulation. SKF38393 responses were inhibited by neomycin and reversed by myo-inositol or by exclusion of LiCl. Compared to inositol phosphate formation in 2-[3H]inositol-prelabeled slices, the CDP-DG responses were proportionately greater, while the agonist EC50 values were similar between the two assays. The D1-receptor antagonist SCH23390 inhibited SKF38393-mediated responses at 0.1-10 microM concentrations, whereas greater concentrations reversed the inhibition. SKF38393 effects were completely blocked by the DG kinase inhibitor R59022, thus precluding any role for phospholipase-D or de novo phosphatidate synthesis in the dopaminergic response. D609 which inhibits phosphatidylcholine-specific phospholipase-C (PLC), potently inhibited both CDP-DG accumulation and inositol phosphate formation. These findings demonstrate that the selective D1-receptor antagonist SCH23390 is a partial agonist at the D1-like dopamine receptor that couples to phosphoinositide signaling, that dopaminergic facilitation of phosphoinositide signaling is independent of de novo phosphatidate synthesis, and that the widely used enzyme inhibitor, D-609, is probably not selective for phosphatidylcholine-specific PLC in brain slice preparations. The greater sensitivity of the CDP-DG measurement presents this assay as a reliable and possibly superior index of dopamine receptor-coupled PLC activation in intact tissues.     

Voltage-activated calcium channels involved in veratridine-evoked [3H]dopamine release in rat striatal slices

The present study explored the role of different sub-types of voltage-activated Ca2+ channels (VACCs) in mediating veratridine-evoked [3H]dopamine (DA) release from rat striatal slices. The release of [3H]DA evoked by veratridine (25 microM) decreased by 50.6+/-2.9% (n=8) in the absence of calcium and was completely abolished by 1 microM tetrodotoxin. The L-type Ca2+ channel blockers nifedipine (10 microM), nitrendipine (10 microM), diltiazem (10 microM) and verapamil (10 microM) did not modulate this release. Similarly, [3H]DA release was affected neither by the N-type VACC blocker omega-conotoxin-GVIA (1 microM) nor by the selective P-type channel blockers omega-agatoxin-IVA and omega-agatoxin-TK at low nM concentrations (30 nM), indicating no involvement of N- and P-type Ca2+ channels. In contrast, higher concentrations of omega-agatoxin-IVA that would also inhibit Q-type VACCs, blocked the release of [3H]DA by 27.9+/-8.1% (n=5) and 37.5+/-13.6% (n=3) at 0.3 and 1 microM, respectively. In addition, application of the Q-type Ca2+ channel blocker omega-conotoxin-MVIIC (0.01-3 degrees M) reduced [3H]DA release in a concentration-dependent manner, with maximum inhibition of 35.3+/-4.1% at 3 microM (n=5). On the basis of these results, it is concluded that the Ca2+ channels that participate in veratridine-evoked [3H]DA release are Q-type Ca2+ channels.     

Influence of dopamine receptor and adrenoceptor blockade on the hemoconcentrating and hypotensive actions of atrial natriuretic peptide

Atrial natriuretic peptide (ANP) lowers mean arterial pressure (MAP) and increases hematocrit through reduction in plasma volume caused by a transcapillary shift of plasma fluid and protein toward the interstitium. We examined the consequences of blockade of the dopaminergic and adrenergic systems on the hypotensive and hemoconcentrating responses to ANP. Changes in MAP, hematocrit, and plasma protein concentration (PPC) were measured in anesthetized acutely binephrectomized rats, during infusion of ANP alone (1 microgram.kg-1.min-1 for 45 min) or in the presence of haloperidol (20 micrograms.kg-1.min-1), phentolamine (15 micrograms.kg-1.min-1), or propranolol (10 micrograms.kg-1.min-1). Infusion of ANP reduced MAP by 8.6 +/- 1.3% and increased hematocrit by 9.0 +/- 0.6% (both p < 0.005 vs. vehicle). PPC increased (4.4 +/- 0.6%; p < 0.005 vs. vehicle) significantly less than hematocrit, indicating extravasation of proteins. The ANP-evoked reduction in MAP was not affected in haloperidol- or phentolamine-treated rats (-8.8 +/- 2.3 and -10.5 +/- 2.4%, respectively; both p < 0.005 vs. vehicle) but was abolished in propranolol-treated rats (+3.2 +/- 1.3%; p = ns vs. vehicle). The ANP-induced increase in hematocrit was slightly attenuated in haloperidol-, phentolamine-, and propranolol-treated rats (7.5 +/- 0.7, 7.3 +/- 0.8, and 6.0 +/- 1%, respectively). In addition, the coefficient of reflection, an index of the permeability to proteins, was higher in these three groups (0.41 +/- 0.06, 0.49 +/- 0.08, and 0.57 +/- 0.14, respectively) than in control rats infused with ANP (0.27 +/- 0.03), indicating an attenuation of the ANP-induced extravasation of proteins. Thus, in binephrectomized rats, the hypotensive activity of ANP requires a beta-adrenergic component, whereas its hemoconcentrating action is, at least in part, dependent upon dopaminergic and adrenergic activation.     

Effects of postnatal stress on dopamine mesolimbic system responses to aversive experiences in adult life

The effects of postnatal stress on mesolimbic dopamine (DA) functioning in 90-day-old mice were investigated. Postnatal stress consisted of 15 min daily exposure to clean bedding (CB) in the absence of the mother for the first two weeks of life. Controls were daily exposed to home cage bedding (HCB) in the absence of the mother. A single brief (5-10 min) exposure to restraint produced a clear-cut increase in DA metabolites (3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3-MT)) in the nucleus accumbens septi (NAS) of adult HCB but not CB mice. Moreover, when tested in an elevated plus maze, CB mice showed more exploration and reduced fearfulness in comparison with HCB mice. Taken together, these results indicate reduced emotional reactivity in adult mice repeatedly stressed during postnatal development. Moreover, HCB mice but not CB mice showed altered behavioral responsiveness to apomorphine following repeated restraint stress (10 daily 120 min) in adult life, although no difference in the behavioral response to either a low or a high dose of apomorphine was observed in adult unstressed mice of the CB and HCB groups. These results indicate that the effects of early experiences on brain DA functioning may not be evident in basal conditions and be revealed only under environmental pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of leg flexion angle on the mechanomyographic responses to isometric muscle actions

INTRODUCTION: An ROC analysis was carried out in order to determine the reliability of digital luminescence radiography review at a PC and this was compared with a radiological work station and with X-ray film on a viewing box. MATERIAL AND METHOD: 54 chest images obtained by digital luminescence radiography were selected, 31 of these contained small pulmonary nodules. In order to evaluate critical detail, five images of a phantom showing round foci were used. Five radiologists examined these, using a Siemens Magic View work station, a PC with proprietary software (ViewMed) and X-ray films on a viewing box. Image processing of the work station used the standard clinical application. ViewMed performs linear scaling of grey levels to 8 Bit. The results were examined statistically by means of a t-test. RESULTS: As far as the chest images were concerned there was no significant difference in the diagnostic value of these methods. There was, however, a highly significant loss of diagnostic information with respect to the round focus phantom when using the PC compared with the other methods. CONCLUSION: In the configuration in which it was used, the PC should not be relied on as a primary means of examination since critical details cannot always be seen. In routine use these play a subordinate role and there was no significant diagnostic loss where the chest images were concerned. We expect that by improvements in the frequency and contrast processing the PC accuracy will be considerably increased.     

Regional differences in neuronal responses to 5-HT: intracellular studies in hippocampal slices

1. Intracellular recordings were obtained from cells in the regions CA1, CA3 and the dentate gyrus (DG) of rat hippocampal slices. 2. Topical application of 5-HT induced a 2-10 mV hyperpolarization in all cells tested. 3. The hyperpolarization was accompanied by a marked reduction in input resistance in CA1 and DG cells, but by a much smaller resistance change in CA3 cells. 4. These effects of 5-HT were not abolished by tetrodotoxin. 5. It is suggested that 5-HT causes an increase in K+ conductance in regions CA1 and DG and that this results in hyperpolarization. A different mechanism might be activated by 5-HT in cells of the CA3 region.