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J M Baraban

Publications and source records attributed to J M Baraban.

16 recordsLinked to original sources
PubMed1992

High basal expression of zif268 in cortex is dependent on intact noradrenergic system.

The transcription factor Zif268 displays high basal levels of expression in cortex that appear to be dependent on physiological synaptic activity. We report that selective lesions of the noradrenergic system induced by DSP4 markedly suppress basal zif268 mRNA levels in cortex. Accordingly, the noradrenergic system which projects extensively to the cortex and is tonically active may play a key role in maintaining normal patterns of gene expression in target neurons.

Animals↗
PubMed1992

Neural-specific expression, genomic structure, and chromosomal localization of the gene encoding the zinc-finger transcription factor NGFI-C.

The nerve growth factor-induced clone C (NGFI-C) gene encodes a zinc-finger transcription factor that is rapidly induced by nerve growth factor in rat pheochromocytoma PC12 cells and by seizure in brain. NGFI-C is closely related to the previously described early response genes, nerve growth factor-induced clone A (NGFI-A or EGR1), EGR2, and EGR3. These four early response (immediate early) proteins all contain very similar zinc-finger DNA binding domains; in addition, analysis of the non-zinc-finger region revealed that they share an additional five highly homologous subdomains, four of which are within the amino terminus. The 5' flanking region of NGFI-C contains several cAMP response elements but does not contain any serum-response elements or CArG boxes [CC(A/T)6GG], cis-acting elements commonly involved in early response gene regulation. NGFI-C mRNA was detected in neural tissues of postnatal animals, but no expression was found in rat embryos. In situ hybridization demonstrated that NGFI-C is rapidly induced in the dentate gyrus of the hippocampus after seizure, but in contrast to NGFI-A, increases in NGFI-C mRNA were not detected in the overlying cortex. By using fluorescence in situ hybridization, NGFI-C was localized to human chromosome 2p13. This region contains a constitutive fragile site that is associated with chromosomal breakpoints and translocations characteristic of some chronic lymphocytic leukemias.

Amino Acid Sequence↗
PubMed1992

Activation of the zinc finger encoding gene krox-20 in adult rat brain: comparison with zif268.

Zif268 and krox-20 are transcription regulatory factors that contain highly homologous zinc finger DNA-binding domains. Recent studies have demonstrated that zif268 expression is rapidly regulated in brain by neuronal stimulation. We now report that, like zif268, krox-20 is rapidly and transiently activated by electroconvulsive shock treatment (ECT), D1 dopamine receptor activation, and opiate withdrawal. These studies indicate that, as found for the leucine zipper family of transcription factors, multiple members of the zinc finger family of transcription factors are induced by neuronal stimulation.

Animals↗
PubMed1992

Phosphoinositide turnover associated with synaptic transmission.

Although pharmacological stimulation of a wide variety of transmitter receptors triggers phosphoinositide (PI) turnover, little is known about the type of synaptic activity required to activate this system. To investigate this question, we have used primary cultures of embryonic cortical neurons, which develop functional glutamate and GABA synapses during maturation in vitro. Mature cultures display spontaneous synaptic activity that is totally suppressed by tetrodotoxin (TTX). PI turnover, assayed by the lithium-sensitive accumulation of [3H]CDP-diacylglycerol, was readily detected under basal conditions and was abolished by TTX. Increased excitatory synaptic activity induced by picrotoxin, an antagonist of GABAA receptor-mediated inhibition, further stimulated PI turnover. Similar results were obtained when PI turnover was assayed using [3H]inositol labeling. With either assay, the magnitude of synaptically induced PI turnover was comparable to maximal responses produced by muscarinic receptor stimulation. Although a component of the spontaneous synaptic currents is sensitive to N-methyl-D-aspartate (NMDA)-preferring glutamate receptor antagonists, blockade of NMDA receptors did not affect PI turnover associated with synaptic transmission. To assess the time course of synaptically mediated PI turnover, the amplitude and duration of spontaneous synaptic currents were reduced by lowering the extracellular Ca2+ concentration from 2.25 to 0.5 mM, a maneuver that suppresses basal PI turnover. Increases in PI turnover were detected as early as 5 min following restoration of the extracellular Ca2+ concentration to 2.25 mM. Taken together, these findings indicate that activation of the PI system is associated with physiological levels of glutamatergic synaptic transmission.

Animals↗
PubMed1992

D1 dopamine receptor activation of multiple transcription factor genes in rat striatum.

Recent studies have shown that dopamine receptor agonists induce expression of Fos-like immunoreactivity in rat striatal neurons. The protooncogene c-fos belongs to a family of immediate early genes that are rapidly induced in fibroblasts by growth factors. In light of previous findings that several immediate early gene mRNAs that encode proven or putative transcription factors are differentially regulated by neuronal stimulation in vivo, we have examined the effect of dopaminergic agents on mRNA levels of several such genes using in situ hybridization and northern blot analysis. d-Amphetamine (2.5-10 mg/kg i.p.) causes a rapid but transient dose-dependent increase in zif268 and jun-B mRNA levels in striatum that was abolished by striatal 6-hydroxydopamine lesions or by pretreatment with the specific D1 receptor antagonist SCH-23390 but not by specific D2 receptor antagonists. Apomorphine, a dopamine agonist that acts at both D1 and D2 receptors, and SKF-38393, a specific D1 receptor agonist, produce similar mRNA changes in rats pretreated with either 6-hydroxydopamine or reserpine, whereas LY-171,555, a specific D2 receptor agonist, has no effect. Direct dopamine agonist effects on these immediate early gene mRNA levels are also blocked by D1 but not by D2 antagonists. We observed similar, although less robust, changes in c-fos and fos-B mRNA levels. These results demonstrate that striatal D1 dopamine receptors are coupled to activation of multiple transcription factor genes, including zif268 and jun-B as well as members of the fos family.

Amphetamine↗
PubMed1992

Role of monoamine systems in activation of zif268 by cocaine.

Rapid activation of transcription factor genes is thought to play a key role in stimulus-induced neuronal plasticity. To help understand the genomic response that may underlie long-term effects of cocaine and amphetamine, we have investigated the effect of these agents on Zif268, a transcription regulatory factor that is expressed at high levels in brain neurons. Like c-fos, zif268 is markedly activated in striatum by cocaine and amphetamine. This response appears to involve the dopamine system, since it is abolished by SCH23390, a selective D1 dopamine receptor antagonist, or by 6-hydroxydopamine lesions. To assess the role of other monoamine systems in regulating the expression of these transcription factors, we have examined the effects of selective monoamine uptake blockers as well as agents that lesion the norepinephrine and serotonin systems. These studies indicate that, in addition to the dopamine system, the norepinephrine and serotonin systems also play prominent roles in the activation of zif268 and c-fos by cocaine and amphetamine.

Amphetamine↗
PubMed1992

Spontaneous synchronous synaptic calcium transients in cultured cortical neurons.

The firing pattern displayed by neuronal aggregates is thought to play a key role in cortical development and physiology. In this study, we have employed optical recording of intracellular calcium to monitor activity of multiple neurons simultaneously in primary cortical cultures. With this approach, we have observed spontaneous synchronous calcium transients among adjacent cortical neurons. These transients appear to be mediated by prominent spontaneous synaptic excitation, as they are enhanced by picrotoxin, a blocker of inhibitory GABAergic transmission, and reduced by antagonism of glutamate receptors or addition of TTX. After picrotoxin treatment, the calcium transients exhibit regular frequency and amplitude, and occur in synchrony with bursts of excitatory synaptic potentials every 10-20 sec. Using electrical stimulation, we have identified a relative refractory period, extending up to 5 sec after a synchronous burst, that may play a role in cell synchronization. NMDA receptor antagonists or reduced extracellular calcium levels lower the amplitude of the calcium transients yet fail to alter their frequency, suggesting that intracellular calcium levels may not be a major determinant of burst frequency. In contrast, mild depolarization with kainic acid (0.5-1 microM) increased burst frequency up to fivefold, suggesting a critical dependence of rhythmic activity on membrane potential. Chronic blockade of electrical activity with TTX beginning a few days after plating of cultures dampens the amplitude and significantly increases the frequency of calcium transients in mature cultures. These studies demonstrate that aggregates of cultured cortical neurons express synchronous firing activity in vitro and that this network activity is dependent in part on neuronal firing during development.

2-Amino-5-phosphonovalerate↗
PubMed1992

Chronic cocaine treatment suppresses basal expression of zif268 in rat forebrain: in situ hybridization studies.

Transcription regulatory factors are rapidly induced in brain by a wide variety of stimuli and may be important in coordinating changes in gene expression underlying neuronal plasticity. In addition to the transient activation profile typically displayed by many of these genes, zif268 exhibits prominent basal expression in the brain that is dependent on synaptic activity. Accordingly, zif268 may play a key role in regulating neuronal gene expression induced by naturally occurring stimuli. Acute cocaine administration (15 mg/kg i.p.) produces a robust and transient induction of several transcription factors in the brain, including zif268. In the present study we report that, in contrast to the acute effects of a single dose, chronic cocaine treatment (15 mg/kg i.p., twice daily for a total of 10 injections), produces a widespread suppression of basal zif268 mRNA levels in rat forebrain between 8 and 24 hr after the last cocaine injection. This reduction is not evident after a single injection of cocaine or comparable chronic treatment with a structural analog, procaine, that does not share cocaine's uptake inhibitor properties. The suppression of basal zif268 expression may provide a mechanism for producing widespread effects of chronic cocaine administration on neuronal gene expression.

Animals↗
PubMed1991

L-type voltage-sensitive calcium channels mediate synaptic activation of immediate early genes.

Although L-type voltage-sensitive calcium channels (VSCCs) have been well characterized electrophysiologically, their role in synaptic physiology has remained unclear. To assess their involvement in synaptic regulation of gene expression, we have examined the effects of selective VSCC antagonists on basal, synaptically mediated activation of several transcription factor genes in cultured cortical neurons. Basal expression of c-fos, jun-B, zif268, and fos-B is rapidly suppressed by exposure to L-type VSCC antagonists and increased by (-)BayK-8644, a VSCC agonist. Although VSCC antagonists block kainate-induced rises in intracellular calcium and gene expression, these agents have little effect on spontaneous electrical activity or synaptically induced calcium transients in these neurons. These findings suggest that even though L-type VSCCs contribute a relatively minor component of synaptic calcium transients, they appear to play a key role in coupling synaptic excitation to activation of transcriptional events thought to contribute to neuronal plasticity.

Animals↗
PubMed1991

Electroconvulsive treatment induces a rapid and transient increase in tyrosine phosphorylation of a 40-kilodalton protein associated with microtubule-associated protein 2 kinase activity.

Recent studies have identified protein tyrosine phosphorylation as a major intracellular signaling pathway. However, little is known about regulation of this signaling pathway in neuronal systems. To help identify changes in levels of protein tyrosine phosphorylation in brain, we have utilized specific anti-phosphotyrosine antibodies to detect phosphotyrosine-containing proteins by immunoblotting techniques. We have found that electroconvulsive treatment induces a selective increase in tyrosine phosphorylation of a soluble 40-kDa protein. The rise is rapid and transient, reaching maximal levels at 1-2 min and returning to basal levels by 8 min. The phosphotyrosine-containing 40-kDa protein is most prominent in hippocampus, smaller in neocortex, and not detected in brainstem or cerebellum. A phosphotyrosine-containing 42-kDa protein present in several cell types has recently been identified as a serine/threonine phosphotransferase, referred to as microtubule-associated protein 2 kinase. Comparison of the levels of tyrosine phosphorylation of the 40-kDa protein and microtubule-associated protein 2 kinase activity during column chromatography of hippocampal extracts demonstrates that the phosphotyrosine-containing 40-kDa protein and microtubule-associated protein 2 co-purify. Moreover, the tyrosine phosphorylation of the 40-kDa protein and microtubule-associated protein 2 kinase activity are increased to a similar extent following electroconvulsive treatment. These findings suggest that the phosphotyrosine-containing 40-kDa protein identified in brain is closely related to microtubule-associated protein 2 kinase.

Animals↗
PubMed1991

Synaptic regulation of immediate early gene expression in primary cultures of cortical neurons.

Neuronal stimulation can rapidly activate several immediate early genes that code for transcription factors. We have used primary cortical cultures to study the regulation of four of these genes, c-fos, c-jun, jun-B, and zif268. Immunocytochemical studies with antibodies to Jun-B, c-Jun, and c-Fos demonstrate intense staining in the nuclei of a subset of cortical neurons in mature cultures (21-25 days in vitro) but not young cultures (3-7 days in vitro). To assess whether this immunoreactivity may be induced by spontaneous synaptic activity that develops with a similar profile, we examined the effects of agents that reduce this synaptic activity. Tetrodotoxin or N-methyl-D-aspartate receptor antagonists suppress basal immunoreactivity to Jun-B and c-Fos, but not c-Jun, indicating that the basal level of c-Jun expression is not dependent on electrical activity. Picrotoxin, an agent that increases synaptic excitation indirectly by blocking inhibitory synaptic currents mediated by gamma-aminobutyric acidA receptors, markedly increases the percentage of neurons displaying immunoreactivity to c-Fos, c-Jun, Jun-B, and Zif268. Northern analysis suggests that the increases in immunostaining induced by picrotoxin are secondary to a rapid increase in mRNA for these proteins. These findings provide evidence for rapid transcriptional regulation of immediate early genes in cortical neurons by synaptic activity.

Animals↗
PubMed1979

Noradrenergic agonists and antagonists: effects on conditioned fear as measured by the potentiated startle paradigm.

Clonidine (10-40 microgram/kg) produced a dose-dependent reduction of fear as measured by the potentiated startle effect (increased acoustic startle in the presence of a cue which had been previously paired with shock). The reduction of potential startle could not be accounted for entirely by a general depressant effect of clonidine on startle nor by an acceleration of extinction. Piperoxane and yohimbine, which are associated with anxiety in humans, increased potentiated startle, whereas propranolol and WB-4101 did not. These results provide further evidence that the potentiated startle paradigm in the rat is sensitive to drug that alter anxiety in humans. Moreover, they support the hypothesis that norepinephrine transmission is important for the expression of fear or anxiety.

Animals↗
PubMed1975

Purification and properties of the light-activated cyclic nucleotide phosphodiesterase of rod outer segments.

Frog (Rana catesbiana) rod outer segment disc membranes contain a cyclic nucleotide phosphodiesterase (EC 3.1.4.17) which is activated by light in the presence of ATP. This enzyme is firmly bound to the disc membrane, but can be eluted from the membrane with 10 mM Tris-HCl buffer, pH 7.4 and 2 mM EDTA. The eluted phosphodiesterase has reduced activity, but can be activated approximately 10-fold by polycations such as protamine and polylysine. The eluted phosphodiesterase can no longer be activated by light in the presence of ATP, that is, activation by light apparently depends on the native orientation of phosphodiesterase in relationship to other disc membrane components. The eluted phosphodiesterase was purified to homogeneity as judged by analytical polyacrylamide gel electrophoresis and polyacrylamide gel isoelectric focusing. The over-all purification from intact retina was approximately 925-fold. The purification of phosphodiesterase from the isolated rod outer segment preparation was about 185-fold with a 28% yield. Phosphodiesterase accounts for approximately 0.5% of the disc membrane protein. The eluted phosphodiesterase (inactive form) has a sedimentation coefficient of 12.4 S corresponding to an approximate molecular weight of 240,000. Sodium dodecyl sulfate polyacrylamide gel electrophoresis separates the purified phosphodiesterase into two subunits of 120,000 and 110,000 daltons. With cyclic 3':5'-GMP (cGMP) as substrate the Km for the purified phosphodiesterase is 70 muM. Protamine increases the Vmax without changing the Km for cGMP. The isoelectric point (pI) of the native dimer is 5.7. Limited exposure of the eluted phosphodiesterase (inactive form) to trypsin produces a somewhat greater activation than is obtained with 0.5 mg/ml of protamine. The trypsin-activated phosphodiesterase has a sedimentation coefficient of 7.8 S corresponding to an approximate molecular weight of 170,000. The 110,000-dalton subunit is much less sensitive to trypsin hydrolysis and the 120,000-dalton subunit is rapidly replaced by smaller fragments. On the basis of the molecular weight of the purified phosphodiesterase (240,000) and the concentrations of phosphodiesterase and rhodopsin in the rod outer segment, it is estimated that the molar ratio ophosphodiesterase to rhodopsin in the rod outer segment is approximately 1:900. Since all of the disc phosphodiesterase molecules are activated when 0.1% of the rhodopsins are bleached, we conclude that in the presence of ATP 1 molecule of bleached rhodopsin can activate 1 molecule of phosphodiesterase.

3',5'-Cyclic-AMP Phosphodiesterases↗