NAC1, A POZ/BTB protein interacts with Parkin and may contribute to Parkinson's disease

Loss-of-function in the Parkin protein is thought to play a part in causing neuronal cell death in patients with Parkinson's disease. This study explores the effect of Parkin degradation, via the overexpression of nucleus accumbens 1 (NAC1), on cell viability. It was found that NAC1 and Parkin are co-localized within the cell and interact with one another, leading to a decrease in Parkin levels. Moreover, NAC1 down-regulates Parkin by presenting it for ubiquitin-dependent proteasome degradation, which causes a decrease in proteasomal activity in neuronal cells. Consequently, this decrease in proteasomal activity leads to an increase in the cells' susceptibility to proteasome inhibition-induced toxicity. It was also found that Parkin and NAC1 are key proteins found to be present mainly in the cytoplasm and are co-localized in neurons of Parkinson's disease patients. Interestingly, mutation in the POZ/BTB domain (Q23L) of NAC1 disrupts the co-localization and interaction of NAC1 with Parkin and it further abrogates the proteasome inhibition-induced toxicity. We further observed that co-transfection of the mutant form of NAC1 with Parkin reversed the proteasome activity and 20S proteasome protein levels. These results indicate a novel interaction between NAC1 and Parkin that leads to neuronal cell death, a main characteristic in Parkinson's disease.

Nucleus Accumbens 1, a Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad protein binds to TAR DNA-binding protein 43 and has a potential role in Amyotrophic Lateral Sclerosis

Protein degradation is a critical component of cellular maintenance. The intracellular translocation and targeting of the Ubiquitin Proteasome System (UPS) differentially coordinates a protein's half-life and thereby its function. Nucleus Accumbens 1 (NAC1), a member of the Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad complex (POZ/BTB) family of proteins, participates in the coordinated proteolysis of synaptic proteins by mediating recruitment of the UPS to dendritic spines. Here we report a novel interaction between NAC1 and TAR DNA-binding protein 43 (TDP-43), a protein identified as the primary component of ubiquitinated protein aggregates found in patients with Amyotrophic Lateral Sclerosis (ALS). In vitro translated full-length TDP-43 associated with both the POZ/BTB domain and the non-POZ/BTB domain of NAC1 in GST pulldown assays. Other POZ/BTB proteins (including zinc finger POZ/BTB proteins and atypical POZ/BTB proteins) showed weak interactions with TDP-43. In addition, NAC1 and TDP-43 were present in the same immunocomplexes in different regions of mouse brain and spinal cord. In primary spinal cord cultures, TDP-43 expression was mainly nuclear, whereas NAC1 was both nuclear and cytoplasmic. In order to mimic ALS-like toxicity in the spinal cord culture system, we elevated extracellular glutamate levels resulting in the selective loss of motor neurons. Using this model, it was found that glutamate toxicity elicited a dose-dependent translocation of TDP-43 out of the nucleus of cholinergic neurons and increased the co-localization of NAC1 and TDP-43. These findings suggest that NAC1 may function to link TDP-43 to the proteasome; thereby, facilitating the post-translational modifications of TDP-43 that lead to the development of ALS.

The POZ/BTB protein NAC1 interacts with two different histone deacetylases in neuronal-like cultures

NAC1 is a cocaine-regulated POZ/BTB (Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad complex) protein. NAC1 is increased by cocaine selectively in the nucleus accumbens, a CNS region important for drug addiction. NAC1's role in the cell, however, is not known. Each of the two NAC1 isoforms, sNAC1 (short NAC1) and lNAC1 (long NAC1), may serve as corepressors for other POZ/BTB proteins. This study investigated whether sNAC1 and lNAC1 demonstrated protein-protein interactions with other corepressors. Histone deacetylase (HDAC) inhibition reversed sNAC1 and lNAC1 repression of Gal4 luciferase, but only in neuronal-like cultures. Because these inhibitors do not distinguish among histone deacetylases, two histone deacetylases were selected for further study. HDAC 3 and 4 both demonstrated protein-protein interactions with sNAC1 and lNAC1. This was shown using coimmunoprecipitations, glutathione-S-transferase (GST) pulldowns and mammalian two-hybrids. Importantly, either the POZ domain or NAC1 without the POZ domain can bind these two HDACs. Other corepressors, specifically NCoR (nuclear receptor corepressor), SMRT (silencing mediator for retinoid and thyroid hormone receptor) and mSin3a, do not exhibit protein-protein interactions with sNAC1 and lNAC1. None showed protein-protein interactions in GST pulldowns or mammalian two-hybrids. Taken together, the results of these experiments indicate sNAC1 and lNAC1 recruit histone deacetylases for transcriptional repression, further enhancing POZ/BTB protein mediated repression.

The mouse nac1 gene, encoding a cocaine-regulated bric-a-brac tramtrac broad complex/pox virus and zinc finger protein, is regulated by ap1

NAC1 cDNA was identified as a novel transcript induced in the nucleus accumbens from rats chronically treated with cocaine. NAC1 is a member of the Bric-a-brac Tramtrac Broad complex/Pox virus and Zinc finger family of transcription factors and has been shown by overexpression studies to prevent the development of behavioral sensitization resulting from repeated cocaine treatment. This paper reports the cloning and characterization of the corresponding gene. The mouse Nac1 gene consist of six exons, with exon 2 containing an alternative splice donor, providing a molecular explanation of the splice variants observed in mouse and rat. Transcripts of Nac1 were ubiquitously detected in different mouse tissues with prominent expression in the brain. The mouse Nac1 gene was localized to chromosome 8, suggesting a highly plausible candidate gene to explain differences in cocaine-induced behaviors between C57BL6/J and DBA/2J mice that had previously been mapped to the area. In addition, a functional AP1 binding site has been identified in an intron 1 enhancer of the Nac1 gene that plays an essential role in the activation of the gene in differentiation of neuroblastoma cells. Co-transfection with c-jun and c-fos expression plasmids, which encode the two subunits of AP1, activated the wild type Nac1 intron 1 enhancer two-fold over basal, nearly at the level of NAC1 enhancer activity seen in differentiated N2A cells. Mutation of the AP1 site completely abrogated all activation of the NAC1 enhancer in differentiated N2A cells. Activation of immediate early genes such as c-fos and c-jun following chronic drug treatments has been well characterized. The present data describe one potential regulatory cascade involving these transcription factors and activation of NAC1. Identification of drug induced alterations in gene expression is key to understanding the types of molecular adaptations underlying addiction.

Differences in expression, actions and cocaine regulation of two isoforms for the brain transcriptional regulator NAC1

BTB/POZ proteins can influence the cell cycle and contribute to oncogenesis. Many family members are present in the mammalian CNS. Previous work demonstrated elevated NAC1 mRNA levels in the rat nucleus accumbens in response to cocaine. NAC1 acts like other BTB/POZ proteins that regulate transcription but is unusual because of the absence of identifiable DNA binding domains. cDNAs were isolated encoding two NAC1 isoforms differing by only 27 amino acids (the longer isoform contains 514 amino acids). The mRNAs for both isoforms were simultaneously expressed throughout the rat brain and peripheral tissues. Semi-quantitative reverse transcription-polymerase chain reaction analysis revealed that the mRNA of the longer isoform was more abundant than the mRNA of the shorter isoform. Western blot analysis demonstrated a similar unequal distribution between the isoforms in the CNS. The longer isoform was the more abundant of the two NAC1 proteins and the ratio between them differed throughout the rat brain. The shorter isoform was not detected in most of the examined peripheral tissues, suggesting differences from the CNS in post-transcriptional processing. Both isoforms repressed transcription in H293T cells using a Gal4-luciferase reporter system. However, the shorter isoform did not repress transcription as effectively as the longer isoform. Transfection of different ratios for both isoforms, in order to replicate the relative amounts observed throughout the CNS, supported an interaction between the isoforms. The net effect on transcriptional repression was determined by the ratio of the two NAC1 isoforms. Each isoform exhibited the subnuclear localization that is characteristic of many BTB/POZ proteins. A rapid and transient increase in the level of the shorter isoform occurred in the nucleus accumbens 2 h following a single i.p. cocaine injection. We conclude that the two isoforms of NAC1 may differentially affect neuronal functions, including the regulation of cocaine-induced locomotion.

The effect of gamma-vinyl-GABA on the consumption of concurrently available oral cocaine and ethanol in the rat

It has frequently been reported that a high percentage of individuals, identified as either alcohol- or cocaine-dependent, concurrently abuse both drugs. The experiments reported here represent a continuing effort to develop an animal model to predict the effects of a potential pharmacotherapeutic agent on concurrently available oral ethanol and cocaine. These experiments utilized drinkometer circuitry to assess the effects of gamma-vinyl-GABA (GVG), a gamma-aminobutyric acid (GABA) transaminase inhibitor, on the consumption and temporal pattern of responses for orally self-administered ethanol and cocaine. The results of these experiments showed that GVG, at doses of 100, 200 and 300 mg/kg, reduced both ethanol and cocaine consumption in a dose-related manner. When compared to vehicle, GVG at all doses significantly reduced ethanol consumption while consumption of cocaine was significantly reduced only at 300 mg/kg. This is consistent with data showing that GVG reduces consumption of these drugs when administered alone and data showing that GVG is more potent in reducing ethanol-induced compared to cocaine-induced extracellular dopamine in the nucleus accumbens. Analysis of the temporal pattern of drinking across the session suggests that GVG's effects are due to a disruption of the reinforcing properties of ethanol and cocaine rather than a more general reduction in motor behavior. These data suggest that GVG has potential for clinical use in populations that abuse either alcohol or cocaine alone or in combination.

Effect of acamprosate and naltrexone, alone or in combination, on ethanol consumption

Both acamprosate and naltrexone have demonstrated clinical utility in reducing relapse to alcohol use in recovering alcoholics. The present experiments examined the effects of acamprosate and naltrexone, either alone or in combination, on basal ethanol consumption in a limited-access model with the use of outbred Wistar rats. Naltrexone, 0.1 mg/kg, significantly reduced ethanol consumption as previously reported. Acamprosate, 50 mg/kg, did not significantly reduce ethanol consumption when administered alone and provided no evidence of additive or synergistic effects when combined with naltrexone. Acamprosate, 200 mg/kg, produced a modest reduction in ethanol consumption when administered alone but no evidence of additive or synergistic effects when combined with naltrexone. From these findings, it is suggested that a combination approach of these drugs may not be any more effective than monotherapy.

Depression of retinal glutamate transporter function leads to elevated intravitreal glutamate levels and ganglion cell death

PURPOSE

Elevated levels of extracellular glutamate have been implicated in the pathophysiology of neuronal loss in both central nervous system and ophthalmic disorders, including glaucoma. This increase in glutamate may result from a failure of glutamate transporters (molecules that ordinarily regulate extracellular glutamate; E:xcitatory A:mino A:cid T:ransporter; EAAT). Elevated glutamate levels can also lead to alterations in glutamate receptor expression. It was hypothesized that selective blockade of glutamate transporters would be toxic to retinal ganglion cells.

METHODS

Glutamate transporters were blocked either pharmacologically or with subtype-specific antisense oligonucleotides against EAAT1. Glutamate levels, transporter levels and ganglion cell survival were assayed.

RESULTS

Pharmacological inhibition of glutamate transporters with either an EAAT2 specific inhibitor or a nonspecific inhibitor of all the subtypes of transporters was toxic to ganglion cells. Treatment with oligonucleotides against the glutamate transporter EAAT1 decreased the levels of expression of the transporter, increased vitreal glutamate, and was toxic to ganglion cells.

CONCLUSIONS

These results demonstrate that normal function of EAAT1 and EAAT2 is necessary for retinal ganglion cell survival and plays an important role in retinal excitotoxicity. Manipulation of retinal glutamate transporter expression may become a useful tool in understanding retinal neuronal loss.

NAC-1 is a brain POZ/BTB protein that can prevent cocaine-induced sensitization in the rat

Levels of the mRNA NAC-1 are increased in the rat forebrain weeks after cocaine exposure. This long-term neuroadaptation occurs during the expression of behavioral sensitization, a model of psychostimulant-induced paranoia. NAC-1, the protein encoded by this cocaine-regulated mRNA, contains a Pox virus and zinc finger/bric-a-brac tramtrack broad complex (POZ/BTB) motif, which mediates interactions among several transcriptional regulators. The present studies demonstrate that NAC-1 acts as a transcription factor. NAC-1 was localized to the nucleus of neurons in the brain. Transfection of NAC-1 in cell culture repressed transcription of a reporter gene. NAC-1 was also able to affect the actions of other POZ/BTB proteins in mammalian two-hybrid studies; these interactions required the presence of the POZ/BTB domain. However, NAC-1 appears to be a unique POZ/BTB transcriptional regulator because it does not contain any zinc finger regions found in these other DNA-binding proteins. Adenoviral-mediated overexpression of NAC-1 protein in the rat nucleus accumbens prevented the development but not the expression of behavioral sensitization produced by repeated administration of cocaine. Thus, NAC-1 may modify the long-term behaviors of psychostimulant abuse by regulating gene transcription in the mammalian brain.

Identification of a growth arrest specific (gas 5) gene by differential display as a candidate gene for determining susceptibility to hyperthermia-induced exencephaly in mice

Neural tube defects (NTDs) are among the most common congenital malformations, affecting approximately 1 per 1,000 liveborn infants in the United States [Nakano, 1973; Richards et al., 1972]. Maternal exposure to hyperthermia, either through recreational sources or due to an infectious agent, is thought to account for approximately 10% of observed NTD cases. The specific genes conferring susceptibility or resistance to hyperthermia-induced NTDs have not been identified. This study used differential display-polymerase chain reaction (DD-PCR) to characterize alterations in gene expression in the anterior embryonic neural tube of two highly inbred murine strains (SWV/Fnn, LM/Bc/Fnn) known to differ in their genetically determined susceptibility to heat-induced NTDs. Herein, we report the neural tube-specific differential expression of the growth arrest specific (gas 5) gene in the highly susceptible SWV/Fnn strain during neural tube closure (NTC). Although the expression of gas 5 did not appear to be altered by the teratogenic heat treatment, its spatial and strain-specific pattern of expression makes it an excellent candidate gene responsible for the observed genetic differences in NTD susceptibility between these two inbred murine strains.

Ribonucleotide reductase subunit R1: a gene conferring sensitivity to valproic acid-induced neural tube defects in mice

Neural tube defects (NTDs), although prevalent and easily diagnosed, are etiologically heterogeneous, rendering mechanistic interpretation problematic. To date, there is evidence that mammalian neural tube closure (NTC) initiates and fuses intermittently at four discrete locations. Disruption of this process at any of these four sites may lead to a region-specific NTDs, possibly arising through closure site-specific genetic mechanisms. Although recent efforts have focused on elucidating the genetic components of NTDs, a void persists regarding gene identification in closure site-specific neural tissue. To this end, experiments were conducted to identify neural tube closure site-specific genes that might confer regional sensitivity to teratogen-induced NTDs. Using an inbred mouse strain (SWV/Fnn) with a high susceptibility to VPA- induced NTDs that specifically targets and disrupts NTC between the prosencephalon and mesencephalon region (future fore/midbrain; neural tube closure site II), we identified a VPA-sensitive closure site II-specific clone. Sequencing of this clone from an SWV neural tube cDNA library confirmed that it encodes the r1 subunit of the cell cycle enzyme ribonucleotide reductase (RNR). The abundance of rnr-r1 mRNA was significantly increased in response to VPA drug treatment. This upregulated expression was accompanied by a significant decrease in cellular proliferation in the closure site II neural tube region of the embryos, as determined by ELISA cellular proliferation assays performed on BrdU-pulsed neuroepithelial cells in vivo. We hypothesize that rnr-r1 plays a critical role in the development of VPA-induced exencephaly.

The NMDA receptor partial agonist, 1-aminocyclopropanecarboxylic acid (ACPC), reduces ethanol consumption in the rat

The present studies assessed the effects of both systemic and intraaccumbens injections of 1-aminocyclopropanecarboxylic acid (ACPC), and NMDA partial agonist, on ethanol consumption in a limited access procedure in Wistar rats. Systemically administered ACPC reduced ethanol consumption in a dose-dependent manner, while a single dose of ACPC administered bilaterally into the nucleus accumbens also reversibly reduced ethanol consumption. Indirect measures of general appetitive behavior showed no effect of ACPC on weight or water intake, which suggests that this effect of ACPC may be specific to ethanol. These data are compatible with the role of NMDA receptors in modulating ethanol consumption and provide the first data showing that ACPC can reduce ethanol consumption. ACPC has neuroprotective effects and does not show the psychotomimetic effects observed with NMDA receptor agents. Thus, ACPC may be helpful in future clinical studies designed to reduce alcohol use.

Interrupted expression of NAC-1 augments the behavioral responses to cocaine

NAC-1 is an mRNA that is increased selectively in the nucleus accumbens after acute and repeated cocaine administration. Antisense or control oligonucleotides were microinjected into the nucleus accumbens of rats to define the role of NAC-1 in the behavioral responses to acute systemic cocaine. Antisense oligonucleotides decreased NAC-1 mRNA levels by 26% and markedly enhanced the motor stimulant response to an acute cocaine injection compared to sense oligonucleotide microinjections. The augmentation in cocaine motor behavior produced by NAC-1 antisense pretreatment in the nucleus accumbens was not associated with increased dopamine release as estimated by microdialysis. In contrast, the behavioral response to dopamine microinjection into the nucleus accumbens was increased after antisense oligonucleotide treatment, while the motor response to mu-opioid receptor stimulation was unaltered. These data suggest that the induction of NAC-1 by cocaine may be a compensatory mechanism that minimizes the behavioral impact of cocaine administration by regulating postsynaptic dopamine transmission within the nucleus accumbens.

Cloning and functional expression of the mouse epithelial sodium channel

The epithelial sodium channel (ENaC) plays a major role in the transepithelial reabsorption of sodium in the renal cortical collecting duct, distal colon, and lung. ENaCs are formed by three structurally related subunits, termed alpha-, beta-, and gammaENaC. We previously isolated and sequenced cDNAs encoding a portion of mouse alpha-, beta-, and gammaENaC (alpha-, beta-, and gammamENaC). These cDNAs were used to screen an oligo-dT-primed mouse kidney cDNA library. Full-length betamENaC and partial-length alpha- and gammamENaC clones were isolated. Full-length alpha- and gammamENaC cDNAs were subsequently obtained by 5'-rapid amplification of cDNA ends (5'-RACE) PCR. Injection of mouse alpha-, beta-, and gammaENaC cRNAs into Xenopus oocytes led to expression of amiloride-sensitive (K(i) = 103 nM), Na(+)-selective currents with a single-channel conductance of 4.7 pS. Northern blots revealed that alpha-, beta-, and gammamENaC were expressed in lung and kidney. Interestingly, alphamENaC was detected in liver, although transcript sizes of 9.8 kb and 3.1 kb differed in size from the 3.2-kb message observed in other tissues. A partial cDNA clone was isolated from mouse liver by 5'-RACE PCR. Its sequence was found to be nearly identical to alphamENaC. To begin to identify regions within alphamENaC that might be important in assembly of the native heteroligomeric channel, a series of functional experiments were performed using a construct of alphamENaC encoding the predicted cytoplasmic NH(2) terminus. Coinjection of wild-type alpha-, beta-, and gammamENaC with the intracellular NH(2) terminus of alphamENaC abolished amiloride-sensitive currents in Xenopus oocytes, suggesting that the NH(2) terminus of alphamENaC is involved in subunit assembly, and when present in a 10-fold excess, plays a dominant negative role in functional ENaC expression.

Effects of prenatal cocaine exposure on embryonic expression of sonic hedgehog

Cocaine use by pregnant women may adversely affect development and behavior in the exposed infants. Sonic hedgehog (shh) is a secreted protein that induces development of many structures in the embryo, including dopaminergic cells in the ventral midbrain, the limb buds, and eyes. Because prenatal cocaine exposure has been shown to adversely affect the morphogenesis of these and other systems, the present study was undertaken to test the hypothesis that maternal cocaine treatment would alter shh mRNA expression. Cocaine HCl (60 mg/kg i.p.) was administered to pregnant mice on gestational days 6-8, the time that immediately precedes the appearance of shh. Control dams received i.p. saline. Embryos from gestational days 9-11 were examined by in situ hybridization. The temporal and spatial patterns of shh expression were indistinguishable between embryos from cocaine- and saline-treated dams. Examination of forebrain, midbrain, and midbody spinal cord coronal sections failed to reveal any differences in the dorsoventral and mediolateral localization of shh. The distribution of mRNA for patched (ptc), the membrane receptor for shh, was also indistinguishable between both groups. Chick embryos were next used to examine the direct application of cocaine into the developing brain. Shh distribution was similarly unaffected in these chick embryos. These data show that maternal cocaine treatment during early neural tube development does not significantly alter the expression patterns of shh or ptc mRNA. Thus, congenital defects and behavioral abnormalities associated with maternal cocaine use do not appear to result from altered expression of the shh-ptc pathway.

Regulation of the Na+/K(+)-ATPase pump in vitro after long-term exposure to cocaine: role of serotonin

Long-term exposure to cocaine can cause persistent behavioral changes and alterations in neuronal function. One cocaine-regulated mRNA in the rat brain is the beta-1 subunit of the Na+/K(+)-ATPase pump. We examined both Na+/K(+)-ATPase function and expression after cocaine treatment of pheochromocytoma cells. One-hour exposure to cocaine did not alter Na+/K(+)-ATPase activity, as measured by the ouabain-sensitive component of rubidium uptake. Four days of cocaine resulted in an approximately 30% decrease in Na+/K(+)-ATPase activity. Western blot analyses demonstrated an approximately 25% decrease in levels of the beta-1 isoform, without changes in pump total alpha subunit levels. Treatment with dopamine type 1 or type 2 receptor agonists for the same period did not affect Na+/K(+)-ATPase activity. The serotonin-selective reuptake inhibitor paroxetine caused an approximately 45% decrease in rubidium uptake after 4 days, whereas pump function was not altered after treatment with either the dopamine-selective reuptake blocker nomifensine or the norepinephrine-selective reuptake blocker desipramine. Chronic treatment with both cocaine and LY 278,584, a serotonin type 3 receptor antagonist, did not replicate the cocaine-associated decrease in pump function. Long-term cocaine exposure regulates expression and function of the Na+/K(+)-ATPase pump in neuronal-like cells; this regulation is mediated in part via the serotonin type 3 receptor. Similar Na+/K(+)-ATPase pump regulation in vivo may selectively alter neuronal function in the mammalian brain.

Expression and localization of epithelial sodium channel in mammalian urinary bladder

The mammalian urinary bladder exhibits transepithelial Na+ absorption that contributes to Na+ gradients established by the kidney. Electrophysiological studies have demonstrated that electrogenic Na+ absorption across the urinary bladder is mediated in part by amiloride-sensitive Na+ channels situated within the apical membrane of the bladder epithelium. We have used a combination of in situ hybridization, Northern blot analysis, and immunocytochemistry to examine whether the recently cloned epithelial Na+ channel (ENaC) is expressed in the rat urinary bladder. In situ hybridization and Northern blot analyses indicate that alpha-, beta-, and gamma-rat ENaC (rENaC) are expressed in rat urinary bladder epithelial cells. Quantitation of the levels of alpha-, beta-, and gamma-rENaC mRNA expression in rat urinary bladder, relative to beta-actin mRNA expression, indicates that, although comparable levels of alpha- and beta-rENaC subunits are expressed in the urinary bladder of rats maintained on standard chow, the level of gamma-rENaC mRNA expression is 5- to 10-fold lower than alpha- or beta-rENaC mRNA. Immunocytochemistry, using an antibody directed against alpha-rENaC, revealed that ENaCs are predominantly localized to the luminal membrane of the bladder epithelium. Together, these data demonstrate that ENaC is expressed in the mammalian urinary bladder and suggest that amiloride-sensitive Na+ transport across the apical membrane of the mammalian urinary bladder epithelium is mediated primarily by ENaC.

NAC-1, a rat brain mRNA, is increased in the nucleus accumbens three weeks after chronic cocaine self-administration

Chronic cocaine use leads to biochemical and behavioral changes that can persist for weeks to months after drug administration is discontinued. Alterations in gene expression in the mammalian CNS may contribute to these long-term neural consequences of cocaine abuse. A combined in situ transcription-PCR amplification strategy was used to isolate a novel mRNA, NAC-1, from the nucleus accumbens of rats 3 weeks after discontinuing 3 weeks of intravenous cocaine self-administration. In rats that self-administered cocaine, levels of NAC-1 were increased approximately 50% in the nucleus accumbens but not in the dorsal striatum or hippocampus, when compared with levels from yoked-saline controls. In situ hybridization analysis demonstrated increased numbers of NAC-1-expressing cells in the nucleus accumbens of rats who had self-administered cocaine. NAC-1 mRNA exists as one form, approximately 4400 nucleotides (nt) in size, and also is present at much lower amounts in non-neural tissues. A full-length cDNA clone was isolated from a whole brain library. The predicted polypeptide sequence contains a POZ domain in the first 120 amino acids; the same POZ domain sequence mediates protein-protein interactions among some transcriptional regulators. NAC-1 mRNA levels were also increased in the nucleus accumbens 1 week after 6 d of noncontingent cocaine treatments. Regulation of NAC-1 mRNA in the nucleus accumbens demonstrates a long-term effect of cocaine use on cellular function that may be relevant in behavioral sensitization or cocaine self-administration.

Cocaine selectively alters neurotransmitter receptor mRNAs in mouse embryos

Alterations in gene expression due to in utero cocaine exposure may adversely affect nervous system development. The present study examined whether or not cocaine administration to pregnant mice alters embryonic mRNA levels for several developmentally-regulated genes. Antisense RNA amplification was performed using RNA from LM/Bc embryos at gestational days 9.5 and 10.5 after three days of cocaine treatment. This technique highlights simultaneous changes that occur in the expression of many genes after a teratogenic insult. Significant changes occurred in the expression pattern on only four genes from a total of 42 candidate cDNAs. These included increases in the relative levels of the alpha and beta 1 subunits of the GABAA receptor without concurrent changes in the non-NMDA glutamate receptor subunits. The results support the hypothesis that in utero cocaine exposure leads to specific changes in gene expression that may ultimately contribute to developmental abnormalities.

Cellular adaptation to opiates alters ion-channel mRNA levels

The chronic use of several drugs, including opiates, results in the stereotypical behaviors characteristic of addiction. Alterations in gene expression have been associated with the use of these addictive drugs. Previous studies, however, have been limited to describing changes in amounts of individual mRNAs from single tissue samples. Cellular adaptation to opiates, reflected in the regulation of the expression of many different mRNAs, seems likely to contribute to the complicated behaviors of addiction. The present studies examined coordinate alterations in the amounts of multiple mRNAs in the rat striatum and in NG108-15 cells after opioid stimulation or the precipitated withdrawal of opioid use. The experimental approach combined amplification of the poly(A)+ RNA population with reverse Northern blot analysis to simultaneously characterize the relative changes in several mRNAs. Morphine treatment of rats for 5 days was associated with a reduction in the amount of striatal RNA for the voltage-sensitive K+ channel without significant changes in other ion channels. In NG108-15 cells stimulation with the delta-opiate receptor agonist [D-Ala2,D-Leu5]enkephalin (DADLE) alone and followed by naloxone (precipitated withdrawal) caused relative changes in the abundances of several mRNAs. The composite effects of alterations in the abundance of multiple mRNAs (and the proteins they encode) in response to opioid use likely contribute to the development and maintenance of opiate-mediated behaviors.

Diversity of glutamate receptor subunit mRNA expression within live hippocampal CA1 neurons

Glutamate-mediated neurotransmission occurs through the activation of multimeric postsynaptic receptors. One mechanism by which functional diversity of glutamate responsiveness may occur is by a single cell expressing multiple receptors containing different subunits. In a direct test of this hypothesis, we examined the glutamate receptor subunit mRNA composition of several individual CA1 neurons in hippocampal slices. Experiments used amplified antisense RNA coupled with expression profiling and polymerase chain reaction amplification to identify and determine the relative amounts of subunit mRNAs co-localized in single cells. The results demonstrate that each CA1 neuron contains varying amounts of most glutamate receptor mRNAs. In addition to relative mRNA levels, the single-cell approach also highlighted other possible sources of receptor diversity. This included the existence of novel, alternatively spliced forms of the N-methyl-D-aspartate receptor type 1 and glutamate-kainate receptor type 2 subunits. Surprisingly, levels of N-methyl-D-aspartate receptor type 1 mRNA were relatively low, compared with those of other glutamate receptor mRNAs. One postulated source of potential heterogeneity, RNA editing, was not a general cellular mechanism. There was no evidence that glutamate receptor type 5 mRNA was edited in any of the cells that were examined. These data show that individual CA1 neurons, in the intact synaptic network of hippocampal slices, generate glutamate receptor mRNA diversity in several ways, which together contribute to the diversity of functional receptors observed electrophysiologically.

Stimulus-induced coordinate changes in mRNA abundance in single postsynaptic hippocampal CA1 neurons

The molecular effects of use-dependent changes in synaptic transmission were studied in individual CA1 pyramidal neurons from rat hippocampal slices. Potentiation of excitatory postsynaptic currents was associated with coordinate changes in the relative abundance of several mRNAs 30 min to 3 hr after stimulation. There was a 300% increase in calcium/calmodulin-dependent protein kinase II mRNA levels concordant with a 50% decrease in protein kinase C beta 1 isoform mRNA. A 2-fold increase in zif-268 mRNA was seen, while increases in c-fos and c-jun mRNA levels were inconsistent, gamma-Aminobutyric acid A receptor beta 1 subunit mRNA levels increased 3-fold. Potentiation-induced changes were prevented by N-methyl-D-aspartate receptor blockade. Changes in mRNA abundance in individual cells, with synaptic and glial interactions intact, combine to produce a molecular fingerprint of a potentiated CA1 neuron.

The molecular biology of addictive drugs

The additive drugs alcohol, morphine, cocaine, and amphetamine are each associated with the development of tolerance and physical dependence. Changes in gene expression occur in cell culture and in vivo with the administration of these centrally-acting drugs. This article reviews those experiments that have studied drug-induced alterations in gene transcription. Ethanol has diverse effects on the amounts of messenger RNA molecules within the central nervous system. Ion channels, neuropeptides, membrane receptors, and immediate early genes represent several regulated mRNAs. The effects are selective, however, as many other specific products are not altered. Evidence for a genetic predisposition to ethanol use reinforces the importance of the genotype. Opioids, cocaine, and amphetamine also affect gene transcription. Messenger RNAs studied have included many of those demonstrated to be altered by alcohol use. Interestingly, use of any of these drugs alters the expression of immediate early genes. These genes may represent an initial step in the pathway that leads to drug addiction. The composite of drug-induced changes in gene expression results in the cellular responses of tolerance and dependence. The characterization of these changes should provide a better understanding of the molecular mechanisms of drug addiction.

The axon reaction of lamprey spinal interneurons

Axotomy and partial denervation of giant interneurons (GIs) and lateral cells (LCs) were produced by complete spinal transection in the larval lamprey spinal cord. Both cell types demonstrated a reduction in cytoplasmic basophilia, increase in cell size, nuclear eccentricity, and formation of a chromophilic nuclear cap. This was quantified in the case of cell diameter. During the first 8 weeks of recovery, the GIs with the largest diameters were found progressively further from the scar and this peak change moved at approximately 0.5 mm/day. The increase in size of GIs remained up to 20 weeks post-transection, long after the time required for their axons to regenerate across the scar and form functioning synapses. GIs injected intracellularly with horseradish peroxidase (HRP) also showed this increase in diameter as well as a simplification of their dendritic trees. Intracellular recordings from GIs revealed changes in the frequency and amplitude of spontaneous synaptic input. In the first two weeks after transection, spontaneous excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) were less frequent than in control cells. After 6 weeks of recovery they became more frequent than in control cells. EPSPs predominated in axotomized GIs, while in control cells they constituted only 36% of the total of spontaneous potentials. A reversible increase in the amplitude of these EPSPs occurred at 3-4 weeks of recovery time. The resting membrane potential was significantly reduced by the 6th week after transection and returned to normal after the 22nd week.

Specificity of synaptic regeneration in the spinal cord of the larval sea lamprey

1. Pairs of central neurones in large larval sea lampreys were impaled with micro-electrodes and studied for synaptic connexions in both unoperated control animals and animals which had recovered from complete spinal transection. Two identified classes of neurones served as post-synaptic targets: giant interneurones (g.i.s) and lateral cells (l.c.s). Several identified neurone types were tested as potential sources of presynaptic input. 2. When synaptic potentials had short, fixed latencies they also persisted during activation of the presynaptic cell at 3.3-33.3 Hz and were not eliminated after addition of lamprey saline containing high (20 mM) Ca2+. These presumably represented monosynaptic connexions. Variable-latency responses were eliminated by faster rates of stimulation of the presynaptic cell and were mediated via polysynaptic pathways. 3. In control animals, g.i.s received monosynaptic input from more caudal g.i.s in fourteen of thirty-two tested cell pairs. These excitatory post-synaptic potentials (e.p.s.p.s) were composite electrochemical responses. The amplitudes of the earlier electrical component averaged 1.66 +/- 0.24 mV (mean +/- S.E. of mean) and the amplitude of the later chemical component averaged 0.79 +/- 0.05 mV. 4. In operated larvae, eight of forty-seven g.i.-g.i. pairs separated by the transection scar were connected by monosynaptic composite e.p.s.p.s. In these pairs the electrical component averaged 0.84 +/- 0.17 mV (P less than 0.05 vs. control) and the chemical component averaged 1.56 +/- 0.40 mV. The average conduction velocity between these cells was less than that in control g.i.-g.i. pairs (0.93 +/- 0.11 vs. 1.61 +/- 0.25 m/s; P less than 0.01). 5. The l.c.s showed monosynaptic e.p.s.p.s after activation of a subset of the bulbar Müller neurones (B2-4) in seven of twelve pairs. In behaviourally recovered larvae three of twenty-two similar pairs separated by the transection scar were also connected via monosynaptic e.p.s.p.s. The average conduction velocity between these experimental neurones was also less than that in control bulbar-l.c. pairs (1.03 +/- 0.03 vs. 1.58 +/- 0.09 m/s; P less than 0.001). 6. Several types of neurones were either infrequently linked or never connected to g.i.s or to l.c.s in control larvae. In animals which had recovered from a spinal transection, no synaptic connexions were found from such neurones on to g.i.s or l.c.s respectively, in 124 tested cell pairs. In addition, dorsal cells (intraspinal primary sensory neurones) received no synaptic input upon stimulation of the spinal cord before or after transection.(ABSTRACT TRUNCATED AT 400 WORDS)

Determinants of directional specificity in the regeneration of lamprey spinal axons

The projection patterns of regenerating spinal axons in the larval sea lamprey (Petromyzon marinus) were determined by intracellular injection of HRP. Four hundred and eighty-six of 562 stained axons and axon-like neurites (87%) arising from Muller and Mauthner axons, giant interneurons, and dorsal cells terminated in an orientation similar to that of their counterpart control cells. Therefore, lamprey spinal axons regenerate selectively along their normal projection paths. During the first 4 weeks of recovery, i.e., before any had regenerated beyond the transection site, 91 of 114 axons and long neurites (80%) projected in the proper direction. Thus, the correctness of the final projection patterns did not result from selective retraction of randomly directed long neurites. When the cords were doubly transected 1 cm apart, orientation of regenerating neurites remained normal both within the 1 cm island and in the adjacent spinal cord. This suggests that the directional specificity of axonal regeneration was determined neither by the location of the scar nor by the availability of channels formed by the degenerating fibers. Finally, removing 1 cm of spinal cord eliminated potential synaptic targets for regenerating axons on either side of the lesion, but did not affect the direction of axonal growth. These findings are consistent with the hypothesis that the regeneration of lamprey spinal axons is guided by local chemical cues that persist long after the pathways are formed early in development.

Functional regeneration following spinal transection demonstrated in the isolated spinal cord of the larval sea lamprey

Axons in the larval sea lamprey can regenerate across the site of a spinal cord transection and form functioning synapses with some of their normal target neurons. The animals recover normal-appearing locomotion, but whether the regenerating axons and their synaptic connections are capable of playing a functional role during this behavior is unknown. To test this, "fictive" swimming was induced in the isolated spinal cord by the addition of D-glutamate to the bathing solution. Ventral root discharges of segments above and below a healed transection showed a high degree of phase-locking. This strongly suggests that the behavioral recovery is mediated by regenerated functional synaptic connections subserving intersegmental coordination of the central pattern generator for locomotion.

Regeneration of functional synapses between individual recognizable neurons in the lamprey spinal cord

In 4- to 5-year-old sea lamprey larvae that had recovered from complete transection of the spinal cord, pairs of giant interneurons on opposite sides of the scar were impaled with microelectrodes. In 4 of 30 pairs, stimulation of the caudal cell elicited a monosynaptic electrochemical excitatory postsynaptic potential in the rostral cell. Fifty percent of such pairs were synaptically linked in control lampreys without transections. These results show regeneration of functional synaptic connections between individual neurons in a vertebrate central nervous system.

Directional specificity in the regeneration of lamprey spinal axons

After spinal transection in ammocoetes (lamprey larvae) 4 to 5 years old, functional recovery is accompanied by a limited regeneration in which axons grow as far as 5 millimeters beyond the scar. In axotomized giant interneurons labeled intracellularly with horseradish peroxidase 16 to 120 days after transection, 74 percent of regenerating neurites grew in their normal projection pattern, rostal and contralateral to the cell body. One third of the neurites originated anomalously from posterior dendrites. Despite their initial abnormal orientation, 80 percent of these neurites looped contralaterally and rostrally to assume the normal projection path. The directional specificity persisted when giant interneurons were located in islands formed by double simultaneous cord transection. This limited regeneration seems to be characterized by directional selectivity that cannot be attributed to nonspecific influences, such as a tendency of neurites to grow in an already established direction or a trophic effect of the zone of injury.