Time course of enkephalin mRNA and peptides in cultured rat adrenal medulla

Regulation of prostate 5alpha-reductase-2 gene expression and prostate weight by dietary fat and caloric intake in the rat

BACKGROUND

High-fat diet is a major risk factor for prostate cancer. 5alpha-reductases are potential targets of dietary fat.

METHODS

Male ACI/Seg rats given either a low-fat or a high-fat diet at weaning or adulthood were sacrificed at 2, 4, and 10 weeks after dietary treatment. Prostate 5alpha-reductase mRNAs, plasma androgens, food consumption, prostate, and body weight were determined.

RESULTS

Prostate 5alpha-reductase-2 mRNA and plasma dihydrotestosterone levels were elevated at 2 weeks, and prostate weight was increased at 10 weeks in neonatal rats fed the high-fat diet. Animals fed the high-fat diet consumed more calories in the first 4 weeks. 5alpha-reductase-1 mRNA, plasma testosterone, and body weight were not different between the two dietary groups. These dietary effects were not observed in adult rats fed the same diets.

CONCLUSION

A high-dietary fat and caloric intake upregulates prostate 5alpha-reductase-2 gene expression, and stimulates prostate growth in neonatal, but not adult rats.

Increases in preproenkephalin mRNA levels in the Syrian hamster: The influence of glucocorticoids is dependent on age and tissue

In adult hamsters, basal proenkephalin (Penk) gene expression in adrenals is independent of glucocorticoids and glucocorticoid receptor blockade, by RU 486, increases striatal preproenkephalin (PPenk) mRNA levels. However, glucocorticoids maintain both basal and induced Penk gene expression in rat adrenal (medulla) and striatum. This suggests species and tissue-specific differences in Penk gene regulation. Since studies show temporal coordination in Penk gene expression in developing hamster adrenal and striatum, we tested the hypothesis that increasing PPenk mRNA levels are dependent, while basal levels are independent of glucocorticoids in developing hamsters. To facilitate this study, we examined the influence of glucocorticoids on the temporal increases in developing hamster PPenk mRNA observed in adrenals between postnatal days 0 and 4 and in striatum between postnatal days 12 and 48. PPenk mRNA levels were determined in hamster pups after treatment with increasing doses of metyrapone (an 11beta hydroxylase inhibitor) or with the glucocorticoid receptor antagonist RU 486 +/- metyrapone between postnatal days 2 and 4. Levels were also determined 36 days after hypophysectomy at age 16-17 days. Although plasma glucocorticoid levels and/or the influence from glucocorticoids were reduced, only developmental increases in PPenk mRNA are influenced by glucocorticoids in hamster adrenals, while basal adrenal mRNA levels are unchanged. However, pituitary influence on striatal PPenk mRNA levels appears complex and may involve steroid and/or non-steroid factors. These results suggest that glucocorticoids regulate hamster Penk gene expression via a mechanism that varies with age and tissue and functions during the induction of the Penk gene and not to maintain basal gene expression. Possible mechanisms and species variation are discussed.

Evolving perspectives on neurobiological research on the addictions: celebration of the 30th anniversary of NIDA

The roots of the Laboratory of the Biology of the Addictive Diseases are in the development of methadone maintenance for the treatment of opiate addiction. Methadone maintenance therapy continues to be one of the major effective forms of addiction pharmacotherapy and underscores the importance of biological factors in the physiology and treatment of the addictive diseases. Recent work in the Laboratory has focused on the neurobiological, neurochemical, neuroendocrine and behavioral aspects of addictive diseases (principally cocaine and the opiate addictions), using an interdisciplinary approach. The models we have focused on range from in vitro molecular biology and neuroscience, to in vivo animal models, to experiments in normal human populations and patients with specific addictive diseases, and most recently to the human molecular genetics of different addictive diseases. Two long-term corollary hypotheses have guided the Laboratory's work: (1) That the endogenous opioid peptide/receptor systems play a central role in the addictive states and therefore in their treatment. (2) That atypical responsivity to stressors (e.g., in the hypothalamic-pituitary-adrenal axis) plays a role in vulnerability and relapse to specific addictive diseases. This atypical responsivity may be drug-induced, environmentally acquired, and/or due to genetic variation.

The clinically available NMDA receptor antagonist dextromethorphan attenuates acute morphine withdrawal in the neonatal rat

We investigated the ability of dextromethorphan, a clinically available NMDA receptor antagonist, to attenuate the behaviors and the expression of c-fos mRNA associated with acute morphine withdrawal in the 7-day-old rat. The intensity of the acute morphine withdrawal behaviors and the elevation in c-fos mRNA expression in the brain induced by acute morphine withdrawal were reduced by dextromethorphan. Thus, dextromethorphan can attenuate acute morphine withdrawal in the developing organism.

Differential regulation of p75 and trkB mRNA expression after depolarizing stimuli or BDNF treatment in basal forebrain neuron cultures

Extensive evidence suggests that BDNF regulates neural function and architecture after depolarization. Expression of BDNF is increased after depolarization, and the ability of BDNF to modulate synaptic function is well documented. To further investigate BDNF signaling after activity, we analyzed the effects of depolarization or BDNF treatment on receptor mRNA expression in cultured basal forebrain neurons. Levels of mRNA coding for the cognate BDNF receptor, trkB, as well as the common neurotrophin receptor, p75, were quantitated simultaneously using a sensitive solution hybridization technique. Depolarization or BDNF treatment increased p75 mRNA expression 94% and 195%, respectively. In contrast, trkB message decreased 23% after depolarization but was unchanged by BDNF treatment. Together, these changes resulted in significant increases in the p75/trkB ratio after depolarization or BDNF treatment that could alter BDNF binding or signal transduction.

Changes in activating protein 1 (AP-1) composition correspond with the biphasic profile of nerve growth factor mRNA expression in rat hippocampus after hilus lesion-induced seizures

In adult brain, nerve growth factor (NGF) gene expression is generally upregulated by neuronal activity. However, a single episode of hilus lesion (HL)-induced limbic seizures stimulates a biphasic increase in NGF mRNA expression with peaks at 4-6 and 24 hr after lesion and an intervening return to control levels at 10-12 hr after lesion. In vitro studies suggest that NGF transcription is regulated via an activating protein 1 (AP-1) binding site in the first intron of the NGF gene. To examine the relationship between seizure-induced AP-1 binding and NGF gene expression in this paradigm, NGF mRNA levels and AP-1 binding were examined after HL seizures. Furthermore, to gain insight into the functional composition of the AP-1 complex, supershift analysis was performed to characterize which Fos and Jun family members are included in the AP-1-binding complex at the different time points analyzed. Solution hybridization analysis verified the biphasic increase in NGF mRNA content of the dentate gyrus after HL seizures. After an initial increase, AP-1 binding slowly declined in a stepwise manner that encompassed, but did not correspond with, the two phases of NGF mRNA expression. However, supershift analyses demonstrated that the relative contributions of JunD and JunB to the AP-1 complex exhibited positive and negative correlations, respectively, with the phases of increased NGF expression after HL. These results suggest that AP-1 complexes containing JunD promote NGF transactivation and that transient changes in the relative contributions of JunD and JunB to AP-1 binding underlie the biphasic increase in NGF gene expression induced by HL seizures.

Comparison of tyrosine hydroxylase and preproenkephalin expression in rat adrenal medullary explants in vitro and transplanted into subarachnoid space

When adrenal medullary cells are cultured in vitro, tyrosine hydroxylase (TH) mRNA, preproenkephalin (PPEnk) mRNA, and methionine enkephalin (Mek) immunoreactivity was markedly increased compared with intact adrenal medullary cells in situ, suggesting an increased biosynthesis of catecholamines and enkephalin-containing peptides. In transplanted adrenal medullary cells in vivo, TH mRNA and TH immunoreactivity are still apparent for at least 1 year after transplantation, indicating continued capacity for catecholamine biosynthesis. PPEnk mRNA levels in surviving adrenal medullary grafted cells increased, particularly in the first week after transplantation, and remained above levels found in the intact adrenal gland for at least 1 year after transplantation. These results support other studies in our laboratory, suggesting that adrenal medullary transplants reduce pain by synthesis and secretion of both catecholamines and enkephalin-containing peptides. The differences in expression of TH mRNA and PPEnk mRNA in the adrenal medulla in situ, in explants in culture and in transplants in the spinal subarachnoid space, indicate that the mechanisms regulating the expression of neurohumoral factors depend upon environmental factors extrinsic to the medullary cells themselves.

Modulation of prohormone convertase 2 in spinal cord during gestation and hormone-simulated pregnancy

Gestation as well as its hormonal simulation (HSP) is characterized by an enhanced spinal dynorphin/kappa-opioid antinociception. This antinociception is accompanied by decreased content of dynorphin precursor intermediates and increased content of mature dynorphin peptides (1-17 and 1-8) in the lumbar spinal region. This suggests that augmented processing of spinal dynorphin precursor intermediates is an adaptive mechanism used by dynorphin neurons to meet increased synthetic demands necessitated by increased dynorphin neurotransmission. Prohormone convertase (PC) 1 and 2 represent major secretory granule proteolytic processing activities capable of converting neuroendocrine and neurotransmitter peptide (dynorphin) precursor intermediates to their mature, biologically active products. Accordingly, the current investigation was undertaken to assess their potential relevance to peptidergic (dynorphin) neuronal functional plasticity in vivo. In order to evaluate a molecular biological parameter of PC2 synthesis, a solution hybridization assay was developed with which to quantify changes in the spinal lumbar content of its mRNA. This study demonstrates that during gestation and HSP, lumbar PC2 protein content, but not that of PC1, is augmented. The increase in lumbar PC2 during HSP indicates that the pregnancy blood concentration profile of 17beta-estradiol and progesterone is a predominant facet of the pregnant condition responsible for its modulation during this condition. In contrast to the elevated content of lumbar PC2 protein, levels of PC2 mRNA in the lumbar cord of pregnant or HSP rats were essentially unchanged. This indicates that increased transcriptional activity is not, necessarily, a prerequisite for increased PC2 protein content to be manifest. These observations suggest positive modulation of PC2 to be a critical component of the mechanism(s) by which spinal dynorphin neurons adapt to the demand-induced increased production of mature dynorphin peptides.

Mu and delta opioid receptor analgesia, binding density, and mRNA levels in mice selectively bred for high and low analgesia

The present study examined mu and delta opioid analgesia, receptor binding, and receptor mRNA levels in lines of mice from two selective breeding projects of relevance to opioid analgesia. Large differences were observed in the analgesic potency of [d-Ala2, NMPhe4, Gly-ol]enkephalin (DAMGO), [d-Pen2,5]enkephalin (DPDPE), and [d-Ala2]deltorphin II (DELT), selective mu, delta1, and delta2 opioid receptor agonists, respectively, in mice selectively bred for high (HA) and low (LA) swim stress-induced analgesia (SIA). HAR and LAR mice, selectively bred for high and low levorphanol analgesia, respectively, display equally large differences in their analgesic sensitivity to DAMGO, modest differences in sensitivity to DPDPE, and no differences in sensitivity to DELT. These sizable genotypic differences in analgesic potency were accompanied by HA/LA and HAR/LAR differences in whole-brain homogenate [3H]DPDPE and/or [3H]DELT, but paradoxically not [3H]DAMGO, binding. Solution hybridization of mRNA extracts encoding mu (MOR-1) or delta (DOR-1) opioid receptors indicated some regional differences in gene expression between high and low lines. Surprisingly, differences in these in vitro markers were often in the direction of LAR>HAR. The present data indicate that selection for either SSIA or levorphanol analgesia produces differential effects on mu and delta opioid analgesia that are accompanied by alterations on in vitro assays, the significance of which remains to be determined. The data are discussed with regard to the utility of in vitro biological markers and genetic models of analgesia.

Differences in delta opioid receptor antinociception, binding, and mRNA levels between BALB/c and CXBK mice

Mu and delta opioid receptors have been demonstrated to mediate supraspinal opioid antinociception. Whereas the recombinant inbred CXBK mouse is notably deficient in mu opioid receptor antinociception, binding density, and mRNA (MOR-1) levels, little is known about delta opioid receptor processes in this strain. The present study thus compared CXBK mice and their BALB/c strain progenitors with respect to delta opioid antinociception, whole-brain receptor binding levels, and mRNA (DOR-1) levels. Following intracerebroventricular injections of the selective delta1 and delta2 opioids DPDPE and [d-Ala2]deltorphin II, respectively, CXBK mice displayed relatively lower antinociception on the tail-flick test, resulting in significantly increased ED50 values for both agonists in this strain. Decreased whole-brain specific binding of [3H][d-Ala2]deltorphin II, but not [3H]DPDPE, was also observed in CXBK mice. Solution hybridization with a probe for the DOR-1 revealed increased transcript levels in the caudate-putamen, frontal cortex, and spinal cord of this strain. The present data demonstrate a deficiency in delta1 and delta2 opioid antinociception in CXBK mice concomitant with reductions in whole-brain delta2 receptor binding and regional increases in DOR-1. Whether these observations are causally related remains to be clarified.

Effect of supraspinal antisense oligodeoxynucleotide treatment on delta-opioid receptor mRNA levels in mice

Studies in vivo demonstrate that antisense oligodeoxynucleotide (ODN) treatment specifically reduces the functions mediated by numerous central nervous system (CNS) receptors, including opioid receptors. However, the effects of antisense ODN on the opioid receptor mRNA target, itself are rarely examined. In the present study, the effect of supraspinal antisense ODN administration on delta-opioid receptor (DOR) mRNA levels in selected CNS regions, was investigated in mice. ODN targeting a 20-nucleotide sequence of the DOR mRNA transcript was administered by intracerebroventricular (i.c.v.) injection twice daily for 3 days. First, to confirm that antisense ODN treatment decreases DOR function in this system, antinociception produced by DOR-selective agonist [D-Ala2]deltorphin II was assessed on day 4. A 2-fold reduction in [D-Ala2]deltorphin II potency was revealed in antisense ODN-treated mice compared to mice receiving control treatments. DOR mRNA levels in selected CNS regions which either mediate antinociception; medial thalamus (MThal), periaqueductal gray (PAG), frontal cortex (FCtx) and spinal cord (SpC) or exhibit relatively high levels of DOR mRNA; nucleus accumbens (Acb) and caudate-putamen (CPu) were then quantitated by solution hybridization. Levels of DOR mRNA in antisense ODN-treated mice were not different from levels in mice treated with saline vehicle, which ranged from 0.07 pg/microg total RNA in MThal and PAG to 0.26 pg/microg total RNA in CPu. These results are both consistent with previous reports that antisense oligodeoxynucleotide (ODN) treatment down-regulates DOR protein in vivo and indicate that this down-regulation is not associated with altered DOR mRNA levels.

Inducible expression of N-methyl-D-aspartate receptor, and delta and mu opioid receptor messenger RNAs and protein in the NT2-N human cell line

Retinoic acid treatment of NT-era2/cl.D1 (NT2) cells, a human teratocarcinoma cell line, yields 95% pure cultures of terminally differentiated neuronal cells. Concomitant with their terminal differentiation into neurons, NT2 cells are induced by retinoic acid to express neuronal N-methyl-D-aspartate receptor channels, which are fully functional. We determined the effects of retinoic acid-induced differentiation of NT2 cells on the levels of N-methyl-D-aspartate, delta opioid and mu opioid receptor messenger RNAs. RNA levels were measured using quantitative solution hybridization assays. The riboprobes were complementary to major portions of the coding regions of the N-methyl-D-aspartate, delta opioid and mu opioid receptor complementary DNAs. After four weeks of exposure to 10 microM retinoic acid, followed by four weeks of treatment with mitotic inhibitors (1 microM of cytosine arabinoside, 10 microM of fluorodeoxyuridine and 10 microM of uridine) the levels of N-methyl-D-aspartate receptor messenger RNA in differentiated NT2-N cells increased 10-fold, delta opioid receptor messenger RNA increased three-fold, and mu opioid receptor messenger RNA increased four-fold. Northern blot analysis revealed two transcripts for the N-methyl-D-aspartate receptor messenger RNA (4.2 and 4.4 kb) and two transcripts for delta opioid receptor messenger RNA (7.0 and 11.0 kb). To determine whether the increases in messenger RNAs were accompanied by an increased synthesis of the respective proteins, we examined the immunoperoxidase localization of N-methyl-D-aspartate receptor and delta opioid receptor antisera. N-Methyl-D-aspartate receptor-like immunoreactivity was seen within the cell bodies as well as on the processes of the retinoic acid-differentiated cells. Although delta opioid receptor-like immunoreactivity was detected within the soma of isolated cells prior to retinoic acid treatment, the apparent number of these labelled cells and their ramified processes were markedly enhanced following retinoic acid differentiation. These results demonstrate parallels between the inducible expression of the N-methyl-D-aspartate and opioid receptor messenger RNAs and proteins during the acquisition of the fully differentiated neuronal phenotype in cultured NT2 cells. Retinoic acid-differentiated NT2 cells express increased levels for the N-methyl-D-aspartate, delta opioid and mu opioid receptor messenger RNAs, providing the opportunity to study the interactions among these receptor systems in human terminally differentiated neuronal cells in culture.

Changes in proenkephalin gene expression in the developing hamster

Proenkephalin (Penk) gene expression is high in the adult hamster adrenal medulla and it is comparable to that found in both the hamster and rat striatum. In addition, Penk gene expression in the hamster adrenal medulla is more typical of adult mammalian adrenals than the rat. Since the nature of Penk gene expression in the developing hamster adrenal is not known, it was examined and compared to that found in the striatum were adult levels in the adrenal and striatum are similar. The results show that Penk gene expression progressively increases in the developing hamster adrenal to peak on postnatal day 4. There is then a small decline to adult levels by postnatal day 12 when the morphology of the developing adrenal resembles the adult. Functional splanchnic nerve activity, as assessed by the ability of reserpine to induce increases in adrenal tyrosine hydroxylase mRNA, is not present until after postnatal day 4. Therefore, early increases in Penk gene expression are independent of splanchnic nerve activity. Adrenal EC peptides resulting from the developmental increases in Penk gene expression appear to be unprocessed and proenkephalin-like. This is based on the very low levels of free enkephalin (met-enkephalin) detected in the adrenals from both newborn and adult hamsters (1-5% of total EC peptide levels). In the developing hamster striatum, Penk gene expression remains low and unchanged until postnatal day 4 and increases six-fold by adulthood. Free enkephalin (met-enkephalin) levels remain high (between 36 and 88% of total EC peptide levels) in the developing and adult hamster striatum. Therefore the results show early increases in adrenal Penk gene expression in the developing hamster that are independent of splanchnic nerve activity and adult Penk gene expression which is high and dependent on splanchnic nerve activity. This differs from what is observed in the frequently studied rat. However, developmental changes in the hamster striatum are similar to those in the rat.

Opiate and cocaine addictions: challenge for pharmacotherapies

Neurobiological and behavioral studies, as well as basic and applied clinical research studies, may all contribute to the development of a pharmacotherapy for a specific addictive disease. This paper reviews recent findings from research work, primarily from one laboratory along with collaborative laboratories, that could have some relevance for the development of pharmacotherapy for cocaine dependency. The much earlier experiences of this laboratory in the development of a pharmacotherapy for opiate addiction will be addressed in the context of providing both some specific suggestions for addictive disease pharmacotherapy development and some warnings about the complexities of the introduction and implementation of a pharmacotherapy once developed. Finally, based on both the earlier perspectives and the more recent research findings, some very specific, though speculative, suggestions will be made about the development of novel pharmacotherapies for early opiate addiction, especially for cocaine abuse or addiction and prevention of relapse to cocaine use. The complex and diverse nature of the challenge for pharmacotherapy for the addictive diseases is presented, including specifically a mandate for broadening educational efforts concerning the basis of addictive diseases and the need for treatment, in parallel with the scientific efforts to develop increasingly sophisticated and targeted pharmacotherapies.

Activation of protein kinase A prevents the ethanol-induced up-regulation of delta-opioid receptor mRNA in NG108-15 cells

We have used a sensitive solution hybridization assay with a riboprobe transcribed from the coding sequence of the delta-opioid receptor gene (DOR) to study the up-regulation of the DOR mRNA by ethanol in NG108-15 cells. Exposure of the cells to compounds that increase cAMP levels (forskolin, forskolin + IBMX, or dibutyryl cAMP) resulted in the attenuation of ethanol-induced up-regulation of DOR mRNA. The inactive analogue of forskolin, 1,9-dideoxy forskolin had no effect. Northern blot analysis of RNA extracts from ethanol-, forskolin- or ethanol + forskolin-treated cells showed proportional changes in each of the multiple DOR mRNA bands, so that no difference was observed in the fraction of the total hybridization signal produced by each band of the DOR mRNA. In the absence of ethanol, forskolin or dibutyryl cAMP reduced the basal levels of DOR mRNA. The cAMP analogue (Rp)-cAMPS, a protein kinase A (PKA) inhibitor, increased DOR mRNA levels. However, the combination of (Rp)-cAMPS and ethanol did not further increase DOR mRNA levels compared to ethanol or (Rp)-cAMPS alone. Signaling through cAMP and PKA down-regulates DOR mRNA levels. The ethanol-induced increase in DOR mRNA levels in NG108-15 cells appears to be mediated via a reduction of PKA.

Quantitative comparison of mu opioid receptor mRNA in selected CNS regions of alcohol naive rats selectively bred for high and low alcohol drinking

We combined solution hybridization, ribonuclease protection and microdissection techniques to quantitatively compare the anatomical distribution of mu receptor mRNA in discrete brain regions of alcohol naive rats selectively bred for high and low alcohol drinking (HAD and LAD lines, respectively). The solution hybridization assay is highly sensitive and can detect mu opioid receptor mRNA in a 100-fold linear range from 4 to 421 amol. HAD and LAD rats exhibited a similar level of mu receptor mRNA in all central nervous system (CNS) regions examined except for the inferior colliculus. Our data suggest that the steady-state level of mu receptor mRNA is not associated with genetic differences in alcohol drinking behavior.

Quantitation of dopamine transporter mRNA in the rat brain: mapping, effects of "binge" cocaine administration and withdrawal

Dopamine transporter (DAT) mRNA from selected brain regions of individual male Fischer rats was quantitated utilizing a sensitive solution hybridization assay in which the levels of RNase-protected 32P-labeled mRNA:cRNA hybrids were measured. DAT mRNA was detected in whole brain regions known to contain abundant DAT mRNA (mean picogram of DAT mRNA/microgram of total RNA +/- SEM): substantia nigra, 7.17 +/- 0.47; ventral tegmentum, 4.71 +/- 0.38. In regions known to contain low levels of DAT mRNA, these levels were detected: central grey, 0.39 +/- 0.06; hypothalamus, 0.14 +/- 0.03. In addition, DAT mRNA was detected in areas where it had not previously been identified: amygdala, 0.19 +/- 0.03; caudate-putamen, 0.15 +/- 0.03; nucleus accumbens, 0.13 +/- 0.01; pons/medulla, 0.12 +/- 0.02; globus pallidus, 0.09 +/- 0.04; pituitary 0.07 +/- 0.01; frontal cortex, 0.05 +/- 0.01. No DAT mRNA was detected in 150 micrograms of rat liver RNA. As cocaine binds to and inhibits the activity of the dopamine transporter, we sought to determine if there were differences in dopamine transporter mRNA levels between saline- and cocaine-injected rats or rats withdrawn from a chronic "binge" pattern (15 mg/kg per dose i.p.; three doses at 1 h intervals each day) cocaine injection. Using trichloroacetic acid precipitation of mRNA:cRNA hybrids from RNA extracted from whole brain regions, we found no significant differences in the substantia nigra or the ventral tegmentum following subacute (3 days) binge, chronic (14 days) binge or 10 days withdrawal from a chronic binge pattern cocaine or saline administration.

Regulation of kappa opioid receptor mRNA in the rat brain by "binge' pattern cocaine administration and correlation with preprodynorphin mRNA

We previously reported that 'binge' pattern administration of cocaine elevates preprodynorphin (ppDyn) mRNA in the caudate-putamen of rats. The present study confirms this finding. In addition, we report here that "binge' pattern administration of cocaine leads to a significant decrease in the mean level of kappa opioid receptor (KOR) mRNA in the substantia nigra, with no significant change in the mean level of KOR mRNA in the caudate-putamen. The decrease in KOR mRNA in the substantia nigra after 3 day or 14 day 'binge' administration of cocaine was comparable to the increase in ppDyn mRNA in the caudate-putamen. While there was no significant change in the mean levels of KOR mRNA in the caudate-putamen following cocaine administration, there was a positive within animal correlation between the levels of ppDyn mRNA and KOR mRNA in the caudate-putamen, both in animals administered saline and in animals receiving 'binge' cocaine for 14 days. Finally, mean levels of ppDyn or KOR mRNA in cocaine treated rats were not different from saline treated controls following a 10 day withdrawal from 14 days of 'binge' cocaine administration. The results provide evidence of regulation of KOR mRNA by cocaine in the substantia nigra.

Retinoic acid-induced increase in delta-opioid receptor and N-methyl-D-aspartate receptor mRNA levels in neuroblastoma x glioma (NG108-15) cells

We determined the effects of all-trans retinoic acid (RA) on the levels of delta opioid receptor (DOR) mRNA and N-Methyl-D-Aspartate receptor (NMDAR1) mRNA in neuroblastoma x glioma hybrid cells (NG108-15) by use of quantitative solution hybridization assays. The assays utilized riboprobes complementary to major portions of the coding region of the DOR and NMDAR1 cDNAs. At 10 microM RA a 3-fold increase in DOR mRNA at 48 h, and later (144 h) alterations were observed in NMDAR1 mRNA levels. Northern blot analysis revealed six transcripts for DOR mRNA ranging in size from 8.7 to 2.0 Kb, and three transcripts for NMDAR1 mRNA ranging in size from 4.1 to 3.5 Kb. Neither the size nor the fractional band intensity was affected by RA treatment. The delayed induction of DOR mRNA suggests an indirect mechanism by which RA acts on transcription of this gene. A surprising induction of DOR mRNA by the protein synthesis inhibitor cycloheximide (CHX) suggests that either a repressor molecule or degrading enzymes/proteases may regulate basal levels of this mRNA. Treatment with RA resulted in a concentration- and time-dependent morphological differentiation characterized by increased size of the cell body and the appearance of numerous short and long processes.

The effect of the irreversible mu-opioid receptor antagonist clocinnamox on morphine potency, receptor binding and receptor mRNA

In these experiments, the effect of the irreversible mu-opioid receptor antagonist clocinnamox on the potency of morphine, opioid receptor binding and mu-opioid receptor mRNA was examined. Mice were injected with clocinnamox (0.32-12.8 mg/kg) and the analgesic potency of morphine was examined 24 h later. Clocinnamox produced a dose-dependent decrease in the potency of morphine; and at the higher dose of clocinnamox the maximal analgesic effect was not observed following doses of morphine in excess of 500 mg/kg s.c. In saturation binding studies in brain, clocinnamox (0.32-25.6 mg/kg) dose-dependently decreased mu-opioid ([3H][D-Ala2,MePhe4,Gly-ol5]enkephalin; DAMGO) receptor Bmax with relatively minimal effects on Kd. Binding to delta-opioid receptor ([3H][D-Pen2,D-Pen5]enkephalin; DPDPE) and kappa-opioid receptor ([3H](5,7,8)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec -8-yl) benzeneacetamide; U69,593) was not affected by clocinnamox. The effect of clocinnamox was time-dependent in that the greatest changes in morphine potency and mu-opioid receptor density were observed within 24 h of administration and decreased with time (336 h). Although mu-opioid receptor density was decreased to less than 30% of control 24 h following clocinnamox (12.8 mg/kg) and had increased to 80% by 5 days, a solution hybridization assay for mu-opioid receptor mRNA transcript revealed no changes in the steady-state levels of this mRNA. These studies indicate that clocinnamox is an irreversible antagonist at the mu-opioid receptor since it appears to selectively affect receptor density with minimal effects on affinity. Furthermore, clocinnamox produces time- and dose-dependent changes in Bmax and these changes appear to be unrelated to changes in mu-opioid receptor mRNA. It is possible that the repopulation of brain by mu-opioid receptors following clocinnamox is mediated by an existing pool of receptors that are activated following treatment.

Assessment of delta opioid antinociception and receptor mRNA levels in mouse after chronic naltrexone treatment

The antinociceptive potency of the delta opioid receptor (DOR) agonist [D-Ala2]Deltorphin II and the levels of DOR mRNA were measured in mice chronically treated with naltrexone. ED50 determinations for [D-Ala2]Deltorphin II, using the tail-flick test with mice that had been treated with naltrexone for 7 days followed by a 24 h naltrexone free period (study day 8), revealed a 7.7-fold increase in antinociceptive potency, indicating functional supersensitivity. Utilization of a micro-dissection technique followed by quantitative solution hybridization measurements of RNA extracts from mouse CNS revealed levels of DOR mRNA ranging from 2.8 pg/microgram RNA in the caudate-putamen to 0.3 pg/microgram RNA in cerebellum. However, despite the functional increase in DOR sensitivity, the DOR mRNA levels in selected brain areas and spinal cord of naltrexone-treated and control mice did not differ. Assessment of DOR mRNA levels in whole brain and selected CNS regions after shorter treatment intervals (1, 6 and 12 h and 2 and 7 days) in naltrexone-treated and control mice revealed a similar pattern of results. Northern blot analysis of mouse whole brain RNA extracts after 7 days of naltrexone treatment did not show any alteration in the size of the DOR transcript. These data demonstrate that DOR mRNA levels are not altered during and after chronic naltrexone treatment and therefore are not associated with opioid-induced DOR up-regulation or DOR functional supersensitivity.

Differential regulation of c-fos, proenkephalin and tyrosine hydroxylase gene expression by metrazole in the hamster adrenal and hippocampus

Metrazole (MTZ) induces sequential activation of c-fos, proenkephalin (Penk) and tyrosine hydroxylase (TH) gene expression in the rat adrenal and c-fos and Penk gene expression in the rat hippocampus. As in the rat, MTZ produced a dose-dependent induction of c-fos mRNA in the hamster adrenal and hippocampus together with an increase in adrenal TH mRNA. Although MTZ-induction of preproenkephalin (PPenk) mRNA was observed in the hippocampus of the hamster, the same treatment failed to induce PPenk mRNA in the hamster adrenal. These results indicate that Penk gene expression in the hamster is differentially regulated in the adrenal and hippocampus. Furthermore, the regulation of adrenal Penk gene expression differs significantly when rat and hamster are compared.

NGF and BDNF are differentially modulated by visual experience in the developing geniculocortical pathway

Neuronal activity and trophic factors have been implicated in shaping the connectivity of functional synaptic circuits. We studied the development and regulation by sensory input of the neurotrophins NGF, BDNF and NT-3 in the developing rat visual system. In the occipital cortex, NT-3 mRNA was transiently expressed in the neonate. In contrast, BDNF and NGF mRNA's increased during postnatal development, and reached mature levels around 3 weeks of age. BDNF mRNA was ten times more abundant than NGF mRNA. In the lateral geniculate nucleus (LGN), NT-3 mRNA was also transiently expressed, whereas NGF and BDNF mRNA's did not vary significantly during development. The high-affinity neurotrophin receptors trkB and trkC were expressed both in the developing LGN and occipital cortex. These receptors for BDNF and NT-3, respectively, were expressed at birth, with little change during development. In contrast, trkA mRNA, which encodes the high-affinity NGF receptor, was undetectable in either region. Visual experience differentially modulated expression of NGF and BDNF mRNA's. NGF mRNA was slightly increased after 3 weeks of light-deprivation. In contrast, BDNF mRNA expression in visual cortex was significantly lower than normal in rats dark-reared from birth. Decreased BDNF expression after sensory deprivation was reversible by exposure to light. Thus, all three neurotrophins were detected in visual cortex and LGN. Differences in abundance developmental profiles, and regulation imply distinct functions for each factor in the visual system.

The transcriptional regulation of the preproenkephalin gene

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NMDA antagonists and clonidine block c-fos expression during morphine withdrawal

The c-fos gene is expressed in the central nervous system (CNS) in response to neuronal stimuli. Induction of c-fos in certain CNS regions occurs following naltrexone precipitated withdrawal in morphine dependent rats. Non-competitive (MK801) and competitive (LY274614) NMDA receptor antagonists and clonidine, an alpha2 partial agonist, attenuate the intensity of naltrexone precipitated withdrawal. We determined the levels of c-fos mRNA by solution hybridization in several brain regions in control and morphine dependent rats following pretreatment with saline, MK801 (1 mg/kg, s.c.), LY274614 (100 mg/kg, i.p.), or clonidine (1.5 mg/kg, i.p.). Morphine treatment increased c-fos mRNA levels in striatum (STR) and amygdala (AMY). Naltrexone did not alter c-fos mRNA levels in placebo-treated rats. However, naltrexone increased c-fos mRNA levels in morphine dependent rats in the nucleus accumbens (NA), frontal cortex (FC), AMY, and hippocampus (HIP) but not in STR or spinal cord. Pretreatment with MK801 blocked this effect of naltrexone in AMY but not in NA, FC, or HIP, while pretreatment with LY274614 or clonidine blocked this effect of naltrexone in AMY and NA but not in FC or HIP. These results further delineate both the neuroanatomical pathways involved in morphine withdrawal and the locus of action of compounds that reduce morphine-withdrawal symptoms.

Quantitative distribution of the delta opioid receptor mRNA in the mouse and rat CNS

We have used a sensitive solution hybridization assay that employs a riboprobe obtained from the mouse delta opioid receptor (DOR) coding sequence to quantitate the relative abundance of DOR mRNA in the central nervous system (CNS) of the adult mouse and rat. In brain Poly A+ RNA extracts this riboprobe hybridized to a single 10 kb transcript from mouse and two transcripts, one of 12 and the other of 4.5 kb in size from rat. In mouse CNS the highest levels of DOR mRNA were found in the caudate-putamen at 3.3 +/- 0.1 (SEM) pg/micrograms RNA. DOR mRNA levels in the range from 2.6 to 2.1 pg/micrograms RNA were measured in frontal cortex, nucleus accumbens, whole brain and olfactory tubercle. Spinal cord, periaqueductal gray and hippocampus had DOR mRNA levels in the range from 1.8 to 1.5 pg/micrograms RNA, while medial thalamus and cerebellum had the lowest levels (0.5 pg/micrograms RNA). These results correlate with the reported relative distribution of DOR mRNA in mouse using an in situ hybridization technique. In rat CNS, the highest levels of DOR mRNA were measured in caudate-putamen at 2.3 +/- 0.1 pg equivalents/micrograms RNA. Whole brain, cerebral cortex, olfactory bulb and brain stem had levels in the range from 1.5 to 0.9 pg equivalents/micrograms RNA while the lowest DOR mRNA levels were measured at 0.5 pg equivalents/micrograms RNA or less in thalamus, hippocampus, substantia nigra and cerebellum. This study demonstrates the ability of solution hybridization assays to quantitate homologous (mouse) as well as similar but heterologous (rat) DOR mRNA levels.

CNS levels of mu opioid receptor (MOR-1) mRNA during chronic treatment with morphine or naltrexone

The CNS levels of mu opioid receptor (MOR-1) mRNA were determined by solution hybridization in rats treated chronically with morphine or naltrexone. Morphine treatment (2 x 75 mg pellets were implanted SC on Day 1 and 2 more on Day 4) resulted in the development of tolerance to morphine's antinociceptive (analgesic) effect, as assessed by the hot plate procedure on treatment Day 7. Following the hot plate test, selected CNS regions were obtained by microdissection. The levels of MOR-1 mRNA in pg/microgram RNA ranged from 0.7 in sensorimotor cortex to 15.3 in medial thalamus. MOR-1 mRNA levels were not altered in the dorsal horn of spinal cord, nucleus raphe magnus, periaqueductal grey, hypothalamus, medial thalamus, or sensorimotor cortex. In a separate experiment, a 2 day exposure to naltrexone (2 x 30 mg pellets) had no effect on CNS levels of MOR-1 mRNA; however, after an 8 day exposure a decrease was detected in the nucleus raphe magnus (by 28%), hypothalamus (by 21%), and medial thalamus (by 27%). Chronic exposure to morphine or naltrexone did not result in alterations in the size of full-length MOR-1 mRNA from rat brain, or in the size of the region protected by the MOR-1 riboprobe (i.e., the entire coding region). Thus, the neuroadaptive processes associated with the development of analgesic tolerance to morphine do not involve concurrent changes in the steady-state levels of MOR-1 mRNA. Chronic treatment with naltrexone appears to produce a region-specific downregulation of MOR-1 mRNA levels, which may be secondary to the naltrexone-induced increase in mu receptor binding.

Supraspinal delta opioid receptor mRNA levels are not altered in [D-Ala2]deltorphin II tolerant mice

Delta opioid receptor (DOR) mRNA levels were studied in mice rendered tolerant to [D-Ala2]deltorphin II by 4 days of repeated intracerebroventricular administration (10 micrograms, [tid]). ED50 determinations on day 5 revealed a 10-fold loss in [D-Ala2]deltorphin II potency with the tail-flick test. Utilization of a microdissection technique followed by quantitative solution hybridization of RNA extracts from mouse brain revealed mean levels of DOR mRNA ranging from 3.9 pg/micrograms RNA in the caudate-putamen to 0.4 pg/micrograms RNA in the cerebellum. DOR mRNA levels were not different when RNA extracts from tolerant and non-tolerant mice were compared. These data suggest that altered DOR mRNA levels are not one of the adaptive changes that occur with delta opioid ([D-Ala2]deltorphin II) tolerance.

Ethanol and naloxone differentially upregulate delta opioid receptor gene expression in neuroblastoma hybrid (NG108-15) cells

We have used a sensitive solution hybridization assay with a riboprobe transcribed from the coding sequence of the delta opioid receptor (DOR) to quantitate the changes in DOR mRNA transcript levels following exposure of NG108-15 cells to ethanol and/or the opioid antagonist, naloxone. Incubation of NG108-15 cells with 200 mM ethanol or 1 microM naloxone, treatments that have previously been shown to upregulate DOR binding, increased DOR mRNA transcript levels 2 to 3 fold. DOR mRNA levels peaked at 24 to 48 h after exposure to either ethanol or naloxone. At 168 h, DOR mRNA levels in NG108-15 cells exposed to naloxone had returned to control (untreated) levels while the levels in ethanol treated cells remained nearly equal to peak values. Exposure to a combination of ethanol plus naloxone for 24 h produced an additive effect, so that DOR mRNA transcripts were increased 3 fold. Northern blot analysis identified six DOR transcript bands ranging in size from 8.7 to 2.1 kb. The above treatments increased each of the six bands proportionately, so that no difference was observed in the fraction of the total hybridization signal produced by each band of the Northern blot. These results demonstrate that each of the DOR transcripts in NG108-15 cells are subject to homologous (naloxone) as well as heterologous (ethanol) upregulation.

Nitric oxide and opioid tolerance

Under conditions in which NG-nitro-L-arginine (NOArg) treatment prevents morphine tolerance, NOArg induces a slow progressive inhibition of nitric oxide synthase (NOS), starting at approx. 20% after a single treatment and increasing to approx. 65% after 10 days. Studies designed to examine potential changes in NOS levels with chronic morphine administration reveal no change. Total NOS activity in both brainstem and cerebellum homogenates is unchanged, as are levels of NOS mRNA in a variety of brain regions. L-Arginine, the precursor of nitric oxide (NO), accelerates tolerance when coadministered with morphine and when given alone L-arginine decreases morphine's potency. Administration of L-arginine alone for 3-10 days shifts morphine's dose-response curve over 2-fold to the right while D-arginine is without effect, as is daily administration of L-arginine along with the NOS inhibitor NOArg. Thus, chronic L-arginine induces "tolerance" in opioid naive mice through NOS. Together, our data indicate an important role for NO in the modulation of opioid analgesia.

An improved method detects differential NGF and BDNF gene expression in response to depolarization in cultured hippocampal neurons

Differential regulation of individual neurotrophins by impulse activity potentially allows transformation of instantaneous signalling into diverse, long-lasting neural alterations. To define the temporal profiles of trophin gene expression we examined nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNAs in dissociated cell cultures of rat hippocampus using an improved solution hybridization technique. Traditional methods lack the precision and sensitivity to detect small changes during brief intervals and the facility to process large sample numbers simultaneously. This improved method has now allowed us to better define the dynamics of depolarization-induced changes in expression of individual trophin genes. Using elevated K+ as a depolarizing stimulus, NGF mRNA increased 40% after 48 h. In contrast, BDNF message rose almost 4-fold within 3 h and attained a maximal 6-fold increase within 6 h. Similar increases in BDNF mRNA levels were exhibited following treatment of cultures with glutamate, an excitatory neurotransmitter. To document the sensitivity of BDNF mRNA to depolarizing conditions, we examined expression after K+ withdrawal. BDNF message began decreasing within one hour post-depolarization, and returned to basal levels after 6 h. Observations indicate that BDNF and NGF mRNAs are induced differentially in response to impulse activity; BDNF message is acutely responsive to ongoing changes, whereas NGF mRNA responds more slowly and sluggishly. The physiological implications of this differential regulation are discussed.

Stimulatory effect of opioid peptides and naloxone on rat spinal cord cells in primary dissociated culture

Opioid peptides leu-enkephalin, a synthetic analog of enkephalin dalargin and an opiate receptor blocker naloxone were studied for their morphological effect on the cells of dissociated cultures of rat spinal cord. Low density seeding of cells (3.10(5);6.10(5) cells/ml) on collagen substrate was performed to document that opioid peptides increase the number of cultured cells and neurite outgrowth and lead to the activation of the initiated processes of aggregate formation. Upon higher density of plating (5.10(6) cells/ml) with poly-L-lysine as a substrate, activation of the aggregate formation process was demonstrated, both opioid peptides and naloxone leading to an increase in the size of aggregates. Statistical treatment of the results obtained in this set of experiments documented that leu-enkephalin, dalargin and naloxone increased 2.2-, 2.2-2.6-, 2.4-fold, respectively, the size of aggregates compared to the control, i.e. the reaction of spinal cord cells to opioid peptides and opiate receptor blocker naloxon was unidirected. The total effect of opioid peptides and naloxon resulted in a 3.6-fold increase in the size of the aggregates compared to the control. The data obtained in this study allow the assumption that opioid peptides and naloxone, while activating spinal cord cells via receptors of a different type, manifest the properties of factors thus increasing survival and adhesion of spinal cord cells in culture.

Competition for DNA steroid response elements as a possible mechanism for neuroendocrine integration

For the analysis of a simple steroid-dependent mating behavior, careful response definition, complete neural circuit delineation and placement of estrogen-responsive cells within this circuit have been accomplished. Molecular studies of two relevant genes have emphasized DNA/RNA hybridization assays and DNA binding techniques. For both the rat preproenkephalin gene and the gene for the progesterone receptor, a strong induction by estrogen, tissue specificity of expression and a sex difference in regulation are prominent phenomena. On the rat preproenkephalin promoter, estrogen (ER) and thyroid receptors may compete for a DNA binding site. Likewise, progesterone (PR) and glucocorticoid receptors may compete for the same sites. On the rat PR gene, interactions between ER and AP-1 binding proteins are of special interest. Such interactions could underlay competitions and synergies between steroid hormones and neurally signalled events in the environment.

Acute and persistent suppression of preproenkephalin mRNA expression in the striatum following developmental hypoxic-ischemic injury

The striatum is vulnerable to hypoxic-ischemic injury during development. In a rodent model of perinatal hypoxia-ischemia, it has been shown that striatal neurons are not uniformly vulnerable. Cholinergic neurons and NADPH-diaphorase-positive neurons are relatively spared. However, it is unknown what classes of striatal neurons are relatively sensitive. One of the major classes of striatal neurons uses enkephalin as a neurotransmitter. We have studied the effect of early hypoxic-ischemic injury on this class of neurons using a quantitative solution hybridization assay for preproenkephalin mRNA in conjunction with in situ hybridization. Hypoxia-ischemia results in an early (up to 24 h) decrease in striatal preproenkephalin mRNA, which is shown by in situ hybridization to occur mainly in the dorsal portion of the striatum. By 14 days, whole striatal preproenkephalin mRNA and total enkephalin-containing peptide levels are normal. However, at 14 days, in situ hybridization reveals that regions of complete preproenkephalin mRNA-positive neuron loss remain in the dorsal region. Normal whole striatal levels are due to an up-regulation of preproenkephalin mRNA expression in the ventrolateral region of the injured striatum. Given the important role that the enkephalin-containing striatal efferent projection plays in regulating motor function, its relative loss may be important in the chronic disturbances of motor control observed in brain injury due to developmental hypoxic-ischemic injury.

Cloning and characterization of hamster proenkephalin gene

Our previous studies have shown that the hamster adrenal, like the human, contains high levels of preproenkephalin (PPenk) mRNA and enkephalin peptides, and may serve as a mammalian model for the in vivo study of proenkephalin (Penk) gene expression, peptide biosynthesis, and release. To define further the factors that may regulate hamster Penk gene expression, the hamster Penk gene was isolated from a genomic library prepared from Syrian hamster liver. The hamster Penk gene contains four exons and three introns and encodes 268 amino acids including six copies of Met-enkephalin containing peptides and one copy of Leu-enkephalin. In the 5' upstream region, there are TATA and GC boxes and multiple putative regulatory elements including the cAMP response element, AP-1, AP-2, AP-4, and the glucocorticoid response element (GRE). Possible GREs are also present in the introns. A comparison with the human and the rat Penk genes indicates that both the human and hamster Penk gene contain three introns, while the rat Penk gene has two introns. The intron missing from the rat Penk gene is short and separates the first and second exons of the hamster and human genes. In addition, the hamster and human genes share a region (100 bases) in the 5' upstream sequence that is 98% homologous. It is of interest that Penk gene expression is high in the adrenal medulla of both human and hamster, but is much lower in the rat. These homologous regions and the extra intron may contain regulatory features responsible for a high level of expression in the human and hamster adrenal medulla.

Metrazole induction of c-fos and proenkephalin gene expression in the rat adrenal and hippocampus: pharmacological characterization

We have previously reported that the administration of metrazole (MTZ) produces a sequential, dose-dependent induction of c-fos and proenkephalin (Penk) gene expression in the rat hippocampus and adrenal. The adrenal is more sensitive to induction of these genes by MTZ. In the present study, we have compared the induction of c-fos and Penk in the hippocampus and adrenal, and examined the consequences of selected pharmacological manipulations. Treatment with LY274614, a competitive NMDA-receptor antagonist, blocked MTZ-induced convulsions and the MTZ-induction of c-fos and PPenk mRNAs in the hippocampus, and PPenk mRNA in the adrenal. However, in the adrenal the MTZ-induction of c-fos was only partially inhibited by LY274614. A combination of peripheral acting cholinergic antagonists (chlorisondamine plus methylatropine) prevented the MTZ-induction of adrenal c-fos and PPenk mRNA without significant alterations in the MTZ-induction of hippocampal c-fos mRNA or convulsions. Trifluoperazine, a calcium/calmodulin inhibitor, attenuated the MTZ-induction of c-fos mRNA while potentiating the MTZ-induction of PPenk mRNA in both the hippocampus and the adrenal. These results demonstrate that the MTZ induction of c-fos and Penk gene expression in the rat adrenal can be modulated by drugs acting in the CNS at NMDA receptors, in the periphery at postsynaptic cholinergic receptors and intracellularly at the calcium/calmodulin signal transduction pathway. Furthermore, we provide additional evidence that MTZ-induction of c-fos and Penk mRNAs can be dissociated by drugs acting at these sites.

A novel approach to screen for cytokine effects on neuronal gene expression

We describe an assay based on reverse transcription-polymerase chain reaction to detect the expression of mRNAs for a variety of transmitter synthetic enzymes and neuropeptides present at low levels in primary neuronal cultures. The assay is specific for mRNA-derived templates and is not affected by the presence of genomic DNA. Using this method, we demonstrate that cholinergic differentiation factor/leukemia inhibitory factor (CDF/LIF) and ciliary neurotrophic factor (CNTF) induce mRNAs for choline acetyltransferase, somatostatin, substance P, vasoactive intestinal polypeptide, cholecystokinin, and enkephalin. The induction of cholecystokinin and enkephalin by CDF/LIF and CNTF had not been shown previously. These data illustrate that the assay can reproduce findings obtained with other methods, as well as provide the sensitivity necessary to produce new results. These results also extend the overlap of CDF/LIF and CNTF in controlling gene expression in cultured sympathetic neurons, supporting the idea that these cytokines may share receptor subunits and signal transduction pathways.

Quantitation of NMDA receptor (NMDAR1) mRNA levels in the adult and developing rat CNS

A rapid and sensitive solution hybridization assay was used to quantitate N-methyl-D-aspartate (NMDA) receptor mRNA levels in the central nervous system (CNS) of rat, mouse and human. A riboprobe labelled with 32P was prepared from a plasmid containing a 1413 base sequence from the cDNA for the functional rat NMDA receptor subunit, NMDAR1. Using a full length sense transcript as the calibration standard, the assay reliably measures 8 pg of NMDAR1 mRNA. When expressed as pg of NMDAR1 mRNA/micrograms total cellular RNA, the highest levels in the adult rat CNS are in the olfactory bulb (20.9 pg/micrograms RNA) and the lowest levels are in the spinal cord (5.2 pg/micrograms RNA). Intermediate levels were found in frontal cortex, hippocampus, cerebellum and whole brain. In the mouse CNS the highest levels of NMDAR1 mRNA were found in the olfactory bulb (12.9 pg equivalents/micrograms RNA), followed closely by hippocampus, frontal cortex and cerebellum. Mouse spinal cord (4.4 pg equivalents/micrograms RNA) had the lowest levels of NMDAR1 mRNA. The NMDAR1 riboprobe hybridizes with the same size transcripts in Poly(A)+ RNA from rat, mouse and human brain. In the developing rat, NMDAR1 mRNA levels in frontal cortex and hippocampus increased nearly 3 fold from postnatal day 3 to day 15 and approximately doubled from day 15 to day 67 (adult). Therefore, from postnatal day 3 to adult (day 67) frontal cortex and hippocampus levels of NMDAR1 mRNA increased nearly 6 fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of the levels of tyrosine hydroxylase and preproenkephalin mRNAs in nigrostriatal sites after 6-hydroxydopamine lesions

Expression of the striatal proenkephalin gene is modulated by dopaminergic input from the substantia nigra (SN). We have used rapid, specific and sensitive solution hybridization assays for the quantitation of tyrosine hydroxylase (TH) mRNA, preproenkephalin (PPenk) mRNA and total cellular RNA to compare ipsilateral and contralateral levels of these RNAs in tissue dissected from the origin and termination of the nigrostriatal pathway of individual rats following sham (vehicle) or 6-hydroxydopamine (6-OHDA) induced lesions of the SN. Three weeks after treatment the rats that had received 6-OHDA, but not sham treated controls, demonstrated a characteristic contralateral rotation in response to apomorphine. Four weeks after 6-OHDA treatment, TH mRNA levels were reduced below the limits of sensitivity of the assay (1 pg/ug RNA) in ipsilateral SN while the levels of TH mRNA in contralateral SN (4.8 pg/ug RNA) did not differ from that in sham treated animals. PPenk mRNA levels in striatum were increased 3 fold to 64.9 pg/ug RNA on the side of the 6-OHDA lesions while the contralateral PPenk mRNA levels (21.6 pg/ug RNA) did not differ from sham treatment. The 6-OHDA treatment did not alter the levels of total cellular RNA in either SN or striatum. These results provide quantitative evidence for the tonic inhibition of striatal proenkephalin gene expression by the dopaminergic nigrostriatal pathway.

Quantitation of preproenkephalin mRNA levels in brain regions from male Fischer rats following chronic cocaine treatment using a recently developed solution hybridization assay

Quantitative solution hybridization assays were used to determine the picogram amounts of preproenkephalin mRNA (PPenk mRNA) and the microgram quanities of total rat RNA in extracts of eight brain regions from rats which had received three daily intraperitoneal injections of cocaine (10 or 30 mg/kg/day) or saline for 14 days. The young adult male Fischer rats were sacrificed 30 min after the final injection. The highest density of PPenk mRNA (pg PPenk mRNA/micrograms total cellular RNA) was found in extracts of striatum (34.08 +/- 1.79 pg/micrograms for 11 saline-treated rats), followed by extracts of nucleus accumbens (10.08 +/- 0.81 pg/micrograms), and extracts of hypothalamus (2.99 +/- 0.31 pg/micrograms). Extracts of frontal cortex (1.78 +/- 0.24 pg/micrograms), pituitary (1.39 +/- 0.08 pg/micrograms), central grey (1.31 +/- 0.16 pg/micrograms), and cerebellum (1.24 +/- 0.09 pg/micrograms) had intermediate values. Extracts of hippocampus (0.53 +/- 0.03 pg/micrograms) had the lowest density. No significant differences were found among the treatment groups in any brain area investigated. Therefore, chronic cocaine treatment as administered in this protocol did not alter expression of the gene encoding proenkephalin.