Sequence and expression of the rat prodynorphin gene

Dopamine control of striatal gene expression during development: relevance to knockout mice for the dopamine transporter

The aim of this study was to determine at which developmental stage and how dopamine regulates the expression of striatal dopamine receptor and neuropeptide mRNAs. For this, we studied the expression of these mRNAs, in relation to dopamine innervation, in normal mice from gestational day 13 (G13) to adult. Particularly, we investigated the adaptive changes in the expression of these markers in mice lacking the dopamine transporter during development. We detected tyrosine hydroxylase, by immunohistochemistry, in the ventral mesencephalon and the striatal anlage in both genotypes at G13, whereas the dopamine transporter appeared in the striatum of normal mice at G14. By in situ hybridization, we detected striatal dopamine D1, D2, D3 receptor, and substance P mRNAs at G13, preproenkephalin A mRNA at G14 and dynorphin mRNA at G17 in normal mice. Although the time of initial detection and the distribution were not affected in mutant mice, quantitative changes were observed. Indeed, D1 and D2 receptor as well as preproenkephalin A mRNA levels were decreased from G14 on, and dynorphin mRNA level was increased from G17 on. In contrast, substance P mRNA level was unaffected. Our data demonstrate that the influence of dopamine on striatal neurons occurs early during the development of the mesostriatal system as quantitative changes appeared in mutant mice as soon as G14. These findings bring new insights to the critical influence of dopamine on the expression of striatal dopamine receptor and neuropeptide mRNAs during development, and suggest that mesostriatal dopamine transmission functions from G14 on.

Endogenous morphine

It is now well accepted that endogenous morphine is present in animals, both in invertebrates and vertebrates. It is a key signaling molecule that plays an important role in downregulating physiological responses, such as those in the immune system, including immune elements in the CNS. It has been demonstrated that a specific mu-opiate-receptor subtype, mu3, mediates these downregulatory effects through release of NO. This article examines morphine as an endogenous signaling molecule, in terms of its role in neural and immune regulation.

Long-lasting regulation of galanin, opioid, and other peptides in dorsal root ganglia and spinal cord during experimental polyarthritis

Mechanisms involved in transition from acute to chronic pain are still not well understood and our means to therapeutically influence this transition are limited. Moreover, very little is known about long-lasting consequences of prolonged exposure to painful stimuli with regard to phenotypic changes and pain experience. In this study we have analyzed long term behavioral and neurochemical effects of intradermal tail injection of heat-killed mycobacterium butyricum suspended in complete Freund's adjuvant. Calcitonin gene-related peptide (CGRP) and galanin mRNA levels were investigated in dorsal root ganglia of polyarthritic rats during the acute (21-) and the remission stage (79 days postinjection), and opioid peptide mRNAs and receptors were studied in the spinal cord. Most of the increases in peptide mRNA levels observed during the acute stage of arthritis were still present in the remission stages. Thus, CGRP and galanin mRNAs in DRGs, and opioid peptide mRNAs and opioid receptors in the spinal cord were still strongly up-regulated, when animals do not exhibit spontaneous pain behavior and inflammation. Hot-plate test in the presence of naloxone, performed in the remission stage, indicated that opiates participate in pain threshold regulation after prolonged painful condition. Finally, X-ray examination revealed a complete destruction of joint structure, thus suggesting a parallel lesion of peripheral nerve endings. These results suggest that in the remission stage of chronic joint inflammation several types of mechanisms are activated aiming at counteracting both inflammatory and neuropathic pain. Thus, opioid systems in the dorsal horn as well as galanin in DRG neurons are upregulated, both alternating pain.

Dynorphin A (1-13) neurotoxicity in vitro: opioid and non-opioid mechanisms in mouse spinal cord neurons

Dynorphin A is an endogenous opioid peptide that preferentially activates kappa-opioid receptors and is antinociceptive at physiological concentrations. Levels of dynorphin A and a major metabolite, dynorphin A (1-13), increase significantly following spinal cord trauma and reportedly contribute to neurodegeneration associated with secondary injury. Interestingly, both kappa-opioid and N-methyl-D-aspartate (NMDA) receptor antagonists can modulate dynorphin toxicity, suggesting that dynorphin is acting (directly or indirectly) through kappa-opioid and/or NMDA receptor types. Despite these findings, few studies have systematically explored dynorphin toxicity at the cellular level in defined populations of neurons coexpressing kappa-opioid and NMDA receptors. To address this question, we isolated populations of neurons enriched in both kappa-opioid and NMDA receptors from embryonic mouse spinal cord and examined the effects of dynorphin A (1-13) on intracellular calcium concentration ([Ca2+]i) and neuronal survival in vitro. Time-lapse photography was used to repeatedly follow the same neurons before and during experimental treatments. At micromolar concentrations, dynorphin A (1-13) elevated [Ca2+]i and caused a significant loss of neurons. The excitotoxic effects were prevented by MK-801 (Dizocilpine) (10 microM), 2-amino-5-phosphopentanoic acid (100 microM), or 7-chlorokynurenic acid (100 microM)--suggesting that dynorphin A (1-13) was acting (directly or indirectly) through NMDA receptors. In contrast, cotreatment with (-)-naloxone (3 microM), or the more selective kappa-opioid receptor antagonist nor-binaltorphimine (3 microM), exacerbated dynorphin A (1-13)-induced neuronal loss; however, cell losses were not enhanced by the inactive stereoisomer (+)-naloxone (3 microM). Neuronal losses were not seen with exposure to the opioid antagonists alone (10 microM). Thus, opioid receptor blockade significantly increased toxicity, but only in the presence of excitotoxic levels of dynorphin. This provided indirect evidence that dynorphin also stimulates kappa-opioid receptors and suggests that kappa receptor activation may be moderately neuroprotective in the presence of an excitotoxic insult. Our findings suggest that dynorphin A (1-13) can have paradoxical effects on neuronal viability through both opioid and non-opioid (glutamatergic) receptor-mediated actions. Therefore, dynorphin A potentially modulates secondary neurodegeneration in the spinal cord through complex interactions involving multiple receptors and signaling pathways.

Striatal fosB expression is causally linked with l-DOPA-induced abnormal involuntary movements and the associated upregulation of striatal prodynorphin mRNA in a rat model of Parkinson's disease

Rats with unilateral dopamine-denervating lesions sustained a 3-week treatment with a daily l-DOPA dose that is in the therapeutic range for Parkinson's disease. In most of the treated animals, chronic l-DOPA administration gradually induced abnormal involuntary movements affecting cranial, trunk, and limb muscles on the side of the body contralateral to the lesion. This effect was paralleled by an induction of FosB-like immunoreactive proteins in striatal subregions somatotopically related to the types of movements that had been elicited by l-DOPA. The induced proteins showed both regional and cellular colocalization with prodynorphin mRNA. Intrastriatal infusion of fosB antisense inhibited the development of dyskinetic movements that were related to the striatal subregion targeted and produced a local specific downregulation of prodynorphin mRNA. These data provide compelling evidence of a causal role for striatal fosB induction in the development of l-DOPA-induced dyskinesia in the rat and of a positive regulation of prodynorphin gene expression by FosB-related transcription factors.

Disruption of the substance P receptor (neurokinin-1) gene does not prevent upregulation of preprotachykinin-A mRNA in the spinal cord of mice following peripheral inflammation

The neuropeptide substance P is thought to play an important role in nociception, although the function of the peptide remains controversial. Following peripheral inflammation there is a pronounced upregulation of substance P expression both in sensory neurons and in postsynaptic neurons within the spinal cord. We have examined the levels of expression of mRNA encoding substance P and dynorphin following the development of inflammatory hyperalgesia in mice in which the substance P receptor gene, also known as the neurokinin-1 receptor gene, has been disrupted by homologous recombination. We show that inflammatory hyperalgesia following injection of complete Freund's adjuvant develops normally in animals that lack the neurokinin-1 receptor and that expression of mRNAs encoding substance P and the neuropeptide dynorphin are upregulated regardless of the genotype of the mouse. This suggests that substance P activity is not required for the development and maintenance of inflammatory hyperalgesia and that the upregulation of substance P expression is mediated by neurotransmitters other than substance P.

Opioid peptide mRNA expression in the colon of the rat

Since the discovery of opioid peptides, several immunohistochemical and radioimmunological studies have demonstrated their localization in the gastrointestinal tract without demonstrating the localization of their common precursor. The present study describes the distribution and the colocalization of proenkephalin and prodynorphin messenger RNAs (mRNAs) in the colon of rat by in situ hybridization. Proenkephalin and prodynorphin mRNAs were found in myenteric plexus, but not in the submucous plexus or in the mucosa. In myenteric plexus, the number of neurons expressing proenkephalin is 2.5 times greater than that of the neurons expressing only prodynorphin. Furthermore, double in situ hybridization histochemistry indicates that at least three groups of opioid neurons can be distinguished, those containing proenkephalin and prodynorphin mRNAs together, and those containing only proenkephalin mRNA or only prodynorphin mRNA.

Region-specific changes in prodynorphin mRNA and ir-dynorphin A levels after kindled seizures

The opioid peptide dynorphin is thought to be implicated in specific types of seizures. In particular, complex partial seizures have been shown to cause release of dynorphin, activation of prodynorphin gene expression, and new peptide synthesis in the hippocampus. In this study, the kinetics of the seizure-induced changes in prodynorphin mRNA and ir-dynorphin A levels in the hippocampus have been compared with those induced in the temporal and frontal cortex, i.e., in other regions involved in the pathophysiology of complex partial seizures. Experiments have been run using kindling, one of the most valuable models of partial epilepsy. In the hippocampus (1) prodynorphin mRNA levels transiently increase (threefold) 1 h after kindled seizures, and return to baseline by 2 h, and (2) dynorphin A levels are slightly decreased at 1 h, but increase (twofold) at 2 h and return to baseline by 6 h. In the temporal and in the frontal cortex, a late (beginning at 2 h) and prolonged (up to 24 h) decrease in both prodynorphin mRNA and ir-dynorphin A levels have been observed. These data suggest that differential changes in dynorphin metabolism occur in different brain areas after seizures. The mechanisms and functional implications of this observation remain to be investigated.

Dopamine-opiate interaction in the regulation of neostriatal and pallidal neuronal activity as assessed by opioid precursor peptides and glutamate decarboxylase messenger RNA expression

Neostriatal GABAergic neurons projecting to the globus pallidus synthesize the opioid peptide enkephalin, while those innervating the substantia nigra pars reticulata and the entopeduncular nucleus synthesize dynorphin. The differential control exerted by dopamine on the activity of these two efferent projections concerns also the biosynthesis of these opioid peptides. Using in situ hybridization histochemistry, we investigated the role of opioid co-transmission in the regulation of neostriatal and pallidal activity. The expression of the messenger RNAs encoding glutamate decarboxylase-the biosynthetic enzyme of GABA-and the precursor peptides of enkephalin (preproenkephalin) and dynorphin (preprodynorphin) were measured in rats after a sustained blockade of opioid receptors by naloxone (s.c. implanted osmotic minipump, eight days, 3 mg/kg per h), and/or a subchronic blockade of D2 dopamine receptors by haloperidol (one week, 1.25 mg/kg s.c. twice a day). The density of mu opioid receptors in the neostriatum and globus pallidus was determined by autoradiography. Naloxone treatment resulted in a strong up-regulation of neostriatal and pallidal mu opioid receptors that was not affected by the concurrent administration of haloperidol. Haloperidol alone produced a moderate down-regulation of neostriatal and pallidal micro opioid receptors. Haloperidol strongly stimulated the expression of neostriatal preproenkephalin and preprodynorphin messenger RNAs. This effect was partially attenuated by naloxone, which alone produced moderate increases in preproenkephalin and preprodynorphin messenger RNA levels. In the neostriatum, naloxone did not affect either basal or haloperidol-stimulated glutamate decarboxylase messenger RNA expression. A strong reduction of glutamate decarboxylase messenger RNA expression was detected over pallidal neurons following either naloxone or haloperidol treatment, but concurrent administration of the two antagonists did not result in a further decrease. The amplitude of the variations of mu opioid receptor density and of preproenkephalin and preprodynorphin messenger RNA levels suggests that the regulation of neostriatal and pallidal micro opioid receptors is more susceptible to a direct opioid antagonism, while the biosynthesis of opioid peptides in the neostriatum is more dependent on the dopaminergic transmission. The down-regulation of mu opioid receptors following haloperidol represents probably an adaptive change to increased enkephalin biosynthesis and release. The haloperidol-induced increase in neostriatal preprodynorphin messenger RNA expression might result from an indirect, intermittent stimulation of neostriatal D1 receptors. The haloperidol-induced decrease of pallidal glutamate decarboxylase messenger RNA expression suggests, in keeping with the current functional model of the basal ganglia, that the activation of the striatopallidal projection produced by the interruption of neostriatal dopaminergic transmission reduces the GABAergic output of the globus pallidus. The reduction of pallidal glutamate decarboxylase messenger RNA expression following opioid receptor blockade indicates an indirect, excitatory influence of enkephalin upon globus pallidus neurons and, consequently, a functional antagonism between the two neuroactive substances (GABA and enkephalin) of the striatopallidal projection in the control of globus pallidus output. Through this antagonism enkephalin could partly attenuate the GABA-mediated effects of a dopaminergic denervation on pallidal neuronal activity.

The distribution of dynorphinergic terminals in striatal target regions in comparison to the distribution of substance P-containing and enkephalinergic terminals in monkeys and humans

Single- and double-label immunohistochemical techniques using several different highly specific antisera against dynorphin peptides were used to examine the distribution of dynorphinergic terminals in globus pallidus and substantia nigra in rhesus monkeys and humans in comparison to substance P-containing and enkephalinergic terminals in these same regions. Similar results were observed in monkey and human tissue. Dynorphinergic fibers were very abundant in the medial half of the internal pallidal segment, but scarce in the external pallidal segment and the lateral half of the internal pallidal segment. In substantia nigra, dynorphinergic fibers were present in both the pars compacta and reticulata. Labeling of adjacent sections for enkephalin or substance P showed that the dynorphinergic terminals overlapped those for substance P in the medial half of the internal pallidal segment, but showed only slight overlap with enkephalinergic terminals in the external pallidal segment. The substance P-containing fibers were moderately abundant along the borders of the external pallidal segment, and enkephalinergic fibers were moderately abundant in parts of the internal pallidal segment. Dynorphinergic and substance P-containing terminals overlapped extensively in the nigra, and both extensively overlapped enkephalinergic fibers in medial nigra. Immunofluorescence double-labeling studies revealed that dynorphin co-localized extensively with substance P in individual fibers and terminals in the medial half of the internal pallidal segment and in substantia nigra. Thus, as has been found in non-primates, dynorphin within the striatum and its projection systems appears to be extensively localized to substance P-containing striatopallidal and striatonigral projection neurons. Nonetheless, our results also raise the possibility that a population of substance P-containing neurons that projects to the internal pallidal segment and does not contain dynorphin is present in primate striatum. Our results also suggest the possible existence of populations of striatopallidal and striatonigral projection neurons in which substance P and enkephalin or dynorphin and enkephalin, or all three, are co-localized. Thus, striatal projection neurons in primates may not consist of merely two types, one containing substance P and dynorphin and the other enkephalin.

Isolation and characterization of the mouse homolog of the preprodynorphin (Pdyn) gene

We have isolated and sequenced the mouse preprodynorphin gene (Pdyn). The Pdyn gene can encode for six biologically active dynorphin peptides. The predicted mouse preprodynorphin has 90%, 67%, and 66% identity with the predicted rat, porcine, and human preprodynorphins, respectively. Using an RT-PCR technique, we show that the Pdyn gene starts being expressed at embryonic day 12.5, with a steep increase of expression by embryonic day 14.5; in the adult mouse it is expressed in the brain, but not in liver, heart, spleen, or kidney.

Invertebrate opioid precursors: evolutionary conservation and the significance of enzymatic processing

Invertebrate tissues contain mammalian-like proenkephalin, prodynorphin, and proopiomelanocortin. Amino acid sequence determination of these opioid gene products reveals the presence of various opioid peptides exhibiting high sequence identity with their mammalian counterparts. These associated peptides are flanked by dibasic amino acid residues, indicating cleavage sites. Together with the presence of various processing enzymes, i.e., neutral endopeptidase 24.11 and angiotensin-converting enzymes, this suggests that opioid precursor processing is also similar to that described in mammals. It is noted that the levels and/or activity of invertebrate neutral endopeptidase 24.11 can be upregulated by signaling molecules shown to perform the same function in mammals, i.e., morphine. Critical to opioid precursor processing are immunocytes that contain the precursors and transport processing enzymes to sites of inflammation, in part, to cleave these peptide precursors, thus liberating immune-stimulating molecules. Furthermore, in response to lipopolysaccharides, Met-enkephalin levels peak immediately and hours after the exposure, revealing a release and induction process. It appears that the opioid precursors and their processing enzymes first evolved in "simple" animals and the have been maintained and embellished during the course of evolution guided by conformational matching.

Orofacial deep and cutaneous tissue inflammation differentially upregulates preprodynorphin mRNA in the trigeminal and paratrigeminal nuclei of the rat

Preprodynorphin (PPD) and preproenkephalin (PPE) gene expression in a rat model of orofacial inflammation were examined in order to further characterize the neurochemical mechanisms underlying orofacial inflammation and hyperalgesia. Deep and cutaneous orofacial inflammation was produced by a unilateral injection of complete Freund's adjuvant (CFA) into the rat temporomandibular joint (TMJ) or perioral skin (PO), respectively. RNA blot analysis of the tissues including the spinal trigeminal complex revealed that the PPD mRNA level ipsilateral to TMJ inflammation was increased by 56.5+/-14.7% (n=4) when compared to the Naive group, and was significantly greater than the contralateral PPD mRNA level (p<0.05). The distribution of neurons that exhibited PPD mRNA after inflammation was localized by in situ hybridization (naive approximately 0). In TMJ-inflamed rats (n=6) PPD mRNA-positive neurons were found ipsilaterally in the medial portion of laminae I-II of the upper cervical dorsal horn (4.5+/-0.3), the dorsal portion of the subnucleus caudalis and caudal subnucleus interpolaris (5.2+/-0.3), and the paratrigeminal nucleus (6.4+/-1.2). A very localized induction of PPD mRNA was also identified in a group of neurons in the intermediate portion of the subnucleus caudalis (2.4+/-0.4) in PO-inflamed rats (n=6). The distribution of these PPD mRNA-positive neurons was somatotopically relevant to the site of injury. There were no significant changes in PPE mRNA expression in both TMJ- and PO-inflamed rats. These results indicate that TMJ inflammation resulted in a more intense and widespread increase in PPD mRNA expression when compared to PO inflammation. These changes may contribute to persistent central hyperexcitability and pain associated with temporomandibular disorders.

Preprodynorphin-like immunoreactivity in medullary dorsal horn neurons projecting to the thalamic regions in the rat

Preprodynorphin (PPD)-like immunoreactive (-LI) neuronal cell bodies in the trigeminal sensory nuclear complex of the rat were found in laminae I and II of the medullary dorsal horn (MDH; caudal spinal trigeminal nucleus) and the paratrigeminal nucleus. A PPD immunofluorescence histochemistry combined with a fluorescence retrograde tract-tracing method revealed that some of the PPD-LI neurons in the MDH and paratrigeminal nucleus projected to the thalamic regions. Nociceptive nature of the PPD-LI MDH neurons projecting to the thalamic regions was also demonstrated by a triple labeling method, using the technique of the noxious stimulus-evoked expression of the immediate-early gene, c-fos. In the rats which were subcutaneously injected with formalin into the upper and lower lips, c-fos protein (Fos) was found in PPD-LI neurons which were labeled with a retrograde tracer injected into the thalamic regions.

Prodynorphin and proenkephalin mRNAs are increased in rat brain after acute and chronic administration of gamma-hydroxybutyrate

The effects of gamma-hydroxybutyrate (GHB) on prodynorphin (PD) and proenkephalin (PE) mRNA expression were examined using in situ hybridization histochemistry in discrete rat brain structures rich in GHB receptors. A single dose of GHB (500 mg/kg i.p.) increased striatal PE mRNA levels (+60%) between 15 and 90 min after injection. An increase in PD mRNA expression was observed in the frontal cortex (+90%) 6 h after GHB administration. Chronic exposure to GHB (500 mg/kg i.p. twice a day) for 10 days induced significant increases in both PE and PD mRNA levels in different brain regions examined, suggesting that PD and PE mRNA expressions are modulated by the endogenous GHBergic system.

Molecular evolution of the opioid/orphanin gene family

Gene duplication is a recurring theme in the evolution of vertebrate polypeptide hormones and neuropeptides. These duplication events can lead to the formation of gene families in which divergence of function is the usual outcome. In the case of the opioid/orphanin family of genes, duplication events have proceeded along two paths: (a) an apparent duplication of function as seen in the analgesic activity of Proenkephalin and Prodynorphin end-products; and (b) divergence of function as seen in the nociceptic activity of Proorphanin end-products or the melanocortin (color change and chronic stress regulation) activity of Proopiomelanocortin end-products. Although genes coding for Proopiomelanocortin, Proenkephalin, Prodynorphin, and Proorphanin have been extensively studied in mammals, the distribution and radiation of these genes in nonmammalian vertebrates is less well understood. This review will present the hypothesis that the radiation of the opioid/orphanin gene family is the result of the duplication and divergence of the Proenkephalin gene during the radiation of the chordates. To evaluate the Proenkephalin gene duplication hypothesis, a 3'RACE procedure was used to screen for the presence of Prodynorphin-related, Proenkephalin-related, and Proorphanin-related cDNAs expressed in the brains of nonmammalian vertebrates.

Effect of repeated L-DOPA, bromocriptine, or lisuride administration on preproenkephalin-A and preproenkephalin-B mRNA levels in the striatum of the 6-hydroxydopamine-lesioned rat

Abnormal involuntary movements, or dyskinesias, plague current symptomatic approaches to the treatment of Parkinson's disease. The neural mechanisms underlying the generation of dyskinesia following repeated l-3,4-dihydroxyphenylalanine (L-DOPA) or dopamine agonist administration in Parkinson's disease remain unknown. However, de novo administration of bromocriptine or lisuride to either l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned primates or patients can alleviate parkinsonian symptoms without the development of dyskinesia. In this study, we have investigated behavioral responses and alterations in the expression of opioid neuropeptide precursors preproenkephalin-A (PPE-A, encoding methionine- and leucine-enkephalin) and preproenkephalin-B (PPE-B), the precursor encoding dynorphins (dynorphin A1-17 and B1-13, leucine-enkephalin, and alpha-neoendorphin) in striatal output pathways of the 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease. Expression was assessed following repeated L-DOPA, bromocriptine, or lisuride administration. Given the functional organization of basal ganglia circuitry into anatomically discrete parallel circuits, we investigated alterations in peptide expression with reference to the detailed topography of the striatum. Following repeated L-DOPA administration (6.5 mg/kg, b.d., 21 days) in the 6-OHDA-lesioned rat a rotational response was observed. This became markedly enhanced with repeated treatment. We have previously characterized the pharmacology of this enhanced response and have suggested that it is a useful model for the elucidation of the cellular and molecular mechanisms underlying L-DOPA- and dopamine agonist-induced dyskinesia. In contrast to l-DOPA, de novo administration of bromocriptine (1 or 5 mg/kg, b.d., 21 days) or lisuride (0.01 or 0.1 mg/kg, b.d., 21 days) did not lead to an enhanced behavioral response. In vehicle-treated, 6-OHDA-lesioned animals, PPE-A expression was elevated rostrally and dorsally, while PPE-B expression was reduced in the striatum at all rostrocaudal levels. Repeated l-DOPA administration was accompanied by elevations in striatal PPE-B mRNA levels and a further elevation, above lesion-induced levels, in PPE-A expression. This further elevation was restricted to the dorsolateral striatum. However, following repeated bromocriptine or lisuride administration no increase in PPE-B expression was observed and the lesion-induced increase in PPE-A expression was normalized to prelesion levels. Increased PPE-A and PPE-B levels may, through decreasing GABA and glutamate release, respectively, in output nuclei of the basal ganglia, play a role in the development of L-DOPA- and dopamine-agonist induced dyskinesia in Parkinson's disease. These studies suggest that anti-parkinsonian treatments which are not associated with an elevation in PPE-B and/or normalize elevated PPE-A precursor expression, such as NMDA-receptor antagonists or long-acting dopamine D2 receptor agonists, e.g., cabergoline or ropinirole, may reduce dyskinesia in Parkinson's disease.

Methamphetamine alters prodynorphin gene expression and dynorphin A levels in rat hypothalamus

Chronic administration of morphine or cocaine affects opioid gene expression. To better understand the possible existence of common neuronal pathways shared by different classes of drugs of abuse, we studied the effects of methamphetamine on the gene expression of the opioid precursor prodynorphin and on the levels of peptide dynorphin A in the rat brain. Acute (6 mg/kg, intraperitoneally, i.p.) and chronic (6 mg/kg, i.p. for 15 days) methamphetamine markedly raised prodynorphin mRNA levels in the hypothalamus, whereas no effect was observed in the hippocampus. Dynorphin A levels increased after chronic treatment in the hypothalamus and in the striatum, whereas no significant changes were detected after acute treatment. These results indicate that methamphetamine affects prodynorphin gene expression in the hypothalamus, which may be an important site (also for its relevant neuroendocrine correlates) for opioidergic mechanisms activated by addictive drugs.

Interaction between anterior pituitary prodynorphin and the secretion of luteinizing hormone (LH)

The purpose of present research was to investigate the possible involvement of prodynorphin (proDYN)-derived peptides acting locally within the anterior pituitary (AP) on the effects of estradiol-17 beta (E2) and gonadotropin-releasing hormone (GnRH) on the release of luteinizing hormone (LH). Exposure of bovine AP cells in primary suspension cultures to E2 increased (P < 0.05) the spontaneous release of proDYN-derived peptides and also augmented (P < 0.05) the GnRH-induced release of LH. Both of these E2-induced responses required either high E2 dosages or prolonged exposure to produce significant changes, but there were a few cases in which the association between E2-induced changes in both parameters was absent. Therefore, it seems unlikely that proDYN-derived AP peptides mediate the effects of E2 on GnRH-induced LH release. Using another approach, cultured cells were exposed for 48 h to an antisense oligodeoxynucleotide (oligo) targeted against the translation initiation site of bovine proDYN. Compared with the two control treatments (scrambled oligo sequence or no oligo treatment), the antisense treatment decreased (P < 0.05) the quantity of LH released in response to challenge of the cells with 5 nM GnRH. There were no concurrent changes in cellular contents of proDYN-derived peptides or mRNA for LH-beta, but the antisense treatment tended to decrease (P < 0.10) the relative abundance of proDYN mRNA. In summary, proDYN-derived peptides probably do not mediate direct intrapituitary effects of E2 on LH, but the antisense treatment interfered in an unknown way with GnRH-induced release of LH from cultured AP cells.

Intrastriatal grafting of a GDNF-producing cell line protects striatonigral neurons from quinolinic acid excitotoxicity in vivo

Glial cell line-derived neurotrophic factor (GDNF) is a neurotrophic factor with a therapeutic potential in neurodegenerative disorders. GDNF is expressed in the adult striatum, but its signalling tyrosine kinase receptor, c-ret, has not been detected in this structure by in situ hybridization. In the present work, we first examined c-ret and GDNF receptor alpha 1 (GFR-alpha 1) expression using an RNAse protection assay, and found that both receptors are expressed in the adult rat striatum. We then examined whether GDNF was able to regulate the phenotype and/or prevent the degeneration of striatal projection neurons in a well-characterized model of excitotoxic damage. A fibroblast cell line, engineered to overexpress GDNF, was grafted in adult rats striatum 24 h before quinolinic acid (QUIN) injection. QUIN injection alone or in combination with the control cell line induced a loss of glutamic acid decarboxylase 67 (GAD)-, preprotachykinin A (PPTA)-, prodynorphin (DYN)- and preproenkephalin (PPE)-positive neurons. GDNF selectively prevented: (i) the loss of a subpopulation of striatonigral neurons expressing GAD and PPTA; (ii) the atrophy of PPTA-positive neurons; and (iii) the decrease in GAD, PPTA and DYN mRNA expression, after QUIN injection. Moreover, in unlesioned animals, GDNF increased the size of PPTA-positive neurons and up-regulated their mRNA levels. In contrast, GDNF showed no effect in intact or lesioned striatopallidal PPE-positive neurons. Thus, our findings show that GDNF selectively regulates the phenotype and protects striatonigral neurons from QUIN-induced excitotoxicity, suggesting that GDNF may be used for the treatment of striatonigral degenerative disorders, e.g. Huntington's disease and multiple system atrophy.

Descending modulation of opioid-containing nociceptive neurons in rats with peripheral inflammation and hyperalgesia

Inflammation and hyperalgesia induce a dramatic up-regulation of opioid messenger RNA and peptide levels in nociceptive neurons of the spinal dorsal horn. Descending axons modulate nociceptive transmission at the spinal level during inflammatory pain, and may play a role in the development of persistent pain. The role of descending bulbospinal pathways in opioid-containing nociceptive neurons was examined. Removal of descending inputs to the spinal cord was performed by complete spinal transection at the midthoracic level. Seven days after spinal transection, rats received a unilateral hindpaw injection of complete Freund's adjuvant, a noxious stimulus that produces inflammation and hyperalgesia. Tissues from the L4 and L5 segments of the spinal cord were removed and analysed by northern blotting and immunocytochemistry. Spinal transection resulted in a further increase in both dynorphin and enkephalin messenger RNA content following complete Freund's adjuvant injection. There was a similar distribution and number of dynorphin-immunoreactive cells in transected rats compared to rats which received sham surgery. These data suggest that increased dynorphin messenger RNA ipsilateral to inflammation, in rats without descending axons, was due to increased expression within the same cells and not to recruitment of additional dynorphin-expressing cells. This reflects a greater dynamic response of nociceptive neurons to noxious stimuli in the absence of descending modulation. Therefore, the net effect of descending afferents on spinal nociceptive circuits may be to reduce the response of opioid-containing neurons to noxious stimulation from the periphery.

Targeted expression of a toxin gene to D1 dopamine receptor neurons by cre-mediated site-specific recombination

Idiopathic Parkinson's disease involves the loss of midbrain dopaminergic neurons, resulting in the presynaptic breakdown of dopaminergic transmission in the striatum. Huntington's disease and some neurodegenerative diseases with Parkinsonian features have postsynaptic defects caused by striatal cell death. Mice were generated in which an attenuated form of the diphtheria toxin gene (tox-176) was expressed exclusively in D1 dopamine receptor (D1R)-positive cells with the aim of determining the effect of this mutation on development of the basal ganglia and on the locomotor phenotype. Transgenic mice expressing Cre, a site-specific DNA recombinase, were crossed with a second line in which a transcriptionally silenced tox-176 gene was inserted into the D1R gene locus by homologous recombination. Young doubly transgenic mutant mice expressing the tox-176 gene displayed bradykinesia, dystonia, and had falls caused by myoclonic jerks. The mutant brain had evidence of apoptosis and reactive gliosis and, consistent with the D1R expression pattern, the striatum was reduced in volume, and the Islands of Calleja were absent. In contrast, the cortex was of normal thickness. D1Rs were not detectable in mutants by in situ hybridization or ligand autoradiography, whereas D2 dopamine receptor (D2R) mRNA and protein was present in the striatum. In addition, substance P and dynorphin, neuropeptides known to be expressed in D1R-positive striatonigral projection neurons were not detectable. Enkephalin, a marker found in D2-positive striatopallidal projection neurons was expressed in the mutant brain. The mutant represents a novel neurodegenerative disease model with a dramatic extrapyramidal phenotype.

Targeted expression of a toxin gene to D1 dopamine receptor neurons by cre-mediated site-specific recombination

Idiopathic Parkinson's disease involves the loss of midbrain dopaminergic neurons, resulting in the presynaptic breakdown of dopaminergic transmission in the striatum. Huntington's disease and some neurodegenerative diseases with Parkinsonian features have postsynaptic defects caused by striatal cell death. Mice were generated in which an attenuated form of the diphtheria toxin gene (tox-176) was expressed exclusively in D1 dopamine receptor (D1R)-positive cells with the aim of determining the effect of this mutation on development of the basal ganglia and on the locomotor phenotype. Transgenic mice expressing Cre, a site-specific DNA recombinase, were crossed with a second line in which a transcriptionally silenced tox-176 gene was inserted into the D1R gene locus by homologous recombination. Young doubly transgenic mutant mice expressing the tox-176 gene displayed bradykinesia, dystonia, and had falls caused by myoclonic jerks. The mutant brain had evidence of apoptosis and reactive gliosis and, consistent with the D1R expression pattern, the striatum was reduced in volume, and the Islands of Calleja were absent. In contrast, the cortex was of normal thickness. D1Rs were not detectable in mutants by in situ hybridization or ligand autoradiography, whereas D2 dopamine receptor (D2R) mRNA and protein was present in the striatum. In addition, substance P and dynorphin, neuropeptides known to be expressed in D1R-positive striatonigral projection neurons were not detectable. Enkephalin, a marker found in D2-positive striatopallidal projection neurons was expressed in the mutant brain. The mutant represents a novel neurodegenerative disease model with a dramatic extrapyramidal phenotype.

Effects of halothane, ketamine and nitrous oxide on dynorphin mRNA expression in dorsal horn neurons after peripheral tissue injury

Peripheral tissue injury is known to induce changes in gene expression in spinal neurons and result in a prolonged alteration of neuronal excitability. The purpose of this study was to examine the effect of halothane on the dynorphin mRNA expression in spinal dorsal horn neurons after peripheral tissue injury by formalin injection and compare the effect to that of ketamine and nitrous oxide. Male Sprague-Dawley rats were anesthetized with 1.3% halothane, ketamine, or 67% nitrous oxide. Fifteen minutes after induction of anesthesia, rats received an intraplantar injection of 150 microliter 5% formalin into the unilateral hindpaw. General anesthesia was maintained for 8 h, and the expression of preprodynorphin (PPD) and preproenkephalin (PPE) mRNAs in the spinal cord (L4-5) was examined by in situ hybridization. The degree of edema of the inflamed foot was not different among the three anesthesia groups and the control (no anesthesia) group. The number of neurons expressing PPD mRNA dramatically increased in the superficial dorsal horn ipsilateral to the formalin injection in the control group compared to the contralateral side. The number of neurons labeled for PPD mRNA in the halothane group was significantly less than the control group. However, the number of PPD mRNA-expressing neurons in both the ketamine and nitrous oxide groups was significantly less than the halothane group. The expression of PPE mRNA was not influenced by these anesthetics. These data indicate that the suppressive effect of halothane anesthesia on the induction of PPD mRNA in dorsal horn neurons was smaller than those of ketamine and nitrous oxide, suggesting an important supplemental way to control the alteration of gene expression in spinal neurons for clinical settings.

Perinatal cocaine decreases the expression of prodynorphin mRNA in nucleus accumbens shell in the adult rat

Preprodynorphin mRNA expression in the striatal-olfactory tubercle complex was studied in adult rats exposed to cocaine (50 mg/kg) during postnatal days (PnD) 11-20. While multiple regions of the striatum and olfactory tubercle were examined, alterations were only found in the nucleus accumbens. A 50% and 20% reduction in expression within the shell region was observed at 1.2 and 1.7 mm rostral to Bregma respectively. While the core regions at these levels were unaffected, the rostral accumbens showed a trend toward an increase in expression in the cocaine-treated rats. These findings, in combination with other behavioral and neurochemical data collected on similarly treated rats, suggest that perinatal cocaine produces a long-term dampening of function in a specific population of neurons within the mesolimbic system

Priming with L-DOPA differently affects dynorphin and substance P mRNA levels in the striatum of 6-hydroxydopamine-lesioned rats after challenge with dopamine D1-receptor agonist

In unilaterally 6-hydroxydopamine-lesioned rats, potentiation of D1-agonist-induced turning behavior by priming with l-DOPA was correlated with changes in striatal neuropeptide mRNA levels. In non-primed rats, administration of the D1-agonist SKF-38393 markedly increased dynorphin and substance P mRNA levels in the lesioned striatum. Priming with l-DOPA dissociated the response of the two neuropeptides to the D1-agonist, with higher dynorphin and reduced substance P mRNA levels.

Increased striatal proenkephalin mRNA subsequent to production of spreading depression in rat cerebral cortex: activation of corticostriatal pathways?

Cortical Spreading Depression (CSD) is a slowly propagating wave of depolarization and negative interstitial DC potential, that when induced in the rat brain extends across the entire homolateral hemisphere. Despite evidence that CSD does not penetrate into subcortical regions, neurochemical changes in areas anatomically connected to cortex have been reported. In this study in situ hybridization histochemistry was used to examine the levels of cholecystokinin (CCK), proenkephalin (ENK) and prodynorphin (DYN) mRNA in cortex and forebrain basal ganglia following KCl-induced CSD. Unilateral CSD was induced by topical application of 3 M KCl ( approximately 10 microliter) onto the right parietal cortex for 10 min and rats were then killed 1-6 h and 1-28 days later. CCK mRNA levels were increased (P<0.01) in the ipsilateral neocortex 3 h after CSD (13% above levels in contralateral side), reached a peak at 2 days ( approximately 70%) and were still elevated at 7 (30%) but not, 14 or 28 days later. Unilateral CSD also produced a rapid and sustained increase (P<0.05) in ENK mRNA in ipsilateral piriform cortex (from 3 h to 2 days; 70-250% above contralateral), and a delayed increase in caudate putamen and olfactory tubercle at 1 and 2 days ( approximately 25% in both regions), but levels were again equivalent to control at 7 days and beyond. In contrast, no marked changes in neocortical ENK mRNA, or DYN mRNA in both cortex and basal ganglia, were observed under these conditions. These findings demonstrate that CSD has specific, rapid and long-lasting effects on neuropeptide expression in neocortex and subcortical areas. CSD-induced changes in mesostriatal ENK mRNA are proposed to reflect synaptic activation of local neurons via cortical afferent projections.

Trimethyltin intoxication induces marked changes in neuropeptide expression in the rat hippocampus

In situ hybridization and immunocytochemistry were applied to investigate changes in the expression of somatostatin, neuropeptide Y, neurokinin B, cholecystokinin, dynorphin, and Met-enkephalin in the rat hippocampus after administration of a single peroral dose of trimethyltin hydroxide (9 mg/kg). Two time intervals were investigated: 5 days after trimethyltin treatment, when CA3 damage becomes manifest and is associated with increased aggression, seizure susceptibility, and memory deficit, and 16 days after trimethyltin, when neuronal damage is almost maximal and seizure susceptibility is declining. Robust but transient increases of neuropeptide Y, neurokinin B, and Met-enkephalin mRNA levels were revealed in the granule cell layer of the dentate gyrus and increased neuropeptide Y and neurokinin B immunoreactivities were found in mossy fibers. In reverse, dynorphin mRNA and immunoreactivity were decreased transiently in the dentate gyrus and mossy fibers, respectively. Strong over-expression of NPY mRNA was also observed in hilar interneurons and in CA1 and CA3 pyramidal cells as well as in the cortex at 5 days postdosing. Cholecystokinin- or neurokinin B-containing basket cells were preserved, while somatostatin-bearing interneurons were damaged by trimethyltin exposure. These neurochemical changes induced by trimethyltin intoxication strikingly parallel to those observed in animal models of temporal lobe epilepsy and may reflect activation of endogenous protective mechanisms. It is also suggested that hilar interneurons respond differently to trimethyltin exposure, for which neuropeptides are valuable markers.

Dynorphin mRNA expression in dorsal horn neurons after traumatic spinal cord injury: temporal and spatial analysis using in situ hybridization

Dynorphin, an endogenous opioid, may contribute to secondary nervous tissue damage following spinal cord injury. The temporal and spatial distribution of preprodynorphin (PPD) mRNA expression in the injured rat spinal cord was examined by in situ hybridization. Rats were subjected to traumatic spinal cord injury at the T13 spinal segment using the weight-drop method. Motor function of these rats was evaluated by their ability to maintain their position on an inclined plane. Two double-labeling experiments revealed that increased PPD mRNA and dynorphin peptide expression were found exclusively in dorsal horn neurons. Neurons exhibiting an increase in the level of PPD mRNA were concentrated in the superficial laminae and the neck of dorsal horn within several spinal segments from the epicenter of the injury at 24 and 48 h after injury. A number of neurons showing increased PPD mRNA were found in gray matter adjacent to the injury areas. Segments caudal to the injury site exhibited a long-lasting elevation of PPD mRNA in neurons, compared to the rostral segments. The number of neurons expressing PPD mRNA in each rat was significantly positively correlated with its motor dysfunction. These findings suggest that increased expression of dynorphin mRNA and peptide in dorsal horn neurons occurs after traumatic spinal cord injury. This also supports the hypothesis that the dynorphin has a pathological role in secondary tissue damage and neurological dysfunction after spinal cord injury.

Specific reductions of striatal prodynorphin and D1 dopamine receptor messenger RNAs during cocaine abstinence

It is well established that the opioid neuropeptide and dopamine systems are altered following the use of cocaine. However very little information is available about their possible involvement during cocaine abstinence. In the present study, the mRNA expression of the dopamine receptors, D1 and D2, and the opioid peptides, prodynorphin and proenkephalin, were analyzed in the rat striatum using in situ hybridization histochemistry. Saline or cocaine (30 mg/kg, i.p.) were administered to rats once daily for 1 or 10 days. To examine cocaine abstinence, animals were treated for 10 days as described followed by a 10-day drug free period. Acute and intermittent cocaine administration elevated the prodynorphin mRNA expression in the dorsal striatum, consistent with previous reports, while the abstinent phase resulted in a significant reduction of prodynorphin mRNA levels in the ventrorostral striatum. The D1-receptor mRNA was decreased in the caudorostral striatum during cocaine withdrawal, a finding opposite to the increase observed following a single injection of the drug. Proenkephalin and the D2-receptor mRNAs were not altered during cocaine abstinence, though proenkephalin was elevated following acute but not repeated cocaine administration. These results show long-term suppression on prodynorphin and D1-receptor systems in specific striatal populations localized mainly in rostral areas during withdrawal from cocaine.

The modulatory role of nitric oxide in the regulation of proenkephalin and prodynorphin gene expressions induced by kainic acid in rat hippocampus

The effect of L-arginine (L-ARG), a nitric oxide donor, or Nomega-nitro-L-arginine (L-NAME), a nitric oxide synthase inhibitor, on the regulation of kainic acid (KA)-induced proenkephalin (proENK) and prodynorphin (proDYN) mRNA expressions in rat hippocampus was studied. The proENK and proDYN mRNA levels were markedly increased 6 h after KA (10 mg/kg, i.p.) administration. The elevations of both proENK and proDYN mRNA levels induced by KA was effectively inhibited by pre-administration of L-ARG (400 mg/kg, i.p.), but was not affected by pre-treatment with L-NAME (200 mg/kg, i.p.). The blockade of KA-induced proENK and proDYN mRNA levels by the pre-treatment with L-ARG was well correlated with proto-oncoprotein levels, such as c-Fos, Fra-2, FosB, JunD, JunB, and c-Jun, as well as AP-1 and ENKCRE-2 DNA binding activities. The pre-administration with L-NAME further increased KA-induced c-jun and c-fos mRNA levels in addition to their protein product levels, although the pre-treatment with L-NAME did not affect KA-induced FosB, Fra-2, JunB, and JunD protein levels at 6 h after treatment. In addition, the pre-administration with L-NAME further increased the KA-induced AP-1 and ENKCRE-2 DNA binding activities. Our results suggest that L-ARG plays an important role in inhibiting KA-induced proENK or proDYN mRNA expression, and its inhibitory action may be mediated through reducing the proto-oncoprotein levels, such as c-Fos, Fra-2, FosB, c-Jun, JunD, and JunB. In addition, L-NAME potentiated the c-Fos or c-Jun gene expression, as well as AP-1 or ENKCRE-2 DNA binding activity. However, these increases did not show the potentiative effect on KA-induced increases of proENK and proDYN mRNA level.

Effects of risperidone and haloperidol on tachykinin and opioid precursor peptide mRNA levels in the caudate-putamen and nucleus accumbens of the rat

We investigated whether the two output pathways of the striatum are differently affected by the novel atypical drug risperidone and the conventional typical antipsychotic drug haloperidol. To this end, changes in mRNA levels of preproenkephalin-A, preproenkephalin-B, and preprotachykinin were determined in the rat striatum following chronic drug treatment for 14 days, using quantitative in situ hybridization. Furthermore, we studied the contribution of the dopamine D2 and serotonin 5-HT2A antagonist components of risperidone in establishing its effects on neuropeptide mRNA levels in the striatum. The results showed that both risperidone and haloperidol had major effects on the preproenkephalin-A mRNA and thus on the indirect striatal output route, whereas they had minor effects on preproenkephalin-B and preprotachykinin mRNA, contained by the direct output route. When both drugs were administered in the same dose, preproenkephalin-A mRNA was much more elevated by haloperidol than by risperidone. However, when doses of risperidone and haloperidol were modified to attain comparable dopamine D2 receptor occupancy, the drugs had comparable effects on preproenkephalin-A mRNA levels. It was further found that 5-HT2A/C receptor blockade with ritanserin had only modest effects on preproenkephalin-B and preprotachykinin mRNA levels and did not affect preproenkephalin-A mRNA levels. We conclude that risperidone and haloperidol, administered in the same dose, differently affect the striatal output routes. Furthermore, the results suggest that the effects of risperidone on neuropeptide mRNA levels are fully accounted for by its D2 antagonism and that no indication exists for a role of 5-HT2A receptor blockade in this action.

Hippocampal plasticity involves extensive gene induction and multiple cellular mechanisms

Long-term plasticity of the central nervous system (CNS) involves induction of a set of genes whose identity is incompletely characterized. To identify candidate plasticity-related genes (CPGs), we conducted an exhaustive screen for genes that undergo induction or downregulation in the hippocampus dentate gyrus (DG) following animal treatment with the potent glutamate analog, kainate. The screen yielded 362 upregulated CPGs and 41 downregulated transcripts (dCPGs). Of these, 66 CPGs and 5 dCPGs are known genes that encode for a variety of signal transduction proteins, transcription factors, and structural proteins. Seven novel CPGs predict the following putative functions: cpg2--a dystrophin-like cytoskeletal protein; cpg4--a heat-shock protein: cpg16--a protein kinase; cpg20--a transcription factor; cpg21--a dual-specificity MAP-kinase phosphatase; and cpg30 and cpg38--two new seven-transmembrane domain receptors. Experiments performed in vitro and with cultured hippocampal cells confirmed the ability of the cpg-21 product to inactivate the MAP-kinase. To test relevance to neural plasticity, 66 CPGs were tested for induction by stimuli producing long-term potentiation (LTP). Approximately one-fourth of the genes examined were upregulated by LTP. These results indicate that an extensive genetic response is induced in mammalian brain after glutamate receptor activation, and imply that a significant proportion of this activity is coinduced by LTP. Based on the identified CPGs, it is conceivable that multiple cellular mechanisms underlie long-term plasticity of the nervous system.

Topographical organization of opioid peptide precursor gene expression following repeated apomorphine treatment in the 6-hydroxydopamine-lesioned rat

Many studies have previously described changes in preproenkephalin-A (PPE-A) and preproenkephalin-B (PPE-B) gene expression in the striatum of the 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (both with or without dopamine replacement treatment). To date, these studies have either taken the striatum as a whole or have focused on a single subregion of the striatum. However, the striatum is organized into anatomically discrete parallel circuits serving different functions (motor, associative, and limbic). We have therefore employed in situ hybridization to examine the detailed topography of changes in opioid precursor expression following dopamine depletion and subsequent treatment with apomorphine (5 mg/kg twice daily for 10 days). In the untreated 6-OHDA-lesioned striatum PPE-A expression was elevated only in the dorsal (sensorimotor) caudate-putamen. Following apomorphine treatment PPE-A mRNA levels were further raised in the sensorimotor striatum (</=77%) and approximately doubled and tripled in the ventral caudate-putamen (associative) and nucleus accumbens (limbic), respectively. These subsequent elevations were mostly restricted to rostral portions of the striatum. Although unchanged following vehicle treatment, PPE-B gene expression in the lesioned caudate-putamen (sensorimotor and associative) was elevated some 30-fold by apomorphine treatment. A smaller rise (fivefold) was seen in rostral regions of the lesioned nucleus accumbens. Thus, differential regulation of opioid peptide transmission exists in motor, limbic, and associative regions of the striatum and may contribute to the generation of motor and cognitive disturbances following long-term treatment of the dopamine-depleted striatum.

Peptide plasticity in primary sensory neurons and spinal cord during adjuvant-induced arthritis in the rat: an immunocytochemical and in situ hybridization study

Chronic polyarthritis due to complete Freund's adjuvant injection is characterized by severe inflammation and pain. In the present immunocytochemical and in situ hybridization study on the rat, we quantitatively investigated peptide and peptide messenger RNA expression in the sensory circuit at the spinal level, i.e. sensory neurons in the dorsal root ganglia and in nerve endings and local neurons in the dorsal horn of the spinal cord. The immunocytochemical experiments were carried out five, 13 and 21 days after complete Freund's adjuvant injection, whereas in situ hybridization study was performed after 21 days from complete Freund's adjuvant injection. The main results in the present study are the following: (i) a decrease in substance P-, calcitonin gene-related peptide- and galanin-like immunoreactivities in dorsal root ganglia is observed five days after complete Freund's adjuvant injection, with recovery (calcitonin gene-related peptide and galanin) or even an increase (substance P) after 21 days; (ii) calcitonin gene-related peptide, substance P and galanin peptide levels are increased in dorsal root ganglia after 21 days; (iii) opioid peptide (enkephalin and dynorphin), substance P and galanin messenger RNAs are strongly up-regulated in dorsal horn neurons after 21 days; (iv) neuropeptide Y content increases in dorsal root fibres and neuropeptide Y messenger RNA levels decrease in spinal neurons after 21 days; and (v) a dramatic decrease in calcitonin gene-related peptide and cholecystokinin messenger RNA levels is found in motoneurons in the ventral horn after 21 days. These data indicate that peptide expression in dorsal root ganglia and the spinal cord is markedly influenced by severe inflammation with distinct and individual temporal patterns, which are also related to the severe rearrangement of joint structure during polyarthritis. The increase in galanin levels in dorsal root ganglia 21 days after complete Freund's adjuvant injection can be related to the structural damage of nerve fibres. Thus, there may be a transition from inflammatory to neuropathic pain, which could have consequences for treatment of patients with rheumatoid arthritis.

Evidence for Fos involvement in the regulation of proenkephalin and prodynorphin gene expression in the rat hippocampus

For a long time Fos has been proposed to play some role in regulation of the proenkephalin (PENK) and prodynorphin (PDYN) gene expression. In recent years, however, evidence has accumulated that the transcription of both genes in several brain regions in vivo is transactivated by the transcription factor CREB rather than by Fos. In the present study, involvement of Fos in the mechanism of the PENK and PDYN gene induction in the hippocampal dentate gyrus during seizures elicited by kainic acid was studied using a knock-down technique. Pretreatment with an antisense oligonucleotide complementary to c-fos mRNA did not influence the kainic acid-elicited convulsions. It inhibited, by about 50%, the induction of Fos protein in the dentate gyrus during seizures. The subsequent induction of PENK and PDYN mRNAs was reduced by more than 60% by the c-fos antisense oligonucleotide, while constitutive expression of three other genes (alpha-tubulin, NMDA receptor-1, and GS protein alpha-subunit) was not affected. The obtained results support the view that Fos may be involved in regulation of the PENK and PDYN gene expression in the dentate gyrus during seizures, which further suggests that the mechanisms triggering the up-regulation of both these genes in the dentate gyrus may differ from these working in other brain regions, such as the striatum and hypothalamus.

Serotonergic regulation of neuropeptide and glutamic acid decarboxylase mRNA levels in the rat striatum and globus pallidus: studies with fluoxetine and DOI

The serotonergic regulation of neuropeptide and glutamic acid decarboxylase (GAD) mRNA level in the rat basal ganglia was investigated by determining the effects of chronic treatment with the serotonin uptake blocker fluoxetine and the serotonin 5-HT2 agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrobromide (DOI). Fluoxetine (10 mg/kg) induced a reduction of preproenkephalin and GAD65 mRNA levels in the caudate-putamen and nucleus accumbens core and shell after 5 days of treatment. In addition, GAD65 mRNA levels were reduced in the globus pallidus. These changes appeared to be transient as they were not found after 15 days of fluoxetine treatment. DOI (7 mg/kg), administered for 9 days, induced a decrease of preprodynorphin mRNA levels in the caudate-putamen and the nucleus accumbens core and shell. No regional differentiation in the effects of fluoxetine and DOI was observed. Based on the present results, we propose that an increased 5-HT tone may reduce enkephalin and GABA mRNA levels in striatal regions and in the globus pallidus. Our results further show that preproenkephalin mRNA is not affected by chronic 5-HT2 receptor stimulation, indicating that the fluoxetine-induced decrease in preproenkephalin mRNA levels involves other 5-HT receptors than the 5-HT2 receptor. Preprodynorphin mRNA levels, on the other hand, were found to be reduced after chronic 5-HT2 receptors than stimulation. This observation, together with our previous finding that the 5-HT2 antagonist ritanserin tends to increase preprodynorphin mRNA levels, suggests a 5-HT2-mediated tonic inhibition of preprodynorphin mRNA levels.

Repeated administration of cocaine, nicotine and ethanol: effects on preprodynorphin, preprotachykinin A and preproenkephalin mRNA expression in the dorsal and the ventral striatum of the rat

It is established that dopamine (DA) controls the expression of preprodynorphin (PPDYN), preprotachykinin A (PPT-A) and preproenkephalin (PPE) mRNAs in striatal structures. Since cocaine, nicotine and ethanol enhance extracellular DA concentration, we have examined whether their repeated administration produced common changes in the expression of these mRNAs. Quantitative in situ hybridization histochemistry was performed in rats 2 h after a final challenge subsequent to repeated subcutaneous injections (3 X a day) of cocaine (12.5 mg/kg), nicotine (0.4 mg/kg) for 14 days and ethanol (160 mg/kg) for 7 days. In the dorsal striatum, cocaine produced simultaneous PPDYN and PPT-A mRNA increases without PPE mRNA change whereas nicotine and ethanol produced no modification. After cocaine, PPDYN mRNA was preferentially increased in striatal patch compartment. In the nucleus accumbens, the effects were more complex. In cocaine-treated rats, we measured concomitant increases of PPDYN and PPE mRNA in the rostral pole, an isolated induction of PPT-A mRNA signals in the core without any change in the two shell subregions: the cone and the ventral shell. In contrast, after nicotine and ethanol, the ventral shell was the only accumbal subregion which showed a neuropeptide mRNA alteration, nicotine leading to decreased PPDYN mRNA and ethanol to increased PPT-A mRNA contents. The neuropeptide regulation after chronic treatment with these psychostimulant drugs does not strictly conform to a general DA control scheme in the dorsal and the ventral striatum. The cocaine effects can be clearly distinguished from those of nicotine and ethanol in terms of neuropeptide regulation and striatal subregions affected.

Pre-emptive intrathecal Mk-801, a non-competitive N-methyl-D-aspartate receptor antagonist, inhibits the up-regulation of spinal dynorphin mRNA and hyperalgesia in a rat model of chronic inflammation

The effects of N-methyl-D-aspartate(NMDA) receptor antagonist, Mk-801, on the expression of spinal dynorphin (DYN) mRNA and the hyperalgesia induced by peripheral inflammation were studied by Northern analysis and behavioral test. Following an unilateral injection of complete Freund's adjuvant (CFA) into the rat hindpaw, there appeared a significant hyperalgesia of inflamed hindpaw and up-regulation of ipsilateral spinal DYN mRNA; while the pre-emptive and continuous intrathecal administration of Mk-801 (10 microg/microl per h) could significantly suppress both the hyperalgesia and the up-regulation of spinal DYN mRNA induced by peripheral inflammation. The results suggest that NMDA receptor activation may contribute to the development and maintenance of the thermal hyperalgesia that is associated with the up-regulation of DYN expression in spinal dorsal horn.

Prodynorphin processing by proprotein convertase 2. Cleavage at single basic residues and enhanced processing in the presence of carboxypeptidase activity

Endoproteolytic processing of the 26-kDa protein precursor prodynorphin (proDyn) at paired and single basic residues is most likely carried out by the proprotein convertases (PCs); however, the role of PCs at single basic residues is unclear. In previous studies we showed that limited proDyn processing by PC1/PC3 at both paired and single basic residues resulted in the formation of 8- and 10-kDa intermediates. Because PC2 is colocalized with proDyn, we examined the potential role of this convertase in cleaving proDyn. PC2 cleaved proDyn to produce dynorphin (Dyn) A 1-17, Dyn B 1-13, and alpha-neo-endorphin, without a previous requirement for PC1/PC3. PC2 also cleaved at single basic residues, resulting in the formation of the C-peptide and Dyn A 1-8. Only PC2, but not furin or PC1/PC3, could cleave the Arg-Pro bond to yield Dyn 1-8. Structure-activity studies with Dyn A 1-17 showed that a P4 Arg residue is important for single basic cleavage by PC2 and that the P1' Pro residue impedes processing. Conversion of Dyn A 1-17 or Dyn B 1-13 into leucine-enkephalin (Leu-Enk) by PC2 was never observed; however, Dyn AB 1-32 cleavage yielded small amounts of Leu-Enk, suggesting that Leu-Enk can be generated from the proDyn precursor only through a specific pathway. Finally, PC2 cleavages at single and paired basic residues were enhanced when carried out in the presence of carboxypeptidase (CP) E. Enhancement was blocked by GEMSA, a specific inhibitor of CPE activity, and could be duplicated by other carboxypeptidases, including CPD, CPB, or CPM. Our data suggest that carboxypeptidase activity enhances PC2 processing by the elimination of product inhibition caused by basic residue-extended peptides.

Preprodynorphin mRNA-expressing neurones in the rat parabrachial nucleus: subnuclear localization, hypothalamic projections and colocalization with noxious-evoked fos-like immunoreactivity

The dorsal lateral subnucleus of the rat pontine parabrachial nucleus is a major target for ascending nociceptive information from the spinal cord. With in situ hybridization histochemistry, using a radiolabelled cRNA probe, we demonstrate that neurones in and near the dorsal lateral subnucleus express preprodynorphin mRNA. The cRNA probe was constructed from a PCR product amplified from rat genomic DNA. Sequencing of the PCR product revealed that it corresponded to the sequence 466-1101 of the rat preprodynorphin gene exon 4. Tract tracing experiments, using injection of cholera toxin subunit B into the hypothalamic median preoptic nucleus, showed a retrograde labelling pattern of neurones in the parabrachial nucleus that was almost identical to that of the preprodynorphin mRNA expressing neurones. Double-labelling, combining immunohistochemical detection of tracer and in situ hybridization, revealed that the retrogradely labelled neurones expressed preprodynorphin mRNA. A similar double-labelling, combining in situ hybridization with immunohistochemical detection of noxious-evoked fos following formalin injection into one hindpaw of awake animals, showed that almost all fos-immunoreactive neurones in the dorsal lateral parabrachial subnucleus also expressed preprodynorphin mRNA. Quantitative analysis suggested that the evoked fos immunoreactivity was accompanied by an increased preprodynorphin mRNA expression. The findings provide evidence that neurones in the dorsal lateral subnucleus produce dynorphin and project to the median preoptic nucleus, and that noxious stimulation in awake animals synaptically activates the dynorphinergic neurones in this subnucleus. These observations are consistent with the idea of a functional and chemical heterogeneity among different parabrachial subnuclei that serves to produce specific homeostatic responses to stimuli that changes the physiological status of the organism, including tissue damage.

Prodynorphin in invertebrates

We have characterized a prodynorphin-like molecule in an invertebrate, specifically in the rhynchobdellid leech Theromyzon tessulatum. The 14270 Da protein was purified by gel permeation chromatography, anti-leucine-enkephalin-affinity column separation followed by reverse-phase HPLC. Its complete characterization was performed by Edman degradation, enzymatic treatments, and matrix assisted laser-desorption time of flight mass spectrometry. This 119 amino-acid protein exhibits 28.8% sequence identity with rat prodynorphin, 22.9% with human prodynorphin, and 21.8% with the pig molecule. Within the leech precursor, alpha-Neo-endorphin, dynorphin-A, and dynorphin B-like peptides are present at the C-terminus as in vertebrate prodynorphin. These biological active peptides exhibit 100%, 50%, and 76.6% sequence identity with their counterparts in mammals, respectively. The amount of leucine-enkephalin is identical to that found in vertebrates. Leech prodynorphin is distinguished from that found in mammals in that the N-terminus is shorter. This report constitutes the first complete biochemical characterization of a prodynorphin in invertebrates.

Involvement of a c-fos-dependent mechanism in caffeine-induced expression of the preprotachykinin A and neurotensin/neuromedin N genes in rat striatum

Striatal c-fos induction was blocked by local administration of phosphorothioated c-fos antisense oligonucleotides (AS-ODN) to examine the possible role of caffeine-induced c-fos expression in transcriptional regulation of striatal preproenkephalin, prodynorphin, preprotachykinin A and neurotensin/neuromedin N. Caffeine (100 mg/kg i.p.) induced both c-fos mRNA and Fos-protein, and this induction was significantly attenuated by intrastriatal injection of 4 (but not 1) nmol c-fos AS-ODN. This suggests that, in addition to translational arrest, other mechanisms may be involved in the mediation of antisense action. The action of the AS-ODN was sequence specific. The antisense blockade of c-fos reduced the effect of caffeine on the expression of mRNAs for preprotachykinin A and neurotensin/neuromedin N in the ventrolateral caudate-putamen. Levels of preproenkephalin and prodynorphin transcripts were unaffected. Thus caffeine induction of striatal preprotachykinin A mRNA and neurotensin/neuromedin N mRNA, but not of preproenkephalin mRNA or prodynorphin mRNA, may at least in part be mediated by a pathway involving Fos protein. The findings illustrate the utility of blockade of gene expression with antisense oligonucleotides for in vivo studies of drug actions.

Sexual impotence is associated with a reduced production of oxytocin and with an increased production of opioid peptides in the paraventricular nucleus of male rats

Oxytocin plays a physiological stimulatory role on sexual behavior. Conversely, opioid neuropeptides play a physiological inhibitory role. Here we show that in sexually impotent rats there is a reduced expression of oxytocin mRNA and an increased expression of proenkephalin and pro-dynorphin mRNA in the paraventricular nucleus of hypothalamus (PVN), a brain structure of key importance for sexual behavior. These data suggest that an imbalance in the production of oxytocin and of opioid peptides in the PVN, with prevalence of opioid peptides, may underlie a condition of sexual impotence.

Chemoarchitecture of the rat lateral septal nucleus

The distribution of neurons and terminal fields that contain a variety of neurotransmitters and steroid hormone receptors has been examined with in situ hybridization and immunohistochemistry in closely spaced series of sections throughout the rostrocaudal extent of the rat lateral septal nucleus, as well as the adjacent septohippocampal and septofimbrial nuclei. The results indicate that the lateral septal nucleus is divided into major rostral, caudal, and ventral parts that differ from the widely used cytoarchitectonic parcellation into dorsal, intermediate, and ventral parts. Furthermore, the rostral, caudal, and ventral parts are turn divided into about 20 zones, regions, and domains on the basis of differential terminal fields and neurons that express particular neuropeptides and steroid hormone receptors. In general, the small zones and regions form dorsoventrally oriented sheets or bands that are arranged in a complex way. Differential connections of these lateral septal components are analyzed in the accompanying paper (Risold, P. Y. and Swanson, L. W., Connections of the rat lateral septal complex, Brain Res. Rev., 24 (1997) 115-195).

Concurrent elevation of the levels of expression of striatal preproenkephalin and preprodynorphin mRNA in the rat brain by chronic treatment with caffeine

Caffeine is a widely consumed substance that elicits psychomotor stimulant effects and also displays addictive properties. In order to assess the effect of caffeine on striatal neuropeptide mRNA expression, male rats were injected (i.p.) with caffeine at 20, 40 or 80 mg/kg of body weight twice daily for 9 consecutive days. Preproenkephalin (PPE), preprotachykinin A (PPT-A) and preprodynorphin (PPD) mRNA levels were determined in coronal sections of brain tissue by in situ hybridization histochemistry. PPE mRNA levels were increased by chronic caffeine in all subdivisions of the striatum at 80 mg/kg (dorsolateral caudate-putamen (dlCPu), +139%; dorsomedial CPu (dmCPu), +42%; ventrolateral CPu (vlCPu), +102%; ventromedial CPu (vmCPu), +20%; and anterior CPu (aCPu), +75% relative to vehicle-injected controls that were normalized to 0% change). Similarly, PPD mRNA expression was increased in all aspects of the striatum at 80 mg/kg (dlCPu, dmCPu, vlCPu, vmCPu and aCPu, +98%, +25%, +104%, +9% and +85%, respectively). In contrast to PPE mRNA, PPD mRNA was increased +117% above control in the nucleus accumbens (NAc) at 20 mg/kg of caffeine. PPT-A mRNA expression was not significantly affected by caffeine treatment in the CPu or NAc. The data demonstrate that repeated exposure to caffeine selectively increases opioid neuropeptide mRNA expression in the striatum and the NAc of the rat brain by a dopamine-independent mechanism.