Rat brain preproenkephalin mRNA. cDNA cloning, primary structure, and distribution in the central nervous system

Localization of enkephalinergic neurons in the central nervous system of the salmon (Salmo salar L.) by in situ hybridization and immunocytochemistry

The distribution of neurons expressing preproenkephalin (PPE) mRNA in the brain of the salmon was investigated by means of non-radioactive in situ hybridization, and directly compared with the distribution of enkephalin-immunoreactive (ENKir) neurons. This approach, utilized here for the first time in a non-mammalian vertebrate for the identification of neurons containing opioid peptides, permitted a detailed analysis of the distribution of putative enkephalinergic neurons in the salmon brain. Several cell groups containing neurons that express PPE mRNA also contain ENKir neurons. Such cell groups are located in the ventral telencephalic area, the nucleus of the rostral mesencephalic tegmentum and another nucleus immediately dorsal to it, the torus semicircularis, the valvula cerebelli and the corpus cerebelli. These cell groups consistently contain larger numbers of PPE mRNA expressing cells than ENKir ones. Some cell groups express PPE mRNA, but do not contain ENKir neurons. These cell groups are located in the dorsal telencephalic area, the inferior lobes of the hypothalamus, the pretectal area, the magnocellular superficial pretectal nucleus, the optic tectum, the oculomotor nucleus, the trochlear nucleus, the magnocellular vestibular nucleus, the secondary gustatory nucleus, the superior and medial reticular nuclei, the motor nucleus of the vagus and the ventral horn of the spinal cord. Moreover, some cell groups contain ENKir neurons, but no PPE mRNA expressing neurons. These cell groups are located in the ventromedial thalamic nucleus, the lateral tuberal nucleus, the nucleus of the lateral recess and the nucleus of the posterior recess. The majority of these periventricular ENKir neurons were of the cerebrospinal fluid-contacting type. ENKir neurons were also located in the dorsal lateral tegmental nucleus and in area B9. The results also permitted a tentative identification of enkephalinergic neurons afferent to the optic tectum, that have previously not been identified with immunocytochemistry, located in the dorsal telencephalic area, as well as enkephalinergic neurons intrinsic to the tectum that may contribute to the laminar arrangement of ENKir fibers in the optic tectum.

C-fos mediates antipsychotic-induced neurotensin gene expression in the rodent striatum

The ubiquitous inducibility of the immediate-early gene c-fos in the central nervous system has led to the search for downstream genes which are regulated by its product, Fos. Recent evidence suggests that c-fos induction by a single injection of the classical antipsychotic haloperidol may contribute to the subsequent increase in neurotensin gene expression in the rodent striatum. Consistent with this proposal, in the present study haloperidol-induced Fos-like immunoreactivity and neurotensin/neuromedin N messenger RNA were found to be expressed by the same population of striatal neurons. Moreover, inhibition of haloperidol-induced c-fos expression by intrastriatal injection of antisense phosphorothioate oligodeoxynucleotides complimentary either to bases 109-126 or 127-144 of c-fos attenuated the subsequent increase in neurotensin/neuromedin N messenger RNA. However, injection of a sense phosphorothioate oligodeoxynucleotide corresponding to bases 127-144 of c-fos did not reduce haloperidol-induced c-fos or neurotensin/neuromedin N expression. Furthermore, constitutive expression of Jun-like immunoreactivity in the striatum was not reduced by either the sense or antisense phosphorothioate oligodeoxynucleotides. Similarly, the sense and antisense phosphorothioate oligodeoxynucleotide failed to reduce proenkephalin messenger RNA, which is located in the same striatal neurons that express haloperidol-induced neurotensin/neuromedin N messenger RNA, which is located in the same striatal neurons that express haloperidol-induced neurotensin/neuromedin N messenger RNA. Lastly, haloperidol-induced increases in nerve growth factor I-A-, JunB- and FosB-like immunoreactivity and fosB messenger RNA were not decreased by intrastriatal injection of either the sense or antisense phosphorothioate oligodeoxynucleotides. These results indicate that the antisense phosphorothioate oligodeoxynucleotides attenuated haloperidol-induced neurotensin/neuromedin N expression by selectively reducing c-fos expression and emphasize the potential importance of immediate-early gene induction in the mechanism of action of this antipsychotic drug.

Stimulation of "prohormone thiol protease" (PTP) and [Met]enkephalin by forskolin. Blockade of elevated [Met]enkephalin by a cysteine protease inhibitor of PTP

Proenkephalin and other prohormones require proteolytic processing at paired basic and monobasic residues for the biosynthesis of active neuropeptides. The novel "prohormone thiol protease" (PTP) has been proposed as a candidate proenkephalin processing enzyme for the production of [Met]enkephalin in chromaffin granules (Krieger, T. J., and Hook, V. Y. H. (1991) J. Biol. Chem. 266, 88376-8383). In this study, PTP was examined during elevation of cellular [Met]enkephalin by forskolin, a direct activator of adenylate cyclase that produces cAMP. Treatment of chromaffin cells with forskolin for 72 h increased enkephalin precursor cleaving activity (measured by following the conversion of the model substrate [35S-Met]preproenkephalin to trichloroacetic acid-soluble radioactivity) in isolated chromaffin granules by 170-180% over controls (100%). The increased activity was associated with the membrane fraction, rather than the soluble fraction, of chromaffin granules. The elevated activity was inhibited by E-64c, which is a potent inhibitor of PTP and cysteine proteases; however, the activity was not inhibited by serine or aspartic protease inhibitors. The elevated activity was identified as PTP based on immunoprecipitation by anti-PTP immunoglobulins. Stimulation of PTP synthesis was involved in the forskolin-induced increase in PTP activity, as demonstrated by a 10-fold increase in [35S]PTP pulse labeling in forskolin-treated chromaffin cells. Forskolin elevation of PTP protein levels within chromaffin granules was also detected in Western blots. Importantly, the forskolin-mediated rise in cellular [Met]enkephalin levels was completely blocked when cells were preincubated with the cysteine protease inhibitor Ep453, which is known to be converted by intracellular esterases to the more effective inhibitor E-64c (Buttle, D. J., Saklatvala, J., Tamai, M., and Barrett, A. J. (1992) Biochem. J. 281, 175-177). Both E-64c and Ep453 inhibit PTP, with E-64c being more potent (Azaryan, A. V., and Hook, V. Y. H. (1994b) Arch. Biochem. Biophys. 314, 171-177). These results demonstrate a role for PTP in proenkephalin processing in chromaffin cells and indicate that [Met] enkephalin formation and PTP are both regulated by cAMP.

The expression of proenkephalin and prodynorphin genes and the induction of c-fos gene by dopaminergic drugs are not altered in the straitum of MPTP-treated mice

The expression of proenkephalin (PENK), prodynorphin (PDYN) and c-fos genes was studied in the striatum of C57B1/6 mice treated with 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP), which are used as a rodent model of Parkinson's disease (PD). Two weeks after systemic administration of MPTP (2 x 40 mg/kg, s.c. 18h apart), the lesion of the substantia nigra (SN) could be visualised by loss of the nigral tyrosine hydroxylase (TH) mRNA hybridization signal and by a 91% decrease in striatal dopamine levels. The levels of PENK and PDYN mRNAs were not significantly changed in the striatum of the lesioned mice, as compared to non-treated controls. The induction of the immediate early gene c-fos by the dopamine D2 receptor antagonist haloperidol was not altered, while the selective D1 receptor agonist SKF 38393 failed to induce c-fos in the striatum of MPTP-treated mice. These results are in contrast to the data concerning rats with the 6-hydroxydopamine (6-OHDA) lesion of the SN, which serve as another rodent model of PD. In the striata of 6-OHDA-lesioned rats, PENK gene is upregulated, PDYN gene is down-regulated and the induction of c-fos gene by D2 receptor antagonists is abolished, whereas selective D1 receptor agonists induce c-fos gene, which does not occur in non-lesioned rats. We presume that the lack of influence of the MPTP lesion in mice on the striatal gene expression was mainly caused by insufficient dopamine depletion in the striatum, which could not be increased in this model. The importance of the changes observed in 6-OHDA-lesioned rats has been discussed in the context of the mouse and primate MPTP models of PD.

D1 and D2 dopamine receptor gene expression in the rat striatum: sensitive cRNA probes demonstrate prominent segregation of D1 and D2 mRNAs in distinct neuronal populations of the dorsal and ventral striatum

The postsynaptic effects of dopamine in the striatum are mediated mainly by receptors encoded by D1, D2, and D3 dopamine receptor genes. The D1 and D2 genes are the most widely expressed in the caudate-putamen, the accumbens nucleus, and the olfactory tubercle. Several anatomical studies, including studies using in situ hybridization with oligonucleotide and cDNA probes, have suggested that D1 and D2 receptors are segregated into distinct efferent neuronal populations of the striatum: D1 in substance P striatonigral neurons and D2 in enkephalin striatopallidal neurons. In contrast, on the basis of several in vivo and in vitro studies, other authors have suggested the existence of an extensive colocalization of D1 and D2 in the same striatal neurons. Our study was undertaken in order to analyze in detail the expression of the D1 and D2 receptor genes in the efferent striatal populations, with special reference to the various striatal areas, and to yield insights into the question about D1 and D2 mRNA localization in the striatum. We have, therefore, used highly sensitive digoxigenin- and 35S-labeled cRNA probes to address this question. The present results demonstrate that the D1 and D2 receptor mRNAs are segregated, respectively, in substance P and enkephalin neurons in the caudate-putamen and accumbens nucleus (shell and core) and in the olfactory tubercle (for their largest part). A very small percentage of neurons may coexpress both genes. These results confirm that the D1 and D2 receptor genes are expressed in distinct populations of striatal efferent neurons in the normal adult rat.

Distribution of enkephalin immunoreactivity in sympathetic prevertebral ganglia and digestive tract of guinea-pigs and rats

The aim of the present study was to determine the distribution of methionine-enkephalin (ME) and leucine-enkephalin (LE) immunoreactivity in the sympathetic prevertebral ganglia (coeliac plexus and inferior mesenteric ganglion) and in the myenteric plexus-muscular layer complex of the digestive tract in guinea-pigs and rats. This study was performed using the same immunological approaches including radioimmunoassays and HPLC characterization as those used previously on cats in order to be able to make inter-region and inter-species comparisons. In rat and guinea-pig prevertebral ganglia, the distributions of the enkephalin immunoreactivities were comparable and were characterized by a low ME/LE concentration ratio, of less than 1. In the digestive tract of rats, the enkephalin immunoreactivities were homogeneously distributed, whereas in guinea-pigs, they were found to be very low in the lower oesophageal sphincter and high in the duodenum. In both species, the ME/LE concentration ratio was around 2. The ME/LE concentration ratio determined in the present study in peripheral nervous structures was much lower than that determined previously in the rat brain. Radioimmunoassay and biochemical data might indicate that different mechanisms are responsible for the processing and/or degradation of enkephalins in the central and peripheral nervous systems. The present study provides further evidences that there are tissue- and species-dependent differences in the distribution of enkephalin immunoreactivities. These differences should be taken into consideration when dealing with the effects and the role of enkephalins in the nervous control of intestinal motility in mammals.

AMPA-induced lesions of the basal forebrain differentially affect cholinergic and non-cholinergic neurons: lesion assessment using quantitative in situ hybridization histochemistry

The direct and transynaptic effects of lesions of the basal forebrain induced by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and ibotenic acid were investigated using quantitative in situ hybridization histochemistry. Probes complementary to the sequences of choline acetyltransferase mRNA, glutamate decarboxylase mRNA and preproenkephalin mRNA were used to assess direct lesion effects within the basal forebrain and probes for postsynaptic M-1 and M-3 muscarinic receptors were used to assess long-term changes in neocortical muscarinic receptor mRNA expression following cholinergic deafferentation. AMPA-induced basal forebrain lesions destroyed significantly more neurons that expressed choline acetyltransferase mRNA than ibotenic acid-induced lesions (90 versus 60%), but significantly fewer neurons which expressed either glutamate decarboxylase or preproenkephalin mRNA (61 versus 83% reduction in glutamate decarboxylase mRNA and 56 versus 79% reduction in preproenkephalin mRNA). AMPA-induced lesions did, however, destroy a significant proportion of the neurons which expressed glutamate decarboxylase and preproenkephalin mRNA (approximately 60%). The neurons spared following AMPA-induced lesions were typically situated dorsolaterally within the dorsal pallidum, although neurons expressing glutamate decarboxylase or preproenkephalin mRNA were frequently observed within the areas of greatest cholinergic neuronal loss, i.e. the region of the nucleus basalis magnocellularis. These findings suggest that there is a population of non-cholinergic pallidal neurons which are insensitive to AMPA but not to ibotenic acid, reflecting a possibly heterogeneous distribution of NMDA and non-NMDA subtypes of glutamate receptors within the rat basal forebrain. AMPA-induced lesions of the basal forebrain were, however, without significant effect on the levels of expression of M-1 and M-3 muscarinic receptor mRNAs in the cerebral neocortex.

Glutamate decarboxylase messenger RNA in rat pallidum: comparison of the effects of haloperidol, clozapine and combined haloperidol-scopolamine treatments

We have investigated the effects of neuroleptic treatments which do, or do not, induce catalepsy on the level of expression of glutamate decarboxylase, the rate limiting enzyme in GABA synthesis, in efferent neurons of the pallidum in adult rats. Different regimens of haloperidol (1 mg/kg s.c., three, seven or 14 days; 2 mg/kg, s.c., 10 days) induced catalepsy in a majority of rats and increased glutamate decarboxylase messenger RNA levels in the globus pallidus (external pallidum) in those rats exhibiting catalepsy. Levels of glutamate decarboxylase messenger RNA were also increased in the entopeduncular nucleus (internal pallidum), but only after 14 days of treatment with haloperidol. The atypical antipsychotic clozapine (seven days, 20 mg/kg, s.c.), which did not induce catalepsy, slightly decreased glutamate decarboxylase messenger RNA levels in the globus pallidus. When co-administered with haloperidol (seven days, 1 mg/kg s.c.), the muscarinic antagonist scopolamine (1 mg/kg, s.c.) completely blocked both haloperidol-induced catalepsy and increases in glutamate decarboxylase messenger RNA levels in the globus pallidus. In contrast, scopolamine was not able to block increased glutamate decarboxylase and enkephalin messenger RNA expression induced by haloperidol in the striatum. These results reveal a good correlation between increases in glutamate decarboxylase messenger RNA levels in the globus pallidus and catalepsy after these drug treatments and suggest that anticholinergic blockade of the behavioral and molecular effects of neuroleptics may involve non-striatal mechanisms.

Effect of lactation on hypothalamic preproenkephalin gene expression

Enkephalin appears to modulate several aspects of reproductive function in female rats. The purpose of this study was to determine if lactation influences preproenkephalin gene expression in one or more hypothalamic nuclei known to be involved in maternal or reproductive behavior and prolactin secretion. Lactating rats were killed on day 3 (LAC 3) or day 10 (LAC 10) of lactation. Controls consisted of regular 4-day cycling rats that were killed on diestrous day 1, with 9 to 12 females per group. We used in situ hybridization histochemistry to assess preproenkephalin gene expression in individual cells in the medial preoptic nucleus, anterior, medial and posterior arcuate nucleus, magnocellular and parvocellular aspects of paraventricular nucleus, and ventromedial nucleus. Preproenkephalin mRNA in the anterior arcuate nucleus increased to reach significance (P < 0.05) at day 10 of lactation. Levels in the medial arcuate nucleus increased significantly (P < 0.001) by day 3 of lactation (LAC 3) and remained elevated on day 10 (LAC 10). No significant differences between lactating and control rats were detected in preproenkephalin mRNA levels in the posterior arcuate nucleus, medial preoptic nucleus or in the ventromedial nucleus. Substantial levels of preproenkephalin mRNA were found in the paraventricular nucleus, particularly in a limited region of the magnocellular portion. However, these levels did not change with lactation. These data provide evidence for differential regulation of the preproenkephalin gene during lactation. This change may contribute to lactational hyperprolactinemia and suppressed GnRH secretion, leading to reproductive acyclicity.

Purification and characteristics of the candidate prohormone processing proteases PC2 and PC1/3 from bovine adrenal medulla chromaffin granules

The prohormone-processing proteases PC1/3 and PC2 belong to the family of mammalian subtilisin-related proprotein convertases (PC) possessing homology to the yeast Kex2 protease. The presence of PC1/3 and PC2 in secretory vesicles of bovine adrenal medulla (chromaffin granules) implicates their role in the processing the precursors of enkephalin, neuropeptide Y, somatostatin, and other neuropeptides that are present in chromaffin granules. In this study, PC1/3 and PC2 were purified to apparent homogeneity from the soluble fraction of chromaffin granules by chromatography on concanavalin A-Sepharose, Sephacryl S-200, pepstatin A-agarose, and anti-PC1/3 or anti-PC2 immunoaffinity resins. PC1/3 and PC2 were monitored during purification by measuring proteolytic activities with 35S-enkephalin precursor and Boc-Arg-Val-Arg-Arg-methylcoumarin amide (MCA) substrates and by following PC1/3 and PC2 immunoreactivity with specific anti-PC1/3 and anti-PC2 sera generated in this study. Purified PC1/3 and PC2 on SDS-polyacrylamide gels each show a molecular mass of 66 kDa. PC2 in the soluble fraction of chromaffin granules was present at 5- and 10-fold higher enzyme protein and activity, respectively, compared with that of PC1/3. PC1/3 and PC2 cleaved paired basic and monobasic sites within peptide-MCA substrates, with Boc-Arg-Val-Arg-Arg-MCA and pGlu-Arg-Thr-Lys-Arg-MCA as the most effectively cleaved peptides tested. PC1/3 and PC2 showed pH optima of 6.5 and 7.0, respectively. Kinetic studies indicated apparent Km values for hydrolysis of Boc-Arg-Val-Arg-Arg-MCA as 66 and 40 microM, with Vmax values of 255 and 353 nmol/h/mg for PC1/3 and PC2, respectively. Specificity of the PC enzymes for dibasic sites was confirmed by potent inhibition by the active site-directed peptide inhibitors (D-Tyr)-Glu-Phe-Lys-Arg-CH2Cl and Ac-Arg-Arg-CH2Cl. Inhibition by EGTA and activation by Ca2+ indicated PC1/3 and PC2 as Ca(2+)-dependent proteases. In addition, PC enzymes were activated by dithiothreitol and inhibited by thiol-blocking reagents, p-hydroxymercuribenzoate and mercuric chloride. These results illustrate the properties of endogenous PC1/3 and PC2 as prohormone-processing enzymes.

Differential expression of mGluR5 metabotropic glutamate receptor mRNA by rat striatal neurons

Metabotropic glutamate receptors (mGluRs) mediate the effects of glutamate neurotransmission on intracellular second messenger systems. Among the seven distinct mGluR receptor isoforms currently identified, the mGluR5 isoform is expressed particularly prominently in the striatum, where it may contribute to neuronal plasticity, motor behaviors, and excitotoxic injury. mGluR5 mRNA expression in striatal enkephalinergic, somatostatinergic, and cholinergic neurons was examined using double label in situ hybridization techniques. mGluR5 expression is abundant in a large number of medium-sized striatal cells but is absent in a significant minority of neurons. Double label in situ hybridization with 35S-dATP- and digoxygenin-dUTP-tailed oligonucleotide probes demonstrated that mGluR5 message is highly expressed by enkephalinergic striatal neurons but is not detectable in cholinergic or somatostatin interneurons. In addition, some nonenkephalin, presumably substance P, neurons were also strongly labeled for mGluR5. The differential expression of mGluR5 in striatal projection neurons vs. interneurons may contribute to the selective vulnerability of these neurons to disease processes.

Protein-DNA interactions during phenotypic differentiation

We have been studying the molecular mechanism of neuronal differentiation through which the multipotent precursor becomes limited to the final transmitter phenotype. Here we focused on the role of the 5' proximal regulatory cassette (-190; +53 bp) of the rat enkephalin (rENK) gene in the developmental regulation of the enkephalin phenotype. Several well characterized cis-elements, including AP2, CREB, NF1, and NFkB, reside on this region of the rENK gene. These motifs were sufficient to confer activity-dependent expression of the gene during neurodifferentiation when it was tested using transient transfection assays of primary developing spinal cord neurons treated with tetrodotoxin (TTX). This region was then used as a DNA probe in mobility shift assays, with nuclear proteins derived from phenotypically and ontogenetically distinct brain regions. Only a few low abundance protein-DNA complexes were detected and only with nuclear proteins derived from developing but not from adult brain. The spatiotemporal pattern of these complexes did not show correlation with enkephalin expression which was assessed by RT-PCR. We employed synthetic probes corresponding to consensus as well as ENK-specific sequences of the individual motifs to identify the nature of the observed bands. Although both consensus NF1 and enkCRE1(NF1) formed complexes with nuclear proteins derived from the striatum and cortex at various ages, the appearance of the bands was not correlated with ENK expression. Surprisingly, no complexes were detected if other ENK-specific motifs were used as probes. We also tested nuclear extracts derived from forskolin-induced and control C6 glioma cells, again using the whole proximal regulatory cassette as well as individual motifs. These experiments showed the formation of elaborate protein-DNA bands. There was no direct correlation between the appearance of bands and forskolin-induced ENK expression. Unexpectedly, all ENK-specific motifs formed specific and highly abundant protein-DNA complexes when nuclear extracts from the human tumor cell line (HeLa), which does not express ENK, were used. Based on these observations, we concluded that: 1. Interactions between the proximal regulatory cassette and additional probably far distant regions of the rENK gene and their binding proteins may be necessary to confer developmentally regulated, cell-specific expression of the ENK gene; and 2. Inducibility of the gene by common cis-elements can be governed by this region; however, the cell-specificity of the induction remains elusive.

Cocaine alters glutamic acid decarboxylase differentially in the nucleus accumbens core and shell

The effects of acute and repeated daily cocaine on the levels of mRNA coding for glutamic acid decarboxylase (GAD), preproenkephalin (PPE), preprotachykinin (PPT), and the dopamine D2 receptor were determined in the striatum, nucleus accumbens core and shell areas (NAcore, NAshell), and medial prefrontal cortex. Rats were given repeated saline or cocaine for 6 days. A cocaine challenge administered 24 h later resulted in an augmented locomotor response in daily cocaine-pretreated rats. Six h after the challenge, rats were sacrificed and Northern blot analysis revealed that acute cocaine increased GAD mRNA levels by 44% in the NAshell, while repeated cocaine prevented the acute cocaine-induced increase. These data suggest that cocaine may differentially regulate GABA release at NA core and shell projection fields.

Chromosomal localization of opioid peptide and receptor genes in the mouse

Opiate receptors are the primary targets for the drugs of abuse morphine and heroin. In this study, we completed the localization on mouse chromosomes of the genes encoding mu (Oprm) and kappa (Oprk) receptors, as well as the genes for the opioid propeptides proenkephalin (Penk) and prodynorphin (Pdyn). The genetic mapping was performed using a panel of DNA samples from an interspecific cross [C3H/HeJ-gld and (C3H/HeJ-gld x Mus spretus)F1] that has been characterized for more than 800 markers throughout the genome. The genes are localized on mouse Chr 1 (Oprk, 10 cM from the centromere), Chr 2 (Pdyn, 75 cM from the centromere), Chr 4 (Penk, 1 cM from the centromere) and Chr 10 (Oprm, 10 cM from the centromere). Interestingly, the gene for the mu receptor is located in the same region as a Quantitative Trait Locus for high morphine consumption, thus raising the possibility of its direct role in drug abuse mechanisms.

Distribution of preproenkephalin messenger RNA in the basal ganglia and limbic-associated regions of the monkey telencephalon

We studied the distribution of preproenkephalin messenger RNA in the monkey forebrain, using a free-floating method for in situ hybridization histochemistry. Autoradiographs reveal a high level of specific hybridization to preproenkephalin messenger RNA in the monkey striatum and forebrain regions. In the monkey striatum, the distribution of preproenkephalin messenger RNA is heterogeneous. There is variation in the general labeling pattern between regions of the striatum. For example, a particularly densely labeled area of preproenkephalin messenger RNA is observed in the ventral part of the caudal putamen. In addition, at the macroscopic level, there are patches of specific hybridization intermingled with areas containing less specific labeling. This forms a mosaic-like pattern. At the microscopic level, densely labeled individual cells are found among those with little or no specific labeling. Adjacent sections, processed for in situ hybridization and immunohistochemistry, show some correlation between the perikarya containing preproenkephalin messenger RNA and enkephalin-positive fibers in the striatum. Specific hybridization to preproenkephalin messenger RNA is evident throughout the cortical mantle, primarily concentrated in layers 2 and 3. Particularly high levels of preproenkephalin messenger RNA are found in specific limbic-associated cortices, including the piriform allocortex, the agranular area of the orbitofrontal cortex, the agranular insular cortex and the caudal field of the entorhinal cortex. Specific labeling is also present in the granular cell layer of the dentate gyrus and in the amygdaloid complex. This study reveals heterogeneous distribution of dense preproenkephalin messenger RNA in the basal ganglia and high levels of preproenkephalin messenger RNA in specific limbic-associated regions of the monkey telencephalon.

The distinct gene expression of the pro-hormone convertases in the rat heart suggests potential substrates

The present study examined the distribution of the pro-hormone convertases PC1, PC2, furin, PACE4 and PC5 in the rat heart. Northern blot analysis of RNA extracted from cardiac tissues showed high levels of furin and PACE4 mRNA in the atria and ventricles, while PC5 mRNA was found to be expressed at high levels in the dorsal aorta. Although undetectable by Northern blot analysis, both PC1 and PC2 mRNA were detected by in situ hybridization and immunohistochemistry in discrete regions of the intracardiac para-aortic ganglia. In situ hybridization studies also showed that furin mRNA was observed in all cardiac tissues and cells, consistent with the previously reported ubiquitous expression of this gene. PACE4 mRNA was highly abundant in both the atria and ventricular cardiomyocytes, with low to undetectable levels observed in blood vessels. Finally, PC5 transcripts were expressed in the endothelial cells lining coronary vessels and the valve leaflets of the heart. The present localization studies in the heart and cardiac blood vessels suggests potential roles for each convertase in the processing of various neuropeptides, hormones and growth factors.

Seizure-induced activation of enkephalin- and somatostatin-synthesizing neurons

The extent of the neuronal network that is activated by kainic acid-induced seizures was anatomically identified and neurochemically characterized. Seizure-activated neurons were identified through the immunocytochemical demonstration of Fos protein in neuronal nuclei. These seizure-activated neurons were characterized by determining if they contained the mRNA for somatostatin or enkephalin, using in situ hybridization procedures. The results demonstrate that a majority of enkephalin- and somatostatin-synthesizing neurons expressed the Fos protein following seizures and that they represent a major component of the kainic acid-induced, seizure-activated neuronal network.

Modulation of preproenkephalin mRNA levels in brain regions and spinal cord of rats treated chronically with morphine

The effect of morphine tolerance/dependence and abstinence on the preproenkephalin (PPE) gene expression was determined in brain regions and spinal cord of the rat. Male Sprague-Dawley rats were rendered tolerant and physically dependent on morphine by SC implantation of six pellets, each containing 75 mg of morphine base, during a 7-day period. Placebo pellet-implanted rats served as controls. In tolerant rats, the pellets were left in place at the time of sacrifice whereas in abstinent rats, the pellets were removed 16 h prior to sacrificing. The levels of PPE mRNA were determined in brain regions (striatum, cortex, pons-medulla, hypothalamus, amygdala, and midbrain) and spinal cord. The levels of PPE mRNA increased significantly in the cortex (62%) and the spinal cord (352%) of morphine-tolerant rats when compared to placebo pellet-implanted control rats. In other brain regions, the levels of PPE mRNA in placebo and morphine-tolerant rats did not differ. On the other hand, in morphine-abstinent rats, the levels of PPE mRNA increased in the striatum (62%) and hypothalamus (34%) but were decreased in pons-medulla (68%), midbrain (51%), and spinal cord (36%) in comparison to the placebo controls. The results clearly demonstrate differential changes in enkephalin gene expression in brain regions and spinal cord of the abstinent and nonabstinent morphine-tolerant/dependent rats.

Distribution of messenger RNAs encoding enkephalin, substance P, somatostatin, galanin, vasoactive intestinal polypeptide, neuropeptide Y, and calcitonin gene-related peptide in the midbrain periaqueductal grey in the rat

The midbrain periaqueductal grey matter (PAG) has numerous functional roles that include mediating nociceptive inhibition and integrating behavioural and physiological responses to potentially threatening or stressful stimuli. Underlying these behaviours is the diverse interconnectivity of this region, and it is possible that neurochemical subdivisions within the PAG reflect the functional properties of the different PAG regions. In this study, using in situ hybridization, we have investigated the distribution in the rat PAG of the messenger ribonucleic acids (mRNAs) encoding seven neuropeptides: enkephalin (ENK), substance P (SP), somatostatin (SST), galanin (GAL), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP). Each peptide mRNA had a distinct topographical distribution in the PAG. Preproenkephalin A (ENK) mRNA-expressing cells were found at all levels of the PAG in three distinct longitudinal columns. Preprotachykinin A (SP)-expressing cells were found at all levels of the PAG, principally in the Edinger-Westphal nucleus and the lateral and dorsal PAG. There was a column of neurons producing mRNA-encoding somatostatin that extended along the rostrocaudal extent of the ventrolateral PAG; there were also labelled cells in the dorsal and dorsolateral subdivisions at some levels of the PAG. Galanin mRNA-producing neurones were limited to the dorsal raphe nucleus and to a second population in the ventral border of the aqueduct. VIP mRNA-producing neurones were found in very localized regions of the PAG, including the cell-sparse region immediately ventral to the aqueduct and the ventral part of the dorsal raphe nucleus. NPY mRNA-producing neurones were localized mainly in some cells of the Edinger-Westphal nucleus and dorsal raphe nucleus. CGRP mRNA-expressing neurons were limited to the oculomotor and trochlear nucleus. The results showed a topographical distribution of neuropeptides over the rostrocaudal extent of the PAG that is compatible with the emerging theory that the anatomical and functional specificity of the PAG is expressed in the form of longitudinally arranged neuronal columns that extend for varying distances along the rostrocaudal axis of the midbrain PAG.

The relationship between MRNA levels and the locomotor response to novelty

Differences in behavioral and neurochemical responses to drugs of abuse and environmental stress have been observed between rats that have a greater locomotor response in a novel environment (high responders: HR) compared to those that have a low response to novelty (low responders: LR). This study examined nuclei associated with the nigrostriatal and mesolimbic systems for differences in mRNA content between HR and LR using Northern blot analysis. These brain regions were chosen because of their role in both drug abuse and stress responses. The mRNAs examined code for either peptide transmitters that interact with the dopaminergic system or components of the dopaminergic system that have not been previously examined for differences between HR and LR. HR rats had approximately 50% lower levels of mRNA for beta-preprotachykinin (PPT) in the core of the nucleus accumbens (NACC) compared to LR. No differences between HR and LR in mRNA levels for dynorphin (DYN), preproenkephalin (PPE), glutamic acid decarboxylase (GAD) or neurotensin (NT) were observed in the core of the NACC. In the shell region of the NACC, HR exhibited a 25% reduction in the level of mRNA for NT compared to LR. No differences between HR and LR in mRNA levels for PPT, DYN, PPE or GAD were observed in the shell of the NACC. In the medial frontal cortex and the dorsal striatum, no differences between HR and LR in mRNA levels for PPT, DYN, PPE, GAD or NT were found. In the substantia nigra and ventral tegmental area no differences between HR and LR in mRNA levels for tyrosine hydroxylase, GAD, cholecystokinin, or NT were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in mRNA levels of D2 receptors and neuropeptides in striatonigral and striatopallidal neurons of rats with neuroleptic-induced dyskinesias

Chronic neuroleptic treatment in rat produces vacuous chewing movements (VCMs), analogous to TD in humans. We hypothesized that these hyperkinetic movements were due to alterations in striatonigral and striatopallidal GABAergic spiny II neurons. Rats were treated for 36 weeks with haloperidol decanoate and withdrawn for 28 weeks. Striatonigral and striatopallidal neurons were assessed using in situ hybridization histochemistry for mRNA levels of D1 and D2 dopamine receptors, preproenkephalin (ENK), prodynorphin (DYN), protachykinin (substance P), and glutamate decarboxylase (GAD67) in the dorsolateral and ventromedial striatum as well as the nucleus accumbens. Rats that did not develop VCMs (-VCM) had increased D2 receptor and DYN mRNA, and reduced substance P mRNA in the dorsolateral striatum. Rats with persistent VCMs (+VCM) had increased D2 receptor, ENK, and DYN mRNA in both striatal regions, and increased ENK and DYN mRNA in the nucleus accumbens, compared with controls. Relative to -VCM rats, however, +VCM rats only had increased ENK mRNA in the nucleus accumbens. Considering the overall pattern of mRNA changes, the data suggest that alterations in both the D1-mediated striatonigral and the D2-mediated striatopallidal pathways play a role in the expression of the VCM syndrome. To the extent that gene expression parallels changes in neuronal activity, this implies that the VCM syndrome is associated with increased activity in both pathways.

Dopaminergic and muscarinic regulation of striatal enkephalin and substance P messenger RNAs following striatal dopamine denervation: effects of systemic and central administration of quinpirole and scopolamine

Striatal dopamine depletion produces an increase in enkephalin and a decrease in substance P messenger RNAs. Subsequent systemic administration of either the D2 dopamine agonist, quinpirole, or the muscarinic antagonist, scopolamine, results in the reduction of the lesion-induced elevation in striatal enkephalin messenger RNA. These changes in enkephalin messenger RNA levels may be mediated solely within the striatum or through trans-synaptic circuits involving the striatum. To dissociate these possibilities, we have compared the effects of systemic and central administration of quinpirole and scopolamine on striatal enkephalin and substance P messenger RNAs using in situ hybridization histochemistry. Systemic administration of both quinpirole and scopolamine blocked the elevation of striatal enkephalin messenger RNA normally observed in 6-hydroxydopamine-lesioned rats. In addition, high doses of systemic scopolamine (25 and 50 mg/kg per day) prevented the lesion-induced decrease in striatal substance P messenger RNA levels. In order to determine whether the effects of these drugs are mediated directly within the striatum, central administration of quinpirole and scopolamine were compared. In contrast to systemic administration, intraventricular and intrastriatal infusion of quinpirole but not scopolamine prevented the lesion-induced change in striatal enkephalin messenger RNA. However, neither quinpirole nor scopolamine administered centrally affected the level of substance P messenger RNA in the striatum of 6-hydroxydopamine-induced lesioned animals. Together, these data suggest that changes in D2 receptor activation directly in the striatum are responsible for the effects of quinpirole on enkephalin messenger RNA. In contrast, the effect of systemic scopolamine on striatal enkephalin and substance P messenger RNAs may not be mediated within the striatum.

GABAergic modulation of striatal peptide expression in rats and the alterations induced by dopamine antagonist treatment

GABAergic modulation of enkephalin, substance P and glutamic acid decarboxylase (GAD67) gene expression and the alterations induced by dopamine receptor blockade were studied in the rat striatum. Following subchronic treatment with the GABA-A agonist muscimol, the GABA-B agonist baclofen or the GABA transaminase inhibitor gamma-vinyl GABA there were no significant changes in striatal peptide and GAD67 gene expression. Following repeated administration of the D-2 antagonists, eticlopride and haloperidol, there was an increase in enkephalin and GAD67 mRNA levels and parallel decrease in that of substance P. These were unaffected by co-administration of gamma-vinyl GABA. The D-1 antagonist, SCH 23390 administered alone or together with gamma-vinyl GABA did not alter peptide or GAD67 mRNA levels. It seems that pharmacological stimulation of GABA receptors has little effect on enkephalin, substance P or GAD67 mRNA expression in striatal output neurons.

Temporal changes in the messenger RNA levels of cellular immediate early genes and neurotransmitter/receptor genes in the rat neostriatum and substantia nigra after acute treatment with eticlopride, a dopamine D2 receptor antagonist

The cellular immediate early genes are involved in the transcriptional events associated with the dopaminergic regulation of neurotransmitter expression within neurons of the neostriatum. To characterize these events in detail, quantitative in situ hybridization histochemistry was used to assess the temporal effects of acute dopamine receptor blockade with eticlopride, a dopamine D2 receptor antagonist, on the messenger RNA expression of the immediate early genes and neurotransmitters/receptors in the caudate-putamen and ventral tegmental area/substantia nigra pars compacta of the rat. Groups of rats were injected with a single dose of either isotonic saline or eticlopride (0.5 mg/kg i.p.) and killed at various time intervals ranging from 5 min to 24 h and frozen brain sections processed by in situ hybridization histochemistry. Using computerized image analysis, the changes in messenger RNA expression for c-fos, c-jun, jun B, jun D, nerve growth factor I-A and nerve growth factor I-B and for neurotensin, glutamate decarboxylase, proenkephalin, the dopamine D1 receptor and the short and long isoforms of the D2 receptor were examined in the caudate-putamen. In the ventral tegmental area and substantia nigra pars compacta, the messenger RNA expression of the above early response genes and that for neurotensin, tyrosine hydroxylase, cholecystokinin and the D2 receptor isoforms were also examined. In the neostriatum, eticlopride caused a rapid increase in c-fos messenger RNA with significantly increased levels at 10 min (P < 0.01). The levels peaked at 30 min and thereafter declined to control levels. A similar profile was observed for jun B messenger RNA, although levels were still significantly (P < 0.01) elevated at 1 h and declined to basal levels thereafter. No significant changes were observed for c-jun, jun D, nerve growth factor I-A and nerve growth factor I-B messenger RNAs. In the dorsolateral neostriatum, there was an increase in proneurotensin messenger RNA 10 min after eticlopride, this increase becoming significant (P < 0.01) at 60 min. Levels were maximal at 2-6 h and decreased after 12 h to basal levels. There were small increases in proenkephalin messenger RNA, but these were not significant (P < 0.05) until 6 h after the injection. Eticlopride did not have any significant effects on the messenger RNA levels for glutamate decarboxylase, the D1 receptor and the short and long isoforms of the D2 receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular cloning and characterization of the hamster preproenkephalin A cDNA

The cDNA for hamster preproenkephalin A (ENK) was cloned from an adrenal gland cDNA library constructed in the lambda ZapII vector. A nearly full-length cDNA was obtained and its 5' end region was completed using the technique of rapid amplification of cDNA ends (RACE). The coding and 3' untranslated regions of the hamster ENK cDNA share a high sequence identity with the rat, human, and bovine cDNAs, whereas the sequence identity is lower for the 5' untranslated region. Southern blot analysis of genomic DNA digests showed that a single copy of the ENK gene is present in the hamster haploid genome. Northern blot analysis of poly(A)+RNA from various hamster tissues indicated the following rank order for ENK messenger RNA abundance: adrenal glands > right atrium > brain > left atrium > right ventricle > ventricular septum > left ventricle, whereas primer extension analysis showed a single, identical transcriptional initiation site for the ENK mRNA in all these tissues. The sequence of the 5' untranslated region of the heart ENK cDNA was found to be identical to that from adrenal glands. This rules out the possibility that structural divergences in the 5' untranslated region of the heart ENK mRNA could decrease its translation efficiency and contribute to the very low level of enkephalin-containing peptides in the heart, compared to the adrenal glands.

Ontogeny and effect of activity on proenkephalin mRNA expression during development of the chick spinal cord

Numerous studies have shown in the adult nervous system that mRNA expression can be regulated by neuronal activity. To examine the effect of activity during embryogenesis, the ontogeny of proenkephalin mRNA expression and expression following activity blockade was investigated during development of chick spinal cord. A cDNA fragment (ca. 0.5 kb) coding for chick proenkephalin was cloned and sequenced. With this cDNA, a cRNA probe was made to examine proenkephalin mRNA expression in the spinal cord during embryogenesis. Proenkephalin mRNA was expressed in spinal cord in clusters of cells located in the developing dorsal horn and intermediate lamina at the earliest stages examined (stage 22; E4). Proenkephalin-positive cells in the intermediate lamina were located immediately adjacent to the ventricular zone. At stage 28 (E6) an additional cluster of proenkephalin mRNA-positive cells was seen at the lateral border of the developing intermediate lamina. At stage 33 (E7.5-5-8) the pattern of hybridization positive cells was similar to earlier stages, but individual cells could be identified. At stage 39 (E13) densely labeled cells were seen throughout the dorsal horn and intermediate laminae including the column of Terni. To determine whether neural activity affects proenkephalin mRNA expression, d-tubocurarine (an inhibitor of neural activity) was injected into developing embryos. Following administration of d-tubocurarine a dramatic decrease was seen in proenkephalin mRNA hybridization in the dorsal horn and intermediate lamina of the spinal cord. This study demonstrates in vivo that changes in the level of neural activity can alter gene expression during embryogenesis and suggests that activity is required for expression of nervous system-specific genes.

Increase in enkephalin-like immunoreactivity in hippocampi of adults with generalized epilepsy

The changes of opioid peptide reactivity in seizure activity have been well studied in animals. Increased enkephalin and dynorphin immunoreactivity in the hippocampi of animals are interpreted as the result of seizure induced mossy fibre sprouting. We studied the hippocampi of six patients with a history of long-standing grand mal seizures and six age-matched control patients with no history of epilepsy or neurologic disease, using frozen sections which were immunostained with antibodies against Leu-enkephalin and Met-enkephalin. The staining intensity in the CA3, CA4 and internal molecular layer of the dentate fascia in each case was quantified using optical densitometry image analysis. The CA3 and CA4 of the epileptic hippocampi showed highly significant increase in Leu-enkephalin-like immunoreactivity compared to the controls (P < 0.005) while the inner molecular layer showed only significant increase (P < 0.05). Met-Enkephalin-like immunoreactivity was only significantly increased in CA4 of the epileptic hippocampi (P < 0.05).

A topographically organized gamma-aminobutyric acid projection from the ventral pallidum to the nucleus accumbens in the rat

Anatomical and electrophysiological studies have indicated that a reciprocal projection from the ventral pallidum back to the nucleus accumbens exists and has functional relevance. In this study, the topographical projection from the ventral pallidum to the nucleus accumbens was examined by using retrograde tracing with fluoro-gold iontophoresed in subcompartments of the nucleus accumbens in rats combined with either in situ hybridization for glutamic acid decarboxylase and preproenkephalin mRNA or substance P immunoreactivity. Deposits made into the medial nucleus accumbens preferentially labeled neurons in the medial ventral pallidum, while deposits into the dorsolateral nucleus accumbens, at or lateral to the anterior commissure, labeled primarily cells in the dorsal and lateral ventral pallidum. A mediolateral to rostrocaudal topography was also observed, with the medial deposits preferentially labeling cells in rostral ventral pallidum and the lateral deposits resulting in retrogradely labeled cells in the ventral pallidum below the crossing of the posterior anterior commissure (subcommissural) as well as below the globus pallidus (sublenticular). The majority of cells retrogradely labeled with fluoro-gold were double-labeled for glutamic acid decarboxylase mRNA. In contrast, very few retrogradely labeled neurons in the ventral pallidum were double labeled for mRNA for preproenkephalin. These data demonstrate a topographically organized projection from the ventral pallidum to the nucleus accumbens that is primarily gamma-aminobutyric acid (GABA)-ergic and reciprocal to the GABAergic projection from the nucleus accumbens to the ventral pallidum.

Proenkephalin transgenic mice: a short promoter confers high testis expression and reduced fertility

The regulation and possible function of the preproenkephalin gene in testis were studied in vivo in transgenic mice containing: (1) bases -193 to +210 of the human proenkephalin gene and an additional one kilobase of 3' proenkephalin flanking sequence driving expression of bacterial chloramphenicol acetyltransferase (CAT), and (2) the same promoter and flanking sequences driving expression of a rat proenkephalin cDNA. Five lines of mice, designated HEC1-5, expressed the first construct and 10, HER1-10, the second. Each HEC male and many HER males showed dramatic expression of the transgene in the testis, although much lower expression was observed in the brain and other enkephalin-producing tissues. High levels of expression in testis can thus be achieved with a very short promoter region and do not require intron A sequences previously considered necessary. Altered enkephalin expression may affect testicular function. One founder, HER8, displayed grossly abnormal testicular morphology and was completely infertile. A second founder, HER6, had low sperm motility. Two offspring from other lines also displayed subnormal fertility. These studies support a role for specific promoter sequences in testis expression and may further support a significant role for proenkephalin in testicular function.

Temporal dissociation between changes in striatal enkephalin and substance P messenger RNAs following striatal dopamine depletion

Changes in the levels of enkephalin and substance P messenger RNA expression were examined in the striatum following dopamine depletion resulting from unilateral injection of 6-hydroxydopamine into the substantia nigra. In response to striatal dopamine depletion, the levels of enkephalin messenger RNA were elevated, whereas substance P messenger RNA was decreased within all regions of the striatum. Examination of the striatal peptide messenger RNAs between one and 21 days after the injection of 6-hydroxydopamine revealed a temporal dissociation between changes in enkephalin and substance P messenger RNAs. Within one day of the 6-hydroxydopamine injection, substance P messenger RNA was significantly decreased by 30% at all levels of the striatum. This decrease was maintained for up to 21 days after the lesion. In contrast, striatal enkephalin messenger RNA was not significantly elevated until three days following the injection of 6-hydroxydopamine, after which there was a gradual increase up to 21 days. In order to correlate alterations in peptide messenger RNA expression with 6-hydroxydopamine-induced changes in striatal dopamine innervation, tissue punches from the striatum were examined for dopamine content at one, two, three and seven days after the lesion. One day after the lesion, striatal dopamine levels were significantly increased by 47%. In contrast, within two days tissue dopamine content was reduced by 77% compared to control levels. A further decrease of 90% or more was observed at three and seven days after the lesion. Taken together, these data demonstrate a temporal dissociation between changes in enkephalin and substance P messenger RNA levels following 6-hydroxydopamine-induced striatal dopamine depletions. This temporal dissociation may reflect a differential response of enkephalin and substance P messenger RNAs to alterations in dopamine release and subsequent receptor activation.

Adaptive changes in rat striatal preproenkephalin expression and dopamine-opioid interactions upon chronic haloperidol treatment during different developmental stages

This study was designed to evaluate the effects of a chronic treatment with the classical neuroleptic drug haloperidol on the preproenkephalin (ppEnk) mRNA synthesis and its consequences for opioid and dopamine (DA) receptor-regulated adenylate cyclase in the developing and adult rat striatum. Prenatal exposure to haloperidol (2 mg/kg, 14 days) caused a 40% reduction of striatal ppEnk mRNA levels, but had no consequences for DA-stimulated or Met-enkephalin-inhibited adenylate cyclase activity in striatal slices from embryonic day 21 (E21) foetal brain. Postnatal treatment of rat pups from day 10 (P10) until P23 and adult rats resulted in significant increases of mRNA levels of 8 and 41%, respectively, a clear reduction of D1 DA receptor-stimulated cAMP production and a profound desensitization of delta-opioid receptors inhibitory coupled to adenylate cyclase. Since striatal D2 receptor-mediated inhibition of adenylate cyclase activity, in contrast to its activation through D1 receptors, is not present in the prenatal period, this study indicates that the tonic inhibitory effect of DA on striatal ppEnk mRNA synthesis is dependent on the presence of adenylate cyclase-coupled D2 receptors which gradually develops postnatally and further supports the idea that striatal D1 and D2 DA receptors have bidirectional effects on enkephalin synthesis in this brain area. The adaptive changes in D1 DA and delta receptor-regulated adenylate cyclase activity are discussed in relation to the well-known increase in the locomotor and reinforcing effects of mu-opioid receptor agonists upon chronic neuroleptic treatment.

Differential influence of haloperidol and sulpiride on dopamine receptors and peptide mRNA levels in the rat striatum and pituitary

We examined the effect of chronic administration (14 days) of haloperidol (2 mg/kg/day) or sulpiride (100 mg/kg/day), on the mRNA levels of various genes in the rat striatum and pituitary by quantitative in situ and Northern blot hybridizations. In the pituitary, haloperidol and sulpiride induced similar increases of mRNAs of pro-opiomelanocortin (POMC) (+65% and +73%), prolactin (PRL) (+821% and +840%) and growth hormone (GH) (+32% and +47%), but sulpiride induced a greater increase of D2R mRNA (+125%) than haloperidol (+92%). In the striatum, sulpiride and haloperidol had different effects: sulpiride induced a higher increase than haloperidol of both preproenkephalin A (PPA) mRNA (+67% versus +47%) and D2 dopamine receptor (D2R) mRNAs (+72% versus +40%). Moreover, haloperidol and sulpiride had opposite effects on substance P (SP) mRNA. Haloperidol decreased the amount of SP mRNA by 20% while sulpiride increased it by 20%. The D1 dopamine receptor (D1R) mRNA level was not significantly modified after either treatment. Our results demonstrate that the effect of a chronic haloperidol treatment on striatal dopamine receptors and neuropeptide mRNA levels is different to that of sulpiride, whereas it is similar on pituitary hormones mRNA levels.

Differences in the regional and cellular localization of c-fos messenger RNA induced by amphetamine, cocaine and caffeine in the rat

Male rats were treated i.p. with either 5 mg/kg amphetamine, 3 and 30 mg/kg cocaine or 100 mg/kg caffeine and killed after 30 min. Brains were sectioned and processed for radioactive in situ hybridization histochemistry for the labelling of either c-fos, enkephalin, substance P, neurokinin B, choline acetyltransferase, somatostatin or adenosine A2A receptor messenger RNA. The distribution of c-fos messenger RNA was investigated both at the regional level using film autoradiography, and at the cellular level using emulsion autoradiography. All drug treatments except 3 mg/kg cocaine induced an increased level of c-fos messenger RNA in cells that had a neuron-like morphology. The cells that contained the c-fos messenger RNA were identified by making pairs of 5-microns sections in which one section was processed for c-fos messenger RNA and the other was processed for one of the other messenger RNA species. After amphetamine treatment, only some 10% of the cells in the striatum were labelled, and to a variable extent. Instead there was prominent labelling of a band in the cortex that runs parallel to the cortical surface. There was also a moderate degree of labelling in the nucleus accumbens. c-fos-positive cells were substance P-positive and negative for enkephalin or A2A receptor messenger RNA. Cocaine (30 mg/kg) induced a modest labelling in the caudate-putamen, as well as in the accumbens. With cocaine treatment (30 mg/kg), about 30% of striatal neuron-like cells were c-fos labelled. Most c-fos-positive cells were substance P-positive, but none of the c-fos-positive cells were enkephalin-positive or A2A-receptor-positive. Cocaine (3 mg/kg) had no significant effect on c-fos. Caffeine gave rise to a strong hybridization signal in the caudate-putamen, particularly the dorsolateral part. No other region examined differed significantly from control. With caffeine treatment, about 73% of neuron-like cells were c-fos labelled in the lateral striatum, but labelling was much less pronounced in the medial part or in the accumbens. c-fos-labelled cells were found in enkephalin-positive and enkephalin-negative, substance P-positive and substance P-negative, neurokinin B-positive and neurokinin B-negative groups. No choline acetyltransferase-positive or somatostatin-positive cells were found that were also c-fos-positive with any of the treatments. We conclude that each of the different CNS stimulant drugs induces a highly specific pattern of c-fos messenger RNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential regulation of glutamate decarboxylase and preproenkephalin mRNA levels in the rat striatum

The mRNA levels encoding for the enzyme glutamate decarboxylase (GAD67) and the peptide enkephalin were measured in the striatum of adult and 15 day-old rats by in situ hybridization histochemistry and radioautography after neonatal injections of 6-hydroxydopamine or after acute pharmacological blockade of dopamine receptors with haloperidol or sulpiride. In adult rats injected as neonates with 6-hydroxydopamine or treated with the D1/D2 dopamine receptors antagonist, haloperidol, an increase in preproenkephalin and GAD67 mRNA levels was measured in the striatum. The D2 dopamine receptor antagonist, sulpiride, did not change the mRNA levels of either GAD67 or PPE in the striatum. In 15-day-old rats, neonatal 6-hydroxydopamine or haloperidol treatment resulted in increased preproenkephalin but unchanged GAD67 mRNA levels compared to controls. In these 15-day-old rats, however, sulpiride produced an increase in GAD67 but not preproenkephalin mRNA levels. Intrastriatal injections to adult rats of pertussis toxin which uncouples Gi/Go proteins from their receptors resulted in a dramatic increase in preproenkephalin without concomitant change in GAD67 mRNA levels. Altogether, these results show that GAD67 and preproenkephalin mRNA levels are modulated in parallel in adult but not in 15 day-old rats after 6-hydroxydopamine injections or dopaminergic blockade. In keeping with evidence of a co-localization of GAD67 and preproenkephalin mRNAs in some striatal neurons, the results indicate that these two mRNAs can be differentially regulated in the same neurons. In addition, the differential effect of haloperidol, sulpiride or pertussis toxin on GAD67 and preproenkephalin mRNA levels suggests that these two mRNAs are regulated through different dopamine receptor subtypes.

Rostrocaudal subregional differences in the response of enkephalin, dynorphin and substance P synthesis in rat nucleus accumbens to dopamine depletion

Quantitative in situ hybridization histochemistry was used to examine the effects of unilateral 6-hydroxydopamine lesions of the ascending dopaminergic fibres on levels of mRNA encoding the neuropeptides enkephalin, dynorphin and substance P in subregions of the nucleus accumbens. The nucleus accumbens was divided into quadrants and changes in mRNA were measured along the rostrocaudal extent of the nucleus. Two weeks after the lesion an increase was found in enkephalin mRNA in the lesioned side compared to the non-lesioned side, whereas a decrease was observed for dynorphin and substance P mRNA. The changes in mRNA levels differed from quadrant to quadrant and were not uniformly distributed along the rostrocaudal axis. Both types of changes, i.e. increase and decrease, were much higher in rostral parts of the nucleus than in caudal parts, indicating regional differences in the effects of blockade of the dopaminergic neurotransmission. The lesion-induced increases and decreases in mRNA levels occurred in both the shell and the core subregions of the nucleus accumbens and were not specifically related to either of these areas. Factors are discussed that may contribute to the rostrocaudal gradient in the changes of enkephalin, substance P and dynorphin mRNA levels. On the basis of their afferent and efferent connections, the rostral and caudal parts of the nucleus accumbens are considered to be involved in different functions. The present results suggest that dopamine depletion may affect these functions in a differential manner.

Adenosine A2a receptor mRNA is expressed by enkephalin cells but not by somatostatin cells in rat striatum: a co-expression study

The cellular co-expression of adenosine A2a receptor mRNA and preproenkephalin A (PPE A) mRNA and A2a receptor mRNA and prosomatostatin (pSRIF) mRNA in rat striatum was studied using a combination of radioactive and non-radioactive in situ hybridization techniques. Cells containing adenosine A2a receptor mRNA were visualised using an 35S-labelled oligonucleotide whilst those containing PPE A mRNA and pSRIF mRNA were detected using alkaline phosphatase-labelled antisense oligonucleotides; both radioactive and non-radioactive hybridization signals were visualized on the same tissue section. Bright field examination of striatal sections hybridized with both the [35S]adenosine A2a receptor probe and the alkaline phosphatase-labelled PPE A probe revealed dense clusters of silver grains overlying cells containing alkaline phosphatase reaction product demonstrating that the two gene transcripts were expressed by the same medium-sized nerve cells. The cellular expression of the two mRNAs was consistently found to be concordant demonstrating that adenosine A2a receptor mRNA is expressed by medium-sized striatal enkephalin cells. In contrast, clusters of silver grains were never detected overlying striatal cells containing pSRIF mRNA indicating that this population of interneurones do not express the adenosine A2a receptor sub-type. The expression of adenosine A2a receptors by enkephalin cells in striatum suggests that adenosine may play a role in modulating the activity of GABA/enkephalin striatopallidal neurones through interaction with A2a receptors.

Dopaminergic and peptidergic mRNA levels in juvenile rat brain after prenatal cocaine treatment

The effects of prenatal cocaine treatment on gene expression in dopaminergic pathways of juvenile rats were investigated by in situ hybridization histochemistry. Pregnant rats from gestational day 8 to 20 were administered one of the following treatments: (A) 40 mg/kg cocaine hydrochloride/3 ml/day s.c.; (B) 0.9% saline/3 ml/day s.c. and pair fed to cocaine-exposed dams; (C) 0.9% saline/3 ml/day s.c. and placement on cellulose-diluted diet to match the caloric intake of the cocaine-treated group without explicit food restriction; (D) no injection and lab chow diet. Levels of mRNA for the dopamine transporter, tyrosine hydroxylase, cholecystokinin, D1 and D2 dopamine receptors and enkephalin were quantitated in relevant dopaminergic regions of forebrain and midbrain of offspring that were sacrificed on postnatal day 21. Quantitative analysis revealed no significant changes in mRNA levels in any of the brain regions examined. In the present animal model, cocaine exposure in utero had no significant effect on mRNA levels of the dopamine transporter, D1 or D2 dopamine receptors, enkephalin, tyrosine hydroxylase, or cholecystokinin in juvenile rats.

Pentylenetetrazole-induced seizures stimulate transcription of early and late response genes

Cellular immediate early gene and neuropeptide gene expression have each been demonstrated to be modulated in hippocampus in response to a variety of seizure-inducing stimuli. In this study, gene transcription for three immediate early genes, c-fos, c-jun and NGFI-A, and three neuropeptide genes, enkephalin, dynorphin and neuropeptide Y, was investigated using nuclear run-on assays following a single injection of the convulsant pentylenetetrazole (PTZ). At 15 min following PTZ injection, only transcription for c-fos was increased. By 6 h following PTZ treatment, transcription for all immediate early genes and for dynorphin and neuropeptide Y was increased; however, this increase was transient in that transcription of all genes returned to control values by 48 h following PTZ treatment. Thus, regulation of immediate early and neuropeptide gene mRNA levels and immunoreactivity occurs, at least in part, at the level of transcription for the genes encoding neuropeptide Y, dynorphin, c-fos, c-jun, and NGFI-A. Moreover, the difference between increased transcription rates reported here and increased mRNA levels reported here and elsewhere suggests that additional post-transcriptional regulation of gene expression occurs in hippocampal neurons.

Effect of acute stress on the expression of hypothalamic messenger ribonucleic acids encoding the endogenous opioid precursors preproenkephalin A and proopiomelanocortin

In addition to the release of adenohypophysial hormones adrenocorticotropin and beta-endorphin, most types of acute stress induce rapid release of prolactin (PRL) from the anterior pituitary lobe. Endogenous opioid peptides are believed to participate in the stress-induced PRL secretion via an action within the central nervous system. In the present study, we have investigated the effect of acute stress on anterior pituitary PRL secretion and the hypothalamic expression of messenger ribonucleic acids (mRNAs) encoding precursors of the endogenous opioids Met-enkephalin and beta-endorphin. Adult male rats were subjected to 1 h of restraint and the stress-induced rise in plasma PRL was measured both during and after termination of the stress paradigm. Using quantitative in situ hybridization histochemistry, it was observed that levels of proenkephalin A mRNA increased significantly within the medial parvocellular subset of the hypothalamic paraventricular nucleus, and within the arcuate nucleus levels of proopiomelanocortin (POMC) mRNA were slightly, but significantly, increased. The employed stress paradigm also induced an elevation of anterior pituitary levels of PRL and POMC mRNAs. The present data suggest that restraint stress activates gene expression of endogenous opioid systems in the hypothalamus and that the employed stress paradigm is of sufficient magnitude to stimulate both mRNA expression and release of PRL in the anterior pituitary lobe.

Effects of intranigral injections of colchicine on the expression of some neuropeptides in the rat forebrain: an immunohistochemical and in situ hybridization study

In the present study, we describe the neurochemical effects of intranigral injections of colchicine in the rat forebrain using immunohistochemistry and in situ hybridization. The observations on the injected side are compared to the contralateral one and to the sham-operated rats. We demonstrate that such injections are able to strongly enhance the immunoreactivity for Met-enkephalin (ME), substance P (SP) and neuropeptide Y (NPY) in numerous nerve cell bodies of the limbic system (injected side), whereas the levels of the corresponding mRNAs are differently modified according to the region examined. A clear correlation between the enhancement of the immunostaining for ME and SP and that of the preproenkephalin (PPA) and preprotachychinin gene transcripts was observed in neuronal perikarya of the medial amygdaloid nucleus (SP), of the dorsolateral hypothalamus (ME) and of the ventromedial hypothalamic nucleus (SP). These observations are interpreted as an induction--or increased expression--of neuropeptide genes in neuronal perikarya postsynaptic to nerve fibers originating in the midbrain and brain stem. In this case, colchicine is thought to block the electrophysiological activity of ascending nerve fibers (anterograde and postsynaptic effect). In the case where the enhancement of the immunoreactivity for the studied neuropeptides was associated with no change or a decreased expression of the corresponding genes in the same brain areas, colchicine may have blocked the axoplasmic transport of peptides in nerve fibers projecting to the midbrain and/or brain stem (6). This may result in a retrograde accumulation of peptides in the nerve cell bodies of origin and, eventually, in a negative feedback regulation of the corresponding encoding genes in these perikarya (retrograde and presynaptic effect of colchicine). The drastic behavioral effects of bilateral intranigral injections of colchicine, on ingestive behavior in particular, have been studied in a following paper.

Preproenkephalin mRNA expression in the developing and adult rat brain

[Met5]-Enkephalin is derived from the protein precursor, proenkephalin A, which in turn is encoded by the preproenkephalin (PPE) gene. [Met5]-Enkephalin is not only a putative neuromodulatory substance, but also serves as a growth factor (= opioid growth factor, OGF). OGF exerts an inhibitory influence on the developing nervous system and is especially targeted to cell proliferative and differentiative events. This study examined the relationship of PPE mRNA expression to late prenatal and postnatal rat brain development. Northern blot analysis of the whole brain and cerebellum showed that message is present in the fetal nervous system on prenatal day 15 (the earliest timepoint examined), is expressed at relatively similar levels within each tissue during the first 2 postnatal weeks, and reaches adult levels by the beginning of the 3rd postnatal week. In situ hybridization methodology revealed that PPE mRNA was prominent in areas associated with cell generation. Message was found in sites of primary (i.e., ventricular region) and secondary (e.g., external germinal layer of the cerebellum) cellular replication, as well as in discrete foci of cell proliferation (e.g., medullary layer of the cerebellum). PPE mRNA was also present for varying periods of time in postmitotic cells. During development, a number of patterns (decrease, increase, and no perceptible change) of PPE mRNA could be detected in relationship to the fetal/neonatal period. Given the strong evidence (e.g., regulation of cell proliferation and differentiation, temporal and spatial patterns of peptide and zeta opioid receptor) that enkephalin immunoreactivity is associated with proliferating and differentiating neurons and glia, these results suggest that the source of [Met5]-enkephalin is both autocrine and paracrine in nature.

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.

Opioid peptide gene expression in the nucleus tractus solitarius of rat brain and increases induced by unilateral cervical vagotomy: implications for role of opioid neurons in respiratory control mechanisms

Neurons expressing messenger RNA encoding the opioid peptide precursors, preproenkephalin and preprodynorphin were localized in the medulla oblongata of the rat by in situ hybridization of specific DNA oligonucleotide probes. Neurons containing preproenkephalin messenger RNA were found throughout the medullary reticular formation in the gigantocellular and paragigantocellular reticular nuclei, the parvicellular and lateral reticular nuclei; commissural, medial and ventrolateral subnuclei in the nucleus tractus solitarius and the nucleus of the spinal trigeminal tract. Labelled cells were also concentrated in the more medial regions of the area postrema. In contrast, neurons containing preprodynorphin messenger RNA had a more restricted distribution and were detected in the commissural and ventrolateral nucleus tractus solitarius and nucleus of the spinal trigeminal tract, especially in the more dorsal regions. Expression of preproenkephalin and preprodynorphin messenger RNA was also examined in the dorsal vagal complex of rats that had undergone a unilateral nodose ganglionectomy or cervical vagotomy. Twenty-four hours after both cervical vagotomy and nodose ganglionectomy, there was a specific 1.5-2-fold elevation in preproenkephalin and preprodynorphin messenger RNA levels in the ventrolateral subnucleus of the contralateral nucleus tractus solitarius relative to levels in the ipsilateral nucleus tractus solitarius and in the nucleus tractus solitarius of sham-operated animals. Previous immunohistochemical studies demonstrating the co-localization of enkephalin and dynorphin in the ventrolateral nucleus tractus solitarius suggest that these changes occurred in the same population of neurons. In light of the suggested role of the ventrolateral nucleus tractus solitarius as a central respiratory centre and the activation of the intact pulmonary afferents that innervate this area following a unilateral vagotomy (which increases inspiration volume and expiratory time by affecting the Hering-Breuer reflex), our results suggest a specific involvement of enkephalin- and dynorphin-containing neurons in the ventrolateral nucleus tractus solitarius in central respiratory control mechanisms.

Immediate early gene activation during the initial phases of the excitotoxic cascade

Direct brain injections of the N-methyl-D-aspartate receptor agonist quinolinic acid (QA) trigger an excitotoxic cascade characterized by rapid neuronal death and glial/immune cell activation. The present study compared the timing of immediate early gene (IEG; c-fos, c-jun, jun-B, and zif/268) induction with the response of neuronal transcripts during the first 24 hr of a QA lesion within the rodent striatum. Following QA exposure, IEG mRNA induction periods extended from 30 min to 24 hr. Several characteristics of this prolonged transcriptional response suggest that separate cell populations (neuronal vs. glial) originate individual IEG phases during the first day of the lesion. The first IEG phase was rapid and peaked at 60 min. This initial IEG phase, likely neuronal in origin, was dominated by robust increases in the expression of c-fos, jun-B, and zif/268 mRNAs in contrast to small increases in c-jun expression. A second, delayed IEG phase was initiated after the first hour and extended to 24 hr. This IEG phase was more intense and continued beyond the period of neuronal survival as detected by the loss of neurotransmitter-specific mRNAs (preprotachykinin, preproenkephalin, and glutamic acid decarboxylase). During this phase, c-jun mRNA levels coordinately increased with c-fos. Interestingly, the transcriptional peak of the delayed IEG phase occurred between 4 and 12 hr, the time which corresponded to the rapid decline of neuronal transcripts.(ABSTRACT TRUNCATED AT 250 WORDS)

GABA and enkephalin projection from the nucleus accumbens and ventral pallidum to the ventral tegmental area

GABAergic and enkephalinergic afferents to the ventral tegmental area were investigated in the rat using retrograde tracing techniques combined with in situ hybridization. Following iontophoretic deposit of Fluoro-Gold in the ventral tegmental area labeling in the forebrain was most dense in the shell of the nucleus accumbens, rostral ventromedial ventral pallidum and diagonal band of Broca. A smaller density was also observed in the lateral septum. In these forebrain regions, the portion of retrogradely labeled cells that contained mRNA for glutamate decarboxylase ranged from 25% to 50%, whereas only 5% to 15% were double-labeled for preproenkephalin mRNA. Cells double-labeled with either glutamate decarboxylase or preproenkephalin mRNA were most numerous in the lateral septum, shell of the nucleus accumbens, rostral ventral pallidum and diagonal band of Broca. Large Fluoro-Gold deposits which invaded the medial substantia nigra resulted in a significant number of retrogradely labeled cells in the core of the nucleus accumbens, and a portion of these neurons also contained mRNA for glutamate decarboxylase or preproenkephalin. These data demonstrate the presence of GABAergic and enkephalinergic neurons projecting from the nucleus accumbens, ventral pallidum and diagonal band of Broca to the ventral tegmental area.

Delta opioid receptor mRNA distribution in the brain: comparison to delta receptor binding and proenkephalin mRNA

The recent cloning of the mouse delta opioid receptor (Evans et al., 1992; Kieffer et al., 1992) has demonstrated it to be a member of the seven transmembrane G-protein coupled family of neurotransmitter receptors. The present study describes the cellular localization in the central nervous system (CNS) of an mRNA encoding this receptor and compares it with the distribution of delta receptor binding and proenkephalin mRNA using a combination of in situ hybridization and receptor autoradiographic techniques. Delta receptor mRNA was visualized with a cRNA probe (472-903 bp) corresponding to transmembrane domains III-VI of the receptor, while proenkephalin mRNA was labeled with a cRNA probe to exon 3 (139-832 bp). A high level of correspondence was observed between the distribution of delta receptor mRNA and delta receptor binding as defined by the selective ligand [3H]D-Pen2-Pen5-enkephalin. Delta receptor mRNA and binding were expressed in the neocortex, caudate-putamen, nucleus accumbens, olfactory tubercle, diagonal band of Broca, amygdala and the nucleus of the solitary tract. Discrepancies in the distribution of delta receptor mRNA and binding in the olfactory bulb, hippocampus, globus pallidus and substantia nigra pars reticulata, may in part be due to differential receptor synthesis and transport. These results are discussed in relation to the distribution of proenkephalin mRNA and how this may affect our understanding of opioid circuitry in the CNS.

Chronic intracerebroventricular infusion of the antiopioid peptide, Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (NPFF), downregulates mu opioid binding sites in rat brain

Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2 (NPFF), an endogenous mammalian antiopioid peptide, has been shown by other laboratories to attenuate the acute antinociceptive effects of morphine, the development of morphine tolerance, and naloxone-induced withdrawal in morphine-dependent rats. The present study determined the effect of chronic NPFF on mu opioid receptors and mRNA for the endogenous opioids dynorphin and enkephalin. Rats received ICV infusions of either saline or NPFF (5 micrograms/h) for 13 days via Alzet 2002 osmotic minipumps. Homogenate binding studies, which used whole brain membranes, demonstrated that NPFF decreased the Bmax of mu binding sites (labeled by [3H][D-Ala2-MePhe4,Gly-ol5]enkephalin) from 262 +/- 12 to 192 +/- 12 fmolmg protein, and increased the Kd from 1.1 to 2.3 nM. Quantitative receptor autoradiography and in situ hybridization experiments were conducted with sections collected at the level of the striatum. The density of mu opioid binding sites labeled by [3H][D-Ala2-MePhe4,Gly-ol5]enkephalin was decreased in all brain areas measured except the corpus callosum, and there was no change in dynorphin mRNA or enkephalin mRNA in the caudate, the nucleus accumbens, or the ventral pallidum. Rats chronically administered ICV morphine sulfate (20 micrograms/h) for 14 days developed tolerance to morphine and a low degree of dependence, as measured by naloxone-precipitated withdrawal. Chronic administration of NPFF concurrently with morphine sulfate did not significantly alter naloxone-induced withdrawal signs or the development of morphine tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Changes in enkephalin immunoreactivity of sympathetic ganglia and digestive tract of the cat after splanchnic nerve ligation

The aim of the present study was to analyze changes in the enkephalin immunoreactivity of sympathetic prevertebral ganglia coeliac plexus and inferior mesenteric ganglion) and intestinal tract (myenteric plexus and external muscle layers) in cats 2 days after left thoracic splanchnic nerve ligation, using radioimmunoassay and immunohistochemical techniques. Specific polyclonal antibodies directed against methionine- and leucine-enkephalin were used. The nerve ligation led to a considerable increase in the enkephalin immunoreactivity in the cranial part of the ligated nerves. This finding confirms the presence, in the cat, of an enkephalin output originating from thoracic spinal structures which are probably enkephalin-containing preganglionic neurons. In prevertebral ganglia the nerve ligation induced a marked decrease in the enkephalin immunoreactivity, which was probably due to the interruption of thoracic enkephalin efferents projecting towards both the coeliac plexus and the inferior mesenteric ganglion. In the digestive tract, the nerve ligation depressed the methionine-enkephalin immunoreactivity only in the gastro-duodenal region, and had no effect on the ileo-colonic region. The results of the present study add to the growing evidence that the sympathetic nervous system is involved in regulating the enteric enkephalinergic innervation, which is probably involved in controlling the intestinal motility.

Effects of neonatal 6-hydroxydopamine injections on glutamate decarboxylase, preproenkephalin and dopamine D2 receptor mRNAs in the adult rat striatum

The effects of neonatal 6-hydroxydopamine injections on the levels and cellular distribution of glutamate decarboxylase (GAD67), preproenkephalin and dopamine D2 receptor messenger RNAs were studied in the striatum of adult rats. Cerebroventricular injections of 150 micrograms or 100 micrograms of 6-hydroxydopamine to 3-day-old neonate rats resulted in the total disappearance of neurons labeled with a tyrosine hydroxylase probe in sections of the substantia nigra and ventral tegmental area. In the striatum of adults, both doses of 6-hydroxydopamine induced an increase in GAD67 and preproenkephalin mRNA levels compared to controls. A smaller but consistent increase in dopamine D2 receptor mRNA levels was also found on adjacent sections of the striatum only in animals injected with 150 micrograms of 6-hydroxydopamine. Regional analysis of labeling showed that the increased GAD67, preproenkephalin or dopamine D2 receptor mRNA levels occurred in all striatal sectors examined. Emulsion radioautographs confirmed the increased GAD67, preproenkephalin and dopamine D2 receptor mRNA labeling at cellular level. The present study demonstrates that bilateral 6-hydroxydopamine lesions of dopamine neurons in neonate rats are able to induce a long-term and widespread alteration in the expression of genes encoding for GAD67, preproenkephalin and dopamine D2 receptor in the striatum. In view of previous results after 6-hydroxydopamine lesions in adults, it appears that the behavioral differences observed after adult or neonatal 6-hydroxydopamine lesions are accompanied by a similar alteration of GAD67, preproenkephalin and dopamine D2 receptor gene expression in presumed striatal projection neurons.