mRNA Levels In Striatum Research Articles

Effects of an early life experience on rat brain cannabinoid receptors in adolescence and adulthood

Neonatal handling is an experimental model of early life experience associated with resilience in later life challenges, altering the ability of animals to respond to stress. The endocannabinoid system of the brain modulates the neuroendocrine and behavioral effects of stress, while this system is also capable of being modulated by stress exposure itself. The present study has addressed the question of whether neonatal handling in rats could affect cannabinoid receptors, in an age- and sex-dependent manner, using in situ hybridization and receptor binding techniques. Different effects of neonatal handling were observed in adolescent and adult brain on CB1 receptor mRNA and [3H]CP55,940 binding levels, which in some cases were sexually dimorphic. Neonatal handling interfered in the developmental trajectories of CB1 receptor mRNA levels in striatum and amygdaloid nuclei, as well as of [3H]CP55,940 binding levels in almost all regions studied. Adult handled rats showed reduced [3H]CP55,940 binding levels in the prefrontal cortex, striatum, nucleus accumbens and basolateral amygdala, while binding levels in prefrontal cortex of adolescent handled rats were increased. Finally, handling resulted in decreases in female [3H]CP55,940 binding levels in the striatum, nucleus accumbens, CA3 and DG of dorsal hippocampus and basolateral amygdala. Our results suggest that a brief and repeated maternal separation during the neonatal period induces changes on cannabinoid receptors differently manifested between adolescence and adulthood, male and female brain, which could be correlated to their stress response.

Striatal Alterations of Secretogranin-1, Somatostatin, Prodynorphin, and Cholecystokinin Peptides in an Experimental Mouse Model of Parkinson Disease

The principal causative pathology of Parkinson disease is the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta projecting to the striatum in the brain. The information regarding the expression of neuropeptides in parkinsonism is very limited. Here we have elucidated striatal neuropeptide mechanisms in experimental parkinsonism using the unilateral 6-hydroxydopamine model to degenerate dopamine neurons. A thoroughly controlled sample preparation technique together with a peptidomics approach and targeted neuropeptide sequence collections enabled sensitive detection, identification, and relative quantitation of a great number of endogenous neuropeptides. Previously not recognized alterations in neuropeptide levels were identified in the unilateral lesioned mice with or without subchronic 3,4-dihydroxy-L-phenylalanine administration, the conventional treatment of Parkinson disease. Several of these peptides originated from the same precursor such as secretogranin-1, somatostatin, prodynorphin, and cholecystokinin. Disease-related biotransformation of precursors into individual peptides was observed in the experimental model of Parkinson disease. Several previously unreported potentially biologically active peptides were also identified from the striatal samples. This study provides further evidence that neuropeptides take part in mediating the central nervous system failure associated with Parkinson disease.

Time-course of SKF-81297-induced increase in glutamic acid decarboxylase 65 and 67 mRNA levels in striatonigral neurons and decrease in GABA A receptor α1 subunit mRNA levels in the substantia nigra, pars reticulata, in adult rats with a unilateral 6-hydroxydopamine lesion

Striatal projection neurons use GABA as their neurotransmitter and express the rate-limiting synthesizing enzyme glutamic acid decarboxylase (GAD) and the vesicular GABA transporter vGAT. The chronic systemic administration of an agonist of dopamine D1/D5-preferring receptors is known to alter GAD mRNA levels in striatonigral neurons in intact and dopamine-depleted rats. In the present study, the effects of a single or subchronic systemic administration of the dopamine D1/D5-preferring receptor agonist SKF-81297 on GAD65, GAD67, PPD and vGAT mRNA levels in the striatum and GABA A receptor α1 subunit mRNA levels in the substantia nigra, pars reticulata, were measured in rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion. After a single injection of SKF-81297, striatal GAD65 mRNA levels were significantly increased at 3 but not 72 h. In contrast, striatal GAD67 mRNA levels were increased and nigral α1 mRNA levels were decreased at 72 but not 3 h. Single cell analysis on double-labeled sections indicated that increased GAD or vGAT mRNA levels after acute SKF-81297 occurred in striatonigral neurons identified by their lack of preproenkephalin expression. Subchronic SKF-81297 induced significant increases in striatal GAD67, GAD65, preprodynorphin and vGAT mRNA levels and decreases in nigral α1 mRNA levels. In the striatum contralateral to the 6-OHDA lesion, subchronic but not acute SKF-81297 induced a significant increase in GAD65 mRNA levels. The other mRNA levels were not significantly altered. Finally, striatal GAD67 mRNA levels were negatively correlated with nigral α1 mRNA levels in the dopamine-depleted but not dopamine-intact side. The results suggest that different signaling pathways are involved in the modulation by dopamine D1/D5 receptors of GAD65 and GAD67 mRNA levels in striatonigral neurons. They also suggest that the down-regulation of nigral GABA A receptors is linked to the increase in striatal GAD67 mRNA levels in the dopamine-depleted striatum.

The regulation of rotenone-induced inflammatory factor production by ATP-sensitive potassium channel expressed in BV-2 cells

Our previous studies have demonstrated that activating ATP-sensitive potassium channel (K ATP channel), not only improved Parkinsonian behavior and neurochemical symptoms, but also reduced iNOS activity and mRNA levels in striatum and nigra of rotenone rat model of Parkinson's disease (PD). In this study, it was first shown that the subunits of K ATP channels are expressed in BV-2 cells, and then it was investigated whether K ATP channel was involved in regulating inflammatory factor production from BV-2 cells activated by rotenone. It was found that K ATP channel was expressed in BV-2 cell and formed by the combination of Kir 6.1 and SUR 2A/2B. K ATP channel openers (KCOs) including pinacidil, diazoxide and iptakalim (Ipt) exerted beneficial effects on rotenone-induced morphological alterations of BV-2 cells, decreased tumor necrosis factor alpha (TNF-alpha) production and the expression and activity of inducible isoform of nitric oxide synthase (iNOS). Either glibenclamide or 5-hydroxydecanoate acid (a selective mitochondrial K ATP channel blocker) could abolish the effects of KCOs, suggesting that K ATP channels, especially mitochondrial ATP-sensitive potassium channels (mitoK ATP channels), played a crucial role in preventing the activation of BV-2 cells, and subsequently the production of a variety of proinflammatory factors. Therefore, activation of K ATP channel might be a new therapeutic strategy for treating neuroinflammatory and neurodegenerative disorders.

Regulation of striatal neuropeptide mRNAs: effects of the 5-HT(2) antagonist SR46349B in adult rats with a neonatal 6-hydroxydopamine lesion.

The intrastriatal injection of 6-hydroxydopamine (6-OHDA) in newborn rats produces a marked striatal dopamine (DA) depletion, accompanied by a serotonin (5-HT) hyperinnervation and an up-regulation of 5-HT receptors. The aim of the present study was to investigate whether the increase in 5-HT(2) receptors could compensate for some of the DA lesion-induced effects, such as the increase in striatal preproenkephalin (PPE) and the decrease in preprotachykinin A (PPT-A) mRNA levels. Three months after the DA lesion, the effect of the selective 5-HT(2) antagonist SR46349B was investigated by a subacute treatment (10 mg/kg, IP, twice per day for 3.5 days). In sham-operated rats, the blockade of 5-HT(2) receptors decreased PPE mRNA levels in the striatum and, by contrast, had no effect on PPT-A mRNA levels. In rats with a unilateral neonatal DA lesion, SR46349B had no more effect on PPE mRNA levels in the intact striatum and was unable to modify the lesion induced-increase in PPE mRNA. The decrease in PPT-A mRNA levels induced by the neonatal DA lesion was not changed after SR46349B treatment in the posterior part of the lesioned striatum. Our results suggest that SR46349B indirectly decreases PPE mRNA levels in striatopallidal neurons in intact animals through a desinhibition of DA neuron activity. This is further evidenced by the lack of PPE mRNA changes in the DA lesioned striatum despite the up-regulation of 5-HT(2) receptor transmission induced in this model. Finally, the absence of any effect of 5-HT(2) antagonist on the expression of PPT-A mRNA in intact animals is discussed. The precise role of 5-HT(2) receptor on PPT-A mRNA biosynthesis after a neonatal lesion should be clarified by further experiments using 5-HT(2) agonists.

Cocaine and Methamphetamine Differentially Affect Opioid Peptide mRNA Expression in the Striatum

In general, administration of methamphetamine and cocaine alters preprodynorphin and preproenkephalin mRNA levels in striatum. However, no study has directly compared the effects of these stimulants on opioid peptides in striatum. This study used in situ hybridization to compare directly the effects of cocaine and methamphetamine on preprodynorphin and preproenkephalin mRNAs in distinct striatal regions. Male Sprague-Dawley rats received a single administration of 15 mg/kg methamphetamine or 30 mg/kg cocaine and were killed 30 min or 3 h later. Methamphetamine and cocaine differentially affected preprodynorphin mRNA in striatum after 3 h. Densitometric analysis of film autoradiograms revealed that cocaine, but not methamphetamine, significantly increased preprodynorphin. This effect was seen throughout rostral striatum and dorsally in caudal striatum. However, specific analysis of "patches" in which preprodynorphin expression is high revealed a significantly greater effect of methamphetamine versus cocaine. In contrast, both cocaine and methamphetamine had similar effects on preproenkephalin mRNA, decreasing levels after 30 min in rostral striatum and in the core of nucleus accumbens. These data suggest that methamphetamine and cocaine have distinct postsynaptic consequences on striatal neurons.

Developmental Regulation of BDNF and NT-3 Expression by Quinolinic Acid in the Striatum and Its Main Connections

Interactions between neurotrophic factors and neurotransmitters participate in the formation and maintenance of appropriate connections, as well as in neurodegenerative processes. Here we have measured changes in the developmental expression pattern of BDNF and NT-3 in the striatum, cortex, and substantia nigra induced by intrastriatal injection of the N-methyl-d-aspartate glutamate receptor agonist quinolinic acid (QUIN). Animals were injected at different postnatal ages, and BDNF and NT-3 mRNA levels were determined 6 h after lesion using a ribonuclease protection assay. Our results show a biphasic increase in BDNF mRNA levels in striatum and in the ipsilateral cortex at postnatal day (P)5 and P21. In contrast, although NT-3 expression did not change in the striatum, it was down-regulated in the ipsilateral cortex at P5 and P30. Intrastriatal QUIN injection did not induce changes in either BDNF or NT-3 expression in the ipsilateral substantia nigra. These findings show that neurotrophin expression is developmentally regulated after excitotoxic injury, which suggests that this endogenous response may be involved in different neuronal maturation and vulnerability during development.

Differential patterns of induction of NGFI-B, Nor1 and c-fos mRNAs in striatal subregions by haloperidol and clozapine

Disturbances of retinoid activated transcription mechanisms have recently been implicated as risk factors for schizophrenia. In this study we have compared the regulation of mRNAs for the nuclear orphan receptor NGFI-B, which forms a functional heterodimer with the retinoid x receptor and the related orphan nuclear receptor Nor1 with c-fos mRNA after acute and chronic treatments with haloperidol and clozapine. The antipsychotic drugs haloperidol and clozapine have different clinical profiles. Haloperidol is a typical neuroleptic giving extrapyramidal side effects (EPS), whereas the atypical compound clozapine does not. Acute haloperidol treatment increased NGFI-B, Nor1 and c-fos mRNAs in nucleus accumbens shell and core as well as medial and lateral caudate putamen. In contrast, clozapine lead to an increase of NGFI-B, Nor1 and c-fos only in the accumbens shell. No haloperidol or clozapine effect on these mRNAs was detected in cingulate, sensory or motor cortex. Chronic haloperidol lead to an increase of NGFI-B mRNA in the accumbens core. Acutely, it is possible that the increased levels of NGFI-B, Nor1 and c-fos mRNA levels in striatum and accumbens might indicate a neural activation which possibly can be used when screening for drugs that do not produce EPS. Also, the increased levels of NGFI-B, which is an important component in retinoid signaling, both after acute and chronic treatments of haloperidol suggests altered sensitivity to retinoids which could be an important component for the beneficial antipsychotic effect.

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.

Modulation of Dopamine D<sub>2</sub> Receptor Expression by an NMDA Receptor Antagonist in Rat Brain

The expression of dopamine D2 receptor mRNA was studied in rat brain following micro-injection of a competitive N-methyl D-aspartate (NMDA) receptor antagonist at the prefrontal cortex. Male Sprague-Dawley rats cannulated bilaterally into the medial prefrontal cortex were injected with a competitive NMDA receptor antagonist (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). The levels of mRNA for NMDA-R1 and dopamine D2 receptors were measured by reverse transcriptase-polymerase chain reaction (RT-PCR), and D2 receptor density was quantified by [3H]spiperone binding in the cortex and striatum of these animals. In the prefrontal cortex, the levels of NMDA-R1 receptor mRNA showed significant decrease in CPP-treated animals compared to control animals. However, NMDA-R1 mRNA levels in striatum remained unchanged in any of the experimental groups. The D2 receptor mRNA levels and [3H]spiroperidol binding in prefrontal cortical membranes showed no significant difference between the CPP-treated and control groups of animals. In the striatum, a significant increase in striatal dopamine D2 receptor mRNA levels was shown in animals treated with CPP. The increase in D2 mRNA level was correlated with an increase in the D2 receptor binding sites in the striatal membranes. These results suggest a possible interaction between prefrontal cortical NMDA receptors and striatal dopamine receptors.

Regulation of NMDA receptor subunit messenger RNA levels in the rat brain following acute and chronic exposure to antipsychotic drugs

Based on anatomical and biochemical observations a role of glutamate in schizophrenia has been postulated. In the present work we have investigated the gene expression for two families of NMDA receptor subunits (NR-1 and NR-2) following acute and chronic treatment with typical (haloperidol) and atypical (clozapine) antipsychotic drug (APD) in rats. A single injection of the two drugs elicited a significant increase in the mRNA levels of NR-2B in the nucleus accumbens, whereas only haloperidol was able to elevate NR-2A and NR-2B in the hippocampus. Following a 21 day treatment, significant differences in the regulatory pattern of NMDA-R subunits were observed. Haloperidol increased their mRNA levels in striatum whereas clozapine, consistent with its relatively weaker influence on nigro-striatal dopamine function, did not change the expression of NR subunits in this region. Both APD's were able to decrease the expression of NR-2 subunits in the hypothalamus, but only clozapine was capable of reducing NR-2C in frontal cortex and accumbens. The regulation of NMDA-R subunits in specific brain regions may represent a novel and important mechanism through which APD's exert some of their effects on brain function.

Does phenylethylamine have a role in schizophrenia?: LSD and PCP up-regulate aromatic l-amino acid decarboxylase mRNA levels

Aromatic l-amino acid decarboxylase (AADC) is rate limiting in the production of 2-phenylethylamine (2PE). AADC activity and 2PE serum concentrations have been found to be increased in schizophrenic patients. Both antipsychotic and psychotogenic drugs, including amphetamine, affect the activity and encoding mRNA levels of AADC. Amphetamine is an analogue of 2PE and has a similar physiological effect. We have looked at the effects of chronic (32 day) treatment of rats with LSD (0.12 μg/kg/day) and phencyclidine (PCP; 10 mg/kg/day) on AADC mRNA levels. Both drugs up-regulated AADC mRNA levels in striatum, nucleus accumbens, hippocampus and cerebellum by between 50% and 150%. A splicing variant of AADC, present in human brain, which lacks the 3rd exon does not appear to be present in rat brain. These results are consistent with the hypothesis that over activity of AADC leading to increased production of 2PE is involved in endogenous psychosis such as schizophrenia.

Clozapine and haloperidol differentially affect AMPA and kainate receptor subunit mRNA levels in rat cortex and striatum

Dopamine is the neurotransmitter most often implicated in the pathogenesis of schizophrenia. However, glutamatergic antagonists can cause psychotic symptoms in otherwise normal humans, and exacerbate these symptoms in schizophrenics. These findings have led to a model of dopamine–glutamate interactions in limbic cortex and striatum as a potential substrate for symptom production in schizophrenia. From this model, we might expect that cortical and striatal expression of non-NMDA ionotropic glutamate receptors would be differentially regulated by antipsychotic treatment. To begin to address this question, we examined the regulation of mRNA levels of the AMPA (gluR1-gluR4), low affinity kainate (gluR5-gluR7), and high affinity kainate (KA1-KA2) receptor subunits by clozapine (20 mg/kg/day) and haloperidol (2 mg/kg/day) treatment for 2 weeks. Both clozapine and haloperidol caused region-specific alterations in the mRNA levels of these subunits, but there was no differential regulation in the cortex vs. the striatum. Haloperidol caused a decrease in gluR2 and gluR4 mRNA levels in both cortex and striatum and an increase in KA2 mRNA levels in the striatum only. However, clozapine treatment caused an increase in gluR7 mRNA expression, and a decrease in gluR3 mRNA expression, in both cortex and striatum while causing an increase in KA2 mRNA levels, and a decrease in gluR4 mRNA levels, in the striatum only. These dissimilarities may represent an interesting mechanism for some of the differential therapeutic or toxic effects of clozapine and haloperidol, and also may be relevant to our understanding of dopamine–glutamate interactions in schizophrenia.

Progressive Augmentation of Striatal and Accumbal Preprotachykinin mRNA Levels by Chronic Treatment with Methamphetamine and Effect of Concurrent Administration of the N-methyl- d-aspartate Receptor Antagonist MK-801

We have assessed the time course of repeated administration of methamphetamine (METH; 4 mg/kg) and withdrawal on the levels of preprotachykinin (PPT) and preproenkephalin (PPE) mRNA abundance in the caudate-putamen (CPu) and nucleus accumbens (NAc) of the rat brain by in situ hybridization histochemistry. Neostriatal PPT mRNA levels rose gradually between days 1 and 6 of treatment, with the greatest elevation observed at day 6. After 6 days of daily injections twice per day, PPT mRNA increases in dorsomedial (172%) and ventromedial (196%) aspects of the CPu were significantly higher than in dorsolateral (147%) and ventrolateral (135%) subdivisions. Similarly, PPT mRNA levels were increased in the anterior CPu (163%) and NAc (121%). Concurrent administration of METH and the NMDA receptor antagonist MK-801 attenuated METH-induced increases of PPT mRNA in all aspects of the CPu at day 6 of treatment and completely prevented the increase in the NAc. Moreover, animals treated with METH for 6 days and then withdrawn for 15 days displayed PPT mRNA levels in striatum and accumbens that were statistically indistinguishable from those of controls. Adjacent sections from the same brains were used to assess PPE mRNA levels. PPE mRNA levels were transiently elevated in dorsal and ventral aspects of the CPu at day 1 and decayed to control levels at days 3 and 6. The results demonstrate that progressive treatment with methamphetamine causes stepwise elevation of preprotachykinin mRNA levels in the neostriatum. Moreover, the increase of neuropeptide mRNA shows selectivity, since PPE mRNA levels did not display progressive accumulation of message. The effects of progressive METH treatment on neostriatal PPT mRNA expression decay when the drug is withdrawn, suggesting that this neuropeptidergic system may not represent a neuroadaptation sustaining enduring sensitization to amphetamines, but may play a role in the progressive augmentation of locomotor activity elicited by this class of drug. © 1997 Elsevier Science Ltd. All rights reserved.

Repeated injections of dizocilpine maleate (MK-801) do not suppress the effects of nigrostriatal dopamine deafferentation on glutamate decarboxylase (GAD67) mRNA expression in the adult rat striatum

The present study examined the effects of glutamate transmission blockade through N-methyl- d-aspartate (NMDA) receptor subtype by repeated administration of dizocilpine maleate (0.2 mg/kg, i.p., twice a day for eight days) alone or in combination with unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic pathway on GABAergic neurons in the adult rat striatum. For this purpose, the expression of the messenger RNA encoding for the 67 kDa isoform of the GABA synthesizing enzyme, glutamate decarboxylase (GAD67 mRNA), was studied in the various conditions by quantitative in situ hybridization. The dizocilpine maleate treatment alone did not induce significant change of GAD67 mRNA levels in the striatum, indicating that NMDA receptors may not have a major role in the transcriptional regulation of GAD67 in the adult rat striatum. As reported previously, the unilateral dopaminergic lesion resulted in marked increases in GAD67 mRNA levels in the ipsilateral striatum. This up-regulation was not significantly affected by the treatment with dizocilpine maleate started 12 days after the unilateral intranigral 6-hydroxydopamine injection. Therefore, NMDA receptors are unlikely to contribute to the dopamine lesion-induced GAD67 mRNA up-regulation in striatal projection neurons. This result is of major interest in comparison with our previous finding that NMDA receptor activation is necessary to maintain the up-regulation of enkephalin expression in the striatum after dopamine lesion.

Activation of arc, a Putative “Effector” Immediate Early Gene, by Cocaine in Rat Brain

As immediate early genes (IEGs) are thought to play a critical role in mediating stimulus-induced neuronal plasticity, several laboratories have characterized the IEG response induced by cocaine to help define the changes in gene expression that may underlie its long-lasting behavioral effects. Although activation of several transcription factor IEGs has been described, little is known about which "effector" IEGs, if any, are also induced. In the present study, we have examined whether cocaine administration affects expression of a recently identified "effector" IEG, referred to as arc (activity-regulated, cytoskeleton-associated). This IEG encodes a protein with homology to spectrin that appears to be associated with the actin cytoskeleton. Using in situ hybridization, we have found that systemic cocaine administration elicits a robust, transient rise in arc mRNA levels in striatum, which is suppressed by D1 dopamine receptor blockade, reserpine treatment, or striatal 6-hydroxydopamine lesions. D2 receptor antagonist triggered arc expression when administered alone. Immunohistochemical studies indicated that Arc protein induced by cocaine is expressed in neuronal cell bodies and dendrites. As Arc appears to be component of the neuronal cytoskeleton, it may be involved in structural alterations underlying neuronal plasticity triggered by cocaine.

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

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

Role of kainate/AMPA receptors in induction of striatal zif/268 and preprodynorphin mRNA by a single injection of amphetamine

The role of kainate/AMPA excitatory amino acid receptors in d-amphetamine (AMPH)-induced behavioral changes and the induction of immediate early gene and preprodynorphin (PPD) mRNA in various regions of rat forebrain was investigated with quantitative in situ hybridization histochemistry. Three hours after a single injection of AMPH (5 mg/kg, i.p.), PPD mRNA and mRNA of the transcription factor zif/268, but not c- fos, was increased in dorsal striatum (caudate). Zif/268 mRNA was also increased in the sensorimotor cortex. Pretreatment of rats with DNQX, a kainate/AMPA receptor antagonist, did not affect the behaviors elicited by AMPH. However, the AMPH-stimulated increase in PPD and zif/268 mRNA levels in striatum, but not zif/268 mRNA in cortex, was blocked by DNQX pretreatment. In contrast, DNQX alone attenuated basal (constitutive) levels of zif/268 mRNA expression in sensorimotor cortical, but not in striatal, neurons. These studies indicate that kainate/AMPA receptors mediate the induction of zif/268 and PPD mRNA expression in the caudate nucleus induced by a single injection of AMPH. The fact that DNQX blocked genomic, but not behavioral, responses to acute AMPH suggests that kainate/AMPA receptor mechanisms may be involved in the long-term (possibly sensitizing) effects, rather than the acute effects, of the drug. In addition, tonic kainate/AMPA receptor stimulation may play a key role in maintaining constitutive expression of the zif/268 gene in cortical neurons.

Transplantation of fetal nigral cells reverses the increase of preproenkephalin mRNA levels in the rat striatum caused by 6-OHDA lesion of the dopaminergic nigrostriatal pathway: a quantitative in situ hybridization study

Unilateral 6-hydroxydopamine (6-OHDA)-induced lesion of the nigrostriatal dopamine (DA) pathway causes a significant increase of preproenkephalin (PPE) messenger RNA (mRNA) levels in the DA-depleted striatum in rat brain. Using an in situ hybridization (ISH) technique and computer-assisted microdensitometry, we quantified the changes in PPE mRNA levels in the striatum. Seven months after lesion, levels of PPE mRNA were 75% higher in the DA-depleted striatum than in the contralateral control striatum of the same animal or in the striatum of sham control animals. The implantation of embryonic dopaminergic neurons into the denervated striatum led to a complete reversal of this increase and, in grafted animals, levels of PPE mRNA were at control values. Moreover, this reversal extended beyond the areas reinnervated by the grafted dopaminergic neurons.

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

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