Comparative effects of electroconvulsive shock and haloperidol on in vivo tyrosine hydroxylation and tetrahydrobiopterin in the brain of rats with 6-hydroxydopamine lesions.

We have evaluated the effects of electroconvulsive shock (ECS) and haloperidol treatment on the in vivo tyrosine hydroxylation rate and the tetrahydrobiopterin levels in the nigrostriatal system of 6-OHDA-lesioned rats. The rate of DOPA accumulation was significantly decreased by 96% in the ipsilateral striatum and by 50% in substantia nigra of the 6-OHDA-lesioned rats compared to the control activity of contralateral non-lesioned striatum and substantia nigra. The loss of total biopterin was found to be 75% and 50% in the ipsilateral striatum and substantia nigra, respectively. Following administration of haloperidol, the rate of DOPA accumulation increased significantly in the striatum and substantia nigra on the lesioned side compared to that in the vehicle treatment group. Application of ECS also significantly increased the rate of DOPA accumulation in the ipsilateral striatum and substantia nigra compared to that obtained in the non-shocked rats. The biopterin levels in the nigrostriatal system of 6-OHDA-lesioned were elevated significantly in the striatum after haloperidol treatment; in contrast the biopterin levels were unchanged in response to ECS. Our results show that both haloperidol and ECS significantly enhanced the rate of in vivo tyrosine hydroxylation in the striatum and substantia nigra of rats with greater than 90% lesions. These results suggest that the nigrostriatal system, although up-regulated following 6-OHDA lesions, still maintains the potential for further up-regulation of dopaminergic function in response to haloperidol and ECS treatment.     

Chronic haloperidol and clozapine differentially affect dynorphin peptides and substance P in basal ganglia of the rat

The effect of chronic neuroleptic treatment, using haloperidol or clozapine, on immunoreactive dynorphin peptide and substance P levels in basal ganglia of rats was examined. The drugs were administered i.p. in daily doses for 10 days (haloperidol 1 mg/kg and clozapine 10 mg/kg). Dynorphin A, dynorphin B and substance P were measured in substantia nigra, striatum, globus pallidus and hypothalamus using specific radioimmunoassays. The most prominent effects were observed with with clozapine which increased levels of all measured peptides in substantia nigra. Haloperidol only affected nigral substance P levels which declined, while nigral dynorphin peptide levels remained unchanged. In striatum, haloperidol slightly reduced dynorphin peptides while substance P was unaffected. Clozapine increased striatal substance P but the dynorphin peptides were not affected. Minor changes in dynorphin peptides found in globus pallidus and hypothalamus were not statistically reliable. Substance P was not changed in these structures after either of the two drugs. High molecular weight fragments (greater than or equal to 5,000) from the dynorphin precursor, proenkephalin B, were measured in substantia nigra and striatum using trypsin digestion and subsequent analysis of generated Leu-enkephalin-Arg6. These high molecular weight fragments were found to be affected in the same manner as the dynorphin peptides. This study indicates that the two types of neuroleptic drugs have different modes of interaction on peptide systems in basal ganglia of rats. Dynorphin peptides and substance P were also differentially affected.     

Dynorphinergic pathways of Leu-Enkephalin production in the rat brain

Leu-Enkephalin (LE) is an endogenous opioid peptide that can arise from two distinct precursors: proenkephalin and prodynorphin.Experiments were designed to differentiate LE derived from proenkephalin versus that derived from prodynorphin. The most dense collections of dynorphin-positive fibers and terminals are in the substantia nigra and posterior pituitary, areas rich in dynorphin-related peptides. The concentration of LE in these regions is significantly higher than that of ME-Arg-Gly-Leu; the ratio of LE to ME-Arg-Gly-Leu is therefore greater than that found in the proenkephalin precursor, which is unity. Globus pallidus deafferentation resulted in a significant decrease of dynorphin B and LE, but not ME-Arg-Gly-Leu, in the substantia nigra. Mild intermittent foot shock (0.2 mA, 20 min) causes a significant increase of dynorphin B and LE in the substantia nigra, but has no effect on ME-Arg-Gly-Leu concentrations. Thus, in the substantia nigra LE may be derived primarily from prodynorphin. Likewise, in the posterior pituitary, osmotic stimulus (e.g., 2% NaCl as drinking fluid) causes marked depletion in dynorphin and LE but has no effect on ME levels suggesting that in the posterior pituitary LE is derived primarily from dynorphin.     

Subchronic haloperidol increases CB(1) receptor binding and G protein coupling in discrete regions of the basal ganglia

The present study was designed to test whether chronic neuroleptic treatment, which is known to alter both expression and density of dopamine D(2) receptors in striatal regions, has effects upon function and binding level of the cannabinoid CB(1) receptor in the basal ganglia by using receptor autoradiography. As predicted, subchronic haloperidol treatment resulted in increased binding of (3)H-raclopride and quinpirole-induced guanosine 5'-O-(gamma-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) in the striatum when compared to that measured in control animals. This increased D(2) receptor binding and function after 3 days washout was normalized after a 2-week washout period. Effect of haloperidol treatment was studied for CB(1) receptor binding and CP55,940-stimulated [(35)S]GTPgammaS in the striatum, globus pallidus, and substantia nigra. (3)[H]CP55,940 binding levels were found in rank order from highest to lowest in substantia nigra > globus pallidus > striatum. Furthermore, subchronic haloperidol treatment resulted in elevated binding levels of (3)[H]CP55,940 in the striatum and the substantia nigra and CB(1) receptor-stimulated [(35)S]GTPgammaS bindings in the substantia nigra after 3 days washout. These increased binding levels were normalized at 1-4 weeks after termination of haloperidol treatment. Haloperidol treatment had no significant effect on CB(1) receptor or [(35)S]GTPgammaS binding levels in globus pallidus. The results help to elucidate the underlying biochemical mechanism of CB(1) receptor supersensitivity after haloperidol treatment.     

In vivo detection of immunoreactive neurokinin A release within rat substantia nigra and its dependency on a dopaminergic input

In the striatum, the tachykinin peptide neurokinin A (NKA) is thought to coexist with substance P in the γ-aminobutyric acid-containing spiny neurones which project to the substantia nigra. We have used in vivo antibody-coated microprobes to directly monitor the release of NKA-like immunoreactivity (NKA-LI) within substantia nigra during various pharmacological manipulations. The data clearly illustrates a basal or resting extracellular presence of NKA-LI restricted to substantia nigra reticulata which was found to be largely dependent on a dopaminergic input. Acute administration of haloperidol (0.1–0.2 mg/kg i.p.) considerably reduced this basal NKA-LI whereas depot administration (14 mg/kg i.m. released over 2 weeks) produced a less substantial reduction. Lesion of nigro-striatal dopamine neurones with the neurotoxic agent 6-hydroxydopamine produced significant reductions in the nigral NKA-LI detected. However, d-amphetamine administration (4 mg/kg i.p.) did not alter the pattern of NKA-LI release for up to 4 h posttreatment. These results indicate that changes in peptide mRNA levels do not necessarily reflect changes in peptide release and suggest that NKA may be the more physiologically relevant tachykinin within the substantia nigra of the rat.     

Brain dynorphin and enkephalin systems in Fischer and Lewis rats: effects of morphine tolerance and withdrawal

Lewis rats are more likely to self-administer various drugs of abuse than Fischer rats. Here these two strains of rats were compared with regard to basal brain opioid peptide levels and the response to chronic morphine treatment and to naloxone-precipitated withdrawal. Lewis rats had lower basal dynorphin peptides in the substantia nogra, striatum (not Leu-enkephalinArg⁶) and VTA (not dynorphin B) and the pituitary gland. Leu-enkephalinArg⁶ levels were also lower in these structures (with the exception of striatum which had higher levels) and in the nucleus accumbens. There were also strain differences in the response to chronic morphine treatment; in the nucleus accumbens, morphine treatment increased dynorphin A levels in Fischer rats only, in the ventral tegmental area effects were opposite with increased dynorphin levels in Fischer and decreased levels in Lewis rats, in the hippocampus dynorphin levels were markedly reduced in Lewis rats only. In Fischer rats, chronic morphine strongly affected peptide levels in the substantia nigra and striatum, whereas Lewis rats responded less in these areas. Leu-enkephalin, which derives from both prodynorphin and proenkephalin, and Met-enkephalin, which derives from proenkephalin, were effected by chronic morphine mainly in Fischer rats, increasing levels in most of the brain areas examined. The results in this study show (1) strain differences in basal levels of prodynorphin-derived opioid peptides, (2) the prodynorphin system to be differently influenced by morphine in Lewis rats than in Fischer rats and 3) the proenkephalin system to be influenced by chronic morphine in brain areas related to reward processes only in Fischer rats.     

Differential effects of haloperidol on phencyclidine-induced reduction in substance P contents in rat brain regions

We investigated the effects of a schizophrenomimetic drug, phencyclidine (PCP), on substance P (SP) contents in the discrete rat brain areas using an enzyme-immunoassay for SP. The acute intraperitoneal (i.p.) administration of PCP (10 mg/kg), which is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) type glutamate receptor and a dopamine uptake inhibitor, reduced the concentration of the peptide in the prefrontal cortex, limbic forebrain, striatum, and substantia nigra, but not in the ventral tegmental area, at 60 or 120 min postinjection. A selective noncompetitive NMDA antagonist, dizocilpine hydrogen maleate ((+)-MK-801) (1 mg/kg, i.p.), also caused a decrease in the SP content in the prefrontal cortex and limbic forebrain but failed to alter the content in the other areas studied 30 min thereafter. Dopamine agonists, methamphetamine (4.8 mg/kg, i.p.) and apomorphine (4.4 mg/kg, i.p.), diminished the SP contents in the striatum and substantia nigra 60 min after their injection without effects in the prefrontal cortex, limbic forebrain, and ventral tegmental area. Furthermore, pretreatment with haloperidol (1 mg/kg, i.p.), a D2 preferable dopamine receptor antagonist and a typical antipsychotic, blocked the ability of PCP to decrease the SP concentrations in the substantia nigra but not in the prefrontal cortex. PCP, therefore, might diminish the SP levels by NMDA receptor-mediated and dopamine-independent mechanisms in the prefrontal cortex and limbic forebrain, but by NMDA receptor-independent and dopamine-dependent mechanisms in the striatum and substantia nigra. The haloperidol-insensitive reduction of the frontal SP could be involved in certain neuroleptic-resistant symptoms of PCP-treated animals, PCP psychosis, or schizophrenia.     

Ethanol-induced Changes in Proenkephalin mRNA Expression in the Rat Nigrostriatal Pathway

Endogenous opioid systems have been suggested to play a key role in ethanol reinforcement mechanisms and alcohol-drinking behavior. Ethanol induces differential alterations in opioid peptide expression in brain areas of the reward circuits, which may be linked to the reinforcing effects of ethanol. In addition, ethanol-induced alterations in opioidergic nigrostriatal transmission could be involved in brain sensitivity to ethanol and play a role in addictive processes. The aim of this work was to study the effects of acute ethanol administration on proenkephalin (proenk) mRNA expression in the rat substantia nigra and caudate–putamen (CP) for up to 24 h post treatment. Male Wistar rats received ethanol (2.5 g/kg) or distilled water by intragastric administration, and proenk mRNA expression was studied by in situ hybridization and densitometry. Ethanol transiently increased proenk mRNA expression in the CP 1 h after drug administration. Proenk mRNA levels remained elevated 2 h post treatment in the anterior–medial and medial–posterior regions of the CP. In contrast, ethanol decreased proenk mRNA expression in the substantia nigra pars compacta and pars reticulata 2 h after drug exposure. Alterations in enkephalin expression in the substantia nigra and CP in response to ethanol exposure could be involved in the mechanisms underlying brain sensitivity to the drug.     

Dominantly inherited apathy, central hypoventilation, and Parkinson's syndrome: clinical, biochemical, and neuropathologic studies of 2 new cases

We describe 2 new patients from a family in which 10 persons in 3 successive generations had a dominant neuropsychiatric disorder characterized by apathy, central hypoventilation, and parkinsonism. Neuropathologically, both patients showed severe neuronal loss and reactive gliosis in the substantia nigra. Neurochemical studies showed a marked depletion of dopamine in substantia nigra, putamen, and caudate nucleus, as well as reduction in serotonin content in the substantia nigra. Glutamate contents were low in frontal cortex and thalamus, and gamma-aminobutyric acid (GABA) contents were low in thalamus and substantia nigra of both patients. In addition, phosphoethanolamine contents were reduced in all brain regions of both patients, especially in the substantia nigra. One patient with severe symptoms had low levels of homovanillic acid, 5-hydroxyindoleacetic acid, and GABA in his CSF repeatedly for 3 years before death (aged 58), while the 2nd patient died (aged 51) of an unrelated cause before developing any symptoms of the familial disorder. Because brain deficiencies of multiple neurotransmitters appear to be involved, this disorder is unlikely to respond to treatment; however, neurochemical studies of CSF may make presymptomatic diagnosis feasible.     

Effects of intranigral injections of dopamine agonists and antagonists, glycine, muscimol and N- methyl-D,L-aspartate on locomotor activity

Previously it has been shown that bilateral intranigral injections of dopamine into rats pretreated with a monoamine oxidase inhibitor induced prolonged stimulation of locomotor activity, while bilateral intranigral injections of haloperidol reduced the locomotor stimulation evoked by systemic amphetamine. In the present studies, the role of the substantia nigra in locomotor activity was further investigated using a variety of dopaminergic and other agonists and neuroleptics. Ergometrine, epinine, (+/-)-2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronapthalene hydrobromide (ADTN), 1,2,3,4-tetrahydro-6,7,-dihydroxyisoquinoline hydrochloride (THIQ), muscimol and glycine elicited locomotor activity when injected into the substantia nigra pars reticulata bilaterally. Additionally the non-dopaminergic agonists also elicited a degree of stereotyped behavior. Locomotor activity induced by intranigral ergometrine was blocked by systemic haloperidol but was not affected by intranigral haloperidol. Locomotor activity elicited by systemic amphetamine was blocked by bilateral intranigral alpha-flupenthixol, but that elicited by bilateral intra-accumbens ergometrine was not affected by alpha-flupenthixol or haloperidol injected into the substantia nigra pars reticulata bilaterally. The results provide further evidence that alterations of neurotransmission in the substantia nigra exert effects on locomotor activity.     

Brain dopamine transporter: gender differences and effect of chronic haloperidol

Gender differences and the effect of chronic haloperidol on the rat brain dopamine transporter is reported. The density of striatal dopamine transporter sites labelled with [³H]GBR 12935, and of substantia nigra dopamine transporter mRNA measured by in situ hybridization were higher in female compared to male rats whereas striatal D2 specific binding labelled with [³H]spiperone was not significantly higher. Daily haloperidol treatment (1 mg/kg, i.p.) for 21 days increased striatal [³H]spiperone specific binding but left unchanged striatal [³H]GBR 12935 binding density and affinity as well as substantia nigra dopamine transporter mRNA levels. A reduce clearance rate of dopamine in the striatum after acute and chronic haloperidol was previously reported; the present results indicate that this may occur without changes in the sites of dopamine transport or in gene expression of this transporter.     

Neuroleptic treatment induces region-specific changes in levels of neurokinin A and substance P in rat brain

The effects of 10 days treatment with haloperidol or sulpiride on tissue levels of neurokinin A-like and substance P-like immunoreactivity (NKA-LI and SP-LI) in various regions of rat brain were studied using reversed phase HPLC and radioimmunoassay. The most marked effect was a decrease in NKA-LI levels in n.accumbens after treatment with both sulpiride and haloperidol. Striatal NKA-LI and SP-LI levels were not clearly affected. NKA-LI levels but not SP-LI levels were decreased in substantia nigra by haloperidol. A low dose of sulpiride increased both NKA-LI and SP-LI levels in ventral tegmental area/n.interpeduncularis. In conclusion, region-specific changes of NKA-LI and SP-LI were seen after subchronic treatment with neuroleptics. It seems likely that NKA and SP are involved in the neuronal adaptation to the repeated treatment with neuroleptics.     

Neuropeptides in striato-nigral pathways

Summary The existence of a neuronal pathway containing Leu-enkephalin and connecting the neostriatum with the globus pallidus has been confirmed combining immunohistochemistry with microinjections of neurotoxic agents (kainic acid, colchicine) and discrete knife lesions.The presence of substance P in nerve terminals of the substantia nigra was demonstrated by the application of a monoclonal antibody against this peptide. Electron microscopic studies revealed immunoreactive sites for substance P in nerve terminals establishing symmetric and asymmetric synapses, mainly over dendritic profiles.The possible peptide-containing neuronal pathways in the nigro-striatal system are discussed.     

In vivo neurochemical and behavioural effects of intracerebrally administered neurotensin and D-Trp11-neurotensin on mesolimbic and nigrostriatal dopaminergic function in the rat

The effects of intracerebral application of neurotensin on the behavioural responses to peripheral dopamine agonist administration to rats, and on the levels of DOPAC voltammetrically determined in the striatum and nucleus accumbens of the anaesthetized rat have been examined. Bilateral application of neurotensin to the nucleus accumbens, like the neuroleptic haloperidol, inhibited the hyperactivity response to the dopamine agonist, n,N-propylnorapomorphine, but, unlike haloperidol, its bilateral intrastriatal application failed to reduce the degree of stereotyped behaviour induced by peripheral apomorphine injection. In the halothane-anaesthetized rat, neurotensin, when applied to the ventral tegmental area, stimulated DOPAC production in the ipsilateral nucleus accumbens, while its application to the substantia nigra did not affect striatal DOPAC levels significantly. Following its intracerebroventricular injection, however, DOPAC levels were considerably enhanced in both regions. The 11-D-tryptophan-substituted analogue of neurotensin potently mimicked the effects of the peptide itself in all studies. The findings of these investigations further confirm in vivo that the functional antagonism of dopamine by neurotensin is selective for the mesolimbic system, and that the effects of neurotensin can be correlated with reports on the regional distribution of its high-affinity binding sites in the rat brain.     

Effects of haloperidol and clozapine on preprotachykinin-A messenger RNA, tachykinin tissue levels, release and neurokinin-1 receptors in the striato-nigral system.

The effects of haloperidol and clozapine on tachykinin tissue levels, preprotachykinin-A messenger RNA, spontaneous and potassium-evoked tachykinin release, dopamine D2 receptors, and [125I]Bolton-Hunter-substance P binding sites in the striato-nigral system were examined. Chronic administration (10 days) of the dopamine receptor antagonist haloperidol (2 mg/kg i.p.) significantly decreased tissue levels of substance P like-immunoreactivity and neurokinin A like-immunoreactivity in the striatum and the substantia nigra. The corresponding preprotachykinin-A mRNA was decreased in the striatum. Haloperidol did not affect the potassium-evoked tachykinin release in the substantia nigra but significantly increased the spontaneous release. Haloperidol increased the number of D2-receptors but left [125I]Bolton-Hunter-substance P binding sites, representing neurokinin 1 (NK-1) receptors, as determined by competition experiments with selective ligands, unchanged. Clozapine (30 mg/kg, i.m.) did not influence nigral and striatal tachykinin tissue levels, preprotachykinin-A mRNA and potassium-evoked release or spontaneous efflux in the substantia nigra, or D2-receptors and [125I]Bolton-Hunter-substance P binding sites. The present data indicate that neuroleptics influence the striato-nigral tachykinin system in different ways. Tachykinins may, therefore, contribute to the therapeutic and/or untoward effects of certain neuroleptic drugs.     

Effect of chronic haloperidol on dopamine release following microinjection of GABA into the substantia nigra zona reticulata in the rat

To investigate the influence of the striatonigral gamma-aminobutyric acid (GABA) system on the nigrostriatal dopamine (DA) system, the release of DA and/or 3,4-dihydroxyphenylacetic acid in the striatum ipsilateral to the injection side was examined by in vivo voltammetry following microinjection of GABA into the substantia nigra zona reticulata (SNR). The microinjection of GABA (100-300 micrograms/2 microliters) into the SNR produced a dose-dependent increase in the electrochemical signals recorded from the caudate nucleus ipsilateral to the injection side. Following chronic treatment with haloperidol, microinjection of GABA into the SNR produced only a slight (non-significant) increase in the electrochemical signals recorded from the caudate nucleus ipsilateral to the injection side. These results provide additional evidence to support the concept that DA cells in the substantia nigra zona compacta are regulated by the SNR non-DA neurons in an inhibitory manner. It appears, furthermore, that chronic treatment with haloperidol reduces the release of DA in the striatum ipsilateral to the injection side and that this effect may be due to a gradual development of depolarization block of DA cells by chronic administration of haloperidol.     

Effects of intranigral administration of dopamine agonists and antagonists and baclofen on concentrations of dopac and dopamine in the striatum and substantia nigra of the rat

Summary Systemic administration of haloperidol to rats failed to alter the concentration of dopamine but increased the concentration of 3, 4-dihydroxy-phenylacetic acid (DOPAC), the major metabolite of dopamine, in both the striatum and substantia nigra. These haloperidol-induced changes in DOPAC were prevented by an intranigral microinjection of baclofen, a drug which reduces nigrostriatal dopaminergic neuronal activity.It has been proposed that nigrostriatal neurons are regulated, in part, by the activation of autoreceptors in substantia nigra. However, intranigral microinjections of high concentrations of several dopaminergic antagonists failed to mimic the biochemical effects resulting from systemic administration of these drugs; instead, they slightly increased the concentrations of both dopamine and DOPAC in the striatum and decreased dopamine in substantia nigra. Intranigral microinjections of the dopamine agonist, apomorphine, failed to alter the concentration of DOPAC in the striatum, but reduced both dopamine and DOPAC in the nigra. If DOPAC concentrations reflect nigrostriatal dopaminergic neuronal activity, the present results suggest that dopaminergic agonists and antagonists acting in substantia nigra do not exert a major influence on the activity of these neurons.     

Cholecystokinin system in striatal-nigral neuronal networks: infusion of quinolinic acid into rat striatum

Unilateral infusions of quinolinic acid (QUIN) into the rat striatum led to an increase in cholecystokinin octapeptide sulfate-like immunoreactivity (CCK8S-LI) in the striatum and substantia nigra 4 days later. These changes were suppressed by the injection of gamma-aminobutyric acid into substantia nigra 30 min before sacrifice. Intraperitoneal administration of haloperidol 40 min before sacrifice also suppressed the effect of QUIN on CCK. These results suggest that nigrostriatal dopaminergic neurons regulate CCK neurons via presynaptic sites in the striatum, and also that striatonigral GABAergic neurons interact with CCK neurons in the substantia nigra.