Zhi-Bing You

The striatonigral dynorphin pathway of the rat studied with in vivo microdialysis--II. Effects of dopamine D1 and D2 receptor agonists.

In vivo microdialysis was used to study the effect of intracerebral administration of dopamine agonists on dynorphin B release in the striatum and substantia nigra of rats. The release of dopamine and GABA was also investigated. Administration of the dopamine D1 agonist SKF 38393 (10-100 microM) into the striatum increased extracellular dynorphin B and GABA levels in the ipsilateral substantia nigra, in a concentration-dependent manner. After a short-lasting increase, nigral dopamine levels were significantly decreased after the highest concentration of striatal SKF 38393. An increase in striatal dynorphin B, GABA and dopamine levels was also observed. When SKF 38393 (10 microM) was administered into the substantia nigra, nigral dynorphin B and GABA, but not dopamine levels increased. No significant effects were observed on striatal levels. Administration of the dopamine D2 agonist, quinpirole (100 microM), into the striatum decreased dopamine levels in both striatum and substantia nigra, while no effect was observed on striatal or nigral dynorphin B and GABA levels. Quinpirole (10-100 microM) given into the substantia nigra, decreased striatal dopamine levels in a concentration manner. In the nigra, a short-lasting increase in dopamine levels was observed following the highest concentration of nigral quinpirole (100 microM). The effect was followed by a decrease in dopamine levels. No significant effects were observed on striatal or nigral dynorphin B and GABA levels. The results show that stimulation of D1 receptors in striatum and substantia nigra leads to activation of the striatonigral dynorphin pathway. A parallel effect could also be seen on nigral GABA release.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of single and repeated methamphetamine treatment on neurotransmitter release in substantia nigra and neostriatum of the rat.

The main purpose of this study was to characterize the initial neurotransmission cascade elicited by methamphetamine, analysing simultaneously with in vivo microdialysis monoamine, amino acid and neuropeptide release in substantia nigra and neostriatum of the rat. The main effect of a single systemic dose of methamphetamine (15 mg/kg, subcutaneously) was an increase in dopamine levels, both in substantia nigra (≈ 10‐fold) and neostriatum (≈ 40‐fold), accompanied by a significant, but lesser, increase in dynorphin B (≈ two‐fold, in both regions), and a decrease in monoamine metabolites. A similar effect was also observed after local administration of methamphetamine (100 µm) via the microdialysis probes, but restricted to the treated region. In other experiments, rats were repeatedly treated with methamphetamine or saline, with the last dose administered 12 h before microdialysis. Dopamine K+‐stimulated release was decreased following repeated methamphetamine administration compared with that following saline, both in the substantia nigra (by ≈ 65%) and neostriatum (by ≈ 20%). In contrast, the effect of K+‐depolarization on glutamate, aspartate and GABA levels was increased following repeated administration of methamphetamine. In conclusion, apart from an impairment of monoamine neurotransmission, repeated methamphetamine produces changes in amino acid homeostasis, probably leading to NMDA‐receptor overstimulation.

Long-term effects of perinatal asphyxia on basal ganglia neurotransmitter systems studied with microdialysis in rat ☆

Asphyxia was induced in pups delivered by caesarean section on pregnant Sprague-Dawley rats. Rats within the last day of gestation were anaesthetised and hysterectomized. The uterus horns including the foetuses were placed in a water bath for various periods of time. Following asphyxia the uterus horns were opened. The pups were removed, stimulated to breathe, left to recover and given to surrogate mothers. Control and asphyctic pups were obtained from each mother. Rats surviving asphyctic periods longer than 20 min at 37 degrees C showed chronic deficits in the release of neurotransmitters monitored with microdialysis in the basal ganglia. The main change observed in 6-month-old male rats that underwent severe perinatal asphyxia was a marked decrease in striatal dopamine release, monitored under basal and D-amphetamine stimulated conditions, as compared with control (normal- or caesarean-delivered) rats. Striatal glutamate and aspartate levels were also decreased following asphyxia. In the substantia nigra, the main effect of asphyxia was a decrease of both gamma-aminobutyric acid (GABA) and aspartate levels. Thus, this study provides evidence that perinatal asphyxia leads to chronic deficits in neurotransmission in the basal ganglia.

On the origin of striatal cholecystokinin release : studies with in vivo microdialysis

Abstract: In the present study, extracellular levels of the neuropeptide cholecystokinin (CCK), of the monoamine dopamine and its metabolites 3, 4‐dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and of the excitatory amino acids glutamate and aspartate were simultaneously monitored by microdialysis in the neostriatum of halothane‐anesthetized rats under basal and K+‐depolarizing conditions. Extracellular CCK and dopamine levels, but not glutamate and aspartate levels, were decreased by perfusion with a Ca2+‐free medium, under both basal and K+‐depolarizing conditions. HPLC revealed that the majority of the CCK‐like immunoreactivity in the perfusates coeluted with CCK octapeptide. Striatal extracellular CCK levels were decreased by decortication plus callosotomy, with a parallel decrease in glutamate levels. Striatal extracellular levels of dopamine, DOPAC., and HVA were significantly decreased in animals treated previously with a unilateral 6‐hydroxydopamine injection into the medial forebrain bundle. In these animals, however, the effect of decortication plus callosotomy on CCK and glutamate levels was not further augmented. Thus, this study supports the hypothesis of a neuronal origin of extracellular CCK and dopamine monitored with microdialysis in the striatum of the rat, and also supports the idea of a partly contralateral origin of corticostriatal CCK and glutamate inputs.

EFFECTS OF SECRETOGRANIN II-DERIVED PEPTIDES ON THE RELEASE OF NEUROTRANSMITTERS MONITORED IN THE BASAL GANGLIA OF THE RAT WITH IN VIVO MICRODIALYSIS

In vivo microdialysis was used to study the effect of secretogranin II-derived peptides on dynorphin B (Dyn B), dopamine, γ-aminobutyric acid (GABA), glutamate and aspartate release in the substantia nigra and neostriatum of halothane-anaesthesized rats.In the substantia nigra, local infusion of secretoneurin (secretogranin II 154–186) (1–50 μM) increased, in a concentration-dependent manner, extracellular aspartate, glutamate, Dyn B, dopamine and GABA levels. The effect was particularly prominent on aspartate and glutamate levels which, following 50 μM of secretoneurin, were increased by >20 and >10 fold, respectively. However, the effect of secretoneurin on Dyn B release appeared to be more specific, since a significant increase (>2 fold) was already observed following 1 μM of secretoneurin. In the neostriatum, Dyn B, glutamate, aspartate and GABA levels were also increased by local secretoneurin infusion, but the effect was less prominent than in the substantia nigra. In the substantia nigra, only Dyn B levels were significantly increased following infusion of 10 μM of the secretoneurin-C terminal (secretoneurin-15C), whereas Dyn B and GABA levels were increased by the same concentration of the secretogranin II C terminus (YM). Only glutamate and aspartate levels were increased by local infusion of 10 μM of secretogranin II 133-151 (LF), a peptide adjacent to secretoneurin in the primary amino acid sequence. In the neostriatum, Dyn B and GABA levels were increased by 10 μM of secretoneurin-15C. Dyn B levels were also increased by 10 μM of YM, and glutamate and aspartate levels were increased by 10 μM of both YM and LF.Thus, secretogranin 11-derived peptides affect extracellular levels of several putative neurotransmitter systems monitored in the basal ganglia of the rat with in vivo microdialysis. The effect of Dyn B appears to be specific and related to a physiological role of secretoneurin, since (i) it occurs in an area where secretoneurin-immunocytochemistry has been observed, (ii) is exerted at comparatively low concentrations, and (iii) is mimicked by secretoneurin-15C. The increases in excitatory amino acid levels produced by high concentrations of secretoneurin and other secretogranin II-derived peptides reflect, perhaps, a potential neurotoxicity produced by abnormal accumulation of these peptides.

EVIDENCE FOR ASPARTATE-IMMUNOREACTIVE NEURONS IN THE NEOSTRIATUM OF THE RAT: MODULATION BY THE MESENCEPHALIC DOPAMINE PATHWAY VIA D1-SUBTYPE OF RECEPTOR

Aspartate-like immunoreactivity was visualized in the neostriatum of rats using indirect immunofluorescence techniques and antibodies raised against aspartate conjugated to keyhole limpet hemocyanine. In normal rats only a few aspartate-positive cell bodies with limited processes were observed. A moderate increase was seen after treatment with (+)methamphetamine and haloperidol. A dramatic increase in the number and fluorescence intensity was observed in the unilaterally 6-hydroxy-dopamine lesioned rats after multiple injections of the D1-dopamine receptor agonist SKF 38393. In these rats strongly fluorescent processes as well as extensive terminal varicose fibre networks were observed. This increase could partly be blocked by the D1-dopamine receptor antagonist SCH 23390. Using a modified technique the aspartate-positive cell bodies and processes were observed even when the antiserum was diluted 1:80,000. Positive cell bodies and fibres were also seen on the ipsilateral side outside the neostriatum, for example in the islet of Calleja and in the piriform cortex. The aspartate-positive cells were negative for dopamine- and cyclic AMP-regulated phosphoprotein-32, a marker for neurons bearing dopamine D1-receptor subtype. A proportion of the aspartate-positive neurons (20%) contained neuropeptide tyrosine-like immunoreactivity. On adjacent sections there was a marked up-regulation of preprodynorphin-like immunoreactivity. The up-regulation of dynorphin and aspartate was only observed when there was an almost complete denervation of the neostriatum as visualized with antiserum to tyrosine hydroxylase, a marker for dopamine fibres. The present results raise the possibility that aspartate may act as a neurotransmitter released from interneurons in the neostriatum.

Endogenous opioids in frontal cortex of patients with Down syndrome

The main purpose of this study was to investigate differences regarding endogenous opioids in post-mortem frontal cortex of adult patients with Down syndrome (DS), patients with Alzheimer disease (AD) and neurologically healthy persons, respectively, using specific radioimmunoassays. The results of this study show that there is an increase in the levels of leu-enkephalin and dynorphin A in the frontal cortex of patients with DS as compared to the control group. An almost identical increase was also observed when comparing patients with AD to controls. In conclusion, the results of this study suggest a relationship between elevated tissue levels of leuenkephalin and dynorphin A in cerebral cortex and cognitive impairments in patients with DS and AD.

Neurocircuitry of the basal ganglia studied by monitoring neurotransmitter release

The neurocircuitries of the basal ganglia are studied with in vivo microdialysis, with special consideration to dopamine transmission and its interaction with other neurotransmitter systems. The aim is to develop experimental models to study the pathophysiology and therapy of neurodegenerative disorders of the basal ganglia, as well as to develop models to study the short- and long-term consequences of perinatal asphyctic lesions. A main goal of these studies is to find and to characterize new treatments for these disorders.

Opioid Effects on 45Ca2+ Uptake and Glutamate Release in Rat Cerebral Cortex in Primary Culture

Abstract: Primary cultures of rat cortex, conveniently prepared from newborn animals, were used to study opioid effects on 45Ca2+ uptake and glutamate release. 45Ca2+ uptake, induced by treatment with glutamate or NMDA, was largely blocked by the NMDA antagonist MK‐801. K+ depolarization‐induced 45Ca2+ uptake was also reduced by MK‐801, indicating that the effect was mediated by glutamate release. Direct analysis verified that glutamate, and aspartate, were indeed released. Opioid peptides of the prodynorphin system were also released and these, or other peptides, were functionally active, because naloxone treatment increased glutamate release, as well as the 45Ca2+ uptake induced by depolarization. Opioid agonists, selective for μ‐, κ‐, and δ‐receptors, inhibited the 45Ca2+ uptake induced by K+ depolarization. The combination of low concentrations of MK‐801 and opioid agonists resulted in additive inhibition of K+‐ induced 45Ca2+ uptake. The results indicate that this system may be useful as an in vitro CNS model for studying modulation by opioids of glutamate release and Ca2+ uptake under acute, and perhaps also chronic, opiate treatment.

The striatonigral dynorphin pathway of the rat studied with In vivo microdialysis—I. Effects of K+-depolarization, lesions and peptidase inhibition

Extracellular levels of dynorphin B were analysed with in vivo microdialysis in the neostriatum and substantia nigra of halothane-anaesthetized rats. Dopamine and its metabolites, 3,4-dihydroxyphenyl-acetic acid and homovanillic acid, as well as GABA were simultaneously monitored. Chromatographic analysis revealed that the dynorphin B-like immunoreactivity measured in perfusates collected under basal and K(+)-depolarizing conditions co-eluted with synthetic dynorphin B. Dynorphin B, GABA and dopamine levels were Ca(2+)-dependently increased by K(+)-depolarization, while 3,4-dihydroxyphenylacetic acid and homovanillic acid levels were decreased. Dopamine and its metabolites, but not dynorphin B or GABA levels, were significantly decreased after a unilateral 6-hydroxydopamine injection into the left medial forebrain bundle. In contrast, following a unilateral injection of ibotenic acid into the striatum, dynorphin B and GABA levels were decreased by > 50% in striatum and substantia nigra on the lesioned side, whereas no significant changes were observed in basal dopamine levels. The inclusion of the peptidase inhibitor captopril (50-500 microM) into the nigral perfusion medium produced a concentration-dependent increase in nigral extracellular levels of dynorphin B. In the striatum, a delayed increase in dynorphin B and GABA levels could be observed following the nigral captopril administration, but this effect was not concentration-dependent. Thus, we demonstrate that extracellular levels of dynorphin B, dopamine and GABA can simultaneously be monitored with in vivo microdialysis. Extracellular dynorphin B appears to originate from neurons, since the levels were (i) increased in a Ca(2+)-dependent manner by K(+)-depolarization, and (ii) decreased by a selective lesion of the striatum, known to contain cell bodies of dynorphin neurons in the striatonigral pathway. Furthermore, (iii) the increase in nigral dynorphin B levels by peptidase inhibition suggests the presence of clearance mechanisms for the released dynorphin peptides.