Modeling individual and relative accuracy of screening tools in geriatric oncology.

BACKGROUND: Classification probabilities reflect to what degree a screening test represents the true disease state and include true positive (TPF) and false positive fractions (FPF). With two tests, one can compare TPF and FPF using relative probabilities which offer advantages in terms of interpretation and statistical modeling. Our objective was to highlight how individual and relative TPF and FPF can be easily estimated and compared within a regression modeling framework. This allows the modeling of tests' accuracy while adjusting for multiple covariates, and thus provides valuable information in addition to the crude TPF and FPF. We illustrate our purpose with the G8 and VES-13 screening tests aimed at identifying elderly cancer patients in need for a comprehensive geriatric assessment (CGA). METHODS: Prospective cohort with a paired design. TPF and FPF of each test, as well as relative TPF and FPF were modeled using log-linear models. RESULTS: G8 detected patients in need for CGA better than VES-13 at the expense of misclassifying a large number of normal patients. Both tests had better TPF with older age and poorer performance status (PS), and for all cancer subtypes compared with prostate cancer. Effect of age and PS on TPF was more pronounced with VES-13. Age affected FPF, but not differentially. CONCLUSIONS: Regression modeling helps provide a thorough assessment of the accuracy of diagnostic tests and should be used more frequently. In the context of screening, we encourage the use of G8 as failing to identify patients in need of a CGA might be more problematic than over-detection. Moreover, although we identified variables associated with the sensitivity of these tests, this association was less pronounced for the G8.

Genetic variation and pesticide exposure influence blood DNA methylation signatures in females with early-stage Parkinson's disease.

Although sex, genetics, and exposures can individually influence risk for sporadic Parkinson's disease (PD), the joint contributions of these factors to the epigenetic etiology of PD have not been comprehensively assessed. Here, we profiled sex-stratified genome-wide blood DNAm patterns, SNP genotype, and pesticide exposure in agricultural workers (71 early-stage PD cases, 147 controls) and explored replication in three independent samples of varying demographics (n = 218, 222, and 872). Using a region-based approach, we found more associations of blood DNAm with PD in females (69 regions) than in males (2 regions, Δßadj| ≥0.03, padj ≤ 0.05). For 48 regions in females, models including genotype or genotype and pesticide exposure substantially improved in explaining interindividual variation in DNAm (padj ≤ 0.05), and accounting for these variables decreased the estimated effect of PD on DNAm. The results suggested that genotype, and to a lesser degree, genotype-exposure interactions contributed to variation in PD-associated DNAm. Our findings should be further explored in larger study populations and in experimental systems, preferably with precise measures of exposure.

Parkinson's disease polygenic risk score is not associated with impulse control disorders: A longitudinal study.

OBJECTIVE: To examine the relationship between a Parkinson's disease (PD) polygenic risk score (PRS) and impulse control disorders (ICDs) in PD. BACKGROUND: Genome wide association studies (GWAS) have brought forth a PRS associated with increased risk of PD and younger disease onset. ICDs are frequent adverse effects of dopaminergic drugs and are also more frequent in patients with younger disease onset. It is unknown whether ICDs and PD share genetic susceptibility. METHODS: We used data from a multicenter longitudinal cohort of PD patients with annual visits up to 6 years (DIG-PD). At each visit ICDs, defined as compulsive gambling, buying, eating, or sexual behavior were evaluated by movement disorders specialists. We genotyped DNAs using the Megachip assay (Illumina) and calculated a weighted PRS based on 90 SNPs associated with PD. We estimated the association between PRS and prevalence of ICDs at each visit using Poisson generalized estimating equations, adjusted for dopaminergic treatment and other known risk factors for ICDs. RESULTS: Of 403 patients, 185 developed ICDs. Patients with younger age at onset had a higher prevalence of ICDs (p < 0.001) as well as higher PRS values (p = 0.06). At baseline, there was no association between the PRS and ICDs (overall, p = 0.84). The prevalence of ICDs increased over time similarly across the quartiles of the PRS (overall, p = 0.88; DA users, p = 0.99). CONCLUSION: Despite younger disease onset being associated with both higher PRS and ICD prevalence, our findings are not in favor of common susceptibility genes for PD and ICDs.

Cholecystokinin: Corelease with dopamine from nigrostriatal neurons in the cat.

Halothane-anaesthetized cats were implanted with push-pull cannulae to demonstrate the in vivo release of cholecystokinin-like immunoreactivity (CCK-LI) in the substantia nigra and the ipsilateral caudate nucleus. The spontaneous and the calcium-dependent potassium-evoked release of CCK-LI were observed in both structures. In addition, the local application of tetrodotoxin (10-6 M) reduced the spontaneous release of the peptide. 6-OHDA lesions made in the substantia nigra pars compacta led to a complete destruction of nigrostriatal dopaminergic neurons. CCK-LI levels were not affected in the caudate nucleus but were reduced substantially in the substantia nigra. The activation of dopaminergic cells induced by the nigral application of alpha-methyl-para-tyrosine (10-4 M) stimulated the release of CCK-LI and dopamine in the ipsilateral caudate nucleus, whilst opposite effects were seen in the substantia nigra. Similar results were obtained when dopaminergic transmission was blocked in the caudate nucleus suggesting that the evoked release of CCK-LI by the alpha-methyl-para-tyrosine treatment originates from dopaminergic nerve terminals and not from other CCK-LI containing fibres in response to released dopamine. Dopamine (10-7 M) as well as the D1 agonist SKF 38393 (10-5 M) stimulated CCK-LI release when applied into the caudate nucleus while the D2 agonist, LY 171555 (10-6 M) slightly reduced peptide release. The local application of cholecystokinin-8 sulfate (CCK-8S) (10-8 M, for 30 min) into the substantia nigra pars compacta increased the firing rate of dopaminergic cells and stimulated the release of newly synthesized 3H-dopamine from dendrites and nerve terminals. These results suggest, but do not definitively prove, that, in the cat, CCK-LI and dopamine are coreleased from nigrostriatal mixed dopaminergic/CCK-LI neurons and that CCK-LI released from dendrites is, like dopamine, involved in the regulation of the activity of these cells.

Substance P and neurokinin A regulate by different mechanisms dopamine release from dendrites and nerve terminals of the nigrostriatal dopaminergic neurons.

Numerous striatal neurons innervating the substantia nigra contain substance P and/or neurokinin A. In contrast to substance P or neurokinin A, little neurokinin B is found in the substantia nigra. This led us to compare the effects of nigral application of these tachykinins on the release of dopamine from dendrites and nerve terminals of nigrostriatal dopaminergic neurons. Experiments were made in halothane-anesthetized cats implanted with one push-pull cannula in the substantia nigra and another in the ipsilateral caudate nucleus [3H]Tyrosine was delivered continuously to each push-pull cannula and the release of newly synthesized [3H]dopamine measured in the superfusate. Unlike substance P or neurokinin A, neurokinin B (10(-8) M) applied for 30 min into the pars compacta of the substantia nigra was without effect on the release of [3H]dopamine from nerve terminals or dendrites. When either substance P (10(-8) M) or neurokinin A (10(-8) M) was applied into the pars compacta, the release of [3H]dopamine from nerve terminals was enhanced. While neurokinin A also stimulated the dendritic release of [3H]dopamine, this was reduced by substance P. At a lower concentration (10(-9) M), neurokinin A induced similar effects to those observed at 10(-8) M whereas substance P (10(-9) M) stimulated moderately [3H]dopamine release from nerve terminals but did not affect the dendritic release of the [3H]amine. When superfused into the pars reticulata, substance P (10(-8) M) still stimulated [3H]dopamine release from nerve terminals but not from dendrites while neurokinin A (10(-8) M) was without effect either in the caudate nucleus or the substantia nigra. Additional experiments were made to determine whether or not substance P (10(-8) M) or neurokinin A (10(-8) M) act directly on nigral dopaminergic neurons when applied into the pars compacta. The effects of substance P on [3H]dopamine release from nerve terminals and dendrites were prevented when 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M), an antagonist of glutamatergic transmission, was applied continuously into the caudate nucleus. In contrast, the stimulatory effects of neurokinin A on [3H]dopamine release from nerve terminals and dendrites were insensitive to 2-amino-6-trifluoromethoxy benzothiazole (10(-5) M). These results suggest that neurokinin A, but not substance P, acts directly on dopaminergic cells. In the light of previous observations, we propose that the effects of substance P on dopaminergic transmission are mediated by a nigro-thalamo-cortico-striatal loop.(ABSTRACT TRUNCATED AT 400 WORDS)

L-glutamate-evoked release of dopamine from synaptosomes of the rat striatum: involvement of AMPA and N-methyl-D-aspartate receptors.

Previously, using purified synaptosomes from the rat striatum, we have shown that agonists of D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors stimulate the release of [3H]dopamine continuously synthesized from [3H]tyrosine. Similar results were obtained with N-methyl-D-aspartate in the absence of magnesium. In the present study, using the same approach, attempts were made to determine whether in the presence of magnesium, the combined stimulation of AMPA receptors allows us to demonstrate the presynaptic facilitation of [3H]dopamine release through N-methyl-D-aspartate receptors. L-Glutamate (10(-3) M) markedly stimulated the release of [3H]dopamine from synaptosomes, this effect being about twice that found with AMPA (10(-3) M) while N-methyl-D-aspartate (10(-3) M) even in the presence of glycine (10(-6) M) was ineffective. In agreement with previous results, a stimulatory effect of N-methyl-D-aspartate and glycine was only observed in the absence of magnesium. This response was blocked by 6,7-dinitro-quinoxaline-2,3-dione (3 x 10(-5) M), confirming that this compound, generally used as an AMPA antagonist, also blocks N-methyl-D-aspartate receptors. The AMPA (10(-3) M)-evoked release of [3H]dopamine was markedly potentiated by the combined application of N-methyl-D-aspartate (10(-3) M) and glycine (10(-6) M) in the presence of strychnine, indicating that the concomitant activation of AMPA receptors removes the voltage-dependent magnesium block of N-methyl-D-aspartate receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of GABA release by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and N-methyl-D-aspartate receptors in matrix-enriched areas of the rat striatum.

Using a new in vitro superfusion device, the release of preloaded [3H]GABA was examined in microdiscs of tissues taken from sagittal slices in matrix-enriched areas of the rat striatum. Potassium (9 mM, 15 mM) stimulated the release of [3H]GABA in a concentration- and calcium-dependent manner and the veratridine (1 microM)-evoked release of [3H]GABA was completely abolished in the presence of tetrodotoxin (1 microM). The selective glutamatergic agonist alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM) enhanced the potassium-evoked release of [3H]GABA as well as the basal outflow of [3H]GABA. This latter effect was found to be calcium-dependent, partially diminished by tetrodotoxin (1 microM), completely blocked by 6,7-dinitro-quinoxaline-2,3-dione (0.1 mM), which is generally used as an antagonist of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors, but not affected by (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK801, 10 microM), a specific antagonist of N-methyl-D-aspartate receptors. Similarly, N-methyl-D-aspartate (1 mM) enhanced both the potassium (9 mM) and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (1 mM)-evoked release of [3H]GABA but when used alone, due to the presence of magnesium in the superfusion medium, was ineffective on the basal efflux of [3H]GABA. A stimulatory effect of N-methyl-D-aspartate (1 mM) on the basal outflow of [3H]GABA was observed, however, when magnesium was omitted from the superfusion medium. The stimulatory effect of N-methyl-D-aspartate (1 mM) observed in the presence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate was not potentiated by glycine (1 microM, in the presence of strychnine 1 microM) and the N-methyl-D-aspartate-evoked response seen in the absence of magnesium was not enhanced by D-serine (1 mM), suggesting that endogenous glycine is already acting on N-methyl-D-aspartate receptors. In fact, in the absence of magnesium, 7-chloro-kynurenate (1 mM) completely abolished the stimulatory effect of N-methyl-D-aspartate on the release of [3H]GABA confirming that under our conditions, the glycine site of the N-methyl-D-aspartate receptor is saturated. N-methyl-D-aspartate-evoked responses were all blocked by MK801 (10 microM). Finally, the N-methyl-D-aspartate-evoked response seen in the absence of magnesium was markedly reduced in the presence of tetrodotoxin (1 microM).(ABSTRACT TRUNCATED AT 400 WORDS)

Specific role of N-acetyl-aspartyl-glutamate in the in vivo regulation of dopamine release from dendrites and nerve terminals of nigrostriatal dopaminergic neurons in the cat.

Levels of N-acetyl-aspartyl-glutamate measured by high-pressure liquid chromatography were found to be very high in the cat substantia nigra, particularly in the pars compacta, while those in the caudate nucleus were much lower. In halothane-anaesthetized cats implanted with push-pull cannulae, N-acetyl-aspartyl-glutamate (10(-8) M) induced a marked and prolonged release of newly synthesized [3H]dopamine, when infused into the posterior but not into the anterior part of the caudate nucleus. In contrast, in the presence of tetrodotoxin (10(-6) M), N-acetyl-aspartyl-glutamate (10(-8) M) reduced the residual release of [3H]dopamine; this effect was also more pronounced in the posterior than in the anterior part. In the conditions used, as indicated by experiments with [3H]N-acetyl-aspartyl-glutamate no glutamate was formed from the infused N-acetyl-aspartyl-glutamate. Ibotenate (10(-5) M) induced changes in [3H]dopamine release in both the absence and presence of tetrodotoxin, which were closely similar to those observed with N-acetyl-aspartyl-glutamate. Responses induced by either N-acetyl-aspartyl-glutamate or ibotenate were not mediated by N-methyl-D-aspartate receptors since N-methyl-D-aspartate stimulated the release of [3H]dopamine only when used in a high concentration (10(-4) M) and applied in a magnesium-free superfusion medium in both the presence of glycine (10(-6) M) and strychnine (10(-6) M). In addition, the stimulatory effect of N-methyl-D-aspartate persisted in the presence of tetrodotoxin; it was of similar amplitude in both parts of the caudate nucleus and of shorter duration than that evoked by either N-acetyl-aspartyl-glutamate or ibotenate alone. N-Acetyl-aspartyl-glutamate interacted with dopaminergic neurons not only presynaptically in the caudate nucleus but also in the substantia nigra since a marked increase in [3H]dopamine release was observed both from local dendrites and from nerve terminals in the ipsilateral caudate nucleus when N-acetyl-aspartyl-glutamate (10(-7) M) was infused locally into the substantia nigra pars compacta. No effect could be seen in contralateral structures. The isomer of natural N-acetyl-aspartyl-glutamate, beta-N-acetyl-aspartyl-glutamate (10(-7) M), had no effect on [3H]dopamine release when applied similarly in the substantia nigra, thus confirming the specificity of the action of N-acetyl-aspartyl-glutamate.

Normal CSF levels of met-enkephalin-like material in a case of naloxone-reversible congenital insensitivity to pain.

In a case of naloxone-reversible congenital insensitivity to pain, met-enkephalin-like immunoreactivity in the CSF was in the normal range and not affected by the administration of naloxone. Chromatographic analysis of the met-enkephalin-like material revealed that it corresponded to at least two classes of molecules. A clear difference in the relative proportions of these two classes was detected in the CSF of the patient insensitive to pain when compared to controls. The possible functional significance of this alteration is discussed in relation to the well known antinociceptive action of enkephalins.

Application of L-glutamic acid and substance P to the substantia nigra modulates in vivo [3H]serotonin release in the basal ganglia of the cat.

L-Glutamic acid or substance P were applied to the caudate nucleus (CN) or substantia nigra (SN) and their effects on local, spontaneous, in vivo [3H]serotonin ([3H]5-HT) release as well as [3H]5-HT release in the contralateral CN and SN were studied using cats implanted with push-pull cannulae. L-Glutamic acid (5 x 10(-5) M), when applied to the CN or SN inhibited the local release of [3H]5-HT but did not affect release in the contralateral CN and SN. In the SN, the L-glutamic acid effect was blocked by L-glutamic acid diethylester. Substance P (10(-7) M) applied to the SN induced an increase in [3H]5-HT release that was delayed in onset. Furthermore, [3H]5-HT release was elevated in the contralateral CN immediately upon the application of substance P to the SN. These results suggest that L-glutamic acid and substance P may control 5-HT transmission in the basal ganglia.

Sensory stimuli differentially affect in vivo nigral and striatal [3H]serotonin release in the cat.

The effect of auditory, visual and peripheral nerve stimulation on in vivo [3H]serotonin release in both caudate nuclei and substantiae nigrae was studied in either awake 'encéphale isolé' or halothane-anesthetized cats. Release of endogenously synthesized [3H]serotonin was estimated in each brain structure, using push--pull cannulae, continuously superfused with [3H]tryptophan. Bilateral and simultaneous application of click noises and light flashes to awake 'encéphale isolé' cats enhanced [3H]serotonin release in both substantiae nigrae but was without effect on striatal [3H]serotonin release. Unilateral, low intensity electrical stimulation of the forepaw of halothane-anesthetized cats diminished [3H]serotonin release in both caudate nuclei and the ipsilateral substantia nigra. No effect was observed in the contralateral substantia nigra. In contrast, high-intensity electrical stimulation of one forepaw increased [3H]serotonin release in the ipsilateral substantia nigra but was without significant effect on release in the other brain areas examined. The results are discussed in light of previously known anatomical data concerning serotoninergic pathways and electrophysiological evidence of the effect of sensory stimuli on serotoninergic neurons. Our findings suggest that serotonin neurons may serve an important function in the integration of sensory information.

Local and remote effects of intra-caudate administration of GABA-related drugs on Met-enkephalin release in the basal ganglia.

The possible influence of GABAergic systems on the activity of enkephalinergic neurones within the basal ganglia was examined by measuring the release of Met-enkephalin in the caudate nuclei and pallida of halothane-anesthesized cats treated by intra-caudate applications of GABA-related drugs. Depending on the concentration used, GABA exerted local stimulatory (at 10 microM of the amino acid) or inhibitory (at 0.5 mM) action on Met-enkephalin release in the cat caudate nucleus. Only the inhibition was reproduced by the GABA agonists muscimol (1 microM) and (-)-balcofen(10 microM) and by diazepam 10 microM). Conversely, the intra-caudate application of the GABA antagonist bicuculline enhanced markedly the local release of the pentapeptide. Complementary studies using slices of the rat striatum (caudate nucleus + putamen) revealed that a low concentration of GABA (10 microM) tended to increase the K+-evoked efflux of Met-enkephalin, whereas a high concentration of the amino acid exerted a strong inhibitory effect on the peptide release. Such in vivo and in vitro findings suggest that the GABA-induced inhibition of Met-enkephalin release took place via the stimulation of specific GABA A and GABA B receptors within the caudate nucleus, whereas the GABA-induced increase of the peptide release might involve some intracellular regulatory processes in striatal neurones containing both GABA and enkephalins. In addition to altering the local release of Met-enkephalin, intra-caudate applications of GABA-related drugs affected the peptide release in the ipsilateral globus pallidus and contralateral basal ganglia. The observed changes suggest that GABA A, but not GABA B, receptors participated in some tonic inhibitory influence of striatal GABAergic neurones on the striato-pallidal enkephalinergic system. Furthermore, the present results confirmed previous studies (Bourgoin et al.) showing that GABAergic neurones can contribute to some bilateral modulation of enkephalinergic neurones within the basal ganglia.

Stimulatory effect of arachidonic acid on the release of GABA in matrix-enriched areas from the rat striatum.

Arachidonic acid was shown to stimulate the release of preloaded [3H]GABA from microdiscs of tissue punched out in matrix-enriched areas of the rat striatum. This effect, which was calcium- and dose-dependent, persisted in the presence of inhibitors of arachidonic acid catabolism. Other fatty acids were less or not effective. Arachidonic acid also inhibited [3H]GABA uptake into purified striatal synaptosomes, however the arachidonic acid-evoked release of [3H]GABA persisted following inhibition of the GABA neuronal uptake process. The stimulatory effect of arachidonic acid on GABA release may largely result from the activation of a protein kinase C since the arachidonic acid response was reduced by several protein kinase C inhibitors. Arachidonic acid also dose-dependently stimulated the release of preloaded [3H]GABA from purified striatal synaptosomes. Similar results were obtained when synaptosomes were previously incubated with [3H]glutamine to study the release of endogenously synthesized [3H]GABA. Further indicating a direct action of the fatty acid on GABAergic neurons, the arachidonic acid-induced release of [3H]GABA from microdiscs was not modified in the presence of the D1 dopaminergic antagonist SCH23390 or of glutamatergic antagonists. Finally, the release of [3H]GABA evoked by the combined application of NMDA and carbachol (a treatment known to markedly stimulate arachidonic acid formation) was reduced by inhibitors of phospholipase A2 further indicating that endogenously formed arachidonic acid significantly facilitates the release of GABA in the striatum.

In vivo modulations by GABA-related drugs of met-enkephalin release in basal ganglia of the cat brain.

The influence of the intrapallidal application of GABA-related compounds on the release of Met-enkephalin in the globus pallidus and the caudate nucleus in the two hemispheres was investigated in vivo in the cat. For this purpose, the 4 structures were continuously superfused with an artificial CSF through implanted push-pull cannulae and Met-enkephalin released in superfusates was determined using a specific radioimmunoassay. GABA (10-500 microM) reduced the local release of Met-enkephalin during its application but once the amino acid was removed from the superfusing fluid, an increase in the peptide release was observed. Diazepam (10 microM) induced only an inhibitory effect whereas muscimol (1 microM) stimulated Met-enkephalin release. Opposite changes in Met-enkephalin release were also seen with the GABA antagonists, bicuculline methiodide (1 microM) and picrotoxin (10 microM), suggesting that the local regulation of Met-enkephalin release by GABA related compounds may be mediated by at least two types of GABA receptors. In several cases, the unilateral pallidal application of GABA agonists and antagonists induced significant changes in Met-enkephalin release at distant structures. The most striking effect was observed with diazepam which markedly reduced the peptide release in both caudate nuclei and pallida. These data suggest that GABAergic systems can contribute to some bilateral regulation of striato-pallidal enkephalinergic neurones.

Effect of nerve activity on the in vivo release of [3H]serotonin continuously formed from L-[3H]tryptophan in the caudate nucleus of the cat.

A new isotopic approach has been developed to study the in vivo release of serotonin (5-HT). 'Encéphale isolé' cats were implanted with a push-pull cannula in the ventrocaudal part of the head of the caudate nucleus to estimate the release of [3H]5-HT continuously synthesized from L-[3H]tryptophan. Both [3H]5-HT and [3H]tryptamine were found in superfusates. Resting steady state in the release of [3H]indoleamines was observed as soon as 20 min after the beginning of the superfusion with L-[3H]tryptophan; the levels of [3H]5-HT in superfusates were 2.5 times those of [3H]tryptamine and about 6 times the blank value. They were markedly enhanced in the presence of fluoxetine (5 x 10(-6)M), a blocker of the 5-HT uptake process. A marked increase in the release of [3H]5-HT was seen during the local depolarization of 5-HT terminals with potassium chloride (60 mM) or batrachotoxin (10(-6)M) or during the stimulation of 5-HT cell bodies in the nucleus raphe dorsalis with L-glutamic acid (5 x 10(-5)M). These treatments did not enhance the efflux of [3H]tryptamine. The potassium-evoked release of [3H]5-HT was reduced by LSD (10(-5)M). LSD added alone in the superfusing fluid was without effect. The batrachotoxin-evoked release of [3H]5-HT was inhibited in the presence of tetrodotoxin (9 x 10(-6)M). The spontaneous release of [3H]5-HT and [3H]tryptamine was markedly reduced in the presence of a calcium-free medium containing cobalt (10 mM). A transient slight reduction in the spontaneous release of [3H]5-HT was observed in the presence of tetrodotoxin (9 x 10(-6)M). The local cooling of 5-HT cell bodies with a cryoelectrode induced a slight reversible decrease in [3H]5-HT release. These last two treatments were without significant effect on [3H]tryptamine efflux in superfusates. These results indicate that the release of [3H]5-HT endogenously formed from [3H]tryptophan is dependent on nerve activity and that this is not the case for [3H]tryptamine. The advantages of the isotopic approach for in vivo studies on the release of 5-HT are discussed.

NMDA and carbachol but not AMPA affect differently the release of [3H]GABA in striosome- and matrix-enriched areas of the rat striatum.

The effects of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA; 10(-3) M), N-methyl-D-aspartate (10(-3) M, in the absence of magnesium or presence of AMPA) and carbachol (10(-3) M) on the release of preloaded [3H]gamma-aminobutyric acid ([3H]GABA) from microdiscs of tissue punched out from sagittal brain slices in striosome- or matrix-enriched areas of the rat striatum have been compared. Although AMPA stimulated similarly the release of [3H]GABA in both striatal compartments, the release of [3H]GABA evoked by either N-methyl-D-aspartate (in the presence of AMPA) or carbachol was more pronounced in matrix- than in striosome-enriched areas. AMPA- and N-methyl-D-aspartate- (in the absence of magnesium) evoked responses were reduced but not abolished in the presence of tetrodotoxin (10(-6) M) in both compartments while the carbachol-evoked release of [3H]GABA was decreased by tetrodotoxin only in the matrix. The interruption of cholinergic transmission by the combined application of atropine (10(-5) M) and pempidine (10(-4) M) was without effect on the AMPA-evoked release of [3H]GABA, but it reduced the N-methyl-D-aspartate- (in the absence of magnesium or presence of AMPA) evoked release of [3H]GABA in both compartments, these reductions being of similar amplitude than those observed with tetrodotoxin.

Lack of autoreceptor-mediated inhibitory control of dopamine release in striatal synaptosomes of D2 receptor-deficient mice.

Mouse purified striatal synaptosomes were used to study the release of newly synthesised [3H]-dopamine ([3H]-DA) or of previously taken up [3H]-DA. Quinpirole (QP, 10 microM), a D2/D3 dopaminergic agonist, was found to reduce the release of newly synthesised [3H]-DA with a larger amplitude when 4-aminopyridine (100 microM) instead than veratridine (1 microM) or potassium (25 mM) was used to evoke DA release. Among the different D2/D3 dopaminergic agonists tested R(-)-propylnorapomorphine (NPA) and quinpirole were the most potent. These compounds reduced, in a concentration-dependent manner, the 4-aminopyridine-evoked release of [3H]-DA previously taken up by synaptosomes (50% maximal inhibition). In contrast, the D3 agonist PD-128,907 had little effect even when used at 100 nM. The QP (100 nM)-induced response was completely antagonised by sulpiride (1 microM). Strikingly, the NPA (100 nM) and PD-128,907 (100 nM)-evoked responses were completely suppressed in D2 receptor-deficient mice. This data strongly suggest that only D2 but not D3 receptors are involved in the autoreceptor-mediated inhibition of the evoked release of [3H]-DA. Interestingly, while amphetamine-induced release of [3H]-DA was not modified, a slight reduction of [3H]-DA efflux induced by the dopamine (DA) uptake inhibitor cocaine was observed in D2 receptor-deficient mice.

Dopamine released from dendrites in the substantia nigra controls the nigral and striatal release of serotonin.

Using push--pull cannulae, the release of endogenously synthesized [3H]serotonin was estimated in both substantia nigra and caudate nuclei of 'encéphale isolé' cats. The unilateral nigral application of dopamine (10(-7) M) reduced [3H]serotonin release in ipsilateral structures whereas alpha-methylparatyrosine (10(-4) M) induced opposite effects. Both treatments decreased [3H]serotonin release in the contralateral caudate nucleus but not in the contralateral substantia nigra. As a working hypothesis it is suggested that the effects observed are related to changes in the activity of nigroraphe neurons regulated by dopamine release from dendrites of the nigrostriatal dopaminergic neurons. However it cannot yet be excluded that the local changes in [3H]serotonin release induced by the nigral application of dopamine or alpha-methylparatyrosine result from presynaptic modulation.

Spontaneous and evoked release of methionine-enkephalin-like material from the rat spinal cord in vivo.

In vivo perfusion of the subarachnoid space with an artificial cerebrospinal fluid (CSF) in paralyzed halothane-anesthetized rats allowed the collection of methionine-enkephalin (Met-Enk)-like material (MELM) released from the spinal cord. Bio-Gel P2 chromatography and high-performance liquid chromatography showed that 65% of this material corresponded to authentic Met-Enk. Under resting conditions, about 1 pg of MELM per minute was regularly released for at least 3 h; for Met-Enk, this value corresponded to a fractional rate constant of 0.002% (i.e. tissue content of the pentapeptide which was released per minute from the whole spinal cord). Perfusion with K+-enriched (40-60 mM) CSF resulted in a marked enhancement (+ 150-200%) of spinal MELM release. Similarly, calibrated pinches of the muzzle and i.p. administration of acetic acid, two strong noxious stimuli in awake animals, induced a significant increase (+ 75-150%) in spinal MELM release. In contrast, pinches applied to the tail did not enhance but instead slightly reduced (-35%) MELM release from the rat spinal cord. These data suggest that mechanisms other than segmental controls could be involved in the activation of spinal enkephalinergic neurons by some nociceptive stimuli.

Biochemical evidence for the 5-HT agonist properties of PAT (8-hydroxy-2-(di-n-propylamino)tetralin) in the rat brain.

In vitro investigations revealed that PAT (8-hydroxy-2-(n-dipropylamino)tetralin) interacted with postsynaptic 5-HT receptors in the rat brain: the drug stimulated 5-HT-sensitive adenylate cyclase in homogenates of colliculi from new-born rats (KAapp 8.6 microM) and inhibited the specific binding of [3H]5-HT to 5-HT1 sites. The PAT-induced inhibition of [3H]5-HT binding showed marked regional differences compatible with a preferential interaction of PAT (IC50 2 nM) with the 5-HT1A subclass. As previously seen with 5-HT agonists, the efficacy of PAT for displacing [3H]5-HT bound to hippocampal membranes was markedly increased by Mn2+ (1 mM) and reduced by GTP (0.1 mM). PAT also affected presynaptic 5-HT metabolism since it inhibited competitively (Ki 1.4 microM) [3H]5-HT uptake into cortical synaptosomes and reduced (in the presence of the 5-HT uptake inhibitor fluoxetine) the K+-evoked release of [3H]5-HT previously taken up or newly synthesized from [3H]tryptophan in cortical or striatal slices. This latter effect was prevented by 5-HT antagonists (methiothepin, metergoline) suggesting that it was mediated by the stimulation of presynaptic 5-HT autoreceptors by PAT. Like 5-HT, PAT counteracted the stimulatory effect of K+-induced depolarization on the synthesis of [3H]5-HT from [3H]tryptophan in cortical slices. It is concluded that PAT is a potent 5-HT agonist acting on both post- and presynaptic 5-HT receptors in the rat brain.