Neurotransmitter receptor binding in bovine cerebral microvessels.

Purified preparations of microvessels from bovine cerebral cortex contain substantial levels of alpha-adrenergic, beta-adrenergic, and histamine 1 receptor binding sites but only negligible serotonin, muscarinic cholinergic, opiate, and benzodiazepine receptor binding. Norepinephrine and histamine may be endogenous regulators of the cerebral microcirculation at the observed receptors.

Serotonin neurons project to small blood vessels in the brain.

Electrolytic lesions of the nucleus raphe dorsalis and medianus reduce the concentration of serotonin (5-hydroxytryptamine) within rat brain intraparenchymal blood vessels. The concentration of serotonin within these vessels increases or decreases after the administration of drugs that modify the biosynthesis and degradation of serotonin or destroy nerve terminals by an uptake-dependent mechanism. These studies provide evidence for the existence of a serotonin-containing pathway seemingly analogous to the neuronal projection that terminates on small parenchymal blood vessels from noradrenergic neurons of the locus coeruleus.

Interferon response heterogeneity: activation of a pro-inflammatory response by interferon alpha and beta. A possible basis for diverse responses to interferon beta in MS.

Interferon gamma (IFN-gamma) stimulates the (pro-inflammatory) type II interferon receptor and is known to exacerbate multiple sclerosis (MS). In contrast, IFN-alpha and IFN-beta are ligands for the (anti-inflammatory) type I interferon receptor and are beneficial in some (but not all) patients with MS. Should IFN-beta elicit a type-II-like pro-inflammatory response, the beneficial effects might be attenuated. These studies were undertaken to test this possibility with the use of quinolinic acid (QUIN) formation as a measure of type II receptor activation. In normal human macrophage cultures, IFN-gamma was the most potent stimulus for QUIN formation. Generally, IFN-beta and IFN-alpha were less potent. However, an unexpected inter-patient variability was observed. In some subjects, IFN-alpha was more potent than IFN-beta. In other subjects, IFN-beta was more potent than IFN-alpha. The present data demonstrate an inter-subject variability for QUIN production following exposure to the interferons. MS patients who demonstrate a pro-inflammatory response to IFN-beta (e.g., increased QUIN) may be less likely to benefit from this therapy.

Synthesis and SAR of 4-aryl-2-hydroxy-4-oxobut-2-enoic acids and esters and 2-amino-4-aryl-4-oxobut-2-enoic acids and esters: potent inhibitors of kynurenine-3-hydroxylase as potential neuroprotective agents.

The synthesis and structure-activity relationship of a series of 4-aryl-2-hydroxy-4-oxobut-2-enoic acids and esters and 2-amino-4-aryl-4-oxobut-2-enoic acids and esters as potent inhibitors of kynurenine-3-hydroxylase are described. These compounds are the most potent inhibitors of the kynurenine-3-hydroxylase enzyme so far disclosed. Additionally methyl 4-(3-chlorophenyl)-2-hydroxy-4-oxobut-2-enoate (2d), 4-(3-chlorophenyl)-2-hydroxy-4-oxobut-2-enoic acid (3d), methyl 4-(3-fluorophenyl)-2-hydroxy-4-oxobut-2-enoate (2f), and 4-(3-fluorophenyl)-2-hydroxy-4-oxobut-2-enoic acid (3f) prevent the increase in the interferon-gamma-induced synthesis of quinolinic acid in primary cultures of cultured human peripheral blood monocyte-derived macrophages.

Anticonvulsants. 5. Derivatives of 5-ethyl-5-phenylhydantoin and 5,5-diphenylhydantoin.

Alkoxymethyl, acyloxymethyl, and mixed alkylalkoxymethyl or alkylacyloxymethyl derivatives of 5-ethyl-5-phenylhydantoin exhibit anticonvulsant activity. Also effective are bis(alkoxymethyl) and mixed alkylalkoxymethyl derivatives of 5,5-diphenylhydantoin. Of particular interest are 1,3-bis(methoxymethyl)-5,5-diphenylhydantoin and 3-acetoxymethyl-5-ethyl-5-phenylhydantoin, which show good activity against maximal electroshock seizures, and 3-methoxymethyl-5-ethyl-5-phenylhydantoin, which is effective against both maximal electroshock and pentylenetetrazole. None of the above compounds show greater activity against maximal electroshock seizures than the parent compounds, however.

Analgesics. 3. Selected 1-substituted and 1,3-disubstituted 5-propionoxy-5-(1-phenylethyl)barbituric acids.

Several 1,3-disubstituted and 1-substituted derivatives of 5-propionoxy-5-(1-phenylethyl)barbituric acid were synthesized and evaluated for analgesic activity. Three of these compounds, 1,3-bis(methoxymethyl)-5-propionoxy-5-(1-phenylethyl)barbituric acid (2), 1,3-dimethyl-5-propionoxy-5-(1-phenylethyl)barbituric acid (7), and 1-methyl-5-propionoxy-5-(1-phenylethyl)barbituric acid (10), exhibited better oral activity than codeine sulfate.

Synthetic analogues of tetrahydrobiopterin with cofactor activity for aromatic amino acid hydroxylases.

Tetrahydrobiopterin (THB) analogues with 6-alkoxymethyl substituents, 3a-j, where the substituents were straight- and branched-chain alkyl ranging from methyl to octyl, have been synthesized by the Taylor method from pyrazine ortho amino nitriles by guanidine cyclization, hydrolysis in aqueous NaOH, and catalytic hydrogenation over Pt in trifluoroacetic acid (TFA). The best of these compounds, 3b, is an excellent cofactor for phenylalanine hydroxylase, tyrosine hydroxylase (V = 154% of THB), and tryptophan hydroxylase, does not destablize the binding of substrate (Kmtyr = 23 microM), and is recycled by dihydropteridine reductase (V = 419% of THB). The compounds are being evaluated as cofactor replacements in biopterin-deficiency diseases.

Aporphines. 14 Dopaminergic and antinociceptive activity of aporphine derivatives. Synthesis of 10-hydroxyaporphines and 10-hydroxy-N-n-propylnoraporphine.

The synthesis of racemic 10-hydroxyaporphine [(+/-)-2a] and 10-hydroxy-N-n-propylnoraporphine [(+/)-2b] is described. The method involved a Reissert alkylation-Pschorr cyclization route. The dopaminergic activity of (+/-)-2b was evaluated in comparison with L-Dopa, (-)-apomorphine (1a), (+/-)-N-n-propylnorapomorphine (NPA) (1b), and (+/-)-11-hydroxy-N-n-propylnoraporphine [(+/-)-11-OH-PNA] by the behavioral model of rotational behavior in animals after unilateral lesion of the ascending DA pathways. The dopaminergic activity of NPA and 11-OH-PNA is essentially equivalent to L-Dopa and (-)-apomorphine, and both are more active than (+/-)-2b. Furthermore, (+/-)-NPA (threshold doses, 5 mug/kg) appears to be even more potent that (-)-apomorphine (threshold doses, 25 mug/kg). The duration of action of NPA and 11-OH-PNA is considerably longer than that obtained with L-Dopa. The antinociceptive activity of (+/-)-2b was evaluated by the tail-flick procedure and compared with 1a, 2b, morphine, and L-Dopa. Weak but significant antinociceptive activity was shown by (+/-)-2b and by (+/-)-1b but not by (-)-apomorphine. This effect was not antagonized by naloxone. The finding that (+/-)-2b and particularly (+/-)-11-OH-PNA are active in doses from 500 to 50 mug/kg, respectively, in causing rotational behavior further supports previous studies indicating that N-n-propyl derivatives of monohydroxylated aporphines were more active than the corresponding parent N-methyl derivatives as DA receptor agonists and that a catechol system is not an absolute requirement for dopaminergic activity in such aporphines.

Quinolinic acid and lymphocyte subsets in the intrathecal compartment as biomarkers of SIV infection and simian AIDS.

Cerebrospinal fluid (CSF) samples were collected from monkeys infected with SIVmac251 (SIV) or HIV-1/SIVmac chimeric viruses (SHIV(HXBc2) and SHIV(89.6P)) to investigate quinolinic acid (QUIN) levels in the intrathecal compartment. CSF levels of QUIN were elevated in the SIV-infected monkeys, especially in animals with end-stage disease, and in those infected with pathogenic SHIV(89.6P), but not after infection with the nonpathogenic construct SHIV(HXBc2). QUIN elevations occurred in association with reduced CD4+ and increased CD8+ lymphocytes, cellular alterations that were more pronounced in CSF than in the blood. These findings support the view that the intrathecal compartment provides a unique window on viral infection, and are in keeping with the a priori prediction that QUIN increases primarily in response to more pathogenic viral strains.

Effects of 540C91 [(E)-3-[2-(4'-pyridyl)-vinyl]-1H-indole], an inhibitor of hepatic tryptophan dioxygenase, on brain quinolinic acid in mice.

Studies were undertaken to assess the role of the liver in the formation of the neurotoxin quinolinic acid in the brain. A selective and potent inhibitor of hepatic tryptophan 2,3-dioxygenase, 540C91 [(E)-3-[2-(4'-pyridyl)-vinyl]-1H-indole], largely prevented the elevation in mouse brain quinolinic acid resulting from parenteral injection of tryptophan (TRP). In contrast, 540C91 did not affect basal levels of the neurotoxin. Following induction of indoleamine dioxygenase with bacterial lipopolysaccharide, 540C91 was less effective in preventing the TRP-induced elevations in quinolinic acid. The data suggest that kynurenines, formed from tryptophan, by the liver and other extrahepatic organs can give rise to brain quinolinic acid.

Slow changes of tyrosine hydroxylase gene expression in dopaminergic brain neurons after neurotoxin lesioning: a model for neuron aging.

Slow neuron regression develops during the adult phase of life in select brain systems of mammals. We describe a model in adult rats that resolves several phases in a slow atrophic process that differentially influences levels of mRNA and protein for tyrosine hydroxylase (TH). Responses of striatal dopaminergic markers to 6-hydroxydopamine (6-OHDA) lesions in rats indicated that the striatal terminals maintained TH protein, despite greater than 3-fold loss of TH mRNA in the substantia nigra pars compacta (SNC) cell bodies whose axons project to the striatum. The loss of TH mRNA/cell was progressive up to 9 months, whereas SNC cell body shrinkage stabilized by 3 months post-lesioning. Consideration of possible mechanisms in protein turnover motivated a search for PEST motifs in the TH of rats and other vertebrates that could be a point of regulation by altering the rate of TH protein turnover.

The effect of intravenous L-tryptophan on prolactin and growth hormone and mood in healthy subjects.

In order to assess the effects of increased central nervous system serotonergic function in humans on prolactin (PRL), growth hormone (GH) and mood, intravenous L-tryptophan (TRP) was administered to ten healthy subjects. The TRP infusion induced robust increases in PRL in all ten subjects. A significant increase in GH concentration was also observed, although the response was more variable. The subjects reported feeling significantly more high, mellow, and drowsy following the TRP infusion in comparison to placebo. These findings indicate an important role for serotonin in PRL and GH secretion, as well as in mood regulation. The intravenous TRP challenge may be of use in the study of serotonergic function in a variety of neurologic and psychiatric diseases.

The effect of IV L-tryptophan on prolactin, growth hormone, and mood in healthy subjects.

In order to assess the effects of increased CNS serotonergic function in humans on prolactin (PRL), growth hormone (GH), and mood, IV L-tryptophan (TRP) was administered to ten healthy subjects. The TRP infusion induced robust increases in PRL in all ten subjects. A significant increase in GH concentration was also observed, although the response was more variable. The subjects reported feeling significantly more 'high', 'mellow', and 'drowsy' following the TRP infusion in comparison to placebo. These findings indicate an important role for serotonin in PRL and GH secretion, as well as in mood regulation. The IV TRP challenge may be of use in the study of serotonergic function in a variety of neurologic and psychiatric diseases.

Activated human microglia produce the excitotoxin quinolinic acid.

We aimed to determine the relative role of quinolinic acid synthesis in purified human microglia, monocyte-derived macrophages and astrocytes in the human brain following immune stimulation. Microglia and macrophages significantly increased quinolinic acid synthesis from tryptophan following activation by either lipopolysaccharide or interferon-gamma. Quinolinic acid synthesis by individual microglia was heterogeneous, and its production by activated macrophages was approximately 32-fold greater than its microglial synthesis. Quinolinic acid synthesis by astrocytes was undetectable. Microglia may, therefore, be the primary endogenous cell type responsible for quinolinic acid synthesis in the brain parenchyma. However, under pathological conditions which precipitate blood-brain barrier compromise and/or leukocytic infiltration, intracerebral quinolinic acid may be derived chiefly from cells of the peripheral immune system such as activated macrophages.

A comparison of the effects of kainic acid on somatostatin, substance P and dopamine in the rabbit retina.

Groups of adult, male Dutch belted rabbits received intravitreal injections of varying doses (30-240 nmol) of the excitatory neurotoxin kainic acid (KA) into one eye and saline vehicle into the other. One week later a segment of each retina was examined histologically and the remainder was assayed for somatostatin-like immunoreactivity (SLI), substance P-like immunoreactivity (SPLI), dopamine (DA) and protein. Histologically, KA at doses of 120 and 240 nmol produced destruction of the inner layers of the retina, with preservation of the photoreceptors. This damage is correlated with a dose-related depletion of retinal protein content. At KA doses of 120 and 240 nmol, both SPLI and DA content were reduced to 5-10% of control values. Although KA significantly reduced the retinal content of SLI even at a dose of 30 nmol, the greatest mean depletion of SLI observed at any dose was 50%. This failure of KA to reduce retinal SLI content by more than 50% at doses of KA which produce severe histologic damage to the neural retina and dramatic depletions of SPLI and DA content demonstrates that the SLI-containing structures of the rabbit retina are partially resistant to the neurotoxic action of KA. We hypothesize that SLI in the rabbit retina is contained in two pharmacologic types of cells in about equal abundance; one type is sensitive to and one type resistant to KA. In contrast, substance P- and dopamine-containing retinal neurons are uniformly sensitive to destruction by KA.

Characterization of the origins of astrocyte response to injury using the dopaminergic neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

We used the dopaminergic neurotoxicant, 1-methyl-1,2,3,6-tetrahydropyridine (MPTP), as a tool to characterize the origins of astroglial response to injury. Radioimmunoassay of the astrocyte protein, glial fibrillary acidic protein (GFAP), was used to quantify the astrocyte reaction to MPTP. Assays of neuron-localized proteins and of dopamine were used to assess neuronal damage caused by MPTP. A single administration of MPTP (12.5 mg/kg, s.c.) to the C57BL/6J mouse resulted in more than a 3-fold increase in striatal GFAP within 48 h, followed by a decline to baseline at 3 weeks. A decrease in the amount of striatal tyrosine hydroxylase (TH), a marker of dopaminergic neurons, preceded the rise in GFAP. The concentration of striatal DARPP-32, a phosphoprotein enriched in neurons receiving dopaminergic input, was not affected by MPTP. Protecting the dopaminergic neurons from the neurotoxic metabolite of MPTP, 1-methyl-4-phenylpyridinium (MPP+), either by blocking its formation or by preventing its uptake into dopaminergic neurons, completely blocked the increase in GFAP. MPTP did not appear to disrupt the blood-brain barrier, therefore, blood-borne elements probably did not mediate the increase in GFAP. In addition, immunoblot data indicated that brain-derived interleukin 1, an astrocyte growth factor, also did not play a role in MPTP-induced gliosis. Together, these findings suggest that diffusible factors derived from damaged dopaminergic neurons initiate the astrocyte response to MPTP and that large increases in GFAP can be induced without the participation of serum-derived growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Pargyline and gamma-butyrolactone enhance tyrosine hydroxylase immunostaining of nigrostriatal axons.

Administration of pargyline or gamma-butyrolactone enhanced immunostaining of tyrosine hydroxylase immunoreactive axons in the striatum. The qualitative characteristics of the enhancement were compound dependent and the enhancement was not associated with an increase in the amount of tyrosine hydroxylase within the striatum. These results demonstrate the pharmacological enhancement of immunostaining for neurotransmitter synthetic enzymes in the absence of increased synthesis.

Elevation of the neurotoxin quinolinic acid occurs following spinal cord trauma.

Excitatory amino acid neurotoxicity and the inflammatory response are suspected as mediators of some of the pathological sequelae occurring as a result of spinal cord injury. Here we report temporal and regional increases of the NMDA receptor agonist, quinolinic acid (QUIN), in an experimental model of spinal contusion injury. These changes occurred at a time when the blood-brain barrier is known to be dysfunctional and the activation state and density of microglia and macrophages are increased. Thus, alterations in tissue QUIN levels may occur as a result of secondary activation of CNS inflammatory cells or from peripherally derived sources across a damaged blood-brain barrier.

Stimulation of retinal dopamine biosynthesis in vivo by exogenous tetrahydrobiopterin: relationship to tyrosine hydroxylase activation.

Intravitreal injection of tetrahydrobiopterin (BH4), the cofactor for tyrosine hydroxylase (TH), increases 3,4-dihydroxyphenylalanine (DOPA) accumulation in retinas of dark-adapted rats, as does exposure to light. In contrast, BH4 had no significant effect on DOPA accumulation in retinas of light-exposed rats. The levels of endogenous retinal BH4 and the uptake of injected BH4 into the retinal tissue were not affected by light exposure. These data indicate that TH is not saturated with endogenous BH4 in the retinas of dark-adapted rats. In addition, the observations support the interpretation that the decrease in apparent Km of TH for the cofactor in response to light exposure is of sufficient magnitude to allow near saturation of TH by endogenous BH4 and, thus, is causally related to the increase of dopamine biosynthesis in response to short-term photic stimulation.

Alpha 1-adrenoceptor denervation supersensitivity in brain: physiological and receptor binding studies.

Electrophysiological and radioligand binding methods were used to characterize noradrenergic denervation supersensitivity at alpha 1-adrenoceptors in rat thalamus. Denervation was accomplished either by intraventricular or intracerebral injection of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA). In the physiological studies, the sensitivity of single lateral geniculate neurons to norepinephrine, carbachol, and serotonin was compared in sham and lesioned animals various times after 6-OHDA. Conducted in parallel were radioligand binding studies in which the density and affinity of thalamic alpha 1-adrenoceptors were measured with the specific antagonist [3H]prazosin. The results indicate that denervation produces a selective increase in the sensitivity of geniculate neurons to alpha 1-adrenergic stimulation and a concomitant increase in alpha 1-adrenoceptor density and agonist affinity.