Immunohistochemical demonstration of catechol-o-methyltransferase in mammalian brain

Serotonin and dopamine turnover in the female rainbow trout (Oncorhynchus mykiss) brain and pituitary: changes during the annual reproductive cycle

Brain serotonin (5HT) and dopamine (DA) turnover were studied at various stages of the reproductive cycle of the female rainbow trout by simultaneous determination by HPLC of neurotransmitters and major related metabolites. An increase of 5HT turnover in telencephalon and hypothalamus and a decrease of DA turnover in pituitary and hypothalamus were observed during the periovulatory period. Some changes also occurred during vitellogenesis: decreased 5HT metabolite in telencephalon and preoptic area and increased DA content in preoptic area. These data suggest that physiological fluctuations of biogenic amines could be involved in both ovarian recrudescence and ovulation, with major effects on the hypothalamo-hypophysial complex during the periovulatory period.

Electrophoretic analysis of low and high activity forms of catechol-O-methyltransferase in human erythrocytes

Analysis of the catechol-O-methyltransferase (COMT) enzyme in human RBC lysates from 15 samples exhibiting inherited variations in level of activity and thermal stability was performed. Electrophoretic blotting and immune fixation was carried out following sodium dodecyl sulfate polyacrylamide gel electrophoresis or isoelectric focusing of lysate protein. These techniques did not reveal a major structural alteration of the protein that could account for the observed variation in enzyme activity or thermal stability. Future studies utilizing molecular genetic techniques should make it possible to determine the basis for inherited variations in human RBC COMT activity and thermal stability.

Cell-free synthesis of rat and human catechol O-methyltransferase. Insertion of the membrane-bound form into microsomal membranes in vitro

The protein-coding capacities of rat and human catechol O-methyltransferase (COMT) DNA clones were analysed by in vitro transcription and translation using bacteriophage RNA polymerase and rabbit reticulocyte lysate. Two types of clones corresponding to the structures of human placental cDNA clones were used. The shorter clones, containing the 663-residue open reading frame for the soluble COMT (S-COMT), produced 24-kDa (rat) and 26-kDa (human) polypeptides. Translation of the longer clones, containing 43 (rat) or 50 (human) amino acid amino-terminal extensions to the S-COMT polypeptides, yielded 28-kDa (rat) and 30-kDa (human) putative membrane-bound COMT (MB-COMT) polypeptides as the main products. These clones also yielded low amounts of the S-COMT polypeptides. Labelling time or ionic conditions during translation did not eliminate the shorter products, suggesting translation initiation from the second S-COMT AUG codon. In accordance with this postulation, the relative amount of S-COMT could be affected by changing the translation initiation contexts preceding the first AUG codon. The 28-kDa and 30-kDa products, but not the 24-kDa and 26-kDa products, associated with microsomal membranes cotranslationally, indicating that the amino-terminal extensions were functional signal sequences. However, the presence of membranes did not affect the mobilities of the proteins in SDS/polyacrylamide gels. The MB-COMT polypeptides could not be released from the microsomes by treatments with phospholipase C or alkali and were not protected by the microsomes against proteinase K digestion. These results indicate that MB-COMT synthesized in vitro is an integral membrane protein having an amino-terminal signal-anchor sequence.

Reserpine-insensitive dopamine release in the substantia nigra?

Dopamine (DA) is synthesized and released not only from the terminals of the nigrostriatal dopaminergic pathway, but also from the dendrites in the substantia nigra (SN). Whether the DA release in the SN is sensitive to reserpine treatment, as it is in the stratum, has, however, not been clarified. We have determined the effects of reserpine on the concentrations of DA, serotonin and their metabolites in the SN and in the striatum and as an index of DA release in vivo we have assessed the accumulation of the DA metabolite 3-methoxytyramine (3-MT) following inhibition of monoamine oxidase by pargyline. The effects of reserpine on the concentrations of DA and its metabolites were different in the SN as compared to in the striatum. In the striatum there was a maximal depletion of DA to 2% of controls, but in the SN the DA concentration decreased only to 17% of controls. In the SN, the increases of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were less pronounced than in the striatum. In the striatum reserpine treatment (given 15 h, 3.75 h, or 1.75 h before pargyline) decreased the pargyline-induced 3-MT accumulation to 30% of pargyline-treated controls. However, in the SN no effects of reserpine were observed. The results indicate that DA in the SN partly is situated in a reserpine insensitive pool and that the release of DA might be insensitive to reserpine. These differences between the SN and the striatum could be due to different storage mechanisms. In the striatum DA is stored in classical storage granulas but in SN DA is partly stored in storage granulas and partly in smooth endoplasmatic reticulum.

Interstitial 3-methoxytyramine reflects striatal dopamine release: an in vivo microdialysis study

Previous ex vivo studies have provided indirect evidence that the dopamine (DA) metabolite 3-methoxytyramine (3-MT) may be a useful index of DA release in vivo. In the present study, in vivo microdialysis was utilized to assess directly the relationship between extracellular DA and 3-MT in the striatum of rats following a variety of pharmacological manipulations. Apomorphine, a DA receptor agonist, produced a rapid, transient decrease in both DA and 3-MT. Conversely, the DA receptor antagonist haloperidol produced a concomitant increase in extracellular DA and 3-MT. Increases in DA and 3-MT were also noted following the administration of the DA uptake inhibitor, bupropion. Local application of tetrodotoxin resulted in the complete elimination of measurable amounts of DA and 3-MT in the dialysate, gamma-Butyrolactone also greatly decreased DA and 3-MT. Finally, d-amphetamine produced a large increase in DA and 3-MT in animals that had been treated previously with gamma-butyrolactone. The Pearson correlation coefficients for DA and 3-MT following these manipulations ranged from 0.87 to 0.97. These data indicate that interstitial 3-MT is an accurate index of DA release. However, when compared with previous ex vivo findings, the present results also suggest that changes in tissue concentrations of 3-MT may not reliably reflect DA release following certain pharmacological manipulations.

Concentrations of tyrosine, L-dihydroxyphenylalanine, dopamine, and 3-O-methyldopa in the cerebrospinal fluid of Parkinson's disease

We determined the concentrations of tyrosine, L-3,4-dihydroxyphenylalanine (DOPA), dopamine (DA), and 3-O-methyldopa (3-OMD) in the cerebrospinal fluid (CSF) of parkinsonian patients and elevated potential interactions between the substances. We found a significant increase in tyrosine, and a significant decrease in DOPA, DA, and 3-OMD. We also found that for a given concentration of DOPA, DA and 3-OMD were proportional. In addition, the ratio of DA to 3-OMD was significantly shifted in favor of DA in parkinsonian patients.

Effects of selective monoamine oxidase inhibitors on the in vivo release and metabolism of dopamine in the rat striatum

Brain microdialysis was used to examine the in vivo efflux and metabolism of dopamine (DA) in the rat striatum following monoamine oxidase (MAO) inhibition. Relevant catecholamines and indoleamines were quantified by HPLC coupled with a electrochemical detection system. The MAO-B inhibitor selegiline only affected DA deamination at a dose shown to inhibit partially type A MAO. Alterations in DA and metabolite efflux were not observed when using the MAO-B-selective dose of 1 mg/kg of selegiline. At 10 mg/kg, selegiline reduced the efflux of DA metabolites to approximately 70% of basal values without affecting DA efflux. K(+)- and veratrine-stimulated DA efflux was not affected by selegiline. Experiments using amphetamine and the DA uptake inhibitor nomifensine demonstrated that the effect of selegiline on DA metabolism was unlikely to be mediated either by inhibition of DA uptake or by an indirect effect of its metabolite amphetamine. The possibility that the effect of selegiline is mediated via a nonspecific inhibition of MAO is discussed. In contrast, the MAO-A inhibitor clorgyline inhibited basal DA metabolism and increased basal and depolarisation-induced DA efflux. A 1 mg/kg dose of clorgyline reduced basal DA metabolite efflux (40-60% of control values) without affecting DA efflux. At 10 mg/kg of clorgyline, DA efflux increased to 253 +/- 19% of basal values, whereas efflux of DA metabolites was reduced to between 15 and 26% of control values. The release of DA induced by K+ and veratrine was not affected by 1 mg/kg of clorgyline but was increased by approximately 200% following pretreatment with 10 mg/kg of clorgyline. The nonselective MAO inhibitor pargyline caused similar but more pronounced alterations in these parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic characteristics of serotonin and dopamine metabolism in the rainbow trout brain: a regional study using liquid chromatography with electrochemical detection

Aminergic metabolism was studied in discrete brain regions of the postovulated female rainbow trout using a liquid chromatography electrochemical detection method. 3 Methoxytyramine (3MT) was the major dopaminergic catabolite, suggesting that catechol-o-methyl transferase is the main dopamine (DA) catabolic enzyme. Two populations of brain regions were found: one with a high DA content and low 3MT/DA ratio (hypothalamus and telencephalon), suggesting that these regions could present a high density of DA perikarya; the other with a high 3MT/DA ratio (pituitary, preoptic area, myelencephalon and optic tectum) suggesting that these regions could present a high density of DA axonal endings. 5 Hydroxytryptamine (5HT) content differed, but an homogeneous distribution of monoamine oxidase was found in different brain regions. High 5HT content was found in the hypothalamus and telencephalon; 5HT was however not detectable in the pituitary.

Striatal L-dopa metabolism studied in vivo in rats with nigrostriatal lesions

We have used cerebral dialysis to monitor striatal metabolism of exogenously administered L-dopa (L-dihydroxyphenylalanine) in rats with unilateral lesions of the substantia nigra. The concentration of extracellular dopamine (DA) increased in both striata following L-dopa administration but the increase was markedly attenuated in the lesioned striatum. The formation of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), the major DA metabolites, was also reduced in the lesioned striata following L-dopa administration; however, the reduction was not as great as was that of DA formation. A significant metabolism of exogenous L-dopa to 3-O-methyldopa occurred in both striata. L-dopa administration transiently increased extracellular levels of 5-hydroxyindoleacetic acid (5 HIAA) in both the lesioned and intact striata. These results suggest that the striatum with a reduction in DA nerve terminals is deficient both in the capacity to synthesize DA and in the storage mechanisms necessary to protect the newly synthesized DA from oxidative metabolism.

Relationship between plasma and cerebrospinal fluid norepinephrine and dopamine metabolites in a nonhuman primate

Major and minor pathways of metabolism in the mammalian CNS result in the formation of 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) and normetanephrine (NMN) from norepinephrine (NE), and homovanillic acid (HVA) and 3-methoxytyramine (3-MT) from dopamine (DA), respectively. The correlational relationships between HVA and 3-MT and between MHPG and NMN in primate CSF and plasma have not been described. These relationships may help to elucidate the usefulness of CSF and plasma metabolites as indices of CNS NE and DA activity. In addition, because NMN is unlikely to cross the blood-brain barrier. CSF NMN concentrations would not be confounded by contributions from plasma, which is a major issue with CSF MHPG. We have obtained repeated samples of plasma and CSF from drug-naive male squirrel monkeys and have measured the concentrations of MHPG, HVA, NMN, and 3-MT to define their correlational relationships. For the NE metabolites, significant correlations were obtained for CSF MHPG and NMN (r = 0.806, p less than 0.001), plasma MHPG and CSF NMN (r = 0.753, p less than 0.001), and plasma and CSF MHPG (r = 0.776, p less than 0.001). These results suggest that CSF and plasma MHPG and CSF NMN may reflect gross changes in whole brain steady-state noradrenergic metabolism. Only a single significant relationship was demonstrated for the DA metabolites, with CSF 3-MT correlating with plasma HVA (r = 0.301, p less than 0.025). The results for the DA metabolites probably reflect regional differences in steady-state brain dopaminergic metabolism.

Synthesis and release of dopamine in rat brain: comparison between substantia nigra pars compacts, pars reticulata, and striatum

Dopamine (DA) is synthesized and released not only from the terminals of the nigrostriatal dopaminergic neuronal pathway, but also from the dendrites in the substantia nigra. We have investigated the regulation of the DA turnover, the DA synthesis rate, and the DA release in the substantia nigra pars compacts (SNpc) and pars reticulata (SNpr) in vivo. As a measure of DA turnover, we have assessed the concentrations of 3,4-dihydroxyphenylacetic acid and homovanillic acid. As a measure of the DA synthesis rate, we have determined the 3,4-dihydroxyphenylalanine accumulation after inhibition of aromatic L-amino acid decarboxylase by 3-hydroxybenzylhydrazine. As a measure of DA release, we have investigated the disappearance rate of DA after inhibition of its synthesis by alpha-methyl-p-tyrosine and the 3-methoxytyramine accumulation following monoamine oxidase inhibition by pargyline. Both the DA turnover and the DA synthesis rate increased following treatment with the DA receptor antagonist haloperidol and decreased following treatment with the DA receptor agonist apomorphine in the SNpc and in the SNpr, but the effects of the drugs were less pronounced than in the striatum. gamma-Butyrolactone treatment, which suppresses the firing of the dopaminergic neurons, increased the DA synthesis rate in the striatum (165%), but had no such effect in the SNpc or SNpr. Haloperidol, apomorphine, and gamma-butyrolactone increased, decreased, and abolished, respectively, the DA release in the striatum, but the drugs had no or only slight effects on the alpha-methyl-p-tyrosine-induced DA disappearance and on the pargyline-induced 3-methoxytyramine accumulation in the SNpc or SNpr. Taken together, these results indicate that the DA synthesis rate, but not the DA release, are influenced by DA receptor activity and neuronal firing in the SNpc and SNpr. This is in contrast to the situation in the striatum, where both the DA synthesis rate and the DA release are under such control.

Isolation of the mRNA encoding rat liver catechol-O-methyltransferase

A highly specific, well characterized rabbit antiserum to purified rat liver catechol-O-methyltransferase (COMT; EC 2.1.1.6) and the procedure of polysome immunoadsorption have been used to isolate a messenger RNA which encodes a single polypeptide when translated in vitro. Western blotting and immune fixation have shown multiple active forms of the enzyme to exist; a major, soluble one with MW of 23,000 and pI of 5.2 and another, membrane-bound one with MW of 26,000 and a pI of 6.2 (1). When translated in vitro, the purified message synthesizes a protein of molecular weight (MW) 23,000 and pI 5.2, values in agreement with those for purified enzyme reported by other investigators (2,3). Only the soluble form is seen after in vitro translation; the other immunoreactive proteins possibly arise due to post-translational modifications which do not occur in the lysate; or perhaps another mRNA exists. Cloning of the COMT cDNA will resolve this issue and should be feasible in light of our data indicating that the mRNA isolated here represents 0.46% of total rat liver polyadenylated message.

Brain 3-methyoxytyramine varies inversely with blood glucose in decapitated rats

Concentrations of the dopamine metabolite, 3-methyoxytyramine, were decreased significantly in the corpus striatum and nucleus accumbens of rats 30 min after the IP injection of D-glucose (2 g/kg). Conversely, 90 min after the administration of regular insulin (6 U/kg), significant increases in the concentrations of 3-methoxytyramine were observed in these two brain regions. Brain levels of the major metabolites of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid, did not correlate well with blood glucose concentration. The significant negative correlation of blood glucose with striatal and accumbens 3-methoxytyramine suggests an inverse relationship between dopamine metabolism and blood glucose concentration, that may be secondary to decapitation-induced anoxia.

Excitatory amino acid treatment of the ventromedial globus pallidus enhances dopamine utilization in the prefrontal cortex of the rat via the thalamic mediodorsal nucleus

Infusion of a low dose (5 microM) of the cell-selective chemical excitant quisqualic acid (QUIS) into rostral ventromedial globus pallidus (GP) had no immediate effect on DA utilization (assessed as [DOPAC]:[DA] and [HVA]:[DA] ratios) in either the medial bank of the prefrontal cortex (FCx) or the agranular insular cortex (AgCx). In contrast, a larger dose (630 microM) of another excitant sodium ibotenate (IBO) produced an immediate bilaterally symmetrical increase in both indices of DA utilization in FCx. There was also a marked trend towards a bilateral increase in these indices of DA utilization in AgCx. In order to determine whether these effects on cortical DA utilization are mediated by a direct cortical route or via the thalamic mediodorsal nucleus (lateral division, MDL), infusions of IBO into GP were repeated in animals with a 1-week-old N-methyl-D-aspartate lesion of MDL. The increase in DA utilization of FCx following infusion of IBO into GP was abolished, although the trend towards increased DA utilization in AgCx was still maintained. Since MDL innervates FCx but not AgCx and since we have previously shown that MDL lesions alone have no effect on DA utilization in either cortical region, the present results suggest that the changes in cortical DA utilization are probably mediated via MD. Thus in addition to the well-documented control exerted by the thalamus over brain DA function, this has now been extended in the present study to include GP, which projects both directly and indirectly to the thalamus.

Influence of a carrier transport process on in vivo release and metabolism of dopamine: dependence on extracellular Na+

In vivo microdialysis was utilized to evaluate the role of extracellular Na+ in regulating dopamine (DA) neurotransmission in the caudate-putamen of halothane-anaesthetized rats. Reduction of the extracellular Na+ concentration by introduction of a perfusion media containing 50mM Na+ (with choline replacement) produced an excessive release of DA that could be effectively blocked by nomifensine and Lu 19-005, potent inhibitors of an amine transport carrier. These results substantiate reports of a carrier-mediated efflux of DA from presynaptic terminals. Pretreatment with amphetamine, considered both a DA uptake inhibitor and releaser, did not, however, influence the efflux of DA induced by the low extracellular Na+ environment. Although the release of DA from an apparent non-granular cytosolic pool was greatly enhanced by the low extracellular Na+ environment, 3,4-dihydrophenylacetic acid (DOPAC) levels, which supposedly reflect metabolism of non-vesicular DA, were minimally effected. In contrast, homovanillic acid (HVA) was sensitive to extracellular Na+ and not directly related to extracellular levels of either DA or DOPAC, suggesting the possibility of a Na+-sensitive (carrier-mediated?) process involved in the formation of HVA. Overall, the results of this paper cannot be completely reconciled with the traditional concept of intracellular organization of DA pools and suggests the possibility of various non-granular pools being differentially sensitive to efflux and metabolism.

Characteristics of antinociception induced by noncatecholic phenylethylamine derivatives: the relation of endogenous norepinephrine to phenylethylamine analog-induced antinociception

Characteristics of the antinociceptive action of phenylethylamine derivatives, amphetamine, beta-phenylethylamine (PEA) and beta-hydroxyphenylethylamine (OHPEA), were examined. The pain threshold of mice was measured by using the hot plate method. Intraperitoneal administration of alpha-methyl-p-tyrosine inhibited antinociception induced by PEA and OHPEA, and intracisternal administration of norepinephrine increased antinociception induced by PEA and OHPEA. Intracisternal administration of phentolamine inhibited the antinociception induced by PEA derivatives. The levels of norepinephrine and normetanephrine in the brain were determined by using HPLC. PEA derivatives decreased norepinephrine in the brain and tended to increase normetanephrine at 15 min after the administration of PEA derivatives. These findings indicate that PEA derivatives cause the release of norepinephrine in the central nervous system, and the released norepinephrine induces antinociception.

In vivo measurement of neuronal uptake of norepinephrine in the human heart

Neuronal uptake (Uptake-1) of the sympathetic neurotransmitter norepinephrine from the circulation in the human heart was assessed in vivo with three techniques. 1) Cardiac removal of intravenously infused tracer-labeled norepinephrine was measured before and after Uptake-1 blockade with desipramine; 2) the difference between the fractional extraction of radioactive norepinephrine and of radioactive isoproterenol, which is not a substrate for neuronal uptake, was used to estimate the removal of norepinephrine by Uptake-1 in the heart compared with other vascular beds (arm, leg, brain, and lungs); and 3) regional arteriovenous differences in radioactive and endogenous dihydroxyphenylglycol (DHPG), an exclusively intraneuronal metabolite of norepinephrine, were compared in these beds. In untreated patients, cardiac removal of radioactive norepinephrine averaged 79%, whereas in desipramine-treated patients, cardiac removal of radioactive norepinephrine averaged 19%, a value similar to that of isoproterenol in untreated patients (14%), confirming that in the heart the non-neuronal removals of isoproterenol and norepinephrine were similar. In the heart, 69% of delivered norepinephrine was estimated to be removed by Uptake-1, a much higher percentage than that in the arm (14%), leg (7%), brain (10%), and lungs (4%). The cardiac arteriovenous increment in endogenous DHPG (137%) far exceeded that of the other beds (49%, 26%, 39%, and -19%, respectively), and radioactive DHPG in the great cardiac vein exceeded arterial levels by 113%, whereas in the other beds, arterial radioactive DHPG exceeded venous levels. The results indicate that the human heart is exceptionally dependent on neuronal uptake for in vivo removal of circulating norepinephrine.

Dynamics of the striatal 3-MT pool in rat and mouse: species differences as assessed by steady-state measurements and intracerebral dialysis

Analysis of dopamine and 3-MT dynamics in the striatum and in striatal dialysates, after pargyline treatment, indicates that the 3-MT pool in the rat is smaller but more dynamic than that in the mouse. The fractional rate constants calculated for the extracellular 3-MT and dopamine pools also indicate that a larger proportion of released dopamine is metabolized to 3-MT in the rat, or alternatively, 3-MT is cleared more slowly from the mouse striatum. Our striatal dialysis data also support previous in vivo voltammetry studies which have demonstrated that the fractional rate constant of the extracellular dopamine pool is at least 10-fold greater than that of the total striatal dopamine pool. These data suggest that multiple striatal dopamine pools exist and that a minimum of 20 to 30% of the extracellular DA pool is metabolized to 3-MT.

Striatal membrane-bound and soluble catechol-O-methyl-transferase after selective neuronal lesions in the rat

Activities of the two forms of catechol-O-methyltransferase (COMT), viz. the soluble (S-COMT) and the membrane-bound (MB-COMT), have been studied in the rat striatum to characterize their localization in relation to the nigrostriatal dopaminergic neurons. Selective unilateral nigrostriatal dopaminergic lesions were produced by an intranigral injection of 6-hydroxydopamine (6-OHDA; 8 micrograms/site). 6-OHDA caused an extensive lesion of the dopaminergic neurons as revealed by non-detectable concentrations of dopamine in the striata of the lesioned sites. In spite of that neither S-COMT nor MB-COMT activities were altered in comparison with the intact control striata. The intrastriatal injection of kainic acid significantly increased S-COMT activity but to some extent decreased MB-COMT activity. Kainic acid did not alter the striatal concentration of dopamine. These results suggest that both S-COMT and MB-COMT reside postsynaptically the nigrostriatal dopaminergic neurons. S-COMT seems to be found mainly in striatal glial cells, whereas striatal MB-COMT might be located both in postsynaptic neuronal and extraneuronal cells.

Intracerebral dialysis: direct evidence for the utility of 3-MT measurements as an index of dopamine release

Intracerebral dialysis was used to monitor the in vivo efflux of striatal dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3-MT) in the pentobarbital anesthetized rat. In untreated rats, there were low levels of extra-cellular DA and 3-MT which were increased 15-fold by treatment with amphetamine. Under basal and drug-stimulated conditions, 3-MT concentrations were maintained at approximately 30% of the extracellular DA levels. These data agree with in vivo turnover estimates which indicate that 20 to 30% of DA turnover is through the 3-MT pool in the striatum. In contrast, extracellular DOPAC and HVA levels were reduced only slightly by amphetamine and with a delayed onset. Our data support the hypothesis that striatal DOPAC is an accurate index of intraneuronal DA metabolism and that 3-MT is an index of the extracellular concentration of DA.

Norepinephrine metabolism in neuronal cultures is increased by angiotensin II

In this study we have examined the actions of angiotensin II (ANG II) on catecholamine metabolism in neuronal brain cell cultures prepared from the hypothalamus and brain stem. Neuronal cultures prepared from the brains of 1-day-old Sprague-Dawley rats exhibit specific neuronal uptake mechanisms for both norepinephrine (NE) and dopamine (DA), and also monoamine oxidase (MAO) and catechol O-methyltransferase (COMT) activity. Separate neuronal uptake sites for NE and DA were identified by using specific neuronal uptake inhibitors for each amine. In previous studies, we determined that ANG II (10 nM-1 microM) stimulates increased neuronal [3H]NE uptake by acting at specific receptors. We have confirmed these results here and in addition have shown that ANG II (1 nM-10 microM, 10-120 min) has no significant effects on neuronal [3H]DA uptake. These results suggest that the actions of ANG II are restricted to the NE transporter in neuronal cultures. It is possible that ANG II stimulates the intraneuronal metabolism of at least part of the NE that is taken up, because the peptide stimulates MAO activity, an effect mediated by specific ANG II receptors. ANG II had no effect on COMT activity in neuronal cultures. Therefore, the use of neuronal cultures of hypothalamus and brain stem we have determined that ANG II can specifically alter NE metabolism in these areas, while apparently not altering DA metabolism.

In vivo assessment of dopamine and norepinephrine release in rat neocortex: gas chromatography-mass spectrometry measurement of 3-methoxytyramine and normetanephrine

A new method with the sensitivity and specificity required to measure regional levels of 3-methoxytyramine (3-MT) and normetanephrine (NMN) in the rat cortex is described. The method utilizes a liquid ion exchanger to isolate the parent amines, dopamine (DA) and norepinephrine (NE), along with their methylated metabolites. These samples are derivatized and analyzed by negative ion gas chromatography-mass spectrometry. Using this method, we examined a number of drug actions on steady-state levels as well as pargyline-induced increases in 3-MT and NMN. In the prefrontal cortex, cingulate cortex, striatum, and olfactory tubercle, nomifensine was found to increase 3-MT steady-state levels and accumulation rates. Similar actions of this drug were observed in the cingulate and prefrontal cortices with NMN. In contrast, clonidine decreased cortical NMN levels and accumulation. A unique action was observed with haloperidol, in that both 3-MT levels and accumulation after pargyline were increased in the nigrostriatal and mesolimbic dopaminergic projections, whereas only the accumulation rates were accelerated in the mesocortical projections. In summary, our data indicate that this new assay is a useful approach for the in vivo evaluation of DA and NE release in cortical regions of the rat. This approach is unique in that no surgery, restraint, or anesthetic is required, thereby permitting more complicated experimental paradigms to be utilized.

Determination of 3-methoxytyramine in rat brain by HPLC with electrochemical detection and its correlation with dopamine function after administration of a monoamine oxidase inhibitor and L-3,4-dihydroxyphenylalanine

3-Methoxytyramine (3-MT), normally a minor metabolite of 3,4-dihydroxyphenylethylamine (dopamine) in brain, becomes the sole product of metabolism following the administration of a monoamine oxidase (MAO) inhibitor. A simplified reverse-phase HPLC method for 3-MT employing electrochemical detection is fully described. This method has a detection limit of 0.1 microgram/g brain wet weight and is sensitive enough to detect 3-MT in individual brain regions after rats have been pretreated with an MAO inhibitor. Administration of tranylcypromine (TCP, 10 mg/kg) and L-3,4-dihydroxyphenylalanine (L-DOPA) (10-50 mg/kg) produced a dose-dependent linear increase in 3-MT concentrations in the dopaminergic brain regions n. caudatus (r = 0.95; p less than 0.01) and n. accumbens (r = 0.96; p less than 0.01). This treatment also produced a dose-dependent increase in behavioural activity in rats (r = 0.88; p less than 0.01). Furthermore, a good correlation was found between the activity responses of individual rats and the accumulation of 3-MT after TCP/L-DOPA in both n. caudatus (r = 0.76; p less than 0.01) and n. accumbens (r = 0.84; p less than 0.01). These data describe a simple and sensitive HPLC analysis technique for 3-MT and demonstrate that following administration of an MAO inhibitor this metabolite may provide a useful monitor of central dopamine function.

Transient midline raphe glial structure in the developing rat

A major glial structure is present during development within the midline raphe of the midbrain, hindbrain, and cervical spinal cord of the rat. It is composed of great numbers of glial cell bodies lying immediately ventral to the cerebral ventricular system and the large radial processes extending from these cells toward the ventral surface of the brain roughly within the midsagittal plane. There is also a smaller group of glial cells on the dorsal surface of the aqueduct and the central canal whose processes extend to the dorsal surface of the brain. The entire structure exhibits an intensely positive immunoreactivity with the antibody to the S-100 protein, a nervous-system-specific protein found primarily in the cytoplasm of astrocytes. This immunoreactivity makes possible a clear visualization of the extent, magnitude, and continuity of this structure from at least embryonic day 15, the first age examined, until postnatal days 7-8, when it is no longer visible by this technique. This glial structure has several prominent morphological characteristics. During prenatal and early postnatal development the fibers forming the ventral aspect of the structure in the midbrain and hindbrain are formed into two parallel plates on either side of the midline with S-100-negative tissue between the plates. As development progresses, S-100-positive fibers are continually added so that the plates become thicker at the expense of the nonstaining intervening area. By postnatal day 4 only a single midline plate of fibers is visible, occupying the entire midline raphe. In the region of the pontine flexure the entire structure takes on a distinctly pleated configuration. This fact produces a curious "sine wave" appearance when the plane of section crosses these vertical pleats. At postnatal day 5 the structure begins to disappear, and it is no longer visible by 7-8 days postnatal. This glial structure does not stain with antisera to glial fibrillary acidic protein, a protein associated with fibrous astrocytes, or routine cell stains such as cresyl violet. With these techniques the raphe area appears essentially devoid of identifiable cellular elements.

The dopamine metabolite 3-methoxytyramine is not a suitable indicator of dopamine release in the rat brain

It has been postulated that changes in the concentration of 3-methoxytyramine (3-MT) in the brain might reflect changes in the release of 3,4-dihydroxyphenylethylamine (DA, dopamine) and, therefore, might be used as an index of dopaminergic activity in the brain. 3-MT is known to accumulate rapidly after death. Killing by microwave irradiation (MWR) is considered to be the method of choice to obtain "undisturbed" 3-MT concentrations. We measured striatal 3-MT concentrations even lower than those following MWR when the brains were excised and frozen in dry ice very rapidly (typical time between decapitation and freezing of the brain 22 s). There was a linear increase in striatal 3-MT concentration when the time between decapitation and freezing was varied between 13 and 300 s. Extrapolation to time zero indicated negligible amounts of 3-MT at the time of decapitation. In addition, it was observed that DA, 3,4-dihydroxyphenylacetic acid, and homovanillic acid decompose during the cooling phase after heating the brain by microwave. It is concluded that MWR induces artifactual changes in the postmortem levels of DA and metabolites. Consequently 3-MT cannot be considered to be a reliable indicator of DA release in the rat brain.

The presence of catechol-o-methyltransferase activity in separately cultured cerebromicrovascular endothelial and smooth muscle cells

The activity of catechol-o-methyltransferase (COMT) was investigated in cultured and propagated cerebromicrovascular endothelial and smooth muscle cells using high performance liquid chromatography and immunocytochemistry. The existence of COMT was detected in both cell types. The demonstration of this enzyme activity in the cerebromicrovascular smooth muscle cells, in addition to the endothelium, indicates that the enzymatic barrier to catecholamine is not limited to capillaries, the main constituents of the blood-brain barrier.

Isolation of the low-molecular-mass form of catechol O-methyltransferase from rat liver and immunocytochemical localization of the enzyme in the glycogen compartment

The low-molecular-mass form of two distinct catechol O-methyltransferase activities (S-adenosyl-L-methionine: catechol O-methyltransferase, COMT, EC 2.1.1.6) has been purified to homogeneity from rat liver using 40-70% ammonium sulfate precipitation, gel filtration on Sephadex G-100, adsorption on hydroxyapatite C and ion-exchange chromatography on DEAE-Sepharose CL-6B. The relative molecular mass Mr, determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis is 22 400 +/- 500. Irradiation of the enzyme in the presence of 8-azido-[methyl-3H]AdoMet results in the specific labeling of the catalytic site of the enzyme. Photolabeling was successful with crude COMT preparations and with the isolated enzyme. Immunocytochemical studies present new information about the localization of the low-molecular-mass form in the liver parenchyma. Subcellularly COMT immunoreactivity could be attributed exclusively to the compartment with glycogen granules. Nucleus, mitochondria and endoplasmic reticulum showed no immunostaining.

Further characterization of brain 3,4-dihydroxyphenylethyleneglycol (DHPG) formation: dependence on noradrenergic activity and site of formation

The dependence of brain and plasma 3,4-dihydroxyphenylethyleneglycol (DHPG) formation upon CNS noradrenergic neutronal activity was evaluated following manipulations that are known to alter the firing rate of the locus coeruleus (LC) neurons and as a consequence, noradrenaline (NA) release and turnover. In addition, the relative degree of intraneuronal formation of brain DHPG was assessed by studying the metabolism of released NA during uptake inhibition. Electrical stimulation of the LC for 20 min induced an increase in rat cortical (40-42%), hypothalamic (22-29%) and plasma (68-79%) total DHPG and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) levels. Two hours following administration of the alpha-2 adrenoceptor antagonist yohimbine (10 mg/kg, i.p.), rat brain cortical conjugated DHPG and MHPG as well as free MHPG concentrations were increased whereas cortical free DHPG levels remained unchanged. The same treatment also increased plasma total DHPG and MHPG levels. In mice given the NA uptake inhibitor desipramine (10 mg/kg, i.p.) 2 h prior to sacrifice, brain free DHPG and MHPG concentrations were significantly reduced by 30 and 40%, respectively, whereas yohimbine (1-20 mg/kg, i.p.) induced a dose-dependent increase in brain DHPG (60-80%) and MHPG (60-220%) concentrations. Pretreatment with desipramine (10 mg/kg, i.p.) 30 min prior to yohimbine reduced, in rat, or abolished, in mice, the yohimbine-induced elevation of brain DHPG levels. In contrast, desipramine augmented the effect of yohimbine on brain MHPG levels resulting in a shift to the left of the dose response curves. These findings indicate that brain and plasma DHPG levels are sensitive to changes in brain noradrenergic neuronal impulse flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiography of high affinity uptake of catecholamines by primary astrocyte cultures

Uptake of D.L-[3H]norepinephrine ([3H]NE) and [3H]dopamine ([3H]DA) by primary astrocyte cultures prepared from neonatal rat brains, which are greater than or equal to 95% glial fibrillary acidic protein (GFAP(+)), was studied by measuring accumulation of tritium label, and localizing such uptake at the cellular level by autoradiography. Uptake of [3H]NE was 95% Na+ dependent at 10(-7) M and 80% Na+ dependent at 7.5 X 10(-7) M [3H]NE. Uptake of [3H]DA at 7.5 X 10(-7) M was 58% Na+ dependent, but total uptake of [3H]DA was greater than uptake of [3H]NE. Autoradiography of cells incubated with 7.5 X 10(-7) M [3H]NE or [3H]DA showed that a high proportion of all the cells in these cultures had a grain density which was clearly above background. When Na+ was omitted from the medium, the temperature was lowered to 4 degrees C, or 10(-7) M desmethylimipramine or 10(-7) M amitryptyline were present, cellular grain density after exposure to both [3H]NE and [3H]DA was greatly reduced, to close to background levels. It also appeared necessary to have inhibitors of both monoamine oxidase (pargyline) and catecholamine-O-methyltransferase (tropolone) present to see clear cellular localization for [3H]DA. In the case of [3H]NE the presence of tropolone alone was adequate to observe cellular localization. These results confirm our previous findings of the existence of a high affinity uptake process for catecholamines in primary astrocyte cultures based on uptake properties, and in the present study also localizes such uptake to the major, astrocytic cell type.

Behavioral and biochemical assessment of time-related changes in globus pallidus and striatal dopamine induced by intranigrally administered neurotensin

Microinjection of neurotensin (NT; 2 and 5 micrograms) into the substantia nigra zona compacta caused an increase in dopamine (DA) and DA metabolites in the rodent globus pallidus and striatum which persisted for at least 20 hours after peptide administration. Similar NT treatments given unilaterally into the nigra caused circling away from the injected side in amphetamine-pretreated rats, but were without effect when microinjected into saline-pretreated animals. Circling also occurred when the animals were given amphetamine 20 hours after intranigral NT administration. Contralateral rotation was observed with unilateral intranigral injections of gamma-hydroxybutyric acid (GHB; 400 micrograms) or with lower intranigral GHB doses (250 micrograms) in amphetamine-pretreated animals. The effects of GHB and NT differed in the manner in which the animals rotated as well as in the profile of DA and DA metabolite changes induced by these drugs. These studies indicated that: dopaminergic functions of the globus pallidus are influenced, like the striatum, by manipulations of the substantia nigra: NT and GHB likely act via different mechanisms to effect nigral dopamine-containing cells; and NT was capable of inducing changes in dopamine neurons which had long term consequences.

Selective destruction of meningeal cells by 6-hydroxydopamine: a tool to study meningeal-neuroepithelial interaction in brain development

The effects of 6-hydroxydopamine (6-OHDA) on meningeal cells were studied at different ages in conjunction with blockade of the neuronal uptake 1 for catecholamines using nomifensine (NMF) and of the extraneuronal uptake 2 using normetanephrine (NMN). Our results show that maximal numbers of meningeal cells over the cerebellum of the newborn rat are destroyed by a threshold dose of 6-OHDA of 25 micrograms. The morphological characteristics which mark the time course of degeneration of meningeal cells were used to assess the effects of 6-OHDA given in conjunction with either NMF or NMN to differentiate between neuronal (uptake 1) and extraneuronal (uptake 2) effects of 6-OHDA. Uptake of 6-OHDA into meningeal cells and their subsequent degeneration was prevented by pretreatment with NMN but not with NMF. This finding indicates that meningeal cells have uptake 2 capacity but no uptake 1 membrane pump and explains both their uptake of 6-OHDA and their extreme sensitivity to the toxic effects of this drug. Application of this pharmacological regimen using NMF and NMN in conjunction with 6-OHDA thus allows selective destruction of meningeal cells which may be used experimentally to study the contribution of meningeal cells to brain development.

Dopamine and serotonin metabolism in striatum and in the septohippocampal pathway of the Snell dwarf mouse

Dopamine and serotonin neurotransmission has been investigated in striatum and in the septohippocampal pathway of the locomotor activity and memory deficient Snell dwarf mouse. In striatum a sharp decrease in 3-MT levels with a concomitant decrease in DA turnover is indicative of a strong decrement in the functional activity of striatal dopaminergic terminals in the mutant mouse. The observed enhancement in serotoninergic markers (5HT, 5HIAA, 5 HTP), at the opposite, provide evidence for an altered relationship between serotonin and dopamine striatal neurotransmission in the mutant mouse as compared to the normal mouse. Impairment in dopamine and serotonin neurotransmission has also been observed in the septohippocampal pathway where the removal of acidic metabolites of these neurotransmitters from brain appears to be disturbed. The data presented here are discussed with regard to previously noted alterations in cholinergic activity as well as to the behavioral disturbances of the dwarf mutant.

Soluble and particulate forms of rat catechol-O-methyltransferase distinguished by gel electrophoresis and immune fixation

Catechol-O-methyltransferase (COMT) was visualized in homogenates and subcellular fractions of rat tissues, including liver and brain, by gel electrophoresis, electrophoretic transfer of proteins to nitrocellulose (Western blotting), and immune fixation with antiserum to highly purified soluble rat liver COMT. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of all tissue homogenates examined revealed three major immune-specific proteins with apparent molecular weights 23,000, 26,000, and 66,000 (23K, 26K and 66K). Centrifugation of homogenates at 100,000 X g for 60 min resulted in the enrichment of the 26K species protein in the pellet whereas the 23K and 66K proteins were the predominant forms in the supernatant. The 66K protein appeared in variable amounts depending on the tissue being examined and the length of transfer of protein and is assumed to be an "aggregate" of the smaller form(s). The 26K protein was essentially the only immunoreactive species seen in a purified preparation of rat liver outer mitochondrial membrane. Isoelectric focusing (IEF) under denaturing conditions and two-dimensional gel electrophoresis of brain and liver fractions showed that the 23K protein was resolved into three bands of pI 5.1, 5.2, and 5.3, whereas the 26K protein had a pI of 6.2. Analysis of COMT activity in slices from nondenaturing IEF gels indicated that the pI 5.1-5.3 species are biologically active; the pI 6.2 species could not be detected under these conditions. COMT activity was demonstrated, however, in outer mitochondrial membranes from rat liver, which contain predominantly the 26K, pI 6.2 immunoreactive species. The major form of COMT in all rat tissues examined is "soluble" with an apparent Mr of 23K and a pI of 5.2. The nature of the modifications giving rise to pI 5.1 and 5.3 forms of this enzyme are not clear, nor is the relationship between the 23K and 26K forms. Further studies are needed to elucidate the relationship of immunoreactive forms of COMT to each other, their intracellular location, and their functional significance.

Effect of alpha-methyl fluorodopa on dopamine metabolites: importance of conjugation and egress

The effects of D,L-alpha-monofluoromethyldopa (MFMD), an inhibitor of aromatic L-amino acid decarboxylase, on the metabolism of dopamine (DA) and 5-hydroxytryptamine was investigated using rat brain and cerebrospinal fluid (CSF). Vehicle or MFMD (100 mg/kg) was given p.o. and 16 h later probenecid (200 mg/kg i.p.). CSF was sampled and the rats killed immediately or after 1 h. Vehicle treated rats showed regional differences of percentage conjugation of DA metabolites: 3,4-dihydroxyphenylacetic acid (DOPAC), striatum 10%, rest of brain 45%, CSF 67%; homovanillic acid (HVA), striatum 20%, rest of brain 35%, CSF 53%. These differences and the proportionately greater increases of conjugates than of free acids after probenecid vitiate regional comparisons of DA metabolism if conjugates are not included. MFMD alone decreased neither 5HIAA (except in the striatum) nor the free DA metabolites but decreased both conjugates in CSF and conjugated DOPAC in rest of brain. The inhibitory effects of MFMD on 5HT and DA synthesis were most evident when measured by the accumulation of 5HIAA or total (DOPAC + HVA) after giving probenecid. MFMD may also inhibit amine metabolite egress and the conjugation of DOPAC and HVA.

Sulfate conjugation of dopamine in rat brain: regional distribution of activity and evidence for neuronal localization

Brain tissue contains at least two forms of phenolsulfotransferase that are involved in the sulfate conjugation of biogenic amines and their metabolites. Two apparent Km values were obtained for p-nitrophenol at pH 7.4 (0.6 microM and 0.3 mM) but only one enzyme had the capacity to conjugate dopamine (Km = 130 microM). Dopamine sulfotransferase activity was found to vary 17-fold in different brain regions, with the highest levels in diencephalon, hippocampus, and striatum. To determine the cellular localization of the enzymes, phenolsulfotransferase activity was measured in striatum following selective destruction of striatal neurons by stereotaxic injection of 2 micrograms kainic acid. Fourteen days after injection the catecholamine sulfotransferase activity in the lesioned striatum was reduced to approximately 40-50% of that in the control contralateral striatum. There was a statistically significant correlation between the ratio of lesioned to control activity for the sulfotransferase and the neuronal marker enzymes glutamate decarboxylase and neuron-specific enolase. p-Nitrophenol sulfotransferase activity was also decreased in the lesioned striatum. These results suggest that PST activity is present within the kainic acid-sensitive neurons of the striatum. The regional variation in activity, together with the results of the kainic acid studies, suggest that sulfate conjugation of biogenic amines and their metabolites in brain may take place within specific types of neurons.

Determination of normetanephrine, 3,4-dihydroxyphenylethyleneglycol (free and total), and 3-methoxy-4-hydroxyphenylethyleneglycol (free and total) in rat brain by high-performance liquid chromatography with electrochemical detection and effects of drugs on regional concentrations

A new, fast and sensitive assay for normetanephrine (NM), free and total 3,4-dihydroxyphenylethyleneglycol (DOPEG), and free and total 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG) in brain tissue is described. The method is based on high-performance liquid chromatography with electrochemical detection. Small Sephadex G 10 columns were used for prepurification. This permitted the additional isolation and quantification of tyrosine, 3,4-dihydroxyphenylalanine, noradrenaline, dopamine, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid. The compounds were determined in six brain areas (striatum, cortex, hippocampus, hypothalamus, brainstem, and cerebellum). Most DOPEG and MOPEG in rat brain was present in the conjugated form, except for the cerebellum, where about 80% of MOPEG was nonconjugated. No postmortem effects on MOPEG levels were observed; a slight increase in DOPEG in certain brain areas was found in microwave-killed rats. The effects of clonidine, yohimbine, N,N-dipropyl-5,6-ADTN, and chlorpromazine on the concentrations of the five noradrenaline (NA) metabolites were determined. Free and total DOPEG and MOPEG provide similar information on NA metabolism, whereas NM (after monoamine oxidase inhibition) reflects a different type of interaction of drugs with NA metabolism. The similarity in the pattern of drug-induced changes in NA metabolism in the various brain areas suggests that adrenoreceptors mediating NA metabolism are homogeneously distributed throughout the brain.

Characterization of membrane-bound and soluble catechol-O-methyltransferase from human frontal cortex

Catechol-O-methyltransferase (COMT; E.C. 2.1.1.6) from human frontal cortex occurs in both a soluble and membrane-bound form. Attempts to solubilize the membrane-bound transferase by repeated washing or by extraction into solutions of high ionic strength were unsuccessful. The finding that Triton X-100 was capable of solubilizing membrane-bound COMT suggested that the membrane-bound transferase is an integral membrane protein. The membrane-bound and soluble enzymes did not differ in their requirements for magnesium ions or in their pH-activity profiles; both enzymes showed an optimum near pH 8.0 when assayed in phosphate buffer. In addition, the two enzymes did not differ in the degree of inhibition caused by CaCl2, both enzymes displaying 65% inhibition at 2.5 mM CaCl2. The competitive inhibitors tropolone and nordihydroguaiaretic acid displayed Ki values for the membrane-bound transferase five- to 10-fold lower than those observed for the soluble transferase. Solubilization of membrane-bound COMT in Triton X-100 resulted in an increase in the apparent Km value of the membrane-bound transferase for dopamine. The increase in Km appeared to be due to apparent competitive inhibition by Triton X-100 and reached a limiting value of approximately 80 microM. These results confirm that membrane-bound COMT is an integral membrane protein that may be structurally distinct from soluble COMT.

Transient expression of selected catecholaminergic traits in cranial sensory and dorsal root ganglia of the embryonic rat

We describe the transient expression of catecholaminergic traits in cranial sensory and dorsal root ganglia of the embryonic rat in vivo. Isolated cells expressing tyrosine hydroxylase (T-OH) immunoreactivity were initially detected in trigeminal (V) ganglion anlages as early as gestational Day 10.5 (E10.5; 18-22 somites). Neurofilament (NF) protein was also evident in V at these early stages. By E11.5 (27-30 somites) clusters of T-OH-positive cells were visible in V. Many of these cells were bipolar; others sent processes into the primitive brainstem. In addition, cells expressing T-OH were apparent in primordia of sensory ganglia serving the glossopharyngeal (IX) and vagal (X) cranial nerves. By this stage (E11.5) all cranial sensory ganglia were rich in NF protein, but immunoreactivity was confined to cellular processes rather than perikarya. By E12 (35-37 somites), only a few, faintly positive T-OH-containing cells were evident in V. However, DBH- and T-OH-positive cells were visible within the more caudal nodose and petrosal ganglia. Furthermore, isolated bipolar cells expressing T-OH were detected in rostral dorsal root ganglia at this stage. Catecholamine fluorescence could not be detected in any sensory ganglia even after maternal treatment with inhibitors of monoamine oxidase. Catecholaminergic cells were not seen at any stage in anlages of the acousticovestibular nucleus. Immunoreactive T-OH was undetectable in all ganglia by E13.5 (46-48 somites). These findings highlight the fact that transient expression of the catecholamine phenotype during development is a widespread phenomenon, evident in a variety of cell types of diverse embryonic origin.

Distribution of tritium label in the neonate rat brain following intracisternal or subcutaneous administration of [3H]6-OHDA. An autoradiographic study

The present report describes the distribution of tritium label after injection of newborn rats with [3H]6-hydroxydopamine ([3H]6-OHDA). The animals were injected either intracisternally (i.c.) or subcutaneously (s.c.), with or without pretreatment with nomifensine, which blocks the high-affinity uptake of both noradrenaline (NA) and dopamine (DA), and sacrificed at intervals from 40 min to 24 h post-injection (p.i.). In i.c. injected animals, tritium label is demonstrable as early as 40 min p.i. in neurons of all known NA and DA cell groups. In NA neurons, it is taken up into cell body, dendrites, preterminal and terminal axons. The intensity of neuronal labeling is highest within the first 4 h p.i. and decreases in most neurons with longer postinjection intervals. A significant proportion of both NA and DA neurons degenerate beginning 6 h p.i., the majority show morphological signs of the axon reaction 24 h p.i. Uptake of [3H]6-OHDA into serotonergic and non-catecholaminergic neurons is not demonstrable. [3H]6-OHDA is accumulated by the following extraneuronal cells of the CNS: ependymal cells, epithelial cells of the choroid plexus, subependymal macrophages, smooth muscle cells in the wall of large intraparenchymal blood vessels, meningeal cells and glial cells. The time course of accumulation and disappearance of the label varies among these extraneuronal elements. The meningeal cells show the highest labeling intensity and degenerate within 24 h p.i. After pretreatment of the animals with nomifensine, the uptake of [3H]6-OHDA into NA and DA neurons is totally blocked; by contrast uptake of the labeled drug into extraneuronal cells is not prevented. These findings show that [3H]6-OHDA is not only accumulated by neurons possessing the high-affinity uptake for NA or DA, but by numerous other, extraneuronal cells which also participate in the metabolism of catecholamines.

High-affinity uptake of [3H]norepinephrine by primary astrocyte cultures and its inhibition by tricyclic antidepressants

Primary astrocyte cultures from neonatal rat brains show uptake of [3H]norepinephrine ([3H]NE). This uptake has a high-affinity component with an apparent Km of approximately 3 X 10(-7) M. At 10(-7) M [3H]NE both the initial rate of uptake and steady-state content of [3H]NE is inhibited by up to 95% by omission of external Na+. The Na+-dependent component of this uptake is totally inhibited by the tricyclic antidepressants desipramine (DMI) and amitryptyline with IC50 values of 2 X 10(-9) and 4 X 10(-8) M, respectively. Inhibition of [3H]NE uptake by DMI shows competitive kinetics. These characteristics are essentially identical to those found for high-affinity uptake of NE in total membrane or synaptosome fractions from rodent brains and suggests that such uptake in neural tissue is not exclusively neuronal.

Localization of membrane-bound catechol-O-methyltransferase

Previous studies of the distribution of catechol-O-methyltransferase (COMT) have concentrated on the soluble enzyme activity. In this study the activity of the membrane-bound enzyme was determined in different brain regions and peripheral tissues of the rat. Membrane-bound COMT, like the soluble enzyme, has a general distribution with high levels in liver, kidney, and vas deferens. However, the ratio of membrane-bound to soluble activity varies almost 30-fold in different tissues, with the highest ratio in brain. Membrane-bound activity varies twofold within brain. In view of their different localization and kinetic properties, it seems likely that the two forms of COMT have different functions in vivo.

Striatal dopamine metabolism in response to apomorphine: the effects of repeated amphetamine pretreatment

The dose-dependent decrease in striatal dopamine (DA) metabolites following apomorphine (APO) administration was utilized as an index of changes in DA receptor sensitivity following the repeated administration of amphetamine (AMPH). The results suggest that: (a) repeated AMPH pretreatment does not alter DA autoreceptor sensitivity; and (b) interpretations of the decline in striatal DA metabolites at high doses of APO (greater than 50 micrograms/kg), in terms of activation of postsynaptic DA receptors, may require re-evaluation.

Distinct cellular localization of membrane-bound and soluble forms of catechol-O-methyltransferase in brain

The cellular localization of the two forms of catechol-O-methyltransferase (COMT) was investigated by measuring their activities in rat striatum following unilateral stereotaxic injection of kainic acid, which causes degeneration of striatal neurons followed by proliferation of astroglial cells. Membrane-bound COMT activity was decreased in the lesioned striatum, while soluble COMT activity was increased. There was a statistically significant correlation between the ratio of lesioned to control activity for membrane-bond COMT and the neuronal marker enzyme glutamate decarboxylase. Similarly the increase in soluble COMT activity paralleled that of the astroglial marker enzyme, glutamine synthetase. These results indicate that the low-Km membrane-bound catechol-O-methyltransferase may be localized predominantly in neurons, whereas the high-Km soluble enzyme is found in glial cells.

Immunocytochemical demonstration of monoamine oxidase B in brain astrocytes and serotonergic neurons

An antiserum to monoamine oxidase B (MAO-B) was used to define the distribution of this metabolic enzyme in the adult rat brain immunocytochemically. MAO-B is specifically located in two major central nervous system cell classes, astrocytes and serotonin-containing neurons. Double-immunofluorescence experiments using antisera to glial fibrillary acidic protein and MAO-B showed that both protoplasmic and fibrillary astrocytes throughout the brain contain MAO-B, whereas oligodendrocytes do not contain the enzyme. Areas lacking a blood-brain barrier, such as the specialized circumventricular organs, also contain MAO-B-positive cells. A double-immunofluorescence experiment using antisera to serotonin and MAO-B enabled the positive identification of neurons containing both molecules. The catecholamine-containing neurons of the brain did not contain detectable amounts of MAO-B. The specific distribution of MAO-B in the adult central nervous system indicates that the role of MAO-B in monoamine metabolism may be more specifically defined than previously believed.