Assay of tyrosine hydroxylase by coupled decarboxylation of DOPA formed from 1- 14 C-L-tyrosine

Effects of i.c.v. lithium chloride administration on monoamine concentration in rat mediobasal hypothalamus

We investigated the acute effects of a single i.c.v. injection of lithium chloride (LiCl) the neuroamine content of the rat mediobasal hypothalamus (MBH). The effects of lithium on amine synthesis and degradation enzymes were also studied in vitro. Noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were reduced 10 min after i.c.v. injection of 24 nmol of LiCl and returned to control values 30 min after the injection. Two nmol of LiCl reduced the concentration of DA (10 and 30 min after injection) and 5-HIAA (30 min after injection). LiCl (0.5-10 mM) inhibited tyrosine hydroxylase activity (catecholamine synthesis) in vitro in a concentration dependent manner. The i.c.v. administration of a high dose of LiCl reduced the content of neuroamines in the MBH. This might result from and inhibition of synthesis. A possible link between the observed changes and some reported side effects of lithium therapy is discussed.

Dopamine D2 synthesis-modulating receptors are present in the striatum of the guinea pig

Dopamine and selective agonists of D1 [(1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride, SKF 38393] and D2 [(3-[2-[N-(3-hydroxyphenylethyl)-N-propylamino]ethyl] phenol, RU 24926] receptors were examined as inhibitors of the activity of tyrosine hydroxylase in the striatum of the guinea pig. In soluble enzyme preparations, the agonists were weak inhibitors of the activity of tyrosine hydroxylase. However, the catechol-containing agonists dopamine (EC50 = 44.7 microM) and SKF 38393 (EC50 = 35.5 microM) were more potent than the non-catechol agonist RU 24926 (EC50 = 447 microM). All of the agonists were much more potent in synaptosome-rich preparations of guinea pig striatum, where stimulation of autoreceptors mediated inhibition of the enzyme (SKF 38393, D1, EC50 = 27 nM; RU 24926, D2, EC50 = 30 nM; dopamine, non-selective, EC50 = 1.5 microM). The D1 antagonist, SCH 23390 [(R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-(1H)-3- benzazepine hydrochloride], did not significantly reduce the action of SKF 38393 or dopamine. Furthermore, the D2 antagonist, (-)-sulpiride, significantly antagonized the inhibitory activity of both RU 24926 and dopamine. Studies in synaptosome-rich preparations from the striatum of the rat showed that both SKF 38393 (EC50 = 398 nM) and RU 24926 (EC50 = 58 nM) were also effective autoreceptor-mediated inhibitors of the activity of tyrosine hydroxylase in the rat. However, in the rat, SCH 23390 and (-)-sulpiride were equally effective in attenuating the inhibitory actions of dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of tyrosine hydroxylase by nicotine in rat adrenal gland

The administration of nicotine activates tyrosine hydroxylase in the rat adrenal gland. This activation is apparently maximal 25 min after a single subcutaneous injection of nicotine at 2.3 mg/kg. Repeated injections of nicotine (seven injections once every 30 min) are associated with a persistent activation of adrenal tyrosine hydroxylase for at least 3 h. The nicotinic receptor antagonist hexamethonium does not significantly inhibit the nicotine-mediated activation of tyrosine hydroxylase in innervated adrenal glands. However, hexamethonium completely blocks the activation of adrenal tyrosine hydroxylase by nicotine in denervated adrenal glands. Furthermore, even though a single injection of nicotine activates tyrosine hydroxylase in both innervated and denervated adrenal glands, repeated injections of nicotine do not activate tyrosine hydroxylase in denervated adrenal glands. Our results suggest that the systemic administration of nicotine activates adrenal tyrosine hydroxylase by two mechanisms: (1) via direct interaction with adrenal chromaffin cell nicotinic receptors; and (2) via stimulation of the CNS leading to the release from the splanchnic nerve of substances that interact with adrenal chromaffin cell receptors other than the nicotinic receptor.

Vasoactive intestinal peptide stimulates catecholamine biosynthesis in isolated adrenal chromaffin cells: evidence for a cyclic AMP-dependent phosphorylation and activation of tyrosine hydroxylase

Vasoactive intestinal peptide (VIP) increased catecholamine biosynthesis in bovine adrenal chromaffin cells by 50-200%. Six related peptides produced no effects. In addition, VIP increased tyrosine hydroxylase (TH) activity measured in gel-filtered supernatants prepared from homogenates of treated cells. The hypothesis that cyclic AMP is the second messenger involved in these effects of VIP was also evaluated. VIP led to an elevation of cyclic AMP levels, and this increase occurred over a similar concentration range and time course as the activation of TH and the increase in catecholamine biosynthesis. Each measure reached maximal levels at 10-20 microM VIP within 1 min and remained elevated for at least 16 min. These changes produced by VIP were paralleled by enhanced phosphorylation of TH, and this phosphorylation occurred on a single tryptic peptide that was the same peptide whose phosphorylation has been previously shown to be stimulated by forskolin. In contrast to VIP and forskolin, 12-O-tetradecanoylphorbol 13-acetate, a phorbol ester known to activate protein kinase C, increased the phosphorylation on a total of three tryptic peptides of TH. Our results indicate that VIP stimulates catecholamine biosynthesis in chromaffin cells through the phosphorylation and activation of TH and support the conclusion that a cyclic AMP-dependent phosphorylation of TH is responsible for these effects.

Prolonged alterations in canine striatal dopamine metabolism following subtoxic doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 4'-amino-MPTP are linked to the persistence of pyridinium metabolites

Single toxic doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).HCl (2.5 mg/kg i.v.) and 4'-amino-MPTP.2HCl (22.5 mg/kg) induce loss of striatal dopamine (DA) and tyrosine hydroxylase (TH) activity and of nigral DA neurons in the dog. To examine the subacute neurochemical changes induced by low doses of MPTP and 4'-amino-MPTP, dose-response studies of these compounds were carried out in the dog, using 6- and 3-week survival times for these two compounds, respectively. Low single doses of MPTP (1.0, 0.5, and 0.1 mg/kg i.v.) and 4'-amino-MPTP (15, 7.5, and 3.75 mg/kg i.v.) did not cause depletion of canine striatal DA or TH or a loss of nigral neurons. However, levels of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were decreased in a dose-related fashion, with significant loss of DOPAC being evident 6 weeks after the lowest administered dose of MPTP and 3 weeks after 4'-amino-MPTP. This selective loss of DA metabolites following nontoxic doses of MPTP and 4'-amino-MPTP led to a shift in the ratio of DA to DOPAC or HVA, which was characteristic for each compound. The measurement of striatal 1-methyl-4-phenylpyridinium (MPP+) and 4'-amino-MPP+ levels revealed that high concentrations (up to 150 microM) persist in the striatum for weeks following administration of a single nontoxic dose of MPTP or 4'-amino-MPTP. A causal relationship between the striatal concentration of MPP+ or 4'-amino-MPP+ and the change in DA metabolism as reflected in the DA/DOPAC ratio is suggested by a significant correlation between these measures. It is suggested that presynaptic sequestration and retention of MPP+ and 4'-amino-MPP+ by striatal DA terminals result in the inhibition of the monoamine oxidase contained within these terminals.

Cytoplasmic alkalinization induced by insulin through an activation of Na(+)-H+ antiporter inhibits tyrosine hydroxylase activity in striatal synaptosomes

Insulin dose-dependently inhibited tyrosine hydroxylase (TH) activity and increased intrasynaposomal pH (pHi) in rat striatal nerve endings. Both these effects of insulin on TH and pHi were prevented by the 5-(N-methyl-N-(guanidinocarbonylmethyl) amiloride (MGCMA), a putative selective inhibitor of the Na(+)-H+ antiporter. Interestingly when, by changing the extracellular pH (pHo), the pHi was increased, from 7.1 up to 7.5, an equivalent inhibition of TH activity occurred. The inhibitory action exerted from insulin on TH activity disappeared when the hormone was added to synaptosomes whose pHi was lowered to 6.83. Collectively, the results of the present study showed that insulin inhibited TH activity in striatal synaptosomes. This effect seems to involve the activation of the Na(+)-H+ antiporter. This exchange system once activated, may induce an intrasynaptosomal alkalinization, a condition in which TH activity is inhibited.

L-3,4-dihydroxyphenylalanine synthesis by genetically modified Schwann cells

We have investigated whether Schwann cells can be modified by gene transfer to synthesize L-3,4-dihydroxyphenylalanine (L-DOPA), the immediate precursor in the formation of dopamine. By using a retrovirus containing a rat tyrosine hydroxylase (TH) cDNA, we established an immortalized rodent Schwann cell line that stably expressed high levels of TH and secreted L-DOPA in vitro when supplied with tyrosine and the essential cofactor biopterin. We also infected primary Schwann cells and demonstrated that cells expressing TH secreted L-DOPA while maintaining their capacity to myelinate neurons in vitro. This study indicate that it may be feasible to utilize autotransplantation of genetically modified Schwann cells to alleviate the movement disorders in Parkinson's disease.

Characterization of nuclear T3 receptors in human neuroblastoma cells SH-SY5Y: effect of differentiation with sodium butyrate and nerve growth factor

Nuclear receptors for the thyroid hormone triiodothyronine (T3) have been identified in vivo in brain tissues and in vitro in mouse and rat neuroblastoma and glioma cells. The present study characterizes nuclear T3 receptors in human neuroblastoma SH-SY5Y cells and compares their level before and after differentiation. Undifferentiated cells, grown in DME/HAM F-12 medium supplemented with 10% fetal calf serum, show an abundant single type of nuclear receptor, indicated by a straight Scatchard plot, with a Kd of 0.11 nmol/l. After treatment with sodium butyrate (0.5 mM for 4 days) or NGF (2 nM for 6 days), the cells showed neuronal-like patterns (extension of neurites, slowing of growth, increased tyrosine hydroxylase activity), with a decrease in the number of nuclear T3 receptors. As sodium butyrate and NGF treatments differentiate neuroblastoma SH-SY5Y cells, these data suggest a down-regulation of T3 receptors with cell maturation.

A tyrosine hydroxylase assay in microwells using coupled nonenzymatic decarboxylation of dopa

A radiometric assay for tyrosine hydroxylase employing a coupled nonenzymatic decarboxylation of L-[14C]Dopa formed from L-[14C]tyrosine has been adapted for performance in a 96 microwell culture plate. The method uses an easily manufactured plate holder to compress blotting paper impregnated with methylbenzethonium hydroxide against the top rim of each well. This forms isolated, airtight compartments in which 14CO2 is evolved and quantitatively absorbed into the blotting paper. The method is sensitive enough to detect the production of less than 5 pmol of 14CO2. A major advantage of this system is that cells can be grown in tissue culture and subsequently assayed for tyrosine hydroxylase activity in the same well. The method is more facile than previously devised procedures, allowing for the simultaneous assay of up to 96 samples totally contained in a single, compact, portable unit.

Light onset stimulates tyrosine hydroxylase activity in isolated teleost retinas

The action of tyrosine hydroxylase is the rate-limiting step in the synthesis of dopamine, the most abundant catecholamine in vertebrate retinas. I have examined the activation and regulation of this enzyme in isolated retinas of green sunfish, Lepomis cyanellus. Exposing previously dark-adapted retinas to constant illumination for a period of 10 min increased enzymatic activity 2.2-fold over that present in retinas incubated in darkness. Thus, light onset activates tyrosine hydroxylase in teleost retinas. Stimulation of the activity of tyrosine hydroxylase under these conditions was associated with a decrease in the apparent Km of the enzyme for its pteridine cofactor without a change in the apparent Vmax of the reaction. This result suggests that short-term exposure to light increases dopamine synthesis by enhancing the affinity of the enzyme for its naturally occurring cofactor. These findings are consistent with the idea that light activates dopaminergic neurons in teleost retinas.

Effects of serotonin on tyrosine hydroxylase and tau protein in a human neuroblastoma cell line

The direct effects of the neurotransmitter serotonin on the catecholaminergic enzyme, tyrosine hydroxylase and the microtubule-associated tau protein were studied in a human neuroblastoma cell line. Undifferentiated LAN-5 cells, cultured in serum supplemented basal medium, or cells induced to differentiate by 6 day exposure to 10 uM retinoic acid were treated for 48 hr with 50 nM and 50 uM serotonin. In undifferentiated cells, serotonin treatment (50 uM) decreased both tyrosine hydroxylase activity and a 50 kD cytoplasmic fraction tau protein while 50 nM serotonin treatment caused this 50 kD protein to increase in the cytoplasmic fraction but decrease in the membrane fraction. While basal tyrosine hydroxylase activity increased in differentiated vs. undifferentiated cells, serotonin treatment had no effect on the enzyme or tau in differentiated LAN-5. This study shows serotonin to have direct effects on the biochemistry and cytoskeleton of undifferentiated cultured human neuroblastoma.

Activation of striatal tyrosine hydroxylase by in vivo electrical stimulation: comparison with cyclic AMP-mediated activation

These studies were carried out to characterize the activation of rat striatal tyroxine hydroxylase produced by depolarization of the medial forebrain bundle and to evaluate the possible role of cyclic AMP as a mediator of this activation. The enzymatic properties of tyrosine hydroxylase following in vivo depolarization were compared to those produced by treatment of striatal synaptosomes with dibutyryl cyclic AMP (dbcAMP). Similar effects were observed with regard to enzyme distribution, altered sensitivity to dopamine-induced inhibition, and activity as a function of tyrosine concentration. However, differences between the two treatments were also apparent. First, treatment with dbcAMP shifted the pH optimum from 6.2 to 7.0. In contrast, electrical stimulation decreased the rate of decline in activity as the pH was increased above the optimum, but did not shift the pH optimum. Second, plots of tyrosine hydroxylase activity versus cofactor concentration revealed two enzyme forms for both control and electrically stimulated preparations. However, dbcAMP treatment converted the enzyme to a single high affinity form. These results can be explained by one of the following: (1) cyclic AMP is the sole mediator of enzyme activation, but does not produce a maximally activated enzyme following in vivo depolarization, (2) cyclic AMP is only one of several mediators involved or (3) cyclic AMP is not involved in depolarization-induced activation, with activation occurring via the mediation of other intracellular messengers, such as calcium.

Effects of cocaine on tyrosine hydroxylase activity in brain areas from SHR and WKY

Basal tyrosine hydroxylase activity was the same in the nuclei accumbens and hypothalami of WKY and SHR. Basal striatal enzyme activity was lower in SHR than in WKY. Acute and subacute cocaine administration altered enzyme activity only in striata and nuclei accumbens of WKY. The central dopaminergic system of SHR appears to be less active and less sensitive to cocaine than that of WKY.

Gene expression of tyrosine hydroxylase in the developing fetal brain

Tyrosine hydroxylase, aromatic L-amino-acid decarboxylase, and dopamine beta-hydroxylase activities were studied in the developing fetal rat brain. A delay of 2-3 days between the detection of the tyrosine hydroxylase and the aromatic L-amino-acid decarboxylase and dopamine beta-hydroxylase activities was observed. For this reason, the expression of tyrosine hydroxylase mRNA was studied. Tyrosine hydroxylase mRNA was visualized in the whole brain from 13 days of gestation, but the largest increase of the expression was observed in the hypothalamus. These results are discussed in terms of the relative gene expressions of the three enzymes involved in the biosynthesis of catecholamines and phenolamines in nervous tissues.

GABA receptor modulation of tyrosine hydroxylase gene expression in the rat adrenal gland

Chromaffin cell gamma-aminobutyric acid (GABA) receptors play a role in modulating catecholamine secretion. The present experiments examined the role of GABA receptors in modulation of tyrosine hydroxylase (TH) induction in rat adrenal gland. Administration of bicuculline, a GABA antagonist, had no effect on TH activity or TH mRNA. However, bicuculline potentiated reserpine's effect on TH activity and TH mRNA induction. These data suggest that GABA receptors modulate induction of TH and TH mRNA in the adrenal gland.

CRF-like effects of sauvagine and urotensin I on synaptosomal tyrosine hydroxylase activity of mouse striatum

In the present study we have investigated whether sauvagine (SVG) and urotensin I (UT), two peptides displaying sequence homology with corticotropin-releasing factor (CRF), could affect synaptosomal tyrosine hydroxylase (TH) activity of mouse striatum in a manner similar to CRF. The enzyme activity was assayed in supernatants obtained following sonication and centrifugation of homogenates preincubated with the peptides. SVG and UT produced a concentration-dependent increase of TH activity with a half-maximal effect obtained at 5 and 10 nM, respectively. SVG and UT were as effective as CRF with maximal stimulations corresponding to 52-58% increase of basal enzyme activity, whereas the rank order of potency was SVG greater than UT = CRF. Kinetic analysis of TH activity versus low concentrations of the pterin co-factor (0.05-0.4 mM) indicated that the stimulations elicited by CRF, SVG and UT were associated with an increase in the Vmax of the enzyme form with high affinity for the co-factor. The CRF receptor antagonist alpha-helical CRF9-41 inhibited the effects of all 3 peptides. Moreover, the combined addition of CRF with either SVG or UT did not produce additive effects on TH activity. The stimulatory effects of CRF, SVG and UT were dependent on the concentration of extracellular free Ca2+, being minimal in a Ca2(+)-free medium and maximal at about 0.5 mM extracellular free Ca2+. These results indicate that SVG and UT can mimic the effect of CRF on synaptosomal TH by acting on a common receptor site associated with a Ca2(+)-dependent mechanism.

Modulation of tyrosine hydroxylase gene expression in the rat adrenal gland by age and reserpine

Tyrosine hydroxylase (TH), TH messenger RNA (TH mRNA) and dopamine (DA) were measured simultaneously in adrenal glands of individual Fischer 344 rats aged 2, 6, 13 and 23 months. Between 2 and 23 months TH activity rose 2-fold as compared to the youngest group. TH mRNA content of the adrenal gland rose 3-fold between 2 and 23 months. A 3-fold increase in adrenal DA content, the first catecholamine product of TH, provides evidence that the increases in TH gene expression are functionally significant. To determine if mechanisms that regulate gene expression are altered by aging, the effects of reserpine on induction of TH mRNA and TH activity were compared in another group of rats aged 2, 12 and 27 months. Consistent with the results of the first experiment, there were age-related increases in both TH activity and TH mRNA in the age-matched control groups. TH activity rose 2-fold and TH mRNA rose more than 6-fold between 2 and 27 months. The discrepancy in the relative magnitudes of increases in TH mRNA and TH protein suggest an uncoupling of regulation of TH mRNA and TH protein levels. Moreover, there were significant age-related differences with respect to modulation of TH gene expression by reserpine treatment. TH activity was induced by reserpine in the youngest group, but not in the two older age-groups. In contrast, reserpine caused significant induction of TH mRNA in all age groups. These results provide evidence that aging is accompanied by alterations in transcriptional and post-transcriptional mechanisms involved in regulation of TH gene expression.

Increased activity of tyrosine hydroxylase in the cerebellum of the X-irradiated dystonic rat

The exposure of the cephalic end of rats to repeated doses of X-irradiation (150 rad) immediately after birth induces a long-term increase in the noradrenaline (NA) content of cerebellum (CE) (+ 37.8%), and a decrease in cerebellar weight (65.2% of controls), which results in an increased NA concentration (+ 109%). This increase in the neurotransmitter level is accompanied by a dystonic syndrome and histological abnormalities: Purkinje cells (the target cells for NA afferents to CE) fail to arrange in a characteristic monolayer, and their primary dendritic tree appears randomly oriented. The injection of reserpine 0.9 and 1.2 mg/kg ip to adult rats for 18 h depletes cerebellar NA content in both controls (15.7 +/- 4 ng/CE and 2.8 +/- 1.5 ng/CE, respectively) and X-irradiated rats (17.1 +/- 1 ng/CE and 8.3 +/- 2 ng/CE, respectively). The activity of tyrosine hydroxylase (TH) in CE of adult rats, measured by an in vitro assay, is significantly increased in neonatally X-irradiated animals when compared to age-matched controls (16.4 +/- 1.4 vs 6.32 +/- 0.6 nmol CO2/h/mg prot., p less than 0.01). As observed for NA levels, a net increase in TH activity induced by the ionizing radiation is also measured: 308.9 +/- 23.8 vs 408.2 +/- 21.5 nmol CO2/h/CE, p less than 0.01 (controls and X-treated, respectively). These results suggest that X-irradiation at birth may induce an abnormal sprouting of noradrenergic afferents to CE. The possibility that these changes represent a response of the NA system to the dystonic syndrome is discussed.

Localization of N-methyl-D-aspartate receptors in the rat striatum: effects of specific lesions on the [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid binding

The binding of [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid ([3H]CPP), a rigid analogue of 2-amino-7-phosphonoheptanoic acid (AP7) and reported to be a selective N-methyl-D-aspartate (NMDA) antagonist, was studied in rat striatal membranes using a centrifugation procedure to separate bound and free radioligand. [3H]CPP bound with high affinity (KD = 272 nM) in a saturable, reversible, and protein concentration-dependent manner. Specific binding was suggested to involve a single class of noninteracting binding sites. The most potent [3H]CPP binding inhibitors tested were CPP, L-glutamate, 2-amino-5-phosphonovalerate, and AP7. NMDA, L-aspartate, and alpha-aminoadipate were also shown to be efficient in inhibiting the binding, whereas quisqualate, D,L-2-amino-4-phosphonobutyrate, kainate, L-glutamate diethylester, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid were found to be essentially inactive. These data are therefore consistent with the view that [3H]CPP selectively binds to NMDA receptors in the rat striatum. Lesions of intrastriatal neurons using local injections of kainic acid revealed a marked decrease in [3H]CPP binding, suggesting an almost exclusively postsynaptic location of binding sites in the striatum. Conversely, bilateral lesion of corticostriatal glutamatergic fibers resulted in an increased number of [3H]CPP striatal binding sites, providing evidence for a putative supersensitivity response to this striatal deafferentation. Interestingly, lesion of the nigrostriatal dopaminergic neurons using intranigral 6-hydroxydopamine injections resulted, 2-3 weeks later, in a similar increase in the number of [3H]CPP striatal binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cold exposure on rat adrenal tyrosine hydroxylase: an analysis of RNA, protein, enzyme activity, and cofactor levels

Long-term cold exposure (5-7 days) is known to induce concomitant increases in the levels of adrenomedullary tyrosine hydroxylase (TH) RNA, protein, and enzyme activity. In this report, we compare the time courses of these changes and investigate the effects of cold exposure on the levels of biopterin, the cofactor required for tyrosine hydroxylation. After only 1 h of cold exposure, TH mRNA abundance increased 71% compared with nonstressed controls. Increases in total cellular TH RNA levels were maximal (threefold over control values) within 3-6 h of cold exposure and remained elevated throughout the duration of the experiment (72 h). TH protein levels increased rapidly after 24 h of cold exposure and reached a maximal value threefold above that of controls at 48-72 h. Despite the relatively rapid and large elevations in TH RNA and protein content, only modest increases in TH activity were detected during the initial 48 h of cold exposure. Adrenomedullary biopterin increased rapidly after the onset of cold exposure, rising to a level approximately twofold that of the nonstressed controls at 24 h, and remained at this level throughout the duration of the stress period. Taken together, the results of this time course study indicate that cold-induced alterations in adrenal TH activity are mediated by multiple cellular control mechanisms, which may include pre- and posttranslational regulation. Our findings also suggest that cold stress-induced increases in the levels of the TH cofactor may represent another key event in the sympathoadrenal system's response to cold stress.

Enhancement of in vivo tyrosine hydroxylation in the rat adrenal gland under hypoxic conditions

We examined the effects of hypoxia (8% O2) on in vivo tyrosine hydroxylation, a rate-limiting step for catecholamine synthesis, in the rat adrenal gland. The hydroxylation rate was determined by measuring the rate of accumulation of 3,4-dihydroxyphenylalanine (DOPA) after decarboxylase inhibition. One hour after hypoxic exposure, DOPA accumulation decreased to 60% of control values, but within 2 h it doubled. At 2 h, the apparent Km values for tyrosine and for biopterin cofactor of tyrosine hydroxylase (TH) in the soluble fraction were unchanged, whereas the Vmax value increased by 30%. The content of total or reduced biopterin was unchanged, but the content of tyrosine increased by 80%. Tyrosine administration had little effect on DOPA accumulation under room air conditions but enhanced DOPA accumulation under hypoxia. After denervation of the adrenal gland, the hypoxia-induced increase in DOPA accumulation and in the Vmax value was abolished, whereas the hypoxia-induced increase in tyrosine content was persistent. These results suggest that in vivo tyrosine hydroxylation is enhanced under hypoxia, although availability of oxygen is reduced. The enhancement is the result of both an increase in tyrosine content coupled with increased sensitivity of TH to changes in tyrosine tissue content and of an increase in dependence of TH on tyrosine levels. The increase in the sensitivity of TH and in the Vmax value is neurally induced, whereas the increase in tyrosine content is regulated by a different mechanism.

Induction of the vesicular monoamine transporter by elevated potassium concentration in cultures of rat sympathetic neurons

The expression of the vesicular monoamine transporter was studied in newborn rat sympathetic neurons and compared to that of the catecholamine biosynthesis enzymes tyrosine hydroxylase and dopamine-beta-hydroxylase. The vesicular monoamine transporter was assayed using the specific ligand [3H]dihydrotetrabenazine. In cultures grown for 10 days in the presence of 35 mM K+, tyrosine hydroxylase activity and the density of [3H]dihydrotetrabenazine binding sites were increased by a similar 2-3-fold factor, while dopamine-beta-hydroxylase activity and protein level were unchanged. Under these conditions, choline acetyltransferase activity was depressed by 90%. The induction of the vesicular monoamine transporter by high K+ was dependent upon Ca2+ entry through slow calcium channels since it was inhibited by the diphenylbutylpiperidine antagonist fluspirilene and by 20 mM Mg2+, and was enhanced by the dihydropyridine agonist, Bay K8644. The induction of the vesicular monoamine transporter by neuronal depolarization indicates the existence of a Ca2(+)-dependent mechanism of coregulation for this intrinsic component of monoaminergic synaptic vesicles and tyrosine hydroxylase. On the other hand, the apparent absence of dopamine-beta-hydroxylase induction is probably due to the continuous secretion of this intravesicular enzyme by the depolarized sympathetic neurons, an effect already observed in trans-synaptically stimulated adult sympathetic ganglion and adrenal medulla.

Activation of adenosine A1 receptor by N6-(R)-phenylisopropyladenosine (R-PIA) inhibits forskolin-stimulated tyrosine hydroxylase activity in rat striatal synaptosomes

We investigated the effect of the relatively selective A1 adenosine receptor agonist N6-(R)-phenylisopropyladenosine (R-PIA) on tyrosine hydroxylase activity (TH) of synaptosomes obtained from rat striatum. TH activity was assayed in supernatant obtained following sonication and centrifugation of the tissue preincubated with the test compounds. R-PIA produced a modest decrease of basal enzyme activity, but significantly reduced the activation of the enzyme by submaximal (0.1-0.5 microM) concentrations of forskolin (FSK) a stimulator of adenylate cyclase. The IC 50 value of R-PIA was 17 nM and the maximal inhibition corresponded to 30-40% decrease of the enzyme activity stimulated by FSK. The S-isomer of PIA failed to affect TH activity under control and stimulated conditions. Moreover, the inhibitory effect of R-PIA was completely antagonized by 8-cyclopentyl- 1,3 -dimethylxanthine, an adenosine receptor blocker. R-PIA inhibited both basal and FSK-stimulated adenylate cyclase activity. These results indicate that in striatal dopaminergic terminals TH activity can be modulated in an inhibitory manner by activation of presynaptic A1 adenosine receptors.

Excitotoxicity of NMDA and kainic acid is modulated by nigrostriatal dopaminergic fibres

The excitotoxic action of N-methyl-D-aspartate (NMDA) and of kinase (KA) has been assessed by measuring glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) activity in the rat striatum 5 days after focal microinjections of NMDA or KA. Prior unilateral lesioning of the nigrostriatal dopaminergic pathway by focal injection of 6-hydroxydopamine decreases the excitotoxic effect of NMDA and of KA.

Cholinergic differentiation of clonal rat pheochromocytoma cells (PC12) induced by retinoic acid: increase of choline acetyltransferase activity and decrease of tyrosine hydroxylase activity

The effects of retinoic acid (RA), a naturally occurring metabolite of vitamin A, on the growth, morphology and neurochemical differentiation of the PC12 clone of rat pheochromocytoma cells were investigated. RA added to the medium inhibited the growth of PC12 cells in a dose-dependent manner up to 10 microM without affecting their morphology. In PC12 cells cultured in the presence of 10 microM RA for 8 days, the specific activity of choline acetyltransferase (ChAT) was increased 2-fold, while the specific activity of tyrosine hydroxylase (TH) was decreased 0.5-fold compared with cells cultured in the absence of RA. Specific activities of acetylcholinesterase (AChE), glutamate decarboxylase (GAD) and lactate dehydrogenase (LDH) were not affected by RA. Both the increase of ChAT and the decrease of TH induced by RA exhibited similar time and dose dependencies. RA inhibited the increase of TH activity induced by nerve growth factor (NGF), an adrenergic neuronotrophic factor on PC12 cells. From these observations it was concluded that RA induces a cholinergic neurochemical differentiation of PC12 cells independent of a morphological differentiation.

Possible involvements of intracellular Ca2+ and Ca2+ -dependent protein phosphorylation in cholinergic differentiation of clonal rat pheochromocytoma cells (PC12) induced by glioma-conditioned medium and retinoic acid

It is known that nerve growth factor (NGF) induces neurite outgrowth and elevation of the activity of adrenergic marker enzyme, tyrosine hydroxylase (TH) in clonal rat pheochromocytoma cells (PC12), whereas glioma-conditioned medium (GCM) induces neurite outgrowth and elevation of the activity of cholinergic marker enzyme, choline acetyltransferase (ChAT) in PC12 cells. In the previous study we have shown that retinoic acid (RA) induces specific elevation of ChAT activity and depression of TH activity without morphological differentiation (Matsuoka, I. et al., Brain Res., 502 (1989]. In the present study, we compared the effects of NGF, GCM and RA on the intracellular signalings in PC12 cells in relation to the mechanism of cholinergic differentiation. Addition of NGF, GCM or RA to the culture medium of PC12 cells caused a rapid rise in intracellular Ca2+ concentration [( Ca2+]i) reaching the level of almost 2.5-fold the resting condition within 3-18 h. Thereafter, [Ca2+]i of NGF-treated cells were decreased to the resting level within 12 h. On the other hand, [Ca2+]i of GCM-and RA-treated cells decreased to a level which was 1.8- to 2-fold the resting condition within 24-48 h and stayed at this level for up to 4-7 days. When homogenates of GCM- and RA-treated PC12 cells were incubated with [gamma-32P]ATP, phosphorylation of a protein with molecular mass of 27 kDa (27 K-protein) was specifically enhanced. The phosphorylation of the 27 K-protein was not seen in the homogenate of the NGF-treated cells. The phosphorylation of the 27 K-protein was dependent on Ca2+ and inhibited by inhibitors of Ca2+-dependent protein kinase, H-7 and W-7. Addition of H-7 and W-7 to the culture medium of PC12 cells abolished the elevation of ChAT activity specifically induced by GCM and RA. These observations suggested that the sustained increase of [Ca2+]i and Ca2+-dependent protein phosphorylation are involved in the intracellular signaling mechanism required for the cholinergic differentiation of PC12 cells induced by GCM and RA.

The role of Ca2+ channels of the L-type in neurotransmitter plasticity of cultured sympathetic neurons

We have studied the effects of Ca2+ antagonists and agonists on the development of choline acetyltransferase (ChAT), tyrosine hydroxylase (TOH) and acetylcholinesterase (AChE) in cultures of rat sympathetic neurons maintained for 6-9 days in low K+ (5 mM) or high K+ (35 mM) medium. Previous experiments have shown that high K+ medium increases TOH activity and TOH-mRNA level up to 3.5-fold and depresses the development of AChE, in particular of its asymmetric A12 form. Moreover, high K+ medium inhibits ChAT induction by 90% in muscle-conditioned medium (Raynaud et al., Dev. Biol., 119 (1987) 305-312; 121 (1987) 548-558). None of the Ca2+ antagonists tested affected the development of ChAT, TOH or AChE in low K+ medium. In high K+ medium, nitrendipine (3 microM) or fluspirilene (1 microM) fully restored ChAT induction by conditioned medium to the level observed in low K+ medium. Other drugs (1 microM) gave partial reversion: flunarizine greater than (+)-PN 200-110 greater than (-)-D-888 greater than cinnarizine = lidoflazine. On the other hand, ChAT induction was not restored by a calmodulin inhibitor, calmidazolium (1 microM). Fluspirilene, PN 200-110, and nitrendipine also totally abolished TOH induction by high K+ medium; fluspirilene (1 microM) suppressed the inhibitory effect of high K+ medium on AChE development and restored the development of A12 AChE. Conditioned medium also depresses AChE and blocks the development of A12 AChE (Swerts et al., Dev. Biol., 103 (1984) 230-234), but these effects were insensitive to fluspirilene. The Ca2+ agonist Bay K 8644 (1 microM) potentiated the effects of elevated K+ on both ChAT and TOH. The data suggest that the effects of long-term depolarization on ChAT, TOH and AChE are mediated by Ca2+ entry specifically through voltage-sensitive channels of the L-type. Our results on cultured sympathetic neurons raise the possibility that Ca2+ antagonists, which are widely used clinically, may affect the expression of neurotransmitter phenotypic traits in vivo and interfere with trans-synaptic induction of enzymes.

In vitro reactivation of rat cortical tryptophan hydroxylase following in vivo inactivation by methylenedioxymethamphetamine

The activity of tryptophan hydroxylase (EC 1.14.16.4) from rat brain was significantly decreased 1 h following a single systemic injection of 3,4-methylenedioxymethamphetamine (MDMA) when assessed ex vivo by radioenzymatic assay or in vivo by the quantitation of 5-hydroxytryptophan accumulation following central L-aromatic amino acid decarboxylase inhibition. Recovery of enzymatic activity in vivo, which occurred within 24 h of low-dose MDMA treatment, appeared not to involve synthesis of new enzyme protein, because the return of enzymatic activity was not prevented by prior cycloheximide. Acutely MDMA-depressed cortical tryptophan hydroxylase activity could be completely restored in vitro by a prolonged (20-24 h) anaerobic incubation in the presence of dithiothreitol and Fe2+ at 25 degrees C; partial reconstitution occurred when 2-mercapto-ethanol was substituted for dithiothreitol. Cortical tryptophan hydroxylase acutely inactivated by methamphetamine or p-chloroamphetamine could be similarly reactivated. MDMA-inactivated cortical tryptophan hydroxylase derived from rats killed later than 3 days after drug treatment could not be significantly reactivated under the conditions described above, indicating the development of irreversible enzymatic damage. Kinetic analysis of enzyme reactivation revealed an approximate doubling of enzyme Vmax with no change in enzyme affinity for either substrate, tryptophan, or pterin cofactor. These studies suggest that MDMA and its congeners inactivate central tryptophan hydroxylase by inducing oxidation of key enzyme sulfhydryl groups. The reactivation capacity of drug-inactivated enzyme at various times after MDMA treatment may provide a means of assessing the development of MDMA-induced neurotoxicity.

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the dog: effect of pargyline pretreatment

Adult beagle dogs of either sex were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-HCl (2.5 mg/kg, i.v.) alone or after pretreatment with pargyline (5.0 mg/kg, s.c., twice), with pargyline alone, or were uninjected. Groups were killed 2 h, 3 weeks, or 3 months after injection, and several brain areas were assayed for biogenic amines and their synthetic and degradative enzymes. MPTP caused a massive and permanent loss of striatal dopamine, tyrosine hydroxylase, and 3,4-dihydroxyphenylalanine decarboxylase activities and the loss of cells within the substantia nigra pars compacta. Dopamine and norepinephrine also were depleted to various degrees in cortex, olfactory bulb, and hypothalamus; however, dopamine beta-hydroxylase activity in cortex was normal. There was no cell loss in the ventral tegmental area or locus ceruleus. The activities of monoamine oxidase (MAO)-A and MAO-B in cortex and caudate were not affected by MPTP. Despite a permanent loss of the nigrostriatal system, the dogs exhibited only a transient hypokinesia lasting 1-2 weeks. Pargyline pretreatment prevented the loss of striatal dopamine and cells from the substantia nigra, but did not prevent a prolonged but reversible decrease in the concentration of dopamine metabolites. It is argued that this apparent inhibition of MAO is due not to suicide inactivation of the enzyme by MPTP, but to reversible inhibition by accumulation of the pyridinium metabolite, 1-methyl-4-phenylpyridinium, selectivity in aminergic terminals.

Involvement of adenylate cyclase inhibition in dopamine autoreceptor regulation of tyrosine hydroxylase in rat nucleus accumbens

In homogenates of rat nucleus accumbens, quinpirole, a dopamine (DA) D2 receptor agonist, inhibited the activation of tyrosine hydroxylase (TH) elicited by either forskolin, an activator of adenylate cyclase, or rolipram, a cyclic nucleotide phosphodiesterase inhibitor. The inhibition produced by 1 microM quinpirole was completely antagonized by the D2 blocker L-sulpiride (2 microM). Quinpirole failed to inhibit the stimulation of TH elicited by dibutyryl cyclic AMP (2 mM), which acts independently of adenylate cyclase. Quinpirole (10 microM) significantly inhibited the stimulation of adenylate cyclase activity elicited by 1 microM forskolin. These results indicate that mesolimbic DA autoreceptors can regulate TH activity by inhibiting a presynaptic adenylate cyclase system.

3-Acetylpyridine-induced degeneration of the nigrostriatal dopamine system: an animal model of olivopontocerebellar atrophy-associated parkinsonism

The effects of 3-acetylpyridine (3-AP) administration to rats on the mesotelencephalic dopamine system were assessed. A single 3-AP injection resulted in biochemical and immunohistochemical evidence of degeneration of the nigrostriatal dopamine system. Six weeks after 3-AP treatment decreases in both striatal dopamine content and the activity of the catecholamine biosynthetic enzyme tyrosine hydroxylase were observed. Immunohistochemical examination suggested a decreased density of striatal tyrosine hydroxylase-immunoreactive fibers and revealed the emergence of a distinctly patchy organization of the dopamine innervation to the dorsolateral striatum. While 3-AP administration resulted in biochemical and anatomical data consistent with the degeneration of nigrostriatal dopamine fibers, no significant changes in dopamine content or the density or pattern of tyrosine hydroxylase-immunoreactive fibers in the anteromedial prefrontal cortex or nucleus accumbens were seen. These data suggest that 3-AP administration may result in a relatively specific degeneration of the nigrostriatal dopamine system. Since 3-AP causes both a profound loss of the climbing fiber input to the cerebellum derived from the inferior olivary nucleus, and the degeneration of nigrostriatal dopamine neurons, 3-AP administration may provide a useful model of olivopontocerebellar atrophy-associated parkinsonism. Moreover, the differences in the neurotoxicity caused by 3-AP and that elicited by another pyridine which causes striatal dopamine depletion (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, MPTP) may offer important insights into the mechanisms of both species- and site-specific pyridine neurotoxins.

Effects of aging on p- and m-octopamine, catecholamines, and their metabolizing enzymes in the rat

Functions of octopamine in the mammalian brain are still not well known. An important aspect of this problem is the relationship between octopamines and catecholamines. Previous data have shown that their respective ontogenic evolutions are not parallel. Do the changes in brain related to aging also differentially affect these two groups of molecules? In order to check this point, the brain levels of p- and m-octopamine, p-tyramine, noradrenaline, and dopamine, as well as the activities of metabolizing enzymes, were determined in young adult and aging rats (20-26 months). Unlike catecholamines, there is a drastic decrease of p-octopamine after 20 months of age in the hypothalamus and telencephalon. p-Tyramine levels are also lowered. This change appears to be due to a decrease of the aromatic L-amino acid decarboxylase activity. These data, as those of ontogenic studies, confirm that p-octopamine and catecholamine metabolisms may have some independent steps and, moreover, that p-octopamine may have a role in the normal activity of the brain.

Basal ganglia lesions in the rat: effects on quinolinic acid metabolism

Experimental basal ganglia lesions were produced in order to examine the effect of neuronal loss on quinolinic acid (QUIN) metabolism. The latter was investigated by measuring the activities of QUIN's biosynthetic enzyme, 3-hydroxyanthranilic acid oxygenase (3-HAO) and its degradative enzyme, quinolinic acid phosphoribosyltransferase (QPRT). Striatal ibotenic acid lesions caused a steady increase in striatal QPRT activity, reaching 280% of control levels 21 days after the lesion. In the same tissue, 3-HAO activity, too, was elevated. It rose to 436% of control after 7 days and to a lesser degree (+309%) after 3 weeks. Immunotitration experiments using anti-rat 3-HAO antibodies and kinetic analysis of lesioned and control striata showed that the increase in 3-HAO was due to de novo production of enzyme protein. The large increases in striatal enzyme activities after 7 days were accompanied by smaller increases in both 3-HAO and QPRT activities in the ipsilateral substantia nigra. Physical destruction of corticostriatal glutamatergic fibers resulted in increases in striatal 3-HAO (+216%) and QPRT (+243%) activities after one week. No changes in nigral or striatal QUIN metabolism were recorded 7 days after an intranigral injection of 6-hydroxydopamine. These data confirm the notion of a largely glial localization of the QUIN system in the basal ganglia, and correlate well with recent observations in brain tissue from Huntington's disease victims.

Prenatal ontogenesis of brain phenolamines and catecholamines in relation to their metabolizing enzymes in Roman avoider strains of rats

Phenolamines, particularly octopamines, are of special importance in avoidance behavior. In the Roman low avoidance (RLA) strain, p-octopamine can induce locomotor behavioral activity that is normally observed in the Roman high avoidance (RHA) strain. For these reasons, the levels of prenatal octopamines (para and meta isomers) have been studied in relation to noradrenaline and dopamine levels. In the hypothalamus and brainstem of RHA, a maximum level of the para isomer is observed at 15 days of embryonic development but, unlike in controls and RLA animals, this level remains almost constant until 20 days. For the meta-isomer and catecholamines, there is a 1-2 day delay in detection between controls and RLA or RHA. The study of related enzyme activities reveals that tyrosine hydroxylase displays a 2-day delay in RHA when compared to the control value at 19 days of fetal life. These results are discussed in terms of the role of p-octopamine in avoidance conditioning and of the possible delayed expression of the tyrosine hydroxylase gene in Roman strains of rats.

Acute effects of S-adenosyl-L-methionine on catecholaminergic central function

Catecholaminergic function was studied in rat brain areas after acute administration of S-adenosyl-L-methionine (SAM: 10 mg/kg i.p.). The noradrenaline (NA) concentration increased in the hippocampus and frontal cortex and decreased in the olfactory bulbs between 1 and 2 h after the SAM injection. NA biosynthesis was stimulated in vivo and the concentration of normetanephrine was increased only in the hippocampus. SAM may indirectly affect NA biosynthesis and metabolism. This effect on noradrenergic function might participate in its putative antidepressive action.

Tyrosine hydroxylase phosphorylation in rat brain striatal synaptosomes

The present studies were carried out to determine if tyrosine hydroxylase phosphorylation in rat brain striatal synaptosomes is activated by dibutyryl cyclic AMP treatment. Incubation of synaptosomes with [32P]orthophosphate, followed by immunoprecipitation and sodium dodecyl sulfate polyacrylamide gel electrophoresis, produced a band of radioactivity associated with a 62 kDa polypeptide. Treatment with the catecholamine neurotoxin, 6-hydroxydopamine, produced parallel losses of: (1) tyrosine hydroxylase enzyme activity, (2) dopamine content, and (3) the 62 kDa band of radioactivity. These data support the identification of this band as a tyrosine hydroxylase-derived polypeptide. Incubation with dibutyryl cyclic AMP produced an increase in soluble tyrosine hydroxylase activity and phosphorylation. These results suggest that the increase in synaptosomal catecholamine synthesis produced by dibutyryl cyclic AMP is mediated by an increase in tyrosine hydroxylase phosphorylation.

Prenatal ethanol exposure impairs lesion-induced plasticity in a dopaminergic synapse after maturity

This study examined the consequences of alcohol (ethanol) exposure during fetal life on lesion-induced dopaminergic synapse responsiveness (plasticity) in the olfactory tubercle of the adult rat. Normally, in the olfactory tubercle, olfactory bulbectomy elicits alterations in pre- and postsynaptic dopaminergic markers, including, respectively, (1) increased tyrosine hydroxylase activity and immunoreactivity, which is associated with dopaminergic axon sprouting, and (2) increased dopaminergic receptor density and potentiated dopamine activation of adenylate cyclase. We have utilized biochemical and quantitative immunocytochemical methodology to examine these synaptic markers in olfactory bulbectomized or sham-operated adult rats. These animals were offspring of dams which were administered one of the following diets during pregnancy: (1) liquid diet containing 35% ethanol-derived calories ad libitum; (2) liquid diet containing an isocaloric amount of maltose-dextrin instead of ethanol, pair-fed; or (3) unaltered liquid diet ad libitum. The results show that prenatal alcohol exposure leads to suppression of the lesion-elicited dopaminergic synapse responsiveness in the olfactory tubercle. There were no significant differences between offspring born to control and pair-fed animals, indicating that the observed abnormalities were not due to alterations in their nutritional status. In conclusion, the present data are a biochemical and quantitative immunocytochemical demonstration of impaired lesion-induced synaptic responsiveness. This renders a new dimension in support of previous evidence indicating that prenatal alcohol exposure leads to altered neuroanatomical, neuroendocrinological and behavioral responsiveness to various challenges. Such impaired synaptic responsiveness may underlie brain functional abnormalities characteristic of fetal alcohol syndrome.

In vitro phosphorylation of bovine adrenal chromaffin cell tyrosine hydroxylase by endogenous protein kinases

Under phosphorylating conditions, addition of Ca2+ or cyclic AMP to the 100,000 g supernatant of purified bovine adrenal chromaffin cells increases both the incorporation of 32P into tyrosine hydroxylase and the activity of the enzyme. Combining maximally effective concentrations of each of these stimulating agents produces an additive increase in both the level of 32P incorporation into tyrosine hydroxylase and the degree of activation of the enzyme. The increased phosphorylation by Ca2+ is due to stimulation of endogenous Ca2+-dependent protein kinase activity and not inhibition of phosphoprotein phosphatases. When the chromaffin cell supernatant is subjected to diethylaminoethyl (DEAE) chromatography to remove calmodulin and phospholipids, tyrosine hydroxylase is no longer phosphorylated or activated by Ca2+; on the other hand, phosphorylation and activation of tyrosine hydroxylase by cyclic AMP are not affected. Subsequent replacement of either Ca2+ plus calmodulin or Ca2+ plus phosphatidylserine to the DEAE-fractionated cell supernatant restores the phosphorylation, but not activation of the enzyme. Reverse-phase HPLC peptide mapping of tryptic digests of tyrosine hydroxylase from the 100,000 g supernatant shows that the Ca2+-dependent phosphorylation occurs on three phosphopeptides, whereas the cyclic AMP-dependent phosphorylation occurs on one of these peptides. In the DEAE preparation, either cyclic AMP alone or Ca2+ in the presence of phosphatidylserine stimulates the phosphorylation of only a single phosphopeptide peak, the same peptide phosphorylated by cyclic AMP in the crude supernatant. In contrast, Ca2+ in the presence of calmodulin stimulates the phosphorylation of three peptides having reverse-phase HPLC retention times that are identical to peptides phosphorylated by Ca2+ addition to the crude unfractionated 100,000 g supernatant. Rechromatography of the peaks from each of the in vitro phosphorylations, either in combination with each other or in combination with each of the seven peaks generated from phosphorylation of tyrosine hydroxylase in situ, established that cyclic AMP, Ca2+/phosphatidylserine, and Ca2+/calmodulin all stimulate the phosphorylation of the same reverse-phase HPLC peptide: in situ peptide 6. Ca2+/calmodulin stimulates the phosphorylation of in situ peptides 3 and 5 as well. Thus, tyrosine hydroxylase can be phosphorylated in vitro by protein kinases endogenous to the chromaffin cell. Phosphorylation occurs on a maximum of three of the seven in situ phosphorylated sites, and all three of these sites can be phosphorylated by a Ca2+/calmodulin-dependent protein kinase.

gamma-Aminobutyric acid function in the rat striatum is under the double influence of nigrostriatal dopaminergic and thalamostriatal inputs: two modes of regulation?

Glutamic acid decarboxylase (GAD), gamma-[3H]-aminobutyric acid [( 3H]GABA) high-affinity uptake into synaptosomes, and endogenous GABA content were measured in the rat striatum 2-3 weeks following 6-hydroxydopamine injection in the ipsilateral substantia nigra to destroy the nigrostriatal dopaminergic pathway and after kainic acid injection into the centromedial-parafascicular complex of the ipsilateral thalamus to lesion the thalamostriatal input. Both lesions resulted in apparent GAD increase concomitant with a decreased [3H]GABA uptake into striatal synaptosomes. GABA content was increased selectively following the dopaminergic lesion. Kinetic analysis of the uptake process for [3H]GABA showed selectively a decreased Vmax following the dopaminergic lesion; in animals with thalamic lesion, however, the change only concerned the Km, which showed a decreased affinity of the transport sites for [3H]GABA. Determination of Km and Vmax for GAD action on its substrate glutamic acid showed an increased affinity of GAD for glutamic acid in the case of the dopaminergic lesion without any change in Vmax, whereas the thalamic lesion resulted in GAD increase concomitant with a selective increase in Vmax. These data suggest that striatal GABA neurons are under the influence of nigrostriatal dopaminergic neurons which may reduce the GABA turnover, whereas the exact nature of the powerful control also revealed on these neurons following thalamic lesion remains to be determined. Both lesions induced adaptive neurochemical responses of striatal GABA neurons, possibly reflecting in the case of the dopaminergic deprivation an increased GABA turnover.

Thyroid hormone control of preganglionic innervation of the adrenal medulla and chromaffin cell development in the rat. An ultrastructural, morphometric and biochemical evaluation

In the rat, functional connections between the splanchnic nerve and the adrenal medulla are immature at birth and do not become fully competent until the first postnatal week. Neonatal administration of triiodothyronine (T3) accelerates this process, and the present study was undertaken to elucidate the underlying mechanisms. Rats were given T3 (0.1 mg/kg, s.c.) daily for 9 days beginning 1 day after birth. Preganglionic innervation of the adrenal medulla was examined by retrograde axonal transport of horseradish peroxidase (HRP). At 10 days of age, there was an increased number of labeled perikarya in the spinal cord of the hyperthyroid pups. Ultrastructural examination revealed a corresponding increase in synaptic density in the adrenal medulla and in the activity of choline acetyltransferase, a marker for preganglionic cholinergic nerve terminals. These effects were attenuated by 25 days of age, whereupon deficits in HRP-labeled neurons and adrenomedullary synapses were noted. Similarly, replication of chromaffin cells was enhanced transiently in the T3 group during the initial stage of hyperthyroidism, but subsequent long-lasting deficits in cell numbers were noted, along with a corresponding retardation of ontogeny of adrenal catecholamine biosynthesis and storage. Thus, neonatal hyperthyroidism accelerates synaptic development in the sympatho-adrenal axis but suppresses maturation of the target chromaffin cells, ultimately leading to impaired adrenomedullary function.

alpha-[3H]Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid binding to rat striatal membranes: effects of selective brain lesions

The binding of alpha-[3H]amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]AMPA), a structural Glu analog, to rat striatal membranes was studied. In the absence of potassium thiocyanate and Cl-/Ca2+, saturation-curve analysis of [3H]AMPA binding suggested that a single class of noninteracting binding sites with a KD value of 340 +/- 27 nM was involved, although AMPA inhibition of [3H]AMPA binding set at a concentration of 100 nM suggested, in contrast, the presence of multiple populations of striatal binding sites. Several other excitatory amino acid receptor agonists and antagonists were tested, and the most potent and selective quisqualic acid (QA) receptor agonists (QA, L-Glu, and AMPA) were found to represent the most potent inhibitors of [3H]AMPA binding. N-Methyl-D-aspartate receptor agonists and antagonists were ineffective as displacers of the [3H]AMPA binding. Lesions of intrastriatal neurons (using kainic acid local injections) and of corticostriatal afferent fibers led 2-3 weeks later to large decreases (63 and 30%, respectively) in striatal [3H]AMPA binding, whereas selective lesion of the nigrostriatal dopaminergic pathway (using nigral injection of 6-hydroxy-dopamine) was without any influence. Taken together, these results suggest that [3H]AMPA binding is primarily associated with postsynaptic intrastriatal neurons. Some [3H]AMPA binding sites may also be located presynaptically on corticostriatal nerve endings. So, in addition to the possibility that [3H]AMPA binding sites may be involved in corticostriatal synaptic transmission, it is interesting that these putative QA-preferring excitatory amino acid receptor sites may also play some role in autoregulatory processes underlying this excitatory synaptic transmission.

Evidence that adenosine A2 and dopamine autoreceptors antagonistically regulate tyrosine hydroxylase activity in rat striatal synaptosomes

Incubation of rat striatal synaptosomes with the adenosine receptor agonist 2-chloroadenosine (2-CADO) produced a concentration-dependent increase of dopamine (DA) synthesis (about 50% of control value). The effect was not additive with the stimulation produced by either 10 microM forskolin or 2 mM dibutyryl cyclic AMP. Pretreatment of striatal synaptosomes with 2-CADO produced an activation of tyrosine hydroxylase (TH) which withstood washing and lysing of the tissue. This activation was largely independent of the presence of Ca2+ ion in the preincubation medium and, when analyzed as a function of different concentrations of the pterin cofactor 6-methyl-5,6,7,8-tetrahydropterin (0.08-0.4 mM), it was associated with an apparent increase in the Vmax of the enzyme. Quinpirole, a selective D2 DA receptor agonist, reduced control synaptosomal DA synthesis and caused a persistent inhibition of TH activity. When added together with 2-CADO, quinpirole depressed the stimulation of DA synthesis and TH activity produced by the adenosine analog. The effect of quinpirole was stereospecifically antagonized by the D2 DA antagonist sulpiride. Quinpirole also inhibited the activation of TH elicited by a submaximal concentration of forskolin, but not that produced by dibutyryl cyclic AMP. The inhibitory effect of quinpirole on basal and 2-CADO-stimulated TH activities was mimicked by DA. These results indicate that presynaptic DA autoreceptors and adenosine A2 receptors interact antagonistically in controlling DA synthesis in rat striatal synaptosomes presumably by exerting opposite inputs on a presynaptic adenylate cyclase system.

Further studies on the neurochemical mechanisms mediating differences in ethanol sensitivity in LS and SS mice

Long-sleep (LS) and short-sleep (SS) lines of mice were selectively bred for differences in CNS sensitivity to ethanol with LS mice exhibiting much greater sensitivity to hypnotic doses of ethanol (4.0-4.5 g/kg) than SS mice. The influence of peripheral and central catecholamine neuronal systems on ethanol sensitivity (sleep time) in LS and SS mice was examined following administration of reserpine, alpha-methyl-p-tyrosine and 6-hydroxydopamine. Ten days after a single dose of reserpine, tyrosine hydroxylase activity was increased in the brain and adrenal gland of LS mice but only in the brain of SS mice relative to untreated mice. Brain catecholamine levels in the reserpine-treated mice were 25-50% lower in both LS and SS mice compared to levels in untreated mice. These changes were associated with a 41% reduction in LS sleep time, but a 90% increase in SS sleep time. SS mice were also more susceptible to the lethal effects of reserpine. The increased mortality of SS mice may relate to a greater degree of reserpine-induced hypothermia and a slower rate of recovery of brain catecholamine levels. Neonatal LS and SS mice treated with 6-hydroxydopamine exhibited increased levels of catecholamines in the locus ceruleus, decreased levels in the cerebellum and unchanged levels in the hypothalamus at 60 days of age. These changes were associated with a modest decrease (10%) in LS sleep time and a marked increase (200%) in SS sleep time. alpha-Methyl-p-tyrosine decreased brain catecholamine levels of both lines by 30-50% while LS sleep times were unchanged and SS sleep times were increased by 45%.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine-independent motor behavior following microinjection of rimorphin in the substantia nigra

The motor-activating effects of rimorphin, an opioid peptide derived from prodynorphin, were examined in the substantia nigra pars reticulata of rats. Unilateral microinjections of rimorphin produced dose-dependent contralateral rotational behavior that was antagonized by naloxone, suggesting that these effects were mediated by opiate receptors. Lesions of midbrain dopamine cells with 6-hydroxydopamine (6-OHDA) produced a 95% or greater depletion of tyrosine hydroxylase in the striatum ipsilateral to the lesion, but failed to reduce the number of circles made by the rats. In addition to an overall preservation of rimorphin-induced circling in animals with 6-OHDA lesions, 50% of these rats exhibited circling that was at least 2 standard deviations above the mean of animals without lesions. The motor activating effects of rimorphin, thus, appear to occur independently of the nigrostriatal dopamine system; these effects may instead be mediated by GABAergic efferents in the pars reticulata.

Postnatal development of phenylethanolamine-N-methyltransferase activity of rat retina

The postnatal development of rat retinal phenylethanolamine-N-methyltransferase (PNMT) activity was measured by radiometric assay. Activity was detected on day 1 of life. Retinal PNMT activity of day 1 neonates approximated 10% that of the adult. There is an increase in enzyme activity before eye opening. By day 30, enzyme activity has peaked. The enzyme during this early period possesses the same substrate specificity and inhibitor sensitivity as that of the adult enzyme. PNMT activity is detected before tyrosine hydroxylase activity.

Regulated expression of the tyrosine hydroxylase gene by epidermal growth factor

The addition of epidermal growth factor (EGF) to cultures of the rat PCG2 pheochromocytoma cell line increased the level of RNA coding for tyrosine hydroxylase (TH). A region of DNA containing 5'-flanking sequences of the TH gene was fused to a heterologous gene and transfected into a rat anterior pituitary cell line, GH4. The TH gene sequences from +27 to -272 contained information sufficient for the induction of TH by EGF. Two regions within this TH DNA were extensively homologous to the EGF regulatory element of the rat prolactin gene.