Newly Synthesized Dopamine as the Precursor for Norepinephrine Synthesis in Bovine Adrenomedullary Chromaffin Cells

The precursor pool of dopamine for norepinephrine synthesis was investigated in cultured bovine adrenomedullary chromaffin cells incubated with [14C]tyrosine. Under conditions where the intracellular [14C]tyrosine specific activity was constant and [14C]dopamine synthesis was maximal, [14C]dopamine and [14C]norepinephrine accumulated over time, and the total intracellular dopamine content more than doubled within 120 min. When [14C]norepinephrine synthesis was calculated at different times based on the specific activity of [14C]dopamine, this rate was approximately equal to the rate of [14C]dopamine synthesis and was, thus, inconsistent with the observed dopamine accumulation. However, the rate of [14C]norepinephrine synthesis based on the [14C]tyrosine specific activity accounted for the dopamine accumulation, an observation suggesting that newly synthesized dopamine, i.e., dopamine with a specific activity equivalent to that of its precursor, [14C]tyrosine, is preferentially utilized for norepinephrine synthesis. Further studies showed that the subcellular distribution of [14C]dopamine was identical to that of norepinephrine and epinephrine and that the accumulated [14C]dopamine could be converted to norepinephrine within the chromaffin vesicle if dopamine uptake was blocked. Taken together, these results suggest that a small intravesicular dopamine pool, rapidly replenished by newly synthesized dopamine, serves as the substrate for dopamine beta-hydroxylase. Several mechanisms to account for this observation are discussed.     

IS THERE BIDIRECTIONAL TRANSPORT OF NORADRENALINE IN SYMPATHETIC NERVES?

The experiments were designed to detect somatopetal transport of [¹⁴C]noradrenaline in the postganglionic sympathetic nerves supplying the cat spleen and sheep eye. The animals were treated with nialamide to protect the radioactive noradrenaline, after uptake into the nerve terminals, from monoamine oxidase. In the spleen, the transmitter stores were labelled by infusion of [¹⁴C]noradrenaline into a branch of the splenic artery. The branches of the nerves to the infused and non-infused sides of the spleen were ligated in an attempt to arrest, distal to the constriction, any noradrenaline transported somatopetally in the axons from their terminals. After 24 hr, however, there was less radioactivity in the nerves distal compared to proximal to the constriction, despite heavier labelling of the terminal transmitter stores in the infused portion of the spleen. The proximal accumulation of radioactivity could be attributed to a somatofugal transport of [¹⁴C]noradrenaline. Experiments were also done on the intact sympathetic nerve supply of the sheep eye. The sympathetic nerve terminals in the smooth muscle of the left eye were heavily labelled 5 days after the injection of [¹⁴C]noradrenaline into the left vitreous humour. However, both superior cervical ganglia were only lightly labelled, and there was no significant difference in the radioactivity present in the two ganglia. The results provide no support for a bidirectional transport of noradrenaline in sympathetic nerves but are consistent with a somatofugal transport of the amine storage vesicles from their site of synthesis in the soma to the axon terminals.     

Uptake of [3H]Dopamine into Dopaminergic and Noradrenergic Neurones of the Isolated Neurointermediate Lobe of the Rat Hypophysis. Effects of Desipramine and Nomifensine

Abstract: The isolated neurointermediate lobe (NIL) of the rat hypophysis accumulates [³H]dopamine from the incubation medium. Column chromatographic analysis showed that 92% of the tissue radioactivity was contained in the catecholamine fraction. [³H]Dopamine represented 70% and [³H]noradrenaline 30% of the [³H]catecholamines. Desipramine (1 μM) prevented the formation of [³H]noradrenaline without affecting the storage of [³H]dopamine. Nomifensine (10 μM) blocked the storage of [³H]dopamine and [³H]noradrenaline. Thus, in the NIL, [³H]dopamine is taken up into dopaminergic and noradrenergic neurones. In the latter, [³H]dopamine is converted to [³H]noradrenaline, indicating a significant dopamine β-hydroxylase activity in the NIL tissue. A selective labeling of the dopamine stores with [³H]dopamine can be achieved in the presence of desipramine.     

Aminergic innervation pattern of the rodent pineal gland: no apparent influence of time of day

Pineal melatonin synthetic activity shows distinct diurnal characteristics. The circadian regulation of melatonin synthesis is provided by noradrenaline-releasing sympathetic nerves. The pineal noradrenaline content shows a circadian rhythmicity tidally related to the changes in melatonin synthesis rate. To evaluate possible circadian changes of pineal noradrenergic fibre arrangement, the nerve distribution in rat and guinea pig pineal glands was visualized by means of glyoxylic acid-induced histofluorescence. Histochemical findings at 08.00 h and 24.00 h did not exhibit any differences: in both species a dense, mainly perivascularly located network of fluorescent fibres was encountered. As indicated by the simultaneous intraneural presence of green-bluish and yellow fluorophores these fibres most likely contain noradrenaline and serotonin. Obviously circadian melatonin synthesis changes are not paralleled by changes in the distribution pattern of pineal sympathetic nerve fibers. Like other sympathetic innervation-related morphological parameters, histofluorescence does not accurately reflect circadian biochemical changes in the pineal gland.     

Distribution of the Two Forms of Monoamine Oxidase Within Monoaminergic Neurons of the Guinea Pig Brain

The relative distribution of type A and type B monoamine oxidase (MAO) inside and outside the monoaminergic synaptosomes in preparations from hypothalamus and striatum of the guinea pig was determined by incubation of synaptosomal preparations of these regions with low concentrations of [14C]5-hydroxytryptamine (5-HT), noradrenaline, and dopamine. The deamination within the monoaminergic synaptosomes was hindered by selective amine uptake inhibitors. In the absence of these inhibitors, both intra- and extraneuronal deamination was measured. The two forms of the enzyme were differentiated with the irreversible and selective MAO-A and MAO-B inhibitors clorgyline and selegiline (l-deprenyl), respectively. [14C]5-HT was deaminated greater than 90% by MAO-A both inside and outside the 5-hydroxytryptaminergic synaptosomes prepared from the guinea pig hypothalamus. The deamination of [14C]noradrenaline within the noradrenergic synaptosomes of the hypothalamic preparation was in the ratio 75:25% for MAO-A:MAO-B; the corresponding ratio outside these synaptosomes was 45:55%. The deamination of [14C]dopamine within dopaminergic synaptosomes in the striatal preparation was 65% type A:35% type B, whereas outside these synaptosomes the ratio was 35:65%. Because the relative amounts and the distribution of the two forms of MAO in the guinea pig brain seem to be similar to those previously detected for the human brain, the MAO in the guinea pig brain may be a good model for the MAO in the human brain.     

Changes in Sympathetic Nerve Terminals in the Heart of Cold-Exposed Rats

Abstract: Changes in sympathetic nerve terminals of the heart after varying periods of exposure of rats to 4°C were investigated. Two indices were used for changes in the number of noradrenaline storage vesicles, i.e., vesicular dopamine β-hydroxylase (DBH) activity and noradrenaline storage capacity. The latter was obtained after uptake of [³H]noradrenaline; endogenous content, uptake of exogenous noradrenaline, and degree of saturation of the vesicles were calculated using the specific activity of the [³H]noradrenaline. As a measure of tyrosine hydroxylase activity, whole ventricular noradrenaline, dopamine, and dihydroxyphenylacetic acid content were used. After 4 h of cold exposure there was an increase in vesicular endogenous noradrenaline content, uptake, storage capacity, and DBH activity as well as a large increase in whole ventricular dopamine. After 6 h in the cold, vesicular endogenous noradrenaline content, storage capacity, and DBH activity were decreased. The results suggest that during cold exposure there is an initial increase followed by a decrease in the number of functional vesicles in the nerve terminal, which could explain the fluctuations in the rate of noradrenaline release.     

Presynaptic Control of the Synthesis and Release of Dopamine from Striatal Synaptosomes: A Comparison Between the Effects of 5-Hydroxytryptamine, Acetylcholine, and Glutamate

The effects of 5-HT and glutamate on dopamine synthesis and release by striatal synaptosomes were investigated and compared with the action of acetylcholine, which acts presynaptically on this system. 5-HT inhibited (28%) synthesis of [¹⁴C]dopamine from L-[U-¹⁴C]tyrosine, at 10-⁵M and above. This contrasts with the action of acetylcholine, which stimulated [¹⁴C]-dopamine synthesis by 24% at 10-⁴ M. Tissue levels of GABA were unaffected by either 5-HT or acetylcholine up to concentrations of 10-⁴ M. The inhibitory action of 5-HT (5 × 10^?5 M and 2 × 10^?4 M) on [¹⁹C]dopamine synthesis was completely abolished by methysergide (2 × 10^?6 M). Higher concentrations of methysergide (10^?4 M) or cyproheptadine (10^?5 M) inhibited [¹⁴C]dopamine synthesis by 28% and 25%, respectively, when added alone to synaptosomes. However, only methysergide prevented the further inhibition of synthesis caused by 5-HT. At concentrations of 2 × 10^?5 M and above, 5-HT stimulated [¹⁴C]dopamine release. This releasing action differed from that of acetylcholine, which occurred at lower concentrations (e.g., 10^?6 M). Methysergide (up to 10^?4 M) or cyproheptadine (2 × 10^?4 M) did not reduce the 5-HT (5 × 10^?5 M)-induced release of [¹⁴C]dopamine, but methysergide (10^?4 M) showed a potentiation (49%) of this increased release. The stimulatory effects of 5-HT (2 × 10^?5 M) and K⁺ (56 mM) on [¹⁴C]dopamine release were additive, indicating that two separate mechanisms were involved. However, when both agents were present the stimulatory effect of K⁺ (56 mM) on [¹⁴C]dopamine synthesis was not seen above the inhibitory effect of 5-HT. Glutamate (0.1-5 mM) did not affect [⁴C]dopamine release or its synthesis from L-[U-¹⁴C]tyrosine. It is concluded that 5-HT modulates the synthesis of dopamine in striatal nerve terminals through a presynaptic receptor mechanism, an action antagonised by methysergide. The releasing action of 5-HT apparently occurs through a separate mechanism which is also distinct from that involved in the response to K⁺ depolarisation.     

Studies on the uptake of [3H]dopamine by synaptic vesicle fraction isolated from bovine brain

1. A synaptic vesicle fraction isolated from bovine caudatolenticular nuclei showed enzymic activities of tyrosine hydroxylase [EC 1.14.16.2] and dopamine beta-hydroxylase [EC 1.14.17.1]. Tyrosine hydroxylase, whose subcellular localization is uncertain, appeared to be associated with the synaptic vesicles. 2. The vesicle fraction took up [3H]dopamine increasingly with time without the aid of ATP (6.3 pmol of [3H]dopamine per mg of vesicle proteins, or 3-4% of the added dopamine, at 30 min). In the presence of ATP, a transient accumulation of the amine was observed, reaching the highest level at 7-10 min (5.6 pmol dopamine/mg protein), and then a rapid release of the amine took place, obeying first-order kinetics with respect to the amine concentration. The amine uptake was strongly inhibited with NEM, regardless of the presence or absence of ATP. 3. The vesicle fraction also exhibited a weak ability to translocate protons inward and ATP-dependently, as monitored by an increase in the fluorescence intensity of ANS. The fluorescence enhancement persisted for at least 30 min and this time-dependent change was not consistent with that of the transient accumulation of [3H]dopamine mentioned above. Since the present vesicle preparation contained a small amount of mitochondrial ATPase (18-20% of the total activity), the proton translocating ability could be attributable to contaminating submitochondrial particles. 4. Therefore these results made it impossible to conclude that the transient uptake of [3H]dopamine by the synaptic vesicles was coupled to ATP hydrolysis.     

Specific distribution pattern of nerve fibers containing catecholamine-synthesizing enzymes, neuropeptide Y (NPY) and C-terminal flanking peptide of NPY (CPON) in the pineal gland of the chinchilla (Chinchilla laniger)--an immunohistochemical study

The sympathetic nerve fibers originating from the superior cervical ganglia and supplying the pineal gland play the most important role in the control of the pineal activity in mammals. NPY and CPON are also present in the majority of the pinealopetal sympathetic neurons. In this study, immunohistochemical techniques were used to demonstrate the existence and coexistence of tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DbetaH) as well as NPY and CPON in the nerve fibers supplying the chinchilla pineal gland. Ten two-year-old female chinchillas housed in natural light conditions were used in the study. The pineals were fixed by perfusion. ABC immunohistochemical technique and immunofluorescence labelling method were employed. TH-immunoreactive (TH-IR) varicose nerve fibers were observed in the pineal gland as well as in the posterior commissural area. Within the chinchilla pineal gland, TH-IR nerve fibers were located in the capsule and connective tissue septa. Numerous varicose TH-IR branches penetrated into the parenchyma and formed a network showing the highest density in the proximal region of the gland. In the central and distal parts of the pineal parenchyma, a subtle network, composed of thin varicose nerve branches, was observed. Double immunostaining revealed that the majority of TH-IR nerve fibers was positive for DbetaH or NPY. TH- and DbetaH-positive neuron-like cells were observed in the proximal region of the gland. The pattern of pineal innervation immunoreactive to CPON was similar to the innervation containing NPY, TH and DbetaH. The chinchilla intrapineal innervation containing TH, DbetaH, NPY and CPON is characterized by the higher density in the proximal part of the gland than in the middle and distal ones. The specific feature of the chinchilla pineal is also the presence of single TH/DbetaH-immunoreactive neuron-like cells in the proximal part of the gland.     

A STUDY OF THE METABOLISM AND RELEASE OF DOPAMINE AND AMINO ACIDS FROM NERVE ENDINGS ISOLATED FROM SHEEP CORPUS STRIATUM

Abstract— Synaptosomes prepared from sheep corpus striatum showed a linear rate of respiration over a 90 min period of incubation in Krebs-bicarbonate medium containing glucose (10 mm ) and the rate of respiration was stimulated by electrical pulses. Dopamine was released from synaptosome beds to the medium by either electrical pulses or 56mm -K⁺ (10min), increasing 108% and 76% respectively above control levels of release. The presence of d- or 1-amphetamine (0.12mm ) in the incubation medium (40 min) increased the accumulation of dopamine in the medium by 310 and 275% respectively and 56mm -K⁺ also caused a significant increase in the release of glutamate, GABA and aspartate. Radioactively labelled dopamine was synthesized by the synaptosomes from l -[¹⁴C]tyrosine, l -DOPA or dl -DOPA, and electrical pulses caused a 35% increase in the rate of dopamine production from [U-¹⁴C] tyrosine. No increased release of [¹⁴C]dopamine in response to depolarizing stimuli was found to occur when synaptosome beds were transferred from medium containing radioactive precursors to fresh medium for further incubation (20 min). In the presence of 1- and d-amphetamine, accumulation of ¹⁴C-labelled doparnine in the incubation media was increased 129% and 380% respectively, the latter was partially depressed by absence of calcium from the medium. Three radioactively labelled metabolites formed by synaptosomes during incubation in dl -[2-¹⁴C]DOPA were detected; the major ones were dihydroxyphenylacetic acid and homovanillic acid and the third was unidentified. When the synaptosome beds were transferred to medium containing no radioactive precursors, it was found that labelled dihydroxyphenylacetic acid was 7 times more abundant than labelled dopamine in the incubation medium (20 min) and one-third as abundant in the synaptosomes. The dihydroxyphenylacetic acid n Ci/dopamine n Ci ratio was greatly affected by K⁺ stimulation, decreasing 52% and 34% in the incubation medium and synaptosomes respectively. A pathway of dihydroxyphenylacetic acid degradation was shown to occur through decarboxylation. These results are discussed in terms of the compartmentation of dopamine and its metabolism. It is proposed that one pool of dopamine is released by depolarizing agents and during the period of incubation it is replaced by synthesis from the endogenous tyrosine (19.5 nmol/100 mg protein) and not by the labelled dopamine in the synaptosome. The synaptosomal pool of dopamine which is radioactively labelled after pulse labelling with dl -[2-¹⁴C]DOPA appears to be prone to oxidation to DOPAC and homovanillic acid which are preferentially released from the synaptosomes.     

Immunofluorescent patterns of clathrin and dopamine beta-hydroxylase in chromaffin cells in culture

Summary Bovine chromaffin cells maintained in culture for eight days were loaded with [³H]noradrenaline and then stimulated by a depolarizing concentration (56 mM) of K⁺. Control and stimulated cells were fixed in 3.7% formaldehyde, treated with acetone or Triton X-100, and then exposed to antibodies raised against dopamine beta-hydroxylase (a secretory granule marker) and clathrin, and purified by affinity chromatography. The cellular distribution of the correspondent antigens was investigated by indirect immunofluorescence. Cells treated with anti-dopamine beta-hydroxylase exhibited a granular pattern of fluorescence in the cytosol of the cell body, neurites, and terminal cones. Chromaffin cells exposed to anti-clathrin also showed a punctate pattern of fluorescence staining. However, in this case, the fluorescent dots were smaller than those observed with anti-dopamine beta-hydroxylase, and they were differently distributed. The speckled anti-clathrin fluorescence was preferentially condensed in the juxtanuclear region of the cell bodies, suggesting the possibility that clathrin was concentrated at the level of the Golgi apparatus.The stimulation of cultured chromaffin cells by 10 pulses of 56 mM K⁺ produced 91±2% (n = 5) depletion in the [³H]noradrenaline cell content and a concomitant displacement of the dopamine beta-hydroxylase fluorescence to the periphery of the cells. Four days after cell stimulation the dopamine beta-hydroxylase fluorescence was similar to that observed in control cells. Under the same conditions of stimulation, the distribution of the clathrin fluorescence was unaltered suggesting either that K⁺induced stimulation of the chromaffin cells does not change the cellular distribution of clathrin, or that the changes in the distribution of clathrin are of such low magnitude that they escape detection by fluorescence microscopy.     

A and B Forms of Monoamine Oxidase Within the Monoaminergic Neurons of the Rat Brain

The inhibition of the A and B forms of monoamine oxidase (MAO) inside and outside serotonergic, noradrenergic, and dopaminergic synaptosomes in homogenates of rat hypothalamus or striatum by clorgyline, a selective and irreversible MAO-A inhibitor, and selegiline, a selective and irreversible MAO-B inhibitor, was examined. Intrasynaptosomal deamination at low concentrations of the substrates [14C]5-hydroxytryptamine ([14C]5-HT; 0.1 microM), [14C]noradrenaline (0.25 microM), [14C]3,4-dihydroxyphenylethylamine ([14C]dopamine; 0.25 microM), and [14C]tyramine (0.25 microM) was hindered by selective uptake inhibitors (citalopram, maprotiline, and amfonelic acid) in the incubation media. Thus, the difference between the deamination of 14C-amine in the absence and presence of the appropriate selective uptake inhibitor provided a measure of deamination in the specific aminergic synaptosomes. This was verified by determining the loss of MAO activity within noradrenergic and serotonergic systems after degeneration of the nerve terminals by the neurotoxins N-chloroethyl-N-ethyl-2-bromobenzylamine and p-chloroamphetamine. Results with the two inhibitors revealed that the A and B forms were responsible for 80 and 20%, respectively, of the deamination of [14C]5-HT within serotonergic synaptosomes from the hypothalamus. The deamination of [14C]noradrenaline within the noradrenergic synaptosomes from the hypothalamus and that of [14C]dopamine and [14C]tyramine within the striatal dopaminergic synaptosomes were due to MAO-A. About 10% of the deamination of [14C]noradrenaline, [14C]dopamine, and [14C]tyramine outside the noradrenergic or dopaminergic synaptosomes was brought about by the B form, with the remainder being deaminated by MAO-A.     

EFFECT OF DIBUTYRYL-CYCLIC AMP and DEXAMETHASONE ON NORADRENALINE SYNTHESIS IN ISOLATED SUPERIOR CERVICAL GANGLIA

Abstract— Incubation with dibutyryl-cyclic AMP increased levels of both noradrenaline and dopamine- β -hydroxylase in isolated rat superior cervical ganglia. Dexamethasone also increased the dopamine- β -hydroxylase content but did not affect noradrenaline levels. Cycloheximide blocked the effect of dibutyryl-cyclic AMP on ganglion dopamine- β -hydroxylase but did not affect the rise in noradrenaline content.
Dibutyryl-cyclic AMP increased the synthesis of noradrenaline from [¹⁴C]tyrosine but not from [³H]DOPA.
The results are discussed in terms of a possible role for cyclic AMP in the control of noradrenaline synthesis in sympathetic ganglia.     

Catecholamine biosynthesis in vitro and in vivo in the chromaffin tissue of the Atlantic cod, Gadus morhua

1. The biosynthesis of [3H]catecholamines from [3H]L-tyrosine in the intact chromaffin tissue of cod posterior cardinal veins was studied in vitro and in vivo at 10 degrees C. 2. The tritiated products dopamine, noradrenaline and adrenaline were separated from the [3H]tyrosine by paper chromatography of tissue extracts and the radioactivity of 1 cm strips of the chromatogram was determined by liquid scintillation spectrophotometry. DOPA could never be demonstrated in the tissue extracts from any of the experiments performed. 3. The content of [3H]noradrenaline in pieces of the cardinal veins incubated in vitro was found to increase rapidly. The tissue content of dopamine and adrenaline remained at lower levels which were reached during the first few hours of the incubation. A similar pattern could be demonstrated in the chromaffin tissue in vivo after infusion of [3H]tyrosine, but the total content of the [3H]catecholamines was lower than in the in vitro experiments. 4. The results are consistent with the view that the methylation of noradrenaline is the rate-limiting step in the biosynthesis of adrenaline in cod chromaffin tissue.     

Biosynthesis of N-Acetyldopamine and N-Acetyloctopamine by Schistocerca gregaria Nervous Tissue

N-Acetyltyramine, N-acetyldopamine and N-acetyloctopamine were the major products when either L-[3H]tyrosine or [3H]tyramine were incubated with thoracic ganglia of the desert locust, Schistocerca gregaria. No label was incorporated into L-DOPA under these conditions, although 2-3% of the radioactivity could be recovered in dopamine and octopamine. Addition of the aromatic amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine (NSD 1015), prevented the formation of N-acetylcompounds from L-[3H]tyrosine, without resulting in an accumulation of label in L-DOPA. In contrast, incubation of samples of haemolymph with L-[3H]tyrosine resulted in the recovery of 7% of label in L-DOPA, which was increased to 17% in the presence of NSD 1015. These results provide evidence that the initial step in the synthesis of dopamine and octopamine by S. gregaria nervous tissue is the conversion of L-tyrosine to tyramine, which is subsequently metabolised to N-acetyltyramine, N-acetyldopamine or N-acetyloctopamine.     

Inhibition of Monoamine Oxidase Within Monoaminergic Neurons in the Rat Brain by (E)-β-Fluoromethylene-m-Tyrosine (MDL 72394)

The irreversible inhibition of the monoamine oxidase (MAO) activity within monoaminergic neurons in the rat brain 24 h after single or repeated administration of (E)-beta-fluoromethylene-m-tyrosine (FMMT, MDL 72394) was examined. The enzyme activity was determined by incubating synaptosome-rich homogenates of hypothalamus or striatum with low concentrations of 5-[14C]hydroxytryptamine (5-HT), [14C]noradrenaline (NA), or [14C]dopamine (DA) in the absence and presence of the selective amine uptake inhibitors citalopram (5-HT), maprotiline (NA), and GBR 12909 (DA). After a single subcutaneous injection of FMMT, the inhibition of MAO within the noradrenergic and dopaminergic neurons was significant but only slightly greater than that outside these neurons. The opposite relationship was observed for the serotonergic neurons. After 7 days' treatment of rats with carbidopa, 20 mg/kg p.o., + FMMT once daily, the preference for the inhibition of MAO within the noradrenergic and dopaminergic neurons was accentuated further. The inhibition outside the serotonergic neurons was still greater than within these neurons. The NA uptake inhibitor CPP 199 antagonized the selective inhibition of MAO within the noradrenergic neurons, which indicates that this preference is due to the accumulation of the active metabolite (E)-beta-fluoromethylene-m-tyramine by the NA transporter.     

LONG-TERM EFFECTS OF TEFLUTIXOL ON THE SYNTHESIS AND ENDOGENOUS LEVELS OF MOUSE BRAIN CATECHOLAMINES

—The long term effects on accumulation of ¹⁴C-labelled dopamine and noradrenaline after [¹⁴C]tyrosine administration and on the endogenous levels of catecholamines in mouse brain were studied after treatment with a new potent thioxanthene neuroleptic, teflutixol. The drug was given as a single dose (5 mg/kg i.p.), as repeated daily doses (1·25 mg/kg p.o.), or as a single dose of the palmitic ester in Viscoleo® (20 mg/kg s.c). After a single dose, teflutixol increased catecholamine synthesis (100%). Noradrenaline synthesis rapidly returned to normal, whereas decreased dopamine synthesis was seen from the third to sixth day, after which it was normal. When the receptors were continuously exposed to teflutixol, either by daily dosage or by the depot preparation, catecholamine synthesis was increased for the first few days but then returned to normal, indicating development of tolerance. Endogenous concentrations of catecholamines were only decreased during the first few days, when the increase in synthesis was greatest. The findings are in accordance with results obtained by Møller Nielsen & Christensen (1975), who found that receptor blockade was followed by receptor supersensitivity after treatment with a neuroleptic compound. The receptor blockade may activate a feedback mechanism that induces increased nervous firing with increased amine synthesis as a consequence. The resulting supersensitivity, if sufficiently great, may lead to reduced nervous firing, followed by slowing of dopamine synthesis.     

Ontogeny of Glucose Metabolism in Sympathetic Ganglia of Chickens. Concurrence of Maximum Rates in the Hexosemonophosphate Shunt and in Synthesis of Lipids but Not of Ribonucleic Acid

Chains of sympathetic ganglia were excised from the lumbar region of white Leghorn chicken embryos, 8-19 days of age, and incubated, usually for 5 h, at 36 degrees C in a bicarbonate-buffered physiological salt solution containing [U-14C]glucose, [1-14C]glucose, [6-14C]glucose, or [5-3H]uridine. Lipid synthesis was measured by the incorporation of 14C into lipids, and RNA synthesis by the accumulation of 3H into macromolecules. The ratio of 14C put out in CO2 during the second hour of incubation in the presence of [1-14C]glucose to that with [6-14C]glucose was used as an index of activity in the hexosemonophosphate shunt (HMS). Both the rate of lipid synthesis and activity in the HMS reached well-defined maxima at about 11 days of embryonic age. There was no evidence of a similar rise and fall of RNA synthesis during the ages studied. Estimates of the rate of NADPH production by the HMS at near-peak lipid synthesis varied over a twofold range that included the rate needed for the observed lipid synthesis. The results thus support, quantitatively as well as qualitatively, the supposition that the HMS is accelerated during development to sustain lipid synthesis.     

Stimulation-depletion of serotonin and noradrenaline from vesicles of sympathetic nerves in the pineal gland of the rat

Summary The pineal gland of the rat receives a rich nervous supply originating from the superior cervical ganglia. These fibers contain serotonin in addition to their neurotransmitter, noradrenaline. Cytochemical studies at the ultrastructural level have shown that both amines are present in the cores of the granular vesicles that are characteristic of these nerves. It is presently shown that the bilateral electrical stimulation of the preganglionic fibers innervating the ganglia markedly reduces the number of small sites reacting cytochemically for both noradrenaline and serotonin, these sites corresponding to the cores of small granular vesicles, while the larger reactive sites (cores of large vesicles) remain unaltered. The vesicles are retained in nerve terminals after stimulation, as observed in conventionally processed tissues, although with altered sizes and shapes. Apart from these cytochemical and structural changes, nerve stimulation also reduces the endogenous noradrenaline content of the pineal gland. Thus, both noradrenaline and serotonin are released from their storage sites in pineal sympathetic nerves after electrical stimulation in vivo. This suggests the possibility that several substances with presumed transmitter or modulatory functions might be simultaneously released by nerve impulses from a given nerve terminal.